An understanding of neurological mechanisms for wheel running by rodents, especially with high exercise activity, would be applicable to a strategy for promotion of exercise motivation in humans. One of several brain regions that are candidates for the regulation of physical exercise is the hippocampus. Here we examined the running activity of Spontaneously-Running-Tokushima-Shikoku (SPORTS) rat, a new animal model for high levels of wheel-running activity, and its relation with the hippocampal norepinephrine (NE) system including the levels of NE, adrenergic receptors, and degradation enzymes for monoamines. In the hippocampus of SPORTS rats, the level of NE in extracellular fluid was augmented, whereas the level in the homogenate of the whole tissue was decreased even for sedentary conditions. Elevated extracellular NE caused downregulation of a 2 -adrenergic receptors in the hippocampus of SPORTS rats. Local administration of a 2 -adrenergic receptor antagonist yohimbine, but not of a 2 -agonist clonidine, into the hippocampus suppressed high running activity in SPORTS rats. The protein expression and the activity levels of monoamine oxidase A (MAOA), a critical enzyme for the degradation of NE, were decreased in the hippocampus of SPORTS rats to increase extracellular NE level. Thus, inhibition of oxidase activity in normal Wistar rats markedly increased wheel-running activity. These results indicate that decreased MAOA activity, elevation of extracellular NE, and a 2 -adrenergic receptors in the hippocampus determine the neural basis of the psychological regulation of exercise behavior in SPORTS rats.
133summarized as follows. Within the range of D, there is a wide 1:l phase-locking region. In the outside of this region, the phase-locking regions with n:ni appear via tangent bifurcations. The tangent bifurcation is caused by the map nearly tangential to the diagonal line (e.g. see the map for D = 0.40). Through this bifurcation, a fixed point with a long period abruptly appears. Interestingly, peculiar to the map of the two process model, the difference of the entrainment ratio In -rnl changes through the tangent bifurcation. Unstable behavior is found in the region where an entrainment ratio changes.
DISCUSSIONIf the two process model could be regarded as a combination of the different oscillator, the thresholds and the exponential switching processes, changmg D would be equivalent to niodifjing interactions between them. Here, as a function of D, we have shown that the model has the different types of the mutual entrainment regions which are intervened by the tangent bifurcation. Such a dynamical system could provide the possible mechanisms underlying the diverse behavior of human circadian system. In addition to the internal desynchronizations investigated in a previous study,3 the phase trapping observed on the way to the complete desynchroni~ation~ could be understood based on the bifurcation properties obtained here; that
Sleep-wake Regulationis, the circle map with a period n fixed point could exhibit the behavior that the sleep-onset phase comes back to its original position every n cycles where n corresponck to the period of the phase trapping. This is realized by an appropriate D < 0.415. Considering these results, our study uniquely provides the biological significance to the bifurcation properties of the two process model.Bifurcations induced by other parameters such as amplitudes of the thresholds and periods of threshold processes remain unknown, which will be the subject of future study.
REFERENCES
AbstractWe investigated whether exposure to the odor of extracted cedar essence (CE) has (i) an influence on spontaneous activity and sleep-wake states of rats and (ii) a sleep-promoting effect on human daytime nap after taking an ordinary night's sleep. In rats exposed to CE, spontaneous activities and amount of wake were significantly decreased, while the amount of non-rapid eye movement (NREM) sleep was significantly increased. In human daytime nap, NREM sleep stage 2 latency was significantly shortened after exposure to CE.
Key wordscedar essence, human daytime nap, odor, spontaneous activity and sleep of rats.
RV strain during pre-load augmentation correlated independently to peak VO and was a powerful predictor in identifying patients with severely reduced exercise capacity.
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