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

Norepinephrine (NE)-containing terminals densely innervate sympathetic preganglionic neurons in the intermediolateral nucleus and somatic mo tor neurons in Onuf's nucleus that project through the hypogastric and pudendal nerves, respectively, to innervate the lower urinary tract. in the present study, we pharmacologically analyzed the role of noradr energic systems on the sympathetic and somatic pathways to the lower u rinary tract and asked: 1) Are alpha-1, alpha-2, or beta-adrenergic re ceptors tonically active along sympathetic and/or somatic reflex pathw ays? And 2) what is the net effect of increasing the extracellular lev els of NE by administration of a NE reuptake inhibitor? To address the se questions, we recorded evoked potentials from the central ends of t he hypogastric and pudendal nerves in response to electrical stimulati on of the pelvic and pudendal nerves in chloralose-anesthetized cats, and the effects of prazosin (1-300 mu g/kg i.v.), an alpha-1-adrenergi c receptor antagonist; idazoxan (1-300 mu g/kg i.v), an alpha-2-adrene rgic receptor antagonist; propranolol (1 mg/kg i.v.), a beta-adrenergi c receptor antagonist; and tomoxetine (0.003-3 mg/kg i.v.), a selectiv e NE reuptake inhibitor, were examined. The results indicate that faci litatory alpha-1-adrenergic receptors are tonically active along both sympathetic and somatic reflex pathways, whereas inhibitory alpha-2-ad renergic receptors are not tonically active. The net effect of acute i nhibition of NE reuptake along sympathetic reflex pathways is increase d activation of inhibitory alpha-2-adrenergic receptors. Along somatic reflex pathways, increased activation of both facilitatory alpha-1- a nd inhibitory alpha-2-adrenergic receptors were recorded after acute N E reuptake inhibition. No role for central beta-adrenergic receptors w as noted.