Intracranial self-stimulation in the thalamus of the rat

Rats were tested for intracranial self-stimulation (ICSS) via bipolar electrodes situated throughout the thalamus. Of 112 animals in the study, 55 met the criteria for ICSS, with scores ranging from 55 to 921 bar-presses in a 15 minute session. A map of both positive and neutral placements is presented. Positive sites for ICSS were found in all aspects of the mediodorsal nucleus, except for the central segment. The ventromedial nuclear complex was also a positive area of ICSS, with the exception of the submedial nucleus (nucleus gelatinosus). Each of the intralaminar nuclei (central medial, parafascicular, paracentral, and central lateral) supported ICSS, as did each of the midline nuclei (rhomboid, paratenial and paraventricular). No placements were found in the nucleus reunions. Both “major” relay nuclei, the ventrobasal and ventrolateral, supported ICSS; but neither the laterodorsal nor the lateral posterior nuclei had positive sites. Positive sites were found in the anterior and posterior nuclear groups, as well as in the paraventricular gray area of the caudal thalamus. As a general rule, ICSS scores appeared to be higher as the electrode placements approached the midline. Sites in which no positive placements were seen included the reticular nucleus, as well as the stria medularis, the mammillothalamic tract, and the fasciculus retroflexus.