NOCICEPTIVE RESPONSES OF THE LATERAL THALAMIC NUCLEUS EVOKED BY PINCH IN ANESTHETIZED RATS

Abstract

Pinch was used as a noxious stimulus and applied to the tail and hindlimbs of rats to investigate the nociceptive responsiveness of neurons in the lateral thalamus. Pinch stimuli were applied with calibrated pincher, and glass micropipettes filled with 3 M NaCl served as recording electrodes. The lateral thalamus of six rats under ketamine anesthesia was probed, including the ventrobasal (VB) complex and the posterior thalamic nucleus ( Po ), while the noxious stimulus was applied. Neuronal responses in the lateral thalamus were identified with the aid of an audio monitoring device and an oscilloscope, and several inclusion criteria had to be met. A total of 168 neurons were studied across the ventral posterolateral thalamic nucleus (VPL), ventral posteromedial thalamic nucleus (VPM), and Po of the thalamus. Of the neurons assessed in the lateral thalamus, 38 responded to the nociceptive stimuli, and most were located within the Po region of the thalamus. Very few were located in the VB. The number of responsive neurons in the anterior region of the lateral thalamus was significantly greater than the number of responsive neurons in the posterior region of the lateral thalamus. This finding indicates that the anterior region of the lateral thalamus, especially the Po area, may respond more vigorously to noxious stimuli than the posterior region.