Neuronal sensitivities in preoptic tissue slices: interactions among homeostatic systems

Hypothalamic TRPM8 and TRPA1 ion channel genes in the regulation of temperature homeostasis at water balance changes

The role of the hypothalamic cold-sensitive ion channels - transient receptor potential melastatin 8 (TRPM8) and transient receptor potential ankyrin 1 (TRPA1) in homeostatic systems of thermoregulation and water-salt balance - is not clear. The interaction of homeostatic systems of thermoregulation and water-salt balance without additional temperature load did not receive due attention, too. On the models of water-balance disturbance, we tried to elucidate some aspect of these problems. Body temperature (Tbody), O2 consumption, CO2 excretion, electrical muscle activity (EMA), temperature of tail skin (Ttail), plasma osmolality, as well as gene expression of hypothalamic TRPM8 and TRPA1 have been registered in rats of 3 groups: control; water-deprived (3 days under dry-eating); and hyperhydrated (6 days without dry food, drinking liquid 4 % sucrose). No relationship was observed between plasma osmolality and gene expression of Trpm8 and Trpa1. In water-deprived rats, the constriction of skin vessels, increased fat metabolism by 10 % and increased EMA by 48 % allowed the animals to maintain Tbody unchanged. The hyperhydrated rats did not develop sufficient mechanisms, and their Tbody decreased by 0.8 °C. The development of reactions was correlated with the expression of genes of thermosensitive ion channels in the anterior hypothalamus. Ttail had a direct correlation with the expression of the Trpm8 gene, whereas EMA directly correlated with the expression of the Trpa1 gene in water-deprived group. The obtained data attract attention from the point of view of management and correction of physiological functions by modulating the ion channel gene expression.

A century of exercise physiology: concepts that ignited the study of human thermoregulation. Part 1: Foundational principles and theories of regulation

This contribution is the first of a four-part, historical series encompassing foundational principles, mechanistic hypotheses and supported facts concerning human thermoregulation during athletic and occupational pursuits, as understood 100 years ago and now. Herein, the emphasis is upon the physical and physiological principles underlying thermoregulation, the goal of which is thermal homeostasis (homeothermy). As one of many homeostatic processes affected by exercise, thermoregulation shares, and competes for, physiological resources. The impact of that sharing is revealed through the physiological measurements that we take (Part 2), in the physiological responses to the thermal stresses to which we are exposed (Part 3) and in the adaptations that increase our tolerance to those stresses (Part 4). Exercising muscles impose our most-powerful heat stress, and the physiological avenues for redistributing heat, and for balancing heat exchange with the environment, must adhere to the laws of physics. The first principles of internal and external heat exchange were established before 1900, yet their full significance is not always recognised. Those physiological processes are governed by a thermoregulatory centre, which employs feedback and feedforward control, and which functions as far more than a thermostat with a set-point, as once was thought. The hypothalamus, today established firmly as the neural seat of thermoregulation, does not regulate deep-body temperature alone, but an integrated temperature to which thermoreceptors from all over the body contribute, including the skin and probably the muscles. No work factor needs to be invoked to explain how body temperature is stabilised during exercise.

The Hypothalamic Preoptic Area and Body Weight Control

The preoptic area (POA) of the hypothalamus is involved in many physiological and behavioral processes thanks to its interconnections to many brain areas and ability to respond to diverse humoral factors. One main function of the POA is to manage body temperature homeostasis, e.g. in response to ambient temperature change, which is achieved in part by controlling brown adipose tissue thermogenesis. The POA is also importantly involved in modulating food intake in response to temperature change, thus making it relevant for body weight homeostasis and obesity research. POA function in body weight control is highly unexplored, and a better understanding of POA circuits and their integration into classic hypothalamic circuits that regulate energy homeostasis is expected to provide new opportunities for the scientific basis and treatment of obesity and comorbidities.

The experienced temperature sensitivity and regulation survey

Individuals differ in thermosensitivity, thermoregulation, and zones of thermoneutrality and thermal comfort. Whereas temperature sensing and -effectuating processes occur in part unconsciously and autonomic, awareness of temperature and thermal preferences can affect thermoregulatory behavior as well. Quantification of trait-like individual differences of thermal preferences and experienced temperature sensitivity and regulation is therefore relevant to obtain a complete understanding of human thermophysiology. Whereas several scales have been developed to assess instantaneous appreciation of heat and cold exposure, a comprehensive scale dedicated to assess subjectively experienced autonomic or behavioral thermoregulatory activity has been lacking so far. We constructed a survey that specifically approaches these domains from a trait-like perspective, sampled 240 volunteers across a wide age range, and analyzed the emergent component structure. Participants were asked to report their thermal experiences, captured in 102 questions, on a 7-point bi-directional Likert scale. In a second set of 32 questions, participants were asked to indicate the relative strength of experiences across different body locations. Principal component analyses extracted 21 meaningful dimensions, which were sensitive to sex-differences and age-related changes. The questions were also assessed in a matched sample of 240 people with probable insomnia to evaluate the sensitivity of these dimensions to detect group differences in a case-control design. The dimensions showed marked mean differences between cases and controls. The survey thus has discriminatory value. It can freely be used by anyone interested in studying individual or group differences in thermosensitivity and thermoregulation.

Dehydration: physiology, assessment, and performance effects

This article provides a comprehensive review of dehydration assessment and presents a unique evaluation of the dehydration and performance literature. The importance of osmolality and volume are emphasized when discussing the physiology, assessment, and performance effects of dehydration. The underappreciated physiologic distinction between a loss of hypo-osmotic body water (intracellular dehydration) and an iso-osmotic loss of body water (extracellular dehydration) is presented and argued as the single most essential aspect of dehydration assessment. The importance of diagnostic and biological variation analyses to dehydration assessment methods is reviewed and their use in gauging the true potential of any dehydration assessment method highlighted. The necessity for establishing proper baselines is discussed, as is the magnitude of dehydration required to elicit reliable and detectable osmotic or volume-mediated compensatory physiologic responses. The discussion of physiologic responses further helps inform and explain our analysis of the literature suggesting a ≥ 2% dehydration threshold for impaired endurance exercise performance mediated by volume loss. In contrast, no clear threshold or plausible mechanism(s) support the marginal, but potentially important, impairment in strength, and power observed with dehydration. Similarly, the potential for dehydration to impair cognition appears small and related primarily to distraction or discomfort. The impact of dehydration on any particular sport skill or task is therefore likely dependent upon the makeup of the task itself (e.g., endurance, strength, cognitive, and motor skill).

Regulation of hypothalamic signaling by tuberoinfundibular peptide of 39 residues is critical for the response to cold: a novel peptidergic mechanism of thermoregulation

Euthermia is critical for mammalian homeostasis. Circuits within the preoptic hypothalamus regulate temperature, with fine control exerted via descending GABAergic inhibition of presympathetic motor neurons that control brown adipose tissue (BAT) thermogenesis and cutaneous vascular tone. The thermoregulatory role of hypothalamic excitatory neurons is less clear. Here we report peptidergic regulation of preoptic glutamatergic neurons that contributes to temperature regulation. Tuberoinfundibular peptide of 39 residues (TIP39) is a ligand for the parathyroid hormone 2 receptor (PTH2R). Both peptide and receptor are abundant in the preoptic hypothalamus. Based on PTH2R and vesicular glutamate transporter 2 (VGlut2) immunolabeling in animals with retrograde tracer injection, PTH2R-containing glutamatergic fibers are presynaptic to neurons projecting from the median preoptic nucleus (MnPO) to the dorsomedial hypothalamus. Transneuronal retrograde pathway tracing with pseudorabies virus revealed connectivity between MnPO VGlut2 and PTH2R neurons and BAT. MnPO injection of TIP39 increased body temperature by 2°C for several hours. Mice lacking TIP39 signaling, either because of PTH2R-null mutation or brain delivery of a PTH2R antagonist had impaired heat production upon cold exposure, but no change in basal temperature and no impairment in response to a hot environment. Thus, TIP39 appears to act on PTH2Rs present on MnPO glutamatergic terminals to regulate their activation of projection neurons and subsequent sympathetic BAT activation. This excitatory mechanism of heat production appears to be activated on demand, during cold exposure, and parallels the tonic inhibitory GABAergic control of body temperature.

Plasma hyperosmolality elevates the internal temperature threshold for active thermoregulatory vasodilation during heat stress in humans

Plasma hyperosmolality delays the response in skin blood flow to heat stress by elevating the internal temperature threshold for cutaneous vasodilation. This elevation could be because of a delayed onset of cutaneous active vasodilation and/or to persistent cutaneous active vasoconstriction. Seven healthy men were infused with either hypertonic (3% NaCl) or isotonic (0.9% NaCl) saline and passively heated by immersing their lower legs in 42 degrees C water for 60 min (room temperature, 28 degrees C; relative humidity, 40%). Skin blood flow was monitored via laser-Doppler flowmetry at sites pretreated with bretylium tosylate (BT) to block sympathetic vasoconstriction selectively and at adjacent control sites. Plasma osmolality was increased by approximately 13 mosmol/kgH(2)O following hypertonic saline infusion and was unchanged following isotonic saline infusion. The esophageal temperature (T(es)) threshold for cutaneous vasodilation at untreated sites was significantly elevated in the hyperosmotic state (37.73 +/- 0.11 degrees C) relative to the isosmotic state (36.63 +/- 0.12 degrees C, P < 0.001). A similar elevation of the T(es) threshold for cutaneous vasodilation was observed between osmotic conditions at the BT-treated sites (37.74 +/- 0.18 vs. 36.67 +/- 0.07 degrees C, P < 0.001) as well as sweating. These results suggest that the hyperosmotically induced elevation of the internal temperature threshold for cutaneous vasodilation is due primarily to an elevation in the internal temperature threshold for the onset of active vasodilation, and not to an enhancement of vasoconstrictor activity.

Efferent projections from the median preoptic nucleus to sleep- and arousal-regulatory nuclei in the rat brain

The median preoptic nucleus (MnPO) has been implicated in the regulation of hydromineral balance and cardiovascular regulation. The MnPO also contains neurons that are active during sleep and in response to increasing homeostatic pressure for sleep. The potential role of these neurons in the regulation of arousal prompted an analysis of the efferent projections from the MnPO. Anterograde and retrograde neuroanatomical tracers were utilized to characterize the neural connectivity from the MnPO to several functionally important sleep- and arousal-regulatory neuronal systems in the rat brain. Anterograde terminal labeling from the MnPO was confirmed within the core and extended ventrolateral preoptic nucleus. Within the lateral hypothalamus, labeled axons were observed in close apposition to proximal and distal dendrites of hypocretin/orexin immunoreactive (IR) cells. Projections from the MnPO to the locus coeruleus were observed within and surrounding the tyrosine hydroxylase-IR cell cluster. Labeled axons from the MnPO were mostly observed within the lateral division of the dorsal raphé nucleus and heavily within the ventrolateral periaqueductal gray. Few anterogradely labeled appositions were present juxtaposed to choline acetyltransferase-IR somata within the magnocellular preoptic area. The use of retrogradely transported neuroanatomical tracers placed within the prospective efferent terminal fields supported and confirmed findings from the anterograde tracer experiments. These anatomical findings support the hypothesis that MnPO neurons function to promote sleep by inhibition of orexinergic and monoaminergic arousal systems and disinhibition of sleep regulatory neurons in the ventrolateral preoptic area.

Central and peripheral thermoreceptors. Comparative analysis of the effects of prolonged adaptation to cold and noradrenaline

This report presents results obtained from many years of study of the effects of prolonged adaptation to cold and noradrenaline on the spike activity of central hypothalamic and peripheral skin thermoreceptors. The involvement of the sympathetic nervous system in forming adaptive changes in the regulatory characteristics of temperature homeostasis and the significance of the various components of thermoreceptor activity to the formation of effector responses are discussed. The roles of different groups of thermoreceptors in forming temperature sensations are analyzed.

Mechanisms and functions of coupling between sleep and temperature rhythms

Energy metabolism is strongly linked to the circadian rhythms in sleep and body temperature. Both heat production and heat loss show a circadian modulation. Sleep preferably occurs during the circadian phase of decreased heat production and increased heat loss, the latter due to a profound increase in skin blood flow and, consequently, skin warming. The coupling of these rhythms may differ depending on whether they are assessed in experimental laboratory studies or in habitual sleeping conditions. In habitual sleeping conditions, skin blood flow is for a prolonged time increased to a level hardly ever seen during wakefulness. Possible mechanisms linking the rhythms in sleep and core body and skin temperature are discussed, with a focus on causal effects of changes in core and skin temperature on sleep regulation. It is shown that changes in skin temperature rather than in core temperature causally affect sleep propensity. Contrary to earlier suggestions of a functional role of sleep in heat loss, it is argued that sleep facilitates a condition of increased skin blood flow during a prolonged circadian phase, yet limits heat loss and the risk of hypothermia. Sleep-related behavior including the creation of an isolated microclimate of high temperature by means of warm clothing and bedding in humans and the curling up, huddling and cuddling in animals all help limit heat loss The increase in skin blood flow that characterizes the sleeping period may thus not primarily reflect a thermoregulatory drive. There is indirect support for an alternative role of the prolonged period of increased skin blood flow: it may support maintenance of the skin as a primary barrier in host defense.

Cortical, thalamic, and hypothalamic responses to cooling and warming the skin in awake humans: a positron-emission tomography study

Thermoregulatory mechanisms are remarkably efficient, ensuring minimal temperature variation within the core of the human body under physiological conditions. Diverse afferent and efferent neural pathways contribute to the monitoring of core and skin temperature, generation of heat, and control of thermal exchange with the external environment. We have investigated the cortical, thalamic, and hypothalamic responses to cooling and warming by using positron-emission tomography activation imaging of subjects clad in a water-perfused suit, which enabled rapid change of their skin-surface temperature. Human brain regions that respond to changes in skin temperature have been identified in the somatosensory cortex, insula, anterior cingulate, thalamus, and hypothalamus, with evidence that the hypothalamic response codes for the direction of temperature change. We conclude that signals from thermosensors in the skin providing crucial afferent information to the brain are integrated with signals from central thermosensors, resulting in thermoregulatory responses that maintain core temperature within a remarkably narrow range.

Synaptic and morphological characteristics of temperature-sensitive and -insensitive rat hypothalamic neurones

1. Intracellular recordings were made from neurones in rat hypothalamic tissue slices, primarily in the preoptic area and anterior hypothalamus, a thermoregulatory region that integrates central and peripheral thermal information. The present study compared morphologies and local synaptic inputs of warm-sensitive and temperature-insensitive neurones. 2. Warm-sensitive neurones oriented their dendrites perpendicular to the third ventricle, with medial dendrites directed toward the periventricular region and lateral dendrites directed toward the medial forebrain bundle. In contrast, temperature-insensitive neurones generally oriented their dendrites parallel to the third ventricle. 3. Both warm-sensitive and temperature-insensitive neurones displayed excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs). In most cases, EPSP and IPSP frequencies were not affected by temperature changes, suggesting that temperature-insensitive neurones are responsible for most local synapses within this hypothalamic network. 4. Two additional neuronal groups were identified: silent neurones having no spontaneous firing rates and EPSP-driven neurones having action potentials that are primarily dependent on excitatory synaptic input from nearby neurones. Silent neurones had the most extensive dendritic trees, and these branched in all directions. In contrast, EPSP-driven neurones had the fewest dendrites, and usually the dendrites were oriented in only one direction (either medially or laterally), suggesting that these neurones receive more selective synaptic input.

The functional role of a bicuculline-sensitive Ca2+-activated K+ current in rat medial preoptic neurons

A Ca2+-activated K+ current was identified in neurons from the rat medial preoptic nucleus. Its functional role for the resting potential and for impulse generation was characterised by using the reversible blocking agent bicuculline methiodide. Acutely dissociated neurons were studied by perforated-patch recordings. The effect of bicuculline methiodide was investigated under voltage-clamp conditions to clearly identify the current affected. At membrane potentials > -50 mV, bicuculline methiodide rapidly (< 1 s) and reversibly blocked a steady outward current. Half-saturating concentration was 12 microM. The current amplitude increased with potential in the range -50 to 0 mV. The bicuculline-sensitive current was identified as an apamin-sensitive, Ca2+-dependent K+ current. It was neither affected by the GABAA receptor blocker picrotoxin (100 microM) nor by a changed pipette Cl- concentration, but was affected by substitution of extracellular K+ for Na+. The current was dependent on extracellular Ca2+ and was sensitive to 1 microM apamin but not to 200 nM charybdotoxin. A role for the Ca2+-dependent K+ current in setting the resting potential and controlling spontaneous firing frequency was observed under current-clamp conditions. Bicuculline methiodide (100 microM) induced a positive shift (5 +/- 1 mV; n = 18) of resting potential in all neurons tested. In the majority of spontaneously firing neurons, the firing frequency was reversibly affected, either increased or decreased depending on the cell, by bicuculline methiodide.

Effects of parenterally administered triazolam on sleep in rats with lesions of the preoptic area

In previous work we have reported that microinjections of triazolam or pentobarbital into the medial preoptic area of the anterior hypothalamus produce a hypnotic effect. This finding raised the possibility that the sleep-enhancing actions after systemic administration of these compounds might be mediated by hypnogenic mechanisms in the preoptic area. The current study examined whether sleep enhancement by triazolam requires the anatomic integrity of the preoptic area. Nine rats with histologically confirmed lesions of the preoptic area induced by ibotenic acid (2.5 microg/microl in 0.4 microl), and 10 rats that had undergone a sham lesion procedure, had 2-h sleep studies that confirmed that by day 5 measures of total sleep time and sleep latency had returned to preintervention values. Rats were then given triazolam 0.8 mg/kg or vehicle intraperitoneally in counterbalanced order, on days 7 and 9 postlesion, in an environment with an ambient temperature of 25 degrees C. Following injections at 1000 h, in conditions in which lights were on from 0800-2000 h, 2-h sleep studies were performed. In the lesioned rats, triazolam significantly decreased sleep latency and increased total sleep time, primarily by increasing NREM sleep, whereas injections of vehicle did not. In summary, parenterally administered triazolam was found to have hypnotic effects in rats who were 1 week post-preoptic area lesion. These data are interpreted in light of previous evidence of redundancy of sleep-regulating mechanisms in the nervous system.

Differential stimulation of c-fos expression in hypothalamic nuclei of the rat brain during short-term heat acclimation and mild dehydration

Activation of central nervous structures involved in the perception and integration of thermo- and osmoregulatory signals was investigated in the Sabra rat. Male rats were either non-treated (C-E), water-deprived for 24 h (C-D), short-term acclimated to 34 degrees C for two days (STHA-E) or subjected to both stimuli (STHA-D). Immunoreactivity for c-Fos protein (Fos-IR) as marker for neuronal activation was quantified in (extra-)hypothalamic structures: organum vasculosum laminae terminalis (OVLT); subfornical organ (SFO); medial (MPA), ventromedial preoptic (VMPO) and lateral hypothalamic (LHA) areas; median preoptic (MnPO), magnocellular supraoptic (SON) and paraventricular (mPVN) nuclei; limbic lateral septal (LS) and thalamic paraventricular (PV) nuclei. Compared to C-E rats, dehydration markedly increased Fos-IR exclusively in neurons of the OVLT, SFO and MnPO known to be involved in osmoreception, in the mPVN and SON, and to a minor extent in the VMPO. The VMPO, MPA, LHA and LS-important (extra-)hypothalamic sites for the perception and integration within the thermoregulatory control circuit-exhibited intense elevation of Fos-IR upon short-term heat acclimation. Of all (extra-)hypothalamic structures involved in central osmoregulation, only the MnPO revealed heat-induced Fos-IR in numerous cells located preferentially in its rostral component. Thus, the MnPO proved to be activated during both thermal and osmotic stimulations applied separately. Subjected to the combined stress (STHA-D), most brain structures investigated showed striking Fos-IR due to thermally enhanced osmotic stimulation, with additive effects demonstrated in the MnPO. The data support differential central activation of c-fos expression due to thermal or osmotic stimulations, with the MnPO acting as putative integrative center for both autonomic control circuits.

Preoptic/anterior hypothalamic neurons: thermosensitivity in wakefulness and non rapid eye movement sleep

Thermosensitive neurons of the preoptic/anterior hypothalamic area (POAH) have been implicated in the regulation of both body temperature and non rapid eye movement (NREM) sleep. During NREM sleep, a majority of POAH warm-sensitive neurons (WSN) exhibit increased discharge compared to wakefulness. Cold-sensitive neurons (CSN) exhibit reduced discharge in NREM sleep compared to wakefulness. To further study the mechanism underlying these processes, the present study compared discharge rate and thermosensitivity (discharge rate change/degree C) of WSNs and CSNs in NREM sleep and wakefulness in freely moving adult cats. The thermosensitivity of 24 WSNs and 31 CSNs from the medial POAH was determined from responses to local POAH warming and cooling. WSNs with increased discharge in NREM sleep exhibited increased thermosensitivity during NREM sleep compared to wakefulness. CSNs with decreased discharge during NREM sleep exhibited decreased thermosensitivity in NREM sleep. The change in thermosensitivity from wakefulness to NREM sleep was correlated with the change in discharge rate in WSNs but not in CSNs. In addition, 9 of 47 neurons that were thermo-insensitive during wakefulness became warm-sensitive during NREM sleep. Changes in POAH neuronal thermosensitivity could be a component of the mechanism for stabilization of state after state transition.

Differences in Fos expression in the rat brains between cold and warm ambient exposures

Fos expression in the rat diencephalon, brain stem, cerebellum, and spinal cord was examined after warm (33 degrees C) and cold (10 degrees C) ambient exposures. Fos expression was examined with use of immunohistochemical method and the number of Fos-positive neurons in each nucleus was quantitatively analyzed. When rats were exposed to cold ambient, significant number of Fos-positive neurons was found in the lateral septal nucleus (LS), preoptic hypothalamic area (POA), parvocellular paraventricular hypothalamic nucleus (pPVN), lateral preoptic area (LPO), zona incerta (ZI), paraventricular thalamic nucleus (PV), ventromedial hypothalamic nucleus (VMH), subparafascicular thalamic nucleus (SPF), posterior hypothalamic area (PH), supramammillary nucleus (SuM), microcellular tegmental nucleus (MiTg), lateral lemniscus nucleus (LL), lateral dorsal central grey (CGLD), lateral ventral central grey (CGLV), dorsal parabrachial nucleus (DPB), locus coeruleus (LC), dorsal tegmental nucleus (DTg), vestibular nucleus (Ves), nucleus of solitary tract (Sol), spinal cord, and cerebellum. When animals were exposed to warm ambient, the numbers of Fos-positive neurons in the LS, POA, PV, LPO, and SuM were significantly increased to be equal to those of cold ambient. However, after warm ambient exposure the numbers of Fos-positive neurons in the DPB and spinal cord were increased but less than those of cold ambient, and those in the pPVN, VMH, ZI, SPF, PH, CGLD, CGLV, MiTg, LL, LC, DTg, Ves, Sol, and cerebellum were not significantly increased as compared with those of control or cold ambient. Abdominal temperature was not changed during cold ambient exposure, but the temperature was significantly increased during warm ambient exposure.(ABSTRACT TRUNCATED AT 250 WORDS)

Anatomic patterns of Fos immunostaining in rat brain following systemic endotoxin administration

To identify brain neurons that participate in the acute phase response, rat brains were examined immunocytochemically for Fos protein following the intravenous administration of bacterial endotoxin (lipopolysaccharide, LPS). Two to three hours after the injection of LPS, 150 micrograms/kg body weight, to adult male Long-Evans rats, a consistent anatomic pattern of Fos immunostained cell nuclei is seen. In the brain stem, prominant Fos immunostaining is induced in tyrosine hydroxylase immunoreactive neurons of the caudal ventral-lateral medulla (the A1 cell group), in both tyrosine hydroxylase positive and negative neurons of nu. tractus solitarius, in the parabrachial nu., and in a few neurons of the locus ceruleus. In the hypothalamus, endotoxin induces Fos expression in magnocellular neurons of the paraventricular and supraoptic nuclei and internuclear cell groups. A higher percentage of oxytocin-immunoreactive cells is double labeled for Fos nuclear immunostaining than vasopressin-immunoreactive cells. A minority of somatostatin immunoreactive periventricular hypothalamic neurons are Fos positive. Other hypothalamic nuclei that contain endotoxin-induced Fos nuclear immunostaining include the parvocellular neurons of the paraventricular nu., the dorsomedial and arcuate nuclei, the lateral hypothalamus, the dorsal hypothalamic area (zona incerta), and the median nucleus of the preoptic area. LPS induces numerous Fos-positive neurons in regions known to respond to a variety of stressful stimuli; these regions include the preoptic area, bed nucleus of the stria terminalis, lateral septum, and the central and medial nuclei of the amygdala. Moreover, Fos nuclear immunostaining is seen in neurons of circumventricular organs: the organum vasculosum of the lamina terminalis, the subfornical organ, and the area postrema. The maximum intensity of Fos nuclear immunostaining occurs 2-3 h after endotoxin administration and declines thereafter. It is attenuated by pretreatment with indomethacin, 25 mg/kg body weight Sc, or dexamethasone, 1 mg/kg IP. These observations are consistent with the participation of a variety of brain neuronal systems in the acute phase response and elucidate the functional neuroanatomy of that response at the cellular level.

Hyperthermia induces c-fos expression in the preoptic area

To identify thermosensitive areas of brain, we exposed rats to warm or cool environments and used the expression of the protein Fos as a marker of neuronal activity. In hyperthermic, heat-exposed rats, the median preoptic nucleus, and the medial and lateral preoptic areas had significantly more Fos immunoreactive neurons than control or cold-exposed animals. These observations add to the physiologic evidence that neurons of the preoptic area participate in thermoregulation and provide a means to identify the neurotransmitter systems involved.

Selective increases in non-rapid eye movement sleep following whole body heating in rats

Afternoon body heating has been reported to increase amounts of slow wave sleep (SWS) during the subsequent night in humans. This delayed effect of body heating on SWS has not been previously studied in laboratory animals. We examined the effect of whole body heating during the last 4 h of the light period on sleep and brain temperature (Tbr) during the subsequent twelve hour period in rats. Whole body heating was accomplished by elevating ambient temperature, typically to 33-35 degrees C, which increased Tbr to 40 +/- 0.5 degrees C. This condition was compared to a sleep-matched control condition, a sleep-deprived control condition and to a baseline condition. Following heating, non-rapid eye movement sleep 2 (NREMS2 or deep NREMS) was significantly increased during the first 2 h of the recovery period compared with baseline and sleep-matched control conditions and during the first hour compared with the totally sleep-deprived condition. NREMS1 was not significantly changed by heating. Rapid eye movement sleep was not different following heating compared to the sleep-matched and sleep-deprived control conditions but was significantly increased during the first hour of the recovery period following heating compared to baseline. Tbr was significantly lower for the first 5 h and the 7th h following heating compared to all three other conditions. Possible relationships between the regulation of sleep and temperature are discussed.

Characterization of the hypnotic effects of triazolam microinjections into the medial preoptic area

We have previously reported that microinjections of the benzodiazepine hypnotic triazolam into the medial preoptic area (MPA) of the hypothalamus enhance sleep in rats. The present study further characterizes this effect, by examining its anatomical specificity, determining whether it is mediated by interaction with central benzodiazepine receptors, and assessing whether sleep induction is associated with changes in core temperature. It was found that microinjections of 0.25 and 0.5 micrograms triazolam into two nearby structures, the lateral preoptic area and diagonal band of Broca, failed to alter sleep. Total sleep time was enhanced by microinjection of triazolam into the MPA, and this effect was blocked by co-administration of the benzodiazepine receptor blocker RO 15-1788. Sleep enhancement by triazolam was not associated with significant alterations in core body temperature. These observations continue to suggest that the MPA may be a site which mediates the hypnotic effect of triazolam, and add to the growing body of data emphasizing the importance of hypothalamic function in the regulation of sleep and waking.