Responses of neurons in bed nucleus of the stria terminalis to microiontophoretically applied morphine, norepinephrine and acetylcholine.

The bed nucleus of the stria terminalis is a basal forebrain nucleus that receives inputs from limbic system nuclei and sends projections to several hypothalamic and brainstem nuclei, proposed to be involved in the physiological response to stressors. The bed nucleus of the stria terminalis also receives norepinephrine- (NE), acetylcholine- (ACh) and opiate-containing projections. The objectives of this experiment were to examine the effects of microiontophoretically applied ACh, NE and morphine sulfate (M) on neurons of the bed nucleus in urethane-anesthetized rats and to determine the degree to which these systems interact on individual neurons. Acetylcholine was excitatory in 43% of the neurons and NE was inhibitory in 70%. Morphine however, elicited two distinct types of response--excitation in 24% of the neurons and inhibition in 28%. Each of these effects was current-dependent and monophasic. Since 77% of neurons of the bed nucleus responded to two or more of the drugs used in this experiment, statistical analysis was used to determine correlations between responses to each of these drugs. This analysis showed that neurons that responded to M with excitation also responded to ACh with excitation, while neurons that responded to M with inhibition, were nonresponsive to ACh. No correlation was found between NE and either M or ACh. Thus, this experiment demonstrated the possible effects of noradrenergic, cholinergic and opioid innervation on firing rates of neurons of the bed nucleus of the stria terminalis and may explain the roles these neurotransmitters play in modulating the response to stress.