Contribution of innate cortical mechanisms to the maturation of orientation selectivity in Parvalbumin interneurons.

The maturation of cortical Parvalbumin-positive (PV) interneurons depends on the interaction of innate and experience-dependent factors. Dark rearing experiments suggest that visual experience determines when broad orientation selectivity emerges in visual cortical PV interneurons. Here, using neural transplantation and in vivo calcium imaging of mouse visual cortex we investigate whether innate mechanisms contribute to the maturation of orientation selectivity in PV interneurons. First, we confirmed earlier findings showing that broad orientation selectivity emerges in PV interneurons by two weeks after vision onset, approximately 35 days after these cells are born. Next, we assessed the functional development of transplanted PV (tPV) interneurons. Surprisingly, 25 days after transplantation (DAT) and more than two weeks after vision onset, we found that tPV interneurons have not developed broad orientation selectivity. By 35 DAT, however, broad orientation selectivity emerges in tPV interneurons. Transplantation does not alter orientation selectivity in host interneurons, suggesting that the maturation of tPV interneurons occurs independently from their endogenous counterparts. Together, these results challenge the notion that the onset of vision solely determines when PV interneurons become broadly tuned. Our results reveal that an innate cortical mechanism contributes to the emergence of broad orientation selectivity in PV interneurons. SIGNIFICANCE STATEMENT Early visual experience and innate developmental programs interact to shape cortical circuits. Visual deprivation experiments have suggested that the onset of visual experience determines when interneurons mature in visual cortex. Here we used neuronal transplantation and cellular imaging of visual responses to investigate the maturation of Parvalbumin-positive (PV) interneurons. Our results suggest that the emergence of broad orientation selectivity in PV interneurons is innately timed.