The Journal of Neuroscience, May 15, 1998, 18(10):3897-3908
Nerve Gas-Induced Seizures: Role of Acetylcholine in the
Rapid Induction of Fos and Glial Fibrillary Acidic Protein in
Piriform Cortex
Lee A.
Zimmer1,
Matthew
Ennis1,
Ronald G.
Wiley2, and
Michael T.
Shipley1
1 Department of Anatomy and Neurobiology, University of
Maryland School of Medicine, Baltimore, Maryland 21201, and
2 Veterans Affairs Medical Center, Vanderbilt University,
Nashville, Tennessee 37232
Soman (pinacolymethylphosphonofluoridate), a highly potent
irreversible inhibitor of acetylcholinesterase (AChE), causes seizures and rapidly increases Fos and glial fibrillary acidic protein (GFAP)
staining in piriform cortex (PC). This suggests that the inhibition of
AChE by soman leads to increased acetylcholine (ACh) and neuronal
excitability in PC. The sole source of cholinergic input to PC is from
the nucleus of the diagonal band (NDB). To investigate the role of ACh
in soman-induced seizures, we lesioned cholinergic neurons in NDB
unilaterally with 192-IgG-saporin. By 10 d, saporin
eliminated staining for choline acetyltransferase (ChAT), the synthetic
enzyme for ACh, in NDB ipsilateral to the lesion. Staining for AChE,
the degradative enzyme for ACh, was eliminated in PC ipsilateral to the
lesioned NDB. By 45-60 min after soman, increased Fos and GFAP
staining in PC was evident only ipsilateral to the unlesioned NDB. By
90-120 min after soman, Fos and GFAP staining increased bilaterally in
PC.
In a second experiment, electrical stimulation electrodes were
implanted unilaterally in the NDB to activate focally the projections to PC in unanesthetized rats. Within 5 min of NDB stimulation, there
were clear behavioral and EEG signs of convulsions. After 45-60 min of
NDB stimulation, there was increased Fos and GFAP staining in layer II
of PC ipsilateral to the stimulation site. Pretreatment with the
selective muscarinic receptor antagonist scopolamine blocked the
convulsions and prevented increased Fos and GFAP staining in PC. These
results suggest that ACh release in PC triggers the initiation of
seizures and gliosis after soman administration, predominantly by the
activation of muscarinic receptors.
Key words:
soman; Fos; GFAP; muscarinic receptors; nucleus of the diagonal band (NDB); 192-IgG-saporin; choline acetyltransferase (ChAT)
Copyright © 1998 Society for Neuroscience 0270-6474/98/18103897-12$05.00/0