NALOXONE MICROINJECTED INTO THE ARCUATE NUCLEUS HAS DIFFERENTIAL-EFFECTS ON VENTILATION IN MALE AND FEMALE RATS

The arcuate nucleus of the hypothalamus, a highly sexually dimorphic b rain region, has been called the bed nucleus for endogenous opioids. T he potential contribution of opioids in this nucleus to modulate contr ol of ventilation in male and female rats has not been investigated. T he purpose of the present study is to determine the effect of microinj ecting naloxone, an opioid receptor antagonist, into the arcuate nucle us of awake male and female rats on ventilation, oxygen consumption, h eart rate, and blood pressure. Results of this study demonstrate that naloxone at doses of 1.5 and 3.0 nmol relative to vehicle caused a dep ression of ventilation due to a decrease of both frequency of breathin g and tidal volume in male rats and a decreased response to a hypercap nic challenge in female rats. Although there were gender differences n oted in oxygen consumption, heart rate, blood pressure, and ventilator y response to a hypoxic challenge, only oxygen consumption was signifi cantly affected by naloxone. Potential mechanisms whereby naloxone may act to depressing ventilation are discussed. (C) 1997 Elsevier Scienc e Inc.