title: Effects of Caffeine on Olfactory Learning in Crickets.
abstract: Caffeine is a plant-derived alkaloid that is generally known as a central nervous system (CNS) stimulant. In order to examine the effects of caffeine on higher CNS functions in insects, we used an appetitive olfactory learning paradigm for the cricket Gryllus bimaculatus. Crickets can form significant long-term memories (LTMs) after repetitive training sessions, during which they associate a conditioned stimulus (CS: odor) with an unconditioned stimulus (US: reward). Administration of hemolymphal injections of caffeine established LTM after only single-trial conditioning over a wide range of caffeine dosages (1.6 µµg/kg to 39 mg/kg). We investigated the physiological mechanisms underlying this enhancement of olfactory learning performance pharmacologically, focusing on three major physiological roles of caffeine: 1) inhibition of phosphodiesterase (PDE), 2) agonism of ryanodine receptors, and 3) antagonism of adenosine receptors. Application of drugs relevant to these actions resulted in significant effects on LTM formation. These results suggest that externally applied caffeine enhances LTM formation in insect olfactory learning via multiple cellular mechanisms.
authors.affiliation: 1 Graduate School of Fisheries and Environmental Sciences, Nagasaki University,Nagasaki 852-8521, Japan.
authors.forename: Seigo
authors.initials: S
authors.lastname: Sugimachi
authors.affiliation: 2 College of Liberal Arts and Science, Tokyo Medical and Dental University,Chiba 272-0827, Japan.
authors.forename: Yukihisa
authors.initials: Y
authors.lastname: Matsumoto
authors.affiliation: 3 Faculty of Science, Hokkaido University, Sapporo 060-0810, Japan.
authors.forename: Makoto
authors.initials: M
authors.lastname: Mizunami
authors.affiliation: 1 Graduate School of Fisheries and Environmental Sciences, Nagasaki University,Nagasaki 852-8521, Japan.
authors.forename: Jiro
authors.initials: J
authors.lastname: Okada
mesh_terms: D000818:Animals; D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D000697:Central Nervous System Stimulants / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects; D006135:Gryllidae / Q000187:drug effects* / Q000502:physiology; D019476:Insect Proteins / Q000235:genetics / Q000378:metabolism; D007858:Learning / Q000187:drug effects*; D008297:Male; D010727:Phosphoric Diester Hydrolases; D018047:Receptors, Purinergic P1; D019837:Ryanodine Receptor Calcium Release Channel; D012903:Smell / Q000187:drug effects*
chemical_list: D000697:Central Nervous System Stimulants; D019476:Insect Proteins; D018047:Receptors, Purinergic P1; D019837:Ryanodine Receptor Calcium Release Channel; D002110:Caffeine; D010727:Phosphoric Diester Hydrolases; D002118:Calcium
keywords: adenosine receptor; caffeine; cricket; olfactory learning; phosphodiesterase; ryanodine receptor