Graduate Student University of Illinois at Urbana-Champaign
This abstract has been invited to present during the Better Patient Outcomes through Diversity Platform poster session This abstract has been invited to present during the Investigators Workshop Platform poster session
Rationale: Reproductive endocrine comorbidities are commonly observed in patients with temporal lobe epilepsy (TLE). Gonadotropin-releasing hormone (GnRH) neurons are the final common output in the neural regulation of hypothalamic-pituitary-gonadal (HPG) axis function, and are thus strong candidates for studies involving epilepsy-associated changes in HPG axis function. Our previous work demonstrated that GnRH neuron firing activity and excitability are disrupted in the intrahippocampal kainic acid (IHKA) mouse model of TLE (1). GABA mediates a major excitatory synaptic input to adult GnRH neurons (2). Here, we examined whether GABAergic transmission to GnRH neurons is altered in the IHKA model. Methods: Adult female GnRH-tdTomato mice on the C57BL/6J background were housed in a standard environment with a 14/10 h light/dark cycle (1900 h lights off). To confirm that all females had properly timed estrous cycles prior to injections, daily estrous cycle monitoring was performed from P42 until the day of injection. Mice were injected with either KA (50 nl of 20 mM) or an equivalent volume of saline in the right dorsal hippocampus on diestrus. 1 month after injection, daily estrous cycle monitoring resumed. Two months post-injection, 300-μm coronal brain sections were prepared from diestrous female mice and bathed in oxygenated artificial cerebrospinal fluid. Whole-cell voltage-clamp recordings of GABAergic spontaneous postsynaptic currents (sPSCs) were performed between 1200-1600 h on GnRH neurons expressing tdTomato red fluorescence identified via brief illumination at 593 nm. Soma locations were recorded in the medial septum (MS), preoptic area (POA), and anterior hypothalamic area (AHA) (1). Estrous cycle data was analyzed to categorize each animal as having either a regular cycle (4-6 d cycle period, “KA-regular”) or a long/disrupted cycle (> 7 d, “KA-long”). Results: Interevent interval (IEI, the time between two successive sPSCs) was significantly decreased in the KA-long group (n=10 cells, 9 mice) compared with both KA-regular (n= 9 cells, 6 mice) and saline-injected controls (n=10 cells, 8 mice) (p < 0.0001 for both comparisons). There was no difference in IEI between the KA-regular and saline groups (p = 0.1). Although group-wise comparisons of sPSC frequency showed no significant differences (p = 0.4), a region-specific comparison preliminarily showed an increase in sPSC frequency in POA GnRH neurons from KA-long mice. Analyses of sPSC amplitude (p = 0.6) and half-width (p = 0.8) showed no significant differences between groups. Conclusions: These findings suggest a change in the pattern of GABAergic transmission to GnRH neurons of diestrous female KA-long mice. As GABAA receptor activation is depolarizing in adult GnRH neurons, this change may at least partially explain previous findings of increased firing activity of GnRH neurons in the MS and POA of diestrous KA-long mice (1). GABAergic transmission to GnRH neurons may thus play roles in driving epilepsy-associated estrous cycle dysfunction in this animal model of TLE.
References: 1. Li et al., 2018 eNeuro 5:e0273-18.2018; 2. DeFazio et al. 2002 Mol Endocrinol 16:2872-2891 Funding: Please list any funding that was received in support of this abstract.: R01 NS105825, R01 NS105825-S1