Cannabinoid receptor expression at the MNTB-LSO synapse in developing rats.

The organization of developing auditory circuits depends on the elimination of aberrant connections and strengthening of appropriate ones. Endocannabinoid mediated plasticity is a proposed mechanism for this refinement. Here we investigated for the anatomical presence of cannabinoid receptors (CB1R) in the lateral superior olive (LSO) and medial nucleus of the trapezoid body (MNTB) of developing rats. We found that CB1R is present within the LSO and that it colocalized with vesicular glutamate transporter (VGLUT3), a presynaptic marker for MTNB terminals. Both before (P5) and around hearing onset (P12), the expression levels of CB1R were higher in the lateral limb of the LSO than in the medial limb. These results suggest that endocannabinoid signaling can modulate the strength of the developing MNTB-LSO synapse.