Biphasic Modulation of Absence Seizures by Lisuride in GAERS: Dissecting the Role of 5-HT2A Receptors

BackgroundSerotonergic signaling plays an important role in the modulation of absence seizures (ASs), and activation of serotonin 2A receptors (5-HT2ARs) with TCB-2 suppresses spontaneous absence seizures (ASs) in Genetic Absence Epilepsy Rats from Strasbourg (GAERS). Lisuride is a pharmacologically complex serotonergic and dopaminergic ligand with low 5-HT2AR signaling efficacy and a receptor profile distinct from that of TCB-2. We therefore investigated its effects on spontaneous ASs and the contribution of 5-HT2ARs to its actions. MethodsThe effects of systemic lisuride (0.1 and 0.5 mg/kg) on spontaneous ASs were examined in freely moving GAERS over 120 min by quantifying time spent in seizure, mean seizure duration and seizure number. The contribution of 5-HT2ARs was investigated by administering lisuride (0.5 mg/kg) following pretreatment with the selective 5-HT2AR antagonist MDL11,939 (0.5 mg/kg). ResultsLisuride produced marked dose- and time-dependent effects on ASs. At 0.1 mg/kg, lisuride elicited modest pro-absence effect. In contrast, 0.5 mg/kg produced a pronounced biphasic response, with a marked reduction in seizure activity during the first 40 min, followed by rebound increase during the second hour. The early suppression involved reductions in both seizure number and duration, whereas the delayed pro-absence effect was predominantly associated with prolonged ASs. MDL11,939 did not prevent the early seizure suppression but blocked the increase in seizure duration while producing a transient increase in seizure number. ConclusionsLisuride is a dose- and time-dependent bidirectional modulator of ASs in GAERS. The persistence of the profound early anti-absence effect during 5-HT2AR blockade indicates that this response does not require 5-HT2AR activation, whereas the modification of the delayed response by MDL11,939 supports a 5-HT2AR-dependent component in the later phase. These findings distinguish lisuride pharmacologically from TCB-2 and suggest that its biphasic effects arise from the dynamic engagement of multiple receptor mechanisms, potentially including dopaminergic signaling.