Excitatory Effects of Astrocytic Hydrogen Sulfide on the Electrical Activity of Oxytocin Neurons in the Supraoptic Nucleus

Abstract

Introduction: In the regulation of oxytocin (OT) neuronal activity, hydrogen sulfide (H₂S), a gaseous neurotransmitter, likely exerts an excitatory role. This role is associated with increased expression of astrocytic cystathionine-β-synthase (CBS), the key enzyme for H₂S synthesis. However, it remains unclear whether H₂S is mainly produced in astrocytes and contributes to the autoregulation of OT neurons. Methods: In hypothalamic slices of male rats, OT and H₂S-associated drug effects were observed on the firing activity and spontaneous excitatory postsynaptic currents (sEPSCs) of putative OT neurons in the supraoptic nucleus (SON) in whole-cell patch-clamp recording. Expression of glial fibrillary acidic protein (GFAP) in the SON was analyzed in Western blots. In addition, changes in the length of rat pups’ hypothalamic astrocytic processes were observed in primary cultures. Results: In brain slices, OT significantly increased the firing rate of OT neurons, which was simulated by CBS allosteric agonist S-adenosyl-L-methionine (SAM) and H₂S slow-releasing donor GYY4137 but blocked by CBS inhibitor aminooxyacetic acid (AOAA). L-α-aminoadipic acid (a gliotoxin) blocked SAM-evoked excitation. OT and SAM also increased the frequency and amplitude of sEPSCs; the effect of OT was blocked by AOAA. Both OT and GYY4137 reduced GFAP expression in the SON. Morphologically, OT or GYY4137 time-dependently reduced the length of astrocytic processes in primary cultures. Conclusions: These findings indicate that the auto-excitatory effect of OT on OT neurons is mediated by H₂S from astrocytes at least partially and astrocytic H₂S can elicit retraction of astrocytic processes that subsequently increase OT neuronal excitability.