CYSTEAMINE AND NALOXONE ATTENUATE ASPARTIC ACID-INDUCED DEPRESSION OFVENTILATION

Aspartic acid (580 mg/kg, SC) causes a long-lasting depression of vent ilation in adult male, but not female rats. The purpose of these exper iments was to determine if the aspartic acid-induced depression of ven tilation in awake male Sprague-Dawley rats is a consequence of the rel ease of endogenous opioids or somatostatin. These neuromodulators have been shown to cause depression of ventilation. Pretreatment of male r ats with the opioid antagonist naloxone (5 mg/kg) 10 min prior to aspa rtic acid attenuated the drop of ventilation from - 138.6 +/- 26.9 ml/ min to - 63.4 +/- 16.6 ml/min (p < 0.01) by affecting both tidal volum e and frequency of breathing. Naloxone administered prior to saline ha d no effect on ventilation. In another experiment, cysteamine (100 mg/ kg), a somatostatin depleter, injected SC 2 h before aspartic acid adm inistration also attenuated depression of ventilation by affecting fre quency of breathing, Cysteamine alone, compared to saline, had no effe ct on ventilation over 24 h. These results suggest that aspartic acid acts by releasing endogenous opioids and somatostatin.