Expansion of receptive fields in raccoon somatosensory cortex in vivo by GABA A receptor antagonism: implications for cortical reorganization

Abstract

The effect of antagonism of GABA(A) receptors on the receptive fields of raccoon primary somatosensory cortical neurons was tested using microiontophoretic administration of bicuculline methiodide (BMI). The size of cutaneous receptive fields was examined using minimal suprathreshold mechanical stimulation before, during, and after BMI administration. In 65 of 102 rapidly adapting neurons, BMI produced a clear expansion of the receptive field. The mean increase in receptive-field size was 286%. The receptive fields on the distal digit, which were initially smaller, showed smaller increases in absolute area than more proximal receptive fields, but the percentage increase did not vary with location. Greater expansion was seen in superficially located neurons than in those below 800 microm. Of particular significance was the finding that the expansion of receptive fields produced by BMI never extended from one digit onto an adjacent digit or onto the palm, even when the original receptive field was at the base of a digit. This finding indicates that intracortical GABAergic inhibition is insufficient to explain cortical reorganization following digit amputation.

Nursing-Induced Somatosensory Cortex Plasticity: Temporally Decoupled Changes in Neuronal Receptive Field Properties Are Accompanied by Modifications in Activity-Dependent Protein Expression

“…Therefore, our data suggest that, unlike GABA inhibition, NMDA-mediated glutamatergic excitation was not critically involved in RF size reshaping. This hypothesis is in keeping with results showing that L-glutamate injected within the SI cortex increased cortical excitability but did not change RF sizes (Tremere et al, 2001a).…”

Attentional Modulation of Spatial Integration of Pain: Evidence for Dynamic Spatial Tuning

“…RFs can be reshaped by inhibitory interneurons (Foeller et al, 2005) and/or by recurrent excitatory connections (Finnerty et al, 1999). For example, local administration of GABA antagonists can change the size of the RFs of dorsal horn (Yokota and Nishikawa, 1982) and SI (Tremere et al, 2001) neurons. RF tuning can be modulated by CNS circuits that convey information about training and/or attentional requirements (Gilbert, 1998).…”

Comparison of reorganization of the somatosensory system in rats that sustained forelimb removal as neonates and as adults

“…An important component of cortical reorganization appears to be an intracortical network of GABAergic neurons (Tremere et al, 2001a). However, modulation of the intracortical GABAergic network cannot solely account for the larger shifts in representational boundaries associated with a digit or limb amputation (Tremere et al, 2001b). Alternatively, both subcortical and cortical mechanisms may be involved in defining the reorganization of SI after a peripheral injury.…”