Effect on temperature of 5‐hydroxytryptamine injected into the cerebral ventricles of cats

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

Section: Discussionmentioning

confidence: 99%

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

Myers¹,

Waller²

1973

“…However, Myers (1968) has suggested that high doses of 5-HT may cause a synaptic block in the monkey. Such a block might also account for the biphasic responses to 5-HT which sometimes occurred in the cat (Banerjee et al 1968) and the discrepancies in the reported effects of 5-HT on the body temperature of the cat (Feldberg & Myers, 1963;Kulkarni, 1967).…”

Section: Central Transmitters and Thermoregulation 389mentioning

confidence: 99%

Influence of ambient temperature on the thermoregulatory responses to 5‐hydroxytryptamine, noradrenaline and acetylcholine injected into the lateral cerebral ventricles of sheep, goats and rabbits

Bligh¹,

Cottle²,

Maskrey³

1971

191

SUMMARY1. The influences of ambient temperature (Ta) on the thermoregulatory effector activities and the body temperature (Tb) of intraventricular injections into the sheep, goat and rabbit of 5-hydroxytryptamine (5-HT), noradrenaline (NA), acetylcholine (ACh), carbachol and eserine, have been interpreted in terms of a simple neuronal model of the pathways between thermosensors and thermoregulatory effectors.2. In all three species 5-HT in minimal doses caused a rise in respiratory frequency (RF) and a fall in Tb at high Ta, and a reduction in EMG activity and a fall in Tb at low Ta. These effects could be interpreted as those of an excitatory transmitter acting on the warm receptor-heat loss pathway. 3. In all three species NA caused a reduction in RF and a rise in Tb at high Ta, and a reduction in EMG activity and a fall in Tb at low Ta. These effects are interpreted as those of an inhibitory transmitter acting both on the warm sensor-heat loss pathways and on the cold sensor-heat production pathway.4. The effects of ACh and the cholinomimetic substances carbachol and eserine are complex and more difficult to interpret. In small doses the effects on the sheep and goat are those of an excitatory transmitter on the cold sensor-heat production pathway. There was an increase in EMG activity and a rise in Tb at low Ta, and a reduction in RF and a rise in Tb at high Ta. At higher dose levels in the goat and at all dose levels in the

“…Thus, * Beit Memorial Research Fellow. M. A. SIMMONDS in the cat, dog and monkey, 5-HT causes a rise in temperature (Feldberg & Myers, 1965; Ruckebusch, Grivel & Laplace, 1965;Feldberg, Hellon & Lotti, 1967;Banerjee, Burks & Feldberg, 1968) while, in the rat, mouse, rabbit, ox and sheep, a fall in temperature is observed (Cooper, Cranston & Honour, 1965;Brittain & Handley, 1967;Feldberg & Lotti, 1967;Findlay & Thompson, 1968;Myers & Yaksh, 1968;Bligh & Cottle, 1969).…”

Section: Introductionmentioning

confidence: 99%

Effect of environmental temperature on the turnover of 5‐hydroxytryptamine in various areas of rat brain

Simmonds¹

1970

SUIMMARY1. Rats were exposed to environmental temperatures of 9, 24 or 320 C and the turnover of 5-hydroxytryptamine (5-HT) was estimated in various areas of brain by two different methods in separate series of experiments. In the first method, small amounts of tritium labelled 5-HT, [3H]5-HT, were injected into the c.s.f. in order to label radioactively the endogenous 5-HT in the brain. The rates of disappearance of [H]5-HT from discrete areas of brain were taken as indices of the rates of turnover of endogenous 5-HT in these areas. In the second method, the rate of accumulation of endogenous 5-HT after inhibition of monoamine oxidase by pargyline was taken as an estimate of 5-HT turnover.2. The results obtained by each method were in agreement. The turnover of 5-HT increased with increasing environmental temperature from 9 to 32' C in specific brain areas. During the first hour of exposure to 32b C, the turnover of 5-HT increased in the preoptic area, hypothalamus and cortex+ hippocampus, but not in striatum or midbrain. During the subsequent 2 hr at 320 C, however, the turnover of 5-HT in the preoptic area and hypothalamus fell while that in the striatum showed a delayed rise.3. It is concluded that 5-HT is involved in several different cerebral pathways which increase their activity upon exposure of the rat to heat. These pathways are not located exclusively in the preoptic area and hypothalamus.