GABA(B) receptors modulate short-term potentiation of spontaneous excitatory postsynaptic currents in the rat supraoptic nucleus in vitro

High-frequency stimulation of afferents to the supraoptic nucleus (SON) res ults in a robust increase in the frequency and amplitude of pharmacological ly isolated, tetrodotoxin-resistant, miniature excitatory postsynaptic curr ents (mEPSCs) lasting for 5-20 min. This increase in mEPSC frequency, terme d short-term potentiation (STP), is tightly coupled to increases in action potential firing in magnocellular neurons (MCNs) suggesting a functional ro le for STP. gamma -Aminobutyric acid (GABA), acting selectively on GABA(u) receptors, has been shown to modulate action potential-dependent EPSCs, as well as mEPSCs in this nucleus. In this study, we examined the role of GABA in STP. Using in vitro hypothalamic slices containing the SON and the nyst atin perforated-patch recording technique to record from MCNs. we tested th e hypothesis that GABA modulates STP. Baclofen, a GABA(B) receptor agonist. caused a reversible decrease in the frequency of mEPSCs as well as a reduc tion in the magnitude and duration of STP. GABA(B) receptor antagonists blo cked the baclofen-induced decrease in mEPSC frequency and reduction in STP. In addition, the antagonists by themselves increased basal mEPSC frequency while prolonging the duration of STP in most cells. By contrast, picrotoxi n. a GABA(A) chloride channel blocker, had no effect on STP. These findings indicate that GABA is tonically present in the SON and its action at the G ABA(B) receptor may determine the magnitude and duration of STP. (C) 2001 P ublished by Elsevier Science Ltd.