Comparison of contributions of thermosensitive tissues in central nervous system on heat loss responses in rabbits

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The preoptic area and anterior hypothalamus(PO/AH), medullary reticural formation(MRF) and spinal cord as thermosensitive tissues in the central nervous system were locally heated with an argon laser in order to induce heat loss responses in rabbits. Increases in ear skin temperature and respiratory rate and decrease in rectal temperature evoked by local heating were compared among the tissues.1. PO/AH and MRF Heating :(1)The Ar laser irradiation guided with a glass fiber is very useful to heat a small area in deep body tissue. (2)PO/AH and MRF were locally heated with Ar laser under no influence of thermal conduction though the thermal signals were transmitted by neurons. (3) The minimal Ar laser powers to induce the heat loss responses were 14.5 mW for PO/AH and 19.0 mW for MRF and it was significant difference,and thermal distributions of increase in brain temperature by Ar laser irradiations at these powers were calculated. (4)The ratio of PO/AH to MRF in products of heated volume and increase in temperature of over 0.50 ﾟC was 1:2.94.2. Spinal Heating : (1)The argon laser guided with a glass fiber(0.4 mm in diameter) irradiated inside a guide tube(0.8 mm in diameter) which was implanted into the peridural space from lumbar vertebrae (L4/L5) to thoracic vertebrae(Th1). (2)The length of spinal cord increased more than 0.5 ﾟC and maximal increase in temperature of spinal cord depended on the irradiation power as follows: 7.3 mm and 1.32 ﾟC for 40 mW, 10.5 mm and 2.02ﾟC for 60 mW, 13.1 mm and 2.73ﾟC for 80 mW. (3) At all locations from Th1 to L4, the heat loss responses were evoked. (4) The heat loss responses induced by the lumbar spinal heating were no significant difference compared with that by the thoracic spinal heating.