At this time, the mechanisms underlying microbiota regulation of behavioral responses remain poorly understood. In an attempt to gain some insight into the differences in important brain structures in mice with depleted gut microbiota, we profiled multiple transcripts related to important synaptic plasticity functions involved in cocaine-mediated behaviors. To accomplish this, we examined mice treated with antibiotics and/or 7 days of cocaine (Fig. 1a), and examined transcripts in the nucleus accumbens (NAc)—a critical brain reward region—24 hours after the final injection. As previous studies examining changes in limbic brain structures after alterations in gut bacteria had reported changes in levels BDNF transcript and protein, albeit in other brain regions4171819, we first examined levels of Bdnf transcript as well as the transcript encoding the BDNF receptor – Tyrosine receptor kinase B (Ntrk2). Levels of Bdnf in the NAc were increased by treatment with antibiotics (Fig. 6a - F(1,37) = 7.308; p = 0.01), but there was no main effect of cocaine (F(1,37) = 0.6841; p = 0.41) or significant treatment interaction (F(1,37) = 2.004; p = 0.17). When levels of Ntrk2
