Potentiation of glutamatergic synaptic transmission onto lateral habenula neurons following early life stress and intravenous morphine self‐administration in rats

Early life stress presents an important risk factor for drug addiction and comorbid depression and anxiety through persistent effects on the mesolimbic dopamine pathways. Using an early life stress model for child neglect (a single 24 h episode of maternal deprivation, MD) in rats, recent published works from our lab show that MD induces dysfunction in the ventral tegmental area and its negative controller, the lateral habenula (LHb). MD‐induced potentiation of glutamatergic synaptic transmission onto LHb neurons shifts the coordination of excitation/inhibition (E/I) balance towards excitation, resulting in an increase in the overall spontaneous neuronal activity with elevation in bursting and tonic firing, and in the intrinsic excitability of LHb neurons in early adolescent male rats. Here, we explored how MD affects intravenous morphine self‐administration (MSA) acquisition and sucrose preference as well as glutamatergic synaptic function in LHb neurons of adult male rats self‐administering morphine. We found that MD‐induced increases in LHb neuronal and glutamatergic synaptic activity and E/I ratio persisted into adulthood. Moreover, MD significantly reduced morphine intake, triggered anhedonia‐like behaviour in the sucrose preference test and was associated with persistent glutamatergic potentiation 24 h after the last MSA session. MSA also altered the decay time kinetics of α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA) receptor (AMPAR) currents in LHb neurons of control rats during this time period. Our data highlight that early life stress‐induced glutamatergic plasticity in LHb may dampen the positive reinforcing and motivational properties of both natural rewards and opioids, and may contribute to the development of anhedonia and dysphoric states associated with opioids. In this study, we demonstrate that early maternal deprivation (MD) in rats alters morphine self‐ administration acquisition, and decreases sucrose preference, and is associated with persistent MD‐induced LHb glutamatergic synaptic plasticity that supports LHb hyperactivity. This persistent MD‐induced glutamatergic potentiation in LHb neurons may contribute to anhedonia to natural rewarding stimuli as well as alter the reinforcing and motivational properties of opioids, potentially facilitating opioid‐related behaviors in adult male rats.