Evoked release of 5-HT and NEFA from the hypothalamus of the conscious monkey during thermorégulation

166

Section: Discussionmentioning

confidence: 99%

Fever produced by prostaglandin E₁

Feldberg¹,

Saxena²

1971

166

“…More recently, some thermosensitive neurones have been found in an area extending from the posterior hypothalamus to the mesencephalon (Nakayama & Hardy, 1969;Cabanac & Hardy, 1969). From the monoamine theory of thermoregulation (Feldberg & Myers, 1964) heat production would be activated by the release of 5-HT within the anterior hypothalamus when an animal is cold (Myers, Kawa & Beleslin, 1969), whereas noradrenaline is released to inhibit the heat production pathway when the animal is warm Myers & Yaksh, 1969). The release of these substances within the thermostat are presumed to occur in response to thermal stimuli, and help to regulate temperature around a given set-point which has been determined inherently .…”

Section: Discussionmentioning

confidence: 99%

The role of sodium and calcium ions in the hypothalamus in the control of body temperature of the unanaesthetized cat

Myers¹,

Veale²

1971

Self Cite

127

SUMMARY1. Isolated regions of the anterior, posterior and other areas of the hypothalamus of the unanaesthetized cat were perfused by means of push-pull cannulae lowered through permanently implanted guide tubes. Each site was perfused for a 30 min interval at a rate of 50 ,ul./min. Concentrations of sodium, calcium, potassium and magnesium ions in the perfusate were altered selectively.2. Sodium ions in a concentration which varied from 13-6 to 68-0 mM in excess of the level in extracellular fluid caused a steep rise in the temperature of the cat when the solution was perfused at sites located within the posterior hypothalamic area. Shivering, vasoconstriction, and piloerection accompanied the increase in temperature. When the chloride was replaced in the perfusate by the toluene-p-sulphonate salt of sodium, the hyperthermia was equally intense. Solutions containing excess sodium ions perfused within the anterior and other hypothalamic areas produced either a slight fall or rise in temperature as well as other physiological changes.3. Calcium ions in a concentration which varied from 2*6 to 10-4 mM in excess of the physiological level perfused at the same sites within the posterior region of the hypothalamus produced a sharp fall in body temperature, which was accompanied by vasodilatation and a decrease in the activity of the cat. When solutions containing excess calcium were perfused in the anterior and other hypothalamic areas, no consistent change in temperature occurred. R. D. MYERS AND W. L. VEALE two to ten times the level in extracellular fluid had virtually no effect on the temperature of the cat when they were perfused in the anterior, posterior or other areas of the hypothalamus.5. We conclude that the constancy in the ratio between sodium and calcium ions in the posterior hypothalamus may be the inherent mechanism by which the set-point for body temperature is determined.

“…stimulus could cause a presynaptic release of 5-HT, and a warm stimulus, the liberation of noradrenaline. In the case of the indoleamine, it has already been shown that 5-HT is released principally from the rostral hypothalamus when the monkey is cooled (Myers, Kawa & Beleslin, 1969;Myers & Beleslin, 1971). However, the evidence for the release of noradrenaline in response to peripheral warming is at present only indirect, since the sole neurochemical change thus far observed within the anterior region is an increase in non-esterified fatty acids following peripheral heating .…”

Section: Discussionmentioning

confidence: 99%

Thermoregulation around a new ‘set‐point’ established in the monkey by altering the ratio of sodium to calcium ions within the hypothalamus

Myers¹,

Yaksh²

1971

Self Cite

SUMMARY1. The cerebral ventricles of the unanaesthetized monkey were perfused at a rate of 50-100 4td./min with artificial cerebrospinal fluid (c.s.f.) containing 11F0-340 mm excess sodium or 23-9-47-9 mm excess calcium ions. By repeated perfusions, a marked hyperthermia elicited by excess sodium or deep hypothermia by excess calcium was sustained for up to half a day.2. During the sodium-induced hyperthermia or calcium-induced hypothermia, the monkey thermoregulated adequately around the new level of temperature in response to either 50 or 150 ml. water heated to 580 C or chilled to 00 C and given by the intragastric route. Cold water produced a transient hypothermia after which temperature returned to the pre-load level; hot water given in the same way evoked a short-lasting hyperthermia, and again the temperature returned just to the new setpoint level.3. Perfusions at 50 #1./min of isolated areas of the diencephalon by means of push-pull cannulae with a solution containing 110-34-0 mm excess sodium ions or 11L3-47-9 mm excess calcium ions altered the body temperature of the monkey only when the sites of perfusion were located in the mammillary region of the posterior hypothalamus. Following the prolonged hyperthermia produced by excess sodium ions or the deep hypothermia evoked by excess calcium ions in the push-pull perfusion fluid, the monkey thermoregulated around the new temperature level again in response to 150 ml. of either hot or cold water given in the stomach. R. D. MYERS AND T. L. YAKSH perature. When EGTA was perfused directly in the posterior hypothalamus by means of push-pull cannulae, a profound hyper-pyrexia ensued which could be abolished immediately by perfusing a solution of excess calcium at the same diencephalic site.5. During the calcium-induced hypothermia, the heart rate declined but the electrical activity of the cortex was relatively unchanged. Feeding was also elicited in the hypothermic monkey by noradrenaline microinjected at a site in the hypothalamus at which eating was evoked when the body temperature was normal.6. The evidence supports the hypothesis that in the primate, the inborn mechanism which establishes the set-point for body temperature at 370 C is the constancy in the intrinsic ratio between sodium and calcium ions within the posterior hypothalamus. If the set-point is elevated or lowered by a disturbance of the balance between these two cations, the monkey nevertheless can thermoregulate normally around the new level of body temperature.