Aftereffects of entrainment on the period of the pacemaker in the eye of the mollusk Bulla gouldiana.

The authors examined the "aftereffects" of entrainment of Bulla gouldiana to 11 h light:11 h dark (LD 11:11) (T22) or LD 13:13 (T26) on the period (tau) of the circadian rhythm of impulse activity recorded in vitro from the eye in constant darkness. When both eyes remained attached to the cerebral ganglion, the average period was 23.9 +/- 0.62 h (mean +/- SD, n = 6) for animals from T22 and 24.9 +/- 0.54 h for animals from T26. The 1-h difference between the periods of the T26 and the T22 animals was significant (p < .01, t test). When eyes were isolated from the cerebral ganglion by severing the optic nerve, the difference in average period between eyes from T22 and eyes from T26 animals was 2.2 h (23.3 +/- 0.72 h [n = 7] vs. 25.5 +/- 0.62 [n = 6], p < .001). When eyes remained attached to the brain but uncoupled from the contralateral eye, the aftereffect of entrainment to non-24-h light cycles was intermediate. For T22 animals, tau was 23.9 +/- 0.29 h (n = 6), whereas for the T26 animals, tau = 25.2 +/- 0.48 h (n = 7). The results show that isolated eyes can express aftereffects and indicate that coupling between ocular pacemakers and efferent signals from the cerebral ganglion diminish the effects of entrainment on the free-running period of the rhythm from the eye.