Effects of blockade of central dopamine D1 and D 2 receptors on thermoregulation, metabolic rate and running performance

To assess the effects of a blockade of central D 1 - and D 2 -dopaminergic receptors on metabolic rate, heat balance and running performance, 10 nmol (2 ώl) of a solution of the D 1 antagonist SCH-23390 hydrochloride (SCH, n = 6), D 2 antagonist eticlopride hydrochloride (Eti, n= 6), or 2 ώl of 0.15 M NaCl (SAL, n = 6) was injected intracerebroventricularly into Wistar rats before the animals began graded running until fatigue (starting at 10 m/min, increasing by 1 m/min increment every 3 min until fatigue, 5% inclination). Oxygen consumption and body temperature were recorded at rest, during exercise and following 30 min of recovery. Control experiments with injection of two doses (10 and 20 nmol/rat) of either SCH or Eti solution were carried out in resting rats as well. Body heating rate, heat storage, workload and mechanical efficiency were calculated. Although SCH and Eti treatments did not induce thermal effects in resting animals, they markedly reduced running performance (−83%, SCH; −59% Eti, p < 0.05) and decreased maximal oxygen uptake (−79%, SCH; −45%, Eti, p < 0.05) in running rats. In addition, these treatments induced a higher body heating rate and persistent hyperthermia during the recovery period. Our data demonstrate that the alteration in dopamine transmission induced by the central blockade of dopamine-D1 and D2 receptors impairs running performance by decreasing the tolerance to heat storage. This blockade also impairs the dissipation of exercise-induced heat and metabolic rate recovery during the post-exercise period. Our results provide evidence that central activation of either dopamine- D1 or D2 receptors is essential for heat balance and exercise performance.