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 astrocyte 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 and blocked by CBS inhibitor aminooxyacetic acid (AOAA). L-α-aminoadipic acid (L-AAA, 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 astrocyte 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 astrocyte processes that subsequently increase OT neuronal excitability.

Dual Oxytocin Receptor-G Protein Signaling in the Autoregulation of Activities of Oxytocin Neurons

“…IP 3 can mobilize intracellular Ca 2+ from endoplasmic reticulum Ca 2+ store to increase cytosolic Ca 2+ levels, which can activate or induce CAMK, cyclooxygenase 2 [Cox-2, a prostaglandin (PG) synthetase] [55], pERK1/2, and some ion channels including Ca 2+ -activated K + channels (K Ca ) [19, 25, 56, 57]. These signals can further influence PG synthesis [24], nitric oxide (NO) production [58], hydrogen sulfide (H 2 S) release [59] and other processes such as decreasing the expressions of transcriptional factor nuclear factor kappa-B, tumor necrosis factor-α, interleukin-1β, and matrix metallopeptidase-9 and enhancing the level of brain-derived neurotrophic factor protein [60].…”

“…In fact, NO production can facilitate burst synchrony after a short inhibition of minutes [125]. H 2 S also contributes to burst and/or their synchrony, which has been demonstrated in the inhibition of H 2 S scavenger on the excitability of OT neurons as well as milk yield, a sign of the milk-ejection reflex and burst activity [59, 126]. Relative to OT and other neurochemical substances, these gaseous signals may contribute to burst synchrony more efficiently and are worthy of further study.…”