490 Studies of the Psychophysiological Markers and the Brain Processing of Nausea in Healthy Humans Using a Novel Virtual Reality Video

Abstract

Hydrogen sulfide(H2S), mainly produced endogenously by two enzymes, cystathionine γlyase(CSE) and cystathionine β-synthase(CBS), is a messenger molecule in the central nervous system, in the GI tract and in sympathetic prevertebral ganglia. Our previous study found, in mouse superior mesenteric ganglion(SMG), that exogenous H2S acts selectively on splanchnic nerve terminals to potentiate fast excitatory post synaptic potentials (F-EPSPs). In this study, we investigated the distribution of CSE and CBS and the role of endogenously produced H2S on central sympathetic input. Methods: The SMG, splanchnic nerve trunks and colonic nerve trunk were dissected from adult SJL/J mice. Immunostaining was performed with antibodies for CSE and CBS and for vesicular acetylcholine transporter(VAChT) to identify cholinergic nerve terminals. Microelectrodes were used for intracellular recordings. Results: CSE immunoreactivity(IR) was found in neurons and glia cells and did not co-localize with VAChT-IR. CBS-IR was found only in glia cells. To determine whether the F-EPSPs could be potentiated by endogenously released H2S, we tested the effect of inhibiting H2S breakdown with stigmatellin, a specific sulfide quinone reductase inhibitor, on F-EPSPs. Stigmatellin(1μM) significantly(P<0.05) increased the amplitude and the area of F-EPSPs evoked by splanchnic nerve stimulation(21.0±4.8mV and 441±107ms●mV with stigmatellin vs. 18.4±5.3mV and 338±108ms●mV before stigmatellin, n=4) but had no significant effect on F-EPSPs evoked by colonic nerve stimulation. In contrast, the CSE inhibitor, dl-propargylglycine(PAG, 1mM), significantly(P<0.05) decreased the amplitude and the area of F-EPSPs evoked by splanchnic nerve stimulation(23.7±3.9mV and 824±288ms●mV with PAG vs. 27.0±4.1mV and 1230±414ms●mV before PAG, n=6), but had no effect on F-EPSPs evoked by colonic nerve stimulation. Surprisingly, the CBS inhibitor, aminooxyacetic acid(AOAA, 0.5mM), increased the amplitude and the area of F-EPSPs evoked by splanchnic nerve stimulation(23.6±12.1mV and 651±455ms●mV with AOAA vs. 20.2±10.9mV and 438±318ms●mV before AOAA, n=4, P<0.05) and increased the amplitude and the area of F-EPSPs evoked by colonic nerve stimulation(36.2±8.2mV and 1609±468ms●mV with AOAA vs. 28.9±8.1mV and 1084±402ms●mV before AOAA, n=6, P<0.05). Bicuculline(20μM), a specific GABA-A receptor inhibitor, blocked the potentiating effect of AOAA suggesting that the AOAA induced potentiation of F-EPSPs was due to the inhibition of GABA transaminase-induced accumulation of GABA. Conclusion: We conclude that endogenously produced H2S in the mouse SMG modulates fast cholinergic synaptic input in a pathwayspecific manner. H2S modulates fast cholinergic synaptic input from central splanchnic nerve terminals but has no affect on input from peripheral cholinergic input. (Funded by NIH DK17238)