At various times in the history of medicine the precise function of the small discrete pea-like structure we have in the centre of our brains, called the pineal gland, was considered to be: a memory valve, a valve controlling circulating vital fluids, the seat of the soul, and the site of a presumed pathology causing certain types of mental illness – “a stony hardness of the pineal gland” (McGillion, 1980).
In the mid nineteen fifties this confusion began to clear when the pineal gland’s true function was discovered and the nature of the link between ourselves and certain events in the skies above us was finally revealed.
The modern systematic study of the pineal gland began in 1954 when, after a review of the existing literature, Mark Altschule and Julian Kitay suggested it could be a productive area for research (Kitay & Altschule, 1954). Their comprehensive review suggested that the gland – until then generally held to be unimportant by modern scientific medicine – appeared to have a number of possible, if minor, physiological roles, many of which had been reported in the literature on the light sensitivity of certain mammals (Fiske, 1941).
Melatonin
It was soon established that the pineal gland produced a number of neuropeptides including one: 5-methoxy, N-acetyltryptamine, considered to be the most important of the pineal hormones and commonly called melatonin, (Figure 1).
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The biosynthesis of melatonin was discovered to be dependent on a number of substrates and co-factors, and on the activity of a number of enzymes including the light-sensitive: hydroxy-indole-O-methyl transferase (HIOMT). (Lerner et al, 1958; 1959).
As Brownstein and Heller (1968) demonstrated, this enzyme – which catalyses the conversion of serotonin to melatonin – is modulated by nerves that impinge directly onto the pineal gland, the activity of which, in turn, depend upon input from the optic nerves. Thus a small proportion of the impulses set up in the optic nerves bypasses the main visual pathway and, instead, takes a circuitous route to the pineal. Stimulation of these nerves increases the activity of HIOMT and, hence, stimulates the synthesis of melatonin.
Bright light inhibits melatonin production by inhibiting nerve tone to the pineal, whereas darkness has the opposite effect and, by increasing neural activity to the gland, stimulates the production of melatonin. This effect of light is dependent both upon its wavelength and its intensity.
In 1973, Cardinali et al showed that red light produced minimal inhibition of melatonin synthesis, whereas green light caused maximal stimulation. In addition, illumination with a light intensity of 0.5 microwatt/cm2 for forty-eight hours produced a fifty per cent decrease in melatonin synthesis in the rat pineal gland.
By way of comparison, sunlight, which strongly inhibits melatonin production, has an intensity of around 50,000 microwatt/cm2, whereas full moonlight has an intensity of around 0.3 microwatt/cm2. (Altschule, 1975).
Because of its low light intensity, the moon was originally thought to have no effect on the production of melatonin by the pineal gland. However, as we discuss below, more recent studies have produced results that suggest there may be some link between lunar phase and the secretion of melatonin (Law, 1986).
In addition to light, other electromagnetic (EM) radiations influence melatonin production, and EM fields of varying strengths and types – including earth strength magnetic fields – have been shown to influence melatonin production to the same degree as the exposure to light does: both in vivo, and in vitro and in a number of species including humans (Reiter & Richardson, 1992; Reiter, 1993a,b; Schneider et al, 1994; Yaga et al, 1993). Further, magnetic fields of this general type have been found to be effective in directly stimulating pineal tissue (Richardson et al, 1992).