The Role Of VPAG Dopamine Neurons In Propofol General Anesthesia

Objective: Recent study showed that electrical stimulation of dopamine neurons in the ventral tegmental area(VTA) can induce more rapid recovery from propofol and isoflurane anesthesia, indicating that the dopamine pathway in brain plays an important role in promoting anesthesia-emergence. Dopaminergic nucleus in the ventral periaqueductal gray area(v PAG) have been shown to modulate sleep behavior. However, it is not clear whether v PAG dopaminergic neurons are also involved in the process of general anesthesia. For this reason, we evaluated the loss of righting reflex time(LORR) and recovery of righting reflex time(RORR) after propofol administration in rats with 6-OHDA-induced lesions in v PAG dopamine neurons and sham-lesioned animals. Subsequently, using patch clamp electrophysiology in acute rats brain slices, we observed the effects of propofol on neuronal spontaneous excitatory postsynaptic currents(s EPSC) and spontaneous inhibitory postsynaptic currents(s IPSC) in v PAG area. The aim of this study is to investigate the effects of propofol on synaptic transmission in v PAG dopaminergic neurons. The present study will make us have a better understanding on the role of v PAG dopamine neurons in general anesthesia.Methods: This experiment was divided into two parts. Part 1: Healthy male SD rats were randomly divided into 6-OHDA-lesioned group(n=30) and sham-lesioned group(n=30). Animals were anesthetized with an intraperitoneal(i.p) injection of sodium pentobarbital(10mg/kg) and were mounted in a stereotaxic frame. Rats received 6-OHDA(4μg/μl,1μl) or vehicle injections into the left of v PAG nucleus. Two weeks later, the rats respectively and daily received various does of propofol(4,5,6,7,8,9,10,11 mg/kg) through tail vein(10 rats per group). We recorded the rate of LORR percentage. Afterwards, in the unlesioned and lesioned group(20 rats per group), rats were intravenously injected with propofol(11mg/kg), and LORR time and RORR time were recorded. Part 2: Brain slices containing v PAG were prepared from the 7-14 days old SD rats. Dopaminergic neurons were identified by immunofluorescence method. The effects of propofol(10μM) on s EPSC and s IPSC in v PAG nucleus dopaminergic neurons were observed under voltage clamp, using the whole-cell recording mode(n=6).Results:(1) Compared with the unlesioned group, the LORR time of lesioned group was significantly shortened(P﹤0.05).(2) Compared with the unlesioned group, the RORR time of lesioned group was significantly prolonged(P﹤0.05).(3) Compared with the unlesioned group, the cumulative dose-response curve of propofol-induced unconsciousness obviously shifted to left in the lesioned group.(4) Propofol(10μM) decreased the frequency(P﹤0.05) of s EPSC without affecting the amplitude and decay time.(5) Propofol(10μM) increased the frequency(P﹤0.05) and prolonged the decay time(P﹤0.05) of s IPSC without affecting the amplitude.Conclusion:(1) Dopaminergic neurons within v PAG area may participate in the process of propofol anesthesia, lesion of dopaminergic neurons within v PAG area can shorten the induction time and prolong the recovery time.(2) Propofol can regulate synaptic transmission of dopaminergic neurons within v PAG area via presynaptic and postsynaptic mechanisms. Propofol may act on presynaptic nerve terminals and then promote GABA release from dopamine neurons. Also, postsynaptic GABAA receptor sensitivity was increased after propofol administration. In addition, propofol may act on presynaptic nerve terminals and then inhibit glutamate release from these dopamine neurons.