Neurotensin

Discovery and Distribution

Neurotensin was first isolated in 1973 by Carraway and Leeman from bovine hypothalamus using a bioassay based on melanocyte-stimulating hormone release inhibition. The peptide is widely distributed in the mammalian central nervous system, with particularly high concentrations in the hypothalamus, amygdala, and nucleus accumbens. In the periphery, neurotensin is found in enteroendocrine N cells of the small intestine, where it functions as a gut hormone regulating lipid absorption and gallbladder motility.

Structure and Receptor Binding

The tridecapeptide sequence is: pGlu-Leu-Tyr-Glu-Asn-Lys-Pro-Arg-Arg-Pro-Tyr-Ile-Leu-OH. The biologically active core comprises the C-terminal hexapeptide (8-13), which retains full receptor-binding affinity. Neurotensin interacts with two high-affinity G protein-coupled receptors: NTS1 (nanomolar affinity) and NTS2 (micromolar affinity). NTS1 couples primarily to Gq/11, activating phospholipase C and mobilizing intracellular calcium. NTS2 signals through Gi/0, inhibiting adenylyl cyclase and modulating potassium channels.

Neurological Functions

In the central nervous system, neurotensin modulates dopaminergic neurotransmission by acting as a stabilizer of dopamine signaling. NTS1 receptors are co-localized with dopamine D2 receptors on medium spiny neurons in the nucleus accumbens, where neurotensin potentiates dopamine D1 signaling while attenuating D2 responses. Central administration of neurotensin produces hypothermia, analgesia, and reduction in locomotor activity. These effects have been linked to interactions with the mesolimbic dopamine pathway.

Peripheral Actions

Intestinal neurotensin is released in response to dietary lipids and stimulates pancreatic enzyme secretion, gallbladder contraction, and jejunal motility. Neurotensin also promotes intestinal epithelial cell proliferation through NTS1-mediated activation of MAPK and PI3K signaling cascades. In the cardiovascular system, neurotensin produces vasodilation through endothelial nitric oxide synthase activation, contributing to local blood flow regulation.

Clinical Relevance

Neurotensin has been implicated in the pathophysiology of schizophrenia, given its modulation of dopaminergic circuits. Elevated plasma neurotensin levels have been reported in patients with non-insulin-dependent diabetes mellitus and inflammatory bowel disease. NTS1-selective agonists and antagonists are being developed as potential antipsychotic and anti-inflammatory agents. The neurotensin analog NT69L shows promise as an atypical antipsychotic with reduced extrapyramidal side effects.

References

1. Carraway R, Leeman SE. The isolation of a new hypotensive peptide, neurotensin, from bovine hypothalami. Journal of Biological Chemistry. 1973;248:6854-6861.
2. Vincent JP, Mazella J, Kitabgi P. Neurotensin and neurotensin receptors. Trends in Pharmacological Sciences. 1999;20:302-309.
3. Boules M, Fredrickson P, Tobacyk J. Neurotensin agonists as potential antipsychotics. Current Drug Targets. 2006;7:1563-1573.