Melatonin In Prenatal Development Hormone Or Pheromone

Briefly consider the perceptual world of the fetus. Consider the role the mother plays in sheltering the fetus from the external environment. In this context, it seems remarkable that the mother is also actively involved in transferring environmental information to the fetus. During gestation, the mother generates signals which allow the fetus to perceive the length of the light portion of the lighting cycle (day length) as well as the phase (timing) of the light-dark cycle. We refer to these two different forms of prenatal communication as maternal-fetal communication of daylength and maternal-fetal communication of circadian phase, respectively (Figure 1). The maternal melatonin rhythm appears to play a role in transmitting both attributes of the lighting cycle from mother to fetus. Melatonin is thus an important component of the perceptual world of the fetus. In this context, it may be worth considering melatonin as a pheromone (a chemical substance from one member of a species which communicates information to another) rather than as a hormone.

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Melatonin And Estrogen Receptor

Figure 1. Schematic models illustrating the roles of melatonin in perception of the prenatal lighting cycle. Top panel: Prenatal Communication of Day Length. The mother (top box) detects light via the eye at a time when the fetus is sheltered from environmental lighting and the anatomical pathways for detection of light are not developed. Rhythms in melatonin (MEL) released from the maternal pineal are accurately reflected in the fetal circulation. Melatonin interacts with target tissues which may include the suprachiasmatic nucleus (SCN) to allow fetal perception of day length, which influences postnatal reproductive development (see section 3). Lower Panel: Prenatal Communication of Circadian Phase. Melatonin is one of several temporal signals whose generation is dependent upon the maternal SCN. Melatonin and dopamine (DA) interact with receptors in the fetal SCN to impart time-of-day information (see section 4). Abbreviations: IGL, inter-geniculate leaflet; RHT, retinohypothalamic tract. Adapted from Ref. 53.

Figure 1. Schematic models illustrating the roles of melatonin in perception of the prenatal lighting cycle. Top panel: Prenatal Communication of Day Length. The mother (top box) detects light via the eye at a time when the fetus is sheltered from environmental lighting and the anatomical pathways for detection of light are not developed. Rhythms in melatonin (MEL) released from the maternal pineal are accurately reflected in the fetal circulation. Melatonin interacts with target tissues which may include the suprachiasmatic nucleus (SCN) to allow fetal perception of day length, which influences postnatal reproductive development (see section 3). Lower Panel: Prenatal Communication of Circadian Phase. Melatonin is one of several temporal signals whose generation is dependent upon the maternal SCN. Melatonin and dopamine (DA) interact with receptors in the fetal SCN to impart time-of-day information (see section 4). Abbreviations: IGL, inter-geniculate leaflet; RHT, retinohypothalamic tract. Adapted from Ref. 53.

The two most widely recognized physiological roles of melatonin are in the seasonal regulation of reproduction and in the regulation of circadian rhythms. In its "pheromonal" role, melatonin influences these important physiological systems even while the developing animal is incapable of detecting light directly or of producing melatonin. This chapter will review these and related roles of melatonin in development. First, a brief discussion of the sources of melatonin reaching the developing animal is necessary.

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