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Copy of an article published by the I.H.S. In "The Herptile" September 1978 - Volume 3 - Number 2.

Effects of Lights
Vision is of course the most obvious effect of light. Of the light that enters the eye a fairly narrow wave band elicits the neurochemical chain of events that produces the stimulus to the brain.

However, light has a number of other effects on the living organism, which for the fore mentioned reasons normally means humans, and those are classified as Direct and Indirect.

Direct:

1. Sunburn. This is a condition peculiar to the industrialised societies particularly of Europe. The average urban human is deprived of the daily exposure to sunlight or even daylight experienced by the normal rural specimen, and spends his daylight hours in the dim, deprived light of artificial illumination. When the sun does shine and the schedule of work provides a brief respite, the urban worker flings off his clothing, lies in the sun and turns a painful red.

Sunburn is caused by a narrow band in the near UV. and is the result of toxins being released from damaged, epidermal capillaries. Two to three hours daily exposure to sunlight provides a protective layer of UV. absorbing pigment (Wurtman, 1975).

2. Sunlight, acting directly on the skin can also induce photosensitive reactions to circulating drugs, e.g. tetracycline or certain food constituents such as riboflavine This produces transient intermediates that are potentially toxic and that can cause rashes an the exposed areas of skin.

The penetrating powers of light are surprisingly high and although the shorter wave length radiation can only just reach the surface capillaries, visible light can penetrate all mammalian tissues to a considerable depth, it has even been detectable within the brain of a living sheep (Wurtman, 1975).

The activation of certain compounds under the skin by light is the basis for treating such conditions as Psoriasis and Herpes virus. In psoriasis a compound called Methoxaden is administered orally and the affected area is irradiated later with long wave UV. This causes a local photosensitisation reaction which causes selective damage to the excessively proliferating cells by inactivating the DNA (Wurtman, 1975).

3. Another good example of the direct effects of light and of the applied use of artificial lighting is in the treatment of hyperbilirubinemia in premature infants (jaundice). The yellow colouration of the skin is caused by excessively high circulating bilirubin released by the immature liver. Bilirubin is a constituent of bile and has a detergent like effect in digestion where it emulsifies fat. It is therefore fat-soluble and if in sufficient concentration will readily enter the brain staining all the tissues therein causing varying degrees of paralysis or mental retardation.

Formally this was a difficult and common problem to treat, 15 to 20 percent of premature infants are affected. Treatment involved large scale transfusions, which are very traumatic to the baby and carry their own inherent risks. Chance observations showed that those children exposed to daylight rapidly lost the yellow coloration and made spontaneous recoveries (Lucey, 1972).

The light bleaches the circulating bilirubin to a derivative that is water soluble, rather than fat soluble, and is readily disposed of by the kidneys. The most effective waveband to elicit this reaction is 440 to 470nm. and lamps specifically designed to emit this wavelength have proved four times more effective as daylight in treating this condition (Thorington et al, 1971).

4. Vitamin D. This is probably the most important of the known direct actions of light as far as reptiles are concerned.

Vitamin D is available in two forms, D2 a dietary source and D3 which is produced by the skin under the stimulus of UV. light. When insufficient Vitamin D is available to the juvenile animal the result is Rickets and as far as Humans are concerned it is largely a modern disease almost entirely restricted to the Northern Industrial zone. From the Industrial Revolution until the 1930's Rickets was the scourge of the poorer classes, a survey of children under the age of four dying in

Dresden between 1901 and 1906 showed that 90 percent suffered from rickets. And of course it is not restricted to humans or indeed to mammals, insufficient Vitamin D prevents adequate uptake of calcium and the net result is soft bones that singly collapse under pressure.

Vitamin D does not occur in significant amounts in the average human diet, except for some fish products, and was first synthesised by Rosenheim and Webster from the fungus Ergot in 1927. They named the irradiated product Ergocalciferol or Vitamin D2. In the ensuing years D2 has been added to dairy products, cereals and other foods on a routine basis almost completely eradicating Rickets. This has been described as a public health triumph of the 20th century, (Neer, 1971).

So statements such as “Rickets is a disease of growing bone- caused by a vitamin deficiency, plus the explanation that the desired vitamin is available in fish products and dairy foods are readily accepted as fact, even when accompanied by explana- tions of the role of sunlight. In fact the whole emphasis of Vitamin D has been reversed. Until recently it has not been possible to distinguish between the two forms of D circulating in the body. However, Haddad and Hahn (see Wuztman, 1975) of the Washington School cf Medicine have shown that 70 to 90 percent of the vitmin D activity in blood was accountable to D3 and its derivatives. In short, most of the body’s requirements were being met by the action of sunlight, and not from dietary sources. Britain and several other European countries have curtailed the fortification of foods with D2 because of recent evidence that large amounts are toxic.

A vitamin, incidentally, is a compound that the organism is unable to synthesise itself but is essential for metabolic function, hence it becomes a dietary necessity. Vitamin D3 is synthesised by terrestial animals and its production is regulated by physiological control and not left to the vagaries of diet. In view of this and also of the eventual function of the vitamin it should rightly be called a hormone and in keeping with many other hormones it is a steroid derived from cholesterol. The final product of the irradiation process is called Calciferol and its function is in the control of blood levels of calcium. Two other hormones interact with calciferol in the maintenance of this balance (Thyrocalcitonin and Parathyroid Hormone) in a manner normal for hormones but totally different from the interactions of the true vitamins (Loomis, 1970).

From the Herpetologist’s point of view therefore, depriving young reptiles of daylight will encourage Rickets. This risk can be offset by dietary supplements of D2, but at a risk to the health of the animal from kidney and heart failure and at variance to the preferred requirements of metabolism.

One fine example of the excessive use of Vitamin additives and the resultant toxic effects are described by Wallach (1966) in a paper entitled “Hypervitaminosis in the Green Iguana”. Captive Green Iguanas were fed a diet continually fortified with vitamin and mineral additives. When the animals succumbed autopsy revealed gross and microscopic lesions of “hypervitaminosis D” which is characterised by massive deposition of calcium salts in the arteries and in the soft tissues. The authors admonish; “?Hypervitarninosis is a malady that should be kept in mind when dealing with captive wild animals especially when their exact nutritional requirements are notknown”.

Excessive use of D2 in snake and lizard husbandry and the symptoms of toxicity are described by Wagner and Slemmer (1976) in their paper on Captive Breeding of Reptiles.

Artificial Light and Calcuim Absorption
Rickets, a disease of the growing bone is now rare (at least in Humans) and the same status is applied to the adult counterpart Osteomalacia. However a third condition, Osteoporosis, is very common mainly among the ever 6o’?s but also occurring in adolescents, young adults and the middle-aged. Although the bone is apparently normal it is gradually dissolved away as if the body, unable to absorb sufficient calcium from the diet, is satisfying its needs at the expense of the skeleton. This is another aspect of “Vitamin C”? deficiency (Neer, 1971).

In an attempt to study the effects of artificial light on calcium uptake in potential sufferers of this complaint, Neer, of the Massachusetts General Hospital, deprived elderly, normal men of access to natural light for a teat period. During this period the men were exposed to the white fluorescent and incandescent lights of their normal indoor environment. At the end of sever. weeks their calcium absorption rate was measured and found to be 40 per cent of the amount they had ingested. They were then divided into two groups. One continued to live under the lighting they had already experienced whilst the test group were exposed for eight hours a day to a fluorescent tube designed to simulate natural light. After four weeks the calcium absorption in the control group had fallen by about 25 percent whilst in the test group it had risen by fifteen percent.

The additional amount of UV. they had received that had caused this increase was very small, approximately equal to the amount experienced by a fifteen minute walk in the summer.

The fluorescent light that had proved so beneficial was Vita-lite (Neer, 1971) In addition to the aforementioned direct effect of light on the body also responds indirectly in many ways and in particular to the Periodicity of light in the establishment of daily rhythms.

It is difficult for us to divorce the concept of twenty four hours representing a day to the sequence of light and darkness which occurs during this period. But to animals time is meaningless. Their lives are regulated by the changes in daylength throughout the year and by the cycle of dark and light that occurs on the day to day basis.

Numerous biological functions are known to respond to light and dark, e.g. sleep and activity, body temperature, metabolic changes and variation in endocrine function. Some of these have been measured with sufficient precision to actually show which wavelength of light is responsible for eliciting each cycle. For example, Wurtman (1975) found that green light will best disrupt the twenty four hour body temperature cycle of rats. Furthermore, the action spectrum coincides with the absorption spectrum of Rhodopsin. In other words light is entering the eyes (rhodopsin is the photosensitive pigment in the retina) and somehow fixing the daily rhythm of body temperature.

However, the best documented indirect effect of light concerns the Pineal Gland. In “lower vertebrates”?, a term much favoured by mammal enthusiasts, such as amphibians and reptiles, e.g. Anguis, Varanidae and Tuatara (Bellairs, 1969) the Pineal Body is a photo-receptor converting the photic impulses into neural impulses thence directly to the brain. This useful function has been modified by the hairy mammals so that the pineal is now a gland producing a hormone called Nelatonin. The route by which light elicits the response in the pineal gland is tortuous. Light impinges on the retina and, bypassing the optic centres of the brain, travels by an alternative neural route to the Hypothalamus on the “lower” surfaces of the brain which in turn influences the Pituitary Gland. This exerts hormonal control over the Pineal. Despite the fact that this complicated chain of events is as well known as the inhibitory effect light has on the Pineal the precise role of Nelatonin is little understood. However, experimental administration of melatonin has a profound effect, in that it;

a. Induces sleep
b. Modifies ECG
c. Raises the level of brain compounds famines)
d. Inhibits ovulation
e. Modifies the secretion of hormones from the Pituitary, gonads and adrenal glands

The only positive thing that can be said about melatonin is that its level increases at night, perhaps spreading the word throughout the body that its dark outside (Wurtman, 1969).

Other Endocrine and Metabolic rhythms that respond to light include;
a. Urine production and chemical content
b. Corticosteroid production
c. Ascorbic Acid content in the ovaries
d. Ovulatory Hormone
e. Ovulation
f. Calcium in the Serum
g. Renin in plasma
h. Glycogen content
i. RNA and DNA and cell division
j. Liver phosphollpid

Each of these functions will eventually be investigated and, like body temperature, will probably show to respond to a precise wavelength; a component of natural light under which the mechanism evolved.

Environmental lighting has also been shown to affect behaviour in humans, for instance students were shown to suffer less from fatigue induced by prolonged studying when under Vita-lite than when under conventional white fluorescent sources (Maas. J., J. Jayson and D. Klauber, 1974).

Sex and Gonadal Development
Puberty is advanced in girls blind (from eye defects) from birth by as much as one year when compared to normal sighted girls. Rats however responded to blindness by retarding the onset of ovulation. Is this difference due to the former being a diurnal species whilst the latter is nocturnal? Women blind from early life do not have regular menstruation and blindness disrupts the regular cycle in previously sighted women. Men, blind since before puberty suffer reduced sexual potency despite unchanged libido (Wurtman, 1968).

However, as far as animal husbandry is concerned, the most important observation in this category centres around experiments performed by Wurtman and Weisel (1969) at the Massachusetts Institute of Technology. They raised two groups of rats under different artificial lights. The controls were born and raised under Cool White fluorescent lamps and the test group were born and raised under Vita-lite. After just twenty days the animals were sacrificed and various tissues weighed and examined. The hearts and gonads of the test group were significantly larger than those of the controls.

Bactericidal Effects of Artificial Light It has long been known that exposure to UV. light kills bacteria, the optimum wavelength being 265 nm. Five percent of the total radiant power of Vita-lite lies between 290 and 380 nm and Himmelfarb, Scott and Thayer (1970) tested its bactericidal effectiveness. In fact several hours exposure to Vita-lite gave significant killing of cells of the common pathagen Staphylococcus aureus. A control test with Cool White fluorescent tubes showed no killings.

Conclusion
I have tried to give a simplified, broad picture of the vast amount of research findings that have snowballed to form the new science of Photobiology. Although no one has yet stated unequivocally that reptiles grow better, breed better and live longer under True-lite, the evidence suggests that they will. The technique professional scientists prefer is to take an animal, subject it to a test procedure then remove the appropriate bit, smash it to pieces and see if it differs in some way to a control animal. They have little time or motivation to sit and watch but, perhaps the amateur can. Therefore, as has been said many times before there is a role for the amateur Herpetologist especially in this burdgeoning field.

Light is a complex mixture of wavelengths, many of which have been shown to have a precise and profound effect on all animals examined. To deprive a captive animal of access to light of the right quality and quantity is perhaps as serious a threat to its long term health, physiology and normal behaviour as is the supplying of inappropriate food. Until we can fulfil this requirement in vivaria design then the animals displayed therein will continue to behave in a manner that is a travesty of their behaviour in the wild.

Acknowledgements

I am indebted to John Greatwood of J.G. Animals of Streatham and to Jon’ Coote for the loan of much of the material reviewed in this article.

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