EXPERIENCE-DEPENDENT DEPRESSION OF VIBRISSAE RESPONSES IN ADOLESCENT RAT BARREL CORTEX

A short period of vibrissae deprivation in an adolescent (approximate to 1 month old) rat can lead to depression of the cortical response to stimulation of the regrown vibrissae, In a barrel column representing the deprived vibrissa, depression is greater for neurons located clos e to the barrel column representing the spared vibrissa. One possible explanation is that the spared vibrissa produces heterosynaptic depres sion of the principal vibrissa response (Glazewski & Fox, 1996). To te st this idea further, we compared the effect of depriving all vibrissa e (no heterosynaptic influence at all) with depriving a single vibriss a (maximal heterosynaptic influence expected). In addition we tested t he origin of the depression by recording from subcortical structures. After 7 days' deprivation and 6-8 days' regrowth, we tested the respon ses of barrel cortex cells, thalamic vPm neurons and trigeminal gangli on cells to stimulation of the regrown vibrissae. We found that depres sion was greater in cortex if a single vibrissa had been deprived than if all vibrissae had been deprived. (Average principal vibrissae resp onses in single vibrissae deprived animals were 36% of those in all vi brissae deprived animals for layer II/III and 41% for later IV.) This implicates the spared vibrissae in actively down-regulating responses to the deprived vibrissae. However, some depression could also be prod uced in animals deprived of all vibrissae (layers II/III were 39% and layer IV 74% of control levels). These results indicate that simple wi thdrawal of activation has a depressive effect on responses but that d epression is far greater if some active inputs remain. Neither form of deprivation had an effect on responses to principal vibrissa stimulat ion in the thalamus or trigeminal ganglion however, suggesting that de pression originates in the cortex. Within the cortex, intracortical co nnections seem most affected as the greatest depression was found in l ayers II/III and in layer IV among cells responding at intermediate la tencies (9-14 ms).