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Intracerebroventricular physostigmine facilitates heat loss mechanisms in running rats

¹Department of Physiology and Biophysics, Institute of Biological Sciences, and ²Laboratory of Exercise Physiology, Department of Physical Education, School of Physical Education, Physical Therapy, and Occupational Therapy, Federal University of Minas Gerais, 31270-901 Belo Horizonte, Minas Gerais; and ³Department of Physiotherapy, Pontificia Universidade Católica, 30535-610 Belo Horizonte, Minas Gerais, Brazil

Submitted 16 July 2003 ; accepted in final form 14 March 2004

The aim of this study was to evaluate the participation of central cholinergic transmission in the regulation of metabolic rate, core temperature, and heat storage in untrained rats submitted to exercise on a treadmill (20 m/min, 5% inclination) until fatigue. The animals were separated into eight experimental groups, and core temperature or metabolic rate was measured in the rats while they were exercising or while they were at rest after injection of 2 µl of 5 x 10^–3 M physostigmine (Phy) or 0.15 M NaCl solution (Sal) into the lateral cerebral ventricle. Metabolic rate was determined by the indirect calorimetry system, and colonic temperature was recorded as an index of core temperature. In resting animals, Phy induced only a small increase in metabolic rate compared with Sal injection, without having any effect on core temperature. During exercise, the Phy-treated animals showed a lower core heating rate (0.022 ± 0.003°C/min Phy vs. 0.033 ± 0.003°C/min Sal; P < 0.02), lower heat storage (285 ± 37 cal Phy vs. 436 ± 34 cal Sal; P < 0.02) and lower core temperature at fatigue point than the Sal-treated group (38.5 ± 0.1°C Phy vs. 39.0 ± 0.1°C Sal; P < 0.05). However, despite the lower core heating rate, heat storage, and core temperature at fatigue, the Phy-treated rats showed a similar running time compared with the Sal-treated group. We conclude that the activation of the central cholinergic system during exercise increases heat dissipation and attenuates the exercise-induced increase in core temperature without affecting running performance.

body temperature; oxygen consumption; central cholinergic system; fatigue

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