| Budget Amount *help |
¥1,900,000 (Direct Cost: ¥1,900,000)
Fiscal Year 1987: ¥300,000 (Direct Cost: ¥300,000)
Fiscal Year 1986: ¥1,600,000 (Direct Cost: ¥1,600,000)
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| Research Abstract |
This project was aimed to clarify whether cold shivering is controlled by midbrain temperature or not. Single gamma efferents were isolated in the preparations of rat whose bilateral preoptic and anterior hypothalamus were electrolytically lesioned to eliminate the influences from the higher center for shivering, and changes in the discharge activity were examined while the midbrain was cooled or warmed by means of a water perfused thermode. Under the normal midbrain temperature, 36% of 64 gamma fibers isolated exhibited periodic fluctuations in spontaneous discharge whereas the rest sustained spontaneous discharge. Of 38 gamma fibers, including both type of fibers, examined for thier thermal reactiveness, 71% produced an increase or a decrease in discharge frequency to a fall below or a rise above the normal midbrain temperature, respectively. Temperature dependency of discharge frequency obtained in the range below 37.5゜C(-1.5<plus-minus>0.1 imp./sec/゜C in perfusion temperature) was
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smaller than the one in the range above 37.5゜C(2.8<plus-minus>0.5 imp./sec/゜C). This behaviour of gamma activity parallels the general pattern of thermoregulatory responses involved inmaintaining a heat balance, e.g., heat production is facilitation in the hypothermic range and suppressed in hyperthermic range. The afferent responses from the muscle spindle primary(43) and secondary endings(7) in the gastrocunemius et soleus to stretches of the muscle which were repeatedly applied during midbrain cooling or warming were analyzed by measuring peak frequency, static frequency and the dynamic index in each stretch response. It was found that midbrain cooling produced not only dynamic gamma activation but also static gamma activation, with the prevalence of former(63%) over the latter(29%). These results indicate that the descending signals derived from the thermosensitive structures in the midbrain also influence gamma motor activities, suggesting that shivering threshold could be altered therpmen Less
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