神經胜肽 S 在壓力誘發小鼠古柯鹼癮頭之角色

Abstract

Neuropeptide S is a 20 amino-acid peptide identified as the endogenous ligand for the Neuropeptide S receptor (NPSR). In mice, NPS-containing neurons are localized in the peri-locus coeruleus (LC) and the parabrachial nucleus (PBN). Previous studies have demonstrated that NPS shares several similar pathophysiological roles as orexins, including stress-induced drug reward. First, stress can activate the NPS-containing neurons in the peri-LC and the PBN, and the orexin neurons in the lateral hypothalamic (LH). Second, intra-LH microinjection of NPS activates orexin neurons, and orexin neuron activation is associated with drug seeking. Third, activating postsynaptic orexin 1 receptors (OX1Rs), a family of Gq-protein coupled receptors, on VTA dopamine neurons leads to phospholipase (PLC) activation and generating diacylglycerol (DAG) that is converted into 2-arachidonoylglycerol (2-AG) by the DAG lipase (DAGL) inside the postsynaptic neuron. The generated 2-AG, an endocannabinoid, travels retrogradely across the synapse to inhibit GABA release by activating presynaptic CB1 receptors (CB1Rs), a disinhibition phenomenon. Fourth, intra-VTA microinjection of orexin A reinstated cocaine relapse via the OX1R-PLC-DAGL-2-AG-CB1R cascade-mediated dopaminergic disinhibition in the VTA. Based on previous study, we proposed that NPS and stress share a similar mechanism that involves endogenous orexin and endocannabinoid systems in inducing cocaine relapse. In order to validate the hypothesis, we use the conditioned place preference (CPP) to measure the cocaine craving of mice. Mice were trained to induced cocaine CPP by a 3-day bias-cocaine CPP training, and then to develop extinction by a 3 day-forced pairing with saline injections. Then a 30-min restraint stress was used to reinstate cocaine CPP in extinguished animals. We found that SHA 68 (50 mg/kg, i.p.), a selective NPSR antagonist, prevented the reinstatement of cocaine CPP. Besides, i.c.v. injection of NPS (1 nmol) induced the reinstatement of cocaine CPP in extinguished mice, and this effect was blocked by selective OX1R and CB1R antagonists, respectively. Through ELISA, we found that i.c.v. injection of NPS (1 nmol) significantly elevated the orexin A level in the VTA, and this effect was prevented by SHA 68. Finally, the immunofluorescence staining showed that , i.c.v. injection of NPS (1 nmol) significantly increased the density of the presence for double labelling to c-Fos and orexin A in the LH. During stress, NPS is released from the PBN or/and peri-LC in mice, to activate LH orexin neurons, releasing orexins. The released orexins may reinstate extinguished cocaine-seeking behavior via a disinhibition mechanism mediated by endocannabinoids generated after activation of the OX1R in the VTA. That is, orexins activate OX1R-PLC-DAGL-2-AG-CB1R signaling cascade, then inhibit GABA releasing. The inhibition of GABAergic synaptic neurotransmission onto dopaminergic neurons in the VTA results in activation of the mesolimbic dopaminergic circuitry, leading to relapse.