Repetitive electrical stimulation of X-area and parabrachial lateral nucleus: effects upon ponto-geniculo-occipital activity in the reserpinized cat.

The ponto-geniculo-occipital (PGO) activity is a characteristic field potential of paradoxical sleep, that can be continually induced by reserpine administration. It has been postulated that the X area (XA) and parabrachial lateral nucleus (Pbl) contain the generator cells for the PGO activity. In this study, repetitive electrical stimulation in the XA and Pbl was applied, with the aim of inducing progressive plastic changes in PGO activity, which was recorded from the lateral geniculate nucleus (LGN). Reserpinized cats were used; they were curarized and maintained with artificial respiration. We analyzed the PGO spike frequency at one, five and sixty minutes after stimulation, which was given every 30 minutes for at least 8 consecutive hours. Stimulation of the XA did not produce changes, while that of the Pbl induced a relatively poor progressive increment in the PGO spike frequency. The findings obtained with XA stimulation discard the possibility of inducing functional plastic changes in this region. On the other hand, the response to Pbl stimulation indicates an activation of the PGO spike generator system. These differences suggest that these nuclei have different influence on PGO activity, although it is possible that the responses found in the Pbl were indirect effects, given its anatomical relationships.