Differential Expression of Melatonin Receptor Subtypes MelIa, MelIb and MelIc in Relation to Melatonin Binding in the Male Songbird Brain

Abstract

Previous autoradiography studies illustrated that several areas of the avian brain can bind the pineal hormone melatonin. In birds, there are three melatonin receptor (MelR) subtypes: MelIa, MelIb and MelIc. To date, their brain distribution has not been studied in any passerine bird. Therefore, we investigated mRNA distribution of MelR subtypes in adjacent sections of the brain of two songbirds, the blackcap and the zebra finch, in parallel with that of 2-[¹²⁵I]-iodomelatonin (IMEL) binding sites in the same brains. The general pattern of receptor expression shown by in situ hybridization of species-specific probes matched well with that of IMEL binding. However, the expression of the three subtypes was area specific with similar patterns in the two species. Some brain areas expressed only one receptor subtype, most brain regions co-expressed either MelIa with MelIb or MelIa with MelIc, whereas few areas expressed MelIb and MelIc or all three receptor subtypes. Since many sensory areas, most thalamic areas and subareas of the neopallium, a cortex analogue, express MelR, it is likely that most sensory motor integration functions are melatonin sensitive. Further, the area-specific expression patterns suggest that the regulatory role of melatonin differs among different brain areas. Since subareas of well-defined neural circuits, such as the visual system or the song control system, are equipped with different receptor types, we hypothesize a diversity of functions for melatonin in the control of sensory integration and behavior.

Exogenous melatonin inhibits neutrophil migration through suppression of ERK activation

“…As the major output of the pineal gland in vertebrates, melatonin plays a vital homeostatic role in the rhythm-dependent basic functions of zebrafish physiology, including sleep (Zhdanova 2011, Elbaz et al 2013, diet (Lima-Cabello et al 2014), development (Kazimi & Cahill 1999, de Borsetti et allearning and memory (Baydas et al 2005, Moriya et al 2007. Almost all of the functional actions of the melatonin system are conducted through the identified receptor 1, 2, or 3 (Fusani & Gahr 2014, Kleber et al 2014, Lee et al 2014. In zebrafish, melatonin and its receptors become functional at w20 h post-fertilization (Danilova et al 2004).…”

Melatonin receptor expression in vocal, auditory, and neuroendocrine centers of a highly vocal fish, the plainfin midshipman (Porichthys notatus)

“…A recent ISH study in two songbirds, the zebra finch ( Taeniopygia guttata castanotis ), and the blackcap ( Sylvia atricapilla ), identifies one or more of the three avian melatonin receptor subtypes (mel1a, mel1b, and mel1c) in sensory systems (visual, vestibular, and somatosensory), although none are expressed in the ascending auditory system (Fusani & Gahr, ). In contrast, midshipman mel1b is expressed in thalamic, midbrain, and hindbrain auditory areas and in the hindbrain lateral line system (Table ) that also encodes acoustic stimuli with natural call properties (Weeg & Bass, ).…”

“…In contrast, midshipman mel1b is expressed in thalamic, midbrain, and hindbrain auditory areas and in the hindbrain lateral line system (Table ) that also encodes acoustic stimuli with natural call properties (Weeg & Bass, ). Similar to the songbirds, midshipman mel1b is expressed in the olfactory bulb (Fusani & Gahr, ). Mel1b , but not mel1a , is in critical nodes of the descending vocal motor pathway of songbirds: the HVC (letter‐based name), the premotor nucleus robustus arcopallialis (RA), and the midbrain vocal center nucleus intercollicularis (ICo; Fusani & Gahr, ), which is consistent with a previous study (Jansen et al, ).…”

“…Similar to the songbirds, midshipman mel1b is expressed in the olfactory bulb (Fusani & Gahr, ). Mel1b , but not mel1a , is in critical nodes of the descending vocal motor pathway of songbirds: the HVC (letter‐based name), the premotor nucleus robustus arcopallialis (RA), and the midbrain vocal center nucleus intercollicularis (ICo; Fusani & Gahr, ), which is consistent with a previous study (Jansen et al, ). Like the midshipman PAG (Kittelberger et al, ; Kittelberger & Bass, ), ICo has been compared to the PAG of mammals (Kingsbury, Kelly, Schrock, & Goodson, ).…”

“…Here, we used in situ hybridization (ISH) to localize predicted mel1b transcripts in the brain of midshipman fish because of its abundance in the vocal control system of birds, the predominant tetrapod model for neural mechanisms of vocal–acoustic communication, and mel1b's role in facilitating vocal network excitability in both songbirds and midshipman fish (Bentley, Perfito, & Calisi, ; Feng & Bass, ; Fusani & Gahr, ; Jansen et al, ). Additionally, we used quantitative real‐time (q) PCR to measure the expression of mel1b throughout four brain divisions.…”