Abstracts

Rationale: Patients with temporal lobe epilepsy (TLE) have a higher risk of reproductive endocrine disorders. Luteinizing hormone (LH) release from the pituitary is driven by hypothalamic gonadotropin-releasing hormone (GnRH) release and is required for reproductive endocrine function in both sexes. Disrupted patterns of LH release are reported in men and women with epilepsy, but underlying mechanisms are unknown. Our lab has observed altered GnRH neuron firing and excitability in the intrahippocampal kainic acid (IHKA) mouse model of TLE. Here, we examined pulsatile rhythms of LH release and acute release of LH in response to systemic GnRH injection in both male and female IHKA mice and saline-injected controls.

Methods: Adult GnRH-Cre mice on a C57BL/6J background were injected in right dorsal hippocampus with KA (IHKA, 50 nl of 20 mM, males n = 3, females n = 18) or saline (males = 3, females n = 12) and implanted 2 wks later with depth EEG electrodes in ipsilateral hippocampus. EEG was collected at 2 mo post-injection for 24 h prior to and during blood sampling. EEG traces were quantified for electrographic seizures. Estrous cycle stage was recorded daily. Tail blood sampling consisted of 6-μl collections every 5 min for 3 h between 0900-1400 h (1900 h lights off) on estrus and diestrus, followed by GnRH injection (150 ng/kg i.p.) and a final tail blood sample collection 15 min later. Males underwent one collection period in the same manner. LH levels in whole blood samples were quantified using an ultrasensitive ELISA. Pituitary gene expression was quantified by qPCR. Data were compared using Kruskal-Wallis tests, Mann-Whitney tests, t-tests and Pearson’s correlations.

Results: There were no differences in basal (p = 0.95) or mean (p = 0.97) LH levels between saline or IHKA female mice at either cycle stage or in males (basal: p = 0.94, mean: p = 0.95). IHKA females and males also showed no changes in LH pulse amplitude (p = 0.34 females, 0.92 males) or inter-pulse interval (p = 0.24 females, 0.81 males) compared to controls. There were no correlations between percent time spent in seizures and any LH pulse parameters. All mice showed higher LH following bolus GnRH injection, but diestrous female IHKA mice showed a larger post-GnRH increase (2.01 ± 0.77 ng/ml) compared to controls (1.42 ± 0.45 ng/ml, p = 0.03). Furthermore, IHKA females examined (n = 6) displayed higher pituitary GnRH receptor (Gnrhr) gene expression levels in comparison to controls (n = 4, p = 0.01), without a difference in LHbeta (Lhb) levels. By contrast, males showed no differences between IHKA and control animals in GnRH-induced LH increment (p = 0.69). There were also no correlations between post-GnRH injection increase and percent time spent in seizures in either sex.

Conclusions: IHKA females, but not males, display elevated GnRH sensitivity, but IHKA mice do not display changes in LH pulse patterns. This female-specific pituitary hypersensitivity may arise as a compensatory mechanism to maintain pulsatile release of LH downstream of seizures.

Funding: R01 NS105825; R24 HD102061