Anorectic effect of calcitonin, neurotensin and bombesin infused in the area of the rostral part of the nucleus of the tractus solitarius in the rat.

The three neuropeptides calcitonin, neurotensin and bombesin can decrease food intake in the rat when injected into the cerebral ventricles or into the paraventricular nucleus of the hypothalamus. The paraventricular nucleus of the hypothalamus is an important site for the integration of visceral and endocrine systems, and has connections with the nucleus of the tractus solitarius which is a major locus for visceral afferents. Since calcitonin, neurotensin and bombesin, or their receptors, have been found to be present in the nucleus of the tractus solitarius, we tested the effects of local infusions of these peptides on food intake. The peptides were microinjected in a 0.25 microliter volume in rats trained to eat for only 3 hours per day. The injections were made in the rostral part of the nucleus and surrounding areas, through the lateral vestibular nuclei, to avoid leakage of the peptides into the cerebrospinal fluid. In the nucleus of the tractus solitarius the three peptides decreased food intake by more than 50%. The peptides were also active in the spinal trigeminal nucleus oralis, and, for calcitonin and bombesin, in the reticular formation under the nucleus of the tractus solitarius. A local diffusion from the point of injection may explain some of these results. Therefore, the area of the nucleus of the tractus solitarius is a nonhypothalamic site where these peptides can act to produce anorexia.