Surgical removal of the optic lobes of the cockroach Leucophaea maderae followed by transplantation of the optic lobes from another individual led to a restoration of the circadian activity rhythm in 4 to 8 weeks. The free-running period of the restored rhythm was determined by the period of the donor rhythm before surgery. The results suggest that the transplanted optic lobe contains a circadian clock that regenerates those neural connections with the host brain that are necessary to drive the circadian rhythm of activity.
Olfactory learning in insects has been used extensively for studies on the neurobiology, genetics, and molecular biology of learning and memory. We show here that the ability of the cockroach Leucophaea maderae to acquire olfactory memories is regulated by the circadian system. We investigated the effect of training and testing at different circadian phases on performance in an odordiscrimination test administered 30 min after training (short-term memory) or 48 h after training (long-term memory). When odor preference was tested by allowing animals to choose between two odors (peppermint and vanilla), untrained cockroaches showed a clear preference for vanilla at all circadian phases, indicating that there was no circadian modulation of initial odor preference or ability to discriminate between odors. After differential conditioning, in which peppermint odor was associated with a positive unconditioned stimulus of sucrose solution and vanilla odor was associated with a negative unconditioned stimulus of saline solution, cockroaches conditioned in the early subjective night showed a strong preference for peppermint and retained the memory for at least 2 days. Animals trained and tested at other circadian phases showed significant deficits in performance for both short-and long-term memory. Performance depended on the circadian time (CT) of training, not the CT of testing, and results indicate that memory acquisition rather than retention or recall is modulated by the circadian system. The data suggest that the circadian system can have profound effects on olfactory learning in insects.biological rhythms ͉ cockroach ͉ differential conditioning ͉ memory I n view of the widespread effects of circadian regulation on behavior and physiology, the possibility that learning and memory processes may be subject to modulation by the circadian system has long been recognized (1). Studies on this problem have suggested that the influence of the circadian system may take several forms. In some instances, the circadian phase may function as a context for learning (time stamping) so that recall and performance are better at 24-h intervals after learning (1-4). In other cases, performance may be modulated by the circadian phase independent of the phase of learning (5), and there have been several recent reports that memory acquisition or consolidation may depend on the circadian phase of training in mollusks (6-8), rodents (9, 10), and humans (11). Finally, there have been reports that disruption of the circadian system by phase shifting (jet lag) can impair memory (12, 13). Although these studies suggest that the circadian system may have widespread effects on various aspects of learning and memory, including acquisition, retention, and recall, there is virtually no information on the mechanisms by which the circadian system regulates these processes.Olfactory learning is an excellent model for exploration of the neural basis of learning and memory because of the remarkable similarity in the organization of olfactory systems acr...
Mating behavior of small populations of virgin males and females of the cockroach Leucophaea maderae were continuously monitored via time-lapse video recording in controlled laboratory conditions. The time of onset of copulation was found to be rhythmic in a light cycle of 12 h light alternated with 12 h of darkness, with the peak of mating behavior occurring near the light to dark transition. This rhythm persisted in constant dim red illumination and constant temperature. In constant conditions, the period of the rhythm was slightly less than 24 h, with a peak of copulation during the late subjective day. These data demonstrated that mating behavior is gated by a circadian clock. When males and females were taken from light cycles that were 12 h out of phase, a bimodal rhythm was observed with one peak in the males' late subjective day and a second peak of equal amplitude in the late subjective day of females. The results indicated that circadian systems in both males and females contribute to the circadian rhythm in copulation. Bilateral section of the optic tracts (OTX) of both males and females abolished the rhythm, but the rhythm persisted when OTX females were paired with intact males or when OTX males were paired with intact females. Furthermore, when OTX males or OTX females were paired with intact animals that were 12 h out of phase, a bimodal rhythm was still observed. These results suggested that the circadian pacemaker in the optic lobes of both male and female cockroaches participates in the control of mating, but that a pacemaker outside the optic lobes is also likely involved. Finally, it was shown that the female's olfactory response (measured by electroantennogram) to components of the male sex pheromone exhibited a circadian rhythm, but the data suggested the peripheral olfactory rhythm is not likely to be involved in the rhythm of mating behavior.
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