Quinolinic acid (QA) is an
N-methyl-D-aspartate receptor agonist that also promotes
glutamate release and inhibits
glutamate uptake by astrocytes. QA is used in experimental models of
seizures studying the effects of overstimulation of the glutamatergic system. The
guanine-based
purines (GBPs), including the
nucleoside guanosine, have been shown to modulate the glutamatergic system when administered extracellularly. GBPs were shown to inhibit the binding of
glutamate and analogs, to be neuroprotective under excitotoxic conditions, as well as
anticonvulsant against
seizures induced by
glutamatergic agents, including QA-induced seizure. In this work, we studied the electrophysiological effects of
guanosine against QA-induced epileptiform activity in rats at the macroscopic cortical level, as inferred by electroencephalogram (EEG) signals recorded at the epidural surface. We found that QA disrupts a prominent basal theta (4-10 Hz) activity during peri-ictal periods and also promotes a relative increase in gamma (20-50 Hz) oscillations.
Guanosine, when successfully preventing
seizures, counteracted both these spectral changes.
MK-801, an
NMDA-antagonist used as positive control, was also able counteract the decrease in theta power; however, we observed an increase in the power of gamma oscillations in rats concurrently treated with
MK-801 and QA. Given the distinct spectral signatures, these results suggest that
guanosine and
MK-801 prevent QA-induced
seizures by different network mechanisms.