Received July 15, 2007
Revised August 29, 2007
Accepted after revision September 5, 2007
Cardiovascular Control [210]
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EXPOSURE TO A HOT ENVIRONMENT CAN ACTIVATE RVLM-PROJECTING NEURONS IN THE HYPOTHALAMIC PVN IN CONSCIOUS RATS
Joo Lee Cham 1
Emilio Badoer 1*
1 RMIT University
* To whom correspondence should be addressed. E-mail: emilio.badoer{at}rmit.edu.au.
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Abstract |
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A major integrative site within the brain for autonomic function is the hypothalamic paraventricular nucleus (PVN). Several studies have suggested 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 neurons 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 neurons 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 neurons in the PVN are activated by heat and whether those neurons are also nitrergic. The results show that, compared to control, exposure of conscious rats to a hot environment of 39°C significantly increased neurons containing a Fos - positive nucleus (a marker of activation) and significantly increased activated RVLM - projecting neurons in the PVN. Secondly, although heating significantly increased the number of activated nitrergic PVN neurons, triple labeled neurons (ie activated, nitrergic and RVLM - projecting) in the PVN were rarely observed. The results suggest that RVLM projecting neurons in the PVN may play a role in responses to heat exposure but these are not nitrergic.
Key Words:
Hyperthermia, Hypothalamus, Rostral ventrolateral medulla
