Medullary-induced alterations in intracranial self-stimulation from the substantia nigra

The intracranial electrical self-stimulation (ICSS) from the substantia nigra (SN) was reduced by simultaneous stimulation of the nucleus of the solitary tract (NTS) in cats. This effect varied with the current intensity and the sequence of NTS stimulation paired with the rewarding SN stimulation. Namely, NTS stimulation preceding the SN stimulation was more effective in lessening ICSS than that following the SN stimulation. Both SN and NTS stimulations produced significant cardiorespiratory effects, when they were applied separately. However, the cardiorespiratory responses to NTS stimulation have no substantial role in altering ICSS, because vagotomy abolished the heart rate effects of NTS stimulation but caused no change in its reducing effect on ICSS. Moreover, no statistically significant correlation was found between the blood pressure changes and the decrease in response rate. These data are interpreted as suggesting that the NTS stimulation may reduce centrally the rewarding value ordinarily derived from ICSS at the SN.