Neonatal capsaicin treatment modulates experience-dependent plasticity in the rat barrel cortex.

Previous studies have reported that capsaicin-induced C-fiber depletion results in expansion of low threshold somatosensory mechanoreceptive fields. Here we used this paradigm to investigate its effect on experience-dependent plasticity in the barrel cortex of rats. All but the D2 vibrissa were first plucked on postnatal day 0 (P0), P5, or P8, and kept plucked for a period of 30 days before being allowed to regrow for 7-9 days prior to the recording session. To assess receptive field characteristics the spared D2 principal whisker (PW) and the deprived D1 adjacent whisker (AW) were moved either singly or in concert, neuronal responses being recorded in layers IV and V of the D2 barrel. In vehicle-treated rats, PW-evoked ON responses (layer IV) were increased only in those animals that first had their vibrissae plucked on P0, whereas AW-evoked ON responses (layers IV and V) were decreased in the P0, P5, and P8 groups. In the capsaicin-treated animals, PW-evoked ON responses (layer IV) were increased in all three groups, but no decrease was recorded in the AW-evoked ON (layers IV and V) responses. In the vehicle- and capsaicin-treated animals, the greatest decrease in inhibitory interactions was observed in the P5 and P0 groups, respectively. These findings indicate that, following the induction of experience-dependent plasticity, the resultant changes in excitatory and integrative circuits can be further influenced by C-fiber depletion.