k-185 and luzindole

The effects of melatonin (MT) were examined on the isolated scale melanophores from dorso-lateral (D-L) and band regions of a tropical fish Rasbora daniconius. Our study primarily aimed for further depiction of the signaling receptors involved in MT mediated pigment translocations in the fish. Melanophore Size Index (MSI) was employed as a recording parameter for the responses of melanophores to MT and various antagonists. MT has induced aggregation as well as dispersion in D-L region and aggregation in band region melanophores during summer season. During winter, MT-induced responses were only of aggregatory type in D-L region, while in the band region there was an increase in the sensitivity. The responses of the melanophores to MT were reversible. The aggregation of innervated melanophores induced by MT on the D-L and band regions was partially mediated through the neurotransmitters released under the influence of MT and partially by the specific MT receptors. Luzindole and K185 have completely blocked the aggregatory responses of D-L and band region melanophores. Aggregatory receptors may be of the conventional α-MT type. Dispersion of D-L and band region melanophores induced by MT in the presence of various antagonists and on denervated band region could be the result of activation of β-MT receptors of dispersive nature. Presence of α and β MT receptors is thus indicated in this fish melanophores.

Topics: Animals; Cell Aggregation; Cyprinidae; Denervation; Dose-Response Relationship, Drug; Female; Fish Proteins; Guanethidine; Indoles; Male; Melanophores; Melatonin; Phentolamine; Propranolol; Receptors, Melatonin; Tryptamines; Yohimbine

The hormone melatonin regulates the biological clock and assist in various other physiologies of vertebrates. Present work is intended to check the affinity of saccharin towards the melatonin receptors and the possible role of saccharin interference in the melatonin physiology. The present in vitro study is based on the working model of isolated scale melanophores in the dorso-lateral region of Labeo rohita. The pigment cells were incubated in the agonist and the antagonists within a limited time frame and subsequently their Melanophore Size Index (MSI) were calculated. The inferences were drafted through the observed signal transduction upshots in pigment translocations within the melanophores. Saccharin, in a wide dose range, has consistently induced a concentration-related aggregation similar to the aggregatory effect as shown by melatonin on the melanophores. Binding of saccharin with the receptors and eliciting its aggregatory effect is partially dependent on the release of neurotransmitters. The aggregatory effects were found to be significantly blocked by luzindole, K185, and prazosin, which are the potent melatonin receptor blockers, at the higher concentrations of saccharin. Hence, all the three subtypes of melatonin receptors viz. MT₁, MT₂, and MT₃ are participating in saccharin-mediated aggregations. Blocking by neomycin shows that Ca²⁺ ions are very crucial in dispensing the aggregatory effect of the sweetener. This research demands that an intensive and careful thorough study should be made about saccharin, specifically its effects upon melatonin physiology, before its unwarranted use as the food ingredients for human use.

Topics: Adrenergic alpha-1 Receptor Antagonists; Animals; Denervation; Fishes; Indoles; Melanophores; Melatonin; Prazosin; Receptors, Melatonin; Saccharin; Signal Transduction; Sweetening Agents; Tryptamines

Melatonin has been reported to present with vasorelaxant and anti-fibrotic properties. We hypothesized that melatonin may down-regulate volume-regulated anion channels (VRAC) in fibroblasts to limit their migration and proliferation. While acute exposure of L929 fibroblasts to melatonin did not result in a significant decrease in VRAC current, pretreatment with 100 μM melatonin for 1 h decreased swelling-dependent activation of anion currents by 83% as measured by whole-cell perforated patch-clamp technique. This down-regulation of VRAC currents was dose-dependent with a half-maximal inhibition of 3.02 ± 0.48 μM. Overnight treatment of cells with 100 nM melatonin had the same inhibitory potency as a 1-h treatment with 100 μM. A similar down-regulatory effect of melatonin on VRAC was observed in primary rat lung fibroblasts. The effect of melatonin was prevented by luzindole and K185 that suggests implication of MT2 receptor. GF109203X, a protein kinase C inhibitor, blocked melatonin's action on VRAC, indicating that MT2 receptor activation results in stimulation of PKC. Consequently, melatonin inhibited regulatory volume decrease following hypotonic swelling of cells. Melatonin also decreased the migration of L929 fibroblasts through the same pathways that blocked VRAC. There was no significant inhibition of cell proliferation. Our study suggests that the attenuation of fibrosis and vascular remodeling by melatonin seen in animal models of hypertension and pulmonary fibrosis might be, in part, related to blunted fibroblast migration possibly through protein kinase C-mediated decrease in chloride channel activity.

Topics: Animals; Cell Movement; Cell Proliferation; Cell Size; Chloride Channels; Fibroblasts; Indoles; Maleimides; Melatonin; Patch-Clamp Techniques; Protein Kinase C; Rats; Receptor, Melatonin, MT2; Tryptamines

The present study was undertaken to ascertain whether the casein derived bitter tastant Cyclo (Leu-Trp) [CLT] has an affinity or not for the particular receptors of the pineal hormone, melatonin, on the melanophores of a major carp Labeo rohita (Ham.). The bitter tastant CLT, in the dose range of 3.34×10(-16) M to 3.34×10(-4) M, has induced an aggregatory effect but not in a dose dependent manner. Binding of CLT with the receptors may vary at different concentrations. Denervation of the melanophores has shown a complete inhibition of the CLT mediated aggregation. Prazosin has partially inhibited the aggregatory effect of CLT. Moreover, the bitter tastant's response is mediated through the α2 adrenoceptors only at particular dose ranges. The MT1 and MT2 melatonin receptor antagonist luzindole and the MT2 specific antagonist K185 have perfectly blocked the aggregatory effects of CLT. We have found that the CLT mediated aggregatory effect is dependent upon the release of neurotransmitters and the two subtypes of melatonin (MT) receptors (MT1 and MT2) possess a perfect affinity towards the bitter tastant CLT. Our study demands a need to further make a clinical research on the effects of bitter tastants on the physiology of the biological rhythm maintaining hormone melatonin.

Topics: Animals; Carps; Caseins; Cell Size; Denervation; Indoles; Melanophores; Neurotransmitter Agents; Piperazines; Prazosin; Receptor, Melatonin, MT1; Receptor, Melatonin, MT2; Receptors, Adrenergic; Tryptamines; Yohimbine

A growing body of evidence indicates the prominent actions of melatonin on the opioidergic system. Nevertheless, effect of melatonin on rewarding properties of morphine is still obscure. In particular, effect of melatonin on the expression of morphine reward is unknown. We evaluated the effect of exogenous administration of melatonin on the expression of morphine reward in mice using a conditioned place preference (CPP) paradigm. The conditioned place preference was induced by morphine (s.c., 3 mg/kg, once each day for 5 consecutive days) in mice. Our data showed that the intraperitoneal (i.p.) administration of melatonin (12.5-50 mg/kg) reversed the expression of morphine-induced conditioned place preference in a dose-dependent manner. Furthermore, the intracerebroventricular (i.c.v.) administration of melatonin (0.125-0.5 mg/kg) also resulted in dose-dependent reversal effect on the expression of morphine-induced conditioned place preference. We further investigated which of melatonin receptor subtypes within the central nervous system was mediating this reversal action in mice using luzindole (2-benzyl-N-acetyltryptamine, a non-selective antagonist for melatonin MT1 and MT2 receptors) and K185 (N-butanoyl-2-(5,6,7-trihydro-11-methoxybenzo[3,4]cyclohept[2,1-alpha]indol-13-yl)ethanamine, a selective antagonist for melatonin MT2 receptor). It was shown that the i.c.v. administration of either K185 (5, 20 microg) or luzindole (6.25, 12.5 microg) significantly antagonized the reversal effect of melatonin (50 mg/kg, i.p) on the expression of morphine-induced conditioned place preference, while the i.c.v. administration of 20 microg of K185 or 12.5 microg of luzindole by itself did not alter the expression of morphine-induced conditioned place preference. These results suggest that melatonin reverses the expression of morphine-induced rewarding effect, and this action is mediated by the activation of melatonin MT2 receptor subtype within the central nervous system.

Topics: Animals; Central Nervous System; Conditioning, Operant; Dose-Response Relationship, Drug; Indoles; Injections, Intraperitoneal; Injections, Intraventricular; Male; Melatonin; Mice; Morphine; Morphine Dependence; Narcotic Antagonists; Narcotics; Receptor, Melatonin, MT1; Receptor, Melatonin, MT2; Tryptamines