Figure 4.

Effects of endomorphin 1 on spontaneous spiking activity of SON oxytocin cells in vitro. Typical original chart records of action potentials recorded with whole cell current-clamp in hypothalamic slices; SON oxytocin cells were identified by their response to a hyperpolarizing pulse as described in the Methods. (A): After stable basal activity was recorded for several minutes, endomorphin 1 (EM1, 100 nM) was added to the superfusate for 2 min. Firing was progressively inhibited, beginning during the endomorphin 1 application, and continuing for at least 5 min after the end of the application. (B): A greater concentration of endomorphin 1 (1 μM) was applied to this cell for 2 min, rapidly causing a small hyperpolarization with near complete inhibition of firing. Application of naloxone (10 μM) 1 min after the end of the endomorphin 1 application caused a rapid reversal of the hyperpolarization and increase in firing rate. This is in contrast to the prolonged inhibition after the end of endomorphin 1 application at a 10 fold lower concentration, without naloxone, seen in (A).