MT2 Receptors (mt2 + receptor)

Distribution by Scientific Domains


Selected Abstracts


Effect of MT1 melatonin receptor deletion on melatonin-mediated phase shift of circadian rhythms in the C57BL/6 mouse

JOURNAL OF PINEAL RESEARCH, Issue 2 2005
M. L. Dubocovich
Abstract:, In the mouse suprachiasmatic nucleus (SCN), melatonin activates MT1 and MT2 G-protein coupled receptors, which are involved primarily in inhibition of neuronal firing and phase shift of circadian rhythms. This study investigated the ability of melatonin to phase shift circadian rhythms in wild type (WT) and MT1 melatonin receptor knockout (KO) C57BL/6 mice. In WT mice, melatonin (90 ,g/mouse, s.c.) administered at circadian time 10 (CT10; CT12 onset of activity) significantly phase advanced the onset of the circadian activity rhythm (0.60 0.09 hr, n = 41) when compared with vehicle treated controls (,0.02 0.07 hr, n = 28) (P < 0.001). In contrast, C57 MT1KO mice treated with melatonin did not phase shift circadian activity rhythms (,0.10 0.12 hr, n = 42) when compared with vehicle treated mice (,0.12 0.07 hr, n = 43). Similarly, in the C57 MT1KO mouse melatonin did not accelerate re-entrainment to a new dark onset after an abrupt advance of the dark cycle. In contrast, melatonin (3 and 10 pm) significantly phase advanced circadian rhythm of neuronal firing in SCN brain slices independent of genotype with an identical maximal shift at 10 pm (C57 WT: 3.61 0.38 hr, n = 3; C57 MT1KO: 3.45 0.11 hr, n = 4). Taken together, these results suggest that melatonin-mediated phase advances of circadian rhythms of neuronal firing in the SCN in vitro may involve activation of the MT2 receptor while in vivo activation of the MT1 and possibly the MT2 receptor may be necessary for the expression of melatonin-mediated phase shifts of overt circadian activity rhythms. [source]


Melatonin and its precursor, L -tryptophan: influence on pancreatic amylase secretion in vivo and in vitro

JOURNAL OF PINEAL RESEARCH, Issue 3 2004
Jolanta Jaworek
Abstract:, Melatonin, considered as a main pineal product, may be also synthetized in the gastrointestinal tract from l -tryptophan. Melatonin has been recently shown to affect insulin release and its receptors have been characterized in the pancreas however, the effects of melatonin on the pancreatic enzyme secretion have not been examined. The aim of this study was to investigate the effects of melatonin or l -tryptophan on amylase secretion in vivo in anaesthetized rats with pancreato-biliary fistulas, and in vitro using isolated pancreatic acini. Melatonin (1, 5 or 25 mg/kg) or l -tryptophan (10, 50 or 250 mg/kg) given to the rats as a intraperitoneal (i.p.) bolus injection produced significant and dose-dependent increases in pancreatic amylase secretion under basal conditions or following stimulation of enzyme secretion by diversion of bile-pancreatic juice. This was accompanied by a dose-dependent rise in melatonin plasma level. Stimulation of pancreatic enzyme secretion caused by melatonin or l -tryptophan was completely abolished by vagotomy, deactivation of sensory nerves with capsaicin or pretreatment with CCK1 receptor antagonists (tarazepide or l -364,718). Pretreatment with luzindole, an antagonist of melatonin MT2 receptor failed to affect melatonin- or l -tryptophan-induced amylase secretion. Administration of melatonin (1, 5 or 25 mg/kg i.p.) or l -tryptophan (10, 50 or 250 mg/kg i.p.) to the rats resulted in the dose-dependent increase of cholecystokinin (CCK) plasma immunoreactivity. Enzyme secretion from isolated pancreatic acini was not significantly affected by melatonin or l -tryptophan used at doses of10,8,10,5 m. We conclude that exogenous melatonin, as well as that produced endogenously from l -tryptophan, stimulates pancreatic enzyme secretion in vivo while increasing CCK release. Stimulatory effect of melatonin or l -tryptophan on the exocrine pancreas involves vagal sensory nerves and the CCK release by these substances. [source]


EFFECTS OF MELATONIN ON BLOOD PRESSURE IN STRESS-INDUCED HYPERTENSION IN RATS

CLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 10 2008
Chun-Mei Xia
SUMMARY 1Melatonin, acting through its receptors, is involved in numerous physiological processes, including blood pressure (BP) regulation. In present study, the effect of melatonin inhibition on stress-induced hypertension was investigated. 2The hypertensive model consisted of male Sprague-Dawley rats subjected to electrical foot-shock combined with noise. Microinjection of melatonin (0.1 and 1.0 mmol/L) into the anterior hypothalamic area (AHA) produced a fall in BP in nomortensive rats and stress-induced hypertensive rats (SIHR). Luzindole (10 mmol/L), a competitive antagonist of melatonin MT1 and MT2 receptors, almost completely abolished the depressor effect of melatonin, the MT2 receptor-specific antagonist 4-phenyl-2-propionamidotetralin (10 mmol/L) partially blocked (by approximately 60%) the depressor effect of melatonin, whereas the MT3 receptor-selective antagonist prazosin (10 mmol/L) failed to antagonize the effects of melatonin. 3Brain microdialysis was performed in the AHA and the rostral ventrolateral medulla (RVLM). Melatonin and amino acids in the dialysate samples collected were detected by high-performance liquid chromatography combined with fluorescence detection. The results indicated that melatonin concentrations in the AHA were reduced in SIHR. Microinjection of melatonin into the AHA decreased glutamate release and increased GABA and taurine release in the RVLM, which were paralleled by a decrease in arterial pressure. 4The mRNA expression of MT2 in the AHA of SIHR was higher than that in normotensive control rats, whereas there was no significant difference in MT1 mRNA expressin between the two groups. 5The results of the present study suggest that both a decrease of melatonin and an increase in the MT2 receptor in the AHA are involved in the manifestation of stress-induced hypertension. Both MT1 and MT2 receptors participated in the antihypertensive effect of melatonin in the AHA. The antihypertensive effect of melatonin was related to the decreases in the excitatory amino acid glutamate and increases in the inhibitory amino acids taurine and GABA in the RVLM. [source]


Melatonin inhibits hippocampal long-term potentiation

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 9 2005
Louisa M. Wang
Abstract The goal of this study is to investigate the effect of the hormone melatonin on long-term potentiation and excitability measured by stimulating the Schaffer collaterals and recording the field excitatory postsynaptic potential from the CA1 dendritic layer in hippocampal brain slices from mice. Application of melatonin produced a concentration-dependent inhibition of the induction of long-term potentiation, with a concentration of 100 nm producing an ,,50% inhibition of long-term potentiation magnitude. Long-duration melatonin treatments of 6 h were also effective at reducing the magnitude of long-term potentiation. Melatonin (100 nm) did not alter baseline evoked responses or paired-pulse facilitation recorded at this synapse. The inhibitory actions of melatonin were prevented by application of the melatonin (MT) receptor antagonist luzindole as well as the MT2 receptor subtype antagonist 4-phenyl-2-propionamidotetraline. These inhibitory actions of melatonin were lost in mice deficient in MT2 receptors but not those deficient in MT1 receptors. In addition, application of the protein kinase A inhibitor H-89 both mimicked the effects of melatonin and precluded further inhibition by melatonin. Finally, the application an activator of adenylyl cyclase, forskolin, overcame the inhibitory effects of melatonin on LTP without affecting the induction of long-term potentiation on its own. These results suggest that hippocampal synaptic plasticity may be constrained by melatonin through a mechanism involving MT2-receptor-mediated regulation of the adenylyl cyclase,protein kinase A pathway. [source]


C-terminal domains within human MT1 and MT2 melatonin receptors are involved in internalization processes

JOURNAL OF PINEAL RESEARCH, Issue 2 2008
Shalini Sethi
Abstract:, Melatonin, a molecule implicated in a variety of diseases, including cancer, often exerts its effects through G-protein-coupled melatonin receptors, MT1 and MT2. In this study, we sought to understand further the domains involved in the function and desensitization patterns of these receptors through site-directed mutagenesis. Two mutations were constructed in the cytoplasmic C-terminal tail of each receptor subtype: (i) a cysteine residue in the C-terminal tail was mutated to alanine, thus removing a putative palmitoylation site, and a site possibly required for normal receptor function (MT1C7.72A and MT2C7.77A) and (ii) the C-terminal tail in the MT1 and MT2 receptors was truncated, removing the putative phosphorylation and ,-arrestin binding sites (MT1Y7.64 and MT2Y7.64). These mutations did not alter the affinity of 2-[125I]-iodomelatonin binding to the MT1 or MT2 receptors. Using confocal microscopy, it was determined that the putative palmitoylation site (cysteine residue) did not play a role in receptor internalization; however, this residue was essential for receptor function, as determined by 3,,5,-cyclic adenosine monophosphate (cAMP) accumulation assays. Truncation of the C-terminal tail of both receptors (MT1Y7.64 and MT2Y7.64) inhibited internalization as well as the cAMP response, suggesting the importance of the C-terminal tail in these receptor functions. [source]


Detection of the human GPR50 orphan seven transmembrane protein by polyclonal antibodies mapping different epitopes

JOURNAL OF PINEAL RESEARCH, Issue 1 2007
Hassina Ould Hamouda
Abstract:, GPR50 is an orphan seven transmembrane protein related to the melatonin receptor subfamily comprising MT1 and MT2 receptors. In the absence of any known ligand for GPR50, other tools are critical for the characterization of this protein. Here, we describe the generation, purification and characterization of the first rabbit polyclonal antibodies generated against peptides corresponding to the N-terminus, C-terminus and two additional regions within the intracellular tail of GPR50. Immune sera were purified on peptide-antigen affinity columns. Antibodies specifically recognized a GPR50-YFP fusion protein on the plasma membrane of HEK 293 cells in immunofluorescence experiments. In Western blot experiments, the monomeric and dimeric forms of GPR50 were detected as proteins of 66 and 130 kDa, respectively. In addition, these new antibodies were sufficiently sensitive to detect GPR50 in brain slices of the rat pituitary and human hippocampus. In conclusion, we successfully produced antibodies against the orphan GPR50 protein that will become valuable tools for functional studies of this protein. [source]


EFFECTS OF MELATONIN ON BLOOD PRESSURE IN STRESS-INDUCED HYPERTENSION IN RATS

CLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 10 2008
Chun-Mei Xia
SUMMARY 1Melatonin, acting through its receptors, is involved in numerous physiological processes, including blood pressure (BP) regulation. In present study, the effect of melatonin inhibition on stress-induced hypertension was investigated. 2The hypertensive model consisted of male Sprague-Dawley rats subjected to electrical foot-shock combined with noise. Microinjection of melatonin (0.1 and 1.0 mmol/L) into the anterior hypothalamic area (AHA) produced a fall in BP in nomortensive rats and stress-induced hypertensive rats (SIHR). Luzindole (10 mmol/L), a competitive antagonist of melatonin MT1 and MT2 receptors, almost completely abolished the depressor effect of melatonin, the MT2 receptor-specific antagonist 4-phenyl-2-propionamidotetralin (10 mmol/L) partially blocked (by approximately 60%) the depressor effect of melatonin, whereas the MT3 receptor-selective antagonist prazosin (10 mmol/L) failed to antagonize the effects of melatonin. 3Brain microdialysis was performed in the AHA and the rostral ventrolateral medulla (RVLM). Melatonin and amino acids in the dialysate samples collected were detected by high-performance liquid chromatography combined with fluorescence detection. The results indicated that melatonin concentrations in the AHA were reduced in SIHR. Microinjection of melatonin into the AHA decreased glutamate release and increased GABA and taurine release in the RVLM, which were paralleled by a decrease in arterial pressure. 4The mRNA expression of MT2 in the AHA of SIHR was higher than that in normotensive control rats, whereas there was no significant difference in MT1 mRNA expressin between the two groups. 5The results of the present study suggest that both a decrease of melatonin and an increase in the MT2 receptor in the AHA are involved in the manifestation of stress-induced hypertension. Both MT1 and MT2 receptors participated in the antihypertensive effect of melatonin in the AHA. The antihypertensive effect of melatonin was related to the decreases in the excitatory amino acid glutamate and increases in the inhibitory amino acids taurine and GABA in the RVLM. [source]