Intrahippocampal Injection Of Kainic Acid Research Articles

Localization studies of γ-hydroxybutyrate receptors in rat striatum and hippocampus

Quantitative autoradiography using [ 3H] γ-hydroxybutyrate was used in combination with anatomic and neurotoxic lesions to localize the γ-hydroxybutyrate (GHB) receptors in the striatum and hippocampus of rat brain. 6-Hydroxydopamine (6-OHDA) lesions of the nigro-striatal pathway failed to reduce [ 3H] γ-hydroxybutyrate binding in the striatum. In contrast, kainic acid (KA) lesions of the caudate-putamen (CPu) resulted in about 45% loss of binding. For hippocampus, lesions of septo-hippocampal pathway did not modify receptor density but intrahippocampal kainic acid injection largely attenuated (50%) [ 3H] GHB binding. These results demonstrate that γ-hydroxybutyrate receptors in the CPu and dorsal hippocampus are principally located on intrinsic neurons which may participate in the functional expression of the role γ-hydroxybutyrate has in these structures.

The neurotoxicity of intrahippocampal kainic acid injection in rats is not accompanied by a reduction of Timm stain

Histopathological changes induced by intrahippocampal injections of low doses of kainic acid (17.5 ng/site) were investigated in rats. Kainic acid produced a selective loss of CA3 pyramidal and hilar neurons. The development of kainic acid-induced neuronal injury was not accompanied by any detectable loss of histologically demonstrable zinc as assessed by means of a modified Timm's sulphide-silver method. It is suggested that the selective injury of hippocampal neurons induced by kainic acid is not contingent on the release of zinc from mossy-fiber terminals.

Increased susceptibility to hippocampal and amygdala kindling following intrahippocampal kainic acid

The effects of unilateral intrahippocampal injection of kainic acid, a potent neuroexcitant and neurotoxin, on subsequent susceptibility to kindling of the contralateral hippocampus or contralateral amygdala were investigated in albino rats. At the chosen doses (0.20 to 1.25 μg dissolved in physiologic saline), the kainic acid-induced lesion was confined to the injected hippocampus and in two cases the ipsilateral entorhinal cortex; never were there contralateral lesions. Approximately 2 to 6 weeks post-injection, each animal received daily afterdischarge-producing electrical stimulations until stage 5 kindled limbic seizures occurred. Kindling in pretreated animals was significantly accelerated compared with controls; the hippocampal kindling rate decreased from 13.2 stimulations to 3.7, the amygdala kindling rate from 7.8 stimulations to 3.0. Many treated animals had first-stimulation stage 5 seizures, compared with none for controls. Importantly, this facilitation of kindling was not reversed by suppression of the acute, induced seizures with the anticonvulsants, diazepam and phenobarbital, which have repeatedly been demonstrated to effectively suppress limbic kindling. Such results, considered together with findings from the literature, suggest that partial kindling does not occur during kainic acid-induced seizures, and that the observed susceptibility to kindling and other epileptogenic agents subsequent to kainic acid treatment may in fact be related to neurophysiologic and neurochemical consequences of kainic acid-induced lesions.

Intrahippocampal injection of kainic acid produces significant pyramidal cell loss in neonatal rats

Previous reports 655 have indicated that pyramidal cells in the developing rat hippocampal formation are not destroyed by intraventricular or inlraperitoneal administration of kainic acid. We examined the neurotoxic properties of kainic acid and ibotenic aeid following intrahippocampal injection in neonatal rats and found significant pyramidal cell death following injection of 1.0 μg kainic acid in 6, 7 and 9-day-old pups. At doses 2.5 or live times this amount, significant pyramidal cell loss was obtained in 5-day-old rats as well. The susceptibility of pyramidal neurons to kainic acid increased as a function of age. The developing hippocampus was considerably more vulnerable to ibotenic acid compared with kainic acid, in contrast to the order of potency reported in adult rats. The increased sensitivity of CA3 pyramidal cells parallels the development of the mossy fiber innervation to the dendrites of these cells supporting the twofold mechanism suggested by Coyle for kainic acid neurotoxicity; that is, a direct cytotoxic action via postsynaptic receptors as well as increased sensitivity due to the presence of excitatory inputs.

Increased kindled-seizure susceptability due to a unilateral intra-hippocampal kainic acid injection

Increased kindled-seizure susceptability due to a unilateral intra-hippocampal kainic acid injection

In vitro and in vivo evidence for the existence of presynaptic muscarinic cholinergic receptors in the rat hippocampus

The intrahippocampal injection of kainic acid cleared 50% of muscarinic receptors and favored the detection of a further 20% loss in hippocampal presynaptic muscarinic receptors produced by electrolytic lesion of the medial septal nucleus as determined by Scatchard analysis of the saturation isotherms of [ 3H]dexetimide binding. In accordance, a decrease of about 20% in the in vivo accumulation of [ 3H]dexetimide in the hippocampus was found in animals lesioned in the medial septal nucleus. This effect occurred at both the dose of 5 μg/kg and at the saturating dose of 100 μg/kg of [ 3H]dexetimide. The results suggest that the loss was due to decreased receptor number rather than decreased receptor affinity.

Amygdaloid lesion increases the toxicity of intrahippocampal kainic acid injection and reduces the late occurrence of spontaneous recurrent seizures in rats

Spontaneous recurrent seizures (SRS) following intrahippocampal kainic acid (KA) injection have been described in a previous paper from our laboratory. The SRSs are clinically similar to the seizures induced by kindling the amygdala and we suggested that the amygdala plays a role in initiating the SRSs. Accordingly, the present paper examines the effect of amygdaloid lesions on intrahippocampal KA-treated rats. There were short- and long-term effects. (1) Short-term: the toxicity of KA was increased in lesioned animals. Status epilepticus followed by death of the animals was evoked with half of the dose required to cause the same effect in intact rats. Moreover, a gross haematuria was encountered 6–12 h after KA injection. This was not observed in non-lesioned rats even following the highest KA doses. (2) Long-term: amygdaloid lesions delayed the occurrence of the SRSs, reduced their incidence and modified their expression. In lesioned animals seizures has began with a period of tonic immobility with no sign of the masticatory movements seen in intact animals. Histological examination of the KA-induced lesions did not show any major differences between lesioned and intact animals. It is suggested that the short-term effects are due to an unspecific effect on homeostatic mechanisms, whereas the long-term ones reflect a specific involvement of the amygdala in the late appearing seizures.

Long-term local and distal increases in tryptophan hydroxylase activity following intracerebral kainic acid injections in the rat

The administration of kainic acid (1–2 μg) into the right striatum of adult rats resulted in a marked local increase in tryptophan hydroxylase activity (+ 54–106%). This change was significant as soon as on the second day after the treatment and persisted for at least 12 days. In addition, long-lasting elevations of tryptophan hydroxylase activity were also observed in the anterior raphe area, septum and ipsilateral hippocampus and cerebral cortex. In contrast, the intrahippocampal injection of kainic acid (1 μg) induced a long-term increase in tryptophan hydroxylase activity only in the injected structure. In all cases, the changes in tryptophan hydroxylase activity were associated with significant increases in the V max of the enzyme with no alteration of its apparent affinities for tryptophan and the pterin cofactor. Studies of the sensitivity of tryptophan hydroxylase from control and from kainic acid-treated rats to in vitro activating conditions (Ca +-dependent phosphorylation, partial trypsinization, exposure to sodium dodecyl sulfate) suggest that the intrastriatal injection of the neurotoxin induced a long-lasting activation of the enzyme. These findings indicate that intracerebral injections of kainic acid may be a valuable approach to explore further the mechanisms controlling tryptophan hydroxylase activity in vivo.

Neuronal location of [formula omitted] binding sites in rat and guinea-pig brain

N 6- cyclohexyl[ 3H]adenosine , ([ 3H]CHA), was used to label adenosine a 1 receptors in crude synaptic membranes prepared from rat and guinea pig brain. The density of [ 3H]CHA binding sites was highest in the rat hippocampus and cerebellum and in the guinea-pig hippocampus. A microdissection of coronal sections of guinea-pig hippocampus revealed that the specific binding capacity for [ 3H]CHA in area CA-1 was 20–30% higher than in area CA-3, dentate gyrus and subiculum. Selective neuronal lesions of serotonergic, noradrenergic and cholinergic afferents to the hippocampus failed to alter [ 3H]CHA binding to hippocampal membranes. These results suggest that [ 3H]CHA binding sites are not associated with axons or terminals of these neurones in the hippocampus. Intrahippocampal injection of kainic acid reduced the number of [ 3H]CHA recognition sites by 30% with no alteration in the affinity of [ 3H]CHA for these receptors. Thus, a significant portion of A 1 receptors may be associated with intrinsic neurones of the hippocampus which do not appear to be innervated by noradrenergic, cholinergic or serotonergic axons.

Long-term effects of intrahippocampal kainic acid injection in rats: A method for inducing spontaneous recurrent seizures

Kainic acid (KA) is known as a powerful convulsant and neurotixic agent. When intracerebrally administered it causes repetitive seizures for about 1 or 2 days and brain damage both locally and in several remote brain regions. In the present paper the longterm effects of intrahippocampal KA administration are reported. Doses from 0.1 to 3.0 μg of KA were injected in the right hippocampus of Wistar rats and both the behaviour and EEG were observed during a period of about 3 months. Following KA doses of 0.8–2.0 μg, 4 distinct phases were observed: (1) acute phase which lasted 1–2 days and corresponded to the pattern of repetitive seizures as already described; (2) silent phase (5–21 days) which was characterized by a progressive return to apparently normal EEG and behaviour, except for some aggressive behaviour in those animals receiving the highest doses; (3) phase of spontaneous recurrent seizures (these seizures started 6–22 days after KA injections and were mostly triggered upon handling and recurred approximately 2 times by day for about 30 days; usually they resembled the amygdaloid kindled seizures); and (4) post-seizure phase where no more seizures were observed but significant spiking activity in the amygdala recordings could be seen. Animals receiving KA doses of 0.1–0.4 μg did not evolve beyond the acute phase whereas those receiving 3.0 μg died during this first phase. Neuropathological examination revealed dose-dependent alterations. These serial events offer a new method to induce spontaneous recurrent seizures with brain damage.

The effect of epileptiform discharges evoked by intrahippocampal injection of kainic acid on cholinergic and catecholaminergic hippocampal afferents

The influence of epileptiform seizures evoked by intrahippocampal injection of kainic acid on morphological changes of hippocampus and related brain regions was analyzed in rabbits using catecholamine histofluorescence, monoamine oxidase, acetylcholinesterase and Nissl staining methods. It was found that kainic acid induced generalized electroencephalographic seizures and a disappearance of hippocampal neurons. These effects did not affect the volume of neurons in septum and locus coeruleus. In the injected hippocampus, kainic acid destroyed hippocampal pyramidal cells and induced some sprouting of catecholamine, acetylcholinesterase-positive and monoamine oxidase-positive nerve fibers near the injection site. These results indicate that intrahippocampal kainic acid injection does not provoke a retrograde, transsynaptic degeneration in the medial septum and locus coeruleus, the brain regions which innervate the hippocampus.

Cyclic AMP-generating systems in rat hippocampal slices

Properties of the norepinephrine- (NE) stimulated, cAMP-generating system were studied in rat hippocampal slices. NE but not other putative neurotransmitters, caused a 3–4-fold rise in cAMP levels in the slices. All 3 main subdivisions of the hippocampus (HPC), the dentate gyrus, areas CA3 and CA1, possessed the capacity to produce cAMP. The latency to the NE stimulation of cAMP formation was about 20 sec but maximal stimulation was reached only after 5–10 min of incubation. Intrahippocampal injection of kainic acid (KA) caused a nearly complete destruction of hippocampal neurons and a marked increase in number of glial cells. NE caused a 12–15-fold rise in cAMP levels in KA-treated HPC. Compared to normal HPC where potency order of noradrenergic agonists indicated activation of a beta-1 receptor type, the pattern for the KA-treated HPC indicated the dominance of beta-2 receptors. The beta-1 antagonist, practolol, and the beta-2 antagonist, H35/25, were about equipotent in blocking the NE-stimulated cAMP formation in normal HPC. In KA-treated HPC, on the other hand, H35/25 was much more potent than practolol in inhibiting NE-stimulated cAMP formation. It is suggested that in the HPC beta-1 adrenergic receptors are primarily neuronal and beta-2 receptors, glial, and that activation of both receptor species results in activation of a cAMP-generating system.

Effects of anaesthetics and anticonvulsants on the action of kainic acid in the rat hippocampus

The effects of anaesthetics and anticonvulsants on the acute behavioral response and neurochemical alterations following intrahippocampal injection of kainic acid were examined. When compared to the effects in animals anaesthetized with a combination of chloral hydrate and pentobarbital (Equithesin), brief anaesthesia with ether or with hexobarbital potentiated whereas prolonged anaesthetia attenuated the action of 0.5 μg of kainic acid. Of the constituents of Equithesin, chloral hydrate offered less protection than pentobarbital. The anticonvulsants, phenobarbital, diazepam, diphenylhydantoin, and carbamazepine offered partial protection when administered in conjunction with ether anaesthetia.

The effect of intrahippocampal kainic acid injections and surgical lesions on neurotransmitters in hippocampus and septum.

AbstractLocal injection of kainic acid (2 μg) was accompanied by destruction of intrinsic neurons in the dorsal part of hippocampus. The lesion was accompanied by a 75% reduction in glutamate decarboxylase activity, a 60% reduction in the high affinity uptake of l‐glutamate, a 40‐60% reduction in the endogeneous levels of aspartate, glutamate and GABA and no changes in the activities of choline acetyltransferase or aromatic amino acid decarboxylase in the dorsal hippocampus. Unilateral destruction of neurons in the dorsal hippocampus was followed by a 20‐40% reduction in the high affinity uptake of glutamate in lateral, but not in medial septum, on both sides. There was no reduction in choline acetyltransferase, glutamate decarboxylase or aromatic amino acid decarboxylase activities in the lateral or medial part of the septum. Transection of fimbria and superior fornix was accompanied by a severe reduction in choline acetyltransferase and aromatic amino acid decarboxylase activity in hippocampus, in the high affinity uptake of glutamate and in the endogenous level of glutamate in the lateral septum. The results are consistent with the concept that in the hippocampus kainic acid destroys intrinsic neurons and not afferent fibres. It seems therefore that all GABAergic fibres in the hippocampus belong to intrinsic neurons whereas glutamergic and aspartergic neurons belong partly to local neurons. The connection from the hippocampus to the lateral septum probably uses glutamate as a transmitter.