Damage induced by systemic kainic acid in rats is dependent upon seizure activity--a behavioral and morphological study

Kainic acid (KA) was injected intraperitoneally into rats at a dose (9 mg/kg) which produced status epilepticus in approximately 50% of the animals. Rats were categorized into groups that displayed status epilepticus, partial seizures or no effect in the 4 hr following kainic acid injection. Behavioral and morphological changes were characterized for each group. Rats that were not affected by kainic acid were indistinguishable from a saline-injected control group. When sacrificed 4 hr after treatment, rats displaying partial seizures showed morphological changes similar to, but less severe than, those exhibiting status epilepticus. Additional groups were tested and sacrificed 7 days (d) after treatment. Rats from the limited seizure group showed little behavioral or morphological response, while animals from the status epilepticus group had marked behavioral deficits and severe lesions. The tissue damage and its distribution were similar to lesions observed after seizures induced by other convulsants, and in spontaneously epileptic dogs. These results suggest that the extent of damage resulting from systemic administration of KA is dependent on the extent of seizure activity, which may in turn be related to the influence of kainic acid and other excitatory amino acids on the limbic system.     

Cycloheximide inhibits neurotoxic responses induced by kainic acid in mice

In the present study, we examined the effect of cycloheximide on various pharmacological responses induced by kainic acid (KA) administered intracerebroventricularly (i.c.v.) in mice. In a passive avoidance test, a 20-min cycloheximide (200mg/kg, i.p.) pretreatment prevented the memory impairment induced by KA. The morphological damage induced by KA (0.1microg) in the hippocampus was markedly concentrated in the CA3 pyramidal neurons and cycloheximide effectively prevented the KA-induced pyramidal cell death in CA3 hippocampal region. In immunohistochemical study, KA dramatically increased the phosphorylation of extracellular signal-regulated protein kinase (p-ERK), c-Jun N-terminal kinase 1 (p-JNK1), and calcium/calmodulin-dependent protein kinase II (p-CaMK II). Cycloheximide attenuated the increased p-ERK, p-JNK1, and p-CaMK II levels induced by KA. Furthermore, cycloheximide inhibited the increased c-Fos and c-Jun protein expression levels induced by KA in the hippocampus. The activation of microglia was detected in KA-induced CA3 cell death region by immunostaining with a monoclonal antibody against the OX-42. Cycloheximide inhibited KA-induced increase of OX-42 immunoreactivity. Our results suggest that the increased expression of the c-Fos, c-Jun, and phosphorylation of ERK, JNK1, and CaMK II proteins may play important roles in the memory impairment and the cell death in CA3 region of the hippocampus induced by i.c.v. KA administration in mice. Furthermore, the activated microglia may be related to phagocytosis of degenerated neuronal elements induced by KA.     

Fetal brain transplantation in kainic acid lesioned caudate nucleus of adult rats.

This study confirmed that bilateral kainic acid (KA) injection at the caudate produces aphagia and adipsia in rats. The reduction in food and water intake was fatal after a higher dosage of the drug. To test the effect of transplantation on the mortality rate, KA was first injected in the left caudate, in one set of rats. After a gap of three days, fetal striatal tissue was unilaterally transplanted at this lesioned site, along with a second injection of KA in the right caudate. Successful transplantation, as ascertained morphologically, did not significantly alter the mortality rate. The morphometric study revealed that the neurons of the transplant were larger in size, and their numerical density lower than those of the caudate of normal rats. Only very few neurons of the transplant developed functional connectivity with the host, as demonstrated by electrophysiological studies.     

Reactive oxidant species in piriform cortex extracellular fluid during seizures induced by systemic kainic acid in rats

Kainic acid (KA) administered systemically to rats produces seizures and brain damage. We measured an increase in reactive oxidant species (ROS) during KA-induced seizures in the extracellular fluid (ECF) of the piriform cortex, a brain region known to be subsequently damaged. Intracerebral microdialysis samples were collected and assayed for isoluminol-dependent chemiluminescence before and after injection of KA (16 mg/kg, ip). Hydrogen peroxide (H₂O₂) concentrations were calculated from catalase-sensitive chemiluminescence, the difference between total and catalase-resistant chemiluminescence. During generalized tonic-clonic seizures, both total and catalase-resistant chemiluminescence increased significantly in samples from brain ECF. Catalase-resistant chemiluminescence, most likely produced by ascorbic acid, increased for a full hour during sustained seizure activity. H₂O₂ concentrations showed a trend towards elevation during seizures. Increased ROS suggest that oxidative stress occurs in brain ECF during sustained seizure activity.     

Intraendothelial accumulation of calcium in the hippocampus and thalamus of rats after systemic kainic acid administration

Summary The accumulation of calcium in the hippocampal and thalamic vascular endothelium and the perivascular space was detected histochemically by means of the pyroantimonate technique 30, 60 and 120 min after systemic kainic acid administration. An increased number of calcium pyroantimonate deposits was found in the endothelial mitochondria 60 min after kainate injection. The mitochondria were swollen at this time and vacuoles containing deposits were observed. After 120 min a pronounced perivascular glial swelling was conspicuous, besides the numerouos endothelial mitochondrial deposits. The swollen glial processes contained a large number of pyroantimonate deposits. It seems likely that the transendothelial calcium transport processes are accompanied by intraendothelial calcium accumulation and mitochondrial calcium sequestration.     

Pharmacokinetics of intracerebroventriculartBuOOH in young adult and mature mice

This in vivo study compared the pharmacokinetics of intracerebroventricularly administered tertiary butylhydroperoxide (tBuOOH) (109.7 mg/kg) among six different brain regions in two age groups of mice (2? and 8-mo-old mice). Brains were dissected at 11 time-points ranging from 0.5–60 min. Pharmacokinetics parameters did not differ between the two age groups. This demonstrates that previously reported age-related differences intBuOOH toxicity may not be owing to pharmacokinetic differences between the two age groups. Differences were found when comparing the pharmacokinetics oftBuOOH among the various brain regions. Area under the curve (AUC) values were highest in the striatum and thalamus, and lowest in the cerebellum. The half-life oftBuOOH varied widely among the regions with the longest half-lives in the cortex and hippocampus, and the shortest in the striatum and cerebellum. The oxidation of glutathione and the induction of DNA damage are critical aspects oftBuOOH toxicity. These data show that region-dependent differences in toxicity reported previously may result from factors, such astBuOOH-induced glutathione oxidation and DNA damage.     

Pharmacological characterization of voltage-clamped catfish rod horizontal cell responses to kainic acid

Excitatory amino acid-induced currents were examined in voltage-clamped rod horizontal cells dissociated from the catfish retina. The cells responded to glutamate (GLU) and the GLU analogues kainate (KA), quisqualate (QA), and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), while N-methyl-D-aspartate (NMDA) produced inconsistent responses. Of the effective agonists, only KA produced large, concentration-dependent current responses. While QA, AMPA, GLU, and NMDA were poor agonists, these compounds were able to block rod horizontal cell responses to KA. The rank order potency for this inhibition was: QA greater than AMPA greater than or equal to L-GLU much greater than D-GLU = NMDA. Several excitatory amino acid receptor antagonists were also able to inhibit rod horizontal cell responses to KA. The rank order potency for the inhibition by the compounds tested was: kynurenate greater than cis-piperidine-dicarboxylic acid much greater than D,L-alpha-amino-adipate. Comparison of the potency of several ligands to inhibit rod and cone horizontal cell responses to KA suggested similarities in the KA binding sites of both cell types.     

Changes in the activity of gamma-glutamyl transpeptidase induced by kainic acid and surgical lesions of the hippocampal formation in young rats

To study possible functional involvement of gamma-glutamyl transpeptidase (GGT) in glutamate transmitter metabolism we lesioned putative glutamatergic structures of the rat hippocampal formation by intracerebroventricular (i.c.v.) injection of kainic acid (KA) or by surgical CA3 axotomy. Unilateral injection of KA into the left lateral cerebral ventricle of 30-day-old rats resulted in decreased GGT activity in hippocampal areas CA3, Ca1 ipsilaterally, and in the contralateral area CA1, four hours after the induction of the chemical lesion. Four days after the injection, the enzyme activity was decreased in all hippocampal areas with the exception of the contralateral dentate gyrus. Four days after bilateral i.c.v. injection of KA, lower GGT levels were found than was seen after bilateral surgical lesion of the CA3 pyramidal cell axons (Schaffer's collaterals). The surgical lesion was followed by a decrease of GGT only in the stratum pyramidale and stratum radiatum of area CA1. In contrast to the effects in 30-day-old rats, unilateral i.c.v. injection of KA on postnatal day 12 did not alter the GGT activity in any studied hippocampal area presumably because of incomplete maturation of structures required for KA vulnerability.     

海人酸致痫大鼠海马细胞外氨基酸类神经递质的变化

目的 分析海马细胞外氨基酸递质在癫痫发生中的作用,探讨海人酸致痫模型大鼠癫痫发生的机制.方法 应用立体定向方法建立海人酸大鼠颞叶癫痫模型,观察大鼠行为学和电生理变化,应用电镜观察大鼠海马超微结构,应用微透析获取大鼠海马细胞外液,高压液相色谱法测定透析液中的兴奋性氨基酸谷氨酸、抑制性氨基酸牛磺酸及γ-氨基丁酸的含量.结果 海人酸注射后大鼠出现典型的颞叶癫痫发作,皮层脑电显示痫性发作,电镜显示兴奋性神经递质增加,高效液相色谱分析显示海马细胞外谷氨酸、牛磺酸和γ-氨基丁酸含量明显高于对照组(P＜0.05),虽然谷氨酸、γ-氨基丁酸都升高,而谷氨酸升高的更明显.结论 兴奋性氨基酸与抑制性氨基酸的失衡在海人酸致痫大鼠模型的癫痫发生过程中发挥重要作用,是癫痫发生的原因之一.     

Behavioral sensitization to kainic acid and quisqualic acid in mice: comparison to NMDA and substance P responses.

Substance P (SP) and the excitatory amino acid (EAA) agonists NMDA, kainic acid (KA), or quisqualic acid (Quis) each produce a transient, caudally directed biting and scratching response (CBS) in mice after their intrathecal injection. We have previously shown that repeated injections of SP result in a decrease in the intensity of CBS, or desensitization. The goals of the present study were (1) to determine whether desensitization also develops to the CBS behavior produced by EAAs in the spinal cord, (2) to characterize the role of interneurons in desensitization, and (3) to examine possible interactions between EAAs and SP. While injection of NMDA at 2 min intervals resulted in desensitization to its CBS behavioral effect, behavioral responses to repeated injections of KA or Quis increased in intensity, exhibiting sensitization. The NMDA antagonist DL-2-amino-5-phosphonovaleric acid failed to alter sensitization to either KA or Quis but inhibited behaviors produced by SP and NMDA, suggesting an NMDA-mediated component in SP-induced behavior. Concanavalin A, which is reported to block desensitization to the electrophysiologic effect of Quis, blocked sensitization to the behavioral effects of both Quis and KA. Strychnine, bicuculline, and 5-aminovaleric acid each inhibited desensitization to SP and NMDA, supporting the notion of recruitment of inhibitory transmitters in the attenuation of NMDA and SP activity. Pretreatment with capsaicin selectively inhibited the development of behavioral sensitization to KA, suggesting an involvement of small-diameter C-fibers in the enhancement of responsivity to KA. Consistent with this, pretreatment with SP selectively potentiated the CBS response to KA. The potentiation of KA effects by SP and dependence of KA behavioral sensitization on C-fiber activity suggest a possible mechanism by which EAAs and SP may be involved in the mediation of pain.     

Propofol administration reduces hippocampal neuronal damage induced by kainic acid in rats

Abstract

The goal of this study was to determine whether propofol has protective effect against kainic acid (KA)I. ndu~ed excftotoxicity. Administration of propofol (25 mg kg-⁷ i.p.) was done 2 h, before KA (10 mg kg-¹ I.P.), Immedlatelyafte:1 and 2h, 4h, 6h, and 12 h afte~ the KAI and twice daily for an additional three days. Neuronal cell death In CA 1 an.d .CA3 subsector of hIppocampus was evaluated quantitatively four days after KA. The KA and propofol-Injected rats had a greater number of surviving neuronal cells than did KA (and vehicle)-Injected rats. Our results suggest that propofol holds potential for the protection of neuronal cells agaInst KA-induced excitotoxicity. [Neural Res 1999; 21: 225-228]     

Propofol administration reduces hippocampal neuronal damage induced by kainic acid in rats

The goal of this study was to determine whether propofol has protective effect against kainic acid (KA)-induced excitotoxicity. Administration of propofol (25 mg kg-1 i.p.) was done 2 h before KA (10 mg kg-1 i.p.), immediately after, and 2 h, 4 h, 6 h, and 12 h after the KA, and twice daily for an additional three days. Neuronal cell death in CA1 and CA3 subsector of hippocampus was evaluated quantitatively four days after KA. The KA and propofol-injected rats had a greater number of surviving neuronal cells than did KA (and vehicle)-injected rats. Our results suggest that propofol holds potential for the protection of neuronal cells against KA induced excitotoxicity.     

Age related differences in stress-induced neurobehavioral responses in rats: modulation by antioxidants and nitrergic agents

The effect of restraint stress (RS) on neurobehavioral and brain oxidative/nitrosative stress markers and their modulation by antioxidants and nitrergic agents were evaluated in young (2 months) and old (16 months) male Wistar rats. Exposure to RS, induced anxiogenesis when tested in the elevated plus maze (EPM) and open field (OF) tests and such changes were greater in the old as compared to the young rats. These behavioral alterations were associated with enhanced levels of malondialdehyde (MDA) and reductions in glutathione (GSH), catalase (CAT) and nitric oxide metabolites (NO(x)) levels in brain homogenates-the effects being greater in intensity in the old as compared to the young animals. Pretreatment with antioxidants, alpha-tocopherol (25 and 50mg/kg) and N-acetylcysteine (100 and 200mg/kg) consistently reversed the RS-induced behavioral and biochemical alterations in both young and old rats. Similar attenuations of RS-induced changes were seen after pretreatment with NO precursor l-arginine (500 and 1000mg/kg) while the NO synthase inhibitor N-nitro l-arginine methyl ester (l-NAME) (50 and 100mg/kg) tended to aggravate the effects of RS in both age groups of rats. The results suggest that susceptibility to stress-induced neurobehavioral alterations may increase with age and interactions of reactive oxygen species (ROS) and nitric oxide in the central nervous system may exert a regulatory influence in such age dependent responses to stress.     

Deficits in spontaneous behavior and cognitive function following systemic administration of kainic acid

Recurrent seizures leading to status epilepticus were induced in rats by a 10 mg/kg subcutaneous injection of kainic acid (KA). After a 4-day recovery period, the KA-treated animals showed a syndrome of increased activity in an open field, hyperreactivity in response to handling, and deficits in acquisition of both passive avoidance and spatial learning tasks. The second experiment demonstrated that KA also caused deficits in learning to approach a visible platform in a water maze. Two months after the initial treatment, the animals were still hyperactive and deficient in passive avoidance acquisition; however, they performed normally on the spatial learning task. These results reflect both the convulsive effects of KA, which produce transient retardation, and the brain damage to limbic system structures, which accounts for the permanent deficits.     

Fear conditioning is impaired in systemic kainic acid and amygdala-stimulation models of epilepsy

PURPOSE: The lateral nucleus of the amygdala is critical for fear conditioning, a paradigm of emotional learning, which requires recognition of an unconditioned stimulus as aversive and association of conditioned stimuli with an unconditioned stimulus. Some patients with temporal lobe epilepsy have amygdaloid damage associated with impaired emotional learning. Fear conditioning also is impaired at least in some animal models of epilepsy. We studied whether contextual or tone-cued fear conditioning is impaired in two status epilepticus models of epilepsy and whether impairment correlates with the extent of damage in the lateral nucleus of the amygdala. METHODS: We induced epilepsy in rats by either systemic kainic acid administration or electrical amygdala stimulation. Behavioral reactions in all phases of fear conditioning were analyzed from videotapes. Damage to the lateral nucleus of the amygdala was analyzed from thionin-stained sections both histologically and by volumetry. RESULTS: Immediate reflexive responses to unconditioned and conditioned stimuli were preserved, whereas the freezing response to an unconditioned stimulus was reduced. Contextual conditioning was severely impaired, whereas tone-cued conditioning was better preserved. The lateral nucleus pathology did not correlate with impaired fear conditioning. CONCLUSIONS: These data suggest that processing of complex contextual stimuli is severely affected in experimental epilepsy, whereas conditioning to simple cues is better preserved.     

Intraparenchymal fetal striatal transplants and recovery in kainic acid lesioned rats

Striatal kainic acid (KA) lesions induce behavioral and biochemical deficits which resemble symptoms encountered in patients suffering from Huntington's disease. In rats with KA lesions, fetal striatal transplants have shown to reverse the pervasive nocturnal hyperactivity induced by the lesion. In the present study 4.6 mm3 of fetal striatal tissue were delivered bilaterally into the anterodorsal portion of the lesioned caudate nucleus. Care was taken to deliver the transplant within the host parenchyma and away from the lateral ventricles. Locomotor behavior analyzed using the Digiscan animal activity monitors before and after the transplants demonstrated a reversal of the hyperactivity following transplants in 70% of lesioned animals. Microinjections of horseradish peroxidase delivered into the globus pallidus and substantia nigra of a small group of functionally recovered transplanted animals, did not reveal evidence for reinnervation between host nigra or pallidum and the transplant at 10 weeks post-transplantation. Other laboratories have reported anatomical connections by 6 months post-transplantation. Ventricular/brain ratios demonstrated that intraparenchymal transplants significantly reduced the ventricular dilation following KA lesion. These results suggest that functional recovery can be obtained when the transplant is immersed into the host's striatal parenchyma regardless of the existence of long-range anatomical connections.     

Central and sympatho-adrenal responses to insulin in adult and neonatal rats

In the mature rat, subcutaneous administration of insulin (0.02 IU/g body wt.) produced hypoglycemia and a profound activation of the sympatho-adrenal pathway, as indicated by a marked depletion of adrenal catecholamines. Cellular glucopenia caused by administration of 2-deoxyglucose also produced a sympatho-adrenal response. In contrast, in 2-day-old rats, the systemic injection of insulin evoked only a small depletion of catecholamines even though severe hypoglycemia was present, and 2-deoxyglucose also produced a diminished response. The central administration of insulin at an equivalent dose (0.02 IU/g brain) stimulated brain ornithine decarboxylase activity in both neonates and adults, but was ineffective in evoking hypoglycemia or adrenal catecholamine release. These results suggest that: (a) direct interaction of insulin with its receptors in the central nervous system is not required for activation of the sympatho-adrenal pathway, and (b) the lack of sensitivity of neonatal adrenal catecholamine release to subcutaneous administration of insulin is likely associated with immaturity of splanchnic neurotransmission rather than with absence of central insulin receptors or impaired peripheral responsiveness to insulin.     

Intracerebroventricular kainic acid administration to neonatal rats alters interneuron development in the hippocampus

The effects of neonatal exposure to excitotoxins on the development of interneurons have not been well characterized, but may be relevant to the pathogenesis of neuropsychiatric disorders. In this study, the excitotoxin, kainic acid (KA) was administered to rats at postnatal day 7 (P7) by intracerebroventricular (i.c.v.) infusion. At P14, P25, P40 and P60, Nissl staining and immunohistochemical studies with the interneuron markers, glutamic acid decarboxylase (GAD-67), calbindin-D28k (CB) and parvalbumin (PV) were performed in the hippocampus. In control animals, the total number of interneurons, as well as the number of interneurons stained with GAD-67, CB and PV, was nearly constant from P14 through P60. In KA-treated rats, Nissl staining, GAD-67 staining, and CB staining revealed a progressive decline in the overall number of interneurons in the CA1 and CA3 subfields from P14 to P60. In contrast, PV staining in KA-treated rats showed initial decreases in the number of interneurons in the CA1 and CA3 subfields at P14 followed by increases that approached control levels by P60. These results suggest that, in general, early exposure to the excitotoxin KA decreases the number of hippocampal interneurons, but has a more variable effect on the specific population of interneurons labeled by PV. The functional impact of these changes may be relevant to the pathogenesis of neuropsychiatric disorders, such as schizophrenia.