title: Cyclic AMP mediates serotonin-induced synaptic enhancement of lateral giant interneuron of the crayfish.
abstract: The lateral giant (LG)-mediated escape behavior of the crayfish habituates readily on repetitive sensory stimulation. Recent studies suggested that the biogenic amines serotonin and octopamine modulate the time course of recovery and/or re-depression of the LG response after habituation. However, little is known of how serotonin and octopamine effect LG habituation and what second-messenger cascades they may activate. To investigate the effect of biogenic amines on LG habituation, serotonin and octopamine were superfused before presenting repetitive sensory stimulation. Serotonin and octopamine increased the number of stimuli needed to habituate the LG response. Their effects were mimicked by mixed application of a cAMP analogue [8-(4-chlorophenylthio)-cAMP (CPT-cAMP)] and a phosphodiesterase inhibitor [3-isobutyl-1-methylxanthine (IBMX)] but not by a cGMP analogue (8-bromoguanosine 3',5'-cyclic monophosphate). Perfusion of the adenylate cyclase inhibitor (SQ22536) abolished the effect of serotonin but not that of octopamine. To investigate the site of action of each biogenic amines in the neural circuit meditating LG escape, the effect of drugs on directly and indirectly elicited postsynaptic potentials in LG was investigated. Serotonin, octopamine, and a mixture of CPT-cAMP and IBMX increased both the direct and indirect synaptic inputs. Simultaneous application of SQ22536 abolished the effect of serotonin on both inputs but did not block the effect of octopamine. Direct injection of the cAMP analogue (Sp-isomer of adenosine-3',5'-cyclic monophosphorothioate) into LG increased both the direct and indirect inputs to LG. These results indicate that serotonin mediates an increase in cAMP levels in LG, but octopamine acts independently of cAMP and cGMP.
authors.affiliation: Division of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo, Japan. arakim@sci.hokudai.ac.jp
authors.forename: Makoto
authors.initials: M
authors.lastname: Araki
authors.forename: Toshiki
authors.initials: T
authors.lastname: Nagayama
authors.forename: Jordanna
authors.initials: J
authors.lastname: Sprayberry
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000225:Adenine / Q000031:analogs & derivatives / Q000494:pharmacology; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000704:Analysis of Variance; D000818:Animals; D003400:Astacoidea; D000242:Cyclic AMP / Q000494:pharmacology*; D006152:Cyclic GMP / Q000494:pharmacology; D004347:Drug Interactions; D004558:Electric Stimulation / Q000379:methods; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D005260:Female; D017952:Ganglia, Invertebrate / Q000166:cytology*; D006185:Habituation, Psychophysiologic; D007395:Interneurons / Q000187:drug effects*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009655:Octopamine / Q000494:pharmacology; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D012701:Serotonin / Q000494:pharmacology*; D013569:Synapses / Q000187:drug effects*
chemical_list: D000316:Adrenergic alpha-Agonists; D004791:Enzyme Inhibitors; D010726:Phosphodiesterase Inhibitors; D009655:Octopamine; C017759:9-(tetrahydro-2-furyl)-adenine; D012701:Serotonin; D000242:Cyclic AMP; D006152:Cyclic GMP; D000225:Adenine; D015056:1-Methyl-3-isobutylxanthine