Inhibitory influences on receptive field size in the dorsal column nuclei

Receptive fields (RFs) of neurons in the dorsal column nuclei (DCN) expand within minutes after the RFs are anesthetized via subcutaneous lidocaine injections (e.g., Pettit and Schwark). The mechanism of this rapid reorganization is of great interest. It has been proposed that such RF expansion results from a decline in inhibition within the DCN that unmasks previously ineffective synapses. To study the role of GABAergic inhibition in the DCN in controlling RF size, we applied by iontophoresis bicuculline methiodide to block gamma-aminobutyric acidA (GABA(A)) receptors and 2-OH-saclofen to block GABA(B) receptors. Blockade of GABA(A) receptors resulted in RF expansions in 79% of the neurons, while blockade of GABA(B) receptors resulted in RF expansions in 53% of the neurons. The effectiveness of receptor blockade in producing RF expansion was not related to neuronal response characteristics. Glutamate application resulted in RF expansions in only 2 of 23 neurons tested, suggesting that RF expansion was not simply due to increased excitability. The modality and adaptation characteristics of the expanded portions of the RFs were similar to those of the original RF. The results of the present study suggest that GABAergic inhibition can play a role in controlling RF size in the DCN, and that both GABA(A) and GABA(B) receptors may be involved in this process.