[Abstract Title]. - Society for Neuroscience

Poster
240. Intrinsic Membrane Properties: Modulation of Neuronal Firing Properties by Inputs
and Activity
Time: Sunday, November 16, 2008, 1:00 pm - 5:00 pm
Program#/Poster#: 240.13/E35
Topic: B.10.c. Activity-dependent plasticity of intrinsic membrane properties
Support: NINDS 24288
Title: Modification of temporal summation and Ih following mossy fiber LTP induction in CA3
interneurons
Authors: *W. D. ANDERSON 1,2 , E. J. GALVAN 1 , G. BARRIONUEVO 1,2 ;
1 Univ. Pittsburgh, Pittsburgh, PA; 2 Ctr. for the Neural Basis of Cognition, Pittsburgh, PA
Abstract: Inhibitory interneurons in hippocampal area CA3 function as a dynamic filtering
system for information transmitted to CA3 pyramidal neurons along mossy fibers (MF) and the
perforant path (PP). We have previously demonstrated that a subset of interneurons in the s.
lacunosum moleculare (SLM) layer exhibit MF activity dependent LTP and a subsequent
increase in the interval over which sequentially activated MF and PP EPSPs summate
supralinearly. Further, we have also shown that supralinearity is present at longer inter-stimulus
intervals when h-channels are blocked by ZD7288. In this report we describe preliminary
evidence which indicates that Ih is downregulated following MF LTP induction in a subset of
SLM interneurons.
First, input resistance (Rin) was increased to a similar extent following ZD7288 application and
during LTP. Next, when cells were held at -60 mV in voltage clamp and stepped to -120 mV
before and after LTP induction, the slowly activating inward current following the capacitive
transient was reduced, suggesting a decrease in a hyperpolarization activated inward current
putatively mediated by h-conductance. In a different set of cells, the application of forskolin -
which raises intracellular cyclic AMP (cAMP) production by activating adenylate cyclase -
resulted in both LTP and a reduction of the slowly activating inward current at -120 mV.
Forskolin application was also shown to increase Rin. These data suggest (a) that Ih is reduced
when LTP is induced at MF synapses and that this reduction contributes to increased supralinear
summation, and (b) that both LTP and Ih downregulation can be induced by a cAMP dependent
signaling pathway. Future experiments are being conducted to (1) determine whether LTP
induction is necessary for the decrease in Ih and (2) establish an explanation for the apparent
decrease in Ih (e.g., decrease in the channel number, single channel conductance, voltage
dependence, and/or channel kinetics). Supported by NINDS 24288.
Disclosures: W.D. Anderson , None; E.J. Galvan, None; G. Barrionuevo, None.