Highlights of EPSG Conferences, 1978-1990:

A Society ahead of its Time

The first conference: Amsterdam 1978

The society whose name is now the European Biological Rhythms Society began life a long time ago (before SRBR, founded in 1988) under the name of the European Pineal Study Group (EPSG). It was founded by Johannes Ariens Kappers and Paul Pevet (see summary and links). It is however remarkable to see how many of today's (2014) hot topics were represented and debated at the very first meetings. The first conference of EPSG was held in Amsterdam in 1978. At this time interest in the neurobiology of biological rhythms was growing fast and the pineal gland provided a perfect link between the environment and body physiology as a photoneuroendocrine transducer. Much work on the neuroanatomy of neuroendocrine systems had taken place (links) and the time was ripe to turn to physiology and even clinical aspects. This meeting was particularly important as the first of its kind, but also because many of the themes which are vigorously pursued today appeared at this time.

We all know now that the effects of light on the circadian system and on photoperiodic seasonal breeders have proved to be of immense importance. In 1978, building on the work of Joe Herbert (1971) Klaus Hoffmann showed for the first time that the pineal, until then considered to be anti-gonadotrophic, was neither specifically anti- or pro-gonadotrophic, but was instead transmitting a signal encoding daylength to which animal physiology responds. At the same meeting, thanks to the development of radioimmunoassay, the change in duration of the pineal hormone melatonin with daylength (long in short days, short in long days) was described in a naturalistic seasonal study in sheep. This in turn was to underpin the later demonstration that administration of short or long duration melatonin would provoke the appropriate seasonal response in sheep and in hamsters. This line of research is very active today notably because the molecular mechanisms of daylength control of gonadotrophin function are being unravelled.

With regard to circadian rhythms, we learned that in rats as little as one minute of light at night would suppress pineal melatonin synthesis very rapidly and phase shift its rhythm, both assessed using the enzyme serotonin-N-acetyl transferase (NAT) driving the melatonin rhythm. Thus a new tool was generated to study the resetting and structure of the central SCN pacemaker. These observations were later supplemented with measurement of melatonin itself and underpin much of today's circadian biology, including the use of light to manipulate circadian rhythms and to treat circadian rhythm disorders, the treatment of seasonal affective disorder, and the recent demonstration of a new photoreception pathway using light sensitive retinal ganglion cells and a new opsin sensitive to short wavelengths - melanopsin, all areas actively researched today.

Early demonstrations of the effects of melatonin (and 5-methoxytryptophol) on hypothalamic neurones appear presaging later fundamental work. In addition to these seminal physiology studies, beautiful demonstrations of the evolution of photosensory pineal cells (CRL, cells of the receptor line) - biochemistry and morphology - lead to the development of an evolutionary tree from lower vertebrates on course today.

Early observations of human melatonin production using the first radioimmunoassays showed clearly a large inter-individual variability but a very stable amplitude within individuals. Thus cross sectional studies require very large numbers of subjects for reliable results. Individuals should be used as their own controls as far as possible: this problem is recognised today but was slow to be adopted in experimental protocols. The possibility of using melatonin therapeutically was mooted: in 2014 it is used therapeutically to treat circadian rhythm disorders underlying sleep problems.
 
Even the development of cancer, of importance today in relation to circadian desynchrony, was linked to the pineal gland.

Importantly, it became clear at this meeting that pineal peptides, intensively studied during the previous 15 years for a possible secretory function, are primarily concerned with pineal function as neurotransmitters.
 

Highlights of other meetings

Giessen 1981

President Johannes Ariens Kappers provided a most elegant, erudite, cultural and historical review of the evolution of pineal concepts from antiquity to today (1981). This included the well known work of Descartes describing 300 years ago his postulated influence of light on pineal function. These ideas were greatly influenced by ancient themes but they form a bridge to modern concepts. From the scientific programme, further development of the comparative morphology of the pineal from work presented at the first meeting was evident. The central innervation of the mammalian pineal was treated in depth. In the same vein the possible links between the known peptides and indoleamines of the pineal were discussed and explored.
Today there is substantial interest in the relative contributions of different spectral qualities of light to non-image forming photoreception. Thus a comprehensive review and pioneering comparative studies in lower vertebrates, of the electrical responses of the pineal/frontal organ/parietal eye to different spectral characteristics and intensity of light, were exceptional.
The characteristics and response to light of mammalian melatonin production (sheep, rats and hamsters) were once again in evidence with duration of the signal again the endpoint. Moreover melatonin production in a large range of species was presented: it is invariably high at night in a normal light-dark cycle. The description of careful long term studies of the pineal influence on circannual rhythms in birds, heralded current investigations into the mechanisms underlying circannual rhythms. The conclusion was that in some birds the pineal played at least some role and probably via the circadian system, shown previously to be dependent on an intact innervated pineal in some species.
Another review and report of comparative research concerned the question of possible pineal control of reproduction in non-mammalian vertebrates. The influence of different environmental factors is clear and the pineal was proposed as an integrating factor.
 

Pecs, 1984

Continuing the theme of the role of the pineal in non-mammalian vertebrates, in a lizard melatonin production may be entrained by photoperiod. In another poikilotherm the Greek tortoise, a major seasonal variation in amplitude is due to temperature changes not to photoperiod. Great species variations are seen, other methoxyindoles may play a role and the pineal may act through melatonin to integrate temperature and photoperiod changes.
New in morphology were the CSF contacting neurone cells of the ependymal layer of the 3rd ventricle of several vertebrate species and the presence of both rod and cone-like photoreceptors in the pineal organ.
We learned of the multiple receptor mechanisms regulating pineal cyclic nucleotides with potentiation by alpha-adrenergic receptors of beta adrenergic receptor activity. Many classic adrenoceptor studies have used the pineal as a model organ (e.g. Axelrod). This multiple regulation has clinical consequences today with regard to suppression and/or activation of melatonin production.
We also heard of melatonin binding sites in the median eminence, later to be attributed to the pars tuberalis.
The complexity of the pacemaker driving pineal melatonin synthesis was amply demonstrated by the differential response of the onset and offset of melatonin synthesis to timed light pulses and the phase response curves associated with each. The influence of photoperiod on the rhythm in melatonin synthesis and on its phase shifting response was similarly reported with far reaching implications ultimately for the therapeutic effects of light in circadian rhythm disorder.
Whilst already shown in the rat, the close correlation between pineal NAT and pineal melatonin was evident in Djungarian hamsters and a comparison between Syrian and Djungarian hamsters showed differences in relation to photoperiod. At this time we knew that timed artificial long duration melatonin in summer would shift the breeding season earlier in the ewe. These observations led to the convincing demonstrations later that infused long and short duration melatonin would induce the appropriate seasonal responses in hamsters and sheep.
At this meeting the importance of melatonin in humans became a theme. For years it was thought that the human pineal was involved in the control of human pubertal timing following observations of the effects of pineal tumours. However no differences in melatonin were seen in a small number of subjects in different stages of puberty. It should be noted that a steep decline in melatonin in younger subjects had been reported. Even now (2014) we do not know what, if any, is the role of melatonin in human puberty, although its long or short duration profile clearly influences pubertal timing in photoperiodic species and this influence begins prenatally.
We also knew by then that during sleep deprivation the rhythm of melatonin correlated with recorded fatigue and that small (2mg) doses of melatonin given to subjects in the late afternoon would advance sleepiness or sleep itself and phase advance the endogenous melatonin rhythm. Thus the stage was set for the therapeutic use of melatonin today in circadian rhythm disorders. The investigation of melatonin in different diseases was underway but without realising at this time the importance of controlling the light environment.
Some early work on melatonin binding sites emerged at this meeting. Further development awaited the availability of a good radioactive ligand (iodomelatonin).

Modena 1987

Professor Oksche in his presidential address emphasised the growth and development of the society particularly since it became largely international. Much of the science presented at early meetings concerned the comparative anatomy and histology of the pineal complex in different species. Prof Oksche provided an integrated summary of current knowledge regarding the modified photoreceptors and classical pinealocytes and the dissection of the molecular characteristics of different classes of pineal cells. He discussed the evolutionary origin of the mammalian pineal from the direct photoreceptive capacity of that of lower vertebrates and highlighted the seminal work of several members and groups within our society.
Further insights in this basic knowledge were presented at the conference leading to current concepts of pineal function and circadian biology. These included the peptidergic innervation of the mammalian pineal and notably the presence of vasoactive intestinal peptide (VIP) using new immunohistochemical techniques. The importance of central vasopressinergic innervation of the European hamster was discussed. This peptide has proved of considerable interest as a neurotransmitter in circadian biology not only within the pineal but also the SCN. Using passive central immunisation against melatonin it was concluded that the influence of melatonin on photoperiodic responses was not via the SCN - the mechanism acting via hypothalamic thyroid hormone has only recently been elucidated. Also, later it was demonstrated that first the SCN itself is modulated by the photoperiod and the pineal melatonin then only reflects processes in the SCN.
The multiple adrenergic regulation of melatonin synthesis was again in evidence with new work on the in vitro sheep pineal raising some controversial issues.
The use of the rat NAT rhythm as a model to study the properties of the circadian pacemaker was highlighted with the qualities of high amplitude, two phase markers- the evening rise and the morning decline, the ability to study immediate response, and transience to steady state effects of light pulses, and the duration of high levels indicating the melatonin signal for photoperiod length. Today circadian responses in humans are characterised by measurement of melatonin itself. There is some evidence for differential response of the rise and fall in man.
However at this time (1987) it had already proved possible to demonstrate a light pulse phase shift of the human circadian clock - in the Antarctic winter using melatonin measurement and in controlled experiments using other rhythm markers. Light was just emerging as the principal zeitgeber for the human circadian system.
We had known since 1983 that melatonin would entrain free-running activity rhythms in rats and since 1984 that when given in the late afternoon that it would shift the timing of sleep and its own rhythm in humans. Thus it could act as a chronobiotic in rats and humans. The first demonstration that melatonin could alleviate jet lag when correctly timed was presented. At this meeting the critical time for phase advance of the activity rest cycle in rats was shown to be from CT9 to CT11.
This meeting highlighted the ability of melatonin to act as a marker rhythm for the circadian system in humans using plasma, saliva, urine or new technology (RIA) for measuring the metabolite 6-sulphatoxymelatonin in urine. The latter is now used extensively world-wide notably for epidemiological studies, and field studies particularly in remote environments.

Guildford 1990

The gradual change of this pineal society into a broad biological rhythms society became evident at this meeting. In his introduction Joe Herbert (Cambridge, UK) drew upon the parallels and commonalities between psychological and photoperiodic time measurement to conceptualise different methods whereby time may be measured by organisms. He proposed experimental approaches to differentiate these mechanisms and emphasised the relative way in which animals interpret for example the melatonin signal for daylength.
The first sections concerned refinements of the neural control of the pineal and both adrenergic and peptidergic mechanisms regulating melatonin synthesis. UV light was implicated in the control of reproductive physiology via an impact on pineal function. The retina emerged as of considerable interest with regard to interrelationships between organs of the visual system, the photoreceptor specific proteins, and the possible function of 5-methoxyindoles other than melatonin within the retina. Whilst melatonin is clearly synthesised within the retina in mammals it does not contribute to circulating levels.
Melatonin receptors were a major aspect of this meeting with descriptions and localisation of high affinity binding sites in the brain and notably the SCN and the pars tuberalis. Numerous other binding sites have now been reported and species differences have become evident with greater numbers in lower vertebrates. Two subtypes were identified, now named MT1 and MT2. The cloning of these two receptors was verbally reported first at this meeting. The site originally identified as the median eminence is now clearly the pars tuberalis (PT) - an organ of no known function at that time. We now know that the PT is an essential part of the photoperiodic time measurement cascade with respect to both prolactin and gonadoptrophin hormones This observation has led to extensive use of the PT to characterise the G-protein linked receptors and their pharmacology, and to characterise melatonin agonists, then under development and now licensed for use in sleep disorders (and one for depression).
In seasonal physiology cranial implants of melatonin in the ewe generate short day effects without changing the concomitant long day profile of endogenous melatonin, indicating clearly that the effects of melatonin are local within the brain. It was shown clearly that a 'melatonin-free interval' was crucial to determine the response to a given duration of the hormone. It became evident from several presentations that prenatal photoperiod governed postnatal development from both a circadian and a pubertal perspective and that maternal melatonin was a photoneuroendocrine transducer in this respect - although in the absence of maternal melatonin other zeitgebers were effective in the case of circadian phase.
Entrainment of the circadian system by melatonin, first reported in the early 1980s had now become 'respectable' . We heard that the effects were photoperiod dependent in rats, that the phase response curve for phase shifts by melatonin was different in nocturnal and diurnal creatures and that the entrainment effects could be used successfully in humans in a number of situations with disturbed circadian rhythms. These included field studies and laboratory studies of jet lag, the entrainment of free-running blind people (initially shown for sleep in 1988) and delayed sleep phase. The combined use of timed bright light and timed melatonin was considered to be the most effective approach, but without evidence as yet for efficacy. All of these threads are exploited today with the addition of the use of melatonin agonists/slow release formulations for sleep problems which do not necessarily have evidence of circadian disruption.
The final sessions of this meeting addressed the possible influence of melatonin on cancer growth in animals. This area has been very active recently (2014) with evidence that shift work/circadian desynchrony is a risk factor for cancer. One hypothesis- that light at night partly suppresses melatonin and thereby increases cancer risk- has been largely replaced by an overall circadian disruption causality. In 2006 the IARC (WHO) published a monograph confirming these concerns. However here is a possible therapeutic outlet for melatonin treatment countering circadian desynchrony which, with rare exceptions, has not properly been exploited i.e. by using correct timing of dose.
 
Joint authors:
 
Paul Pevet, Helena Illnerova, Josephine Arendt

August 2014