Exp Brain Res (1989) 74:549-554 E ,x _'mental BranResearch 9 Springer-Verlag 1989 Muscle blood flow changes during sleep as a function of fibre type composition P. Lenzi, T. Cianci, G.S.Leonardi, A. Martinelli, and C. Franzini Institute of Human Physiology,University of Bologna, Porta S. Donato 2, 1-40127 Bologna, Italy Summary. In rabbits blood flow was measured in 19 muscles with the radioactive microsphere technique. Fibre type composition (SO, slow-twitch oxidative; FOG, fast-twitch oxidative-glycolytic; FG, fast- twitch glycolytic) was determined histochemically for the same muscles. While no significant changes occur in the transition from quiet wakefulness (QW) to synchronized sleep (SS), in desynchronized sleep (DS) blood flow decreases in SO and increases in FOG and FG fibres. These changes may be related to the changes in motor activity characteristic of DS: muscle atonia and twitches, respectively. Key words: Sleep - Muscle atonia - Twitches - Muscle blood flow - Muscle fibre composition DS. Moreover, vasomotor control of peripheral circulation is altered during this sleep state (Mancia et al. 1971). Both these factors are likely to affect muscle circulation. Further, the logic underlying muscle blood flow regulation during sleep could operate according to muscle groups (topographical or functional grouping) or according to muscle fibre type (fibre composition in different muscles). The present experiments address these issues. Given the correspondence between muscle fibre types and anatomo-functional properties of moto- neurons (Burke 1981), indirect evidence concerning motoneuron activation during sleep is also discussed briefly. Introduction Two different conditions have been distinguished in the sleep process: one (synchronized sleep, SS) characterized by a closed loop mode of operation in most physiological controls, the other (desyn- chronized sleep, DS), characterized by the opening of most control loops (poikilostatic condition) (Par- meggiani 1980). This functional dichotomy makes the sleep cycle an especially suitable two-state model for studying physiological regulations. As far as the control of muscle circulation is concerned, this model might allow the distinction between peripheral fac- tors, which only change quantitatively during sleep, and central vasomotor patterns, which instead are likely to be state-dependent in the different states of the sleep cycle. Changes in motor system activity (atonia and muscle twitches) represent a distinctive feature of Offprint requests to: P. Lenzi (address see above) Methods Measurements of radioactivity Radioactivitywas measured with a well-typegamma counter (The Nucleus, Oak Ridge, TN, modified from model 1000). Isotope separation was performed by computer using differ- ent distribution matrices for the different heights of samples within the vials. The batches of microspheres (NEN, Boston, MA, 15 + 1 ~tm, labelled with 57Co, n3Sn or 85Sr) after being checked for proper labelling, size, and lack of fragmentation and/or aggregation, were kept in saline with 0.01% Tween 80 and an antifungal agent (amphotericin B). Experimental procedure Twelve New Zealand white rabbits (3200-3800 g) were prepared under general anaesthesia (sodium pentobarbitone 40 mg/kg s.c. 45 rain after premedication with flunitrazepam 0.5 mg/kg i.m.) (Guillaume et al. 1982) and with sterile procedures. In addition to electrodes for standard electroencephalographic, electromyo- graphic and electrooculographic recordings, two Silastic catheters (0.63 mm i.d., 1.17 mm o.d.) were positioned; one in the left ventricle via the common carotid artery, under continuous pressure monitoring (Bhattacharya and Beilin 1980), and the other