When administered into the cerebroventricular system of the rat, neurotensin (NT) produces a variety of effects, including a decrease in colonic temperature and an increase in nociceptive threshold. The previous study described in detail the localization of immunohistochemical NT in the rat bran. In this study, bilateral injections of NT were made into 223 separate loci in the rat brain and a map was generated showing the brain regions where NT produced a decline in colonic temperature and an increase in hot plate response latency. It was found that some of the brain areas which contain immunohistochemically identified NT responded to locally administered NT. Further, most NT-sensitive brain loci contain NT cell bodies as well as fibers. Areas in the brain where NT produced an antinociceptive response were not the same areas where NT evoked hypothermia. An antinociceptive response was consistently produced after NT injection into the nucleus amygdaloideus centralis, rostral area praeoptica medialis, the ventral thalamus dorsomedial and medial to the lemniscus medialis, rostral mesencephalic periventricular gray, and medial pontine formatio reticularis. Less-consistent antinociception was also observed in the mesencephalic formatio reticularis and the caudal diagonal band of Broca. Hypothermia was induced by NT in the area praeoptica medialis contiguous with the area anterior hypothalami, nucleus ventralis tegmenti (Tsai), floor of the fourth ventricle, and tractus spinalis nervi trigemini. Less profound hypothermia was also produced in the posterior hypothalamus. The fact that all these responsive brain areas contain NT indicates that the microinjection of NT may be mimicking the effects of endogenously released NT, thus supporting the possible physiological significance of NT as an endogenous modulator of body temperature or nociceptive sensory information.
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