Intracranial self-stimulation in the parafascicular nucleus of the rat

A behavioral analysis of intracranial self-stimulation was provided for parafascicular nucleus. To evaluate whether intracranial self-stimulation in this nucleus could be site-specific and to determine if the positive sites are the same parafascicular areas that facilitate learning when stimulated, rats were tested via monopolar electrodes situated throughout the parafascicular nucleus. Animals were trained to self-stimulate by pressing a lever in a conventional Skinner box (1-5 sessions). Twenty-two of the 42 animals included in the study, had the electrode at the parafascicular nucleus. Only two of them showed intracranial self-stimulation. Histological analyses indicated that the latter rats had the electrode implanted at the anterior area of the medial parafascicular. Other two animals also showed intracranial self-stimulation but they had the electrode in a more posterior brain region, between the Dark-schewitsch nucleus and the red nucleus. The animals implanted at the parafascicular showed higher response rates than the other two rats. These results confirm that: (a) the anterior region of the medial parafascicular is a positive site for stable and regular intracranial self-stimulation behavior, and (b) these positive sites do not coincide with the parafascicular regions related to learning improvement.