sr-142948 and levocabastine

Neurotensin is a neuropeptide involved in dopaminergic signalling. We have recently reported that neurotensin stimulates the phosphorylation of DARPP-32 (dopamine- and cAMP-regulated phosphoprotein of Mr 32 kDa) at Thr34 (PKA-site) by activating dopamine D1-type receptors in neostriatal neurons. DARPP-32 is also phosphorylated by cyclin-dependent kinase 5 on Thr75, and the phosphorylated form of DARPP-32 at Thr75 inhibits protein kinase (PKA) activity. In this study, we examined the effect of neurotensin on DARPP-32 Thr75 phosphorylation using mouse neostriatal slices. Neurotensin decreased the level of phospho-Thr75 DARPP-32 at 2 min of incubation, maximally to about 50% of control at a concentration of 1 micro m. Pretreatment with a combined neurotensin receptor type 1 (NTR1)/type 2 (NTR2) antagonist, SR142948, reduced the basal level of phospho-Thr75 DARPP-32 and abolished the ability of neurotensin to decrease DARPP-32 Thr75 phosphorylation. However, neither an NTR1 antagonist, SR48692, an NTR2 antagonist, levocabastine, nor the two combined affected the basal level and the neurotensin-mediated decrease in DARPP-32 Thr75 phosphorylation. The effect of neurotensin was abolished by tetrodotoxin (TTX) or MK801 plus CNQX, but not by SCH23390 or raclopride. These results indicate that neurotensin stimulates the release of glutamate by activating a hypothesized unidentified neurotensin receptor, resulting in the dephosphorylation of DARPP-32 at Thr75 by activating NMDA and AMPA receptors expressed at medium spiny neurons. Thus, neurotensin, by removing the inhibition of PKA by phospho-Thr75 DARPP-32, potentiates its signalling via the dopamine/D1 receptor/PKA/phospho-Thr34 DARPP-32/PP-1 cascade.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Anesthetics, Local; Animals; Benzazepines; Dizocilpine Maleate; Dopamine and cAMP-Regulated Phosphoprotein 32; Dopamine Antagonists; Dose-Response Relationship, Drug; Drug Interactions; Excitatory Amino Acid Antagonists; Glutamic Acid; Histamine H1 Antagonists; Immunoblotting; In Vitro Techniques; Male; Mice; Mice, Inbred C57BL; Neostriatum; Nerve Tissue Proteins; Neurons; Neurotensin; Phosphoproteins; Piperidines; Pyrazoles; Quinolines; Raclopride; Receptors, Neurotensin; Signal Transduction; Tetrodotoxin; Threonine; Time Factors

Neurotensin modulates dopaminergic transmission in the nigrostriatal system. DARPP-32, a dopamine- and cAMP-regulated phosphoprotein of Mr 32 kDa, is phosphorylated on Thr34 by cAMP-dependent protein kinase, resulting in its conversion into a potent inhibitor of protein phosphatase-1 (PP 1). Here, we examined the effect of neurotensin on DARPP-32 Thr34 phosphorylation using mouse neostriatal slices. Neurotensin stimulated DARPP-32 Thr34 phosphorylation by 4-7-fold with a K(0.5) of approximately 50 nM. The effect of neurotensin was antagonized by a combined neurotensin receptor type-1 (NTR1)/type-2 (NTR2) antagonist, SR142948. It was not antagonized by a NTR1 antagonist, SR48692 or by a NTR2 antagonist, levocabastine; neither was it antagonized by the two combined. Pretreatment with TTX or cobalt abolished the effect of neurotensin. The effect of neurotensin was antagonized by a dopamine D1 antagonist, SCH23390, and by ionotropic glutamate receptor antagonists, MK801 and CNQX. These results indicate that neurotensin stimulates the release of dopamine from nigrostriatal presynaptic terminals in an NMDA receptor- and AMPA receptor-dependent manner, leading to the increase in DARPP-32 Thr34 phosphorylation. Neurotensin stimulated the phosphorylation of Ser845 of the AMPA receptor GluR1 subunit in wild-type mice but not in DARPP-32 knockout mice. Thus, neurotensin, by stimulating the release of dopamine, activates the dopamine D1-receptor/cAMP/PKA/DARPP-32/PP 1 cascade.

Topics: Animals; Cobalt; Dopamine; Dopamine and cAMP-Regulated Phosphoprotein 32; Dopamine Antagonists; Excitatory Amino Acid Antagonists; Glutamine; In Vitro Techniques; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Neostriatum; Nerve Tissue Proteins; Neurons; Neurotensin; Phosphoproteins; Phosphorylation; Piperidines; Pyrazoles; Quinolines; Receptors, Dopamine D1; Receptors, Neurotensin; Signal Transduction; Tetrodotoxin

SR 142948 is an original and extremely potent neurotensin receptor antagonist developed in a promising approach to novel antipsychotic drugs. The X-ray structure was elucidated and compared to SR 48692 and levocabastine, providing new informations about the possible recognition process of NT receptor subtypes.

Topics: Animals; Crystallography, X-Ray; Mice; Models, Molecular; Piperidines; Protein Conformation; Pyrazoles; Quinolines; Rats; Receptors, Neurotensin