Pituitary-brain transport of neurotensin: Functional significance of retrograde transport

The ability of the peptide neurotensin (NT) to affect central nervous system function after pituitary-brain transport was examined in adult male rats. Animals were anesthetized and maintained under ether and their pituitaries were exposed by the pharyngeal route. They were then given NT or physiological saline solution by various routes of administration, and colonic temperature (CT) was monitored over a 2-h period. Animals given intracerebroventricular injections of 10 μg NT showed significantly lower colonic temperatures over the 2-hmeasurement period compared to rats injected intraventricularly with the solvent vehicle (0.15 M NaCl). Intrapituitary injection of 10 or 50 μg NT also markedly decreased CT in a dose-related manner compared to rats given similar injections of the solvent vehicle. Section of the pituitary stalk 24 h before injection of 50 μg NT into the pituitary totally abolished the hypothermic effect of the peptide. NT in a dose of 50 μg did not significantly modify CT when injected either iv or into the space between the pituitary and the dura compared to animals given the solvent vehicle. The results suggest that peptides may undergo retrograde transport from the pituitary to appropriate sites in the central nervous system and retain their ability to affect brain function.