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Stéphane Marinesco"Le systeme serotoninergique de l'Aplysie et sa fonction dans l'éveil et la memoire".

Abstract :


S
erotonin (5-HT) plays an important role in memory encoding in the marine mollusk Aplysia. During sensitization of defensive reflexes, 5-HT mediates facilitation of sensorimotor synapses, thus contributing to the increase in reflex efficacy. Although 5-HT’s effects on primary sensory neurons are now well characterized from a molecular point of view, the function of the serotonergic system during memory encoding is still poorly understood at a systems level. The development of an electrochemical 5-HT detection technique in Aplysia allowed us to directly investigate 5-HT release during learning.
We showed that : (1) 5-HT is released in the central nervous system (CNS) in response to noxious stimuli that typically induce sensitization, (2) this increased 5-HT release corresponds to the persistent activation of a distributed serotonergic network within the CNS, and (3) the serotonergic system is implicated in the defensive arousal response induced by noxious stimulation and modulates reflex efficacy at multiple neuronal sites within the reflex circuit. Interestingly, serotonergic activation reflected by increased firing rates in 5-HT neurons can lead to either inhibition or sensitization of the reflex circuit. To predict the sign of serotonergic plasticity it is necessary to determine the exact concentrations that are released within restricted sites within the CNS. Such level of analysis can only be achieved by electrochemical techniques. This detailed analysis of serotonergic modulation in Aplysia suggests that memory encoding relies on at least two different mechanisms: synaptic plasticity at sensorimotor synapses and persistent activity in serotonergic networks.
These two mechanisms, which are believed to underlie more complex forms of learning in mammals, can be directly investigated in Aplysia, from a molecular, cellular or systems point of view. (S.M. was a postdoctoral researcher in Dr. Thomas J. Carew’s laboratory between 1999 and 2004, at Yale University and UC Irvine)

Selected publications

S. Marinesco, K.E. Kolkman and T.J. Carew (2004)
Serotonergic modulation in Aplysia : I. A distributed serotonergic network activated by sensitizing stimuli.
J Neurophysiol; 92 : 2468-2486.

S. Marinesco, N. Wickremasinghe, K.E. Kolkman and T.J. Carew (2004)
Serotonergic modulation in Aplysia : II. Cellular and behavioral consequences of increased serotonergic tone.
J Neurophysiol ; 92 : 2487-2496.

Barbas D, DesGroseillers L, Castellucci VF, Carew TJ, Marinesco S (2003)
Multiple serotonergic mechanisms contributing to sensitization in Aplysia: evidence of diverse serotonin receptor subtypes.
Learn Mem; 10: 373-386.

S. Marinesco and T.J. Carew (2002)
Improved electrochemical detection of biogenic amines in Aplysia using base-hydrolyzed cellulose-coated carbon fiber microelectrodes.
J Neurosci Meth; 117: 87-97.

S. Marinesco and T.J.Carew (2002)
Serotonin release evoked by tail-nerve shock in Aplysia: characterization and relationship to heterosynaptic plasticity.
J Neurosci; 22: 2399-2312.

François Gonon