Sexually dimorphic perineuronal nets in the rodent and primate reproductive circuit

Perineuronal nets are extracellular glycoprotein structures that have been found on some neurons in the central nervous system and that have been shown to regulate their structural plasticity. Until now work on perineuronal nets has been focused on their role in cortical structures where they are selectively expressed on parvalbumin-positive neurons and are reported to restrict the experience-dependent plasticity of inhibitory afferents. Here, we examined the expression of perineuronal nets subcortically, showing that they are expressed in several discrete structures, including nuclei that comprise the brain network controlling reproductive behaviors (e.g., mounting, lordosis, aggression, and social defense). In particular, perineuronal nets were found in the posterior dorsal division of the medial amygdala, the medial preoptic nucleus, the posterior medial bed nucleus of the stria terminalis, the ventrolateral ventromedial hypothalamus and adjacent tuberal nucleus, and the ventral premammillary nucleus in both the mouse and primate brain. Comparison of perineuronal nets in male and female mice revealed a significant sexually dimorphic expression, with expression found prominently on estrogen receptor expressing neurons in the medial amygdala. These findings suggest that perineuronal nets may be involved in regulating neural plasticity in the mammalian reproductive system.