Cortical and subcortical plasticity of the rat vibrissal representation following chronic subtotal deafferentation

De-Meral Liu, University of Pennsylvania


A major impediment to understanding observed plasticity changes in the neocortex has been untangling the contributions of cortical and subcortical mechanisms. Activity-dependent neocortical plasticity may reflect autonomous intracortical plasticity or may be a passive reflection of subcortical alterations. A unilateral spared C3 mystacial vibrissa (SC3), in neonatal rat was used to study cortical and subcortical plasticity following a chronic subtotal deafferentation using several techniques. Following chronic deafferentation, the functional (metabolic) representation of the SC3 vibrissal stimulation, demonstrated using the (($\rm\sp{14}C$)-2-deoxyglucose) method, in the posterior medial barrel subfield (PMBSF) of the somatosensory cortex was dramatically enlarged by 403%, and moderately increased in the thalamic ventroposteriormedial nucleus by 212%, but increases in the brainstem trigeminal complex were not significant. In contrast, only a moderate anatomical expansion (164%) was observed in the layer IV SC3 barrel using the cytochrome oxidase technique. Multi-dimensional and multi-modality analysis demonstrated a radial expansion in the SC3 functional representation in the PMBSF and anatomical elongation of the SC3 barrel into the neighboring C2 and C4 regions. These results indicate that both intracortical and thalamic-dependent plasticities contribute to this chronic deafferentation-produced anatomical and functional changes in the SC3 PMBSF. The anatomical expansion of the SC3 barrel observed in cytochrome oxidase studies suggests that deafferented C2 and C4 barrel structures are underdeveloped but the SC3 barrel structure invades into these territories. Analysis of thalamic retrograde labeling patterns following injection of horseradish peroxidase into the PMBSF indicated that expansion of SC3 thalamocortical projections was minimal and suggest that alterations in intracortical signal processing may underlie the greatest part of the expanded functional SC3 representation. Analysis of evoked multiunit extracellular response of the SC3 PMBSF revealed significant alterations in the response latency and amplitude that suggest alterations in signal processing characterized by decreased intracortical inhibition and a potentiation of excitatory intracortical connectivities. Immunohistochemical analysis of glutamic acid decarboxylase labeling revealed a down-regulation in deafferented regions of the SC3 PMBSF and increased GAD labeling intensity in the SC3 barrel, consistent with the presence of decreased intracortical inhibition.

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Recommended Citation

Liu, De-Meral, "Cortical and subcortical plasticity of the rat vibrissal representation following chronic subtotal deafferentation" (1995). Dissertations available from ProQuest. AAI9532235.