Abstract
Recent studies have postulated that the left and right caudal photoreceptors (CPR-L and CPR-R, respectively) of the crayfish show asymmetry of spontaneous activity in darkness and responses induced by white light. Two photopigments have been identified; the first one sensitive to blue light and the second one sensitive to green light. This study explores blue and green monochromatic light responsiveness with respect to both CPR-L and -R, as well as the effects of temperature on these photoreceptors. We performed simultaneous extracellular recordings of the firing rate of action potentials from CPRs of the crayfish Cherax quadricarinatus (n = 12). At room temperature (24 ± 1 °C), CPR-L and -R showed a significant difference in the spikes from most of the comparations. CPRs in the dark exhibited spontaneous asymmetric activity and displayed sensitivity to both monochromatic light sources. CPR responses were light intensity dependent within a range of 1.4 logarithmic intensity units, showing approximately 0.5 logarithmic intensity units more sensitivity to blue than to green light. The CPRs displayed an asymmetrical response to both colors by using a constant light intensity. At 14 (±1) °C, activity in darkness diminished while asymmetry persisted, and the CPRs improved responses for both monochromatic light sources, displaying a significant asymmetry. Here, we provide additional evidence of the asymmetric activity in darkness and light response from the CPRs. The new data allow further investigations regarding the physiological role of caudal photoreceptors in the crayfish.
Highlights
This study addresses the physiology of caudal photoreceptor in crayfish, as model preparation for the analysis of neuronal control mechanisms of circadian rhythmicity and photoreception by light-sensitive non-visual neurons [1,2]
Freshwater crayfish are a suitable model to study the functional role of three photo-sensitivity systems: (1) in the retina, (2) non-visual photoreceptors in the supraesophageal ganglion, and (3) caudal photoreceptors in the sixth abdominal ganglion (AG) [1,5,6,7]
We found a significant difference in the amplitude, peak to peak, and duration in extracellular spikes between CPR-L and CPR-R in most of the comparations
Summary
This study addresses the physiology of caudal photoreceptor in crayfish, as model preparation for the analysis of neuronal control mechanisms of circadian rhythmicity and photoreception by light-sensitive non-visual neurons [1,2]. Natural fluctuations of light and darkness modulate the physiology and behavior of crustacean decapods. Illumination during the day varies ~9 logarithmic intensity units [3]. For instance, receive a proportion of blue and green light which depends on the distance from the surface water [4]. Freshwater crayfish are a suitable model to study the functional role of three photo-sensitivity systems: (1) in the retina, (2) non-visual photoreceptors in the supraesophageal ganglion (brain), and (3) caudal photoreceptors in the sixth abdominal ganglion (AG) [1,5,6,7].
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