Day-night differences in ventilation, metabolism, and body temperature during normoxia, hypoxia and hypercapnia in the awake adult rat

grantor: University of TorontoDuring normoxia, metabolism and body temperature were significantly $(P<0.05)$ higher at 10 pm than at 10 am, and ventilation and tidal volume remained unchanged while respiratory frequency was significantly higher at 10 pm than at 10 am. At 10 am, metabolism decreased in response to hypoxia, but body temperature did not suggesting that the thermic and metabolic responses to hypoxia are independently controlled. Both ventilation and mean inspiratory airflow are elevated at 10 am compared with 10 pm suggesting that the ventilatory response to hypoxia may follow a circadian rhythm. The increase in ventilation in response to hypercapnia was significantly greater at 10 pm than at 10 am. Mean inspiratory airflow was also elevated at 10 pm compared with 10 am. These observations suggest that the hypercapnic ventilatory response may follow a circadian rhythm.M.Sc

Connections between respiratory neurones in the neonatal rat transverse medullary slice studied with cross-correlation

In the transverse medullary slice prepared from neonatal rats the hypoglossal nerve rootlets exhibit a bursting ‘respiratory’ rhythm as do neurones in the pre-Bötzinger complex (PBC). We used cross-correlation analysis of the rhythmic multiunit discharges recorded from hypoglossal nerve rootlets, hypoglossal nucleus neurones and PBC neurones to investigate the connections between these groups. All cross-correlograms computed between left and right hypoglossal nerves, and between hypoglossal neurones and contralateral hypoglossal nerves, displayed central peaks with broad half-amplitude widths (mean ± s.d. of 29.6 ± 10.4 and 37.3 ± 6.0 ms, respectively), which we interpreted as evidence for activation from a common source. Five of the 18 cross-correlograms computed between left and right PBC neurones displayed peaks either side of time zero with narrower half-amplitude widths (mean ± s.d. of 9.3 ± 1.9 ms) superimposed on broader central peaks, which we interpreted as evidence for mutual excitation and common activation, respectively. Cross-correlograms computed between PBC neurones and contralateral hypoglossal neurones or nerves did not display consistent features, but some of those computed between PBC and ipsilateral hypoglossal neurones (two of eight) or nerves (two of five) displayed peaks with broad half-amplitude widths (mean ± s.d. of 36.8 ± 6.9 ms), offset from time zero by 6 ms (except for one at 18 ms), which we interpreted as evidence for excitation of hypoglossal neurones and motoneurones by PBC neurones. We concluded that rhythm is synchronised between left and right sides by mutual excitatory connections between left and right PBC neurones. The rhythm is transmitted to ipsilateral hypoglossal neurones by a paucisynaptic pathway. Both hypoglossal neurones and PBC neurones receive a common activation from as yet unidentified sources

Dopamine neurons in the ventral tegmental area modulate REM sleep.

identified periods of 'active sleep' that are marked by rapid-eye-movements that alternate with 'quiescent sleep' periods in human infants. Several years later Dement and Kleitman showed that rapid-eye-movements are correlated with specific patterns of brainwave activity and that vivid dreaming occurs during periods of rapid-eye-movements in human adults. Shortly thereafter, Jouvet identified a similar behavioural state in cats, showing that cats also experience periods of rapid-eye-movements that occur during periods of muscle atonia and wake-like cortical activity. REM sleep, or REM sleep-like states, have subsequently been identified in a variety of animals, including marsupials, birds, fish, insects, octopi, and lizards. These observations suggest that REM sleep is conserved across the animal kingdom and imply that REM sleep plays a role in normal biology and physiology. Although REM sleep was initially characterized by rapid-eye-movements, we now know that it is also characterized by a range of physiological features, including reduced amplitude and faster frequency cortical electroencephalogram (EEG) that is reminiscent of waking, high-amplitude theta waves in the hippocampus, active suppression of skeletal muscle activity (i.e., REM atonia), intermittent muscle twitches, autonomic and respiratory activation, fluctuations i