Striatal cholinergic receptors and dyskinetic motor activity in the rat

Analysis of the brain regions involved in myoclonus produced by intracerebral picrotoxin

Picrotoxin caused myoclonic jerking of the opposite forelimb when applied to the striatum and the cortical surface of rat brain. Intrastriatal picrotoxin increased [3H]2-deoxyglucose uptake by the ipsilateral frontal cortex, thalamus and subthalamic nucleus. Electrolyte and ibotenic acid lesions made in the globus pallidus prevented striatally evoked myoclonus without affecting the movements elicited from the cortex. Electrolytic lesions in the subthalamic nucleus and thalamus affected striatally evoked myoclonus more than the cortically elicited response. It is concluded that striato-pallidal-thalamic-cortical circuitry is responsible for striatally evoked myoclonus.

Neuropathology and amphetamine-induced turning resulting from AF64A injections into the striatum of the rat

The putative specific cholinergic neurotoxin AF64A was prepared by a micro-scale procedure which afforded the neurotoxin in greater than 95% purity and was microinjected unilaterally into the striatum of male albino rats. The AF64A-injected animals displayed amphetamine- and apomorphine-induced ipsilateral turning indicating disruption of normal striatal pathways. These turning effects were absent in the control injected animals. Histological examinations of the brains revealed that AF64A in amounts as low as 1 nmole produced regions of necrosis in the striatum in some cases extending along the cannula tract up to and including the cortex. These results indicate that the striatum is highly sensitive to relatively low doses of AF64A, and that consideration should be given to the possibility of gross tissue damage when interpreting behavioral data.

d-Tubocurarine causes neuronal death when injected directly into rat brain

d-Tubocurarine (d-TC) is a drug commonly used to produce muscle paralysis. Although it has been demonstrated to produce seizures when injected directly into the cerebral ventricles, no lasting neurotoxic effects have been reported. Data presented here suggest that amounts of d-TC as small as 1 microgram injected directly into rat hippocampus resulted in selective damage to dentate granule cells. Larger doses (5 to 10 micrograms) induced limbic and motor seizures with damage to hippocampal pyramidal cells. Other brain regions showed a differential sensitivity to direct injections. Pharmacologic studies suggest a nicotinic mechanism for both actions. The neurotoxic effects could not be elicited if d-TC was administered systemically, even when the blood-brain barrier was disrupted.

Effects of dopamine agonists, catecholamine depletors, and cholinergic and GABAergic drugs on acute dyskinesias in squirrel monkeys

It has been suggested that the neuroleptic-induced acute dyskinetic syndrome in monkeys may be a useful model of extrapyramidal dysfunction. Various drugs that have well-characterized effects on clinical extrapyramidal syndromes and on catecholaminergic, cholinergic, or GABAergic neurotransmission were assessed in dyskinesia-susceptible squirrel monkeys. Catecholamine depletors (alpha-methyl-p-tyrosine, tetrabenazine) induced the syndrome, as do dopamine (DA) receptor antagonists, and d-amphetamine reversed the effects of tetrabenazine. The haloperidol-induced syndrome was reversed by the indirectly acting DA agonists amantadine and L-dopa. Neither of the DA autoreceptor agonist TL-99 or 3-PPP elicited this syndrome, suggesting that these agents lack extrapyramidal involvement. Anticholinergics reversed haloperidol-induced dyskinesias and the cholinomimetic arecoline was capable of inducing dyskinesias. When coadministered repeatedly with haloperidol, benztropine suppressed the emergence of susceptibility to neuroleptic-induced dyskinesias. These results confirm that the acute dyskinetic syndrome in the monkey is characterized by DA deficiency and acetylcholine excess. Diazepam and baclofen, which have been reported to have some clinical benefit in tardive dyskinesia, suppressed haloperidol-induced acute dyskinesias without causing gross motor depression. Pharmacological manipulation of GABAergic pathways from striatum may constitute a fruitful approach to the treatment of dyskinetic motor disorders.

Role of acetylcholine and dopamine in myoclonus induced by intrastriatal picrotoxin

Rats injected intrastriatally with picrotoxin and carbachol showed sustained myoclonic jerks of the contralateral forelimb. The role of acetylcholine and dopamine in picrotoxin myoclonus was examined by measuring the effects of intrastriatal pharmacological agents on the frequency and intensity of the jerks. Atropine and hemicholinium-3, which reduce acetylcholine function, antagonized the myoclonus. Apomorphine, which has been shown to reduce striatal dopamine function via "autoreceptors", potentiated the jerking, whereas D-amphetamine antagonized the myoclonus. The findings are discussed in relation to proposed interconnections of striatal neurones.