Circadian rhythms in light-evoked responses of the fly's compound eye, and the effects of neuromodulators 5-HT and the peptide PDF

• Published in: Journal of Comparative Physiology 1999-11, Vol.185 (5), p.393-404
• Main Authors: Chen, B., Shaw, S. R., Meinertzhagen, I. A.
• Format: Article
• Language: English
• Subjects: Antibodies; Axons; Cell size; Circadian rhythm; Circadian rhythms; Compound eye; Crustaceans; Darkness; Eye; Hemolymph; Immunoreactivity; Neuromodulation; Peptides; Pigment-dispersing factor
• ISSN: 0340-7594; 1432-1351
• DOI: 10.1007/s003590050400

Two sets of wide-field neurons extend neurites into the fly's optic lamina, where monopolar cells receive photoreceptor input. They exhibit immunoreactivity to antibodies raised against either 5-hydroxytryptamine or the crustacean peptide PDH, respectively. Both are proposed whole-field neuromodulators of vision, apparently regulating a circadian rhythm of monopolar cell size. Seeking functional correlates, we have re-examined the electroretinogram for circadian rhythmicity, and for responses to locally injected 5-hydroxytryptamine and peptide. Long-term electroretinogram recordings from Calliphora entrained to a light/dark cycle and then transferred to constant darkness, uncovered a gradual, modest increase during the subjective night in the electroretinogram's ON- and OFF-transients, from the lamina's monopolar cells. Five to twenty nl of 5-hydroxytryptamine (10−3 mol · 1−1) injected into the head haemolymph strongly enhanced the electroretinogram transients, an action reversed by 5-hydroxytryptamine antagonists. Injected into the eye, 5-hydroxytryptamine (10−4 mol · 1−1) had the opposite effect; the rapid onset there suggests direct action, whilst the opposing effect from haemolymph injection suggests a different receptor site. Pigment-dispersing hormone (2.2 × 10−5 mol · 1−1) injected into the haemolymph increased the electroretinogram transients along a biphasic course, with a slow partial recovery; injected into the eye, it lacked effect.