Cortical Plasticity Induced by Inhibitory Neuron Transplantation

Inflexible Timing for Flexibility During critical periods in early life, sensory experience molds circuits in the brain. In the visual cortex, blurring or occluding vision in one eye triggers a rapid reorganization of neuronal responses known as ocular dominance plasticity. The critical period for this plasticity depends on inhibitory neurotransmission. Southwell et al. (p. 1145) show that by transplanting embryonic precursors of inhibitory neurons into mice, a period of ocular dominance plasticity can be induced after the end of the normal critical period. These observations suggest that transplantation of inhibitory neurons has therapeutic potential for brain repair and for treating neurological disorders and inducing periods of brain plasticity. Plasticity in the mouse brain’s visual cortex can be re-induced by neurons embedded by an earlier transplantation. Critical periods are times of pronounced brain plasticity. During a critical period in the postnatal development of the visual cortex, the occlusion of one eye triggers a rapid reorganization of neuronal responses, a process known as ocular dominance plasticity. We have shown that the transplantation of inhibitory neurons induces ocular dominance plasticity after the critical period. Transplanted inhibitory neurons receive excitatory synapses, make inhibitory synapses onto host cortical neurons, and promote plasticity when they reach a cellular age equivalent to that of endogenous inhibitory neurons during the normal critical period. These findings suggest that ocular dominance plasticity is regulated by the execution of a maturational program intrinsic to inhibitory neurons. By inducing plasticity, inhibitory neuron transplantation may facilitate brain repair.