Opioid peptide regulation of neurons in the bed nucleus of the stria terminalis: a microiontophoretic study.

Single unit activity was recorded from neurons in the bed nucleus of the stria terminalis (BNST) in response to single or combined microiontophoretic ejection of D-Ala2-Met5-enkephalinamide (DAME) and naloxone. BNST neurons showed predominantly excitatory responses following small iontophoretic applications of DAME, and these responses were antagonized by naloxone. In contrast, inhibitory responses that were elicited by DAME required larger ejection currents and usually failed to show naloxone antagonism. The results indicate that activation of enkephalin-sensitive BNST neurons by DAME is primarily, but not exclusively, excitatory, which suggests that these responses may reflect differences in receptor sensitivity to the applied agonist.