Kazutaka Homma

Induction of rapid testicular growth in Japanese quail by phasic electrical stimulation of the hypothalamic photosensitive area

SummaryOptic fibers were implanted stereotaxically into the brain of immature male Japanese quail reared under short-day photoperiod (lights on from 1000 to 1800 h), and photosensitive sites in the hypothalamus were examined using gonadal growth and associated hormonal changes as the indices.In the subsequent experiments, bipolar (coaxial) electrodes were implanted chronically using predetermined coordinates for highly photosensitive sites. Henceforth the birds received brief electrical stimulation (square wave, 100 Hz, 100μA, 2 min) once daily for 21 consecutive days. When the electrical stimulation was applied early in the dark period, marked gonadal growth was induced, but identical stimulation given in the light period resulted in no testicular growth. The response curve of testicular weight vs clock time of electrical stimulation has a prominent peak at 3 h after the onset of dark. Apparently, the neural complex in the photosensitive area of the quail hypothalamus responds to electrical stimulation as it does to light. We conclude that in photoperiodic birds the principal factor which determines the magnitude of gonadal responses is not the intensity of the stimulus but its timing (circadian phase).

Detection of neural connection to the infundibular complex by partial or complete hypothalamic deafferentation in male quail

To elucidate the stimulatory and inhibitory neural systems for photoperiodic control of avian reproduction, immature male Japanese quail were subjected to partial or complete hypothalamic deafferentation, followed by exposure to long and short photoperiods. The results indicated that when the encephalic photosensitive area (infundibular complex, INF) was preserved after hypothalamic deafferentation, birds were able to respond to long days and their gonads eventually recrudesced, and that testicular atrophy under short days was prevented by the semicircular cuts posterior to INF or by orbital enucleation. It is concluded that in male Japanese quail, INF plays the pivotal role in photoperiodic gonadostimulation and regulatory neurons in the retina and anterior hypothalamus may have neural connection to the posterior side of INF.

Important role of the eyes controlling the locomotor rhythm in quail

Abstract Whether the eye of quail is a driving oscillator or not was studied by examining the locomotor activity rhythm. The circadian rhythmicity was assessed by the actogram and chi‐square periodogram. The bird showed clear diurnal rhythmicity under 24 h light‐dark (LD) condition. By bilateral enucleation, the activity during dark phase increased, and the diurnal rhythmicity became obscure in some birds when the actogram was inspected visually. The periodogram showed, however, that the significant daily rhythm was maintained in all birds examined in this condition. Thus, the brain photoreceptor could mediate LD information responsible for the locomotor activity. Under constant dim light condition, the circadian rhythmicity was found in intact quail. Unilateral enucleation has no substantial effect on these circadian rhythmicities. However, there was a disruption of circadian rhythmicity following bilateral enucleation. These observations suggest that the ocular system of quail may be classified as one o...

Retinal modulation of the hypothalamic sensitivity to testosterone feedback in photoperiodism of quail

This experiment was performed on two groups of male Japanese quail. One had been maintained in our laboratory as a closed colony (S-group), and the other had been obtained from a commercial source (R-group). Different responses of gonadal function were found between two groups following either testosterone treatment or exposure to short days. Immature birds of these groups responded to long days with rapid gonadal growth, but after sexual maturity, exposure to short days for 3 weeks induced testicular atrophy only in S-group. Involvement of the feedback effect of androgen in the photoperiodic response was then examined. Under long-day conditions, intraperitoneal placement of testosterone propionate (TP)-filled Silastic tube for 2 weeks decreased testicular weights in S-group but not in R-group. Apparently, sensitivity to short days is closely correlated with sensitivity to testosterone in the adult male. By bilateral enucleation, quail of S-group became less sensitive to both gonad inhibitory effect of short days and the negative feedback effect of TP. These results suggest that the photoperiodic mechanisms that are primarily mediated by the retinal system play a role in altering sensitivity to steroid feedback at the hypothalamus.