Long-term habituation to spatial novelty modifies posttrial synchronized sleep in rats

To assess the role of posttrial synchronized sleep in the processing of a nonassociative task, adult male Sprague-Dawley rats with chronically implanted cortical electrodes for EEG recording were exposed to a Làt-maze, and horizontal (HA; corner crossing) and vertical (VA; rearings) activities were monitored during two 10-min test trials made at a 3-h (experiment 1) or 24-h (experiment 2) interval. EEG conventional recording was taken during 3 h under baseline conditions (day 1), and following exposure to the maze (day 2), and analyzed as to the amount (a), number (n), and mean duration (d) of synchronized sleep (SS) episodes followed by wakefulness (SS-->W) or by paradoxical sleep (SS-->PS). In both experiments there was a significant intertrial decrement (long-term habituation: LTH) for horizontal activity (LTH-HA), vertical activity (LTH-VA), and emotionality (LTH-E). In experiment 1, in comparison to baseline values, the posttrial SS-->PS(a) increased, mainly for the appearance of SS-->PS episodes in the 1st h. SS-->W(a) also increased in the first h. Correlative analyses among behavioral and sleep parameters showed that SS-->PS(n) and (d) covaried positively with LTH-HA relative to the entire test, and with LTH-VA relative to the second part of the test in the third h. Negative correlations were present between SS-->PS(n) and (d), and LTH-E. In experiment 2, exposed rats showed a lower SS-->PS(n) in the first hour and an increased SS-->PS(d) in the second hour. No change was observed as to SS-->W episodes.(ABSTRACT TRUNCATED AT 250 WORDS)