Tullia Cianci

Brain circulation during sleep and its relation to extracerebral hemodynamics

Regional cerebral blood flow (rCBF) was measured in rabbits during the sleep-waking cycle, using radioactive microspheres. rCBF does not change significantly in the transition from wakefulness (W) to synchronized sleep (SS), while it significantly increases during desynchronized sleep (DS). No correlation was found between CBF changes and changes in cardiac output or regional blood flows in the transition from SS to DS. This suggests that the CBF increase in DS is not relevantly affected by changes in extracerebral hemodynamic factors.

Brain blood flow and extracerebral carotid circulation during sleep in rat.

Cerebral blood flow (CBF) and blood flow (BF) in extracerebral head structures were measured during the sleep-wake cycle in rats using radioactive microspheres. While no statistically significant changes occurred in the transition from Waking to quiet sleep (also referred to as synchronized or non-REM Sleep), CBF increased significantly in active sleep (AS, also referred to as desynchronized or REM Sleep) in all structures considered, with the sole exception of the cerebellum. In extracerebral head structures, no significant state-dependent BF changes were found. Factor Analysis however extracted a common factor accounting for BF variability in the external carotid circulation. This factor was uncorrelated with CBF changes in AS, suggesting independent regulation of the two vascular beds in this sleep state.

Inguinal subcutaneous temperature changes in cats sleeping at different environmental temperatures

Abstract In unrestrained cats carrying chronically implanted electrodes and transducers inguinal subcutaneous temperature was studied during sleep at different environmental temperatures. Statistical analysis of the data shows that the slopes of inguinal subcutaneous temperature are negatively and positively correlated with environmental temperature during slow-wave and fast-wave sleep respectively. No correlation is observed between the slope of inguinal subcutaneous temperature and the slope of hypothalamic temperature during fast-wave sleep. The slope of hypothalamic temperature during fast-wave sleep is primarily correlated with hypothalamic temperature itself. The evidence suggests that fast-wave sleep is characterized by a change from homoiothermic to poikilothermic regulation probably caused by an alteration in the hypothalamic control of homeostasis during this phase of sleep.

Brain Capillary Perfusion during Sleep

Brain capillary perfusion was evaluated in the different states of the wake–sleep cycle—quiet wakefulness (QW), quiet sleep (QS), and active sleep (AS)—in rats. The extent of the perfused capillary network was determined by intravascular distribution of a fluorescent marker, Evans blue (EB); it remained unchanged across the three behavioral conditions, QW, QS, and AS. The anatomical network was assessed by alkaline phosphatase (AP) endothelial staining, which is known to underestimate the number of existing capillaries. The resulting number of AP profiles were, therefore, significantly lower than the number of EB profiles, but the percentage of AP-stained capillaries that were perfused (96%) was also unchanged across the behavioral conditions. The results indicate that no capillary recruitment accompanies the wake–sleep cycle. Capillary surface area is a relevant factor in determining exchanges across the blood–brain barrier. In the absence of capillary recruitment (relative constancy of the surface area), the CBF changes during sleep should preferentially affect flow-limited with respect to diffusion-limited transport.

Shivering during sleep: Relationship between muscle blood flow and fiber type composition

The present study considers in rabbit: i) the relationship between muscle blood flow (BF) increase and fiber-type composition during shivering; ii) the influence of the vigilance states (Quiet Wakefulness, QW; Synchronized Sleep, SS; Desynchronized Sleep, DS) on this relationship. The results show that muscle BF increase during shivering is proportional to the slow-twitch oxidative (SO) fiber component in QW and SS; in DS the proportionality is lost. This is in accordance with the disappearance of shivering, together with all thermoregulatory effector responses, in this sleep state. Another muscle circulation pattern occurring at low ambient temperature, the relationship between BF increase and muscle depth, also disappears in DS. This confirms that the integrative control of muscle circulation, like other integrative mechanisms, is impaired during DS.

Sleep-Related Brain Activation Does Not Increase the Permeability of the Blood-Brain Barrier to Glucose

We compared blood-brain barrier (BBB) permeability to glucose between quiet wakefulness and rapid-eye-movement (REM) sleep to assess whether changes in BBB permeability play a role in coupling glucose supply to the physiologic metabolic needs of the brain. Male Sprague-Dawley rats were prepared with electrodes for wake-sleep state scoring and with arterial and venous catheters. Using the single-pass, dual-label indicator method, unidirectional glucose extraction by the brain and cerebral blood flow (CBF) were simultaneously measured during states of quiet wakefulness (n = 12) or REM sleep (n = 7). The product of BBB surface area and permeability to glucose (PS product) was computed in each state. During REM sleep, CBF significantly exceeded that during quiet wakefulness in all regions but the cerebellum, whereas the difference in the PS product between quiet wakefulness and REM sleep was not statistically significant in any brain region. In the brain as a whole, CBF significantly increased 29% from quiet wakefulness to REM sleep, while a nonsignificant 0.8% increase occurred in the PS product. During REM sleep, the increase in CBF indicates a higher rate of brain glucose consumption than in quiet wakefulness, given the tight flow-metabolism coupling in the brain. Therefore, these data show that modulation of BBB permeability to glucose is not a mechanism that provides ‘energy on demand’ during the physiologic brain activation characterising REM sleep.

Influence of brown adipose tissue on deep cervical temperature during sleep in the young rabbit

In young rabbits the slope of the temperature in the deep cervical region close to brown adipose tissue increased during desynchronized sleep at low ambient temperature. No increase occurred at neutral ambient temperature. In control rabbits (after disappearance of brown adipose tissue), the slope of deep cervical temperature did not increase during desynchronized sleep at low or neutral ambient temperatures.

Interactions between temperature regulation and emotional arousal in the rabbit.

SummaryIn our study we examined, in the rabbit, the interactions between temperature regulation and the state of increased vigilance and emotional arousal induced by a Classical Aversive Conditioning Procedure. A Delay Conditioning Procedure was used. The Conditioned Stimulus (CS) was a 1350 Hz, 85 dB tone, the Unconditioned Stimulus (UCS) a 1 mA, 0.5 s shock. Testing sessions were run at different ambient temperatures from 5 to 30 ° C.At all ambient temperatures considered the CS induced desynchronisation of the EEG and stereotyped changes in all the autonomic variables studied. Hypothalamic temperature (Thy) first increased, then decreased below its initial value, whereas ear skin temperature (Ts) showed opposite changes. Respiratory frequency (RF) initially increased, then tended to revert to its original value. The average time course of this complex pattern was 300 s from the CS. The overall effect of the CS sequence in a session was a significant decrease in Thy and Ts and a significant increase in RF compared to control values at the beginning of the session. Both in the short (single trial) and long terms (whole session) the autonomic responses induced by the emotional stress (polypnoea and vasoconstriction) were not coherent from the point of view of thermoregulation. The hypothesis of an effect of emotional arousal in shifting set point temperatures can therefore be discarded in favour of a direct action of emotional stress on effector controllers for respiration and vasomotion.

Spinal cord blood flow changes during the sleep-wake cycle in rat.

Regional spinal cord blood flow was measured in rats during the sleep-wake cycle with the use of radioactive microspheres. Spinal cord blood flow decreases from wakefulness to quiet (synchronized) sleep while increasing in active (desynchronized) sleep. Blood-flow changes depend on changes in vascular resistance whose mechanisms have yet to be elucidated. Blood-gas tension or mean arterial pressure, however, do not play a relevant causal role.

Muscle blood flow changes during sleep as a function of fibre type composition

SummaryIn 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, fasttwitch 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.