Neurotoxicity of kainic acid: evidence against an interaction with excitatory glutamate receptors in rat olfactory bulbs

Selectivity of kainic acid as a neurotoxin within the dorsal lateral geniculate nucleus of the cat: a model for transneuronal retrograde degeneration

In situ injections of the cytotoxin kainic acid were used to make localized lesions of the dorsal lateral geniculate nucleus in the adult cat to produce a model for studying the effects of postsynaptic target loss. Kainic acid has been used extensively to produce lesions of neuronal cell bodies within the central nervous system. However, the selectivity of kainic acid has been questioned, as it may also affect afferent terminals or axons of passage. Retinal projections to degenerated geniculate nuclei were visualized 1 week after kainate injection using anterograde labelling with horseradish peroxidase and electron microscopy. The results demonstrate the presence of afferent terminals within regions of neuronal loss, and hence the selectivity of kainic acid for intrinsic geniculate neurons.

Potentiation by kainate of excitatory amino acid release in striatum: complementary in vivo and in vitro experiments

The effect of kainate on extracellular levels of amino acids in corpus striatum was investigated in vitro and in vivo, to elucidate the mechanism underlying its neurotoxicity. Kainate increased extracellular glutamate and aspartate in both striatal slices in vitro and intact striatum in vivo, as previously reported. Both in vitro and in vivo, DL-threo-3-hydroxyaspartate increased extracellular glutamate and aspartate levels (to between 150 and 200% of basal), and also enhanced their kainate-evoked release. The action of kainate in vivo was reduced by prior frontal decortication, whereas in vitro the kainate-evoked responses were only slightly reduced by tetrodotoxin, and remained above control values. These results confirm that kainate increases extracellular glutamate and aspartate, and provide evidence that this is due to synaptic release evoked by an action on receptors on glutamatergic neurone terminals. These findings may be relevant to the understanding of epilepsy.

Kainic acid-induced changes of extracellular amino acid levels, evoked potentials and EEG activity in the rabbit olfactory bulb

The effect of kainic acid (KA) on the extracellular content of amino acids in the rabbit olfactory bulb was investigated, both in vivo with the brain dialysis technique and in vitro with a superfused tissue slice preparation. Olfactory bulb EEG activity and lateral olfactory tract (LOT)-evoked field potentials were monitored simultaneously during dialysis experiments. KA induced a rapid (within 5 min) increase of extracellular aspartate, glutamate, GABA, phosphoethanolamine and taurine in vivo. LOT-evoked potentials were altered concomitantly in a concentration- and time-dependent manner. The antidromic invasion of mitral/tufted cells was depressed and the synaptic activation of granule cells was abolished in the presence of KA. Olfactory bulb EEG activity was also affected. Oscillatory bursts in olfactory bulb EEG were abolished by 10 mM in most experiments, whereas sustained oscillations were induced by 1 mM KA. The effects of KA may partly be due to a blockade of amino acid reuptake since dihydrokainate (DKA) perfusion was found to increase extracellular aspartate and glutamate. However, DKA had no significant effect on EEG or evoked potentials. In vitro, aspartate and glutamate were selectively increased during KA perfusion.

Cardiorespiratory effects produced by application of L-glutamic and kainic acid to the ventral surface of the cat hindbrain

The purpose of our study was to determine the cardiorespiratory effects of exciting cell bodies at the rostral (area M), intermediate (area S), and caudal (area L) chemosensitive sites on the ventral surface of the medulla. To do this, L-glutamic and kainic acid were applied bilaterally to each chemosensitive site while monitoring tidal volume (VT), respiratory rate (f), mean arterial pressure (BP), and heart rate (HR) in chloralose-anesthetized cats. Application of solutions (5 microliter) of L-glutamic acid ranging from 62.5 to 2000 mM to the intermediate area produced concentration-dependent increases in VT (from 2.0 +/- 0.6 ml to 14 +/- 1.1 ml) and BP (from 2.0 +/- 1.7 mm Hg to 39 +/- 5.3 mm Hg). No significant changes in f and HR were noted. Similar effects were observed with application of kainic acid. Application of L-glutamic acid to the caudal area produced hypotension (-24 +/- 5.4 mm Hg) with no accompanying changes in VT and f. No responses were observed after application of L-glutamic acid to the rostral area. These data suggest that activation of cell bodies on the intermediate area produces simultaneous stimulatory effects on BP and VT, whereas activation of cell bodies at the caudal area produces selective depressant effects on BP.

Kainic acid stimulation of the lateral septum elicits tachycardia

Electrical stimulation of the lateral septum results in a transient cardiodeceleration which may represent parasympathetic rebound to a brief sympathetic activation. Kainic acid (KA) is a potent neuronal excitant. Stimulation of the lateral septum by KA produced a short-latency tachycardia. Vehicle injections, as well as KA administration to adjacent structures, did not effect significant changes in heart rate. Intraventricular KA, however, did result in a significant tachycardia. Knife cuts of the fornix, interrupting the glutamatergic innervation of the septum, completely blocked the cardiovascular response to KA. Pharmacological treatments reducing sympathetic activity prevented or reversed KA-elicited tachycardia. Thus, it appears that septal administration of KA produces sympathetic activation. KA may serve as a useful tool in studies assessing central regulation of the autonomic nervous system, and the interrelationship between autonomic activity and seizure-induced neuronal loss.

Kainic acid receptors and neurotoxicity in adult and immature rat cerebellar slices

The neurotoxic actions of kainate were examined in incubated slices of adult and immature rat cerebellum using light- and electron-microscopy. In the adult, Purkinje cells and inhibitory interneurones became selectively necrotic at concentrations between 5 micro M and 20 micro M. At 30 micro M, granule cells also became affected. In the immature cerebellum, at an age (8 days after birth) when the parallel fibres (thought to use glutamate as transmitter) are largely yet to be developed, selective toxicity was still evident but Purkinje cells and inhibitory interneurones were about 10-fold, and granule cells about 30-fold, less sensitive to kainate than in the adult. Kainate and other excitotoxins also increased cyclic GMP levels in cerebellar slices, apparently through the activation of excitatory amino acid receptors. In the adult tissue, the dose-cyclic GMP response curve to kainate was biphasic suggesting the presence of two components. The lower concentrations of kainate eliciting the first component mirrored those inducing selective necrosis of Purkinje cells and inhibitory interneurones while the second component correlated with necrosis of granule cells. Similar correlations applied to the immature cerebellum, but here kainate neurotoxicity appeared to be associated with the activation of receptor types different from those evident in the adult. It is suggested that kainate receptors, whose activation is associated with both neurotoxic damage and elevation of cyclic GMP levels, are located on all cell types in the adult cerebellum, with Purkinje cells and inhibitory interneurones displaying a higher sensitivity to kainate than granule cells. The lower sensitivity of immature cerebellum to the neurotoxic effect of kainate is probably due to lower levels of kainate receptors.

Neurotransmitter receptor ligand binding and enzyme regional distribution in the pigeon visual system

The relative importance of acetylcholine, dopamine, endogenous opiates, gamma-aminobutyric acid (GABA), glutamate, glycine, noradrenaline, and serotonin as transmitters in the pigeon visual system was estimated by measuring the activity of choline acetyltransferase (ChAT), glutamic acid decarboxylase (GAD), and aromatic amino acid decarboxylase (AAD) as well as the binding of dihydroalprenolol, etorphine, kainic acid, muscimol, serotonin, spiroperidol, strychnine, and quinuclidinyl benzilate (QNB) in the tectum opticum, nucleus rotundus, ectostriatum, dorsolateral thalamus, and hyperstriatum (Wulst). As a nonvisual reference structure, the paleostriatal complex was included in the examination. The regional distribution of most of these parameters was very similar to data reported in the mammalian CNS supporting the hypothesis that the avian tectofugal and thalamofugal visual systems are homologous to the mammalian tecto-thalamo-cortical and retino-geniculo-striate pathways, respectively. On the basis of the low values of their parameters, some transmitters can be excluded as significant contributors in a number of structures. As a hypothesis for further investigations, the presence of cholinergic and serotoninergic systems in the Wulst, possibly originating in the dorsolateral thalamus and nucleus raphe, respectively, and of glycinergic and dopaminergic terminals in the paleostriatal complex is proposed.

Stimulatory role for medial preoptic/anterior hypothalamic area neurones in growth hormone and prolactin secretion. A kainic acid study

The role of preoptic/anterior hypothalamic area (PO/AHA) neurones in the regulation of basal patterns of growth hormone (GH) and prolactin (Prl) secretion was investigated in unanesthetized male rats prepared with chronic indwelling venous cannulae. PO/AHA injections of the neurotoxin kainic acid (KA) substantially reduced both GH and Prl secretion. Histological examination of tissue sections indicated that KA treatment had produced extensive neuronal loss and gliosis in the medial (m) but not the periventricular (p) PO/AHA. These findings suggest that m-PO/AHA neurones are facilitatory to the basal secretion of both GH and Prl. It is proposed that GH-facilitatory m-PO/AHA neurones provide an inhibitory input to the GH release-inhibiting factor neurones which are known to reside in the p-PO/AHA. Prl-facilitatory m-PO/AHA neurones may secrete, or stimulate the secretion of a Prl releasing factor.

A search in rat brain cortex synaptic vesicles for endogenous ligands for kainic acid receptors

Conditions were found for stabilizing rat brain cortex kainic acid (KA) receptors. Such receptors had the same Hill number (about 0.6) for KA and for glutamate. The receptors were then used as detectors for endogenous ligands present in brain cortex synaptic vesicle (SV) soluble extracts. When these SV extracts were fractionated by gel filtration on Sephadex G-10, by thin-layer chromatography, or by high voltage electrophoresis, a single endogenous component, that in all cases comigrated with glutamic acid, was found.

Kainic acid neurotoxicity does not depend on intact retinal input in the goldfish optic tectum

Kainic acid neurotoxicity has been studied in the optic tectum of the goldfish 4 weeks after eye enucleation. The effect of drug treatment has been tested with respect to both neurochemical and morphological parameters. The neurotransmitter-related enzymes, choline acetyltransferase, acetylcholinesterase and glutamate decarboxylase, show about 50% decrease in the deafferented tectum 6 days after kainic acid administration. Relevant morphological alterations of the tectal structure can also be noticed at the same stage. The neurotoxic effects of kainic acid in the deafferented optic tectum are therefore quite similar to the effects of previously noticed for the intact optic tectum of normal fish. Control experiments on the effect of optic nerve degeneration by itself on the levels of the neurotransmitter-related enzymes in the optic tectum, have shown no significant decrease in glutamate decarboxylase, a slight decrease in acetylcholinesterase and a more marked drop in choline acetyltransferase. The findings are discussed with reference to some of the hypotheses advanced in order to explain kainic acid neurotoxicity. It is proposed that the neurotoxic effect of kainic acid after removal of specific excitatory afferents, may vary in different nervous centers depending on differences of the remaining extrinsic connections and of the intrinsic neural circuits.

Localization of kainic acid-sensitive cells in mammalian retina

Short-term (15 minutes) in vitro exposure to kainic acid (KA), a rigid structural analog of L-glutamic acid (Glu), caused two morphologically distinct neuronal lesions in retinas of several species. In rabbit retina, one type of lesion was characterized by rapid swelling after exposure to low concentrations of KA (10(-4)M). This lesion was observed in elements of both plexiform layers and, more specifically, in cell bodies and neurites of horizontal cells that contact cones. A few cell bodies from the amacrine cell layer showed some limited swelling. The swelling was completely blocked when sodium was removed from the incubation medium. The second type of lesion was generally seen after longer exposures of after exposure to higher concentrations of KA and was evidenced by degeneration of neurons in the amacrine and ganglion cell layers. One exception was noted in that a few cells from the ganglion cell layer degenerated even under low exposure conditions. The second type of lesion was not blocked by removal of sodium ions. Photoreceptor cells appeared resistant to all effects of KA. The results suggest that a correlation may exist between certain KA-induced lesions of the retina and putative glutamoreceptive neurons. At the same time, the two types of retinal lesions produced by KA are morphologically and chemically differentiable and may be useful in elucidating the differences between specific, Glu-related toxicity and nonspecific toxicity of KA.