Effect of unilateral deafferentation on extracellular potassium concentration levels in rat thalamic nuclei

The autotomy performed by rats after unilateral section of the dorsal roots corresponding to the brachial plexus was frequently attributed to an abnormal painful sensation felt in the peripheral deafferented area. We studied the values of potassium (K +) extracellular concentration ([K +] e) in thalamic nuclei of somatic projection in this animal model of deafferentation pain. Potassium concentrations were measured with microelectrodes sensitive to K + (K +-ISM). When such microelectrodes are gradually inserted into the thalamus, a sudden transient increase of K + concentration appears after each step lasting for about 30 s. This is followed by a stabilization of K + values, which is present for several hours. We measured this stable concentration of K + (resting [K +] e) for 3–5 min in different nuclei of the somatic projection to the lateral thalamus of controls and deafferented groups of adult rats under Equithesin anaesthesia. The following thalamic nuclei were explored: the ventral posterior medial and lateral (VPM and VPL) and the adjacent posterior oral (PO) as well as the lateral dorsal (LD) and posterior (LP) and ventral anterolateral (VAL). In the control group (12 rats), the mean values of resting [K +] e expressed in mmol/l in these nuclei were between 3.26 and 3.62. All these values of the K + concentration were significantly higher than those in the cerebrospinal fluid for P