Precise location within the preoptic area where noradrenaline produces hypothermia

Noradrenaline (5 microgram in 0.5 microliter) was microinjected into 87 different sites within the preoptic anterior hypothermic area of cat brain to determine the anatomical location most sensitive to the hypothermic action of the amine. At 26 of these sites noradrenaline produced a hypothermia greater than 0.5 degrees C. Such falls in body temperature were invariably accompanied by vasodilation and sometimes by a marked increase in respiratory rate. During the hypothermia most animals appeared sedated. Histological analysis of the sites where hypothermia was produced indicated that the site of maximum sensitivity occurred between the optic chiasm and the anterior commissure at A 15.0, L 2.5, H--2.5. The results are discussed in terms of the physiological control of body temperature.