Positive allosteric modulator of GABAB receptor alters behavioral effects but not afterdischarge progression induced by partial hippocampal kindling

Hippocampal seizures decreased the function of GABAB receptors, which may further increase seizure susceptibility and contribute to development of schizophrenia-like behaviors. Recent literature indicates that GABAB receptor agonist may normalize schizophrenia-like behaviors and prevent drug-induced behavioral sensitization. We hypothesized that positive modulation of GABAB receptor function during seizure induction will reduce seizure-induced schizophrenia-like behaviors. Using a partial hippocampal kindling model, afterdischarges were induced after injection of saline or dimethyl sulfoxide (vehicle-kindled rats), or a GABAB receptor positive allosteric modulator CGP7930, at 1 mg/kg i.p. (CGP1-kindled) or 5 mg/kg i.p. (CGP5-kindled). The increase in the primary afterdischarge duration during kindling was not different among the groups. However, the CGP5-kindled group showed a lower afterdischarge starting frequency as compared to vehicle-kindled or CGP1-kindled groups. Partial hippocampal kindling (21 afterdischarges) resulted in decreased prepulse inhibition and decreased gating of hippocampal auditory evoked potentials in vehicle-kindled and CGP1-kindled rats, as compared to saline-injected non-kindled rats, recorded 3-4 days after the last afterdischarge. However, CGP5-kindled rats showed normal prepulse inhibition and hippocampal auditory gating (compared to non-kindled rats), which was significantly higher than the respective measure in vehicle-kindled rats. CGP5-kindled group also showed methamphetamine-induced locomotion that was significant lower than the vehicle-kindled or CGP1-kindled group, but slightly higher than the saline-injected non-kindled rats. In conclusion, this study provides original data that a GABAB receptor positive allosteric modulator could therapeutically prevent or normalize some seizure-induced behavioral disruptions in a model of temporal lobe epilepsy.