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The positive outcome that hypothermia contributes to brain and cardiac protection following ischemia has stimulated research in the development of pharmacological approaches to induce a hypothermic/hypometabolic state. Pharmacological manipulation of central autonomic thermoregulatory circuits could represent a potential target for the induction of a hypothermic state. Here we present a brief description of the CNS thermoregulatory centers and how the manipulation of these circuits can be useful in the treatment of pathological conditions such as stroke or brain hemorrhage.

The dependence of BAT thermogenesis on the availability of metabolic substrates suggests that metabolic signals from the viscera could influence the sympathetic outflow driving BAT thermogenesis. Viscerosensory afferents in the proximal end of the sectioned left cervical vagus nerve were activated with electrical stimulation in anesthetized, ventilated rats while recording the SNA to the contralateral interscapular BAT pad. Paired-pulse VNS delivered once every 5 sec evoked excitatory evoked potentials in BAT SNA with a peak latency of ~ 180 ms, followed by a ~2 s period of quiescent BAT SNA. Within a few seconds of stimulus onset, continuous, single-pulse VNS at 2 Hz produced a complete inhibition of cold-evoked BAT SNA that was sustained for at least 2 hrs of maintained VNS. Similarly, activation of neurons in the intermediate nucleus of the solitary tract (iNTS), at the level of the area postrema, with nanoinjections (60 pmol) of bicuculline also inhibits the VNS-evoked excitation of BAT SNA. Inhibition of neurons in the rostral ventromedial medullary raphe pallidus region also eliminates the VNS-evoked excitation of BAT SNA. These data support the existence of populations of vagal afferents whose stimulation can (1) increase BAT SNA via activation of BAT sympathetic premotor neurons or (2) inhibit BAT SNA via activation of BAT sympathoinhibitory neurons in the iNTS (see Am. J. Physiol. Regul. Integr. Comp. Physiol., 299:R277-R290, 2010. PMC2904145).

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Energy balance and body weight are regulated by complex processes in the brain, and our understanding of the relevant signaling pathways is still evolving. The main anorectic neurons of the hypothalamus contain pro-opiomelanocortin (POMC). We have previously shown that bone morphogenetic protein 7 (BMP7) acts centrally to reduce appetite. Now we demonstrate that a type 1 BMP receptor, BMPR1A, is co-localized with POMC neurons and ablation of BMPR1A in those neurons results in hyperphagia with a lack of obesity, even on a high-fat diet. This was due to a compensatory increase of BMPR1A expression in non-POMC neurons of the hypothalamus of the knock-out mice, accompanied by an increase in energy expenditure and improved cold-tolerance. Brown adipose tissue (BAT) of knock-out animals showed greater thermogenic capacity and increased sympathetic innervation, and removal of the sympathetic drive to BAT by surgical denervation resulted in hyperphagic weight gain in the knock-out mice. Wild-type mice injected intracerebroventricularly (i.c.v.) with BMP7 displayed an acute increase in energy expenditure and rats injected i.c.v. with BMP7 displayed a specifi c increase in sympathetic nerve activity (SNA) in BAT, along with increased BAT temperature and energy expenditure. In these animals, blockade of type 1 BMP receptor signaling by pre-treatment with a pharmacological inhibitor blunted the ability of BMP7 to increase energy expenditure or BAT SNA. Together, these data demonstrate an important novel role for hypothalamic BMP signaling in the regulation of appetite and activation of brown fat-mediated energy expenditure. Supported By: American Diabetes Association (1-14-JF-55 to K.L.T.)

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The positive outcome that hypothermia contributes to neuroprotection following brain ischemia has stimulated recent clinical interest in the development of techniques to induce a hypothermic and hypometabolic state. Despite, the increased use of therapeutic hypothermia, the available induction techniques, employing various cold-exposure approaches rather than pharmacological methods, could be of limited utility in reaching an appropriate hypothermic state due to the activation of the central thermoregulatory responses that counteract the fall in temperature by reducing heat loss (cutaneous vasoconstriction) and increasing thermogenesis through brown adipose tissue (BAT) and shivering. Hibernating animals can reduce their energy expenditure by suspending both shivering and non-shivering thermogenesis, even in the face of marked falls in skin and core temperatures. In these species, activation of A1 adenosine receptors in the brain is thought to play a key role in triggering the torpor state. In the current studies, we investigated: 1) the potential for the A1 adenosine receptor agonist, N6-cyclohexyladenosine (CHA), to induce hypothermia in the rat (a non-hibernating species); 2) the precise thermo-effector mechanisms contributing to the fall in body temperature; 3) the brain circuits involved in the adenosine agonist-induced hypothermia; and 4) the effect of CHA-induced hypothermia on the outcome of ischemic stroke. In inactin-anesthetized (85mg/kg i.v.), Wistar rats, icv administration of CHA (10μl, 1mM) decreased core, skin and BAT temperatures, reduced expired CO2, heart rate (HR), BAT sympathetic nerve activity (SNA) and shivering EMG activity. In awake rats in a 15°C ambient, a similar icv injection of CHA decreased BAT temperature and induced a torpor-like state, in contrast to icv injection of saline vehicle which had no effect on BAT temperature or observed behavioral state. In urethane/chloralose anaesthetized rats, direct nanoinjection of CHA (60nl, 1mM) in the nucleus of the solitary tract (NTS) produced reductions in cold-evoked BAT SNA, BAT temperature, expired CO2 and HR concomitant with an increase of mean arterial pressure. These effects were reversed by local nanoinjection of muscimol (60nl, 1mM) and prevented by pretreatment of the NTS with an A1 adenosine receptor antagonist. We conclude that A1 adenosine receptor stimulation in the NTS produce hypothermia and torpor-like effect in the rat through inhibition of BAT and shivering thermogenesis. This pharmacological approach could provide the basis for induction of a rapid, sustained and controlled hypothermia, improving current methods for inducing hypothermia for neuroprotection following brain ischemia. Supported by NIH grant NS40987.

Objectives: The Rostral Ventromedial Medulla (RVMM) is a key area in the control of autonomic function and metabolism, promoting thermogenesis (1). In the present study, the effects on sleep and cardiovascular parameters of the induction of a torpor-like state by the pharmacological inhibition of RVMM were investigated in the rat. Methods: Male Sprague–Dawley rats (n = 18, 300–350 g) adapted to an ambient temperature (Ta) of 25C, were implanted, under general anaesthesia (diazepam, 5 mg/kg, i.m., ketamine, 100 mg/kg, i.p.), with electrodes for EEG and EMG recording, a thermistor for detecting hypothalamic temperature (Thy), a catheter for arterial blood pressure recording, and a microcannula within the RVMM. After a week of recovery, animals were kept for 3 days at Ta 15C and then they were microinjected within the RVMM (1 injection/h, for 6 h) with either the GABAA agonist muscimol [1 mM, 100 nl; Group 1 (n = 6) and Group 2 (n = 6)] or saline [0.9%, 100 nl, Group 3 (n = 6)]. In order to favour the return to normothermia, 1 h after the last injection Ta was raised to 28C for Groups 1 and 3 and, for Group 2, to 37C, which was kept for 1 h and then taken to 28C. Results: Muscimol induced a deep hypothermia (Thy: 22.8 ± 0.8C) which was accompanied by: (i) a reduction of EEG activity; (ii) a decrease in heart rate (HR), from 440 ± 13 to 201 ± 12 bpm; (iii) a substantial maintenance of mean arterial pressure (MAP) at normal levels. Group 2 recovered normothermia faster than Group 1. Recovery was characterized by: (i) a progressive normalization of HR; (ii) the occurrence of a peak in MAP compared to saline (Group 3, 92 ± 4 mmHg), that was larger (P < 0.01) in Group 2 (125 ± 4 mmHg) than in Group 1 (116 ± 2 mmHg); (iii) the building up, in Groups 1 and 2, of a large SWS rebound in NREM sleep and of a not significant rebound in REM sleep. Conclusion: The effects of RVMM inhibition on cardiovascular and sleep parameters resembled those observed in natural torpor (2, 3). The increase in MAP observed during the recovery may be favoured by an excess in sympathetic activity. The effects on sleep observed after the recovery of normothermia indicate that the hypothermic bout and/or the rewarming generated a homeostatic need for SWS, but not for REM sleep. References: 1) Morrison S, Nakamura K. Front Biosci (2011) 16: 74–104. 2) Swoap SJ, Gutilla MJ. Am J Physiol RICP (2009) 297:R769–774. 3) Deboer T, Tobler I. Sleep (2003) 26: 567–72.

Prostaglandin E2 (PGE2) in the preoptic area (POA) mimics fever by stimulating thermogenesis in brown adipose tissue (BAT), skeletal muscle via shivering and the heart via tachycardia, as well as by reducing heat loss via skin vasoconstriction. PGE2-evoked stimulations of BAT, shivering EMGs and heart rate (HR) are postulated to arise from disinhibition of thermogenesis-promoting neurons in the dorsomedial hypothalamus (DMH), and possibly in the rostral raphe pallidus (rRPa), due to the EP3 receptor (EP3-R)-mediated inhibition of GABAergic, warm-sensitive neurons in the POA that project to inhibit DMH (and possibly rRPa) neurons. We tested the hypothesis that neurons in the medial preoptic (MPO) provide the necessary excitatory drive to downstream, thermogenesis-promoting neurons for febrile heat production. Bilateral muscimol injection in the MPO completely inhibited the shivering EMGs and reversed the increases in BAT temperature and HR following injection of PGE2 into the POA. We conclude that the MPO contains neurons whose activity is necessary to support thermogenesis during fever. The data are consistent with a model in which a population of MPO neurons provides a tonically-active, excitatory (glutamatergic) input to DMH (and rRPa?) neurons that drives thermogenesis upon disinhibition of DMH neurons during EP3-R activation in the POA and potentially during cold exposure. Support NIH grant NS40987.

Introduction: The periods of torpor are typically followed by the occurrence of high-Delta power NREM sleep (NREMS) (1). In the present study, this phenomenon was investigated in rats through the induction of a torpor like state by the pharmacological inhibition of the Rostral Ventromedial Medulla (RVMM), a key area in the central nervous control of metabolism, promoting thermogenesis (2). Methods: Eighteen male Sprague-Dawley rats (300–350 g) were surgically implanted, under general anaesthesia (Diazepam, 5 mg/ kg, i.m., ketamine, 100 mg/kg, i.p.), with electrodes for chronic EEG recording, a thermistor for the detection of the hypothalamic temperature (Thy), a catheter for arterial blood presssure recording, and a microcannula for drug delivery within the RVMM. Before the experiment, animals were exposed for three days to ambient conditions that are known to favor the occurrence of a natural torpor bout: ambient temperature (Ta) 15C, constant darkness and a highfat diet. Three groups of animals were microinjected within the RVMM (1 injection/h, for 6 h) with the GABAA agonist muscimol (1 mM, 100 nl; Group 1 (n = 6) and Group 2 (n = 6)) or with saline (0.9%, 100 nl, group 3 (n = 6)). One hour after the last injections, Ta was raised to 28C for groups 1 and 3, and to 37C for Group 2 to favour the return to normothermia. Results: In both Group 1 and 2, a deep hypothermia was observed during the 6-h microinjection period (Thy fell to 22.80 ± 0.8C) which was accompanied by a decrease of EEG activity and a progressive shift of the EEG spectral power towards the low-frequency region. After the injection period, EEG activity showed a progressive increase and the EEG spectral power shifted to the high frequency region. In particular, after the recovery of normothermia, a powerful intensification of Delta power in NREMS was observed, which lasted about 6 h. The peak in Delta power was significantly higher in Group 1 than in Group 2 (P < 0.01). No significant effects were observed in Group 3. Conclusion: The dynamics of EEG changes during and after the torpor-like state induction were similar to those described in natural torpor. The increase in Delta power in NREMS was attenuated under environmental conditions promoting the restoration of normothermia, suggesting a role for the degree of sympathetic activation during restoration in its determination. 1. Deboer T, Tobler I. Sleep. 2003; 26: 567–72. 2. Morrison S, Nakamura K. Front Biosci., 2011; 16: 74–104.

Introduction: The antagonism of hypocretins (HCRT) has been proposed as a new approach to the treatment of insomnia. Since HCRT is exclusively synthesized by neurons located within the lateral hypothalamus (LH) [1], in the present study, we have evaluated the effects on sleep induced by a prolonged pharmacological inhibition of the LH at both normal laboratory (25C) and low (10C) ambient temperature (Ta), a condition which is known to dysfacilitate sleep ocurrence [2]. Methods: Twelve male Sprague-Dawley rats (300–350 g) were surgically implanted, under general anaesthesia (Diazepam, 5mg/ kg, i.m., ketamine, 100 mg/kg, i.p.), with electrodes for chronic EEG recording, a thermistor for the detection of the hypothalamic temperature, a catheter for arterial blood presssure recording and two microcannulas for drug delivery within the LH. Two groups of animals were studied under a 6-day (D1–D6) protocol. Animals from group 1 (n = 5) were injected with either the GABAA agonist Muscimol (100 nl, 1 mM, 1 injection/h for 6 h, from 11:00 h to 16:00 h) or vehicle (saline, 0.9%; according to the former protocol) during D2 and D5, respecitvely. In group 2 (n = 7), the same experimental protocol was carried out, but Ta was lowered to 10C in both D2 and D5, from 9:00 h to 17:00 h. Results: In the six experimental hours, muscimol injection induced a significant increase in NREM sleep amount at both Ta 25C (+6099 ± 574 s) and Ta 10C (+4896 ± 408 s) compared to what observed after vehicle (P < 0.01, for both comparisons). In both groups, a concomitant suppression of REM sleep was obsereved after muscimol injection Conclusion: The acute inhibition of LH neurons in free behaving rats produces a long bout of NREM sleep, even in environmental condition unfavourable to sleep occurence. This effect can be explained by the inhibition of the activity of HCRT neurons, which would favor the activation of the circuits promoting NREM sleep occurrence. The suppression of REM sleep may be due to the concomitant inhibithion of a group of melanin concentrating hormone (MCH) neurons located in the LH, which have been shown to be involved in REM sleep regulation [3]. 1. Sakurai T, Mieda M, Tsujino N. Ann N Y Acad Sci 2010, 1200: 149–61. 2. Cerri, M. Ocampo-Garces, A. Amici R, Baracchi F, Capitani P, Jones CA, Luppi M, Perez E, Parmeggiani PL, and Zamboni G. Sleep 2005, 28: 694:705. 3. Sapin E, Berod A, Leger L, Herman PA, Luppi PH, Peyron C. PLoS One 2010, 5: e11766.

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