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Anne Pereira de Vasconcelos, Sylvette Boyet, Violette Koziel, and Astrid Nehlig. INSERM U272 ... to sustained seizure activity in a specific way ac cording to its ...
Journal oj Cerebral Blood Flow and Metabolism 15:270-283 © 1995 The International Society of Cerebral

Blood Flow and Metabolism

Published by Raven Press, Ltd., New York

Effects of Pentylenetetrazol-Induced Status Epilepticus on Local Cerebral Blood Flow in the Developing Rat Anne Pereira de Vasconcelos, Sylvette Boyet, Violette Koziel, and Astrid Nehlig INSERM U272, Universite de Nancy I, Nancy, France

Summary: The quantitative autoradiographic e4Cl­ iodoantipyrine technique was applied to measure the ef­ fects of a 30-min period of pentylenetetrazol (PTZ)­ induced status epilepticus (SE) on local cerebral blood flow (LCBF) in rats 10 (PlO), 14 (PI4), 17 (P17), and 21 (P21) days after birth. The animals received repetitive, timed injections of subconvulsive doses of PTZ until SE was reached. At PIO, SE induced a 32 to 184% increase in the rates of LCBF affecting all structures studied. In PI4and PI7 PTZ-treated rats, LCBF values significantly in­ creased in two-thirds of the structures belonging to all systems studied and were not changed by SE in the pa­ rietal cortex, dorsal hippocampus, and dentate gyrus. At P2I, rates of LCBF were still increased in 48 of the 73 structures studied; however, LCBF values were de­ creased by SE in most cortical areas, the hippocampus,

and the dentate gyrus. CBF and cerebral metabolic rate for glucose (CMRglc) remained coupled in both controls and PTZ-exposed rats. Our results show that changes in LCBF with seizures are age dependent. At the most im­ mature ages, PlO and PI4, both LCBF and local CMRglc (LCMRglc) values are largely increased by long-lasting seizures. At PI7 and P2I, the blood flow response to SE becomes more heterogeneous, with specific decreases in the hippocampus and cortex at P2I. The absence of mis­ match between LCBF and LCMRglc in PTZ-exposed rats at all ages may explain at least partly why the immature brain is more resistant to seizure-induced brain damage than the adult brain. Key Words: [14C]Iodoantipyrine­ Pentylenetetrazol-Postnatal development-Quantitative autoradiography-Seizure.

Severe neonatal and infantile seizures are associ­ ated with poor neurological outcome, including hemiplegias, mental retardation, extended intellec­ tual impairment, alteration of cognitive function, and lesional epilepsies, in later life (Aicardi and Chevrie, 1970; Aicardi, 1977; Cull, 1988; Legido et aI., 1991). Increases in cerebral blood flow (CBF) accom­ pany epileptic seizure discharges in humans and ex­ perimental animals (Penfield et aI., 1939; Plum et aI., 1968; Meldrum and Nilsson, 1976; Horton et aI., 1980). In adults, the greatest increases in blood flow occur in the hippocampus, thalamus, and neocortex (Horton et aI., 1980). Blood flow rises within sec-

onds of the onset of seizure activity (Meldrum and Nilsson, 1976) and this increase is greatest in the first 4 min (up to 900%), falling to 300% of control values after 2 h. During generalized seizure activity in newborn animals, there is a widespread elevation in local CBF (LCBF) but of a lesser amplitude than in adults, about 30-160% over control values (Young et aI., 1984; Fujikawa et aI., 1986; Park et aI. , 1987). In adult animals and humans, local rates of cere­ bral energy metabolism and LCBF are tightly cou­ pled in most physiological and pharmacological states (Kuschinsky, 1982-1983). This is also the case in immature animals and human infants (Chugani and Phelps, 1986; Nehlig et aI., 1988, 1989; Chiron et aI., 1992). Autoradiographic studies on coupling between flow and metabolism during seizures in adult animals suggest that neuronal dam­ age may result from a mismatch between LCBF and metabolism (Ingvar and Siesjo, 1983; Wasterlain et aI., 1984). An experimental model of status epilepticus (SE) in the immature rat has been developed in our lab-

Received December 27, 1993; final revision received April 7 , 1994; accepted M a y 3 , 1994. Addre s s correspondence and reprint requests to Dr. A. Pereira de Vasconcelos at Centre de Neurochimie, 5 rue Blaise Pascal, F-67084 Strasbourg Cedex, France. Abbreviations used: GABA, ,),-aminobutyric acid; lAP, io­ doantipyrine; LCBF, local cerebral blood flow; LCMRgl , local c cerebral metabolic rate for glucose; NO, nitric oxide; PIO, 10 days after birth, etc.; PTZ, pentylenetetrazol; SE, status epilep­ ticus.

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CEREBRAL BLOOD FLOW AND SEIZURES IN RAT PUPS

oratory using repetitive intraperitoneal injections of subconvulsive doses of pentylenetetrazol (PTZ) (EI Hamdi et ai., 1992). The immature brain responds to sustained seizure activity in a specific way ac­ cording to its maturational state. At 10 and 14 days after birth, SE induces a marked increase in local cerebral metabolic rates for glucose (LCMRglc ) af­ fecting almost all structures, with particularly high values recorded in limbic and motor cortices and in the brain stem. At 17 and 21 days, a redistribution in LCMRglc occurs, with increases in the brain stem, midbrain, hypothalamus, and septum, decreases in the cortex, hippocampus, and sensory areas, and no change in many motor and limbic structures (Pereira de Vasconcelos et al., 1992). The purpose of the present study was to measure the effects of generalized seizures induced by PTZ on the rates of LCBF in the developing rat between 10 and 21 days after birth by the quantitative auto­ radiographic e4C]iodoantipyrine (lAP) technique. The second objective was to determine whether lev­ els of LCBF (the present study) and LCMRglC (Pereira de Vasconcelos et al. , 1992) are coupled in the developing rat during PTZ-induced SE. MATERIALS AND METHODS Animals

Adult Sprague-Dawley rats (lffa-Credo Breeding Lab­ oratories, l' Abresle, France) were housed together in mating groups of one male and two females and con­ stantly maintained under standard laboratory conditions on a l21I2-h light/dark cycle (lights on at 0600). After delivery, litter sizes were reduced to 10 pups for homo­ geneity. The experiments were performed on a total of 50 rats, 24 controls and 26 PTZ-treated rats at 10 (PI0), 14 (PI4), 17 (PI7), and 21 (P21) days after birth. The day of birth was considered day O. Rats from three to five litters were used in each age group. All animal experimentation was conducted in conformity with the "Guiding Princi­ ples for Research Involving Animals and Human Be­ ings. " A femoral artery and vein were catheterized with poly­ ethylene tubing (Clay-Adams PE-IO; I.D., 0. 28 mm; O. D., 0. 61 mm) under light halothane anesthesia. Both catheters were threaded under the skin up to the neck and externalized through a small opening in the skin. A loop was made in the end of the catheters, which were then replaced under the skin, and the small opening was su­ tured. The animals were returned to their mothers in their normal environment. LCBF measurement procedures were performed on the following day. Pharmacological treatment

To reach a SE of a controlled intensity and long dura­ tion, the animals received repeated intraperitoneal injec­ tions of subconvulsive doses of PTZ (10 mg/ml) dissolved in saline as described previously (EI Hamdi et aI. , 1992). All rats were first injected with 40 mg/kg, followed by 20 mg/kg 10 min later. After the first two injections, rats received additional intraperitoneal administrations of 10

271

mg/kg PTZ every 10 min, until SE was reached. Control animals received the same number of saline injections as their paired PTZ-exposed congeners. Measurement of LCBF

LCBF rates were measured on freely moving animals by means of the [14C]IAP method described by Sakurada et al. (1978) and adapted to the immature rat by Nehlig et al. (1989). 4-lodo-N-[methyl-14C]iodoantipyrine (sp act, 1.84-2.22 GBq/mmol; Dupont NEN Research Products, Les Ulis, France) was injected into the animals through the femoral vein at a concentration of 925 Bq/ml, 30 min after the onset of SE. Control rats were injected with the radioactive tracer 5 min after their paired PTZ-exposed rats. The period of measurement of LCBF was approxi­ mately 1 min in duration, during which variable amounts of the lAP solution were administered to the rats. The volumes injected ranged from 130 to 270 fl.l, according to the age studied. The intravenous infusion was conducted at a progressively increasing rate to produce a rising ar­ terial concentration of the tracer approximating a ramp input function. Throughout the period of lAP administra­ tion, timed arterial blood samples, freely flowing from the arterial catheter, were collected in glass capillary tubes. The last sample was taken at the time of killing and as long as blood could be withdrawn from the arterial cath­ eter. The rats were killed by decapitation at about 1 min after the beginning of lAP infusion and brains were re­ moved within 1 min, frozen in isopentane chilled to - 30°C, coated with chilled embedding matrix (4% car­ boxymethyLcellulose in water), and stored at -80°C in plastic bags until sectioned. The content of each capillary tube was transferred to a preweighed scintillation vial that was immediately cov­ ered and reweighed after blood collection. The blood samples were then treated with 0. 5 ml of tissue solubilizer (Optisolv; Pharmacia, Saint Quentin, France) and 0. 5 ml of hydrogen peroxide (30%). The blood concentration of lAP was then determined by liquid scintillation counting in 10 ml of scintillation mixture (Optiphase Hisafe; Phar­ macia) in a Beckman scintillation counter (Model LS 1801; Beckman Instruments, Fullerton, CA, U. S. A.). The concentration of tracer per unit volume of blood in each sample was calculated from the measured amount of 14C, the weight of the blood sample, and an assumed specific gravity of 1. 06 g/ml for blood. The frozen brains were cut into 20-fl.m coronal sections at -22°C in a cryostat. Sections were picked up on glass coverslips and dried on a hot plate (60°C). Sections were autoradiographed on Kodak SB5 film along with cali­ brated [14C]methylmethacrylate standards (Amersham) using a special set of low 14C concentration standards for animals 10 and 14 days old. All standards were calibrated for their 14C concentration in brain sections, as described previously (Sokoloff et aI. , 1977). Adjacent sections were fixed and stained with thionine for histological identifica­ tion of specific nuclei. Autoradiographs were analyzed by quantitative densi­ tometry with a computerized image-processing system (Biocom 200, Les Ulis, France) or a manual microdensi­ tometer (Macbeth, TD 901; Kollmorgen Co., Newburgh, NY, U. S. A.). Optical density measurements for each structure anatomically defined according to the develop­ ing rat brain atlas of Sherwood and Timiras (1970) were made bilaterally in a minimum of four brain sections. Tis­ sue 14C concentrations were determined from the optical J Cereb Blood Flow Metab, Vol.

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densities of the autoradiographs of the tissue sections and a calibration curve obtained from the autoradiographs of the calibrated standards.

creased significantly, by 13 to 21%, in P14, P17, and P21 PTZ-treated rats compared to controls and was not affected by seizures at PI0 (Table 1).

Calculation of LCBF

Throughout the period of measurement of LCBF, blood samples were collected at the distal end of an ar­ terial catheter to determine the continuously changing lAP concentration in the arterial blood at the proximal end of the catheter. The correction for both the time lag and the washout effect was taken into account for final calculations of LCBF, as described previously (Jay et al. , 1988; Nehlig et al. , 1989). Finally, LCBF values were calculated according to the Fick equation using a brain­ blood partition coefficient of 0.8 (Sakurada et al. , 1978). Physiological variables

Just prior to the first administration of PTZ (0 time) and prior to infusion of lAP (after 30 min of SE), the mean blood pressure of the animals was measured with an air­ damped mercury manometer and the hematocrit value was determined. Arterial pH, Po2, and Peo2 were also measured on 40-1-11 blood samples by means of a blood gas analyzer (Corning Model 158; Corning Medical and Sci­ entific, Halstead, UK) just before the first PTZ injection and before the onset of LCBF procedure. PlO and P14 rats were maintained under a heating lamp to keep their body temperature in the physiological range. Statistical analysis

LCBF values were determined in 73 cerebral structures in four age groups of controls and four similar age groups of seizing rats. A two-way analysis of variance was per­ formed to test the effects of age, seizures, and age versus seizures. LCBF values in each group of rats were com­ pared with those in the immediately preceding age by means of Bonferroni' s mUltiple-comparison procedures. Moreover, at each age, values of LCBF in PTZ-treated rats were compared with those in the control by means of a nonpaired Student's t test. The slopes of the regression lines between LCMRglc and LCBF were compared by means of Student' s t test. RESULTS Influence of PTZ-induced SE on behavior and physiological variables

PTZ-induced SE, as confirmed by EEG record­ ings (Nehlig, unpublished data), started with the lost of quadrupedic posture. Thereafter, the animals developed typical sequences of behavioral expres­ sion of generalized seizures that varied with age and were previously described in detail (El Hamdi et al. , 1992). The mean dose of convulsant necessary to induce SE was 109 mg/kg at PIO and 80-85 mg/kg at P14, P17, and P2l (Table 1). In PTZ-treated rats, arterial blood pressure was significantly increased, by 18 to 36%, over control values at all ages, 30 min after the onset of SE (Table 1). Arterial pH de­ creased significantly at all ages in seizing rats by 3 to 8% 30 min after the onset of SE, i. e. , just before the lAP injection. Arterial P02 increased signifi­ cantly, by 20 to 56%, at all ages, while Pco2 deJ

Cereb Blood Flow Metab, Vol. 15, No. 2, 1995

Effects of PTZ-induced SE on LCBF

Two-way analysis of variance The results of the two-way analysis of variance, which are not given in the tables, indicate that there was an effect of age on LCBF values, with p values ranging from 10-4 to 0. 027 in all structures studied, except in the dorsal hippocampus, The effect of the nature of the pharmacological treatment was also significant in almost all areas (10-4 < P < 5 . 10-3), except in six cortices and the hippocampus. No in­ teraction between age and the nature of the phar­ macological treatment was seen in 65 of the 73 structures studied, The interaction was significant in four cortical structures, the dorsal hippocampus, and the dentate gyrus. Postnatal evolution of LCBF in saline- and PTZ­ treated rats (Bonferroni's t test) In saline- and PTZ-treated rats, LCBF increased between PI0 and P17 in all structures studied: These differences reached significance in half of the structures in saline-treated rats and one-third of the brain areas in PTZ-treated rats (Tables 2-6). Be­ tween P17 and P21, LCBF values did not change in most areas while decreasing significantly in 10 and 17 structures in saline- and PTZ-treated rats, re­ spectively (Tables 2-6). Influence of PTZ-induced SE on LCBF at differ­ ent postnatal ages (Student's t test) In PIO PTZ-treated rats, LCBF significantly in­ creased over control values by 32 to 184% in 68 structures (Tables 2-6, Figs. 1 and 2). The highest increases (> 100%) were recorded in the accumbens and septal nuclei, amygdala, mesencephalic reticu­ lar formation, and zona incerta (Table 3), almost all hypothalamic and thalamic structures (Table 4, Fig. 1), the dorsomedian caudate and facial nuclei, and the substantia nigra (Table 5, Fig. 2). More moder­ ate increases in LCBF (30 to 55%) were recorded in sensory areas, olfactory and visual cortices, the su­ perior olive, and the vestibular nucleus (Table 2), limbic structures such as the parietal cortex, ventral hippocampus, and dentate gyrus (Table 3), the mammillary body (Table 4), and cerebellar nuclei (Table 5). In P14 PTZ-treated rats, significant increases in LCBF values over controls (42 to 173%) were re­ corded in 43 structures. The highest increases (> 100%) occurred in the dorsal tegmentum (Table 3), motor structures (Table 5), and all posterior veg­ etative nuclei (Table 6). In contrast, LCBF was not significantly affected by seizures in 29 structures,

CEREBRAL BLOOD FLOW AND SEIZURES IN RAT PUPS

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TABLE 1. Effects of PTZ-induced seizures on physiological variables of developing rats PIO Body weight (g) C PTZ PTZ dose (mg/kg) Arterial blood pres sure (mm Hg) o time C PTZ 30 min of S E C PTZ Hematocrit (%) o time C PTZ 30 min of S E C PTZ Arterial pH o time C PTZ 30 min of S E C PTZ Arterial P02 (mm Hg) o time C PTZ 30 min of S E C PTZ Arterial Peo2 (mm Hg) o time C PTZ 30 min of S E C PTZ

PI4

PI7

P21

32 ± 2 34± 2 85 ± 20

37± 2 38 ±3 80±19

53±2 51±3 83±II

38 ± 3 39±3

46±4 50±5

57 ±5 56± 3

73±5 70±5

37±3 49±8d

45±4 61 ±7d

54 ± 2 69± 5 d

72 ±2 85±IIC

25 ±3 25 ±3

25± 2 26± 2

25± 2 26 ±3

27± 2 30±3a

25±3 25±3

25± 2 27± 2

24± 2 29±3"

28± 2 34±3d

7.42±0.04 7.43±0.02

7.41 ±0.02 7.43 ±0.03

7.46±0.02 7.45±0.05

7.38±0.02 7.01±O.l7d

7.39±0.02 6.91 ±0.16d

7.44±0.02 6.83±0.05d

24±3 24 ± 3 109± 21

7.38±0.03 7.16±0.lld

91± II 109±13e

29±3 27± 5

85±4 85± 2

88± 2 84±5

84 ±5 85±5

85±9 102 ±10c

81±5 112 ±16d

81 ± 2 126± lId

30± 2 30± 2

30± 2 30±3

31±2 35±3

32 ± 2 28± 2 c

34 ± 2 27 ±3d

32 ± 2 27 ±3a

Values are means ± SD of five or seven animals. ap < 0.05, cp < 0.01, and dp < 0.001, statistically s ignificant differences between controls (C) and PTZ-treated rats at a given age.

belonging to all the systems, except hypothalamic and posterior vegetative areas (Tables 2-6, Figs. 1 and 2). At P17, PTZ administration induced a significant, 29 to 110%, increase in LCBF values that affected 49 structures. In seizing rats, the highest increases (>80%) were located in the superior colliculus (Ta­ ble 2), some hypothalamic areas (Table 4, Fig. 1), and posterior vegetative structures (Table 6). In 24 structures, belonging to all systems, except hypo­ thalamic and posterior vegetative areas, LCBF showed no significant differences in the PTZ group compared to controls. In P21 PTZ-treated rats, LCBF significantly in­ creased over control values in 47 structures. These increases ranged from 30 to 121%, with the highest changes (>80%) in posterior limbic areas (Table 3), the subthalamic nucleus, the substantia nigra (Table 4, Fig. 2), and some thalamic nuclei (Table 5, Fig.

1). At that age, PTZ treatment also induced a sig­ nificant, 29 to 43%, decrease in seven structures: the auditory, visual, parietal, and motor cortices, hippocampus, dorsal and ventral parts, and dentate gyrus (Tables 2, 3, and 5, Figs. 1 and 2). In 19 struc­ tures LCBF was not significantly different between the two groups of P21 rats. Relationship between LCBF and LCMRgIc in controls and PTZ-treated rats

Figure 3 illustrates the relationship between LCMRglc and LCBF in 73 anatomical structures of control and PTZ-treated rats. LCMRglc values were recorded in a separate group of rats (Pereira de Vas­ concelos et al., 1992). At all ages, there was a linear relationship between LCMRglc and LCBF for' all structures in both groups of animals, but the corre­ lation was poorer in seizing animals than in controls (Fig. 3). At PI0, P14, and P17, the slope deJ

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TABLE 2. Effects of PTZ-induced seizures on LCBF in sensory systems of developing rats

Auditory system Auditory cortex C PTZ Medial geniculate body C PTZ Inferior colliculus Dorsomedial nucleus C PTZ Ventrolateral nucleus C PTZ External nucleus C PTZ Lateral lemniscus C PTZ Superior olive C PTZ Cochlear nucleus C PTZ Visual system Visual cortex C PTZ Lateral geniculate body C PTZ Superior colliculus Superficial gray layer C PTZ Intermediate gray layer C PTZ Olfactory system Olfactory cortex C PTZ Vestibular system Ve stibular nucleus C PTZ

PIO

PI4

P17

23.3 ± 7.9 43.2 ± 14.6c

49.6 ± 14.3* 69.3 ± 24.7**

80.7 ± 12.0** 99.9 ± 21.7**

38.4 ± 9.3 62.7 ± 13.8c

73.8 ± 21.2** 109.5 ± 40.7*

P21

85.2 ± 21.8 56.9 ± 14.0b**

104.9 ± 14.9* 119.5 ± 27.7

92.7 ± 20.6 113.7 ± 23.0

53.8 ± 14.6c

54.3 ± 15.9* 99.4 ± 38.0"**

90.4 ± 19.4** 117.3 ± 33.5

67.3 ± 12.1* 105.2 ± 14.0d

35.9 ± 7.1 67.1 ± 19.0c

75.3 ± 20.6 139.9 ± 47.1"**

142.1 ± 34.0** 177.2 ± 42.0

95.4 ± 15.4** 146.9 ± 26.5"

42.6 ± 6.1 73.2 ± 19.0c

88.7 ± 28.8** 142.0 ± 47.2**

135.7 ± 29.6** 160.8 ± 38.7

91.2 ± 17.4** 130.8 ± 17.7C

46.4 ± ILl 76.0 ± 14.3d

76.9 ± 20.1* 116.3 ± 23.0"**

93.2 ± 17.9 143.8 ± 15.9d

127.2 ± 23.3c

58.5 ± IS.6

100.8 ± 30.9*

90.0 ± 18.5c

152.3 ± 43.6*

130.7 ± 37.7 193.4 ± SO.2"

101.3 ± 18.8 161.3 ± 54.0"

60.4 ± 12.4 79.1 ± 20.4

97.8 ± 31.5* 158.9 ± 58.1**

129.9 ± 19.8 181.8 ± 48.3a

113.1 ± 24.4 122.1 ± 31.0*

24.1 ± 7.1 37.0 ± 12.2"

50.2 ± 13.9** 66.4 ± 24.5**

72.3 ± 13.7* 83.3 ± 18.S

73.3 ± 18.1 43.1 ± 6.lc**

33.8 ± 7.9 55.3 ± 16.1c

S5.9 ± 18.1*

75.6 ± S.6*

74.9 ± 28.4

84.3 ± 18.1

73.2 ± 16.2 73.2 ± 10.8

23.6 ± 5.6 42.6 ± 8.7d

43.1 ± 13.9* 65.8 ± 23.3

68.2 ± 10.S** 121.3 ± 27.4b**

66.6 ± 17.1 104.3 ± 18.0c

22.2 ± 4.8 47.6 ± 10.3d

41.7 ± 14.5* 69.8 ± 24.7"

68.9 ± 11.3** 127.6 ± 25.7d**

68.3 ± 16.4 120.4 ± 23.3d

5S.1 ± 12.4 73.0 ± 17.7"

78.0 ± 19.2 89.1 ± 32.8

86.2 ± 16.9 IIS.7 ± 26.2"

76.7 ± 20.3 84.4 ± 20.4

133.4 ± 2S.7 192.7 ± 45.2"

103.3 ± 2S.0 ISO.4 ± 36.2"

30.0 ± 6.1

66.8 ± IS.I 101.7 ± 20.9c

101.4 ± 33.1* 195.9 ± 51.0"**

80.2 ± 13.4

Value s are means ± SD of five to seven animal s , expressed as ml 100 g-I min-I. "p < 0.05, bp < 0.02, cp < 0.01, and dp < 0.001, statistically significant differences between controls (C) and PTZ-treated rats at a given age . *p < 0.05 and **p < 0.01, statistically significant differences between one age and the preceding age.

rived from linear regression analyses showed a sig­ nificant difference (p < 0.01) between the two groups, with lower values in PTZ-treated rats. In PIO and P14 PTZ-treated rats, seizure activity in­ duced a slight shift of the regional flow-metabolism couple to lower values of LCBF compared to met­ abolic rates (Fig. 3). In P17 seizing rats, LCMRglc values tended to remain close to control levels, while LCBF values were increased. At P2I, there was no significant difference in the slope of the re­ gression lines between the two parameters studied in both groups of rats. However, seizure activity J

Cereb Blood Flow Metab, Vol. 15, No. 2, 1995

induced a shift toward a higher value of LCBF, in­ dicating a moderate hyperemia at that age, though not statistically significant (Fig. 3). DISCUSSION Postnatal evolution of LCBF

The postnatal evolution of LCBF in saline rats (Tables 2-6) confirms the results of a previous study from our laboratory, showing that the most striking feature in the postnatal evolution of the rates of LCBF in the rat under normal physiological condi-

CEREBRAL BLOOD FLOW AND SEIZURES IN RAT PUPS

275

TABLE 3. Effects of PTZ-induced seizures on LCBF in limbic and functionally nonspecific areas of developing rats

Prefrontal cortex

e

PTZ Anterior cingulate cortex

e

PTZ Parietal cortex

e

PIO

P14

29.2 ± 6.6 49.6 ± 17.2c

59.8 ± 16.1** 75.1 ± 32.3

69.5 ± 11.3 105.0 ± 24.3c

27.6 ± 5.6 48.3 ± 14.6c

59.1 ± 17.2** 70.1 ± 29.1

70.6 ± 12.0 94.6 ± 21.2a

P17

P21

68.3 ± 14.9 55.5 ± 31.7** 68.5 ± 16.9 55.9 ± 33.9*

40.3 ± 11.9

88.0 ± 21.0**

PTZ Entorhinal cortex

62.4 ± 18.0b

89.9 ± 35.0

28.6 ± 7.7

PTZ Accumbens nucleus

55.9 ± 15.1d

40.5 ± 8.5 57.9 ± 19.6

30.1 ± 9.5 61.3 ± 13.8d

52.7 ± 16.3** 78.8 ± 18.6a

59.8 ± 10.3 100.4 ± 23.0c

34.5 ± 5.8 66.4 ± 14.6d

49.0 ± 15.4 80.1 ± 25.0a

73.3 ± 21.3* 115.6 ± 33.3b*

26.2 ± 3.4 56.0 ± 18.3d

40.1 ± 15.2 72.1 ± 21.8b

60.9 ± 20.6* 111.3 ± 19.3d**

36.4 ± 8.5 73.9 ± 14.3d

52.3 ± 14.3*

57.8 ± 5.6

50.5 ± 8.8

68.7 ± 24.2

84.4 ± 18.3c

61.8 ± 14.0*

25.4 ± 7.9 57.7 ± 14.3d

52.3 ± 22.8** 61.4 ± 23.0

57.7 ± 4.2 74.5 ± 15.9a

53.7 ± 10.8 58.3 ± 11.6

30.9 ± 5.0 68.0 ± 15.6d

48.3 ± 16.5 79.3 ± 24.2a

e

e

PTZ Medial septum

e

PTZ Lateral septum

e

PTZ Medial amygdala

e

PTZ Basolateral amygdala

e

PTZ Zona incerta

e

PTZ Dorsal hippocampus

e

PTZ Ventral hippocampus

e

PTZ Dentate gyrus

e

PTZ Medial habenula

e

PTZ Lateral habenula

e

PTZ Ventral tegmental area

e

PTZ Dorsal tegmentum

e

PTZ Mesencephalic reticular formation

e

PTZ Medial raphe

e

PTZ Dorsal raphe

e

PTZ Locus ceruleus

e

PTZ Pontine gray

e

PTZ

117.1 ± 29.1 103.2 ± 26.5 53.9 ± 7.8* 76.7 ± 12.2c

82.9 ± 20.1** 142.5 ± 33.3c**

89.2 ± 22.3 59.8 ± 15.1b* 49.2 ± 10.8 62.8 ± 21.7 57.1 ± 11.3 85.9 ± 14.0c 56.9 ± 12.1 106.7 ± 10.8d 54.8 ± 14.9 85.0 ± 11.9c*

66.5 ± 13.9 131.8 ± 18.3d

37.4 ± 10.6

57.9 ± 15.2*

49.4 ± 20.6

57.6 ± 31.6

66.2 ± 8.6 50.8 ± 21.1

57.8 ± 11.8 32.8 ± 7.ld

25.4 ± 7.1 39.6 ± 14.3a

41.0 ± 11.6* 62.7 ± 16.2a**

54.2 ± 5.1 73.8 ± 12.7c

51.4 ± 12.0 36.3 ± 6.9c**

33.6 ± 8.2 51.0 ± 18.8a

55.2 ± 12.7** 63.8 ± 25.5

69.3 ± 7.6 57.9 ± 13.0**

55.2 ± 10.5* 34.1 ± 6.6d**

42.2 ± 5.4 65.8 ± 20.4a

66.8 ± 23.2 88.8 ± 26.7

45.3 ± 4.9 77.0 ± 16.7c

75.8 ± 29.1 100.2 ± 39.9

36.2 ± 7.4 66.0 ± 13.0d

54.9 ± 18.6 87.2 ± 25.7a

48.2 ± 10.3 94.6 ± 24.ld

88.5 ± 22.8 114.1 ± 27.4*

79.3 ± 19.1 80.5 ± 11.4*

99.0 ± 30.9

79.7 ± 15.0 103.3 ± 19.0a,

142.5 ± 30.4a, 82.2 ± 18.1* 122.7 ± 24.0c,

66.7 ± 18.1 125.5 ± 22.2d

143.7 ± 49.2a

95.9 ± 24.0' 171.7 ± 54.4a

135.6 ± 23.0d

26.7 ± 6.6 64.3 ± 13.8d

52.9 ± 14.5* 102.3 ± 34.5b

94.4 ± 26.7** 145.7 ± 42.4a,

68.9 ± 20.1* 143.8 ± 27.5d

41.3 ± 7.9 70.6 ± 15.9d

59.3 ± 19.9 109.3 ± 41.6a*

88.5 ± 20.1* 148.9 ± 33.3c*

71.4 ± 16.5 130.6 ± 20.9d

36.5 ± 9.0 70.9 ± 14.6d

57.0 ± 22.1 105.7 ± 40.9a

83.8 ± 14.0' 146.8 ± 50.8b

65.3 ± 20.6 128.6 ± 25.7d

47.7 ± 8.7 92.2 ± 14.3d

134.1 ± 47.9a

138.8 ± 32.2b

110.4 ± 15.3d

39.1 ± 10.3 74.7 ± 15.9d

59.0 ± 11.9* 106.2 ± 40.2a

72.7 ± 9.3 129.2 ± 26.2d

62.9 ± 13.0 119.7 ± 22.2d

70.6 ± 19.2

69.7 ± 15.9

94.0 ± 17.4*

81.3 ± 11.4

65.5 ± 14.1**

Values are means ± SD of five to seven animals, expres sed as ml 100 g-I min-I. ap < 0.05, bp < 0.02, cp < 0.01, and dp < 0.001, statistically significant differences between controls (e) and PTZ-treated rats at a given age. *p < 0.05, and **p < 0.01, statistically significant differences between one age and the preceding age.

J

Cereb Blood Flow Metab, Vol. 15, No. 2, 1995

A. PEREIRA de VASCONCELOS ET AL.

276

TABLE 4. Effects of PTZ-induced seizures on LCBF in the hypothalamus and thalamus of developing rats PIO

PI4

P17

27.3 ± 6.1 61.6 ± IS.Od

41.9 ± 13.6 71.4 ± 17.6h

5S.0 ± 14.7 121.6 ± 26.0d**

39.0 ± 7.7 64.7 ± IS.3c

53.S ± 15.2 76.4 ± 16.9a

125.2 ± 29.1c**

101.S ± 12.7d

Area Hypothalamic Anterior hypothalamus C PTZ Anterolateral hypothalamus C PTZ Paraventricular nucleus C PTZ Ventromedian hypothalamus C PTZ Dorsomedian hypothalamus C PTZ Median forebrain bundle C PTZ Posterior hypothalamus C PTZ Mammillary body C PTZ Thalamic Ventrolateral thalamus C PTZ Anteroventral thalamus C PTZ Ventromedian thalamus C PTZ Centro median thalamus C PTZ Mediodorsal thalamus C PTZ Posterior thalamus C PTZ Parafascicular thalamus C PTZ

75.9 ± 23.0

P21

56.5 ± 15.9 94.1 ± 13.0d* 62.9 ± 19.4

33.S ± 5.3

51.1 ± 15.2

76.0 ± 18.8d

80.1 ± 16.9b

72.0 ± 19.1* 134.7 ± 23.3d**

67.6 ± 16.4 \08.5 ± 19.8c*

37.1 ± 7.4 74.7 ± 15.3d

47.1 ± 14.5 76.1 ± 16.2b

66.0 ± 15.2* 116.0 ± 18.1d**

58.7 ± 16.4 86.9 ± 15.1c*

27.2 ± 5.6 58.8 ± 13.0d

41.8 ± 14.8 71.1 ± 18.1b

62.6 ± 15.4* 119.9 ± 17.ld**

56.5 ± 13.7 98.5 ± 18.8d

35.2 ± 6.1 63.9 ± 14.0d

49.5 ± 16.1

72.4 ± 20.3*

75.5 ± 16.9a

122.2 ± IS.9c**

57.4 ± 13.9 \06.3 ± 21.7c

114.0 ± 22S

35.2 ± 6.6

53.1 ± 17.2

68.2 ± 15.6d

79.9 ± 20.8a

82.2 ± 20.6* 132.7 ± 30.9"*

35.5 ± 8.5 51.2 ± 11.1b

58.6 ± 16.8** 78.9 ± 25.5*

109.6 ± 21.2c*

65.3 ± 8.5 90.7 ± IS.3b

24.3 ± 6.1 51.0 ± 19.0c

50.5 ± 13.2* SO.4 ± 32.3

95.4 ± 28.2** 126.8 ± 46.3*

82.2 ± 21.8 107.4 ± 15.3a

38.8 ± 7.9 67.5 ± 25.lb

72.5 ± 25.9* 97.3 ± 43.4

121.6 ± 29.1** 134.3 ± 60.3

90.4 ± 17.2* 104.3 ± 16.9

24.2 ± 7.1 68.7 ± 17.5d

50.8 ± 13.4*

101.4 ± 22.8**

80.2 ± 18.1

95.2 ± 38.5a

157.8 ± 50.0a*

143.9 ± 33.6c

31.6 ± 5.0 82.1 ± 24.9d

65.5 ± 17.0* 108.9 ± 48.7

108.7 ± 21.9** 166.9 ± 51.2*

76.9 ± 20.3* 148.8 ± 31.2c

31.0 ± 3.2 75.3 ± 22.5d

52.3 ± 11.4 85.5 ± 26.7a

95.0 ± 21.7** 137.5 ± 50.2*

73.3 ± 17.7 148.8 ± 31.2c

33.0 ± 8.5 76.9 ± 22.2d

58.2 ± 13.4 107.1 ± 40.2a

105.4 ± 25.2** 148.9 ± 47.5

7S.6 ± 20.3* 121.4 ± 22.8c

33.6 ± 7.4 78.0 ± 20.4d

55.9 ± 13.2 104.1 ± 41.2a

98.4 ± 25.0** 154.5 ± 50.9a*

76.1 ± 19.5 138.3 ± 27.0d

79.6 ± 11.3*

64.6 ± 15.7

Values are means ± SD of five to seven animals, expre ssed as ml 100 g-' min - '. ap < 0.05, bp < 0.02, cp < 0.01, and dp < 0.001, statistically significant differences between controls (C) and PTZ-treated rats at a given age. *p < 0.05 and **p < 0.01, statistically significant differences between one age and the preceding age.

tions is a peak at 17 days followed by a decline between 17 and 21 days (Nehlig et ai., 1989). In PTZ-treated rats, the postnatal evolution in LCBF rates follows the same pattern as in controls, dem­ onstrating that the vascular reactivity is similar un­ der normal physiological conditions and during se­ vere epileptic seizures in the rat at different post­ natal ages. Effects of PTZ-induced SE on LCBF in the developing rat

PTZ is a central nervous stimulant extensively used in experimental models of epilepsy. However, J

Cereb Blood Flow Me tab, Vol. 15, No. 2, 1995

its mechanism of action has not yet been fully clar­ ified. This agent has been reported to interact with the benzodiazepine--y-aminobutyric acid (GABA) receptor or ionophore complex (MacDonald and Barker, 1977; Ramanjaneyulu and Ticku, 1984). Until now, data on the effects of epileptic sei­ zures on LCBF in immature animals have been fo­ cused mainly on newborns of different species, such as dogs (Young et ai., 1984), monkeys (Fu­ jikawa et ai., 1986), and piglets (Park et ai., 1987). However, there are no quantitative data available on the effects of epileptic seizures on LCBF at dif­ ferent postnatal ages. In the lO-day-old rat, 30 min

CEREBRAL BLOOD FLOW AND SEIZURES IN RAT PUPS

277

TABLE 5. Effects of PTZ-induced seizures on LCBF in motor areas of developing rats P10

Motor cortex C PTZ Dorsomedian caudate nucleus C PTZ Ventral caudate nucleus C PTZ Substantia nigra pars reticulata

C PTZ Substantia nigra pars compacta C PTZ Subthalamic nucleus C PTZ Pontine nuclei C PTZ Facial nucleus C PTZ Inferior olive C PTZ Cerebellar cortex C PTZ Cerebellar nuclei Dentate nucleus C PTZ Interpositus nucleus C PTZ Fastigial nucleus C PTZ

PI4

PI7

P21

40.0 ± 9.8 66.4 ± 16.4c

87.6 ± 16.1 85.6 ± 27.4

108.2 ± 25.5 113.7 ± 26.2

21.5 ± 6.1 44.1 ± 11.9d

50.4 ± 15.9 59.1 ± 25.7

63.0 ± 7.1 75.9 ± 26.5

65.9 ± 15.4 59.5 ± 13.2

34.7 ± 10.6

63.9 ± 16.3 81.7 ± 32.3

72.6 ± 18.6 87.5 ± 19.6

60.7 ± 13.5

60.2 ± 11.6d 28.1 ± 4.8 56.4 ± 1O.8d

44.1 ± 13.6 76.1 ± 27.9a

69.5 ± 17.6 108.3 ± 27.4b

50.4 ± 12.3 111.3 ± 22.0d

30.3 ± 4.5 63.3 ± 11.4d

48.4 ± 15.7 84.9 ± 26.0b

75.2 ± 15.4 130.7 ± 26.2c

62.9 ± 15.4 121.7 ± 19.6d

44.9 ± 7.9 82.7 ± 19.6d

67.1 ± 20.3 108.3 ± 32.3a

108.4 ± 30.1 171.9 ± 47.5b

78.1 ± 17.9 148.4 ± 25. JC

60.5 ± 11.0

56.8 ± 14.7 76.9 ± 21.7

27.5 ± 9.0 51.2 ± 8.5d 26.4 ± 5.3

49.1±11.9 68.5 ± 27.7

85.1 ± 24.1a

45.7 ± 12.3

67.5 ± 23.3

69.8±14.0d

124.1 ± 55.lb

101.9 ± 42.5

48.9 ± 11.6 82.1 ± 18.0c

73.8 ± 22.8 165.0 ± 49.0b

106.1 ± 16.4 173.1 ± 29.2c

24.7 ± 7.1 28.4 ± 11.9

39.7 ± 7.2 59.4 ± 25.5

43.9 ± 8.7 55.7 ± 13.2 49.0 ± 8.5

56.7 ± 9.1 78.4 ± 14.8c

74.6 ± 23.5* 157.1 ± 64.2a** 82.2 ± 24.4*

64.8 ± 9.3

55.6 ± 18.1 81.8 ± 22.2a 87.5 ± 15.4 144.1 ± 36.8C 52.5 ± 11.0 59.1 ± 10.8

127.3 ± 21.8** 178.9 ± 49.9a

103.1 ± 21.7

109.2 ± 33.3

65.3 ± 13.5b

178.1 ± 57.9a**

126.2 ± 22.5** 171.9 ± 55.7

51.2 ± 10.8

84.1 ± 27.3* 180.6 ± 61.0a**

120.9 ± 20.8* 167.3 ± 54.1

68.7 ± 14.0a

84.9 ± 22.5 56.7 ± 14.0b

143.0 ± 28.0a

141.5 ± 30.7 97.8 ± 18.6 130.4 ± 25.4a

Values are means ± SD of five to seven animal s , expressed as ml 100 g-I min -I . ap < 0.05, bp < 0.02, cp < 0.01, and dp < 0.001, statistically significant differences between controls (C) and PTZ-treated rats at a given age. *p < 0.05 and **p < 0.01, statistically significant differences between one age and the preceding age.

of PTZ-induced SE produced a widespread and gen­ eral increase in the rates of LCBF, as shown pre­ viously in newborns of different species during bicuculline-induced seizures (Young et aI., 1984; Fujikawa et aI., 1986; Park et aI., 1987) but these increases are generally less marked than in adults (Meldrum and Nilsson, 1976; Horton et aI., 1980; Ingvar and Siesj6, 1983). In PTZ-treated rats, high­ est increases are noticed at all ages in midbrain and brainstem areas, all thalamic and hypothalamic nu­ clei. These results are in accordance with previous studies showing a redistribution of blood flow in favor of the brain stem during bicuculline-induced seizures in newborn marmoset monkeys (Fujikawa et aI., 1986) and dogs (Young et aI., 1984). This redistribution of CBF rates can be considered as a protective mechanism to autonomic functions as

also shown during hypoxia in immature animals (Ashwal et aI., 1984; Bilger and Nehlig, 1993). The increases in LCBF values in the brain stem, thalamus, and hypothalamus at all ages might be related to the well-known participation of subcorti­ cal areas, mainly diencephalic and brainstem re­ gions in this type of seizure (Miller et aI., 1987; Miller and Ferrendelli, 1988). Indeed, the thalamus, hypothalamus, and brainstem reticular formation play a facilitatory role in PTZ seizure expression (Jinnai et aI., 1969; Miller et aI., 1987; Miller and Ferrendelli, 1990) and brain stem has been demon­ strated to be a low threshold region for the excit­ atory and convulsive action of PTZ (Fain:gold, 1978). These structures are the only ones that show increases in both LCMRglc (Pereira de Vasconcelos et aI., 1992) and LCBF (the present study) during J

Cereb Blood Flow Metab, Vol. 15, No. 2, 1995

A. PEREIRA de VASCONCELOS ET AL.

278

TABLE 6. Effects of PTZ-induced seizures on LCBF in posterior vegetative nuclei and white matter areas of

developing rats

Posterior vegetative nuclei Spinal trigeminal nucleus C PTZ Ambiguus nucleus C PTZ Parvocellularis nucleus C PTZ Gigantocellularis nucleus C PTZ Nucleus of the solitary tract

C PTZ Medullary reticular formation C PTZ White matter areas Genu of the corpus callosum C PTZ Internal capsule C PTZ Cerebellar white matter C PTZ

PIO

PI4

PI7

P21

46.5± 12.2 75.6± 22.8b

73.6 ± 19.5* 158.6± 45.6b**

105.6 ± 26.2* 156.1 ± 41.4a

83.2 ± 11.6 125.9 ± 30.7b

55.6± 14.0

76.4 ± 22.4 178.4± 51.4c**

105.0 ± 22.3*

81.6 ± 11.4

93.6± 21.2c

176.2± 44.4c

124.9 ± 30.7b

40.8± 11.1 71.5± 18.5c

151.7± 55.8c**

82.6± 18.1* 159.6 ± 40.2c

125.3± 26.5"

76.9± 18.8d

54.9 ± 15.4 149.9 ± 57.3"**

73.8 ± 12.5 142.7± 38.8c

118.7 ± 23.0d

28.0 ± 6.9 66.7± 15.9d

46.3 ± 14.3* 109.5 ± 41.6c*

59.9 ± 12.0 123.9 ± 34.2c

55.1 ± 15.2 102.5± 24.9C

34.1 ± 10.3 63.7 ± 15.ld

52.9 ± 16.8 127.0 ± 53.6b*

81.4 ± 19.4* 144.9 ± 42.6C

119.4 ± 29.9C

42.0 ± 9.1* 60.1 ± 16.9a

34.6 ± 8.1 31.1 ± 6.1*'

47.9± 11.5 60.2 ± 15.4

41.2 ± 10.0 35.9 ± 7.9*'

53.0 ± 13.5 66.1± 17.6

46.9 ± 11.8 50.8 ± 12.2

40.5± 10.8

59.5 ± 16.8

21.3± 5.0

30.6± 10.1

34.3± 12.4a

46.5 ± 16.7

70.9 ± 15.4

63.6 ± 15.4

61.9 ± 14.8*

Values are means ± SD of five to seven animals, expressed as ml 100 g-I min -I. ap < 0.05, bp < 0.02, cp < 0.01, and dp < 0.001, statistically significant differences between controls (C) and PTZ·treated .rats at a given age. *p < 0.05 and **p < 0.01, statistically significant differences between one age and the preceding age.

PTZ-induced SE at all ages. The greater vasodila­ tory capacity of the brainstem vasculature com­ pared with that of the forebrain could also be re­ lated to the greater degree of maturation of the brain stem. Conversely to PI0, the age at which LCBF is increased by seizures in almost all brain areas, LCBF is not changed by seizures in one-third of the structures of P14-P21 PTZ-treated rats. These structures are mainly the cortical areas, auditory and visual midbrain relay nuclei, hippocampus, caudate nucleus, and white matter. Moreover, at P21, PTZ-induced seizures lead to a significant de­ crease in LCBF values in cortical areas and hippo­ campus. These results are in contradiction with the well-known increase in CBF during seizures in both adult and newborn animals. Indeed, in adults the increase in CBF is very rapid within seconds after the onset of a generalized seizure and is consecutive to a rise in mean arterial blood pressure and to a reduction in cerebrovascular resistance (Plum et ai., 1968; Meldrum and Nilsson, 1976; Ingvar and Siesj6, 1983). The results obtained in the present study are not readily comparable to those of most studies, which were performed in paralyzed, artifiJ

Cereb Blood Flow Metab, Vol. 15, No. 2, 1995

cially ventilated adult animals. However, several investigators have reported a decline in the magni­ tude of the increase in LCBF during recurrent or prolonged seizures in adult rats that is not depen­ dent upon blood pressure (Meldrum and Nilsson, 1976; Horton et ai., 1980; Ingvar and Siesj6, 1983; Kreisman et ai., 1991). In the present study, at 30 min after the onset of SE, i.e., at the time of LCBF measurement, seizure-induced hypertension is of the same order of magnitude at all ages; therefore, the age variations in LCBF responses to PTZ­ induced SE cannot be explained by changes in ar­ terial blood pressure and arterial hypotension can­ not be involved in the decrease in LCBF values in some regions of P21 PTZ-treated rats. Kreisman et ai. (1991) demonstrated in adult rats that the relative decrease in LCBF during prolonged seizures could be attributed to the return of cerebrovascular resis­ tance to normal levels, causing a decrease in cere­ bral oxygenation during the late seizure period. However, in all these studies reported in adult rats, values of LCBF remain higher than or not changed compared to controls even after 1 or 2 h of SE, which differs from our results observed in P21-PTZ­ treated rats.

CEREBRAL BLOOD FLOW AND SEIZURES IN RAT PUPS

PI0

PI4

279

PI7

P2I

PI7

P2I

CONTROLS

PI0

PI4 SEIZURES

[ '4C ] IAP

autoradiographs of rat brain coronal sections at different postnatal ages, taken at the level of the dorsal hippocampus and the thalamus. At all ages, 30 min of SE induced an increase in brain density in all thalamic and hypothalamic nuclei, particularly marked at PH and P21. In contrast, the hippocampus is poorly labeled in P1 7 and P21 PTZ-treated rats

FIG. 1.

compared to controls.

Convulsive drugs, including PTZ, have been shown to induce changes in blood-brain barrier per­ meability, confined to anatomically limited brain ar­ eas that differ between immature and adult animals (Nitsch and Klatzo, 1983; Ziylan and Ates, 1989). However, Nitsch et ai. (1985) showed that during generalized seizures in adult rabbits, there is no re­ lationship between the rise in LCBF and the re­ gional pattern of blood-brain barrier opening. The same conclusion holds true for the present study, since in rats aged 6--15 days after birth the blood­ brain barrier is preferentially opened in the cerebel­ lum, hypothalamus, and hippocampus during PTZ­ induced seizures (Ziylan and Ates, 1989), while LCBF increases at all ages in the two former struc­ tures and is not changed or decreased from P14 to P21 in the latter one (the present study). Correlation of LCBF and LCMRgIc

While LCBF and LCMRglc both increase widely at early ages during PTZ-induced SE, they are able to increase, decrease, or not change with seizures by the end of the third postnatal week (Pereira de Vasconcelos et ai., 1992; present study). The de­ crease in LCBF rates in cortices and hippocampus in P21 PTZ-treated rats may be related to the de­ creases in LCMRglc seen in these areas (Pereira de

Vasconcelos et ai., 1992). In adult animals, LCBF has been shown to be affected by various factors related to metabolic changes during seizures that can be independent of blood pressure (Meldrum and Nilsson, 1976; Winn et ai., 1980; Pinard et ai., 1987). To our knowledge, there has been no report showing the postnatal evolution of the relationship between LCBF and LCMRglc during seizures. In the developing rat, whatever the age, there is no mismatch between the rates of LCBF recorded during PTZ-induced SE (the present study) and LCMR glc measured under the same conditions (Pereira de Vasconcelos et ai., 1992) despite a mild hypoperfusion at PI0 and P14 and hyperemia at P17 and P21. In adult animals, LCBF and LCMRglc usu­ ally increase to a similar degree during the early phase of generalized seizures. In structures consid­ ered vulnerable such as the neocortex and hippo­ campus, a mismatch between flow and metabolism develops late in the course of SE, i.e., after 2 h, with reduced LCBF and still high metabolic rates (Siesj6 et ai., 1983). Conversely, the immature rat has been shown to be quite resistant to the devel-· opment of seizure-induced brain damage. Usually, neuronal damage is not seen in immature rats after generalized seizures until the age of P25-P30 (NiJ

Cereb Blood Flow Metab, Vol. 15, No . 2, 1995

A. PEREIRA de VASCONCELOS ET AL.

280

PIO

Pl7

Pl4

P21

CONTROLS

r ···,······ · · . · · ·

'

PIO

Pl7

Pl4

: � ,:

� ..-�.. . .. . .. 'i� .�.....

,�

.



�,

.,

P21

SEIZURES [ 14C] lodoantipyrine

autoradiographs of rat brain coronal sections at different postnatal ages, taken at the level of the substantia nigra. At all ages, SE induced an increase in brain density in all subcortical areas, particularly marked at P1 7 and P21.

FIG. 2.

In contrast, dorsal hippocampus and cortical areas were poorly labeled in P21 PTZ-treated rats compared to controls.

tecka et aI., 1984; Sperber et aI., 1991; Hirsch et aI., 1992). Rates of LCBF (present study) and LCMRglc (Pereira de Vasconcelos et aI., 1992) increase all over the brain at PI0 and P14 during seizures, while these two parameters increase mainly in the brain stem, thalamus, and hypothalamus and decrease in the neocortex and hippocampus in seizing P17 and P21 rats. The parallel changes recorded in LCBF and LCMRglc in PTZ-exposed PIO-P21 rats may be one of the reasons why the immature brain is more resistant to seizure-induced brain damage than the adult brain. Regulation of CBF during PTZ seizures

The present study demonstrates marked age­ dependent and regionally specific vascular effects of PTZ-induced seizures in rats. Although the pre­ cise mechanism for CBF elevations during seizures remains unknown, the increase has been attributed partly to cerebral vasodilation mediated by local chemical factors, including neurotransmitters. The age-variations in LCBF changes during PTZ­ induced seizures in the present study may be due to the maturation of the GABA system involved in this type of seizures. At birth, the GABA synthetic en­ zyme reaches only 5% of its adult level and the GABA-receptor activity represents about 30% of the adult binding, with an increase to adult levels by J

Cereb Blood Flow Metab. Vol. 15, No. 2, 1995

the fourth week (Coyle and Enna, 1976). Therefore, the CBF response to PTZ, which acts mainly at the level of the GABA receptor, may be affected by the maturation of the GABA system. Likewise, the role of excitatory amino acid receptors, primarily the N-methyl-o-aspartate receptor, in adult epilepsy has been studied extensively (Jobe and Laird, 1987). The relative immaturity of these systems is able to modify their potential for mediating excitat­ ing phenomena during postnatal development of the rat (Ikonomidou et aI., 1989). For example, during ischemia, no aspartate or glutamate is released be­ fore PI0 (Cherici et aI., 1991). Therefore, the het­ erogeneity of LCBF response recorded in the present study during SE at P17 and P21 may reflect the maturation of the different components of the excitatory amino acid system. One neuromodulator that could be partly in­ volved in the seizure-induced increase in LCBF is adenosine (Schrader et aI., 1980; Winn et aI., 1980). Adenosine is known to be an important regulator of CBF (Phillis, 1989) even during the neonatal period (Laudignon et aI., 1990). The role of adenosine in CBF regulation during seizures may depend on the degree of brain maturation. Newborn rats have low brain adenosine concentrations, which progres­ sively increase postnatally to the adult value (Aranda et aI., 1989). The dilatory responses of ce-

CEREBRAL BLOOD FLOW AND SEIZURES IN RAT PUPS ;:-- 200 I c:

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