Journal of Neuroscience, Vol 16, 220-228, Copyright © 1996 by Society for Neuroscience
Persistent dentate granule cell hyperexcitability after neonatal infection with lymphocytic choriomeningitis virus
BD Pearce, SC Steffensen, AD Paoletti, SJ Henriksen and MJ Buchmeier
Emory University School of Medicine, Department of Psychiatry, Atlanta, Georgia 30322, USA.
Infection of neonatal Lewis rats with lymphocytic choriomeningitis virus
(LCMV) produces distinct retinal, cerebellar, and hippocampal
neuropathology. To understand the neurophysiological consequences of
LCMV-induced hippocampal pathology, we studied evoked monosynaptic
potentials and electro-encephalographic (EEG) activity in the dentate gyrus
and CA1 and CA3 subfields of the hippocampus in vivo. Lewis rats were
inoculated intracerebrally with LCMV at postnatal day 4. In rats studied
84-107 d postinfection, virus was cleared from the dentate gyrus and the
number of dentate granule cells was decreased by 70%. No viral antigen or
cell loss was apparent in CA1 or CA3. The hippocampal EEG of LCMV-infected
rats 84-102 d postinfection was dominated by continuous theta. Although
evoked potentials elicited in CA1 and CA3 by monosynaptic afferent
stimulation revealed no differences between sham- and LCMV-infected rats,
there was a site-specific dissociation of synaptic [population excitatory
postsynaptic potential (pEPSP)] and cellular (population spike) responses
and a suppression of GABA- mediated recurrent inhibition in the dentate
gyrus of LCMV-infected rats. These findings indicate that GABA-mediated
inhibition was markedly decreased in LCMV-infected rats. In support of
this, parvalbumin-immunoreactive cell bodies and neuronal processes were
decreased in LCMV-infected rats, suggesting that a subpopulation of GABA
interneurons was affected. These findings indicate that abnormalities in
synaptic function persist after clearance of infectious virus from the
central nervous system and suggest that decreased inhibition subsequent to
pathological sequence in a subpopulation of GABA interneurons may be
implicated in the hyperexcitability of dentate granule cells.