EFFECTS ON TEMPERATURE OF AMINES INJECTED INTO THE CEREBRAL VENTRICLES. A NEW CONCEPT OF TEMPERATURE REGULATION

On the role of central nervous system catecholamines and 5-hydroxytryptamine in the nialamide-induced behavioural syndrome

1. Intraperitoneal administration of nialamide, 200 mg/kg, to mice elicited a pronounced increase in motor activity and rectal temperature concomitant with a gradual increase in the concentrations of 5-hydroxytryptamine (5-HT), noradrenaline (NA) and dopamine in the brain.2. In mice treated with L-tryptophan, 300 mg/kg, 1 h before nialamide, the increase in motor activity appeared earlier than after nialamide alone, and the hyperthermia was more pronounced. The increase in 5-HT concentrations in the brain was more pronounced in these animals, whereas the concentrations of NA and dopamine were of the same magnitude as after nialamide alone.3. Treatment with p-chlorophenylalanine methylester-HCl (PCPA), 400 mg/kg, 24 h before nialamide partially antagonized the increase in motor activity and the accumulation of NA and dopamine was not significantly different from that observed after nialamide alone.4. Treatment with PCPA, 800 mg/kg, 72, 48 and 24 h before nialamide, completely antagonized the increase in motor activity and rectal temperature. The accumulation of brain 5-HT was greatly depressed in these animals. The concentrations of dopamine 1, 3 and 6 h and the concentration of NA 6 h after the nialamide injection were significantly lower in the mice given PCPA 800 mg/kg x 3, than in the mice given nialamide alone.5. Administration of DL-5-hydroxytryptophan, 30 mg/kg, 1 h after the nialamide injection, to mice pretreated with PCPA, 800 mg/kg x 3, restored the increase in motor activity and rectal temperature.6. L-Tryptophan, 300 mg/kg, given 1 h before nialamide to mice pretreated with PCPA, 800 mg/kg x 3, elicited a moderate increase in motor activity and a slight increase in the accumulation of 5-HT in the brain when compared to that after PCPA, 800 mg/kg x 3, and nialamide.7. Administration of alpha-methyltyrosine methylester, 200 mg/kg, 2 h before nialamide partially antagonized the increase in motor activity and completely antagonized the increase in rectal temperature elicited by nialamide alone. The accumulation of brain NA and dopamine was inhibited in these animals.8. It is concluded that the excitation in mice, elicited by nialamide, is mediated largely via brain 5-HT, but that also the brain catecholamines seem to contribute to this effect.

thermoregulatory effects of intraventricular injection of noradrenaline in the mouse and the influence of ambient temperature

1. At an ambient temperature of 20 degrees C, intraventricular injection of noradrenaline in the mouse resulted in hypothermia accompanied by a fall in metabolic rate and by cutaneous vasodilatation. Subcutaneous injection of noradrenaline resulted in hyperthermia with raised metabolic rate and cutaneous vasodilatation.2. The hypothermia and fall in oxygen consumption rate following intraventricular noradrenaline were prevented by pre-treatment with subcutaneous propranolol, while the cutaneous vasodilatation was un-affected. However, the effects of subcutaneously injected noradrenaline were completely abolished by subcutaneous propranolol. Intraventricular propranolol did not modify the hypothermic effect of intraventricular noradrenaline.3. The direction of the effect on body temperature of intraventricular noradrenaline was dependent upon ambient temperature; hypothermia occurring at low (15 degrees C) and hyperthermia at high (36 degrees C) ambient temperatures. However, when the possibility of any peripheral action of noradrenaline escaping into the systemic circulation was prevented by prior subcutaneous injection of propranolol, significant hypothermia could be detected at temperatures as high as 32 degrees C.4. The possibility that the effects of intraventricular noradrenaline could be due to complete abolition of central temperature regulation was further excluded by the occurrence of thermal salivation in all animals during experiments performed at 36 degrees C.5. It is suggested that, in the mouse, the hypothermic actions of intraventricular noradrenaline are due to a central effect, while its hyperthermic effects at high ambient temperature are due to escape of noradrenaline into the peripheral circulation. The hypothermia could be the result of selective activation of central heat loss mechanisms.6. Intraventricular noradrenaline was without effect on brain plasma-space although exposure to 100% oxygen caused a detectable fall.

Abolition of the morphine effect on body temperature in midbrain raphe lesioned rats

The hyperthermia and the hypothermia elicited by 5 mg/kg, i.p. or 30 mg/kg i.p. of morphine in rats are abolished by a previous lesion of the midbrain raphe resulting in a lowering of forebrain 5-HT and 5-hydroxyindolacetic acid. Lesions lateral to the midbrain raphe which do not modify brain 5-HT are without effect on body temperature changes induced by morphine. Animals lesioned in the midbrain raphe are still able to respond with a hyperthermia or with a hypothermia when they are treated respectively with 2,4-dinitrophenol or phentolamine.

Release of 5-hydroxytryptamine from caudate nucleus and septum

1. The anterior horn of one lateral ventricle was perfused in anaesthetized cats treated with inhibitors of monoamine oxidase, and the effluent was tested for 5-hydroxytryptamine (5-HT).2. The basal release of 5-HT varied from 0.25 to 4 ng in 25 min, and was usually about 1 ng.3. The basal release rose and fell with body temperature.4. Electrical stimulation for 15 min of the nucleus linearis intermedius or of the nucleus linearis rostralis caused a release of 5-HT which rarely outlasted the collection period of 25 min.5. Low frequencies (0.5/sec) were, per stimulus, more effective than high frequencies in releasing 5-HT. Over a 15 min period of stimulation, however, the highest total yield was at 20/sec; it fell abruptly at still greater frequencies.6. No release was obtained if the stimulating electrode was positioned in a variety of brain structures outside the two linear nuclei.7. The experiments indicate that 5-HT acts as a transmitter of impulses in neurones originating in the linear nuclei and terminating in caudate nucleus and septum.

Changes in body temperature produced by cholinomimetic substances injected into the cerebral ventricles of unanaesthetized cats

1. The effects on body temperature of a number of substances injected into a lateral cerebral ventricle were examined in the unanaesthetized cat.2. Nicotine (50 and 100 mug) caused a fall in body temperature ranging from 0.95-2.1 degrees C associated with skin vasodilatation, tachypnoea and panting. These responses were prevented by the intraventricular injection of hexamethonium or mecamylamine, but not of atropine or phentolamine.3. Carbachol (5 mug) caused a rise in temperature associated with skin vasoconstriction, piloerection and severe shivering. These effects were prevented by the intraventricular injection of atropine, but not of hexamethonium or mecamylamine.4. An acetylcholine/eserine mixture (10 mug of each) had no reproducible effect on body temperature. Because of the variability in the response, interaction studies with antagonist drugs were not performed.5. Hexamethonium (100 mug) or mecamylamine (100 mug) caused a prolonged rise in temperature, together with skin vasoconstriction, piloerection and intense shivering. Atropine (200 mug) was without effect on body temperature.6. Noradrenaline (100 mug) caused a fall in temperature with skin vasodilatation. The fall was converted to a rise with skin vasoconstriction, piloerection and vigorous shivering following an intraventricular injection of phentolamine (100 mug).7. These observations suggest the existence of cholinergic heat loss and heat gain mechanisms in the hypothalamic thermoregulatory pathways of the cat and the interaction studies with hexamethonium, mecamylamine and atropine, support the involvement of ;nicotinic' and ;muscarinic' receptors within the cholinergic thermoregulatory system.

Effects of adrenoceptor blocking agents on body temperature

1. The effect on rectal temperature of adrenoceptor blocking agents, injected through a cannula chronically implanted into a lateral cerebral ventricle, was examined in unanaesthetized rabbits, cats and rats, kept at room temperature (19-22 degrees C).2. In rabbits, the alpha-adrenoceptor blocking agent phenoxybenzamine (50 or 100 mug) produced marked hypothermia when injected intraventricularly but not when injected intravenously. In some rabbits as little as 1 mug was effective on intraventricular injection. Phentolamine and ergotamine, the other alpha-adrenoceptor blocking agents examined, had a much weaker hypothermic action when injected intraventricularly, whereas the beta-adrenoceptor blocking agents propranolol, pronethalol and Trasicor had no effect.3. In rabbits in which the noradrenaline stores of the hypothalamus were depleted by intraventricular injections of reserpine, the hypothermic effect of phenoxybenzamine was abolished and remained abolished for a few days.4. In cats, an intraventricular injection of phenoxybenzamine (200 mug) produced long-lasting hyperthermia, but not in all cats, and only with the first, or the first two or three injections. Injected intraperitoneally, this dose had no effect on temperature. Phentolamine (100 or 200 mug) had a very weak hyperthermic effect and phentolamine (500 mug), a hypothermic effect, but only on intraventricular injection, whereas ergotamine (100 and 200 mug) had a weak hyperthermic effect both on intraventricular and intraperitoneal injection. Propranolol and Trasicor had no effect on temperature when injected intraventricularly.5. In rats, phenoxybenzamine (5 or 20 mug) produced long-lasting hypothermia on intraventricular injection.6. Some of the temperature effects produced by intraventricular injections of the alpha-adrenoceptor blocking agents are explained on the assumption that they prevent the effect on temperature produced by a continuous release of noradrenaline from adrenergic neurones innervating the anterior hypothalamus.

Evidence for the presence of -adrenoceptors in the central thermoregulatory mechanism of rabbits

1. The effects of intracerebroventricular administration of some alpha- and beta-adrenoceptor stimulants and antagonists on the body temperature of rabbits were investigated.2. Noradrenaline produced a dose dependent rise in body temperature. Other catecholamines were less active.3. The noradrenaline response was blocked by alpha-adrenoceptor blocking agents while beta-adrenoceptor antagonists had no effect.4. alpha-Methyl-noradrenaline and metaraminol had some hyperthermic effect, but significantly reduced the response of noradrenaline.5. The possible presence of alpha-adrenoceptors in the central thermoregulatory mechanisms is suggested.

Fever produced by prostaglandin E1

Prostaglandin E(1) (PGE(1)) produces a rise in rectal temperature when injected into the cerebral ventricles of unanaesthetized cats, rabbits and rats. An effect is obtained with as little as 20, and sometimes even with 10 ng.

Changes in body temperature of the unanaesthetized monkey produced by sodium and calcium ions perfused through the cerebral ventricles

1. In the unanaesthetized Rhesus monkey, solutions containing sodium, calcium, potassium or magnesium in excess of the normal concentration of extracellular fluid were perfused from a lateral to the fourth ventricle through chronically implanted cannulae.2. Sodium (11.0-88.0 mM in excess of the physiological concentration) perfused through the ventricles, caused an immediate rise in body temperature which was accompanied by vasoconstriction, piloerection and shivering. The latency of the hyperthermia was related directly to the rate of perfusion and the concentration of sodium, whereas the magnitude of the response depended upon the concentration only. When the perfusion was terminated, shivering ceased and the temperature of the monkey returned to the base line level.3. When calcium ions were perfused in concentrations 2.5-47.9 mM in excess of that of extracellular fluid, a fall in the temperature of the animal occurred. The magnitude of the decreases depended upon the concentration of calcium in the perfusion fluid. Vasodilatation, sedation and a reduction in withdrawal reflexes accompanied the calcium-induced hypothermia. After the perfusion ended, the temperature continued to fall until the monkey began to shiver and vasoconstriction was observed in many skin areas.4. The perfusion through the cerebral ventricles with modified Krebs solution alone or with the Krebs solution which contained potassium or magnesium ions in concentrations five to ten times normal had virtually no effect on the temperature of the monkey.5. Since the temperature of the monkey was unchanged as long as the physiological ratio of sodium to calcium in the perfusion fluid remained constant, we conclude that the balance between these two essential cations within the brain stem could determine the neural mechanism whereby the set-point for body temperature of the primate is established.

Comparison of the effects of morphine, pethidine and pentazocine in rabbits pretreated with a monoamine oxidase inhibitor

1. Rabbits were premedicated with pargyline and the changes in rectal temperature measured after the intravenous infusion of morphine, pentazocine and pethidine.2. Pethidine produced pronounced rises in rectal temperature which were dose dependent. One out of the four rabbits given 1 mg/kg died in hyperthermia. Four out of the four rabbits given 5 mg/kg died in hyperthermia. Doses of 10 mg/kg of pethidine caused no significant change in the rectal temperature of rabbits not pretreated with pargyline.3. Morphine and pentazocine in doses of 1 mg and 10 mg/kg did not significantly alter the rectal temperature of rabbits pretreated with pargyline except for one rabbit which developed a delayed hyperthermia following the injection of morphine 1 mg/kg.

Hypothermia produced in mice by histamine acting on the central nervous system

1. In mice 1-10 mug histamine injected intraventricularly produces hypothermia.2. This hypothermia was not antagonized by chlorcyclizine administered subcutaneously or intraventricularly, but chlorcyclizine injected intraventricularly was effective in antagonizing the hypothermia produced by a subcutaneous injection of histamine.3. Pretreatment with atropine was without effect on the hypothermia produced by an intraventricular injection of 10 mug histamine.4. Amphetamine and tranylcypromine not only effectively reduced the intensity of, or abolished, the hypothermia but also reversed the response to an intraventricular injection of 10 mug histamine so that hyperthermia was produced. Pargyline was without effect.5. Tolazoline strongly potentiated the hypothermia produced by the intraventricular injection of 10 mug histamine, but phentolamine did not.6. It is concluded that at least part of the hypothermia produced by a subcutaneous injection of histamine arises as a result of an action on the central nervous system.7. The possible mechanisms by which histamine acting on the central nervous system produces hypothermia and the suggestion that histamine may have a physiological role in thermoregulation are discussed in the light of these findings.

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

1. The influences of ambient temperature (T(a)) on the thermoregulatory effector activities and the body temperature (T(b)) 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 T(b) at high T(a), and a reduction in EMG activity and a fall in T(b) at low T(a). 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 T(b) at high T(a), and a reduction in EMG activity and a fall in T(b) at low T(a). 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 T(b) at low T(a), and a reduction in RF and a rise in T(b) at high T(a). At higher dose levels in the goat and at all dose levels in the rabbit these substances had the reverse effects which are attributed to a synaptic block due to the excess of the excitatory substance.5. The effects of ambient temperature and injected substances upon ear temperature are consistent with the predictions of the model if it is assumed (a) that at high and low ambient temperatures direct thermal effects on ear vessels dominate those of the sympathetic innervation, and (b) that the warm sensor influence is to lower peripheral vasomotor tone, and the cold sensor influence is to increase it.6. The conclusion reached is that when consideration is given to species differences in the thermoneutral ambient temperature and to the possibility that excitatory substances have reversed effects at high dose levels, the effects of 5-HT, NA and ACh in the control of body temperature are very similar in the sheep, goat and rabbit: 5-HT is excitatory on the heat loss pathway, ACh is excitatory on the heat production pathway and NA has an inhibitory influence on both pathways.

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

1. 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 mul./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.4. Potassium or magnesium ions in concentrations which varied from 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.

Effects of catecholamines infused into the brain of young chickens

1. (-)-Noradrenaline, (-)-alpha-methylnoradrenaline and (-)-isoprenaline were infused into various brain regions of 12-21 day chicks. When infused into the hypothalamic area, but not the cerebral hemisphere or posterior mesencephalon, these amines produced behavioural sleep, lowered temperature and blood pressure and reduced oxygen consumption; electrocortical sleep activity usually ensued but this was not marked and frequently dissociation between electrocortical activity and behaviour occurred. After monoamine oxidase inhibition, which prolonged the action of noradrenaline, dopamine had similar effects.2. The effects of the catecholamines were prevented or substantially reduced by pretreatment with phenoxybenzamine given intravenously or into the hypothalamus but not by intravenous injection of propranolol. However, intrahypothalamic infusion of propranolol prevented the temperature, but not the behavioural effects of noradrenaline. The implications of this are discussed.3. That the effects were similar but more intense, apart from electrocortical changes, and of longer duration than those seen after intravenous injection of catecholamines suggests that in young chicks these amines penetrate from the blood into the brain and elicit their effects through a localized region, presumably the hypothalamus.

Microelectrophoresis of biogenic amines on hypothalamic thermosensitive cells

The rat hypothalamus contains thermally insensitive, normally sensisitive, and highly thermosensitive cells. The responses of thermosensitive neurons to microelectrophoretically applied acetylcholine, norepinephrine, and 5-hydroxy-tryptamine were the same in both rats and cats. The firing rate of warm-sensitive interneurons was accelerated by acetylcholine and inhibited by norepinephrine. The firing rate of cool-sensitive interneurons was accelerated by norepinephrine and, in one case, was inhibited by 5-hydroxytryptamine. Thermodetector cells were relatively insensitive to these amines, but were sensitive to current flow. These results from the rat, but not from the cat, agree with the data for thermoregulatory responses following microinjection of these amines into the hypothalamus.

Body temperature: possible ionic mechanism in the hypothalamus controlling the set point

The body temperature of many mammals is set at or around 37 degrees C. The mechanism for this set point appears to depend on a constant and inherent balance between sodium and calcium ions within the posterior hypothalamus. When this region is perfused in unanesthetized cats, an extracellular excess or a normal physiological concentration of sodium ions evokes a rise in body temperature if calcium is not in the perfusate. At the same site, an excess or normal concentration of calcium ions causes the temperature to fall when sodium is absent.

Mode of action of alpha-methylnoradrenaline on temperature and oxygen consumption in young chickens

1. Temperature, oxygen consumption, electromyographic activity, plasma non-esterified fatty acids and blood sugar were estimated in conscious unrestrained young chickens under conditions of thermoneutrality (31 degrees C) and below thermoneutrality (16 degrees C). In some chickens carotid arterial pressure was also recorded.2. At thermoneutrality, alpha-methylnoradrenaline lowered temperature and oxygen consumption in intact or chronically vagotomized chicks. alpha-Methylnoradrenaline was ineffective on temperature in chicks with transection of the brain-stem posterior to the hypothalamus but anterior to the respiratory centre. Hypothermia due to alpha-methylnoradrenaline was associated with a significant reduction of plasma non-esterified fatty acids but blood sugar was not significantly altered. Lowering of temperature by alpha-methylnoradrenaline occurred despite vasoconstriction which would hinder heat loss.3. Temperature and oxygen consumption were reduced by alpha-methylnoradrenaline in chronically thyroidectomized chicks to the same extent as in intact chicks but recovery did not occur unless the chicks were taken from the metabolism chamber and warmed artificially. In contrast, chronically thyroidectomized chicks given replacement thyroxine were relatively resistant to alpha-methylnoradrenaline.4. Oxygen consumption of tissue slices from different parts of the chick's brain, including the diencephalon, was not altered by alpha-methylnoradrenaline over an extensive dose range. The effects of alpha-methylnoradrenaline on temperature and oxygen consumption in intact chickens were unlikely, therefore, to be due to depressed metabolism of neurones.5. In an environment below thermoneutrality (16 degrees C) temperature was considerably reduced and carotid arterial pressure fell 40-50 mmHg. In contrast, electromyographic activity, oxygen consumption and plasma non-esterified fatty acids were markedly raised whereas blood sugar was insignificantly elevated.6. In experiments at 16 degrees C, alpha-methylnoradrenaline markedly reduced oxygen consumption although values were still higher than those at thermoneutrality. Temperature fell further, but whereas the reductions in oxygen consumption and temperature were long-lasting, electromyographic activity (shivering) was only transiently diminished. Plasma non-esterified fatty acids were reduced after alpha-methylnoradrenaline but not significantly so; blood sugar was not significantly altered. The time-course for recovery of oxygen consumption following a-methylnoradrenaline paralleled recovery from its blood pressure effects but the effect on oxygen consumption was not a consequence of the blood pressure changes. The effects of a-methylnoradrenaline on temperature, oxygen consumption and electromyographic activity were similar to those of another central depressant, pentobarbitone.

Acute effects of a monoamine oxidase inhibitor, tranylcypromine, on thermoregulation in the conscious rabbit

1. The effect of a single injection of the monoamine oxidase inhibitor, tranylcypromine, administered intravenously (20 mg/kg) or into the lateral cerebral ventricle (5-10 mg), on hypothalamic and rectal temperature, has been investigated.2. Intravenous tranylcypromine causes a significant rise in body temperature, which is due, at least in part, to cutaneous vasoconstriction; this vasoconstriction is augmented by sympathectomy. It is concluded that this vasoconstrictor effect is not mediated via the central nervous system.3. Intraventricular tranylcypromine caused a transient but significant fall in core temperature. This is interpreted as being compatible with selective augmentation of hypothalamic levels of 5-hydroxytryptamine.