Volume 17, Number 6,
Issue of March 15, 1997
pp. 2168-2180
Copyright ©1997 Society for Neuroscience
Differential and Time-Dependent Changes in Gene Expression for
Type II Calcium/Calmodulin-Dependent Protein Kinase, 67 kDa Glutamic
Acid Decarboxylase, and Glutamate Receptor Subunits in Tetanus
Toxin-Induced Focal Epilepsy
Received Oct. 21, 1996; accepted Dec. 20, 1996.
Fengyi Liang and
Edward G. Jones
Department of Anatomy and Neurobiology, University of California,
Irvine, California 92697
To study potential molecular mechanisms of epileptogenesis in the
neocortex, the motor cortex of rats was injected with tetanus toxin
(TT), and gene expression for 67 kDa glutamic acid
decarboxylase (GAD-67), type II calcium/calmodulin-dependent protein
kinase (CaMKII), NMDA receptor subunit 1 (NR1), and AMPA receptor
subunit 2 (GluR2) was investigated by in situ
hybridization histochemistry. Injections of 20-35 ng TT induced
recurrent seizures after a postoperative period ranging from 4 to
13 d. A majority of rats perfused 5-7 d after TT injection showed
altered gene expression, but the changes varied in their areal extent,
ranging from most neocortical areas on the injected side in some rats
to mainly the frontoparietal cortex or the motor cortex in others.
Epileptic rats perfused 14 d after TT injection showed a focus of
increased GAD-67 and NR1, and of decreased
-CaMKII and GluR2 mRNA
levels at the injection site. A zone of cortex surrounding the focus
showed changes in
-CaMKII, GAD-67, and NR1 mRNA levels that were
reciprocal to those in the focus. The results suggest that TT-induced
seizure activity initially spread to a variable extent but was
gradually restricted 2-3 d after seizure onset. The focus and the
surround showing reciprocal changes in gene expression are thought to
correspond to the electrophysiologically identified epileptic focus and
inhibitory surround, respectively. The findings suggest that lateral
inhibition between neighboring cortical regions will be affected and
contribute to a neurochemical segregation of an epileptic focus from
surrounding cortex.
Key words:
epilepsy;
motor cortex;
rat;
NMDA receptor;
AMPA;
-aminobutyric acid;
protein kinase;
inhibition