Octopamine cyclic release and its modulation of visual sensitivity in crayfish

Area of Science:

• Neuroscience
• Chronobiology
• Crustacean Biology

Background:

• Biogenic amine octopamine (OA) influences invertebrate behavior.
• OA's role in visual sensitivity and diurnal cycles is largely unknown.

Purpose of the Study:

• Investigate diurnal variations in crayfish octopamine (OA) levels.
• Determine OA release from eyestalks and its effect on retinal light sensitivity.

Main Methods:

• Measured hemolymph OA and tyrosine using liquid chromatography.
• Assessed OA release from isolated eyestalks and its calcium dependency.
• Examined OA's impact on photoreceptor light responses in crayfish.

Main Results:

• Crayfish hemolymph OA levels exhibited 24-hour variations, peaking before light offset.
• OA was present in all eyestalk structures, with higher concentrations in the retina-lamina ganglionaris.
• Octopamine (OA) injection or application reduced photoreceptor light response amplitude in a dose-dependent manner.

Conclusions:

• Crayfish OA release is linked to the circadian cycle.
• OA regulates diurnal decreases in photoreceptor sensitivity.
• This regulation likely promotes exploratory locomotion during the dark phase.