PHOTOPERIODIC ACTIVATION OF FOS-LIKE IMMUNOREACTIVE PROTEIN IN NEURONS WITHIN THE TUBERAL HYPOTHALAMUS OF JAPANESE-QUAIL

Photoperiodic stimulation of quail (Coturnix coturnix japonica) result ed in the appearance of a nuclear fos-like protein within neurones of the basal tuberal hypothalamus. On transfer to long days the number of neurones containing this fos-like immunoreactivity increased from abo ut 150 to 700, the neurones being scattered throughout the length of t he tubero-infundibular complex. This activation had occurred by early in the second long day and was maintained for at least three long days . Over this period circulating levels of LH increased seven-fold, indi cating that photoperiodic induction had taken place in the birds. A si milar time-course of fos-like induction occurred in castrated quail ex posed to a single long day and then returned to short days. Activation mirrored the long-term changes in LH secretion found in this paradigm and fos-like immunoreactivity showed the same ''carry-over'' characte ristics of photoperiodic induction, being maximal two days after the q uail had been exposed to the single long day (and were again on short days) and when LH secretion was at its maximum. Activation of fos-like immunoreactive cells did not take place when long-day quail were tran sferred to short photoperiods. The evidence supports the view that the neurones being activated are involved in a specific fashion in the av ian photoperiodic response.