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

Monitoring oxytocin signaling in the brain: More than a love story

More than any other neuropeptide, oxytocin (OXT) is attracting the attention of neurobiologists, psychologists, psychiatrists, evolutionary biologists and even economists. It is often called a "love hormone" due to its many prosocial functions described in vertebrates including mammals and humans, especially its ability to support "bonding behaviour". Oxytocin plays an important role in female reproduction, as it promotes labour during parturition, enables milk ejection in lactation and is essential for related reproductive behaviours. Therefore, it particularly attracts the interest of many female researchers. In this short narrative review I was invited to provide a personal overview on my scientific journey closely linked to my research on the brain OXT system and the adventures associated with starting my research career behind the Iron Curtain.

Editor's Highlight: Formulation and Toxicology Evaluation of the Intrathecal AYX1 DNA-Decoy in Sprague Dawley Rats

The longevity of pain after surgery is debilitating and limits the recovery of patients. AYX1 is a double-stranded, unprotected, 23 base-pair oligonucleotide designed to reduce acute post-surgical pain and prevent its chronification with a single intrathecal perioperative dose. AYX1 mimics the DNA sequence normally bound by EGR1 on chromosomes, a transcription factor transiently induced in the dorsal root ganglia-spinal cord network following a noxious input. AYX1 binds to EGR1 and prevents it from launching waves of gene regulation that are necessary to maintain pain over time. A formulation suitable for an intrathecal injection of AYX1 was developed, including a specific ratio of AYX1 and calcium so the ionic homeostasis of the cerebrospinal fluid is maintained and no impact on neuromuscular control is produced upon injection. A GLP toxicology study in naïve Sprague Dawley rats was conducted using 3 dose levels up to the maximum feasible dose. Clinical observations, neurobehavioral observations, clinical pathology and histopathology of the nervous system and peripheral tissues were conducted. An additional nonGLP study was conducted in the spared nerve injury model of chronic neuropathic pain in which EGR1 is induced in the dorsal root ganglia and spinal cord. Similar testing was performed, including a modified Irwin test to assess a potential impact of AYX1 on autonomic nervous system responses, locomotion, activity, arousal, sensorimotor, and neuromuscular function. No AYX1-related adverse events were observed in any of the studies and the no-observed-adverse-effect-level was judged to be the maximum feasible dose.

The physiology of artificial hibernation

Incomplete understanding of the mechanisms responsible for induction of hibernation prevent translation of natural hibernation to its artificial counterpart. To facilitate this translation, a model was developed that identifies the necessary physiological changes for induction of artificial hibernation. This model encompasses six essential components: metabolism (anabolism and catabolism), body temperature, thermoneutral zone, substrate, ambient temperature, and hibernation-inducing agents. The individual components are interrelated and collectively govern the induction and sustenance of a hypometabolic state. To illustrate the potential validity of this model, various pharmacological agents (hibernation induction trigger, delta-opioid, hydrogen sulfide, 5'-adenosine monophosphate, thyronamine, 2-deoxyglucose, magnesium) are described in terms of their influence on specific components of the model and corollary effects on metabolism. Relevance for patients: The ultimate purpose of this model is to help expand the paradigm regarding the mechanisms of hibernation from a physiological perspective and to assist in translating this natural phenomenon to the clinical setting.

Hypothermic effect of sodium acetysalicylate on afebrile monkeys

1 Afebrile monkeys (Macaca cyclopis) receiving systemic (100-300 mg/kg, i.p.) or central (5-20 mg into the 3rd cerebral ventricle) administration of sodium acetylsalicylate showed a dose-dependent reduction in rectal temperature in a thermoneutral environment (25 degrees C).2 Administration of sodium acetylsalicylate (10 mg) into the 3rd cerebral ventricle produced a hypothermia with a temperature decrement of 1.0 degrees C, ehile an intraperitoneal injection of 300 mg/kg was required for a temperature decrement of 0.9 degrees C. The ratio between the total doses given by the two toutes was 1 to 120.3 Following the administration of sodium acetylsalicylate, a decline in rectal temperature was accompanied by a tail cutaneous vasodilatation.4 The data suggest that sodium acetylsalicylate can lower the normal body temperature by activating heat loss or decreasing the normal (tonic) inhibition of the heat loss mechanism via the central nervous system.

In vivo monitoring of the transfer kinetics of trace elements in animal brains with hyphenated inductively coupled plasma mass spectrometry techniques

The roles of metal ions to sustain normal function and to cause dysfunction of neurological systems have been confirmed by various studies. However, because of the lack of adequate analytical method to monitor the transfer kinetics of metal ions in the brain of a living animal, research on the physiopathological roles of metal ions in the CNS remains in its early stages and more analytical efforts are still needed. To explicitly model the possible links between metal ions and physiopathological alterations, it is essential to develop in vivo monitoring techniques that can bridge the gap between metalloneurochemistry and neurophysiopathology. Although inductively coupled plasma mass spectrometry (ICP-MS) is a very powerful technique for multiple trace element analyses, when dealing with chemically complex microdialysis samples, the detection capability is largely limited by instrumental sensitivity, selectivity, and contamination that arise from the experimental procedure. As a result, in recent years several high efficient and clean on-line sample pretreatment systems have been developed and combined with microdialysis and ICP-MS for the continuous and in vivo determination of the concentration-time profiles of metal ions in the extracellular space of rat brain. This article reviews the research relevant to the development of analytical techniques for the in vivo determination of dynamic variation in the concentration levels of metal ions in a living animal.

Predictors and clinical implications of shivering during therapeutic normothermia

BACKGROUND

Shivering during induced normothermia (IN) remains a therapeutic limitation. We investigated potential risk factors and clinical implications of shivering during IN.

METHODS

Post hoc analysis was performed on 24 patients enrolled in a clinical trial of an automated surface cooling system to achieve IN. Hyponatremia was defined as serum levels <136 mmol/L and hypomagnesaemia as levels <1.5 mg/dL. Continuous heat energy transfer (kcal/h) was averaged hourly. Glasgow Coma Scale (GCS) scores were recorded every 2 h. Shivering status was documented hourly. Mixed effects modeling was used to determine clinical measures associated with shivering. Generalized estimating equation (GEE) models were used to compare baseline-adjusted repeated-measures GCS scores.

RESULTS

About of 24 (39%) patients demonstrated shivering. Shivering was associated with men (67% vs. 21%, P = 0.03), hyponatremia (44% vs. 7%, P = 0.03), and hypomagnesaemia (56% vs. 7%, P = 0.02). The average kcal/h (158 +/- 645 kcal/h vs. 493 +/- 645 kcal/h, P = 0.03) was greater in shivering patients. Shivering was positively associated with increases in heart rate (P < 0.001), respiratory rate (P < 0.001), and kcal/h (P < 0.001). Non-shivering patients showed a greater increase from baseline GCS (GEE, P = 0.02) at 24 h. No differences in sedative doses or fever burden were noted between shiverers and non-shiverers.

CONCLUSIONS

Men, hyponatremia, and hypomagnesaemia may predispose febrile patients treated with IN to shivering. Shivering dramatically increases the amount of heat transfer required to maintain normothermia, and may be associated with adverse effects on level of consciousness.

Age and temperature related changes in behavioral and physiological performance in the Peromyscus leucopus mouse

Age-related and ambient temperature-related changes in motor activity, body temperature, body weight (b.w.), and food consumption were studied in the long-lived Peromyscus leucopus mouse at environmental temperatures of 29 and 21 degrees C. Major changes in physiological performance were observed between the young (6 months) and old (60-72 month) age groups. The number of daily activity episodes, and total activity output was significantly lower in old mice. Maximum, average and minimum daily body temperature was lower in the old mice and a significant ambient temperature-by-age interaction was found. Maximum, minimum, and average daily b.w. was higher in old mice. Motor activity was evenly distributed over the active (night) phase in young mice but in old mice activity was significantly greater in the late night partition of the active cycle than in the early night partition. Both groups were significantly more active at night than during the day. Most of the food consumption in both groups occurred at night, but young mice consumed significantly more during the late night partition than the early night partition, and the consumption rates for old mice were not significantly different between early and late night partitions. The percentage of activity episodes involved with food consumption in both groups was significantly higher during the night partition, but the percentage during the early night partition was significantly higher in old mice than in young mice. Significant episodes of circadian torpor occurred in a high percentage of old mice at 06:00, on consecutive days, at both environmental temperatures, but young mice expressed no evidence of torpor.

Macrophage inflammatory protein-1: unique action on the hypothalamus to evoke fever

Macrophage inflammatory protein (MIP-1) administered systemically causes a fever not blocked by a prostaglandin (PGE) synthesis inhibitor. The purpose of this study was to examine the central mechanism of pyrexic action of this cytokine in the unrestrained rat. After guide cannulae for microinjection were implanted stereotaxically just above the anterior hypothalamic preoptic area (AH/POA), the body temperature of each rat was monitored by a colonic thermistor probe. Saline control vehicle or MIP-1 was microinjected into the AH/POA in one of eight concentrations ranging from 0.0028-9.0 ng per 0.5 mu 1 volume. MIP-1 induced a biphasic or monophasic fever of short latency characterized by an inverse dose-response curve. The potency of MIP-1 was in the femtomolar (10(-15)) range with the lowest dose of 0.028 ng producing a fever of over 2.0 degrees C with a latency of 15 min or less. To determine whether a PGE mediates MIP-1 fever, indomethacin was administered either intraperitoneally in a dose of 5.0 mg/kg or directly into the MIP-1 injection site in a dose of 0.5 microgram/0.5 mu 1, both injected 15 min before MIP-1. Pretreatment of the injection site in the AH/POA with indomethacin failed to prevent the febrile response evoked by MIP-1 injected at the same locus. Further, the dose of systemic indomethacin, which blocks PGE-induced fever in the rat, attenuated only partially the MIP-1 fever. The results demonstrate that MIP-1 is the most potent endopyrogen discovered thus far, and that its action is directly in the region of the hypothalamus which contains both thermosensitive and pyrogen-sensitive neurons. The local action of MIP-1 on cells of the AH/POA in evoking fever is unaffected by the PGE inhibitor which indicates, therefore, that a cellular mechanism operates in the hypothalamus to evoke fever independently of the central synthesis of a PGE.

CSF ion composition and manipulation during thermoregulation in an avian species, Gallus domesticus

1. At thermoneutrality (28 degrees C), CSF Na+:Ca2+ in hens was 61.66; under thermal stress (39 degrees C), it changed to 59.38 (30 min), 62.58 (3 hr), and 52.44 (10 hr); no change in ratio occurred at 15 degrees C. 2. ICV Ouabain and/or EGTA increased body temperature (TR) but not respiration rate (RR) at 39 degrees C. 3. At 28 degrees C, Ouabain decreased, and EGTA increased, TR and RR. 4. Ca2+ may be more critical than Na+ in thermoregulation. 5. Heat stress appears to stimulate Na+-transport mechanisms other than Na+-ATPase. 6. RR appears to be a function of TR, not of ion balance.

Cerebrospinal fluid calcium homeostasis: evidence for a plasma membrane Ca2+-pump in mammalian choroid plexus

A major unanswered question in central nervous system physiology concerns the mechanism by which cerebrospinal fluid (CSF) Ca2+ homeostasis is maintained in the face of hypo- or hypercalcemia. To address this question, we sought and found a protein of Mr approximately 140,000 in choroid plexus plasma membranes that forms a phosphorylated intermediate with characteristics of a plasma membrane Ca2+-pump. A choroid plexus plasma membrane protein of this molecular weight also bound to a monoclonal antibody prepared against the human erythrocyte plasma membrane Ca2+-Mg2+ ATPase Ca2+-pump. When this monoclonal antibody was used for immunohistochemical localization, the plasma membrane Ca2+-pump was found primarily in the CSF-facing membranes of choroid plexus cells from rats, cats, and man. The localization of a plasma membrane Ca2+-pump in the CSF-facing membranes of the choroid plexus suggests that the choroid plexus, by mechanisms including this pump, may regulate CSF Ca2+ concentrations.

Activation of dihydropyridine receptors differentially regulates temperature responses in rat

Rats receiving the dihydropyridine Ca++ agonist BAY K8644 (0.1-3 mg/kg SC) displayed increasing loss of body temperature. At the highest dose tested (3 mg/kg) rats exhibited decreased motor activity, ataxia, increased vocalization upon handling and increased auditory sensitivity. Nimodipine (1 mg/kg SC) produced antagonism of this response when used as pretreatment at 15 and 30 minutes. The phenylalkylamine, verapamil (5 mg/kg) and the benzothiazepine diltiazem (10 mg/kg) did not alter BAY K8644-induced hypothermia. None of the three Ca++ channel antagonists produced changes in body temperature at the antagonist doses used. BAY K8644 (3 mg/kg SC) produced stimulation of Ca++/Mg++ ATPase activity by 31% in hypothalamus but not in cortex or cerebellum. This stimulation of enzyme activity was selectively prevented by nimodipine but not verapamil or diltiazem. No changes in enzyme activity were observed when Ca++ channel antagonists were used alone. These studies demonstrate that the Ca++ agonist BAY K8644 produces receptor mediated hypothermia which is dihydropyridine receptor dependent. Activation of Ca++ ATPase in the hypothalamus suggests that activation of dihydropyridine receptors may be coupled to Ca++ transport systems in this brain region and may reinforce the Ca++ set point theory of thermoregulation.

Neuroanatomical mapping of hypothalamic regions mediating verapamil hyper- and hypothermia in the cat

Guide cannulae for microinjection and push-pull perfusion in the unrestrained cat were implanted bilaterally in the anterior hypothalamic, preoptic area (AH/POA) and posterior hypothalamus (PH). Postoperatively, the region was first identified in AH/POA which was reactive to norepinephrine or in PH to excess Ca++ ions; in both cases a hypothermic response was produced. Then either an artificial CSF control vehicle or the Ca++ ion channel blocking agent, verapamil, was perfused for 30 min by means of push-pull cannulae at a rate of 25.0 microliters/min. Verapamil 0.4, 2.0 and 4.0 micrograms/microliter) induced a concentration-dependent hypothermia when perfused within AH/POA sites but hyperthermia when perfused in the caudal hypothalamus. An anatomical analysis of the sites of perfusion revealed that verapamil's thermolytic effect was localized within the classical thermosensitive region of the cat's diencephalon, a region ventral to the anterior commissure and dorsal to the optic chiasm. On the other hand, the loci in which verapamil evoked thermogenesis were localized to a region dorsal to the mammillary bodies and caudal to the descending columns of the fornix. It is suggested that verapamil interferes with Ca++ ion channels in the PH to shift the cat's "set-point" temperature. Conversely, however, verapamil apparently could act on catecholaminergic terminals in AH/POA to enhance the presynaptic release of norepinephrine which, in turn, stimulates the heat loss pathway to yield hypothermia.

Elevation of the panting threshold of the desert iguana, Dipsosaurus dorsalis, during dehydration: potential roles of changes in plasma osmolality and body fluid volume

Dehydration of the desert iguana, Dipsosaurus dorsalis, resulted in a progressive elevation in the magnitude of the skin temperature necessary to elicit thermal panting (i.e., the panting threshold). Panting threshold increased from 43.4 +/- 0.8 degrees C at 100% initial body weight (IBW) to 45.4 +/- 1.2 degrees C at 90% IBW to 45.7 +/- 0.9 degrees C at 80% IBW. Plasma osmolality showed no significant change with dehydration to 80% IBW. Changes in plasma osmolality, whether induced by NaCl or non-ionic sucrose loading, had a significant impact on panting threshold. Increasing plasma osmolality resulted in an elevation of panting threshold while decreasing plasma osmolality resulted in lower panting thresholds. Decreasing body fluid volume by exsanguination of 1 ml whole blood/100 g body weight resulted in a mean increase in panting threshold by 0.7 +/- 0.2 degrees C. Volume loading with 160 mM NaCl (approximately isosmotic) had no significant effect on panting threshold. These data suggest that plasma osmolality and decreases in body fluid volume may be potent modulators of panting threshold during periods of water deprivation. However, at least in desert iguanas, increases in plasma osmolality would not appear to be an important factor in the elevation of panting threshold during dehydration to 80% IBW.

Body temperature and plasma arginine vasotocin in fowls adapted to high- and low-NaCl diets

The effects of high- and low-NaCl diets on body temperature, plasma osmolality, plasma electrolytes and arginine vasotocin (AVT) were studied in the domestic fowl. Body temperature as a function of time increased or decreased significantly in the high- and low-NaCl groups respectively. Plasma osmolality, sodium and chloride concentrations and AVT concentration were significantly higher in the high-NaCl adapted group. An overall significant correlation was found between body temperature and plasma sodium-to-calcium ratio (r = 0.62). These findings support the concept of an altered hypothalamic thermoregulatory set-point, induced by changes in plasma sodium-to-calcium ratio.

Divergent action of verapamil perfused in two hypothalamic areas on body temperature of the cat

Guide cannulae for push-pull perfusion were bilaterally implanted stereotaxically within the anterior hypothalamic, preoptic area (AH/POA) and posterior hypothalamus (PH) of the cat. Catecholamine-reactive sites were identified within AH/POA in which a microinjection of norepinephrine (NE) (5.0 micrograms) evoked a characteristic, transient hypothermia. Similarly the cation-reactive region within the PH was identified in which excess Ca2+ (25 mM) also evoked a hypothermic response. When verapamil was perfused at a rate of 25.0 microliters/min in a concentration of 0.4 or 2.0 micrograms/microliter within AH/POA at a NE-sensitive site, a concentration-dependent decline in the core temperature of the cat occurred. Conversely, verapamil perfused in the same manner with a Ca2+-reactive site caused an intense rise in the cat's body temperature which also was concentration dependent. These results show that the localized blockade of slow Ca2+ channels exerts direct, differential physiological effects within central nervous system tissue. In this case, verapamil mimics noradrenergic effects within the AH/POA; however, the hyperthermic response following Ca2+ channel blockade within tissue of the PH resembled that produced by ethyleneglycoltetraacetic acid or Na ions.

Hypothermic effect of 2,4-dinitrophenol infused ICV in the cat

The effects of body temperature and behavior of 2,4-dinitrophenol injected into the cerebral ventricles of the cat was investigated in these experiments. Infused in a volume of 0.1-0.2 ml, 2,4-dinitrophenol produced a dose-dependent fall in body temperature, the duration of which was also dose-dependent. Apart from hypothermia, 2,4-dinitrophenol evoked mydriasis, respiratory irregularities, urination, vomiting, ataxia, muscular weakness, sedation and occasional clonic-tonic convulsions. Of all the autonomic effects, the most consistent was the effect on thermoregulation. The possible mechanisms of action in the brain of 2,4-dinitrophenol on the thermoregulatory mechanisms are discussed.

Control of evaporative heat loss during changes in plasma osmolality in the cat

1. The effects of intravenous infusion of hypertonic saline and distilled water into normally hydrated and dehydrated cats have been examined at both high and neutral ambient temperatures.2. In hydrated cats measurements of body temperature (T(b)) and evaporative heat loss (e.h.l.) show that infusion of 30% saline (1.5 ml./kg) at an ambient temperature of 38 degrees C, lowers e.h.l. by an average of 0.21 W/kg (P < 0.001) and elevates T(b) by 0.43 degrees C (P < 0.01).3. At 25 degrees C alterations in these two parameters were in the same direction, though not statistically different from pre-infusion levels (P > 0.05).4. Infusion of distilled water (15 ml./kg) into dehydrated animals produced significant increases in e.h.l. (+0.35 W/kg, P < 0.001) and reductions in T(b) (-0.45 degrees C, P < 0.001) at 38 degrees C. No significant effects were observed at 25 degrees C.5. Infusion of water into normally hydrated animals at 38 degrees C also significantly increased e.h.l. (+0.13 W/kg, P < 0.05) and insignificantly lowered T(b) (-0.03 degrees C, P > 0.05).6. Local heating of the preoptic hypothalamic area in four animals indicated that hypertonic saline infusion into normally hydrated animals caused a reduction in the slope and displacement to the right of the relationship between hypothalamic temperature and e.h.l.7. Conversely, water infusion into dehydrated animals increased the slope and shifted this relationship to the left.8. These experiments provide evidence for an osmotic interaction in body temperature regulation which acts to alter the responsiveness of the hypothalamus to increasing temperature. This osmotic component may be an important factor in the alterations in thermoregulation seen in dehydrated animals.

Dynorphin (1-13): analgesia, hypothermia, cross-tolerance with morphine and beta-endorphin

Intracerebroventricular administration of 20, 40 and 60 nmol of dynorphin (1-13) produced analgesia, as assessed by flinch/jump response to footshock, and hypothermia in the rat. Rats developed tolerance to both the analgesic and thermic effects of the 20 nmol dose of dynorphin. Dynorphin and beta-endorphin showed cross-tolerance with respect to their analgesic but not their thermic effects. Dynorphin and morphine also produced cross-tolerant analgesic effects. Naloxone (10 mg/kg, IP) completely blocked the barrel rolling produced by 20 nmol dynorphin but did not alter its analgesic or thermic effects.

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.

Homotaurine and muscimol mimic taurine and GABA effects on muscle tone and temperature regulation

Taurine, homotaurine, GABA and muscimol, given intraventricularly to the conscious, unrestrained rabbit cause hypothermia and a reduction in skeletal muscle tone. Taurine and homotaurine desynchronize areas of the motor and limbic cortices, with GABA and muscimol synchronize both tracings and markedly depress the arousal reaction following external stimuli.

Influence of EGTA on an exercise-induced elevation in the colonic temperature of the rat

The purpose of this study was to determine if an exercise-induced rise in body temperature could be affected by the chelation of Ca++ in the extracellular fluid surrounding the hypothalamus of the rat. Following the implantation of a guide tube above the hypothalamus, each animal was familiarized with exercising on a motor-driven treadmill. In random order, on separate days, a solution containing 3.6 mM EGTA, 26 mM Ca++ or an artificial cerebrospinal fluid (ACSF) solution was perfused through the guide tube while the animal was running. Colonic (Tc) and tail-skin (Tt) temperatures were monitored continuously. The perfusion of EGTA produced a significant increase in Tc when compared with the perfusion of the ACSF solution. The perfusion of excess Ca++ produced a significant decrease in Tc. These results suggest that Ca++ may play an important role in the mediation of heat dissipation during exercise.

Thresholds for Na+ and Ca++ effects on thermoregulation

The evidence for threshold concentrations of Na+ and Ca++ that alter body temperature when introduced into (a) the hypothalamus and cerebral ventricles, and (b) intravenously and by oral ingestion is examined. For hypothamic and ventricular perfusion the threshold for any increase in core temperature (Tc) at rest with excess Na+ is about 10 mM, while there is a linear relationship between the level of excess Ca++ and the decrease in Tc, with a correlation co-efficient of 0.85. With intravenous and oral ingestion the resting threshold plasma concentration for an excess Na+ effect is about 5 mEq/1 per 0.1 degrees C rise in Tc, and the excess Ca++ level is about 1 mEq/1 per 0.1 degrees C decrease in Tc. With exercise, there is a dose-dependent attenuation of the rise in core temperature that is also about 0.1 degrees C per mM excess Ca++.

Brain calcium in the rabbit: site of action for the alteration of body temperature

Body temperature was recorded in the unanesthetized rabbit during push-pull perfusion of regions of the hypothalamus. Both the anterior and posterior hypothalamus were perfused with physiological solutions containing Ca++ in a concentration 2.0 or 5.0 times that of extracellular fluid. The animals were placed in an ambient temperature of 4.0 +/- 2.0degrees C for at least 1 hr before the perfusion and all experiments were carried out at this temperature. In the posterior hypothalamic area Ca++ produced a sharp fall in body temperature but did not cause body temperature to alter when it was perfused through the anterior hypothalamic area. These results indicate that the rabbit is similar to the cat and monkey since the effect of Ca++ on body temperature is localized to the posterior hypothalamic region.

Hypothalamic Na+ and Ca++ ions and temperature set-point: new mechanisms of action of a central or peripheral thermal challenge and intrahypothalamic 5-HT, NE, PGEi and pyrogen

The effects of changes in ambient and central temperature, amines, PGEu and pyrogen were investigated with respect to the mechanism of Na+-Ca++ ratio in the posterior hypothalamus of the unrestrained cat. Guide tubes were implanted bilaterally above the posterior hypothalamic area of 23 cats so as to accommodate push-pull cannulae. After a Na+ or Ca++ sensitive site was identified by perfusion at 50 mul/min of an artificial CSF containing 10.4 mM excess Ca++ ions or 13.6 mM excess Na+ ions, several types of experiments were undertaken with the results summarized as follows: if the cat was exposed to a cold or warm environmental temperature as the posterior hypothalamus was perfused with excess cation, the typical hypothermia was produced by Ca++ and hyperthermia by Na+ ions. However, if the cat was exposed to peripheral cooling or warming 30 min prior to the perfusion, the fall or rise produced by Ca++ or Na+ was attenuated or prevented. In other experiments, 1.0 muCi 45Ca++ was injected in the ion sensitive site in the posterior hypothalamus to label stores of the cation. Raising of ambient temperature caused a retention of 45Ca++ in this hypothalmic area, whereas a cold environmental temperature enhanced the efflux of 45Ca++ at the same perfusion site. The magnitude of change in 45Ca++ efflux depended upon the intensity of the thermal challenge. Similarly, warming of the anterior hypothalmic, preoptic area by means of implanted thermodes caused an immediate diminution in 45Ca++ efflux in the posterior hypothalamus, whereas cooling of this anterior region augmented the extrusion of 45Ca++ ions from the posterior area. When substances which produce a temperature change were applied to the same thermosensitive zone, the direction of shift in 45Ca++ flux in the posterior area corresponded to the signal for heat production or heat loss. That is, the microinjection of 5-HT, PGE1 or Salmonella typhosa into the anterior hypothalamus enhanced the efflux of 45Ca++ in the posterior hypothalamus as hyperthermia developed, whereas a similar microinjection of norepinephrine reduced the 45Ca++ output from the same sites. Finally, locally anesthetizing the cells of the anterior hypothalamus by the nerve blocker, procaine, prevented the cold and heat-induced 45Ca++ eflux and retention, respectively. These results suggest that if the Na+-Ca++ ratio in the posterior hypothalamus establishes and maintains the set-point for body temperature of 37 degrees -38 degrees C, the mechanism of lability of Ca++ through changes in binding characteristics, transport, or metabolism of the cation serves two purposes: (1) the active defense of the set-point temperature through gradations in ion shifts; and (2) the upward or downward change in set-point value, pathological or normal, triggered by virtue of impulses relayed from the anterior hypothalamus.

Sodium and calcium ions in the control of temperature set-point in the pigeon

1 The effect of altering the ionic balance of the cerebrospinal fluid (CSF) on cloacal temperature of unanesthetized pigeons kept at room temperature (20-25 degrees C) was examined by injection or infusion of solutions of different ionic composition into a cannulated lateral cerebral ventricle. 2 An increase in the concentration of calcium ions caused a fall in temperature and behavioural sedation. The effects were the same whether the calcium was present as calcium chloride or as the calcium disodium salt of ethylenediamine tetra-acetic acid (CaNa2EDTA). 3 When the concentration of sodium ions in the CSF perfusate was increased by addition of NaCl or that of calcium ions was decreased by addition of Na2EDTA a rise in temperature was often produced but this was not consistent. NaCl sometimes had either no effect or lowered the temperature. Na2EDTA while producing a rise when first injected failed to do so when repeated a few hours, 24 h and often 72 h later. Prolonged infusion of either agent caused intense behavioural excitement leading to death. 4 Potassium ions, like sodium ions, caused a rise in temperature but only when infused continuously. Behavioural excitement was only rarely observed. 5 Magnesium produced a fall in temperature. The concentration required was much higher than that of calcium but the hypothermia was more prolonged suggesting a slower elimination of the magnesium ions from the CSF. Magnesium ions caused tremors, nystagmus and ataxia as opposed to sedation caused by calcium. 6 All these were central effects as they were not obtained when the substances were injected intravenously. 7 Since changes in body temperature of the pigeon produced by injection of calcium or sodium ions into the CSF were similar to those seen in various species of mammal, it is concluded that the relative concentration of these ions within the brain plays an important role in establishing the temperature setpoint in both birds and mammals.

Is prostaglandin fever mediated by the presynaptic release of hypothalamic 5-HT or norepinephrine?

An array of guide tubes to accommodate concentric push-pull cannulae was implanted chronically within the diencephalon of the rhesus or other species of macaque monkey which was accustomed to a primate chair. Colonic and skin temperatures were monitored continuously during each experiment in which a circumscribed site in the monkey's hypothalamus had been labelled by microinjection of 50-100 muCi serotonin (3H-5-HT) or 50-100 muCi or norepinephrine (3H-NE). Consecutive push-pull perfusions with an artificial CSF were carried out for 10 min at a rate of 50 mul/min at 20 min intervals. Under the control condition, a declining washout curve of radioactivity was obtained over 8-10 perfusions. Prostaglandin (PG) E1 in a concentration of 10-20 ng/min was added to the artificial CSF during the third and fifth successive perfusions. Nonlabelled PGE1 failed to exert a precise and consistent effect on the characteristic pattern of efflux of either tritiated 5-HT or NE from perfusion sites distributed widely throughout the hypothalamus and adjacent structures. However, in some experiments, an enhanced efflux of the indoleamine label did occur after the temperature had begun to rise following a perfusion with the PGE. In still other experiments, 15-20 muCi 3H-PGE1 was microinjected to label a perfusion site. Again the addition of either nonlabelled 5-HT or NE to the perfusion fluid produced an unreliable change or no alteration in the efflux of 3H-ge1 from sites in the anterior as well as other parts of the hypothalamus. These findings indicate that prostaglandin injected into the brain does not evoke hyperthemia by way of a pathological disturbance to the balance in the presynaptic release of 5-HT and NE within nerve endings in the rostral hypothalamus of the monkey. Conversely, neither 5-HT nor NE influences the prostaglandin activity within the hypothalamus, at least in so far as a functional change in the body temperature of the primate is concerned.

Feeding and body temperature in the rat: diencephalic localization of changes produced by excess calcium ions

In the unanesthetized rat, Ca++ ions in solutions ranging from 2.6 to 112.0 mM in excess of the normal level in CSF were applied at different sites in the brain and by three separate procedures, Colonic temperature was monitored and in certain experiments, the amount of food pellets and water consumed was measured simultaneously following the administration of excess Ca++ ions. An infusion into the lateral cerebral ventricle of excess calcium in a volume of 5.0 mul produced a concentration-dependent hypothermia, This fall in temperature was not attenuated by a prior intraventricular infusion of mecamylamine and often enhanced by atropine. Depending on the site, a microinjection of excess Ca++ ions in a volume of 0.5 to 1.0 mul directly into the hypothalamus produced hypothermia or feeding. The sites of maximum sensitivity at which excess calcium caused a decline in temperature were clustered in the caudal hypothalamus, whereas those at which calcium elicited feeding were distributed widely in caudo-lateral, medial and rostral hypothalamic areas. Push-pull perfusions at a rate of 20 to 25 mul per min for 10 to 20 min at homologous sites caused similar responses but the cation concentration required to evoke feeding or hypothermia was significantly less than that of either microinjection or intraventricular infusion. These findings demonstrate species continuity in the rat concerning anatomical localization of the postulated set-point mechanism for body temperature. Several different pathways in the feeding system are affected by an alteration in the hypothalamic level of calcium.

Further studies on the role of prostaglandin in fever

1. Experiments were carried out in unanaesthetized cats to find out if a prostaglandin is the mediator (a) for the long lasting fever which often follows injections of phsyiological salt solutions into the cerebral ventricles or into the cisterna magna, as well as their perfusions through the cerebral ventricles, and (b) for the sodium fever which occurs during a perfusion of the cerebral ventricles with calcium-free artificial c.s.f. A fever mediated by prostaglandin should be accompanied by an increase of prostaglandin activity in cisternal c.s.f., and be abolished or prevented by antipyretics like paracetamol or indomethacin which inhibit prostaglandin synthesis. Both criteria were applied.2. The fever which follows injections or perfusions of physiological salt solutions appears to be mediated by a prostaglandin of the E series, probably E(2) (PGE(2)) because it was accompanied by increased prostaglandin E-like activity in the c.s.f. and abolished by paracetamol and indomethacin. During the first few days after pre-treatment of the cats with intramuscular chloramphenicol the injections were rarely followed by fever.3. The fever which occurs during a perfusion with calcium-free artificial c.s.f. appears not to be mediated by prostaglandin, because it was not associated with increased prostaglandin activity in the cisternal effluent, and not prevented by paracetamol or indomethacin, although these antipyretics usually attenuated the fever.4. A perfusion of the cerebral ventricles with artificial c.s.f. containing calcium in an abnormally high concentration (6.25 mM) brought down fever produced by PGE(1), or PGE(2), or bacterial pyrogen.

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.

The influence of centrally applied noradrenaline on shivering and body temperature in the pigeon

1. Noradrenaline (NA) was injected in a volume of 1.0 mul. through chronically implanted cannula into the hypothalamus of the unanaesthetized pigeon.2. In doses of 1-15 mug NA caused complete inhibition of shivering of dose-dependent duration. Histological mapping of the brain showed that NA was exerting its inhibitor action in the region above the optic chiasma bordering on the posterior hypothalamus and the anterior preoptic nucleus.3. At low ambient temperature, the NA induced inhibition of the cold tremor caused a fall of core temperature which lasted as long as shivering was inhibited. Shivering induced by local cooling of the spinal cord, and by the combined cooling of the skin and the spinal cord, was likewise inhibited by the cerebral application of NA. There was no evidence of an adjustment of the temperature set-point by NA.4. A rapid rise in skin temperature of the unfeathered feet, whenever NA was injected indicated a reduction in peripheral vasomotor tone.