IS THERE A BULBAR PACEMAKER RESPONSIBLE O F ULTRADIAN RHYTHM DURING RAPID EYE-MOVEMENT SLEEP

Since there are complex regulations of paradoxical sleep at the supra- pontine level, the chronic pontine preparation appears to be the best model for studying the mechanisms of the ultradian rhythm of PS (tau') . In these preparations, which are ectothermic, tau' is considerably d ependent upon temperature conditions. a) PS never occurs above a centr al temperature (Tc) of 36 degrees C which constitutes the absolute thr eshold for PS. b) If Tc is regulated at a plateau between 34.5 degrees C and 35.5 degrees C, the duration of tau' corresponds to about 60 mi n (circhoral) whereas the duration of PS is 5 min, thus the cyclic rat io: tau'/duration of PS is 12. During deep hypothermia (from 35 degree s C to 25 degrees C), tau' of PS is temperature-compensated. It remain s close to 60 min, so that its Q10 is about 1. c) However, in the same conditions, the duration of PS episodes increases from 5 min to 55 mi n, so that the Q10 of PS is 0.1 (8% at 35 degrees C - 80% at 25 degree s C). These data are discussed in the light of the present theories ex plaining tau' (i.e., the reciprocal inhibition between monoaminergic p ermissive systems and cholinergic executive systems). An increase in P S during hypothermia might be possible provided that it should be prov ed that permissive mechanisms are excited by heat while executive mech anisms would be cold-sensitive. But there are no data on this point. H owever, even this ''differential thermosensitivity hypothesis'' would not explain the striking fixity of tau' between 35 degrees C and 25 de grees C. For this reason, one should hypothetize that there is a tempe rature-compensated oscillator or pacemaker which would act upon both e xecutive and permissive mechanisms. This oscillator would also be cont rolled by metabolic factors as shown by the effect of O-2 and prolacti n.