Central cholinergic mechanisms in electrical self-stimulation and in drug-induced tremor in rats.

Oxotremorine, a specific stimulant of central muscarinic acetylcholine receptors, inhibited lateral hypothalamic self-stimulation at a dose-level less than one-tenth of that necessary to produce body tremor. Tremor induced by oxotremorine (0.5 mg/kg) was inhibited by pretreatment with hyoscine (scopolamine) (0.3 mg/kg) or propranolol (20 mg/kg) but not by methylhyoscine (0.3 mg/kg) or apomorphine (0.3 mg/kg). Inhibition of self-stimulation by oxotremorine (.03 mg/kg) was prevented by hyoscine (0.3 mg/kg) but not by any other of the drugs tested and thus constitutes a uniquely specific in vivo model for assessing central antimuscarinic activity. The results confirm the presence of centrally situated ACh receptors eleciting tremor and inhibiting self-stimulation but provide no evidence of an effect on tremor by central adrenergic beta-receptors.

Thiamin deprivation in ventromedial hypothalamic hyperphagic rats: anorexia, specificity of food aversion, and a dietary consideration.

The anorexic consequence of thiamin deprivation was investigated in ventromedial hypothalamic (VMH) hyperphagic rats under either high-fat or low-fat thiamin-free diet conditions. The low-fat diet maintained feeding significantly longer in thiamin-deprived VMH rats than in intact rats, whereas the hig-fat diet sustained feeding in thiamin-deficient intact rats and accelerated anorexia onset in vitamin B1 deprived VMH rats. This effect was noted under both ad lib and pair-feeding conditions. Thiamin-deprived VMH rats subjected to weight control developed anorexia sooner than intact subjects regardless of the diet employed. The VMH rats fed a high-fat diet failed to resume feeding after thiamin readministration, which was interpreted as a permanent aversion to this diet. The relation between dietary intake and conditioned taste aversion is discussed with reference to the VMH and intact rat.

Reliable method for cannulation of the third ventricle of the rat.

A method for chronic or acute cannulation of the third ventricle of the rat is described. This technique, in which successful cannulation is verified by the aspiration of a minute quantity of cerebrospinal fluid, is simple, reliable and produces minimal tissue distortion. The results of an experiment employing the technique and which compared the effects of direct intrahypothalamic and intraventricular administration of phentolamine on stimulus-bound feeding are briefly described.

Water intoxication death following hypothalamic lesions in the rat.

Rats received large, bilateral lesions of the ventromedial hypothalamus. Water or saline intakes, urine outputs and body temperatures were observed for up to 24 hr after surgery. Fifty percent of the operated animals drank excessively and died within 4-6 hr when permitted access to water. Urine outputs were low and symptoms of water intoxication were evident. When allowed access to saline, outputs rose and the number of animals which survived increased as the saline concentration increased. Body temperatures approached 40 degrees C during drinking, but did not differ from operated animals which refused to drink. It was concluded that the deposition of metallic ions strongly stimulates a hypothalamic drinking system which results in overhydration and water intoxication death.