Distribution of thalamic nociceptive neurons activated from the tail of the rat

The purpose of the present study was to map systematically in the thalamus the distribution of neurons processing nociceptive information from the tail of the rat. Pentobarbital-anesthetized and gallamine-paralyzed rats were used. Glass microelectrodes were used to record extracellularly from thalamic neurons. Noxious radiant heat stimuli were applied to the tail with a tail-flick apparatus, and the recorded neurons were localized with horseradish peroxidase deposits or by marking electrodes left in situ. A number of 121 neurons were tested of which 45 responded. Of these, 13 were located in the ventrobasal complex (VB), 17 were located in the central lateral nucleus and the parafascicular nucleus of the intralaminar nuclei (ILN). The rest of the responding neurons were located in the posterior group, the reticular thalamic nucleus, and the zona incerta. The nucleus submedius was not examined specifically. It is concluded that the VB and the ILN are two of the most important thalamic nuclei for processing nociceptive information from the tail of the rat.