Sex-specific changes in voluntary alcohol consumption and nucleus accumbens synaptic plasticity in C57BL/6J mice exposed to neonatal maternal separation

Abstract

The long-term influence of early-life stress on brain neurophysiology has been extensively investigated using different animal models. Among these, repeated maternal separation (RMS) in rodents is one of the most commonly adopted. In this study, we elucidated the long-lasting effects of exposure to postnatal RMS in C57BL/6J adult mice on voluntary alcohol consumption and nucleus accumbens (NAc) neurophysiology. Mice were separated from their dam for 360 min daily from postnatal day 2 (PND2) to PND17, and experiments were then performed in adult (PND60) animals. In addition, as recent evidence showed that circulating estrogens may play a protective role against stress effects on brain function, including the organization and activation of neuronal structures, we also evaluated the effect of a single injection of β-estradiol 3-benzoate (EB) at PND2, which is known to disrupt male sex differentiation, in male RMS mice. The RMS exposure was associated with an increased voluntary alcohol consumption and preference in male mice, but not in female mice or male mice treated with a single injection of EB. Patch clamp experiments conducted in NAc medium spiny neurons (MSNs) revealed that excitatory but not inhibitory synaptic transmission and long-term plasticity of glutamatergic synapses were significantly impaired in male but not in female mice exposed to the RMS protocol. This effect was again prevented in RMS male mice treated with EB. Our findings strengthen the idea of a sex-dependent influence of early-life stress on long-lasting modifications in synaptic transmission and plasticity in brain areas involved in goal-directed behavior and alcohol intake.

Keywords: Alcohol consumption; Early-life stress; Glutamate; Repeated maternal separation; Sex; Synaptic plasticity.