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This Article Full Text Full Text (PDF) All Versions of this Article: 102/5/2825    most recent 00477.2009v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Jin, N. G. Articles by Crow, T. PubMed PubMed Citation Articles by Jin, N. G. Articles by Crow, T.

RESEARCH-ARTICLE

5-HT and GABA Modulate Intrinsic Excitability of Type I Interneurons in Hermissenda

Department of Neurobiology and Anatomy, University of Texas Medical School, Houston, Texas

Submitted 2 June 2009; accepted in final form 24 August 2009

ABSTRACT

The sensory neurons (photoreceptors) in the visual system of Hermissenda are one site of plasticity produced by Pavlovian conditioning. A second site of plasticity produced by conditioning is the type I interneurons in the cerebropleural ganglia. Both photoreceptors and statocyst hair cells of the graviceptive system form monosynaptic connections with identified type I interneurons. Two proposed neurotransmitters in the graviceptive system, serotonin (5-HT) and -aminobutyric acid (GABA), have been shown to modify synaptic strength and intrinsic neuronal excitability in identified photoreceptors. However, the potential role of 5-HT and GABA in plasticity of type I interneurons has not been investigated. Here we show that 5-HT increased the peak amplitude of light-evoked complex excitatory postsynaptic potentials (EPSPs), enhanced intrinsic excitability, and increased spike activity of identified type I_e(A) interneurons. In contrast, 5-HT decreased spike activity and intrinsic excitability of type I_e(B) interneurons. The classification of two categories of type I_e interneurons was also supported by the observation that 5-HT produced opposite effects on whole cell steady-state outward currents in type I_e interneurons. Serotonin produced a reduction in the amplitude of light-evoked complex inhibitory PSPs (IPSPs), increased spontaneous spike activity, decreased intrinsic excitability, and depolarized the resting membrane potential of identified type I_i interneurons. In contrast to the effects of 5-HT, GABA produced inhibition in both types of I_e interneurons and type I_i interneurons. These results show that 5-HT and GABA can modulate the intrinsic excitability of type I interneurons independent of the presynaptic effects of the same transmitters on excitability and synaptic efficacy of photoreceptors.