The influence of seasonal changes in light on hormones in normal cats and in cats with lesions of the superior colliculi and pretectum

Abstract

Two groups of cats with lesions of the superior colliculi and adjacent pretectal nuclei and two groups of sham‐operated cats were subjected simultaneously to artificial “bright winter” and “dim summer” lighting conditions and their endocrine state determined. Urinary excretion of 11‐hydroxycorticoids, adrenalin, and norad‐renalin were specified with fluorometric techniques, and thyroid function was assessed with an uptake measure of radioiodide and with a rate of release measure of radioiodide‐labelled hormones from the thyroid gland. The results indicated that the cats in the bright winter condition had much higher indices of thyroid and glucocorticoid function. No effect of the lighting schedules on the catecholamines, urinary volume or body weight was detected, and no effect of the lesion was detected. A comparison of these data with our previous longitudinal studies in cats, as well as with the literature on other species, indicates that (1) light is the Zeitgeber for the annual glucocorticoid rhythm; (2) even though light influences the activity of the thyroid gland, it is difficult to consider it as the Zeitgeber because thyroid rhythms do not exhibit annual rhythms; (3) with regard to the role of light in entraining the catecholamines, the results were equivocal, possibly because of the sampling times. The raison d'etre of biological rhythms is considered, and it is suggested that their provision of order to the temporal milieu may be viewed as a higher order aspect of homeostasis.

Abstracting keywords:

• Cats
• endocrine rhythms
• photoperiodicity
• pretectum
• seasonal
• superior colliculi

Notes

Dept. of Psychology, Univ. of Iowa, Iowa City, Iowa 52242, U.S.A.