This is a continuing project, i.e. the activity of single neurons of the limbic system (cingulate, septum and hypothalamus) was recorded with the microelectrode technique. Unit activity was markedly augmented by morphine and the increased activity was antagonized by subsequent i.v. diazepam. A few experiments were performed with phenothiazine compounds, due to brain tissue movement during hypotension produced by chlorpromazine or perphenazine, neuronal activity was difficult to record. The tentative results show that phenothiazine did not antagonize morphine-induced neuronal activity. It is planned to apply the neuroleptics via the microiontophoretic technique to avoid hypotensive effects. The following new projects are proposed: I. Studies on the Centrally Acting Antihypertensive Agents on Medullary Vasomotor Neurons of the Cat. A specific method was designed to identify cardiovascular (CVN) neurons. By using microiontophoresis the CVNs were depressed by clonidine, a centrally acting hypotensive agent. This work will be extended to other antihypertensive agents. II. Electrical Stimulation of the Ventral Surface of the Brainstem on Arterial Blood Pressure. Faldberg (1972) reported that when drugs are applied to a localized portion of the ventral brainstem surface, a marked increase in blood pressure was produced. It is planned to explore this region by electrical stimulation and to investigate the significance of these findings.