Abstracts

Rationale: Angelman syndrome (AS) is associated with unique behavioral phenotypes such as developmental and motor delays, profound language and communication impairments, seizures, and abnormal electroencephalographic (EEG) activity. Complete deletion of the maternally imprinted UBE3A gene, which encodes ubiquitin protein ligase E3A (Ube3a) and causes AS, is mimicked by the Ube3a maternal deletion rat model. AS children are more likely than the general population to develop febrile seizures (FS) during illness in infancy and may experience FS as the initial seizure event prior to developing epilepsy. Previously, we found that when exposed to hyperthermia as pups, AS rats showed a lower temperature threshold to FS than wildtype (WT) littermates and increased epileptiform activity. It is not known if loss of neuronal Ube3a alters the response to FS-induced neuroinflammation. Additionally, the impact of FS and neuroinflammation on AS phenotypes is not characterized. Here we evaluated ultrasonic vocalizations (USVs) in AS rat pups before and after induction of FS and collected brain tissue to examine neuroinflammatory markers.

Methods: To determine if FS were associated with USV deficits, AS and WT rat pups underwent maternal isolation for two minutes during which USVs were recorded at postnatal day 8 (P8). At P11, pups were exposed to either hyperthermic (FS; >41.5°C) or normothermic (NT; 32-35°C) temperatures for 30 minutes, followed by a second USV recording at P15. Brain tissue from a separate cohort was collected from FS and NT rat pups 1 hour post-FS to determine levels of the neuroinflammatory markers interleukin 1β (IL1-β), glial fibrillary acidic protein (GFAP), and ionized calcium binding adapter molecule 1 (IBA1) using western blot. Samples were also examined using a Luminex rat cytokine panel to examine a wider spectrum of neuroinflammatory markers.

Results: At baseline, AS rat pups exhibited mild deficits in the number of USVs during maternal isolation at P8 compared to WT littermates corroborating previous work. Additional pilot studies showed that following FS, the AS group exposed to hyperthermia exhibited a lower number of USV calls compared to the NT AS group. The FS WT group exhibited a moderate reduction in USV calls compared to the normothermic WT group. Brain tissue from AS rats from the FS group exhibited higher levels of the glia-specific inflammatory markers GFAP and IBA1. The cytokine panel further revealed that interleukin levels in the AS hyperthermic group were similar to the normothermic AS group, whereas in the WT hyperthermic group cytokines were downregulated compared to the WT normothermic group (p< 0.01).