Aspartic acid in the arcuate nucleus attenuates the depressive effects of naloxone on ventilation

Ventilation, oxygen consumption, the ventilatory equivalent for oxygen, and ventilatory responses to hypoxia and to hypercapnia were evaluated in cons cious male rats who received each of four treatments: (1) microinjection of artificial cerebrospinal fluid (aCSF) into the arcuate nucleus and subcuta neously saline (CS); (2) aspartic acid into the arcuate nucleus and saline subcutaneously (AS); (3) aCSF into the arcuate nucleus and naloxone subcuta neously (CN); and (4) aspartic acid into the arcuate nucleus and naloxone s ubcutaneously (AN). Rats treated with CN exhibited a depression of ventilat ion, ventilatory equivalent, ventilatory response to hypercapnia, and tidal volume response to hypoxia and to hypercapnia. AS had no effect on any par ameters. Administration of both aspartic acid and naloxone attenuated all t he effects of CN except the depression of minute ventilation in response to hypercapnia. Therefore the naloxone (a mu opioid receptor antagonist) indu ced a depression of ventilation that was attenuated by aspartic acid acting on N-methyl-D-aspartic acid receptors in the arcuate nucleus. (C) 1998 Els evier Science B.V. All rights reserved.