Switch time-point for rapid experience-dependent changes in zinc-containing circuits in the mouse barrel cortex

It has been previously demonstrated that in the mouse barrel cortex, synaptic zinc is regulated by sensory experience. In adult mice, cutting selected vibrissae produced a rapid but transient elevation of synaptic zinc in the corresponding barrels several hours later, whereas in 8 day-old animals this procedure did not affect synaptic zinc. In the present study, we wished to determine the postnatal age at which zinc-containing terminals gain the ability to respond rapidly to a restriction of sensory input. We therefore examined the effects of 1-day sensory deprivation starting at different postnatal ages. For this purpose we unilaterally trimmed all rows of vibrissae, except for row C, and we then visualized synaptic zinc in the barrel cortex 24h later. Up to postnatal day 15 such procedure had no effect on the level of synaptic zinc. However, beginning at postnatal day 16, 1-day sensory deprivation produced an increase in synaptic zinc within hollows of deprived rows of barrels as compared to non-deprived rows. These results show that during development there is a specific time-point after which zinc-containing circuits may respond rapidly to altered sensory inputs. A comparison of these findings with previous results obtained after chronic sensory deprivation suggests that a specific time window exists in development for persistent alterations in zinc-containing circuits.