Circadian rhythms in light-evoked responses of the fly's compound eye, and the effects of neuromodulators 5-HT and the peptide PDF.
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 x 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.
Chen
B
B
Neuroscience Institute, Dalhousie University, Halifax, Nova Scotia, Canada.
Meinertzhagen
I A
IA
Shaw
S R
SR
D000818:Animals; D002940:Circadian Rhythm / Q000187:drug effects* / Q000502:physiology; D004175:Diptera / Q000187:drug effects* / Q000502:physiology; D029721:Drosophila Proteins; D004596:Electroretinography / Q000187:drug effects; D005123:Eye / Q000187:drug effects*; D016166:Free Radical Scavengers / Q000494:pharmacology*; D019476:Insect Proteins / Q000494:pharmacology*; D007447:Invertebrate Hormones / Q000494:pharmacology / Q000502:physiology; D009479:Neuropeptides / Q000494:pharmacology* / Q000502:physiology; D010455:Peptides / Q000494:pharmacology / Q000502:physiology; D010775:Photic Stimulation; D012701:Serotonin / Q000494:pharmacology* / Q000502:physiology; D012702:Serotonin Antagonists / Q000494:pharmacology
D029721:Drosophila Proteins; D016166:Free Radical Scavengers; D019476:Insect Proteins; D007447:Invertebrate Hormones; D009479:Neuropeptides; D010455:Peptides; D012702:Serotonin Antagonists; C113883:pdf protein, Drosophila; D012701:Serotonin; C027714:melanophore-dispersing hormone