Acute effects of the neurotoxin kainic acid on neurons of the pigeon basal ganglia. Electrophysiological and light and electron microscopic observations

The effects of kainic acid on the cochlear ganglion of the rat

The effects of locally applied kainic acid on cells and fibers in the rat cochlea were examined in a quantitative and ultrastructural study. Doses of 5 nM per microliter of artificial perilymph destroyed part of the spiral ganglion type I cell population, with no ototoxic effects on cochlear hair cells or supporting cells. Type II cells also appeared unaffected. A quantitative evaluation of the cell loss with the 5 nM dosage showed that 34% of spiral ganglion neurons were lost 10 days after treatment. Doses of 20 nM per microliters and 40 nM per microliters did not result in increasing neuronal loss. This differential toxicity could reflect the presence of a sub-population of spiral ganglion cells with an increased number of KA receptors.

Further postmortem examination of a case of familial ataxia with cerebrospinal fluid abnormality: an electron microscopic study of the intracytoplasmic eosinophilic inclusion bodies in the central nervous system

As reported previously, the peculiar intracytoplasmic eosinophilic inclusion bodies (IEIBs) extensively appeared in the autopsied brain tissue from a 49-year-old man having familial ataxia with cerebrospinal fluid abnormality, and histochemically showed abundant proteins, but few lipids and carbohydrates. Ultrastructurally, many membrane-bound vacuoles derived from the distended cisterns of rough-surfaced endoplasmic reticulum (RER) appeared in the neurons. They were filled with fine granular, less dense materials. The IEIBs, shown as a homogeneous dense core, were found in some of the vacuoles. Similar vacuoles also appeared in astrocytes, oligodendrocytes, vascular pericytes, ependymal and choroidal epithelial cells. It is suggested that the vacuoles result from the accumulation of metabolic products in the distended RER cisterns of the cells in the central nervous system, presumably representing a genetically determined functional abnormality of the RER in protein synthesis and/or transport.

Role of pontomedullary reticular formation neurons in horizontal head movements: an ibotenic acid lesion study in the cat

Single-cell recording, electrolytic lesion and electrical stimulation studies have indicated that the pontomedullary reticular formation (PMRF) plays a role in head movement (HM) control. However, recent studies utilizing excitotoxin lesions of the PMRF have reported no effect on HM. In the present study, we have examined the acute and chronic motor effects of injecting ibotenic acid (IBO) into the nucleus reticularis pontis oralis, nucleus reticularis pontis caudalis and rostral medullary nucleus gigantocellularis of the feline PMRF. IBO injections in all of these regions induced tonic flexion of the head toward the ipsilateral side. This effect lasted 4-16 h. It was followed by a second phase in which head flexion and whole body circling were directed toward the contralateral side. Although this forced contralateral head turning disappeared within two days, the tendency to turn contralaterally and the impaired ability to make rapid ipsilateral HMs were present throughout survival periods lasting more than 4 months. Unilateral IBO PMRF lesions reduced the amplitude of vestibular induced quick phase (anti-compensatory) HMs toward the ipsilateral side and resulted in abnormally large and persistent slow compensatory HMs toward the contralateral side. Following IBO injections, the threshold intensity for HMs evoked by electrical stimulation at the injection site was elevated, and the amplitude and velocity of evoked HMs reduced. Histological data indicated that the reticular area involved in HM control was relatively large and probably extended beyond the PMRF region examined here. However, lesions including the nucleus reticularis pontis caudalis (NRPC) produced more severe and persistent HM deficits than those including the nucleus reticularis gigantocellularis. These data together with available anatomical and electrophysiological evidence indicate that PMRF neurons play a critical role in the generation of fast horizontal HMs toward the ipsilateral side.

Motor functions of the striatum in the rat: critical role of the lateral region in tongue and forelimb reaching

The findings of this study indicate a critical and selective role of the rat's lateral striatum in performance of tongue and forelimb reaching. To test the hypothesis of regional specificity of motor control in the striatum, the effects of bilateral, ibotenate-induced lesions of either the lateral or the medial regions of the striatum on reaching movements of the tongue and the forelimbs were examined. Lesions of the lateral striatum caused severe and chronic impairments of movement initiation, postural synergisms and amplitude of both tongue and forelimb reaches. In contrast, lesions of the medial striatum produced mild or no chronic alterations of these motor parameters. These findings support the hypothesis of a selective role of the lateral striatum in the initiation and execution of reaching movements.

The toxin kainic acid: a study of avian nerve and glial cell response utilizing tritiated kainic acid and electron microscopic autoradiography

Three questions are asked regarding the toxin kainic acid (KA). Does it destroy specific glial cells as well as neurons? Does KA gain access to the cytoplasm in intact cells and to which organelles does it bind? Intracerebral injections of tritiated KA into the pigeon (Columba livia) paleostriatal complex (basal ganglia) coupled with electron microscopic autoradiography revealed the following major points. Kainic acid destroyes oligodendrocytes, with pathophysiology apparent by 30 min after challenge with KA leading to cell destruction by 4 h. The response of astrocytes at the longest observation period (4 h) involves swelling of perivascular endfeet and processes in the neuropil. Reactive microglial-like cells show an accumulation of label in their cytoplasm, but no apparent morphological changes. The label appears in the cytoplasm of intact cells, both glia and neurons early after challenge with the toxin. Label is associated (bound) with mitochondria at an incidence significantly above chance at 30 min, 2 and 4 h after challenge with KA. Two hours after exposure to KA is the critical period where metabolic, physiological and morphological changes occur that lead to cell death. Cell destruction may be a consequence of KA-induced energy depletion. Kainate may interfere with adequate energy production by uncoupling glycolysis and the Krebs cycle in the mitochondria.

L-pyroglutamate: an alternate neurotoxin for a rodent model of Huntington's disease

Intrastriatal injections of L-Pyroglutamate (L-PGA) in mice produced behavioral and neuropathological effects that resemble in part the kainate-injected rat striatal model of Huntington's Disease (HD). The behavioral responses induced after unilateral injections of L-PGA included circling, postural asymmetry of head and trunk and possible dyskinesias. The neuropil in the injected striatum contained dilated profiles, degenerating neurons and oligodendroglia, and numerous phagocytic microglial-like cells. A dose response relation existed. The size of the lesion (expressed as a percent volume of the striatum destroyed) ranged from 1 +/- 0.18% at 0.02 mumoles to 20.2 +/- 3.97% at 200 mumoles L-PGA (pH = 7.3). L-PGA is a weak neurotoxin when compared to kainic acid. Several factors raise interest in the possible role of L-PGA in HD, including the recently reported elevated plasma levels of L-PGA in some HD patients, and these considered in the discussion.