Influence of paradoxical sleep deprivation on the intermediate stage of sleep in the rat.

In the rat, paradoxical sleep (PS) is preceded by a short-lasting stage characterized by high amplitude cortical spindles and low frequency hippocampal theta rhythm. This intermediate stage (IS) is massively extended at the expense of PS by barbiturates and benzodiazepines. To further study the relationship between the IS and PS, six rats were PS deprived for 48 h by sitting on one of three small platforms surrounded by water. A control group of six other rats remained in dry cages with shavings. After 24 h PS deprivation the latency of IS occurrence increased, was unchanged after 48 h deprivation and decreased during recovery on shavings after 52 h deprivation. The total IS duration, number of episodes and mean duration per episode were unchanged during deprivation but increased during recovery. This recovery was characterized by an increase in the number of PS episodes and the total duration while the latency of PS occurrence decreased. The frequency of theta rhythm, unchanged for PS, increased for the IS during deprivation and recovery. In conclusion, the IS did not substitute for PS after selective deprivation.