Changes in Cholinergic but Not in GABAergic Markers in Amygdala, Piriform Cortex, and Nucleus Basalis of the Rat Brain Following Systemic Administration of Kainic Acid

Three days after systemic administration of kainic acid (15 mg/kg, s.c.), selected cholinergic markers (choline acetyltransferase, acetylcholinesterase, muscarinic acetylcholine receptor, and high-affinity choline uptake) and GABAergic parameters [benzodiazepine and gamma-aminobutyric acid (GABA) receptors] were studied in the frontal and piriform cortex, dorsal hippocampus, amygdaloid complex, and nucleus basalis. Kainic acid treatment resulted in a significant reduction of choline acetyltransferase activity in the piriform cortex (by 20%), amygdala (by 19%), and nucleus basalis (by 31%) in comparison with vehicle-injected control rats. A lower activity of acetylcholinesterase was also determined in the piriform cortex following parenteral kainic acid administration. [3H]Quinuclidinyl benzilate binding to muscarinic acetylcholine receptors was significantly decreased in the piriform cortex (by 33%), amygdala (by 39%), and nucleus basalis (by 33%) in the group treated with kainic acid, whereas such binding in the hippocampus and frontal cortex was not affected by kainic acid. Sodium-dependent high-affinity choline uptake into cholinergic nerve terminals was decreased in the piriform cortex (by 25%) and amygdala (by 24%) after kainic acid treatment. In contrast, [3H]flunitrazepam binding to benzodiazepine receptors and [3H]muscimol binding to GABA receptors were not affected 3 days after parenteral kainic acid application in any of the brain regions studied. The data indicate that kainic acid-induced limbic seizures result in a loss of cholinergic cells in the nucleus basalis that is paralleled by degeneration of cholinergic fibers and cholinoceptive structures in the piriform cortex and amygdala, a finding emphasizing the important role of cholinergic mechanisms in generating and/or maintaining seizure activity.     

Responses of Heat Shock Proteins hsp27, αB-Crystallin, and hsp70 in Rat Brain After Kainic Acid-Induced Seizure Activity

We determined the changes in the levels of the mammalian small heat shock protein of 25-28 kDa (hsp27) and the hsp alphaB-crystallin in various regions of rat brain after kainic acid-induced seizure activity by means of specific immunoassays. The levels of hsp27 in the hippocampus and entorhinal cortex were markedly increased and reached a maximum (1.5-2 microg/mg of protein) 2-4 days after the seizure. The levels of hsp27 in these regions were considerably high even 10 days after the seizure. A marked increase in levels of mRNA for hsp27 was also observed in the hippocampus of rats 1-2 days after the seizure. A severalfold increase in the levels of alphaB-crystallin was observed in the hippocampus and entorhinal cortex of rats 2 days after the seizure. However, the maximum levels were <50 ng/mg of protein. The levels of protein sulfhydryl group and glutathione were significantly reduced in the hippocampus of rats at 24 h after the seizure, which might have enhanced the expressions of hsp27 and alphaB-crystallin. The expression of inducible mammalian hsp of 70 kDa (hsp70) was also enhanced in the hippocampus of rats after the seizure, as detected by western and northern blotting analyses. Immunohistochemically, an intensive staining of hsp27 was observed in both glial cells and neurons in the hippocampus, piriform cortex, and entorhinal cortex of rats with kainic acid-induced seizure. However, in the cerebellum, where the receptors for kainic acid are also rich, hsp27 was barely induced in the same rats. This might be due to high levels of the cerebellar calcium-binding proteins parvalbumin and 28-kDa calbindin-D, which might have a protective effect against the kainic acid-inducible damage.     

Some regional anatomical relationships of TRH to 5-HT in rat limbic forebrain

It is now a recognized principle that various neuropeptides are neuronally co-localized with biogenic amine or aminoacid neurotransmitters. In the rat CNS it has previously been shown that TRH is co-localized with 5-HT (and also with substance P) in cell bodies of the posterior raphe that project to the spinal cord. Although TRH cell bodies are known to be widely distributed throughout the forebrain there is no other known co-localization with 5-HT. In this study we further specify the anatomical relationship of TRH with 5-HT by use of surgical and neurotoxic lesioning with reference to limbic forebrain regions wherein TRH is greatly increased following seizures. In groups of rats, the fimbria-fornix was lesioned alone, or combined with a lesion of the dorsal perforant path or the ventral perforant path. There was a sham lesioned control group. Additional groups were lesioned with 5, 7 dihydroxytryptamine, 100 g i.v.t., 45 min. after i.p. desipramine, 25 mg/kg. All rats were sacrificed three weeks after lesions. Indoleamines were determined by HPLC in left anterior cortex, left pyriform/olfactory cortex, left dorsal hippocampus and left ventral hippocampus. TRH was determined by specific RIA in the corresponding right brain regions. The modal n was 7 rats. The surgical lesions reduced 5-HT to below the detection limit in dorsal hippocampus in all three groups, and to 31–52% of control in all the ventral hippocampus groups. 5-HIAA was reduced to 19–37% of control in dorsal and to 30–51% of control in ventral hippocampus. TRH was reduced to 44–61% of control in dorsal hippocampus and to 48–53% of control in ventral hippocampus. As was repeatedly observed in our previous reports all TRH levels in ventral hippocampus were higher than in dorsal hippocampus. The 5, 7 dihydroxytryptamine treatment nearly eliminated the indoleamines from all the forebrain regions examined while TRH levels were unchanged. These results can be explained by our previous data showing that immunoreactive TRH is intrinsic and localized to the vicinity of both CA and dentate granule cells of the hippocampus, but about half of hippocampal TRH enters via fibers of the fimbria-fornix. The perforant path appears to contribute no TRH to hippocampus, but, results with the combined lesion groups showed some reduction of 5-HIAA in ventral hippocampus as is expected from the known perforant path contribution of 5-HT. Since the neurotoxic lesion had no effect on TRH, the 5-HT pathway through the fimbria-fornix is probably anatomically separate from a parallel TRH pathway there. This study shows that co-localization of TRH with 5-HT is very unlikely in four specific limbic forebrain regions.Special issue dedicated to Dr. Morris H. Aprison.     

Changes in Neurofilament Protein NF-L and NF-H Immunoreactivity Following Kainic Acid-Induced Seizures

Abstract: Postlesion plasticity of neuronal processes might contribute to secondary spontaneous seizures after kainic acid administration. In this study, neurofilament (NF) proteins were examined following intraperitoneal injection of kainic acid, and special reference was given to temporal changes in quantity and quality of the NF light (NF-L) and heavy (NF-H) subunits. A pronounced decrease in phosphorylation-related immunoreactivity of NF-H occurred as early as 1 day after the injection in the amygdala/pyriform cortex, hippocampus, striatum, and dorsal cerebral cortex. A shift of NF-H from the phosphorylated to nonphosphorylated form was evident in immunoblots, suggesting dephosphorylation contributed to the decrease. Decreases in NF-L and phosphorylated NF-H contents in the limbic structure at 3 days were correlated with the increasing kainic acid doses from 2.5 to 10 mg/kg. The degradation pattern in immunoblots with antibodies against NF-L indicated that the decrease in NF-L was probably due to calcium-activated proteolysis. NF-L and phosphorylated NF-H contents secondarily increased from 9 days onward, with ∼20% above the control level of phosphorylated NF-H immunoreactivity at 27 days in the amygdala/pyriform cortex and ventral hippocampus. Immunohistochemical examination of the hippocampus revealed that an increase of NF staining in the mossy fiber system may contribute to the NF recovery in this region. Furthermore, the temporal changes of NF-L and phosphorylated NF-H contents were positively correlated with those of the neuronal cell adhesion molecule, a neuritic growth cone marker, substantiating postlesion regenerative reactions of NF proteins. Functional consequences of the NF plasticity remain to be identified.     

BDNF mRNA expression in the developing rat brain following kainic acid-induced seizure activity.

Brain-derived neurotrophic factor (BDNF) mRNA expression was studied in the hippocampus at various developmental stages in normal rats and following kainic acid (KA)-induced seizure activity. Systemic administration of KA strongly elevated BDNF mRNA levels in all hippocampal subregions after postnatal day 21. In contrast, even though KA induced intense behavioral seizure activity at postnatal day 8, the seizures were not associated with elevations of BDNF mRNA levels, indicating a clear dissociation between behavioral seizures and increases in BDNF mRNA levels and contradicting the view that BDNF mRNA expression is principally regulated by neuronal activity. In the dentate gyrus at postnatal day 13, intense BDNF mRNA expression was limited to a defined area at the border between granule cell and molecular layers, suggesting the possibility that segregation of BDNF mRNA into defined subcellular compartments may play a role in establishing the well-delineated patterns of innervation in the hippocampus.     

Role of limbic structures in the mechanisms of post-traumatic epilepsy]

It was shown in the experiments on rats that intracerebroventricular administration of kainic acid (0.01, 0.05 microgram) after brain trauma, resulted in the occurrence of behavioral and electrographic convulsive disturbances; maximal expression of epileptic activity was obtained in entorhinal cortex and ventral hippocampus. Kainic acid induced epileptic reactions in nontraumatized rats only if injected in dose 0.1 microgram. Brain trauma did not lead to changes in seizures intensity induced by systemic picrotoxin administration. It is concluded that the formation of generator of pathologically enhanced excitation in limbic structures via increase of excitor glutamatergic neurotransmission is the important mechanism of traumatic epilepsy.     

Adrenalectomy Attenuates Kainic Acid-Induced Spectrin Proteolysis and Heat Shock Protein 70 Induction in Hippocampus and Cortex

Abstract: Glucocorticoids have been shown to exacerbate the damaging effects of a variety of neurotoxic insults in the hippocampus and other brain areas. Evidence suggests that the endangering effects of glucocorticoids may be due to augmenting the cascade of events, such as elevations in intracellular calcium levels, because of excitatory amino acid (EAA) receptor stimulation. A potential mechanism responsible for EAA-induced neuronal damage is activation of calcium-sensitive proteases, such as calpain, which then proteolytically degrade cytoskeleton structural proteins, such as spectrin. The present study was designed to determine if glucocorticoids can regulate the spectrin proteolysis produced by the EAA agonist, kainic acid. Rats were adrenalectomized (ADX) or sham operated and 7 days later injected with kainic acid (10 mg/kg). Twenty-four hours later rats were killed and tissues obtained for western blot analyses of the intact spectrin molecule and the proteolytically derived breakdown products. Kainic acid produced an approximate sevenfold increase in the 145–155-kDa spectrin breakdown products in the hippocampus relative to ADX or sham rats injected with vehicle. ADX attenuated the kainic acid-induced increase in breakdown products by 43%. In a similar way, kainic acid produced a large 10-fold increase in spectrin breakdown products in the frontal cortex, which was also significantly attenuated (?80%) by ADX. Induction of heat shock protein 70 (hsp70) by neurotoxic insults has been suggested to be a sensitive indicator of cellular stress in neurons. Kainic acid induced large amounts of hsp70 in both hippocampus and frontal cortex of sham-operated rats that was markedly attenuated (85–95%) by ADX. There was a strong positive correlation between the amount of spectrin proteolysis and the degree of hsp70 induction in both the hippocampus and frontal cortex. In contrast, kainic acid did not significantly produce spectrin proteolysis and induced only a very modest and inconsistent increase of hsp70 in the hypothalamus. This is consistent with the observation that the hypothalamus is relatively insensitive to the neurotoxic effects of systemically administered kainic acid. The dose of kainic acid (10 mg/kg) used in this experiment produces a 10-fold elevation in circulating corticosterone levels at both 1 and 3 h after administration. These results suggest that part of the endangering effects of glucocorticoids on hippocampal and cortical neurons may be due to augmentation of calpain-induced spectrin proteolysis. The attenuation of kainic acid-induced synthesis of hsp70 by ADX indicates that the cellular stress produced by EAAs is regulated in part by glucocorticoids. In addition, the elevation in endogenous corticosterone levels produced by kainic acid appears to be a significant factor contributing to the neuronal damage produced by this agent.     

Intraventricular 6-hydroxydopamine increases thyrotropin-releasing hormone (TRH) content in regions of rat brain

Rats were given intraventricular (ivt) injections of various doses (50-400 micrograms, hydrobromide salt) of 6-hydroxydopamine (6-OHDA) and killed 1, 3 or 6 days later. Brains were removed, dissected into 11 regions, and the thyrotropin-releasing hormone (TRH) content of each region was measured by radioimmunoassay. 6-OHDA (400 micrograms) caused significant elevations in the TRH content of 6 regions: olfactory bulb, anterior cortex, brainstem, posterior cortex, hippocampus, and amygdala-piriform cortex. The magnitude of these increases ranged from 59% in olfactory bulb to 497% in hippocampus and was, in all cases, greatest at 3 days. These results suggest that the TRH content of certain brain regions may be regulated by catecholamine neurotransmitters.     

Effect of intrahippocampal kainic acid on the behavior of rats and functional state of mitochondria in brain structures

Cognitive processes and functional state of mitochondria in brain structures of Wistar rats were studied after intrahippocampal injection of kainic acid, an agonist of glutamate receptors. A single administration of 0.25 μg kainic acid into the dorsal part of the left and right hippocampi affected task retrieval and decreased inhibition of unrewarded responses. The injection of 0.75 μg kainic acid induced recurrent seizures and completely disorganized animal behavior. The functional state of mitochondria, as an important marker of excitotoxicity, was studied after intrahippocampal injections of kainic acid in the same doses. Kainic acid at 0.25 μg proved to activate the oxidative phosphorylation in hippocampal mitochondria. A higher (epileptogenic) dose of kainic acid inhibited mitochondrial respiration in the frontal cortex, but had an insignificant effect on mitochondrial respiration in the hippocampus. The disturbed interaction between the hippocampal system and frontal cortex after kainic acid administration can be the main factor of the revealed cognitive dysfunctions.     

Effect of electroconvulsive shock on the content of thyrotropin-releasing hormone in rat brain

Five grand-mal seizures were electrically induced in rats on alternate days. Forty-eight hours following the last seizure, TRH was quantitated in extracts of anterior cortex, hippocampus, striatum, thalamus plus midbrain, and hypothalamus. When compared to sham treated controls, TRH was found to be elevated 5-fold in the hippocampus and 2-fold in the striatum with no changes observed in the remaining regions. Since the time chosen for analysis excludes acute post-ictal effects, these results draw attention to a prolonged alteration of TRH levels in specific brain regions in an animal model of electroconvulsive treatment.     

Enhanced Rate of Expression and Biosynthesis of Neuropeptide Y After Kainic Acid-Induced Seizures

Recent studies have shown marked increases in brain content of neuropeptide Y (NPY) after seizures induced by intraperitoneal injection of kainic acid and after pentylenetetrazole kindling in the rat. We have now investigated possible changes in the rate of biosynthesis of NPY after kainic acid treatment, by using pulse-labeling of the peptide and by determining prepro-NPY mRNA concentrations. For pulse labeling experiments, [3H]tyrosine was injected into the frontal cortex, and the incorporation of the amino acid into NPY was determined after purifying the peptide by gel filtration chromatography, antibody affinity chromatography, and reversed-phase HPLC. At 2 and 30 days after kainic acid treatment, the rate of tyrosine incorporation was enhanced by approximately 380% in the cortex. In addition, concentrations of pre-pro-NPY mRNA were determined in four different brain areas by hybridization of Northern blots with a complementary 32P-labeled RNA probe 2, 10, 30, and 60 days after kainic acid treatment. Marked increases were observed in the frontal cortex (by up to 350% of controls), in the dorsal hippocampus (by 750%), and in the amygdala/pyriform cortex (by 280%) at all intervals investigated. In the striatum only a small, transient increase was observed. The data demonstrate increased expression of prepro-NPY mRNA and an enhanced rate of in vivo synthesis of NPY as a result of seizures induced by the neurotoxin kainic acid.     

Chronic ingestion of ethanol or glucose solutions affects hypothalamic and limbic TRH metabolism in dams and their pups

The effect of chronic ethanol consumption during pregnancy and lactation on thyrotropin releasing hormone (TRH) metabolism was investigated in the hypothalamus and limbic areas of female rats and their weaned pups. Pregnant female rats received ethanol or isocaloric glucose solution during pregnancy either alone, or also during the 3 weeks of lactation. Thyrotropin (TSH) and corticosterone levels were measured in serum; TRH and TRH-gly concentrations were determined in hypothalamus, hippocampus, n.accumbens, frontal cortex and amygdala of dams and pups at 21 days after parturition. Ethanol or glucose consumption during pregnancy and lactation produced a decrease in TSH levels compared with control animals fed at libitum; water replacement during lactation normalized TSH levels only in glucose-fed dams. Pups from ethanol or pair-fed dams showed low weight and increased TSH levels compared with normal rats. Variations in TRH metabolism were detected in limbic areas. Chronic ethanol caused a decrease in the levels of TRH in the hippocampus and frontal cortex of dams. In contrast, glucose chronic ingestion increased TRH content specifically in n.accumbens and amygdala of dams. Most of the variations in TRH content of limbic areas of pups were not specific for glucose or ethanol treatment and correlated with the deleterious effect of the mother's thyroid condition, although some differences were observed depending on pup's gender. These results support the involvement of TRHergic neurons in the limbic system of the female rat exposed to alcohol or glucose during pregnancy and lactation.     

Chronic ethanol or glucose consumption alter TRH content and pyroglutamyl aminopeptidase II activity in rat limbic regions

Thyrotropin-releasing hormone (TRH), its receptors and inactivating enzyme (PPII) are present in limbic regions. Nutritional changes or acute ethanol administration in male rats differentially modulate TRH or PPII expression. Chronic ethanol effect was studied in male (3, 6 and 8 weeks) and female rats (6 weeks) including naive and pair-fed (glucose) groups. Daily solid food and liquid intake, serum TSH and corticosterone, TRH content and PPII activity in limbic regions, were quantified. Gender differences were found in ethanol and total caloric intake and body weight gain, TSH and corticosterone levels. Ethanol consumption decreased TRH content and PPII activity in frontal cortex of male rats after 3-6 weeks. In contrast, glucose ingestion altered, by the third week, TRH content in amygdala, hippocampus, hypothalamus and nucleus accumbens, PPII activity in hippocampus and frontal cortex; by the sixth week, TRH content in amygdala and n. accumbens of male and females. Withdrawal at 24 h after 3-week ethanol ingestion decreased TRH content in amygdala and PPII activity in n. accumbens, while withdrawal from glucose reverted some of the effects produced by chronic glucose ingestion. Variations in TRH content or PPII activity support a region specific involvement of TRH neurons that depend on the treatment.     

The expression of TRH, its receptors and degrading enzyme is differentially modulated in the rat limbic system during training in the Morris water maze

TRH administration induces arousal, improves cognition, and modulates glutamatergic and cholinergic transmission in hippocampal neurons. To study the possible involvement of TRH neurons in learning and memory processes, gene expression of TRH, its receptors, and pyroglutamyl peptidase (PPII), were measured in limbic regions of water-maze trained rats. Hypothalamus and amygdala showed changes related to the task but not specific to spatial learning while in hippocampus, pro-TRH and TRH-R1 mRNA levels were specifically increased in those animals trained to find a hidden platform. Variation of TRH content and mRNA levels of pro-TRH, TRH-R1, TRH-R2 and PPII are observed in conditions known to activate TRH hypophysiotropic neurons. Changes in some of these parameters could indicate the activation of TRHergic neurons and their possible involvement in some memory related process. Male Wistar rats were immersed (10 times) for 1, 3 or 5 days in a Morris water-maze containing, or not (yoked control) a platform and sacrificed 5, 30 and 60 min after last trial. TRH content and TSH serum levels were determined by radioimmunoassay; mRNA levels of pro-TRH, TRH-R1, TRH-R2, and PPII, by RT-PCR. Exclusive changes due to spatial training were observed in posterior hippocampus of rats trained for 5 days sacrificed after 60min: decreased TRH content and increased mRNA levels of pro-TRH and TRH-R1, particularly in CA3 region (measured by in situ hybridization). The hypothalamus-pituitary axis responded in both yoked and trained animals (increasing serum TSH levels and pro-TRH expression, due to swim-stress); in the amygdala of both groups, pro-TRH expression increased while diminished that of both receptors and PPII. Differential expression of these parameters suggests involvement of TRH hippocampal neurons in memory formation processes while changes in amygdala could relate to TRH anxiolytic role. The differential modulation in anterior and posterior portions of the hippocampus is discussed.     

Convulsants induce interleukin-1 beta messenger RNA in rat brain.

The effects of systemic administration of kainic acid and pentylenetetrazol on interleukin-1 beta gene expression in the rat brain was studied. After the administration of kainic acid in a convulsive dose (10 mg/kg i.p.), Interleukin-1 beta mRNA was induced intensely in the cerebral cortex, thalamus and hypothalamus, moderately in the hippocampus and weakly in the striatum, but not in the midbrain, pons-medulla and cerebellum. Pentylenetetrazol induced Interleukin-1 beta mRNA in the cerebral cortex, hypothalamus, and hippocampus with a faster time-course than kainic acid. Diazepam suppressed both the convulsion and the induction of Interleukin-1 beta mRNA produced by kainic acid. Dexamethasone suppressed the induction of Interleukin-1 beta mRNA, but did neither the convulsion nor the induction of c-fos mRNA following the injection of kainic acid. These results provide the first evidence that intensive neuronal excitation induces Interleukin-1 beta mRNA in particular regions of the brain.     

Kainic acid-induced seizures: changes in brain extracellular ions as assessed by intracranial microdialysis

The effect of kainic acid on extracellular [K+], [Ca2+], and [Na+] in the rat piriform cortex and hippocampus was studied by means of intracranial microdialysis. Either a dialysis fiber loop or horizontal Vita fiber were stereotaxically implanted within the piriform cortex or hippocampus, respectively. About 24 h later, fibers were perfused (1 ml/min) with Krebs-Ringer bicarbonate solution. Effluent samples were collected before (four at 30 min intervals), and after (six at 30 min intervals) administration of kainic acid (16 mg/kg, i.p.) or kainic acid vehicle. Kainic acid induced sequential signs of lethargy, staring, "wet-dog shakes," forepaw clonus, and tonic-clonic convulsions. In these awake free-moving rats, kainic acid induced a rapid and prolonged increase in extracellular [K+] and an apparent, but not statistically significant, decrease in extracellular [Ca2+] within the hippocampus. In the piriform cortex, kainic acid induced increases in extracellular [K+] and [Na+], which were associated with early pre-convulsive signs. In contrast to the pronounced ion changes commonly seen when the brain is activated by factors such as local application of excitatory substances or when the brain is made ischemic or hypoxic, extracellular ion concentrations are relatively well maintained during parenteral kainic acid-induced seizures.     

Involvement of caspase-3-like protease in the mechanism of cell death following focally evoked limbic seizures

The cysteine protease caspase-3 may be involved in the mechanism of cell death following seizures. Using a rat model of focally evoked limbic epilepsy with continuous electroencephalography monitoring, we investigated seizure-induced changes in caspase-3 protein expression and processing, enzyme activity, and the in vivo effect of caspase-3 inhibition. Seizures were induced by intraamygdaloid injection of kainic acid (0.1 microg) and were terminated after 45 min by diazepam (30 mg/kg) administration. Animals were killed 0-72 h following diazepam administration. Levels of the 32-kDa proenzyme form of caspase-3 were unaffected by seizures. Levels of the 17-kDa cleaved (active) fragment of caspase-3 were almost undetectable in control brain, but were increased significantly at 4 and 24 h within ipsilateral hippocampus and cortex in seizure animals. Caspase-3-like protease activity was increased within the ipsilateral hippocampus at 8 and 24 h following seizures. Caspase-3 immunoreactivity was increased within the vulnerable ipsilateral CA3/CA4 subfield at 24 and 72 h following seizures and was associated predominantly, but not exclusively, with neurons exhibiting DNA fragmentation. The putatively selective caspase-3 inhibitor N-benzyloxycarbonyl-Asp(OMe)-Glu(OMe)-Val-Asp(OMe)-fluoromethyl ketone significantly improved neuronal survival bilaterally within the hippocampal CA3/CA4 subfields following seizures. Collectively, these data suggest that caspase-3 may play a significant role in the mechanism by which neurons die following seizures.     

Does phenobarbital protect against trimethyltin-induced neuropathology of limbic structures?

Because of the similarity in the pattern of limbic sites damaged by both compounds, it has been suggested that trimethyltin (TMT) may be an excitotoxin like kainic acid (KA). KA produces seizures which eventually result in neuronal damage similar to that found in epilepsy. Anticonvulsants reduce both the seizures and pathology associated with KA. Because TMT may also produce seizures, we undertook to determine whether or not some of the TMT-induced limbic neuropathology could result from seizure activity. To do this, a single dose of TMT chloride (either 7.5 or 15 mg/kg) was given per os to rats, and then phenobarbital (30 mg/kg) was administered subcutaneously in repeated doses. Treatment with phenobarbital did not prevent pathologic changes in the hippocampus, dentate gyrus, and pyriform or prepyriform cortex. Since phenobarbital did not protect against TMT-induced neuronal damage, as it has been reported by others to protect against KA-induced damage, the present findings suggest that these two toxicants probably produce hippocampal pathology via different mechanisms and that the TMT-induced pathologic changes do not require sustained electrical seizure activity.     

Comparative study of the epileptogenic effect of kainic acid injected into the cerebral cortex, hippocampus and amygdala in adult cats chronically implanted

Intracerebral injection of kainic acid in cerebral cortex, hippocampus or amygdala in cats chronically implanted showed that: 1) Hippocampus and amygdala presented a greater sensitivity than the cerebral cortex, while hippocampus presented a greater sensitivity than the amygdala to the generation of an epileptic focus. 2) Comparison of latency, mean duration of afterdischarges, and the mean time period to obtain the peak intensity of the afterdischarge in the three cited structures, showed that mean latency of the first afterdischarge was significantly shorter in hippocampus and amygdala compared with the cerebral cortex. Moreover the mean time period to reach the peak intensity of the afterdischarge was again shorter in the subcortical structures. 3) The epileptic foci both in hippocampus and amygdala were blocked by CNQX and muscimol. 4) The behavioral changes depended on the intensity of the epileptic process. Tonic-clonic convulsions appeared only when the motor cerebral cortex was involved. Finally, 5) kainic acid injections in hippocampus and amygdala elicited an intense neuronal destruction and gliosis of these structures. We conclude that intracerebral injection of low doses of kainic acid in cats represent a good model to study focal epileptic thresholds in the CNS.