The Role of the Eye and of the Hypothalamus in the Photostimulation of Gonads in the Duck

Abstract

The successive phases of the photosexual reflex in birds involve the eye, the hypothalamus, the adenohypophysis and the gonads. On June 6, I reviewed structural components of the retino-hypothalamo-hypophyseal pathway in the duck (Anas platyrhynchos). Today, I shall rapidly review the successive experiments which, since thirty years, enabled me and my collaborators to ascertain the rBle of effective light radiations in this mechanism, as well as the properties of the two photoreceptors which seems to be complementarily involved in the photosexual reflex : the superficial, retinal photoreceptor, and the deep, hypothalamic photoreceptor. I. Experiments demonstrating the r6le of the eye as superficial photore-1. Illumination of immature male ducks whose heads are covered by a black cloth, does not stimulate the testes. However light does bring about a testicular growth when limited to the ocular region, the remaining parts of the head and the body being kept away from light (Benoit, 1935 a, 1937) (FIGURE la, b ) . Blackening, or removal of the lids does not prevent the optosexual reflex. On the contrary, no testicular development occurs in response to light supplied to the side of the head when the ocular globe has been removed and replaced by a metallic or rubber plate (Benoit 1937, 1938 a ) (FIGURE ceptor. Hence light acts at the level of the ocular region.

Responses of poultry to ultraviolet radiation

“…The efficiency with which light penetrates to the hypothalamus is dependent upon its wavelength, with shorter wavelengths experiencing more absorption by the cranial tissues than longer wavelengths (Benoit, 1964;Hartwig and van Veen, 1979;Foster and Follett, 1985). Some failures of shorter wavelengths of radiation to elicit a photosexual response may be due to their suboptimal ambient illuminance rather than a lack of a response to the wavelength per se (Benoit et al, 1950).…”

Vertebrate ancient opsin photopigment spectra and the avian photoperiodic response

“…Birds possess photoreceptors located within the medio-basal hypothalamus (MBH) that regulate photoperiodic responses to daylength [1]. An action spectrum for this response showed the involvement of an opsin/vitamin A photopigment with a spectral maximum at 492 nm, suggesting that daylength measurements are mediated by such a molecule [2].…”

Exploring avian deep-brain photoreceptors and their role in activating the neuroendocrine regulation of gonadal development

“…Specifically, the eyes (Menaker et al, 1970;Harrison, 1972;Oishi and Lauber, 1973;Follett and Davies, 1975;McMillan et al, 1975;Wilson, 1989Wilson, , 1991, suprachiasmatic nucleus , and pineal gland (Harrison and Becker, 1969;Homma and Sakakibara, 1971;Siopes and Wilson, 1974;Gwinner, 1981;Wilson, 1991) have not been found to be critical components for transducing photoperiodic information into an appropriate behavioral and physiological response for successful reproduction at the proper season each year as has been found in mammals (Figure 1). The primary sensory system shown to detect photoperiodic cues is thought to be nonretinal, nonpineal deep brain photoreceptors (DBP; Benoit, 1964;Wilson, 1991;Foster et al, 1994;Vigh et al, 2002).…”