Sex differences in behavioral pathology induced by subconvulsive stimulation during early postnatal life are overcome by epileptic activity in the pre-juvenile weanling period.

Chronic subconvulsive activity in early life leads to sex-related autistic-like deficits in handling, object recognition, and social performance in pre-pubertal rats. Since autism and epilepsy are common neurodevelopmental disorders with high coincidence, we tested whether early-life chronic subconvulsive activity compared to convulsive activity alters handling, spatial memory, lateralization, coping strategy and the seizure threshold in a sex-dependent manner. A hypothesis is that convulsive seizures may alter sex differences induced by subconvulsive (SC) activity. Serial subconvulsive doses of kainic acid (KA) were administered postnatally (0.25-1 mg/kg) for 15 days to induce the chronic subconvulsive phenotype (SC group). Age-matched controls and a subset of SC pups were exposed to a convulsive dose of KA (KA and SC + KA groups; 7.5 mg/kg) or flurothyl vapors. In our open handling test, controls and the ASD groups escaped to a similar degree whereas after convulsive seizures, the pups exhibited freezing behavior; no escapes occurred. In the spontaneous alternating T-Maze control males and females entered the left arm with higher frequency. The SC males but not SC females entered left and right arms to a similar degree; alternation rates were reduced to chance revealing a sex difference. However, in KA and SC + KA groups, there was a sharp loss of spontaneous alternation rates. The rapid repetitive entries shifted to the right in both sexes possibly be due to hippocampal injury and changes in network activity induced by status epilepticus. In the forced swim test (FST), control and CS females were more active than corresponding males. After convulsions, immobility was reduced and vertical mobility was increased in SC and SC + KA males suggesting an elevated coping strategy compared to females. Onset and severity of KA induced status epilepticus was delayed in SC males and females possibly due to desensitization of KA receptors. Following flurothyl exposure, control males had faster onset of twitches and clonic seizures than control females which disappeared after the sub-convulsive pre-treatment. Data suggest that behavioral manifestations are more readily detectable between males and females when low levels of hyperexcitation are present chronically in early postnatal development but diminished after tonic-clonic convulsions persist. Therefore, therapeutic interventions may benefit patients if initiated upon the initial onset of sex-related autistic pathologies, particularly in males, which may reduce subsequent vulnerability to seizures.

Oestradiol Regulates Neuropeptide Y Release and Gene Coupling with the GABAergic and Glutamatergic Synapses in the Adult Female Rat Dentate Gyrus.

Neuropeptide Y (NPY) is an endogenous modulator of neuronal activity affecting both GABAergic and glutamatergic transmission. Previously, we found that oestradiol modifies the number of NPY immunoreactive neurones in the hippocampal dentate gyrus. In the present study, we investigated which oestrogen receptor type is responsible for these changes in the number of NPY-positive neurones. Furthermore, we determined the effects of oestrogen receptor activation on NPY release. Finally, we examined the contribution of oestrogen toward the remodelling of the GABAergic and glutamatergic gene networks in terms of coupling with Npy gene expression in ovariectomised rats. We found that activation of either oestrogen receptor type (ERα or ERß) increases the number of NPY-immunopositive neurones and enhances NPY release in the dentate gyrus. We also found that, compared to oestrogen-lacking ovariectomised rats, oestrogen replacement increases the probability of synergistic/antagonistic coupling between the Npy and GABAergic synapse genes, whereas the glutamatergic synapse genes are less likely to be coupled with Npy under similar conditions. The data together suggest that oestrogens play a critical role in the regulation of NPY system activity and are also involved in the coupling/uncoupling of the Npy gene with the GABAergic and glutamatergic synapses in the female rat dentate gyrus.

Sex-specific behavioral traits in the Brd2 mouse model of juvenile myoclonic epilepsy.

Idiopathic generalized epilepsy represents about 30-35% of all epilepsies in humans. The bromodomain BRD2 gene has been repeatedly associated with the subsyndrome of juvenile myoclonic epilepsy (JME). Our previous work determined that mice haploinsufficient in Brd2 (Brd2+/-) have increased susceptibility to provoked seizures, develop spontaneous seizures and have significantly decreased gamma-aminobutyric acid (GABA) markers in the direct basal ganglia pathway as well as in the neocortex and superior colliculus. Here, we tested male and female Brd2+/- and wild-type littermate mice in a battery of behavioral tests (open field, tube dominance test, elevated plus maze, Morris water maze and Barnes maze) to identify whether Brd2 haploinsufficiency is associated with the human behavioral patterns, the so-called JME personality. Brd2+/- females but not males consistently displayed decreased anxiety. Furthermore, we found a highly significant dominance trait (aggression) in the Brd2+/- mice compared with the wild type, more pronounced in females. Brd2+/- mice of either sex did not differ from wild-type mice in spatial learning and memory tests. Compared with wild-type littermates, we found decreased numbers of GABA neurons in the basolateral amygdala, which is consistent with the increase in aggressive behavior. Our results indicate that Brd2+/- haploinsufficient mice show no cognitive impairment but have behavioral traits similar to those found in patients with JME (recklessness, aggression). This suggests that either the BRD2 gene is directly responsible for influencing many traits of JME or it controls upstream regulators of individual phenotypes.

Prenatal corticosteroids modify glutamatergic and GABAergic synapse genomic fabric: insights from a novel animal model of infantile spasms.

Prenatal exposure to corticosteroids has long-term postnatal somatic and neurodevelopmental consequences. Animal studies indicate that corticosteroid exposure-associated alterations in the nervous system include hypothalamic function. Infants with infantile spasms, a devastating epileptic syndrome of infancy with characteristic spastic seizures, chaotic irregular waves on interictal electroencephalogram (hypsarhythmia) and mental deterioration, have decreased concentrations of adrenocorticotrophic hormone (ACTH) and cortisol in cerebrospinal fluid, strongly suggesting hypothalamic dysfunction. We have exploited this feature to develop a model of human infantile spasms by using repeated prenatal exposure to betamethasone and a postnatal trigger of developmentally relevant spasms with NMDA. The spasms triggered in prenatally primed rats are more severe compared to prenatally saline-injected ones and respond to ACTH, a treatment of choice for infantile spasms in humans. Using autoradiography and immunohistochemistry, we have identified a link between the spasms in our model and the hypothalamus, especially the arcuate nucleus. Transcriptomic analysis of the arcuate nucleus after prenatal priming with betamethasone but before trigger of spasms indicates that prenatal betamethasone exposure down-regulates genes encoding several important proteins participating in glutamatergic and GABAergic transmission. Interestingly, there were significant sex-specific alterations after prenatal betamethasone in synapse-related gene expression but no such sex differences were found in prenatally saline-injected controls. A pairwise relevance analysis revealed that, although the synapse gene expression in controls was independent of sex, these genes form topologically distinct gene fabrics in males and females and these fabrics are altered by betamethasone in a sex-specific manner. These findings may explain the sex differences with respect to both normal behaviour and the occurrence and severity of infantile spasms. Changes in transcript expression and their coordination may contribute to a molecular substrate of permanent neurodevelopmental changes (including infantile spasms) found after prenatal exposure to corticosteroids.

Hippocampal afterdischarges in rats. I. Effects of antiepileptics.

Hippocampal afterdischarges (ADs) are considered to be a model of complex partial seizures. To study the pharmacology of these ADs, stimulation electrodes were implanted into the dorsal hippocampus of 33 male Wistar rats. Stimulation (15-s series of monophasic rectangular pulses with a duration of 1 ms and frequency of 8 Hz) was applied four times with interstimulation intervals of 15 min. Drugs (carbamazepine 50 and 100 mg/kg; clonazepam 0.2 and 0.5 mg/kg; ethosuximide 125 and 250 mg/kg; phenobarbital 40 and 80 mg/kg) as well as solvent and isotonic saline were injected intraperitoneally 2 min after the cessation of the first AD. Duration of AD, of the latent period between AD and recurrent AD and duration of recurrent AD and the number of wet dog shakes were measured. ADs were markedly shortened by both doses of clonazepam and phenobarbital and by the higher dose of carbamazepine. The action of ethosuximide was negligible. Wet dog shakes were influenced in the same way as AD duration. Recurrent ADs were more sensitive to antiepileptics than ADs and wet dog shakes.

Temporal lobe epileptogenesis and epilepsy in the developing brain: bridging the gap between the laboratory and the clinic. Progression, but in what direction?

The origins of human mesial temporal lobe epilepsy and hippocampal sclerosis are still not well understood. Hippocampal sclerosis and temporal lobe epileptogenesis involve a series of pathologies including hippocampal neuronal loss and gliosis, axonal reorganization, and maybe hippocampal neoneurogenesis. However, the causality of these events is unclear as well as their relation to the factors that may precipitate epileptogenesis. Significant differences between temporal lobe epileptogenesis in the adult and immature brain may require differential approaches. Hereditary factors also may participate in some cases of hippocampal sclerosis. The key point is to identify the significance of these age-dependent changes and to design preventive treatments. Novel strategies for the prevention and treatment of mesial temporal lobe epilepsy and hippocampal sclerosis may include rational use of neuroprotective agents, hormonotherapy, immunizations, and immunotherapy.

Prenatal methotrexate exposure delays onset of low Mg(2+)-induced epileptiform discharges in the entorhinal cortex.

We determined the effects of prenatal exposure to DNA synthesis inhibitor methotrexate (MTX) on: (a) the susceptibility to low Mg(2+)-induced epileptiform activity in deep layers (IV-V) of medial entorhinal cortex in vitro; and (b) neuronal counts in this area. Low Mg(2+)-induced discharges developed significantly later in slices from prenatally MTX-exposed rats than in control slices. Neuronal counts were increased in the layer V of medial entorhinal cortex of prenatally MTX-exposed rats. Results indicate that: (a) MTX-induced prenatal brain DNA impairment is antiepileptogenic; and (b) simple increases in neuronal numbers may not be associated with epileptogenic effects.

Neuroprotective effects of estrogens on hippocampal cells in adult female rats after status epilepticus.

PURPOSE: Estrogens have neuroprotective effects in ischemia, stroke, and other conditions leading to neuronal cell death (e.g., Alzheimer's disease). The present study examined whether estrogens may have neuroprotective effects after seizures. METHODS: The kainic acid model was used to determine if estrogens protect hippocampal cells after status epilepticus in adult female rats. Rats were ovariectomized 1 week before hormone replacement. beta-Estradiol benzoate (EB; 2 microg in 0.1 mL of oil) was injected subcutaneously 48 and 24 hours before seizure testing. We administered kainic acid (16 mg/kg intraperitoneally) and behaviorally monitored the rats for 5 hours. After this time, all rats were injected with pentobarbital (50 mg/kg intraperitoneally) irrespective of seizure severity. Some rats received two additional doses of EB, one immediately and one 24 hours after the seizures. Another group of rats received only these two doses of EB after the seizures, and yet another group of rats received pretreatment with the intracellular EB receptor antagonist tamoxifen before each of four EB injections. Control rats received oil instead of EB. Rats were killed 48 hours after seizures. Neuronal damage was evaluated in silver-impregnated and Nissl-stained sections. RESULTS: Estrogen treatment before kainic acid administration significantly delayed the onset of kainic acid-induced clonic seizures, whereas it did not change the onset of status epilepticus compared with oil-treated controls. Furthermore, estrogen treatment significantly protected against kainic acid-induced seizure-related mortality. In control rats, examination of Nissl-stained and silver-impregnated slides revealed severe neuronal damage in the vulnerable pyramidal neurons of the hippocampal CA3 subfield and in the hilus of the dentate gyrus. Estrogen pretreatment, as well as the combination of pretreatment and posttreatment, significantly reduced the number of argyrophilic neurons in both the CA3 and the dentate gyrus. Posttreatment only had no protective effects. The data indicate that intracellular EB receptors mediate this type of neuroprotective effect, because the tamoxifen pretreatment abolished EB neuroprotection. CONCLUSIONS: Our results suggest that estrogens can be beneficial in protecting against status epilepticus-induced hippocampal damage. Hormonal conditions may have differential effects on underlying epileptic state in some patients. Therefore, more studies are necessary to determine the prospective therapeutic advantage of hormonal treatment in seizure-related damage.

Plasticity of excitatory amino acid transporters in experimental epilepsy.

PURPOSE: To examine the relationship between seizures and excitatory amino acid transporter (EAAT) activity and whether up-regulation of EAAT activity alters epileptogenicity. METHODS: In this study, we exposed rat hippocampal slices to different convulsants before measuring EAAT activity. Rats were exposed to the EAAT inhibitor pyrrolidine-2,4-dicarboxylic acid (PDC) before entorhinal cortex/hippocampal slices were obtained. These slices were exposed to low-Mg2+ buffer while electrophysiological recordings were obtained from the entorhinal cortex. mGluR III acting agents were used to study whether activation of mGluR III could regulate EAAT activity and if this regulation could overcome the effects on EAAT activity induced by the convulsants. RESULTS: Veratridine, kainic acid (KA), and pilocarpine reduced EAAT activity in rat hippocampal slices. L-2-Amino-4-phosphonobutyric acid (an mGluR III agonist) restored EAAT activity and reduced epileptiform activity to near control levels. The saturation curve for glutamate uptake in slices from KA-seized rats killed 2 hours after the first forelimb clonus was displaced to the left, suggesting a compensatory change for the enhanced excitation. On the other hand, rats injected with the EAAT inhibitor PDC (by intracerebroventricular injection) had more severe KA-induced seizures and N-methyl-D-aspartate epileptiform activity than control rats. Furthermore, hippocampal slices from KA- or KA+PDC-treated rats exposed to low Mg2+ reduced their firing rate to nearly zero once they returned to normal solution, whereas their control counterparts continued to fire, although at a lower rate. CONCLUSIONS: These results suggest a significant contribution of EAATs in some experimental epilepsy models and point to their short-term regulation by mGluR III as a possible source of their plasticity.

Effect of ganaxolone on flurothyl seizures in developing rats.

PURPOSE: To determine the effects of a newly synthesized epalon, ganaxolone (GNX), on primarily generalized seizures in rats of various ages during development. Epalons are classified as neuroactive steroids that interact at unique site of the GABAA receptor-Cl- channel complex in the central nervous system. METHODS: Sprague-Dawley male rats were used at 9, 15, 30, and 60 postnatal days (PN). GNX dissolved in 2-hydroxypropylbeta-cyclodextrine was administered intraperitoneally in different doses at various time points before flurothyl testing. The incidence and threshold of clonic and tonic-clonic flurothyl seizures were evaluated. Behavioral changes were also assessed. RESULTS: In all age groups, the effects of GNX were dose dependent and more prominent 10 min after its administration. In PN 60 and PN 30 rats, GNX had dose-dependent anticonvulsant effects; tonic-clonic seizures were more sensitive to GNX treatment than clonic seizures. In PN 15 and PN 9 rats, GNX demonstrated dose-and time-dependent anticonvulsant effects against both types of flurothyl-induced seizures. GNX was more effective in PN 15 rats than in other age groups, but at doses that altered motor behavior. CONCLUSIONS: GNX has anticonvulsant effects against flurothylinduced seizures in all age groups tested. Its effects are more prominent in the two younger age groups, especially in PN 15 rats, but are associated with motor side effects.

Prenatal morphine exposure enhances seizure susceptibility but suppresses long-term potentiation in the limbic system of adult male rats.

The present study examined the effects of prenatal morphine exposure on NMDA-dependent seizure susceptibility in the entorhinal cortex (EC), and on activity-dependent synaptic plasticity at Schaffer collateral and perforant path synapses in the hippocampus. During perfusion with Mg(2+)-free ACSF, an enhancement of epileptiform discharges was found in the EC of slices from prenatally morphine-exposed male rats. A submaximal tetanic stimulation (2x50 Hz/1 s) in control slices elicited LTP at the Schaffer collateral-CA1 synapses, but neither LTP nor LTD was evoked at the perforant path-DG synapses. In slices from prenatally morphine-exposed adult male rats, long-term potentiation of synaptic transmission was not observed at Schaffer collateral-CA1 synapses, while the submaximal tetanus now elicited frank LTD of synaptic EPSPs at perforant path synapses. These data suggest that prenatal morphine exposure enhances the susceptibility of entorhinal cortex to the induction of epileptiform activity, but shifts long-term plasticity of hippocampal synapses in favor of LTD.

Prenatal methotrexate exposure decreases seizure susceptibility in young rats of two strains.

Effects of prenatal exposure to methotrexate (MTX) administered in Sprague-Dawley (one 5 mg/kg dose of MTX on gestational day 15; E15) or Wistar (one 5 mg/kg dose of MTX on E14 or E15 or two such doses on E15) pregnant rat dams were studied in developing offspring. Young Sprague-Dawley rats were subjected to rapid kindling on postnatal days (PN) 15 and 16, and to flurothyl seizures on PN 15 and PN 30. Offspring of the Wistar strain were tested in flurothyl on PN 30. In Sprague-Dawley rats, prenatal exposure to MTX decreased susceptibility to kindling-induced seizures on PN 15 and to flurothyl-induced clonic seizures on PN 30. In Wistar rats, a single dose of MTX on E15 was ineffective, but two doses significantly decreased susceptibility to flurothyl-induced seizures. Additionally, due to a shorter duration of pregnancy in Wistar rats, exposure to a single dose of MTX on E14 also decreased susceptibility to flurothyl seizures. MTX, as folic acid antagonist, interferes with DNA synthesis. However, unlike other treatments that suppress DNA synthesis (such as methylazoxymethanol exposure or X-ray radiation), MTX exposure results in anticonvulsant effects in surviving offspring. The data suggest that not all prenatal impairments of DNA have proconvulsant features postnatally.

Prenatal morphine exposure alters N-methyl-D-aspartate- and kainate-induced seizures in adult male rats.

The purpose of the present study was to investigate whether prenatal exposure to morphine has effects on excitatory amino acid-induced seizures. Adult male rats, exposed on embryonic days 11-18 to saline or morphine, were injected with N-methyl-D-aspartate (NMDA) (150, 175, 200, 225, and 250 mg/kg) or kainic acid (KA) (15 or 20 mg/kg) in adulthood to assess the occurrence and latency to onset of stereotypy and seizures. The latency to onset of stereotypy was significantly increased after 175 mg/kg, and decreased after 200 mg/kg of NMDA in morphine-exposed animals. The lowest dose of NMDA (150 mg/kg) induced seizures in prenatally saline-treated control male rats but not in the morphine-exposed male rats. In the KA-injected group, prenatally morphine-exposed males had shorter latency to onset of wet-dog shakes, but there were no effects on the latency to onset of clonic seizures. The data suggest that prenatal morphine exposure has long-term effects on seizure susceptibility and the onset of stereotypy in the excitatory amino acid-induced seizure models.

Region-specific modulation of limbic seizure susceptibility by ovarian steroids.

Gonadal steroid hormones can markedly affect seizure susceptibility. Ovariohysterectomized female rats given ovarian steroid hormone supplements were used to evaluate the effects of ovarian steroids on epileptiform activity in hippocampal slices in vitro and on flurothyl-induced seizures in vivo. Seizure susceptibility was compared in the entorhinal cortex (EC) and CA1 regions of the hippocampus perfused with Mg(2+)-free medium, which leads to epileptiform discharges caused by a relief of voltage-dependent NMDA receptor block. After in vivo treatment with 500 microg of progesterone for 2 h prior to slice preparation, the latency to onset of low Mg(2+)-induced epileptiform activity of slices was significantly prolonged compared to slices from controls. In contrast, progesterone replacement accelerated the development of epileptiform activity in the CA1 region. Neither estrogen alone (2 x 2 microg of estradiol benzoate, 48 and 24 h prior to the experiment), nor a combined treatment with estrogen plus progesterone, significantly affected seizure susceptibility in either CA1 or the EC. There were no consistent effects of estrogen or progesterone, alone or in combination, on flurothyl-induced seizures in vivo. The data suggest that in vitro, progesterone alters seizure susceptibility in a site- and seizure model-specific fashion. The differential effects of progesterone may be due to differential expression of progesterone receptor isoforms or metabolites in specific brain areas suggesting that selective modulation of NMDA receptor-dependent epileptiform activity may play a role in hormonal effects on epileptogenesis.

Age-specific N-methyl-D-aspartate-induced seizures: perspectives for the West syndrome model.

PURPOSE: With intraperitoneal N-methyl-D-aspartate (NMDA; 15-200 mg/kg) administration, we attempted to develop an animal model of age-specific West syndrome to serve for testing of putative anticonvulsant drugs and to determine the mechanisms of this disorder. METHODS: Experiments were performed in 12-, 18-, and 60-day-old (adult) rats. The effects of systemic pretreatment with hydrocortisone (5-25 mg/kg), pyridoxine (20-250 mg/kg), and sodium valproate (VPA; 200 and 400 mg/kg) against the NMDA-induced automatisms, emprosthotonic (hyperflexion), and clonic-tonic seizures were determined. NMDA-induced EEG changes and alterations of the performance in horizontal bar, rotorod, open field, and elevated plus-maze tests were recorded. RESULTS: In young rats, hydrocortisone had proconvulsant effects. High doses of pyridoxine induced epileptiform activity independent of and distinct from that induced by NMDA. Only VPA had moderate effects against the NMDA-induced syndrome. EEG consisted of periods of suppression mixed with ictal activity of serrated waves and high-voltage chaotic EEG activity. In adult rats, EEG alterations involved spike and spike-and-wave activity. NMDA also deteriorated performance of young rats in the open field, rotorod, and elevated plus maze tests. CONCLUSIONS: NMDA syndrome in rats fulfills some, but not all, criteria of the West syndrome model, such as occurrence of flexion seizures, nonspecific diffuse EEG changes, refractoriness to antiepileptic therapy (but a response to VPA), as well as long-term alteration of behavioral tasks. However, NMDA-induced seizures represent an acute model without the occurrence of spontaneous seizures, whereas in the clinical situation, both the seizures and neurologic deterioration are chronic. Further, in the West syndrome and the NMDA seizure model, there is an incongruent response to therapy with antiepileptic drugs.

Bicuculline-induced rhythmic EEG episodes: gender differences and the effects of ethosuximide and baclofen treatment.

PURPOSE: There are gender differences in the expression of seizures. We tested rhythmic EEG episodes induced by low doses of bicuculline in rats for gender differences. To verify the validity of these discharges as a model of absence seizures in both male and female rats, we tested the antiabsence drug ethosuximide (ESM) and a gamma-aminobutyric acid (GABA(B))-receptor agonist, baclofen, which may exacerbate absence seizures. METHODS: Adult rats of both sexes were used. Under general anesthesia, EEG electrodes were implanted over frontal and occipital cortex, and some females were ovariectomized. After recovery, male, intact female rats, and female rats ovariectomized and ovariectomized rats with estradiol replacement were compared for occurrence of rhythmic EEG episodes (approximately 6 cycles/ s) induced by 2.5 mg/kg of bicuculline, s.c. Because of gender differences in sensitivity to bicuculline, further pharmacologic effects of ESM (125 and 250 mg/kg, i.p.) and baclofen (2 mg/kg, i.p.) were tested separately in male (3.0 mg/kg of bicuculline), and female (2.5 mg/kg of bicuculline) rats. RESULTS: After the identical dose of bicuculline, s.c., male and female rats differed in the incidence of rhythmic episodes and in the latency to onset of the first as well as the generalized episode. Female rats with natural or exogenous estrogens (but not ovariectomized rats) developed EEG episodes more often than did males, and this effect could be attributed to the presence of estrogens. ESM pretreatment suppressed the episodes, whereas baclofen enhanced their occurrence, as well as the total duration of episodes without gender-specific differences. CONCLUSIONS: The study demonstrates gender differences (related probably to the presence of circulating estrogens) in the susceptibility of rats to develop rhythmic EEG episodes induced by threshold doses of bicuculline. This activity has some features of an acute absence seizure model.

Prenatal morphine exposure alters ovarian steroid hormonal regulation of seizure susceptibility.

The present study examined the ovarian hormonal regulation of seizure susceptibility in prenatally morphine- and saline-exposed adult female rats in the flurothyl seizure model in vivo, and in low-magnesium-induced epileptiform activity in brain slices, in vitro. All females were ovariohysterectomized (OVX); some received either estrogen (E) or progesterone (P) replacement, while others were injected with E + P sequentially. In prenatally saline-treated control females, there was an increase in the flurothyl-induced clonic seizure threshold (anticonvulsant effect) in the presence of both hormones (E + P) compared to OVX controls. In morphine-exposed females, there was an increase in the flurothyl-induced clonic seizure threshold after an E injection alone while there was a reduced tonic--clonic seizure threshold in the presence of both hormones (E + P) compared to the hormone treatment-matched group of saline-exposed females. In control females, in low magnesium medium in vitro, the development of two types of epileptiform activity (seizure-like events and status of short discharges) was not affected by the different hormonal conditions. However, prenatal morphine exposure suppressed the development of both types of epileptiform activity in the E-injected females compared to the E-injected, control females. The present data demonstrate that the anticonvulsant effects of P on seizure susceptibility requires the presence of E. Furthermore, prenatal morphine exposure alters ovarian steroid hormone-regulated seizure susceptibility.

Site-specific effects of local pH changes in the substantia nigra pars reticulata on flurothyl-induced seizures.

Local cerebral changes of acid-base balance may interfere with neuronal communication. Acidosis enhances and alkalosis suppresses GABAA receptor neurotransmission while there are opposite effects on NMDA receptor transmission. In this study, we determined site-specific effects of acidified solutions of Na-HEPES-artificial cerebrospinal fluid infused into the anterior or posterior area of the substantia nigra pars reticulata (SNR) in rats. Two levels of pH were compared: 6.7 and 7.4. Rats were challenged with flurothyl and the threshold for clonic and tonic-clonic seizures was determined. In the anterior SNR, there were no differences between the effects of the solution with pH 6.7 and 7.4 on flurothyl seizures. In contrast in the posterior SNR, microinfusions with pH 6.7 had proconvulsant effects. The results suggest that local pH changes may have site-specific effects on seizure susceptibility in vivo.

Proconvulsant effects induced by pyridoxine in young rats.

High doses of pyridoxine (vitamin B6) can be neurotoxic in adults. Effects of intraperitoneally administered B6 (100, 250 and 400 mg/kg) were studied in 7, 12, 18 and 60 day old rats. B6 elicited epileptiform EEG discharges without any motor correlate in all age groups. In contrast, motor seizures were rare, seen only in 18 day old rats (250 mg/kg of B6). Data indicate that in young rats, B6 may have proconvulsant effects in doses relevant to those sometimes used in pediatric neurology.

Extracellular acidosis and high levels of carbon dioxide suppress synaptic transmission and prevent the induction of long-term potentiation in the CA1 region of rat hippocampal slices.

Long-term potentiation (LTP) is a long-lasting increase in synaptic strength induced by high frequency stimulation. LTP may participate in learning and memory formation. In many synaptic systems, LTP is dependent on intact function of N-methyl-D-aspartate (NMDA) receptors. NMDA receptors may be inhibited in different conditions involving also extracellular acidosis. A decrease in the extracellular pH accompanies many pathological states such as ischemia, hypoxia, and the CNS injury. The study was designed to determine whether comparable extracellular acid-base imbalances are able to interfere with the LTP induction. Hippocampal slices from adult rats were stimulated with high frequency stimulation (1 x 100 Hz/1 s) at Schaffer collateral-commissural synaptic system in the environment with different pH (6.7-7.8) and the field responses were recorded in CA1. Acidosis was achieved by supplying excessive CO2 or by HCO3-decrease in standard bicarbonate-containing buffer or by a direct acidification of the buffer containing Na-HEPES. Invariably, all forms of acidification suppressed the efficacy of normal, low frequency synaptic transmission and prevented the induction of LTP in a reversible manner; i.e., after reperfusion of the slices at pH 7.3 and restimulation, there was a return of synaptic transmission back to baseline, and a significant amount of LTP occurred. In contrast, alkalization to pH 7.8, although enhancing synaptic transmission efficacy, did not further increase the LTP magnitude compared to control environment with pH 7.3. The results suggest that extracellular acidosis associated with several pathological conditions in the CNS may significantly diminish the LTP induction, and thus negatively affect all physiological processes that utilize LTP.