title: 5-HT and GABA modulate intrinsic excitability of type I interneurons in Hermissenda.
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 gamma-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.
authors.affiliation: Department of Neurobiology and Anatomy, University of Texas Medical School, Houston, Texas 77030, USA.
authors.forename: Nan Ge
authors.initials: NG
authors.lastname: Jin
authors.forename: Lian-Ming
authors.initials: LM
authors.lastname: Tian
authors.forename: Terry
authors.initials: T
authors.lastname: Crow
mesh_terms: D000818:Animals; D001703:Biophysics; D004558:Electric Stimulation / Q000379:methods; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D049870:Hermissenda / Q000166:cytology*; D053444:Inhibitory Postsynaptic Potentials / Q000187:drug effects; D007395:Interneurons / Q000145:classification / Q000187:drug effects*; D008564:Membrane Potentials / Q000187:drug effects* / Q000502:physiology; D018408:Patch-Clamp Techniques / Q000379:methods; D010775:Photic Stimulation / Q000379:methods; D012701:Serotonin / Q000494:pharmacology*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
chemical_list: D012701:Serotonin; D005680:gamma-Aminobutyric Acid