[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#: 240.14/E36
Topic: B.10.c. Activity-dependent plasticity of intrinsic membrane properties
Support: NIH AG 20506
NIH R37 AG08796
US-Israel Binational Science Foundation #2005370
Title: Learning-related increases in synaptically-evoked intrinsic excitability
Authors: *B. M. MCKAY, J. F. DISTERHOFT;
Dept of Physiol., Northwestern Univ., Chicago, IL
Abstract: The learning-related increase in the afterhyperpolarization (AHP), elicited by a train
of action potentials delivered to the soma, is a well documented phenomenon. It has been
established in the CA1 and CA3 of rabbits, CA1 of rats, and piriform cortex of rats to occur after
learning tasks as divergent as trace eyeblink conditioning, water maze, and odor discrimination
learning. However, in the behaving animal, the AHP is elicited by activation of synapses located
in the dendrites. It has not yet been demonstrated that learning-related decreases in the AHP can
be elicited using synaptic stimulation. To this end, we trained rats at trace eyeblink conditioning,
a hippocampus-dependent task. In this task, animals receive repeated presentations of a tone
(conditioned stimulus, CS) followed by an air puff to the cornea (unconditioned stimulus, US),
separated by a 250msec stimulus-free interval. Pseudoconditioned control animals receive equal
number of stimuli, never explicitly paired in time. After 5 training sessions, hippocampal slices
were prepared. CA1 was isolated by cutting off CA3, and a stimulating electrode was placed in
the stratum radiatum. Five action potentials at 50Hz were elicited by stimulation of the Schaffer
collaterals (synaptic) or via the somatic recording pipette (somatic). Consistent with what has
previously been published, I observed smaller somatically-evoked AHPs in cells from trained
animals compared to naïve and pseudoconditioned controls. In unmodified aCSF, there was no
difference in the hyperpolarization following 5 synaptically-evoked action potentials, which
includes both the AHP and an inhibitory postsynaptic potential (IPSP). However, when measures
were made in the presence of the GABA-A blocker gabazine and the GABA-B blocker
SCH50911, the synaptically-evoked AHP was smaller in cells from trained animals compared to
controls. These data demonstrate that a learning-related increase in intrinsic excitability can be