Competition between lever-pressing behavior and thermoregulatory behavior on exposure to heat in intracranial self-stimulating rats

To investigate the relationship between the thermoregulatory system and the brain-reward system, we examined effects of heat exposure and tail amputation on lever-pressing behavior in intracranial self-stimulating rats. Rats that continuously pressed a lever voluntarily for 1 hour at an ambient temperature (T_a) of 22°C interrupted lever pressing and showed heat loss behaviors, such as grooming and body extension, at a T_a of 36°C. Hypothalamic temperature (T_hy) at the time of the first body extension was higher than that after 1 hour of lever-pressing at a T_a of 22°C. Tail amputation experiments showed the same result. T_hy at the onset of the body extension after tail amputation was higher than that at the end of 1 hour of lever-pressing under control conditions. The data suggest that thermal factors, especially T_hy, are important in the control of lever-pressing behavior.