An in vitro electrophysiological and Co2+-uptake study on the effect of infraorbital nerve transection on the cortical and thalamic neuronal activity

Changes of neuronal membrane characteristics in somatosensory barrel cortex and barreloid thalamus were investigated in rats following unilateral tran section of the infraorbital nerve. Kainate induced Co2+-uptake method and i mage analysis were used to assess the Ca2+ permeability of non-NMDA (N-meth yl-D-aspartate) glutamate receptors. Changes in some biophysical parameters of the affected cortical neurons were also investigated by intracellular r ecording in slice experiments. The altered neuronal activity was measured o n days 1, 5 and 14 after surgery. Kainate induced Co2+ uptake increased mar kedly reflecting enhanced Ca2+ permeability of alpha-amino-3-hydroxy-5-meth yl-isoxazole-4-propionate/kainate (AMPA/KAIN)-type receptors. Changes were more pronounced in the cortex than in the thalamus and peaked on the first day following nerve transection. After that, parameters gradually returned to the normal level. However, a small enhancement was still detectable in t he cortex at the end of the 2-week-long observation period. In parallel wit h the increased Co2+-uptake, moderate membrane potential changes, stronger spiking activity and enhanced excitability were characteristic for cortical neurons. The observed alterations in neuronal characteristics underlie the reorganization and regeneration processes following injuries or surgeries. We can conclude that immediate change of the receptive field in the barrel cortex following unilateral nerve transection is based on changes in bioph ysical parameters of the neurons. Altered peripheral activation evokes chan ges in the neuronal activity, thus providing opportunity for a quick synapt ic rearrangement. AMPA/KAIN-type glutamate receptors have a decisive role i n the regulation of these processes. This kind of synaptic plasticity is mo re significant in the cortex than in the thalamus. (C) 1999 Published by El sevier Science B.V. All rights reserved.