Selective deletion of the oxytocin gene remodels the number and shape of dendritic spines in the medial amygdala of males with and without sexual experience

Oxytocin has central actions that modulate synaptic plasticity and the occurrence of social behavior in rodents. The posterodorsal medial amygdala (MePD) composes a sexually dimorphic neural circuit for the display of male sexual behavior. Local dendritic spines are notably plastic and affected by context-dependent social stimuli. Here, we examined the effects of the selective deletion of the OT gene (OTKO) in the number and shape of Golgi-impregnated dendritic spines in the MePD of näive and sexually experienced (SexExp) male mice (n = 6 each group). Compared to the control wild-type mice (WT), OTKO näive mice did not differ in the density of dendritic spines, but there was a significant and more intense reduction in the number of spines in the WT/SexExp (∼40%) than in the OTKO/SexExp (∼25%). This structural change had a spine-specific feature. That is, sexual experience induced a decrease in the number of thin (∼50%) and mushroom-like spines (∼35%) at the same time that increased (∼30%) the number of stubby/wide spines. In addition, the OTKO/SexExp animals have more thin and mushroom spines than the WT/SexExp ones (∼25% and 55%, respectively; p < 0.01 in all cases). In conjunction, these novel data indicate that OT participates in the spine remodeling, synaptic refinement, and social stimuli-dependent plasticity in the MePD of male mice.