Functional Adaptation in the Brain Habenulo–Mesencephalic Pathway During Cannabinoid Withdrawal

During cannabinoid withdrawal, the mesolimbic reward system shows reduced function, which may drive aversive states leading to relapse. The lateral habenula (LHb) exerts negative control over the ventral tegmental area (VTA) via the rostromedial tegmental nucleus (RMTg), suggesting a convergence point for opponent processes. In adult male rats treated with THC (15 mg/kg, i.p.) twice daily for 6.5–7 days, rimonabant-precipitated withdrawal reduced VTA dopamine neuron firing and burst activity, prolonged RMTg-evoked inhibition, and depressed spontaneous activity in both RMTg and LHb neurons. The authors propose that functional changes in the habenulo–mesencephalic circuit contribute to substance use disorders.

Study at a glance

Abstract

The mesolimbic reward system originating from dopamine neurons in the ventral tegmental area (VTA) of the midbrain shows a profound reduction in function during cannabinoid withdrawal. This condition may underlie aversive states that lead to compulsive drug seeking and relapse. The lateral habenula (LHb) exerts negative control over the VTA via the GABA rostromedial tegmental nucleus (RMTg), representing a potential convergence point for drug-induced opponent processes. We hypothesized that the LHb–RMTg pathway might be causally involved in the hypodopaminergic state during cannabinoid withdrawal. To induce Δ9-tetrahydrocannabinol (THC) dependence, adult male Sprague–Dawley rats were treated with THC (15 mg/kg, i.p.) twice daily for 6.5–7 days. Administration of the cannabinoid antagonist rimonabant (5 mg/kg, i.p.) precipitated a robust behavioral withdrawal syndrome, while abrupt THC suspension caused milder signs of abstinence. Extracellular single unit recordings confirmed a marked decrease in the discharge frequency and burst firing of VTA dopamine neurons during THC withdrawal. The duration of RMTg-evoked inhibition was longer in THC withdrawn rats. Additionally, the spontaneous activity of RMTg neurons and of LHb neurons was strongly depressed during cannabinoid withdrawal. These findings support the hypothesis that functional changes in the habenulo–mesencephalic circuit are implicated in the mechanisms underlying substance use disorders.