Involvement of GluA1-AMPAR-mediated LTP in time-dependent decline of cognitive function in rats with temporal lobe epilepsy

Abstract

Background: Cognitive impairment is one of the common comorbidities in patients with temporal lobe epilepsy (TLE), but the underlying mechanisms remain largely unknown. Previous studies have found significant decay of hippocampal long-term potentiation (LTP) in TLE rats with cognitive impairment. As the activation of α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors (AMPARs) is responsible for LTP formation and learning and memory, we investigated whether AMPARs are involved in the LTP inhibition and the TLE-associated cognitive impairments. Methods: TLE rat model was established by intraperitoneal injection of lithium chloride-pilocarpine on postnatal day 21 (P21). Learning and memory performance, hippocampal expression of membrane GluA1-AMPARs, and hippocampal LTP were tested by behavioral tests, western blotting, and field potential recording, respectively, at 1, 5 and 13 weeks after induction of status epilepticu (SE). Finally, the effects of (S)-AMPA, an agonist of AMPARs, on LTP and cognitive function were tested. Results: Results of behavioral tests revealed an time-dependent decline in the learning and memory of TLE rats when compared to the age-matched controls at week 5 and 13, rather than at week 1 after the induction of SE. Western blotting showed that the hippocampal expression of membrane GluA1 was significantly decreased in a time-dependent manner in the TLE rats when compared to the age-matched controls at weeks 5 and 13, rather than at week 1 after the induction of SE. Similarly, the hippocampal LTP was inhibited in a time-dependent manner in TLE rats at weeks 5 and 13, rather than at week 1 after the induction of SE. Moreover, intra-hippocampal injection of (S)-AMPA ameliorated the deficits in learning as well as spatial and emotional memory in a dose-dependent manner, and partially reversed the inhibition of CA1 LTP in the TLE rats at week 13 after the induction of SE. Conclusions: The reduced expression of hippocampal membrane GluA1 may be involved in LTP decay in CA1 and cognition impairment in TLE rats.