Vol. 300, Issue 1, 305-313, January 2002

The Effects of Deleting the Mouse Neurotensin Receptor NTR1 on Central and Peripheral Responses to Neurotensin

Douglas J. Pettibone, J. Fred Hess, Patricia J. Hey, Marlene A. Jacobson, Michael Leviten, Edward V. Lis, Pierre J. Mallorga, Danette M. Pascarella, Melissa A. Snyder, Jacinta B. Williams and Zhizhen Zeng

Department of Neuroscience, Merck Research Laboratories, West Point, Pennsylvania (D.J.P., J.F.H., P.J.H., M.A.J., E.V.L., P.J.M., D.M.P., M.A.S., J.B.W., Z.Z.); and Department of Molecular Genetics, Deltagen Incorporated, Menlo Park, California (M.L.)

Mice deficient in the neurotensin (NT)-1 receptor (NTR1) were developed to characterize the NT receptor subtypes that mediate various in vivo responses to NT. F2 generation (C57BL6/Sv129J) NTR1 knockout (/) mice were viable, and showed normal growth and overt behavior. The / mice lacked detectable NTR1 radioligand binding in brain, whereas NTR2 receptor binding density appeared normal compared with wild-type (+/+) mice. The gene deletion also resulted in the loss of NTR1 expression as determined by reverse transcription-polymerase chain reaction and in situ hybridization. Intracerebroventricular injection of NT (1 µg) to +/+ mice caused a robust hypothermic response (5-6°C) and a significant increase in hot-plate latency. These effects were absent in the / mice. Similar results were obtained with i.p. injections of the brain-penetrant NT analog NMe-Arg-Lys-Pro-Trp-Tle-Leu (NT-2, 1 mg/kg i.p.). NT-2 administration also impaired rotarod performance in wild-type mice, but had no effect on motor coordination in knockout mice. In vitro, NT and NT-2 at 30 nM caused predominantly contraction and relaxation in isolated distal colon and proximal ileum, respectively, from +/+ mice, but no responses were observed with tissues from / mice. A similar loss of the contractile effects of NT was observed in the isolated stomach fundus from the knockout mice. In vivo, NT-2 administration reduced colonic propulsion substantially in wild-type mice. In contrast, NT-2 had no effect in NTR1 null mice, whereas the hypomotility effect of clonidine was intact. These data indicate that NTR1 mediates several of the central and peripheral effects of NT.