PHARMACOLOGICAL ANALYSIS OF THE NORADRENE RGIC CONTROL OF CENTRAL SYMPATHETIC AND SOMATIC REFLEXES CONTROLLING THE LOWER URINARY-TRACT IN THE ANESTHETIZED CAT

Terminals containing norepinephrine densely innervate sympathetic preg anglionic neurons in the intermediolateral nucleus and somatic motor n eurons in Onuf's nucleus that project through the hypogastric and pude ndal nerves, respectively, to innervate the lower urinary tract. The p resent study pharmacologically analyzed the role of noradrenergic syst ems on the sympathetic and somatic pathways to the lower urinary tract and posed the following questions: 1. Are alpha(1), alpha(2), or beta adrenergic receptors tonically active along both sympathetic and soma tic reflex pathways? 2. What is the net effect of increasing the extra cellular levels of norepinephrine by administration of a norepinephrin e-reuptake inhibitor? And 3. does inhibition of sympathetic and somati c reflexes, which occurs during micturition contractions, involve adre nergic mechanims? To address these questions, activity was recorded fr om the central ends of the hypogastric and pudendal nerves in response to electrical stimulation of the pelvic or pudendal nerves in chloral ose-anesthetized cats, and the effects of prazosin (1-300 mu g/kg i.v. ), an alpha(1) adrenergic receptor antagonist; idazoxan (1-300 mu g/kg i.v.), an alpha(2) adrenergic receptor antagonist; propranolol (1 mg/ kg i.v.), a beta adrenergic receptor antagonist; and tomoxetine (0,003 -3 mg/kg i.v.), a selective norepinephrine reuptake inhibitor were exa mined. The results indicate that facilitatory alpha(1) adrenergic rece ptors are tonically active along both sympathetic and somatic reflex p athways, while inhibitory alpha(2) adrenergic receptors are not tonica lly active. The net effect of acute inhibition of norepinephrine reupt ake is increased activation of inhibitory alpha(2) adrenergic receptor s along sympathetic reflex pathways and increased activation of both f acilitatory alpha(1) and inhibitory alpha(2) adrenergic receptors alon g somatic reflex pathways. Adrenergic antagonists had no effect on inh ibition of sympathetic and somatic reflexes that occur during micturit ion contractions. No role for central beta adrenergic receptors was no ted.