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APPETITE, OBESITY, AND DIGESTION

Energetic responses to cold temperatures in rats lacking forebrain-caudal brain stem connections

¹Graduate Groups of Psychology and Neuroscience, University of Pennsylvania, Philadelphia, Pennsylvania; ²Department of Biology and Center for Behavioral Neuroscience, Georgia State University, Atlanta; ⁴Department of Foods and Nutrition, University of Georgia, Athens, Georgia; and ³Department of Morphophysiological Sciences, State University of Maringá, Maringá, Brazil

Submitted 28 April 2008 ; accepted in final form 10 July 2008

Hypothalamic neurons are regarded as essential for integrating thermal afferent information from skin and core and issuing commands to autonomic and behavioral effectors that maintain core temperature (T_c) during cold exposure and for the control of energy expenditure more generally. Caudal brain stem neurons are necessary elements of the hypothalamic effector pathway and also are directly driven by skin and brain cooling. To assess whether caudal brain stem processing of thermal afferent signals is sufficient to drive endemic effectors for thermogenesis, heart rate (HR), T_c, and activity responses of chronic decerebrate (CD) and control rats adapted to 23°C were compared during cold exposure (4, 8, or 12°C) for 6 h. Other CDs and controls were exposed to 4 or 23°C for 2 h, and tissues were processed for norepinephrine turnover (NETO), a neurochemical measure of sympathetic drive. Controls maintained T_c for all temperatures. CDs maintained T_c for the 8 and 12°C exposures, but T_c declined 2°C during the 4°C exposure. Cold exposure elevated HR in CDs and controls alike. Tachycardia magnitude correlated with decreases in environmental temperature for controls, but not CDs. Cold increased NETO in brown adipose tissue, heart, and some white adipose tissue pads in CDs and controls compared with their respective room temperature controls. These data demonstrate that, in neural isolation from the hypothalamus, cold exposure drives caudal brain stem neuronal activity and engages local effectors that trigger sympathetic energetic and cardiac responses that are comparable in many, but not in all, respects to those seen in neurologically intact rats.

energy balance; thermoregulation; anterior hypothalamus; heart rate; body temperature; sympathetic drive; norepinephrine turnover; white adipose tissue; brown adipose tissue

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