OBJECTIVE Cannabis can be rewarding or aversive.Cannabis reward is believed to be mediated by activation of cannabinoid CB1 receptors(CB1 Rs) on GABAergic neurons that disinhibit dopaminergic neurons in the ventral te...OBJECTIVE Cannabis can be rewarding or aversive.Cannabis reward is believed to be mediated by activation of cannabinoid CB1 receptors(CB1 Rs) on GABAergic neurons that disinhibit dopaminergic neurons in the ventral tegmental area(VTA).However,little is known about the mechanisms underlying cannabis aversion in rodents.Our study aimed at dig the mechanisms underlying cannabis aversion.METHODS We first created CB1-floxed mice and then generated conditional CB1-knockout mice(VgluT2-CB1-/-) in glutamatergic neurons that express vesicular glutamate transporter 2(VgluT2).We then used immunohistochemistry and RNAscope in situ hybridization assays to examine whether CB1 Rs are expressed in VTA GABAergic neurons and glutamatergic neurons.We also used Cre-dependent viral vector to express light-sensitive channelrhodopsin-2 into VTA glutamatergic neurons.Next,conditioned place preference and intracranial self-stimulation(ICSS) maintained by optical activation of VTA glutamatergic neurons were employed to evaluate the effects of Δ9-THC on brain reward function.RESULTS CB1 Rs are found not only on VTA GABAergic neurons,but also on VTA glutamatergic neurons that express vesicular glutamate transporter 2(VgluT2).Photoactivation of VTA glutamatergic neurons produced robust intracranial self-stimulation(ICSS) behavior,which was dose-dependently blocked by DA receptor antagonists,but enhanced by cocaine.In contrast,Δ9-tetrahydrocannabinol(Δ9-THC),the major psychoactive component of cannabis,produced dose-dependent conditioned place aversion and a reduction in the above optical ICSS in VgluT2-cre control mice,but not in VgluT2-CB1-/-mice.CONCLUSION Activation of CB1 Rs in VgluT2-expressing glutamate neurons produces aversive effects that might explain why cannabinoid is not rewarding in rodents and might also account for individual differences in the hedonic effects of cannabis in humans.展开更多
文摘OBJECTIVE Cannabis can be rewarding or aversive.Cannabis reward is believed to be mediated by activation of cannabinoid CB1 receptors(CB1 Rs) on GABAergic neurons that disinhibit dopaminergic neurons in the ventral tegmental area(VTA).However,little is known about the mechanisms underlying cannabis aversion in rodents.Our study aimed at dig the mechanisms underlying cannabis aversion.METHODS We first created CB1-floxed mice and then generated conditional CB1-knockout mice(VgluT2-CB1-/-) in glutamatergic neurons that express vesicular glutamate transporter 2(VgluT2).We then used immunohistochemistry and RNAscope in situ hybridization assays to examine whether CB1 Rs are expressed in VTA GABAergic neurons and glutamatergic neurons.We also used Cre-dependent viral vector to express light-sensitive channelrhodopsin-2 into VTA glutamatergic neurons.Next,conditioned place preference and intracranial self-stimulation(ICSS) maintained by optical activation of VTA glutamatergic neurons were employed to evaluate the effects of Δ9-THC on brain reward function.RESULTS CB1 Rs are found not only on VTA GABAergic neurons,but also on VTA glutamatergic neurons that express vesicular glutamate transporter 2(VgluT2).Photoactivation of VTA glutamatergic neurons produced robust intracranial self-stimulation(ICSS) behavior,which was dose-dependently blocked by DA receptor antagonists,but enhanced by cocaine.In contrast,Δ9-tetrahydrocannabinol(Δ9-THC),the major psychoactive component of cannabis,produced dose-dependent conditioned place aversion and a reduction in the above optical ICSS in VgluT2-cre control mice,but not in VgluT2-CB1-/-mice.CONCLUSION Activation of CB1 Rs in VgluT2-expressing glutamate neurons produces aversive effects that might explain why cannabinoid is not rewarding in rodents and might also account for individual differences in the hedonic effects of cannabis in humans.
