Nmol Kainic Acid Research Articles

Alterations of the Electroretinogram by Intravitreal Kainic Acid in the Rat

Purpose: To relate the electrophysiological changes in the retina induced by the excitatory neurotoxin, kainic acid (KA), to its receptor sites in the rat. Methods: Fifty-five Wistar rats were injected intravitreally with 100, 50, 25, 12.5, 6.25, 3.12, or 1.56 nmol of KA. The electroretinograms (ERGs) including oscillatory potentials (OPs) elicited by a series of increasing intensities were recorded before, and 6 hours, 1 day, 1 week, and 1 month after the injection of KA. Results: After KA injection, the a-waves showed no significant change at all intensity levels ( P > .05), but the amplitudes and implicit times of the b-wave were significantly altered. The abolition of the b-wave by KA resulted in a negative response, which decreased progressively with time. The implicit times of the b-wave showed a marked prolongation after injection of 100 nmol of KA ( P < .01). The OPs disappeared at the KA dose of 6.25 nmol and higher; doses of 1.56 to 3.12 nmol of KA depressed the Ops. Conclusions: We conclude that KA altered the above-mentioned ERG components in a dose-dependent manner. These alterations of the ERG can be explained by alterations of neurons in the inner retinal layers.

Temporal profiles of the in vitro phosphorylation rate and immunocontent of glial fibrillary acidic protein (GFAP) after kainic acid-induced lesions in area CA1 of the rat hippocampus: demonstration of a novel phosphoprotein associated with gliosis

The in vitro phosphorylation rate and immunocontent of glial fibrillary acidic protein was studied in slices of area CA1 of the rat hippocampus after stereotaxic injection of 1 nmol of kainic acid. For controls the contralateral hippocampus was injected with saline. Hippocampal tissue was incubated with [ 32P]phosphate and analysed by two-dimensional electrophoresis for phosphorylation rate and by immunoblotting for immunocontent. Both these parameters decreased during the first 4 days after injection and then started to increase at 10 days and continued to increase until at least 84 days. Except for a small excess of phosphorylation rate at 28 days, the relationship between immunocontent and in vitro phosphorylation rate of glial fibrillary acidic protein remained constant, indicating that the reactive gliosis was not associated with hypo- or a major hyperphosphorylation of this protein. Histology showed a pronounced loss of CA1 pyramidal cells 1 day after injection. At 28 days after injection the pyramidal cells had disappeared and only a few abnormal neurones were present. In contrast, immunocytochemistry after 28 days showed a marked increase in astrocytes reacting positive to the antibody in the strata radiatum and lacunosum moleculare. Besides glial fibrillary acidic protein the expression of several other proteins was upregulated as a result of the injection of kainic acid. These included phosphovimentin and an unknown phosphoprotein designated pp25 which co-migrated on 2-D gels with a prominent phosphoprotein expressed in primary cultures of astrocytes. Pp25 was expressed in lesioned tissue more frequently than phosphovimentin and with a time course that started earlier. Of particular interest was the expression of pp25 in the contralateral saline-injected hippocampus 1 day after injection of kainic acid. It is possible that pp25 will prove to be a sensitive marker of gliosis.

DNA fragmentation characteristic of apoptosis and cell loss induced by kainic acid in rabbit retinas

We have examined whether in vivo exposure to the glutamate analogue, kainic acid, induces cell loss through apoptosis and/or through necrosis. The vulnerability of rabbit retinal cells was evaluated by routine histopathology. The DNA fragmentation was examined using an in situ method (TUNEL: TdT-mediated biotin-dUTP nick-end labelling) and agarose gel electrophoresis of extracted retinal DNA. Retinas were examined at 30 min, and 4, 16, 24 and 36 h, and 2–5 days following the intraocular administration of 140 nmol kainic acid. Although pyknotic cells could be seen already at 30 min post-injection, TUNEL-labelled nuclei were first observed 4 h after the injection. A relatively large number of pyknotic cells and of TUNEL-labelled nuclei were still seen at 5 days post-injection. Pyknotic cells were seen throughout the inner nuclear layer (mostly in the proximal half of the layer) and in the ganglion cell layer. The TUNEL-labelled nuclei were almost only seen in the proximal inner nuclear layer. Analysis of DNA by electrophoresis revealed the presence of large molecular weight fragments 4 h after the injection, and of oligonucleosome-size fragments between 16 h and 2 days after the injection. The present study thus presents evidence that, in our model, the retinal cell loss induced by kainic acid is preceded, probably in most cells, by a fragmentation of DNA characteristic of apoptotic cell death. The process of cell loss following kainic acid administration was found to be relatively slow, further suggesting that a programmed type of cell death, which eventually induces apoptosis, is involved. No indication that cells were lost also through necrosis was obtained.

Kainic acid decreases hippocampal neuronal number and increases dopamine receptor binding in the nucleus accumbens: an animal model of schizophrenia

Intracerebroventricular (i.c.v.) administration of kainic acid (KA) produces graded neuronal loss in the hippocampus and other regions of the medial temporal lobe. Many of these brain regions send excitatory projections to the nucleus accumbens, a dopaminergic brain area implicated in psychotomimetic and antipsychotic drug action. In the present study, neurochemical function in the nucleus accumbens and anterior caudate-putamen was examined one week after i.c.v. administration of 1.5, 4.5, or 6.6 nmol of KA. As expected, i.c.v. KA produced dose-dependent neuronal loss in the dorsal and ventral hippocampus. Extrahippocampal neuronal loss was also observed in the thalamus and piriform cortex in some of the KA-treated rats. While ambient levels of dopamine turnover and excitatory amino acids in the nucleus accumbens were unaltered by KA, administration of the highest KA dose elevated [ 3H]spiperone binding exclusively in the accumbens. Finally, behavioral hyperactivity was observed in KA-treated rats over a five-week period following i.c.v. administration. The pattern of neuronal loss, receptor upregulation, and behavioral hyperactivity found after i.c.v. KA administration may provide a useful animal model of the limbic neuropathology and neurochemical dysfunction associated with schizophrenia.

Distribution of GABA immunoreactivity in kainic acid-treated rabbit retina.

Ischaemic retinal cell degeneration seems to involve both NMDA and non-NMDA receptor over-stimulation. However, different retinal cell types differ largely in their susceptibility to excitatory amino acid-induced neurotoxicity. We have investigated the vulnerability of GABAergic cells in the rabbit retina to the non-NMDA receptor agonist kainic acid (KA). The distribution of GABA immunoreactivity (GABA-IR) was examined in the central inferior retina at different survival times (5 h-6 days) following an intra-ocular injection of 140 nmol KA and compared to that of control and untreated retinas. In the normal retina, the majority of GABA-positive cells (79%) were located in the inner nuclear layer (INL), in one to four cell rows next to the inner plexiform layer (IPL), and in one cell row next to the outer plexiform layer (OPL). The remainder (21%) were found in the ganglion cell layer (GCL). Dense immunoreactivity was seen throughout the IPL. In the OPL, stained dots and occasional immunoreactive large processes could be seen. KA-exposed retinas processed for GABA immunocytochemistry 5 and 24 h after the injection showed an 85% reduction in the number of GABA immunoreactive cells. About the same degree of depletion was seen among GABA-IR cells located at different retinal levels. However, at these survival times, immunostaining was observed in three distinct bands in the IPL, indicating that the vulnerability to KA is not uniformly distributed among all GABAergic cells. At 48 h, an additional decrease in the number of labelled cells was noted, but immunoreactive cells were still found both in the INL and GCL. Even 6 days after KA treatment, a few stained cell bodies were seen in the INL next to the IPL, as well as a few processes in the IPL. The study shows that KA receptor overstimulation induces a marked depletion of the endogenous cellular GABA pools of the central rabbit retina, most likely as a result of GABAergic cell loss. However, a small population of GABAergic cells located in the INL appears to be less vulnerable to the toxic effects of 140 nmol KA.

Effects of kainic acid, quisqualic acid, and their antagonist, pCB-PzDA, on rat electrocorticograms and monoamine metabolite levels in rat striatum.

The action of kainic acid (KA), quisqualic acid (QA), and 1-(4-chlorobenzoyl)-piperazine-2,3-dicarboxylic acid (pCB-PzDA) was investigated in the central nervous system of male Sprague Dawley rats. Intracerebroventricularly injected KA and QA (100 nmol) induced spike discharges, and pCB-PzDA (100 nmol) suppressed electrocorticograms for one hour. pCB-PzDA enhanced the KA-induced spike discharges and inhibited those induced by QA. 2,3-Di-hydroxyphenylacetic acid(DOPAC) and homovanillic acid (HVA) levels were increased transiently by 10 nmol and continuously by 100 nmol of KA. KA dose-dependently increased 5-hydroxyindoleacetic acid (5-HIAA) levels 2 hours after administration. While 10 nmol of QA slightly increased the HVA level, 100 nmol of QA significantly increased DOPAC, HVA, and 5-HIAA levels. DOPAC and HVA levels were increased by 100 nmol of pCB-PzDA, although this agent inhibited KA-induced increases in DOPAC, HVA, and 5-HIAA levels. On the other hand, while pCB-PzDA first inhibited QA-induced increases in DOPAC, HVA and 5-HIAA levels for one hour, DOPAC and HVA levels thereafter increased additively. These findings suggest that pCB-PzDA may act not only as a NMDA antagonist, but that it may also act directly on dopaminergic neurons.

Effects of anaesthetics, anticonvulsants and glutamate antagonists on kainic acid-induced local and distal neuronal loss

A semi-quantitative estimation has been made of the effect of anaesthetics, anticonvulsants and glutamate antagonists on the extent of neuronal loss in the hippocampus caused by the local injection of the excitotoxin kainic acid, and on the vulnerability of neurons in various extrahippocampal regions due to the resulting seizure activity. Following the intrahippocampal injection of 0.47 nmol kainic acid (a submaximal dose), the amount of neuronal loss in the dorsal hippocampus was greater when given under the short-acting anaesthetics halothane and ketamine (a non-competitive glutamate antagonist), than when given under pentobarbital anaesthesia (with or without co-administration of ketamine (30 mg/kg)). When kainic acid was injected under halothane or ketamine anaesthesia a greater number of extrahippocampal limbic regions (distal toxicity) were also affected, usually on the ipsilateral side, and the extent of damage in each of these regions was generally more extensive. The anticonvulsants MK 801 and diazepam, or multiple injections of ketamine over a period of 5 h, decreased both the local and distal toxicity of kainic acid injected under short duration anaesthesia, to levels similar to those found under pentobarbital anaesthesia. However, these compounds, even at high doses, could not reliably prevent all seizure-related damage in extrahippocampal areas.

A peptidase-resistant cyclic octapeptide analogue of somatostatin (SMS 201–995) modulates seizures induced by quinolinic and kainic acids differently in the rat hippocampus

Electroencephalographic (EEG) seizures were measured in rats after intrahippocampal injection of 120 nmol quinolinic acid into the stratum radiatum CA1 or 0.19 nmol kainic acid in the dentate gyrus or in the stratum radiatum. Injection of 5 μg SMS 201–995, a peptidase-resistant cyclic octapeptide analogue of somatostatin, into the stratum radiatum, 15 min before quinolinic acid, did not significantly modify the number of seizures and the total time in seizures. Five μg SMS 201–995 injected into the stratum radiatum reduced the number of seizures induced by kainic acid in the same area and the total time spent in seizures by 58% and 75%, respectively (Student's t-test; P < 0.01). In both instances the latency to the first ictal episode was not significantly modified. Lesions of the medial septum, which reduced the activity of choline-o-acetyl-transferase (CAT) in the dorsal hippocampus by >90% after one week did not significantly affect seizures induced by quinolinic acid. In rats lesioned in the medial septum, 5 μg SMS 201–995 reduced the total time spent in seizures by 43%, without changing the number of ictal episodes and raised the latency to the first quinolinic acid-induced seizure by 53% (ANOVA 2 × 2, P < 0.05) but had no effect on these measures in the corresponding sham-operated group. A significant, 50% reduction of the total time spent in seizures and a 20% increase in the latency to the first quinolinic acid-induced seizure, with no changes in the number of ictal episodes, were observed when 5 μg SMS 201–995 was injected intrahippocampally with 10 μg atropine (ANOVA 2 × 2, P < 0.05), a muscarinic receptor antagonist, which per se did not significantly change seizures caused by quinolinic acid. Five μg of the peptide into the dentate gyrus reduced the total time spent in seizures induced by kainic acid, in the same area by about 60% and significantly reduced the number of seizures by 33% (Dunnett's test; P < 0.05). Picrotoxin (2 mg/kg, i.p. or 1.5 nmol into the dentate gyrus), a GABA A receptor antagonist, did not alter the EEG pattern induced by kainic acid in the dentate gyrus or modify the anticonvulsant effect of SMS 201–995 on seizures induced by kainic acid.

N-[1-(2-Thienyl)cyclohexyl]-piperidine (TCP) does not block kainic acid-induced status epilepticus but reduces secondary hippocampal damage

Distant damage, localized in the CA3 and CA1 areas, was observed in the hippocampus of rats as a consequence of status epilepticus (SE) induced by the injection of 2.5 nmol of kainic acid (KA) into the amygdala. In animals pretreated with an intraperitoneal injection of the non-competitive antagonist of the N- methyl- d-aspartate receptor, N-[1-(2-thienyl)cyclohexyl]-piperidine (TCP) (20 mg/kg), distant neuronal damage was reduced (CA1 neurons were always spared) whereas the rats still developed SE with an earlier onset. These results demonstrate the protective effect of TCP and confirm that epileptic activity and brain damage may be dissociated by NMDA receptor antagonists.

Intrahippocampal kainic acid reduces glutamine synthetase

Kainic acid was injected into the hippocampus of rats and glutamine synthetase was measured to determine whether astrocytes are involved in the early effects of this neurotoxic agent. Glutamine synthetase was reduced by 38%, 24 h after the stereotaxic application of 4 nmol of kainic acid to this region. The reduction in glutamine synthetase by kainic acid was not due to direct inhibition of the brain enzyme. This effect also was not due to seizure activity since rats peripherally injected with a convulsant dose of kainic acid were found to have normal hippocampal glutamine-synthetase activity. Exposure of astrocyte cultures to kainic acid for 24 h produced no evidence of gliotoxicity and no change in glutamine synthetase activity. The effect of intrahippocampal kainic acid on glutamine synthetase appears to be indirect, most likely produced secondarily to its neuronal effects. Several studies have shown that endogenous glutamate is involved in kainate neurotoxicity. A reduction in glutamine synthetase by kainic acid may impair the capacity for astrocytes to metabolize glutamate. Such an impairment could contribute to the glutamate-mediated cell death following kainic acid exposure.

The quinolinic acid model of Huntington's disease: Locomotor abnormalities

In contrast to other excitotoxins, such as kainic acid, quinolinic acid (QA) may spare a specific population of striatal neurons that is also spared in Huntington's disease (HD). Although several histological and biochemical experiments support the use of QA as a model for HD, to date no behavioral experiments have been performed to examine the suitability of this model. The present study explored the behavioral effects of bilateral intrastriatal microinjections of four doses (75, 150, 225, 300 nmol) of QA in the male rat. Using a multidimensional analysis of spontaneous locomotion (Digiscan activity) and a record of metabolic indicators, such as weight loss, a dose-dependent effect was found. The 75-nmol dose had no significant effect on locomotion or feeding behavior. In contrast, the 150- and 225-nmol doses induced hyperactivity and weight loss, whereas the 300-nmol dose was lethal. The results obtained suggest that striatal injections of 150–225 nmol of QA induce behavioral deficits qualitatively similar though quantitatively less than those which are seen after similar injection of 3 nmol of kainic acid and which have been reported to be comparable to the symptomatology of HD. Together with QA's possible greater histological selectivity, the present results support the use of QA-induced striatal lesions as a behavioral model of Huntington's disease.

“In vivo” studies on the interactions between excitotoxins and gangliosides

In contrast to other excitotoxins, such as kainic acid, quinolinic acid (QA) may spare a specific population of striatal neurons that is also spared in Huntington's disease (HD). Although several histological and biochemical experiments support the use of QA as a model for HD, to date no behavioral experiments have been performed to examine the suitability of this model. The present study explored the behavioral effects of bilateral intrastriatal microinjections of four doses (75, 150, 225, 300 nmol) of QA in the male rat. Using a multidimensional analysis of spontaneous locomotion (Digiscan activity) and a record of metabolic indicators, such as weight loss, a dose-dependent effect was found. The 75-nmol dose had no significant effect on locomotion or feeding behavior. In contrast, the 150- and 225-nmol doses induced hyperactivity and weight loss, whereas the 300-nmol dose was lethal. The results obtained suggest that striatal injections of 150–225 nmol of QA induce behavioral deficits qualitatively similar though quantitatively less than those which are seen after similar injection of 3 nmol of kainic acid and which have been reported to be comparable to the symptomatology of HD. Together with QA's possible greater histological selectivity, the present results support the use of QA-induced striatal lesions as a behavioral model of Huntington's disease.

Effects of kainic acid and other excitotoxins in the rat superior colliculus: Relations to glutametergic afferents

In this study we have performed surgical, chemical and combined surgical/chemical lesions in order to elucidate neurotransmitter mechanisms in the superior colliculus (SC) of albino rats. Visual cortex (VC) ablation reduced high affinity (HA) uptake of d-Asp by 32% in the deafferented SC. Local injection of kainic acid (KA) into SC reduced HA d-Asp uptake selectively in the lower dose range ( < 1nmol) by 50–60%. The GABAergic marker glutamate decar☐ylase (GAD) was decreased by maximally 60% only at doses exceeding 2 nmol. Choline acetyltransferase (ChAT), however, was not affected at any of the doses administered. VC ablation provided an almost complete protection against 1 nmol KA. When KA was injected 2 days prior to VC ablation an additive effect on HA d-Asp uptake of the two lesions was observed. From these observations we infer that the notion of a glutamatergic projection from VC to SC has been strengthened. Moreover, local neurons in intermediate layers account for about 60% of the HA d-Asp uptake in SC, and these are most likely impinged upon by the glutamatergic afferents. The neurotoxic effects of KA were compared with those of some suspected endogenous excitotoxins, i.e. N-methyl tetrahydrofolic acid (Me-THF), other folates and the tryptophan metabolite quinolinic acid (QA). N-methyl tetrahydrofolic acid, Me-THF (4 and 10 nmol) reduced HA d-Asp uptake by about 50%, only when coinjected with ascorbic acid. GAD and ChAT were not affected at either of the doses. QA was about 100-fold less potent than KA on a molar basis, and the maximal reduction of GAD was similar in QA and KA injected animals, whereas the maximal reduction of HA d-Asp was only 40% after QA injection in SC. We conclude that Me-THF, QA and KA exert their neurotoxic actions by different mechanisms as judged by the behavioral, histopathological and biochemical sequelae seen after local injections of the respective substances in intermediate layers of SC and corroborate data obtained from other brain areas.

Visual deficits following intraocular treatment of chicks with glutamate or kainic acid

After intraocular treatment with kainate or glutamate, chicks were tested for visual discrimination performance, pecking aim, bead detection, optokinetic response and pupillary response. Kainate at an amount of 6 nmol per eye impaired performance in all of the tests except pupillary response. No effects were seen after 0.6 nmol of kainic acid. Glutamate at 6000 nmol impaired performance on all tests but the optokinetic and pupillary response. Although glutamate caused less severe deficits in visual behaviour than the high dose of kainate, cellular organization of the retina, at least in some regions, was more disrupted in these animals. Glutamate at 600 nmol caused a late onset defect in visual discrimination performance but no effects on optokinetic response.

Kainic acid selectively alters auditory dendrites connected with cochlear inner hair cells

Cochleas of adult guinea pigs and rats, and 6-day-old rat pups, were injected, through the round window, with 2 μ1 of artificial classical Konishi perilymph containing 1 nmol kainic acid (KA). 5 min later, they were fixed, removed, and processed for electron microscopy. In all KA-treated cochleas, the injection resulted in a severe swelling of auditory dendrites below the inner hair cells (IHCs). Below the outer hair cells (OHCs), the swelling appeared only in the 6-day-old rats, not in adult animals. These results are significant in three different ways: (1) They confirm the strong difference between afferents innervating the IHCs and the OHCs in adult cochleas. (2) They shed some light on the synaptic plasticity found at the OHC level during synaptogenesis. (3) They support the hypothesis that glutamate, or a related substance, is the IHC neurotransmitter.

Sequential treatment with low doses of kainic acid alters sensitivity of retinal cell types

Examination of chick retinae soon after treatment with a single intraocular injection of 5 nmol kainic acid revealed degenerative changes in a small population of neurons located in the outer aspect of the inner nuclear layer, consistent with either bipolar and/or horizontal cells. Damage to the outer plexiform layer was also present. After one week, affected retinae were clear of neuronal debris. Following a second, identical injection, one week after the first, there was degeneration of a different population of neurons confined to the inner aspect of the inner nuclear layer indicative of amacrine cells. As amacrine cells were the only cell type affected by the second injection, our results suggest that they are directly affected by the second dose of kainic acid. The pattern of neuronal damage following successive doses of kainic acid appears to be potentially useful technique in elucidating retinal circuitry.

Intraocular kainic acid injection suppresses fast axonal transport in the developing rat optic nerve

A single intraocular injection of 1 or 3 nmol kainic acid (KA) into the right eye of rats aged 5 days postnatal (5 dpn) significantly reduced the incorporation of 3H-proline into retinal proteins and suppressed the amount of 3H-proline-labeled materials fast axonally transported in the optic nerve for at least 2 weeks thereafter. Intraocular KA injection within this dose range had no adverse effect on the optic axon population compared to normal nerves determined at 21 dpn; however, doses above 3 nmol (i.e., 6 nmol) caused significant axonal degeneration. Although partially recovered by 21 dpn this effect of KA on protein synthesis and axonal transport suggests that, as in the adult, retinal ganglion cells are also KA-sensitive during postnatal development.

Kainic acid-induced denervation supersensitivity of nicotinic, cholinergic receptors in ganglion cells of the rat retina

The rat retina contains both nicotinic and muscarinic cholinergic receptor sites as demonstrated by specific, high affinity binding of the nicotinic ligand, [ 3H]-α-bungarotoxin, and the muscarinic ligand, [ 3H]-quinuclidinyl benzylate. Seven days after an intraocular injection of 5 nmol of kainic acid, nicotinic binding was increased three-fold. We suggest that nicotinic sites may be located on ganglion cells because previous studies have shown that many ganglion cells are spared after kainic acid treatment and in fact, have an increased physiological response to ACh under these conditions. The increase in nicotinic sites may reflect a supersensitivity response to the loss of acetylcholine input after the kainic acid lesion. In contrast, muscarinic binding was decreased by 70% after kainic acid treatment. These data suggest that muscarinic sites are located on amacrine cells since these cells are destroyed by kainic acid treatment and some are known to be cholino-receptive. Some of the retinal muscarinic sites may function as inhibitory autoreceptors which regulate acetylcholine release from cholinergic amacrine cells.

GABAergic and cholinergic indices in various regions of rat brain after intracerebral injections of folic acid

Unilateral lesions were induced in the substantia innominata (SI) of rats by 3 methods: electrocoagulation, 2 nmol kainic acid (KA) injection or 50–200 nmol folic acid (FA) injection. Histological examination by cresyl violet and GABA-transaminase staining and biochemical evaluation by glutamic acid decarboxylase (GAD) and choline acetyltransferase (ChAT) measurement were undertaken of the SI and several remote areas. Injections of FA into the SI produced much less local but more severe distant neuronal damage than did injections of KA. Both produced sustained epileptiform activity. Electrolytic lesions, on the other hand, produced only local neuronal damage and no epileptiform activity. Biochemical measurements of GAD and histochemical staining for GABA transaminase indicated many of the neurons in the distant areas affected following FA injections were GABAergic, but cholinergic neurons were relatively spared. Damage to the cortical areas was heaviest in the superficial layers. Dose-related losses were seen in GAD in a number of regions, with the most severe distant damage being in the amygdala and pyriform cortex and significant but lesser extent in the frontal, entorhinal and temporal cortices, and in the thalamus. The striatum and hippocampus were spared. The distant damage, except in the thalamus, seemed to parallel the density of cholinergic innervation from the SI as revealed by relative drops in ChAT following KA injections into the SI. Reduction in both seizure-like activity and remote damage was brought about by pretreatment of the animals with valium (20 mg/kg) or scopolamine (50 mg/kg). The protective action of scopolamine is consistent with the possibility that cholinergic neurons may mediate much of the remote damage to GABA neurons, although they themselves are little affected. Distant effects of injections of FA into the striatum were comparable in kind but much less in magnitude to those after SI injection while amygdala injections of FA did not produce significant losses in GAD in any of the regions examined.

Evidence for a cholinergic projection to neocortex from neurons in basal forebrain.

Unilateral stereotaxic injection of 3.5 nmol of kainic acid into the ventral globus pallidus of rats reduced biochemical cholinergic neuronal markers by 45-50% and virtually eliminated histochemical staining for acetylcholinesterase in neocortex ipsilateral to the lesion. At the lesion site, the large, multipolar neurons that stain densely for acetylcholinesterase were absent when compared with the uninjected side. Kainate was as effective as electrocoagulation for reducing cholinergic markers although it did not affect aminergic projections ascending through the lesioned area. The conclusion that the cholinergic projection originated in neuronal perikarya at the lesion site was supported by the failure of kainate or electrolytic lesions in contiguous regions to produce similar effects. These studies provide strong evidence for a cholinergic projection to neocortex from neurons in the forebrain in the nucleus basalis.