Timed daily administrations of hormones and antagonists of neuroendocrine receptors alter day-night rhythms of allograft rejection in the gulf killifish, Fundulus grandis.

Immune activity during scale allograft rejection, measured by melanophore destruction, is two to three times greater at night (12-hr scotophases) than during the day (12-hr photophases) in gulf killifish (Fundulus grandis). In the present study of killifish, hormones and antagonists of neuroendocrine receptors were administered daily at 0800 or 2000 hr during either 12-hr photoperiods (light onset: 0800 hr) or continuous light to examine possible neuroendocrine regulation of the allograft rejection rhythm. Immune activity peaked 0-12 hr after the time of daily growth hormone injections (0800 or 2000 hr) in fish held under continuous light and examined twice daily (0800 and 2000 hr) for melanophore breakdown. Immune activity peaked 12-24 hr after the time of day when cortisol-supplemented meals were provided (light onset or light offset) whether fish were treated throughout the days of melanophore examinations or pretreated for 3 days only prior to melanophore examinations. Daily rhythms of immune activity were not observed in fish treated with propranolol or naloxone at light offset only, growth hormone or atropine at light onset only, or prolactin at either light onset or light offset; these timed-treatments also reduced (prolactin or growth hormone) or prolonged (propranolol or naloxone) the length of time needed to destroy all melanophores within an allograft compared with controls. These results demonstrate that neuroendocrine factors can modulate a daily rhythm of immune function in fish.

Nonphotic stimuli alter a day-night rhythm of allograft rejection in gulf killifish.

The influence of environmental stimuli on a daily rhythm of immune activity during scale allograft rejection was investigated in gulf killifish, Fundulus grandis. Although melanophore destruction in the grafts is largely restricted to the scotophases in killifish held on 12 h daily photoperiods (LD 12:12), timed daily netting (tank-transfer "stress"), thermoperiods (from 20 degrees to 30 degrees C for 4 or 12 h), and feeding altered the expression of this rhythm. Melanophore breakdown peaked 0-12 h after netting or thermoperiod onset and 12-24 h after feeding, whether the fish were exposed to these nonphotic daily stimuli at the onset or offset of 12-h photoperiods. In fish held under continuous light and pretreated with these daily stimuli, 24-h immune activity rhythms persisted in the altered phases for several days after the daily treatments were stopped. These findings suggest that a daily rhythm of immune activity may have adaptive significance in fish.

A day-night rhythm of immune activity during scale allograft rejection in the gulf killifish, Fundulus grandis.

The circadian variation of scale allograft rejection was studied in teleost fish maintained on 12-h daily photoperiods (LD 12:12). Immune activity, measured by melanophore breakdown, was two to three times greater during the dark than during the light whether scale allografts were transplanted at light onset or light offset. Because rejection occurred predominantly at night, survival times of both primary and secondary allografts were about 0.4 days longer when the transplants were made at light onset. Immune activity undergoes a robust daily variation in a teleost fish.