Journal of Neuroscience, Vol 11, 2786-2794, Copyright © 1991 by Society for Neuroscience
Excitatory synaptic potentials in kainic acid-denervated rat CA1 pyramidal neurons
DA Turner and HV Wheal
Department of Surgery (Neurosurgery), Duke University, Durham, North Carolina.
Intracellular recordings were performed in the CA1 region of the rat
hippocampus following an ipsilateral intraventricular injection of kainic
acid. Seven days postlesion, graded bursts of up to four action potentials
could be evoked by stimulation of the stratum radiatum. The evoked EPSPs
underlying these bursts showed a prolonged 10-90% rise time and half-width
compared to control EPSPs, an absence of a significant inhibitory phase,
and an increase in magnitude and duration at depolarized resting levels.
The evoked EPSPs also exhibited a significant decrease in amplitude and
time course in response to D-APV (D-2-amino-5-phosphonovaleric acid; 1-20
microM), though this effect was variable from cell to cell. The prolonged
time course, voltage sensitivity, and response to a selective NMDA
antagonist confirmed that the major component of the EPSP in neurons from
lesioned slices was mediated by NMDA receptors. The partial denervation of
the CA1 area induced by the kainic acid led to both an enhanced
NMDA-mediated excitatory phase and a decrease in postsynaptic inhibition,
resulting in the pronounced hyperexcitability noted in the lesioned slices.