A1 NORADRENERGIC MODULATION OF AV3V INPUTS TO PVN NEUROSECRETORY-CELLS

PHASICALLY active neurosecretory neurons in the paraventricular nucleu s (PVN) of urethane-anesthetized rats displayed orthodromic excitation , inhibition or no response following electrical stimulation of the an teroventral third ventricle (AV3V) region, and exhibited orthodromic e xcitation or no response following electrical stimulation of the Al no radrenergic region of the ventrolateral medulla. Of the 14 neurons tha t responded to both the stimuli, Al region stimulation at the subthres hold current significantly enhanced the excitation induced by AV3V reg ion stimulation, and the enhancement was abolished by iontophoreticall y applied phentolamine, an alpha-adrenoceptor antagonist, but not by t imolol, a beta-adrenoceptor antagonist. These results suggest that A1 noradrenergic projections may act to potentiate the excitatory inputs from the AV3V region to vasopressinergic PVN neurons through alpha-adr enoceptor mechanisms.