Early calcium increase triggers the formation of olfactory long-term memory in honeybees.
BACKGROUND
Synaptic plasticity associated with an important wave of gene transcription and protein synthesis underlies long-term memory processes. Calcium (Ca2+) plays an important role in a variety of neuronal functions and indirect evidence suggests that it may be involved in synaptic plasticity and in the regulation of gene expression correlated to long-term memory formation. The aim of this study was to determine whether Ca2+ is necessary and sufficient for inducing long-term memory formation. A suitable model to address this question is the Pavlovian appetitive conditioning of the proboscis extension reflex in the honeybee Apis mellifera, in which animals learn to associate an odor with a sucrose reward.


RESULTS
By modulating the intracellular Ca2+ concentration ([Ca2+]i) in the brain, we show that: (i) blocking [Ca2+]i increase during multiple-trial conditioning selectively impairs long-term memory performance; (ii) conversely, increasing [Ca2+]i during single-trial conditioning triggers long-term memory formation; and finally, (iii) as was the case for long-term memory produced by multiple-trial conditioning, enhancement of long-term memory performance induced by a [Ca2+]i increase depends on de novo protein synthesis.


CONCLUSIONS
Altogether our data suggest that during olfactory conditioning Ca2+ is both a necessary and a sufficient signal for the formation of protein-dependent long-term memory. Ca2+ therefore appears to act as a switch between short- and long-term storage of learned information.
Perisse
Emmanuel
E
Centre de Recherches sur Cognition Animale, Université de Toulouse, CNRS, Toulouse, France. eperisse@cict.fr
Raymond-Delpech
Valérie
V
Néant
Isabelle
I
Matsumoto
Yukihisa
Y
Leclerc
Catherine
C
Moreau
Marc
M
Sandoz
Jean-Christophe
JC
D000818:Animals; D001245:Association Learning / Q000187:drug effects; D001516:Bees / Q000502:physiology*; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D000697:Central Nervous System Stimulants / Q000494:pharmacology; D002614:Chelating Agents / Q000494:pharmacology; D003214:Conditioning, Classical / Q000187:drug effects; D005233:Fatty Alcohols / Q000494:pharmacology; D000441:Hexanols / Q000494:pharmacology; D008568:Memory / Q000187:drug effects / Q000502:physiology*; D008570:Memory, Short-Term / Q000187:drug effects; D023421:Models, Animal; D009812:Odorants; D009833:Olfactory Pathways / Q000502:physiology; D014176:Protein Biosynthesis; D012903:Smell / Q000502:physiology
D000697:Central Nervous System Stimulants; D002614:Chelating Agents; D005233:Fatty Alcohols; D000441:Hexanols; D002110:Caffeine; C014713:1-nonanol; D002118:Calcium