title: Denervation of pigment cells lead to a receptor that is ultrasensitive to melatonin and noradrenaline.
abstract: Pigment granule aggregation and dispersal can be studied in the melanophores of isolated scales from the cuckoo wrasse (Labrus ossifagus L.). Stimulation of a melanophore alpha2-adrenoceptor or the sympathetic nerve innervating the cell causes pigment aggregation. When the stimulation ceases, the pigment granules disperse throughout the cell. Studying this migration has been a useful tool in pharmacological research, particularly in investigations of the alpha2-adrenoceptor. Denervation of melanophores creates a receptor that is ultrasensitive to noradrenaline and melatonin. After three to four weeks of isolation, the denervated melanophores exhibit a 10(9)-fold increase in sensitivity. The efficacy of melatonin is increased from a negligible pigment-aggregation ability to the level of a full agonist. The melatonin-induced aggregation can, however, be counteracted by the alpha2-adrenoceptor antagonist yohimbine, but not by alpha1-adrenoceptor antagonist prazosin, indicating that the ultrasensitive receptor possesses alpha2-adrenoceptor features. Consequently, we conclude that the ultrasensitive receptor may represent an alpha2-adrenoceptor that has, due to denervation of the melanophore, become sensitive to melatonin.
authors.affiliation: Dept. of Pharmacology, Faculty of Health Sciences, Linköping, Sweden. Lena.Martensson@far.liu.se
authors.forename: L G
authors.initials: LG
authors.lastname: Moartensson
authors.forename: R G
authors.initials: RG
authors.lastname: Andersson
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D005576:Colforsin / Q000494:pharmacology; D003714:Denervation; D005399:Fishes; D008543:Melanins / Q000494:pharmacology; D008547:Melanophores / Q000187:drug effects / Q000502:physiology*; D008550:Melatonin / Q000494:pharmacology*; D009638:Norepinephrine / Q000494:pharmacology*; D017933:Peripheral Nervous System / Q000502:physiology*; D011224:Prazosin / Q000494:pharmacology; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D008543:Melanins; D005576:Colforsin; D015016:Yohimbine; D008550:Melatonin; D009638:Norepinephrine; D011224:Prazosin