The deep rostral piriform cortex contains a site (area tempestas) in w
hich focal application of picomole amounts of bicuculline, a GABA anta
gonist, triggers limbic motor seizures which are dependent upon activa
tion of both N-methyl-D-aspartate and alpha-amino-3-hydroxy-5-methylox
ole-4-proprionate subtypes of glutamate receptors. In the present stud
y we determined whether nitric oxide can influence the local modulatio
n of seizure initiation by bicuculline. Nitric oxide and the nitric ox
ide precursor L-arginine, alone or in combination with low doses of bi
cuculline were focally administered into the area tempestas of rats. W
hile nitric oxide alone had no significant convulsant effect, L-argini
ne alone (30-240 nmol) induced brief myoclonic episodes. Nitric oxide
(0.7 nmol) and L-arginine (30 nmol) markedly potentiated the seizures
evoked by a low dose of bicuculline. The effect of L-arginine was prev
ented by focal pretreatment with an inhibitor of nitric oxide synthesi
s, N-nitro-L-arginine methyl eater. However, N-nitro-L-arginine methyl
ester did not attenuate the convulsant effect of bicuculline or kaina
te alone when focally administered into area tempestas. The data demon
strate that exogenously applied nitric oxide or its precursors can enh
ance seizure triggering activity. However, the data also indicate that
L-arginine-nitric oxide pathway does not normally contribute to seizu
re expression from area tempestas, as N-nitro-L-arginine methyl ester
alone did not attenuate focally-evoked seizures. Copyright (C) 1996 IB
RO. Published by Elsevier Science Ltd.