Abstracts

Rationale:
Clinical studies suggest a differential association of the localization of left- vs. right-sided seizure foci and downstream reproductive endocrine comorbidities in women with temporal lobe epilepsy (TLE). Specifically, right-sided foci are associated with hypothalamic amenorrhea and left-sided foci with polycystic ovarian syndrome. Currently, no animal model recapitulates such lateralized effects. Estrous cycle disruption develops in approximately 75% of chronically epileptic female mice in the intrahippocampal kainate (IHKA) mouse model of TLE by 2 months after KA injection in the right dorsal hippocampus (1). This disruption also occurs in the absence of ovarian pathology, suggesting that this model aligns with phenotypes seen in women with right-sided foci. Here, we examined whether targeting left or right hippocampus in the IHKA model leads to differential development of hypothalamic-pituitary-ovarian (HPO) axis dysfunction and distinct seizure patterning.
Method:
Adult female C57BL/6J mice were injected with KA (50 nl of 20 mM) or saline in the left or right dorsal hippocampus and 14 IHKA mice were implanted 2 weeks later with depth EEG electrodes in the ipsilateral hippocampus. Continuous 24/7 video+EEG recordings were collected for 3 weeks at 2 months post-injection. EEG traces were quantified for electrographic seizure frequency and duration, with minimum seizure duration of 5 s. Estrous cycle stage was recorded daily for both EEG-recorded and non-recorded mice. Trunk blood and ovaries were collected for hormone ELISA analysis and histological follicle counts.
Results:
Estrous cycle length was increased in IHKA mice compared with controls (saline: 5.1 ± 1.03 d, n = 42; KA: 7.3 ± 2.7 d, n = 22; p = 0.002). However, no differences based on laterality of KA injection were seen in estrous cycle length (left: 6.6 ± 4.1 d n=15; right: 7.3 ± 4.03 d, n = 7, p = 0.14), or percent time in diestrus (left: 41 ± 13%; right: 46 ± 15%, p=0.47). No differences in ovarian histopathology were observed (antral follicles, p = 0.3; corpora lutea p = 0.7). Progesterone and testosterone levels also showed no differences based on injection side (p > 0.2 for both). However, in left-injected mice estradiol levels were trending lower (2.8 ± 0.3 ng/ml) than observed in right-injected mice (3.7 ± 0.5 ng/ml, p = 0.09). Seizure frequency (seizures per hour: left, 34.5 ± 10.3; right, 32.7 ± 17.2; p = 0.8) and seizure duration (left, 49.8 ± 30.6 s; right, 33.4 ± 31.8 s; p = 0.4) were not different between left- (n = 8) and right-injected (n = 6) mice. Similar trends in cycle length (left: 6.6 ± 2.3 d n = 16; right: 6.3 ± 1.6, n = 10, p = 0.7), and time in diestrus (left: 41 ± 11%; right: 39 ± 6%, p = 0.6) persisted at 4 months post-injection.
Conclusion:
These results suggest that laterality of IHKA injection does not produce differences in seizure burden, estrous cyclicity, or ovarian follicle counts as measured at 2-4 months after IHKA injection. Both left- and right-injected IHKA mice are thus prone to estrous cycle disruption and may be used to model impacts of epilepsy on the reproductive cycle. References: 1. Li et al., 2017 Epilepsia Open 2:39-47
Funding:
:R01 NS105825; R03 NS103029