This minimal stimulation protocol revealed that in slices from IO rats the minimally evoked EPSC amplitude (excluding failures; “potency”) was greater compared to that in slices from sham animals (Figure 8C). The potency for single fiber activation is dependent on quantal size and number of functional synaptic connections. There was a 37% increase in quantal size measured using Sr-evoked mEPSCs (Figure 7), whereas the potency increase was approximately 65%, demonstrating that IO nerve resection additionally causes an find more increase in the number of functional TC synapses in L4. Taken together,

the results show that IO nerve resection causes plasticity of the spared TC input by BMN 673 in vitro increasing both quantal amplitude and number of functional synapses. The present study investigates the mechanisms and sites of plasticity induced

by loss of whisker sensory input in 6-week-old rats using a combined MRI and slice electrophysiology approach. In contrast to the expectation that plasticity at this age is mediated by modification of cortico-cortical inputs, we found that a prominent plasticity of TC input to L4 underlies the robust increase in spared barrel cortex activation detectable by fMRI. This plasticity was due to a selective increase in quantal amplitude and number of functional synaptic contacts at the TC input to L4 stellate cells while maintaining excitatory/inhibitory balance. This combined MRI and slice electrophysiology approach therefore allows for an analysis of sites and mechanisms of plasticity, which could be broadly applied to many paradigms. The results show that TC inputs can mediate plasticity after the end of the previously defined critical period for this input. IO nerve resection was the sensory

manipulation used to induce experience-dependent plasticity in barrel cortex. The IO nerve carries all sensory information from the whiskers, but does not contain motor afferents; therefore, this manipulation results in a complete loss of whisker-dependent sensory input with no loss Amisulpride of motor innervation to the whiskers. The increase in cortical BOLD-fMRI responses after 2 weeks of IO nerve resection in response to electrical stimulation of the spared whisker pad is likely due to increased cortical neuronal activity. Although there are a few examples in which BOLD-fMRI has not been associated with corresponding changes in neuronal activity (Maier et al., 2008 and Sirotin and Das, 2009), a proportional increase of BOLD and neuronal signals has been observed in functional mapping studies across a variety of species including rodent, monkey, and human (Heeger et al., 2000, Logothetis et al., 2001, Ogawa et al., 2000 and Rees et al., 2000), including for somatosensory cortex (Goloshevsky et al., 2008 and Hyder et al., 2002).