TEMPERATURE CHANGES PRODUCED BY AMINES INJECTED INTO THE CEREBRAL VENTRICLES DURING ANAESTHESIA

The effects of the protein synthesis inhibitor anisomycin on the febrile responses to intracerebroventricular injections of bacterial pyrogen, arachidonic acid and prostaglandin E2

1. Anisomycin (15 mg/kg) was administered s.c. to cats at ambient temperatures of 5 degrees C, 20 degrees C and 38 degrees C. It produced biphasic effects on body temperature at 5 degrees C and 20 degrees C, an initial fall in temperature followed by a rise in body temperature, and a rise in body temperature of long latency at 38 degrees C. 2. Anisomycin (15 mg/kg) attenuated the hyperthermic responses to centrally injected PGE2 (1 microgram) at all ambient temperatures studied and also completely abolished the hyperthermic response to arachidonic acid (100 ng i.c.v.) at 20 degrees C. 3. Shigella dysenteriae (100 ng i.c.v.) raised the body temperature of cats by increasing heat production and reducing heat loss at 5 degrees C and 20 degrees C, and by increasing heat conservation at 38 degrees C. Anisomycin (15 mg/kg s.c.) pretreatment did not affect the temperature responses to the pyrogen at 20 degrees C and 38 degrees C, but did reduce the responses to Shigella dysenteriae (100 ng and 1 microgram i.c.v.) at 5 degrees C. 4. Anisomycin (15 mg/kg s.c.) was administered to cats, 90 min after the injection of Shigella dysenteriae (100 ng i.c.v.), at 20 degrees C at the onset of hyperthermia in control experiments. Under these conditions, no hyperthermia was observed over a 2 h period following anisomycin injection. 5. It is concluded that anisomycin interferes with pyrogen induced fever by acting at a site after PGE2 in the pathway to fever.

Changes in body temperature after administration of antipyretics, LSD, delta 9-THC, CNS depressants and stimulants, hormones, inorganic ions, gases, 2,4-DNP and miscellaneous agents

This survey concludes a series of complications of data from the literature, primarily published since 1965, on thermoregulatory effects of antipyretics in afebrile as well as in febrile subjects, LSD and other hallucinogens, cannabinoids, general CNS depressants, CNS stimulants including xanthines, hormones, inorganic ions, gases and fumes, 2,4-dinitrophenol and miscellaneous agents including capsaicin, cardiac glycosides, chemotherapeutic agents, cinchona alkaloids, cyclic nucleotides, cycloheximide, 2-deoxy-D-glucose, dimethylsulfoxide, insecticides, local anesthetics, poly I:poly C, spermidine and spermine, sugars, toxins and transport inhibitors. The information listed includes the species used, route of administration and dose of drug, the environmental temperature at which the experiments were performed, the number of tests, the direction and magnitude of body temperature change and remarks on the presence of special conditions such as age or lesions, or on the influence of other drugs, such as antagonists, on the response to the primary agents.

Dopamine in the hypothalamus of the cat: pharmacological characterization and push-pull perfusion analysis of sites mediating hypothermia

Within the rostral diencephalon of the cat, 113 sites were examined for their reactivity to 2.33--14.0 microgram dopamine (DA) or 2.33--14.0 microgram norepinephrine (NE) microinjected in a volume of 0.75 microliter. During each experiment, colonic temperature was monitored and additional physiological measures were recorded continuously. In contrast to CSF controls, an intrahypothalamic injection of either catecholamine at circumscribed sites evoked a dose-dependent fall in the cat's body temperature, with NE ordinarily evoking a more profound hypothermic response. The morphological sites of maximum sensitivity were localized in the anterior hypothalamic, preoptic region. At some but not all sites, a prior microinjection of 3.5--7.0 microgram phentolamine attenuated the magnitude of the DA-induced hypothermia and delayed its onset. Conversely, at all loci, the pretreatment by the injection of this alpha-adrenergic antagonist markedly reduced the absolute magnitude of the NE-induced fall in the cat's temperature. Similar pretreatment of a reactive hypothalamic locus with a beta-adrenergic receptor blocking agent, practolol (3.5 microgram), failed to alter the hypothermia following a microinjection of DA. Either of two DA receptor antagonists, haloperidol (0.04--7.0 microgram) or d-butaclamol (0.48--1.47 microgram), when given in a sufficient dose, effectively delayed the onset of the DA-hypothermia and reduced its absolute magnitude; however, the NE-induced decline in the cat's temperature was unaffected by DA receptor blockade. Endogenous stores of DA and/or NE in the cat's hypothalamus were radio-labeled with either 3H- or 14C-catecholamines or both, microinjected through the implanted guide tube into an identified amine-sensitive site. By using push-pull cannulae, the site was subsequently perfused for 5 min with artificial CSF at a rate of 25 microliter/min with samples collected at 15 min intervals. During either the third or fourth perfusion, the ambient temperature of the cat's chamber of 22--24 degrees C was elevated to 35--45 degrees C and maintained at this level for 15 or 30 min. This environmental warming evoked a release of either DA o; NE or both amines from certain circumscribed sites within the cat's rostral hypothalamus. Overall, these results provide pharmacological, physiological and anatomical evidence for a differential role of DA in the hypothalamic mechanism which mediates the heat loss processes.

Analysis of the effects on body temperature of intracerebroventricular injection in anaesthetized dogs of gamma-aminobutyric acid

1 The cerebral ventricles of dogs under intravenous pentobarbitone sodium anaesthesia, were perfused with artificial cerebro-spinal fluid (CSF) at a rate of 0.4-0.5 ml/min from the ventricular to the aqueductal cannulae. The effluent was collected from the aqueductal cannula in 20 min samples. The animals' temperatures were recorded from the rectum.2 gamma-Aminobutyric acid (GABA) 0.1-5 mg when injected into the ventricles produced variable temperature effects. Doses of 0.1 and 0.5 mg always produced hyperthermia and 1 and 5 mg doses sometimes produced hyperthermia and sometimes hypothermia.3 Intraventricular perfusion with 2-bromolysergic acid diethylamide (BOL) and hyoscine did not block hyperthermia. Tests on the rat isolated stomach strip or the guinea-pig isolated superfused ileum for the possible release, respectively, of 5-hydroxytryptamine or acetylcholine by GABA were negative.4 When tested for the presence of prostaglandin E(PGE)-like substances on the isolated rat stomach strip, both the control effluent and the GABA effluent showed activity, the latter being much more potent. There was a temporal correlation between this effect and hyperthermia. Intraventricularly administered sodium salicylate converted the GABA-induced hyperthermia to hypothermia and blocked the release of PGE-like substances.5 Hypothermia induced by GABA alone or in the presence of sodium salicylate was associated with the release of noradrenaline into the effluent.6 Intraventricular administration of GABA in reserpinized dogs produced hyperthermia and not hypothermia. Similar results were obtained with phentolamine perfusion in normal dogs.7 Perfusion with calcium-free solution blocked both the noradrenaline-releasing and hypothermic actions of GABA.8 It is concluded that hyperthermia associated with intraventricular injections of GABA is due to the release of PGE-like substance and hypothermia is due to the release of noradrenaline.

Role of 5-hydroxytryptamine in ketamine-induced hypothermia in the rat

1. Intraperitoneal injection of graded doses of ketamine produced a dose-dependent fall in body temperature of rats. Similarly, intracerebral injection of much smaller doses produced hypothermia.2. Pretreatment of the rats with p-chlorophenylalanine (PCPA) greatly attenuated the hypothermic response to ketamine whereas the intraperitoneal injection of 5-hydroxytryptophan in PCPA-treated rats restored the hypothermic effect of ketamine.3. Depletion of the brain monoamines by reserpine completely prevented the ketamine-induced hypothermia. Treatment with sodium diethyldithiocarbamate (DEDTC), however, did not modify the hypothermic effect of ketamine.4. Pretreatment of the rats with pargyline potentiated the ketamine-induced hypothermia.5. Depletion of brain monoamines by reserpine in combination with inhibition of noradrenaline biosynthesis (DEDTC) resulted in a long lasting fall in temperature which was not modified by ketamine.6. When the ambient temperature was raised from 26 degrees C to 32 degrees C, ketamine-induced hypothermia was much reduced and superimposed on a hyperthermia which occurred in all animals.7. It is concluded that ketamine produces hypothermia in rats possibly through the release of 5-hydroxytryptamine in the hypothalamus and that this effect is similar in some respects to that produced by morphine in non-tolerant rats.

The hypothermic effect of tetrodotoxin in the unanaesthetized cat

1. The hypothermic effect on unanaesthetized cats of tetrodotoxin injected I.V. or into the lateral cerebral ventricle was examined.2. At an ambient temperature (T(a)) of 22 degrees C, tetrodotoxin given intraventricularly was over 400 times more potent in lowering body temperature (T(b)) than when given I.V. The magnitude of the hypothermia was dose-dependent for both routes. Decreases in T(b) as great as 6.8 degrees C were induced by infusions or multiple injections of tetrodotoxin into the ventricle.3. Tetrodotoxin also lowered T(b) at T(a) = 13, 30 or 35 degrees C. Tachypnoea, which lasted for longer durations and which became more intense the higher the T(a), accompanied development of hypothermia. Shivering was observed only during recovery from hypothermia at 13 degrees C.4. During the tetrodotoxin-induced hypothermia, animals were still able to regulate against environmental thermal stresses.5. EDTA disodium salt, leucocytic pyrogen and prostaglandin E(1) antagonized the hypothermic effect of tetrodotoxin when they were administered during recovery from tetrodotoxin.6. Activation of heat-loss mechanisms, and the absence of compensatory shivering during development of hypothermia after tetrodotoxin administration, plus lowering of T(b) by tetrodotoxin at T(a) above as well as below the thermoneutral temperature, indicate that lowering of the thermoregulatory set-point is the mechanism by which centrally or peripherally administered tetrodotoxin lowers T(b). Further evidence for set-point lowering after intraventricular administration of tetrodotoxin is provided by persistence of the ability to regulate against both heat and cold stresses during hypothermia. The possibility that the decrease in set-point could be due to the well known action of tetrodotoxin to block transient increases in membrane sodium ion conductance is discussed in terms of a recent hypothesis regarding ionic control of the thermoregulatory set-point.

Further studies on prostaglandin E 1 fever in cats

1. Micro-injections of a few nanograms of prostaglandin E(1) (PGE(1)) into the anterior hypothalamus of unanaesthetized cats produced a rise in rectal temperature, whereas temperature was not affected when micro-injections of even larger doses were made into the posterior hypothalamus. The hyperthermia produced by injections of PGE(1) into the cerebral ventricles is therefore attributed to an action of PGE(1) on the anterior hypothalamus.2. During a pentobarbitone sodium anaesthesia the sensitivity of cats to the hyperthermic effect of PGE(1) injected into the cerebral ventricles was found to be greatly reduced, particularly during the early stage of anaesthesia when body temperature was falling steeply.

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.

Effects of monoamine oxidase inhibitors and amphetamine on hypothermia produced by halothane

1. In cats, the effects of tranylcypromine and pheniprazine, two monoamine oxidase (MAO) inhibitors with strong amphetamine-like actions, of pargyline, an inhibitor without amphetamine-like actions, and of amphetamine itself, were examined on the hypothermia produced by a 2 hr period of halothane inhalation.2. The hypothermia was prevented by intraperitoneal injections of the three MAO inhibitors. Tranylcypromine and pheniprazine acted in doses of a few milligrams, pargyline in doses of over 100 mg.3. The hypothermia was prevented by injections into the cerebral ventricles of tranylcypromine and pheniprazine, in doses which were effective also on intraperitoneal injection; intraperitoneal injections were sometimes more effective. The large doses of pargyline needed to prevent the hypothermia when injected intraperitoneally were not tested by the intraventricular route, as the injections had to be made in a volume of 0.1 ml. In smaller doses intraventricular pargyline was not effective.4. The hypothermia was prevented by an intraperitoneal or intraventricular injection of amphetamine in a dose as little as 1 mg; intraperitoneal injections were sometimes more effective.5. The effects of tranylcypromine and pargyline given intraperitoneally, and of amphetamine given intraventricularly as well, were also examined on the hypothermia produced by an intraventricular injection of 200 mug noradrenaline. The two MAO inhibitors and amphetamine prevented the hypothermia, or greatly reduced it.6. It is concluded (a) that even on intraventricular injection the MAO inhibitors must first be absorbed into the blood stream before they can prevent the hypothermia of a halothane anaesthesia; (b) that their action may not be solely on the anterior hypothalamus; and (c) that they may not act only through MAO inhibition.

Effects of monoamine oxidase inhibitors on the hypothermia produced in cats by halothane

1. In cats, the effects of intraperitoneal injections of four monoamine oxidase (MAO) inhibitors, tranylcypromine, pheniprazine, pargyline, and nialamide, were examined on rectal temperature and on the hypothermia during anaesthesia produced by a 2 hr period of halothane inhalation.2. A 2 hr period of halothane inhalation produced a steady fall in temperature amounting to between 2 degrees and 3.5 degrees C. After discontinuation of halothane inhalation, temperature quickly returned to the pre-anaesthetic level but no pyrexia developed. A peculiar stiffness of the leg muscles occurred in several experiments either at the beginning of the inhalation or after its discontinuation.3. An injection of tranylcypromine (5 mg/kg) caused a rise in rectal temperature and prevented the hypothermia of halothane anaesthesia. This effect lasted for at least 4 hr; 20 hr after the injection, halothane again caused hypothermia.4. An injection of pheniprazine (10 mg/kg) usually caused a small rise in temperature which was not sustained. Pheniprazine not only prevented the hypothermia of halothane anaesthesia during the subsequent 20 hr, but during the first few hours after the injection halothane inhalation actually produced a steep rise in temperature.5. An injection of pargyline (50 mg/kg) had no effect on temperature but the hypothermia due to halothane inhalation was prevented 1 hr after the injection and attenuated after 20 hr. Injection of 200 mg/kg caused a steady rise in temperature which was accelerated when halothane was administered 1 hr later.6. An injection of nialamide (10, 25 or 50 mg/kg) had no immediate effect on temperature, but pyrexia developed overnight after the two larger doses. The effect on the hypothermia due to halothane inhalation was greater 20 hr after the injection than it was after 1 to 2 hr. Twenty hours after injection of the two larger doses, halothane no longer produced hypothermia but caused a lethal rise in temperature either during or after its inhalation.7. In rabbits, the effect on temperature of halothane inhalation varied. Either temperature rose slightly or it fell, but not as much as in cats. In one rabbit in which the inhalation had produced a transient rise, pyrexia developed 40 min after discontinuation of halothane.

Body temperature responses in cats and rabbits to the monoamine oxidase inhibitor tranylcypromine

1. In unanaesthetized cats tranylcypromine (1-10 mg/kg) had scarcely any effect on rectal temperature when injected intraperitoneally, yet such injections prevented the deep and long-lasting fall in rectal temperature which normally occurs when the cat is anaesthetized by intraperitoneal pentobarbitone sodium or intravenous chloralose. The anaesthesia itself, however, was not affected. In some of the experiments with pentobarbitone sodium rectal temperature even rose to fever level.2. In anaesthetized as well as in unanaesthetized cats injections of tranylcypromine (0.1-1 mg) into the cerebral ventricles caused a rise in rectal temperature.3. In rabbits, rectal temperature was scarcely affected when surgical anaesthesia was produced by intravenous infusions of pentobarbitone sodium under the same condition in which, in cats, intraperitoneal pentobarbitone sodium produced a deep and long-lasting fall in temperature, i.e. when no external heat was applied but excessive dissipation of heat was prevented by placing the rabbit on a cotton-wool pad. However, when it was placed on the metal surface of an operating table, the anaesthesia was associated with a deep fall in rectal temperature.5. In anaesthetized and unanaesthetized rabbits tranylcypromine had no effect on rectal temperature when injected intraperitoneally (10 mg/kg) or into the cerebral ventricles (1 mg).5. These results are discussed in relation to the theory that the three monoamines in the hypothalamus, 5-hydroxytryptamine (5-HT), adrenaline and noradrenaline, act as central transmitters in temperature regulation.

Effects on temperature of monoamines injected into the cerebral ventricles of anaesthetized dogs

1. In dogs anaesthetized with pentobarbitone sodium an injection of adrenaline or noradrenaline into the cerebral ventricles through a cannula implanted into the left lateral ventricle caused a fall in rectal temperature as a result of cessation of shivering, loss of muscle tone, and skin vasodilatation. 5-Hydroxytryptamine (5-HT) similarly applied caused shivering and a rise in rectal temperature.2. The hypothalamus of the dog thus appears to react to the three monoamines in the same way as in the cat, and not as in the rabbit and sheep.

Effect of 5-hydroxytryptophan acting from the cerebral ventricles on 5-hydroxytryptamine output and body temperature

1. In cats anaesthetized with intraperitoneal pentobarbitone sodium the third ventricle, the anterior or inferior horn of the left lateral ventricle, was perfused with 5-hydroxytryptophan (5-HTP) in different concentrations, and the effluent assayed for 5-hydroxytryptamine (5-HT) on the rat stomach strip preparation of Vane (1957).2. On perfusion of the third ventricle with 5-HTP the output of 5-HT in effluent increased, the increase depending on the 5-HTP concentration: with 1/50,000 it increased 44-69 times (mean 55), with 1/25,000, 81-83 times (mean 82) and with 1/10,000, 71-200 times (mean 128). The 5-HT output depended also on the initial output during the preceding perfusion with artificial c.s.f. The greater this initial output the greater was the maximum output reached during the 5-HTP perfusion.3. The increase in 5-HT output during perfusion of the third ventricle with 5-HTP was usually associated with shivering and a rise in rectal temperature. This association, however, was not invariably obtained, probably because of a central depressant effect of 5-HTP itself.4. On perfusion of the anterior or inferior horn of the left lateral ventricle with 5-HTP, the output of 5-HT in the effluent also increased, but to a lesser extent than in the effluent from the third ventricle. There was no association with shivering nor with a rise in rectal temperature.5. An injection of 1 or 2 mg 5-HTP into the cerebral ventricles of unanaesthetized cats produced a biphasic rise in temperature, shivering, constriction of the skin vessels followed by vasodilatation, tachypnoea, wiping and scratching movements, miaowing and long lasting sleep.6. The biphasic rise in temperature is explained as the result of two opposing effects: increased formation of 5-HT which would raise body temperature, and a central depressant effect of 5-HTP itself or of one of its metabolites which would lower body temperature.7. The initial rise in temperature and the shivering in response to an intraventricular injection of 5-HTP varied from cat to cat. In those in which these effects were strong the 5-HT output during a subsequent perfusion of the third ventricle with artificial c.s.f. was higher, and the maximum 5-HT output reached on perfusion with 5-HTP was greater than in those in which these effects had been weak.

Appearance of 5-hydroxytryptamine and an unidentified pharmacologically active lipid acid in effluent from perfused cerebral ventricles

1. In cats anaesthetized with intraperitoneal pentobarbitone sodium, three regions of the cerebral ventricles, the third ventricle, the inferior or the anterior horn, were perfused with artificial c.s.f. and the effluent was tested on the fundus strip of the rat's stomach.2. Effluent from all three regions contracted the fundus strip. The contractions were due to at least two substances as revealed by treatment of the strip with 2-bromolysergic acid diethylamide (BOL). The contractions that were sensitive to BOL are attributed to 5-hydroxytryptamine (5-HT) whereas the BOL resistant contractions appear to be due to an unknown hydroxy acid related to irin or the prostaglandins.3. The contractions produced by effluent collected from the third ventricle were due wholly or mainly to 5-HT, those from the inferior horn to the unknown hydroxy acid, and those from the anterior horn to both substances in varying proportions. In addition, some samples of effluent from the third ventricle seemed to contain catecholamines as well.4. The 5-HT in the effluent from the third ventricle is thought to be derived from the hypothalamus. The amounts assayed in 1 ml. effluent-the volume collected during 10 or 20 min perfusion-varied between 0.4 and 12 ng 5-HT. Output of 5-HT was initially high, then usually decreased but sometimes increased again during prolonged perfusion when temperature began to rise as anaesthesia lightened or when additional pentobarbitone sodium was given intravenously.5. When perfusion of the third ventricle was continued after death the 5-HT content in the effluent increased 3 to 24-fold during the first hour and then gradually declined. This post mortem rise in 5-HT output suggests an abnormal state of release of 5-HT from the hypothalamus. The theory is discussed that the same may happen in certain cases of brain injury and that the abnormal release of 5-HT would explain the pyrexia and shivering seen in such cases.6. The intraperitoneal injection of 5-hydroxytryptophan greatly increased the output of 5-HT in the effluent from the perfused third ventricle but only when this precursor of 5-HT was injected in large doses which caused respiratory arrest thus necessitating artificial ventilation. Upon the injection of 150 mg/kg the output of 5-HT rose to 90 ng/ml. and a further rise to 180 ng/ml. occurred when perfusion was continued after death.7. It was not possible to establish a relation between the presence of the hydroxy acid in the effluent from the inferior horn and neuronal activity.8. The 5-HT detected in the effluent from the anterior horn is assumed to have been released from the caudate nucleus.