Differential action upon sleep states of ventrolateral and central areas of pontine tegmental field.

In order to study oral pontine mechanisms of the sleep- wakefulness cycle (SWC), modifications in the total amount, frequency, and duration of episodes of wakefulness (W), drowsiness (D), slow sleep (SS) and paradoxical sleep (PS) together with modifications in the hourly distribution of both sleep states were analyzed in 15 adult cats. Three animals were used as sham-operated controls. Six of them, Group I, received unilateral lesions in ventral and lateral areas of the nucleus reticularis pontis oralis (RPO) and rostral nucleus reticularis pontis caudalis (RPC). The remaining 6 cats, Group II, had unilateral lesions in the central part of the same nuclei. After ventrolateral lesions (Group I) decrease of PS and SS occurred, but only PS changes reached statistically significant values; while, on the contrary, a significant increase of SS and PS followed central lesions (Group II). Hourly distribution analysis indicated that in Group I decrease of both sleep states took place mainly at night, while in Group II increase of both SS and PS occurred during day. These results suggest a complex and non- uniform influence of the pontine tegmental area on SWC mechanisms. Effects obtained after unilateral lesions, precisely located in ventral and lateral or central parts, point to the existence of two functionally distinct, although almost overlapping, systems, at this level.