Abstracts

Rationale: Status epilepticus (SE) is a life-threatening medical emergency defined by sustained seizure activity. Current treatments fail to terminate SE in all patients, highlighting a critical need to better understand the mechanisms driving SE severity and duration. Seizures are associated with a rapid increase in glucocorticoid levels, which can modulate neuronal excitability in the hippocampus through the activation of glucocorticoid (GRs) and mineralocorticoid receptors (MRs). Previous studies suggest that corticosterone (CORT) exposure can be pro-convulsant and that GR antagonism after SE can reduce hippocampal cell death. However, with widespread expression across the brain and body, the precise role of GRs in the hippocampus during SE is unclear. Here, we tested the hypothesis that GR deletion from ventral hippocampal glutamatergic neurons will decrease SE severity.

Methods: To delete GRs, adult male and female GR^fl/fl (B6.Cg-Nr3c1^tm1.1Jda/J) mice on a C57BL/6 background underwent bilateral stereotaxic injection of AAV9.CaMKII.Cre-mCherry (3.5e9 viral particles/hemisphere) into the ventral hippocampus (GRKO, N = 23). Controls included GR^fl/fl mice injected with AAV9.CaMKI-mCherry and GR^wt/wt mice injected with the Cre-mcherry virus (Control, N=25). Two weeks later, mice received pilocarpine (400 mg/kg, s.c.) to induce SE. GR deletion was confirmed with immunohistochemistry and SE severity was determined using a modified Racine scale. Survivors received diazepam at 75-min post-pilocarpine and were sacrificed at 48hrs post-SE.

Results: GR deletion primarily affected hippocampal dentate granule cells, mossy cells, and variable numbers of CA1, CA3 and subicular pyramidal neurons. Latency to Racine class III partial seizures after pilocarpine injection was reduced among GRKO mice (p< 0.0001). Paradoxically, latencies to both class IV (p=0.0036) and V (p=0.0263) convulsive seizures were increased among GRKO mice. Although overall mortality was high in both groups (Con: 85%, GRKO: 65%), GR deletion increased survival times (p=0.0119). Baseline morning corticosterone (CORT) concentrations were not impacted by GRKO (p=0.85). Measures of serum CORT revealed a rapid increase after the onset of SE; however, increases were similar between control and GRKO mice (p=0.94).

Conclusions: GR deletion from ventral hippocampal glutamatergic neurons had divergent effects on early vs late seizure pathology during SE, which may reflect the state-dependent action of hippocampal GRs. During early seizures, GR deletion accelerated the development of focal seizure activity. This is consistent with the unopposed action of membrane-bound MR activation upon initial CORT exposure, which has been reported to rapidly increase excitability. In contrast, GR deletion slowed the progression to later, more generalized seizure classes and death, suggesting that as SE progresses and CORT remains elevated, GR signaling worsens SE pathology. These preclinical data shed light on the mechanism by which the stress response contributes to seizure pathology during SE, building rationale for the exploration of GR-modulating drugs as potential adjunctive SE treatment.

Funding: Please list any funding that was received in support of this abstract.: 1F31NS122484-01 awarded to Kraus, K.L.