Central autonomic effects of dermorphin in conscious rats

Central cardiovascular and respiratory effects of dermorphin were studied in conscious rats. Intracerebroventricular administration (0.1 or 1 nM) of dermorphin increased the systolic and diastolic blood pressure whereas a high dose (50 nM) decreased blood pressure. Dermorphin at 1 nM increased respiratory rate but caused hypoxia, acidosis and hypercapnia; at 50 nM, respiratory rate was suppressed. Both of these doses produced catalepsy. Stimulation of the sympathoadrenomedullary axis at the pressor period elicited by 1 nM dermorphin was evident by high circulating levels of epinephrine and norepinephrine. N-methyl-atropine reversed the severe bradycardia induced by dermorphin and completely prevented this phenomenon if given as pretreatment. Neither blood pressure nor respiratory depression was altered by the muscarinic blocker. Naloxone (1 mg/kg) reversed the respiratory, cardiovascular and sympathetic effects of dermorphin as well as the catalepsy. These data show that dermorphin has central autonomic effects which are naloxone reversible and mediated by both sympathetic and parasympathetic pathways.