The Caudal Photoreceptor in the Crayfish: An Overview (pp. 59-78)
Authors: (Leonardo Rodríguez-Sosa, Gabina Calderón-Rosete, Víctor Anaya, Gonzalo Flores, Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México, Ciudad Universitaria, México, D.F., and others)
Abstract: This chapter deals primarily in the physiological properties of the caudal photoreceptor (CPR) in crayfish (Procambarus clarkii and Cherax quadricarinatus), in the context of their functional role in the circadian rhythms of decapod crustaceans. We describe the cellular physiology of the CPR, one neuron on each side of the sixth abdominal ganglion. The CPR is a nonvisual photosensitive neuron that shows spontaneous activity and phasic–tonic responses to pulses of light. We then comment on the influence of temperature and the biogenic amines serotonin and dopamine on CPR activity in the isolated ganglion, recorded with conventional extracellular electrodes. We also discuss the circadian rhythmicity both in basal activity and the photoresponse of the CPR in organ culture at constant conditions. With regard to the main characteristics of these rhythms, we found that spontaneous activity varies with a period of 24.7-h while light-induced activity shows a period of 24.24-h. We examine the effects of injuring or blinding the sixth abdominal ganglion on the circadian rhythm of locomotor activity in crayfish, under constant light conditions, by using the video camera and software. Both experimental groups of crayfish exhibit a phase shift with respect to the control group. This effect is time-dependent in damaged crayfish, and reversible in blinded crayfish. Finally, the perspectives of research on the CPR are included. Taken together, this data suggests that the caudal photoreceptor is a candidate for forming part of a distributed
circadian system of pacemakers in crayfish. Additionally, this data supports the hypothesis that the CPR also participates in the entrainment the locomotor circadian rhythm in these invertebrates. In other words, the functionality of the CPR is essential for maintaining a synchronization of the circadian rhythmicity in locomotor in crayfish, within the 24-h light-dark cycle.
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