CHANGES OF CHARACTERISTICS OF PREOPTIC NEURONS AND NA METABOLISM IN HYPOTHALAMUS OF GROUND-SQUIRREL (CITELLUS-DAUTIEUS) IN DIFFERENT SEASONS AND HIBERNATING PHASES

The unit firing activities of neurons in the preoptic area (POA) of gr ound squirrel hypothalamic tissue slices were recorded and the metabol ism of NA in hypothalamus was measured with high performance liquid ch romatography (HPLC). Thermosensitivity, proportions, the critical temp erature (Tc) and the lowest temperature (TL) of firing activity of the above-mentioned neurons, and NA metabolism in hypothalamus were compa red in different seasons and hibernating phases. In comparison with th at in summer euthermar, it was shown that (i) the percentage and therm osensitivity of the POA neurons varied respectively in the hibernating phases; (ii) TL and Te of the POA neurons in winter, both euthermar a nd hibernation, were markedly decreased; (iii) the POA neurons in hibe rnation became much more sensitive to NA, and the response of cold-sen sitive neurons to NA changed from inhibiting pattern in summer to exci ting one in hibernation; (iv) the contents and metabolism of NA in hyp othalamus decreased significantly in the entering phase and deep hiber nation phase, while the metabolism of NA increased remarkably in the a rousal phase. These changes might explain the regulatory mechanism how ground squirrel actively decreases body temperature (Tb) in entering into hibernation and quickly recovers body temperature in arousal phas e.