Abstract
Neonatal whisker trimming followed by adult whisker regrowth leads to higher responsiveness and altered receptive field properties of cortical neurons in corresponding layer 4 barrels. Studies of functional thalamocortical (TC) connectivity in normally reared adult rats have provided insights into how experience-dependent TC synaptic plasticity could impact the establishment of feedforward excitatory and inhibitory receptive fields. The present study employed cross-correlation analyses to investigate lasting effects of neonatal whisker trimming on functional connections between simultaneously recorded thalamic neurons and regular-spike (RS), presumed excitatory, and fast-spike (FS), presumed inhibitory, barrel neurons. We find that, as reported previously, RS and FS cells in whisker-trimmed animals fire more during the earliest phase of their whisker-evoked responses, corresponding to the arrival of TC inputs, despite a lack of change or even a slight decrease in the firing of thalamic cells that contact them. Functional connections from thalamus to cortex are stronger. The probability of finding TC-RS connections was twofold greater in trimmed animals and similar to the frequency of TC-FS connections in control and trimmed animals, the latter being unaffected by whisker trimming. Unlike control cases, trimmed RS units are more likely to receive inputs from TC units (TCUs) and have mismatched angular tuning and even weakly responsive TCUs make strong functional connections on them. Results indicate that developmentally appropriate tactile experience early in life promotes the differential thalamic engagement of excitatory and inhibitory cortical neurons that underlies normal barrel function.