Intermittent hypoxic training regulates the microglia phenotype by increasing melatonin receptor expression.

Reduced orthostatic tolerance (OT) is a serious concern facing space medicine. This work sought to evaluate the effects of intermittent hypoxic training (IHT) on OT in humans before and after 3 days of head-down bed rest (HDBR) used to model microgravity. The study was carried out in 16 male volunteers aged 18 to 40 years and included 2 series of experiments with 11-day and 21-day IHT administered on a daily basis. During the first IHT session, the concentration of oxygen in the inspired gas mixture was 10%; for other sessions it was adjusted to 9%. OT was assessed by a 20-minute-long orthostatic tilt test (OTT) conducted before and after HDBR. Before HDBR, orthostatic intolerance was observed in 3 participants, while after HDBR, it was observed in 9 of 16 volunteers (p < 0.05). During OTT conducted after HDBR, the heart rate (HR) exceeded control values by 26.8% (p < 0.01). Preexposure to any of the applied IHT regimens led to a reduction in the number of volunteers with orthostatic intolerance. After the 11-day IHT program, there was a less pronounced increase in HR during OTT before HDBR; with the extended IHT regimen, less pronounced changes were observed for HR, systolic, diastolic and mean blood pressure (BP). The increase in HR during OTT after HDBR was significantly lower in the group that had completed the 11-day IHT program, while BP remained stable. The changes in HR and systolic BP were less pronounced in the group that had completed the 21-day IHT program than in the control group (p < 0.05). Thus, IHT reduced the risk of orthostatic disorders and mitigated changes in cardiovascular parameters during the orthostatic test.

Download Full-text

What is the role of melatonin within the anterior pituitary?

Journal of Endocrinology ◽

10.1677/joe.0.1700493 ◽

2001 ◽

Vol 170 (3) ◽

pp. 493-501 ◽

Cited By ~ 33

Author(s):

DG Hazlerigg

Keyword(s):

Anterior Pituitary ◽

Cellular Level ◽

Prolactin Secretion ◽

Receptor Expression ◽

Melatonin Receptors ◽

Seasonal Effects ◽

Pars Tuberalis ◽

Melatonin Receptor ◽

Functional Studies

The pineal hormone, melatonin, is uniquely defined by its role as hormonal time, but the processes whereby cells extract temporal information from the melatonin signal are not understood. Melatonin receptors are expressed in the pars tuberalis (PT) and, during fetal and perinatal life, in the pars distalis (PD). Functional studies suggest that the PT mediates the seasonal effects of melatonin on prolactin secretion, whilst the PD may be involved in photoperiodic programming of the developing gonadotrophic axis. To understand these effects at the cellular level we need to know the phenotype of melatonin-responsive cells. This review summarises current understanding in this area, and highlights present shortcomings. A case is presented for exploring the hypothesis that there is a functional association between melatonin receptor expression and cell differentiation in the anterior pituitary.

Download Full-text

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

Brain Behavior and Evolution ◽

10.1159/000367984 ◽

2014 ◽

Vol 85 (1) ◽

pp. 4-14 ◽

Cited By ~ 12

Author(s):

Leonida Fusani ◽

Manfred Gahr

Keyword(s):

Expression Patterns ◽

General Pattern ◽

Passerine Bird ◽

Brain Regions ◽

Receptor Expression ◽

Receptor Subtype ◽

Receptor Subtypes ◽

Melatonin Receptor ◽

Brain Areas ◽

Specific Expression

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.

Download Full-text

Responsiveness to melatonin and its receptor expression in the aging circadian clock of mice

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1997.273.6.r1855 ◽

1997 ◽

Vol 273 (6) ◽

pp. R1855-R1860 ◽

Cited By ~ 4

Author(s):

Susan Benloucif ◽

Monica I. Masana ◽

Margarita L. Dubocovich

Keyword(s):

Suprachiasmatic Nucleus ◽

Phase Shifts ◽

Receptor Expression ◽

Circadian Activity ◽

Melatonin Receptor ◽

Activity Rhythms ◽

Age Related ◽

Melatonin Administration ◽

Timing System ◽

Circadian Timing System

This study determined the effect of age on the efficacy of melatonin treatment to phase shift circadian activity rhythms and on melatonin receptor expression in the suprachiasmatic nucleus (SCN) and paraventricular nucleus of the thalamus (PVNT) of C3H/HeN mice. The circadian rhythm of 2-[125I]iodomelatonin binding, assessed at three times of the day [circadian times (CT) 2, 10, and 18], showed a modest age-related decrease in the SCN but not the PVNT of old C3H/HeN mice (24 mo). There was a tendency for age to reduce Mel1a melatonin receptor mRNA expression in the suprachiasmatic nucleus during the day, but not during the night. The magnitude of phase shifts of circadian activity rhythms (advances or delays) induced by administration of melatonin at CT 10 or CT 2 was identical in young and old C3H/HeN mice. Together, these results suggest that the decrease in melatonin receptor expression in the SCN had little effect on melatonin-induced phase shifts of circadian activity rhythms. We conclude that the responsiveness of the circadian timing system to melatonin administration does not decrease with age.

Download Full-text