title: The role of serotonin in feeding and gut contractions in the honeybee.
abstract: Serotonin (5-hydroxytryptamine, 5-HT) is involved in the regulation of feeding and digestion in many animals from worms to mammals. In insects, 5-HT functions both as a neurotransmitter and as a systemic hormone. Here we tested its role as a neurotransmitter in feeding and crop contractions and its role as a systemic hormone that affected feeding in adult foraging honeybees. We found 5-HT immunoreactive processes throughout the gut, including on the surface of the oesophagus, crop, proventriculus, and the midgut, as well as in the ventral nerve cord. mRNA transcripts for all four of the known bee 5-HT receptors (Am5-ht1A,2α,2β,7) were expressed in the crop and the midgut suggesting a functional role for 5-HT in these locations. Application of a cocktail of antagonists with activity against these known receptors to the entire gut in vivo reduced the rate of spontaneous contraction in the crop and proventriculus. Although feeding with sucrose caused a small elevation of endogenous 5-HT levels in the haemolymph, injection of exogenous 5-HT directly into the abdomen of the bee to elevate 5-HT in the haemolymph did not alter food intake. However, when 5-HT was injected into directly into the brain there was a reduction in intake of carbohydrate, amino acid, or toxin-laced food solutions. Our data demonstrate that 5-HT inhibits feeding in the brain and excites muscle contractions in the gut, but general elevation of 5-HT in the bee's haemolymph does not affect food intake.
authors.affiliation: Centre for Behaviour and Evolution, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne NE1 7RU, UK.
authors.forename: Alice S
authors.initials: AS
authors.lastname: French
authors.affiliation: Centre for Behaviour and Evolution, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne NE1 7RU, UK.
authors.forename: Kerry L
authors.initials: KL
authors.lastname: Simcock
authors.affiliation: Department of Biochemistry and Biology, University of Potsdam, Potsdam D-14476, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Rolke
authors.affiliation: Centre for Behaviour and Evolution, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne NE1 7RU, UK.
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Gartside
authors.affiliation: Department of Cell Biology and Neuroscience, Goethe University Frankfurt, Oberursel D-61440, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Blenau
authors.affiliation: Centre for Behaviour and Evolution, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne NE1 7RU, UK. Electronic address: jeri.wright@ncl.ac.uk.
authors.forename: Geraldine A
authors.initials: GA
authors.lastname: Wright
mesh_terms: D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D001516:Bees / Q000502:physiology*; D002851:Chromatography, High Pressure Liquid; D005247:Feeding Behavior / Q000502:physiology*; D041981:Gastrointestinal Tract / Q000502:physiology; D007150:Immunohistochemistry; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D009119:Muscle Contraction / Q000502:physiology; D009424:Nervous System Physiological Phenomena; D060888:Real-Time Polymerase Chain Reaction; D011985:Receptors, Serotonin / Q000235:genetics / Q000378:metabolism; D012701:Serotonin / Q000097:blood / Q000235:genetics / Q000378:metabolism*; D013395:Sucrose / Q000378:metabolism
chemical_list: D011985:Receptors, Serotonin; D012701:Serotonin; D013395:Sucrose
keywords: 5-HT; 5-HT receptor; Apis mellifera; Gut contractions; Honeybee; Serotonin