Gonadal steroid actions on the paraventricular magnocellular neurosecretory cells of the male rat.

One-hundred and ten paraventricular (PV) neurosecretory cells were identified antidromically in castrated male rats anesthetized with urethane. After classifying the antidromically driven units into tonically and phasically firing groups, the latency, threshold, relative refractory period and wave form of the antidromic response were studied. Estradiol and testosterone had no effect on these parameters or on the wave form of antidromic responses in both cell groups. Testosterone caused a significant acceleration of the mean firing rate of the tonically firing cells (from 2.9 +/- 0.6 to 5.1 +/- 0.5 Hz) but estradiol did not affect it. These observations suggest that testosterone modulates the basal firing activity of the tonically firing PV neurosecretory cells in the male rat.