HYPEROXIA INCREASES PARADOXICAL SLEEP RHYTHM IN THE PONTINE CAT

Pontine cat is an ectothermic preparation, whose central temperature c an artificially be lowered from 36 degrees C to 26 degrees C; this gra dual hypothermia is accompanied by a dramatic increase in paradoxical sleep (PS). Two main hypotheses might explain this result: executive s ystems of PS might be switched on gradually by cold-sensitive thermode tectors, whereas inhibitory monoaminergic mechanisms appear to be warm -sensitive. On the other hand, energy saving mechanisms peculiar to hy pothermia might promote PS appearance. Indeed, in normal animals, PS i s selectively suppressed both by hyperthermia and hypoxia. The inhibit ory effect of hypoxia might explain why hypothermia, which protects th e brain against hypoxic alterations, might facilitate PS. If this last hypothesis is correct, the putative increase in cerebral oxygen suppl y might increase PS. For this reason, we submitted eight pontine carot id-deafferented cats, kept at the same central temperature (34 +/- 0.5 degrees C: temperature clamp) to periodic hyperoxia (PaO2 = 58 +/- 7 kPa) or room air (PaO2 = 17 +/- 2 kPa) alternatively during 4- or 12-h periods. Hyperoxia induced an 85% increase in PS, mainly due to an in crease in PS rhythm (PS cycle duration was 65 +/- 4 min in normoxia an d 45 +/- 4 min in hyperoxia, p < 0.0001). In five animals, after hyper oxia, PS cycle returned gradually back to control values in 4 to 12 h. These findings show that PS is exquisitely sensitive to conditions th at impair oxidative metabolism. The role of cholinergic executive PS s ystems as putative metabolic-sensitive neurons remains to be establish ed. (C) 1998 Elsevier Science B.V. All rights reserved.