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金沢大学医薬保健研究域薬学系, Nitric oxide (NO), a gaseous neurotransmitter, is involved in a variety of brain functions, including drug addiction. Although previous studies have suggested that NO plays an important role in the development of cocaine addiction, the brain region(s) in which NO acts and how it contributes to cocaine addiction remain unclear. In this study, we examined these issues using a cocaine-induced conditioned place preference (CPP) paradigm and ex vivo electrophysiological recordings in rats. Specifically, we focused on the medial prefrontal cortex (mPFC) and laterodorsal tegmental nucleus (LDT), brain regions associated with cocaine CPP development and cocaine-induced plasticity. Intra-mPFC injection of the non-selective NO synthase (NOS) inhibitor L-NAME or the neuronal NOS (nNOS) selective inhibitor L-NPA during the conditioning phase disrupted cocaine CPP. Additionally, intra-mPFC injection of L-NPA prior to each cocaine injection prevented the induction of presynaptic plasticity, induced by repeated cocaine administration, in LDT cholinergic neurons. These findings indicate that NO generated in the mPFC contributes to the acquisition of cocaine CPP and the induction of neuroplasticity in LDT cholinergic neurons. Together with previous studies showing that NO induces membrane plasticity in mPFC neurons, that mPFC neurons project to the LDT, and that LDT activity is critical for the acquisition of cocaine CPP, the present findings suggest that NO-mediated neuroplasticity induced in the mPFC-LDT circuitry is critical for the development of cocaine addiction. © 2017 Elsevier B.V., Embargo Period 12 months

Stress augments the rewarding memory of cocaine, which plays a critical role in inducing cocaine craving. However, the neurobiological mechanisms underlying the enhancing effect of stress remain unclear. Here, we show that noradrenaline (NA) transmission in the medial prefrontal cortex (mPFC) mediates stress-induced enhancement of cocaine craving. When mice were exposed to acute restraint stress immediately before the posttest session of the cocaine-induced conditioned place preference (CPP) paradigm, the CPP score was significantly higher than that in non-stressed mice. Because extracellular NA levels have been reported to be increased in the mPFC during stress exposure, we assessed the effects of NA on mPFC layer 5 pyramidal cell activity. Whole-cell recordings revealed that NA application induces depolarization and a concomitant increase in spontaneous excitatory postsynaptic currents (sEPSCs). The NA effects were inhibited by terazosin, but not by yohimbine or timolol, and the sEPSC increase was not observed in the presence of tetrodotoxin, suggesting the involvement of postsynaptic α1, but not α2 or β, adrenoceptors in the NA effects. Additionally, intra-mPFC injection of terazosin before stress exposure attenuated the stress-induced increase in cocaine CPP. Intra-mPFC injection of phenylephrine, an α1 adrenoceptor agonist, before the posttest session without stress exposure significantly enhanced cocaine CPP. Furthermore, chemogenetic suppression of mPFC pyramidal cells with inhibitory DREADD (designer receptors exclusively activated by designer drugs) also suppressed the stress-induced CPP enhancement. These findings suggest that the stress-induced increase in NA transmission activates mPFC pyramidal cells via α1 adrenoceptor stimulation, leading to enhancement of cocaine craving-related behavior.