Organophosphate poisoning is associated with adverse effects on the central nervous system such as
seizure/convulsive activity and long term changes in neuronal networks. This study reports on investigations designed to assess the consequences of
soman exposure on
excitatory amino acids receptors in the rat brain. In addition, the protective effects of
caramiphen which acts at these receptors, and
scopolamine, which does not, was determined on
soman-induced alteration in rat brain functions. Administration of
soman (1xLD50) to
pyridostigmine pretreated rats produced seizure activity (measured by EEG monitoring) in all animals tested. Estimation of [3H]
MK-801 binding to brain membranes from intoxicated rats revealed a marked decrease in Bmax value 24 but not 2 hrs following
soman administration. The specific nature of these effects of
soman was demonstrated by the findings that [3H]
flunitrazepam binding to central
benzodiazepine receptors remained unchanged in
soman-poisoned rat brain membranes. Both
scopolamine and
caramiphen, when used prophylactically prevented the lethal effect of
soman and completely blocked the development of electrographic seizure activity (EGSA). In contrast, only
caramiphen abolished
soman-induced modifications in
NMDA/
ion channel characteristics.
Caramiphen displaced [3H]
MK-801 bound to the
NMDA/
ion channel complex, possibly by interacting with the Zn2+ site whereas
scopolamine did not. Moreover,
caramiphen, but not
scopolamine, partially protected mice from
NMDA-induced lethality. Thus, it is suggested that an important component of the protective efficacy of
caramiphen against
organophosphate poisoning might be attributed to its ability to modulate
NMDA receptors in addition to its
anticholinergic properties.