Activation of brain areas in rat following warm and cold ambient exposure.
ABSTRACT Environmental thermal stimuli result in specific and coordinated thermoregulatory response in homeothermic animals. Warm exposure activates numerous brain areas within the cortex, hypothalamus, pons and medulla oblongata. We identified these thermosensitive cell groups in the medulla and pons that were suggested but not outlined by previous physiological studies. Using Fos immunohistochemistry, we localized all the nuclei and cell groups in the rat brain that were activated by warm and cold ambient exposure. These neurons located in the hypothalamus and the brainstem, are part of a network responsible for the thermospecific response elicited by thermal stress. Comparison of the distribution of Fos-immunoreactive cells throughout the rat brain revealed topographical differences between the patterns of activated cells following warm and cold environmental exposure. Among several brain regions, warm exposure elicited c-fos expression specifically in the ventrolateral part of the medial preoptic area, the central subdivision of the lateral parabrachial nucleus and the caudal part of the peritrigeminal nucleus, whereas cold stress resulted in c-fos expression in the ventromedial part of the medial preoptic area, the external subdivision of the lateral parabrachial nucleus and the rostral part of the peritrigeminal nucleus. These neurons are part of a network coordinating specific response to warm or cold exposure. The topographical differences suggest that well-defined cell groups and subdivisions of nuclei are responsible for the specific physiological (endocrine, autonomic and behavioral) changes observed in different thermal environment.
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ABSTRACT: We assessed the contribution of the paraventricular nucleus (PVN) in the heat stress-mediated changes in sympathetic nerve activity and blood flow redistribution from the core to the skin surface. Renal sympathetic nerve activity (RSNA), mean arterial pressure (MAP), heart rate (HR), and body and tail temperatures were recorded in anesthetized rats after bilateral microinjection of cerebrospinal fluid (CSF), lidocaine or NG-monomethyl-L-arginine (L-NMMA) into the PVN during heat stress. Heat stress was induced by a graded increase in the temperature of a heating pad for 30 min. Heat stimulus after blockade of the PVN with lidocaine resulted in a blunted RSNA response (ΔRSNA: 117.6 ± 17.0% versus 11.3 ± 7.3%), as well as blunted MAP and HR (ΔMAP: 22 ± 2 versus -0.04 ± 7.2 mmHg; ΔHR: 93.4 ± 9.3 versus 43.4 ± 18.8 bpm). Body temperature threshold for tail vasodilation was unaffected by lidocaine treatment. The increase in RSNA, MAP and HR due to heat stress in L-NMMA-treated rats reached similar levels as CSF-treated control rats. However, a higher body temperature threshold for tail vasodilation was observed after L-NMMA injection (37.3 ± 0.1 versus 37.8 ± 0.2 °C). In conclusion, an intact PVN contributes to an increase in renal sympathetic activity provoked by heat stress, resulting in cardiovascular adjustments that influence core blood redistribution to the periphery. Furthermore, during heat stress, the effect of the PVN on cutaneous vasodilation is dependent on a nitric oxide mechanism.Experimental Biology and Medicine 05/2012; 237(5):570-7. · 2.80 Impact Factor
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ABSTRACT: A major integrative site within the brain for autonomic function is the hypothalamic paraventricular nucleus (PVN). Several studies have suggested that the PVN may be involved in the responses regulating body temperature. Hyperthermia elicits redirection of blood flow from the viscera to the periphery and involves changes in sympathetic nerve activity mediated by the central nervous system. The hypothalamic PVN includes neurones that project to the rostral ventrolateral medulla (RVLM), an important autonomic region involved in the tonic regulation of sympathetic nerve activity. This pathway could contribute to the cardiovascular changes induced by hyperthermia. The PVN has a high concentration of nitrergic neurones and it is known that nitric oxide within the brain mediates heat dissipation. Thus the aims of this study were to determine whether RVLM-projecting neurones in the PVN are activated by heat and whether those neurones are also nitrergic. The results show that, compared with control conditions, exposure of conscious rats to a hot environment of 39 degrees C significantly increased the number of neurones containing a Fos-positive nucleus (a marker of activation) and significantly increased the number of activated RVLM-projecting neurones in the PVN. Also, although heating significantly increased the number of activated nitrergic PVN neurones, triple-labelled neurones (i.e. activated, nitrergic and RVLM projecting) in the PVN were rarely observed. The results suggest that RVLM-projecting neurones in the PVN may play a role in responses to heat exposure but these are not nitrergic.Experimental Physiology 02/2008; 93(1):64-74. · 2.79 Impact Factor
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ABSTRACT: Reflex responses to hyperthermia include sweating, salivation and a redirection of blood flow from the viscera to the periphery, and involve changes in peripheral nerve activity mediated by the central nervous system (CNS), including specific areas of the ventral lower brainstem. The lower brainstem contains nitrergic neurones and neurones that project to intermediolateral cell column; however, it is not known whether these populations of neurones in the lower brainstem are activated following hyperthermia. The aims of the present study were to determine whether lower brainstem neurones activated by acute hyperthermia are nitrergic and/or whether they also project to the spinal cord. Retrogradely transported rhodamine-tagged beads were microinjected into the spinal cord. The rats were heated (environmental temperature 39 degrees C) for 1 h. Following perfusion/fixation, brain sections were processed to detect Fos (a marker of neuronal activation) and NADPH-diaphorase activity (a marker of nitrergic neurones). The results showed a significant increase in activated neurones in the mid-line (by fivefold), ventromedial (by eightfold) and ventrolateral lower brainstem (by ninefold). Some of these neurones were nitrergic, particularly in the ventromedial lower brainstem (5% of the activated neurones in this region were nitrergic). A small proportion of activated neurones were spinally projecting neurones (2-3% of activated neurones were spinally projecting). There were no triple-labelled neurones at any level of the lower brainstem examined. These findings indicate that only a small proportion of nitrergic neurones and spinally projecting neurones are activated by hyperthermia.Experimental Physiology 06/2007; 92(3):529-40. · 2.79 Impact Factor