Differential release of acetylcholine from the hypothalamus and mesencephalon of the monkey during thermoregulation

Abstract

SUMMARY1. In unanaesthetized monkeys acclimated to primate chairs, 101 isolated sites in the hypothalamus and mesencephalon were perfused at a rate of 30-50,sl./min by means of push-pull cannulae. The perfusate, which contained an anticholinesterase, was assayed for acetylcholine (ACh) activity on the guinea-pig ileum in the presence of neostigmine.2. The body temperature of each animal was monitored continuously during an experiment by colonic and brain thermistors. To alter the ambient temperature by 15-20' C, either a stream of warm air was passed over the monkey's trunk or containers of ice were placed in its chair chamber to cool the same region.3. Assays of the effluent revealed that the release of ACh varied according to the ambient temperature as follows: elevated only during cooling; elevated only during warming; elevated by both thermal stimuli; suppressed only by cooling; suppressed only by warming; suppressed by both thermal stimuli; elevated during cooling but suppressed by warming; and elevated by warming and suppressed by cooling. 4. A composite anatomical 'mapping' of all perfusion sites revealed that in response to either peripheral cooling or warming, the output of ACh varied at only 36 % of all sites anterior to the mid-hypothalamic plane, but at 65 % of those loci caudal to this coronal plane.5. In the anterior, preoptic area, cooling enhanced the output of ACh at 88 % of the active releasing sites, whereas warming reduced the release of ACh at 80 % of these perfusion loci. Posterior to this region, ACh release was elevated by cooling at about half of the active releasing sites, but lowered by warming at nearly every active perfusion locus. Within the mesencephalon, the ratio of the temperature-induced change in ACh release was similar but in an opposite direction, since the level of ACh in

Decrease in selected temperature after intracranial dopamine injections in goldfish

“…A similar study in the rhesus monkey (Myers and Beleslin, 1971), where serotonin levels were monitored found that cooling evoked an increased release of serotonin whereas heating either did not affect or inhibited serotonin release. Similar results were found for acetylcholine levels in another study on the rhesus monkey (Myers and Waller, 1973). To conclude, an overview will be given of the evidence in support of a physiological role for dopamine in thermoregulation:…”

The effect of noradrenaline, injected into the hypothalamus, on thermoregulation in the cat.

“…These authors also suggested that NA inhibits the cholinergic heat production pathway but does not activate a heat-loss pathway which they concluded apparently does not exist within the AH/POA. They obtained evidence for a cholinergic heat-loss pathway in the cat and monkey but only within the posterior hypothalamus (Myers & Yaksh, 1969;Myers & Waller, 1973, 1975 (Myers & Chinn, 1973) provide a basis for the suggestion that NA may activate heat loss pathways directly.…”

“…Our data suggests that this model requires modification and we propose that NA be given an additional role as acting in an excitatory manner within a heat loss pathway in the AH/POA. Such noradrenergic neurones may project to a cholinergic heat loss pathway which has been identified within the posterior hypothalamus (Myers & Yaksh, 1969;Myers & Waller, 1973, 1975.…”

Detection of Radiofrequency Radiation – Induced Whole Body Heating Following Chemical Impairment of Thermoregulation

“…It has been postulated that 5-HT acts peripherally resulting in changes in cardiovascular and/or respiratory function or may act by depressing general activity (Myers and Waller, 1977). …”