Introduction

Serotonin (5-hydroxytryptamine, 5-HT) presents a wide distribution in the central nervous system (CNS), and thus plays important roles in various behavioral and physiological processes, including activity rythms, food-intake, locomotor activity, behavioral inhibition or emotional states. There is increasing evidence showing that 5-HT is concerned with cognitive functions, especially learning and memory and attentional processes.24 These functions are not independent from each other or from other behavioral levels. There are indeed some relationships between anxiety and memory, or between learning and behavioral inhibition. It is thus clear that 5-HT may modulate learning and memory by direct or indirect ways. If memory functions are mainly and more directly controlled by other neurotransmitter systems such as the glutamatergic and the cholinergic, it is presently well-established that, by interacting with these systems, 5-HT plays an unneglectible role in memory formation via its various receptors

From Messengers to Molecules: Memories Are Made of These, edited by Gernot Riedel and Bettina Platt. ©2004 Eurekah.com and Kluwer Academic / Plenum Publishers.

Figure 1. What does serotonin do in the main neuronal circuits underlying memory? The flow of inputs from the environment reaches specialized cortical areas, related information is then transmitted through the entorhinal cortex to the hippocampus where it is processed before being distributed, via the subiculum, to cortical areas. The corticohippocampo-cortical communication allows the consolidation of information into long-term memory. Major anatomical structures underpinning memory processes are interconnected by glutamatergic routes. Acetylcholine, from the nucleus basalis magnocellularis and septum, subserves a cross-talk with these major pathways, hence modulating learning mechanisms. Anatomical structures are illustrated by autoradiography on rat brain sections with specific ligands labeling 5-HT1A ([3H]8-OH-DPAT, for hippocampus, entorhinal cortex and cortex), and 5-HT1B (S-CM-G[125I]TNH2, for subiculum, septum and basal nucleus) receptors.1

Figure 1. What does serotonin do in the main neuronal circuits underlying memory? The flow of inputs from the environment reaches specialized cortical areas, related information is then transmitted through the entorhinal cortex to the hippocampus where it is processed before being distributed, via the subiculum, to cortical areas. The corticohippocampo-cortical communication allows the consolidation of information into long-term memory. Major anatomical structures underpinning memory processes are interconnected by glutamatergic routes. Acetylcholine, from the nucleus basalis magnocellularis and septum, subserves a cross-talk with these major pathways, hence modulating learning mechanisms. Anatomical structures are illustrated by autoradiography on rat brain sections with specific ligands labeling 5-HT1A ([3H]8-OH-DPAT, for hippocampus, entorhinal cortex and cortex), and 5-HT1B (S-CM-G[125I]TNH2, for subiculum, septum and basal nucleus) receptors.1

This chapter thus intends to analyse behavioral and neurobiological data emphasizing the contribution of serotonin in memory, with special reference to the receptor side as the specific multidimentional "target" for serotonin to influence memory systems.

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