Relationship between hypothalamic astrocytes and gonadotropin-releasing hormone-neurons in the female plains vizcacha

Astrocytes play an essential role in the control of gonadotropin-releasing hormone (GnRH) neurons. However, limited information is available in non-conventional animal models. This study aimed to explore hypothalamic astrocyte distribution in the plains vizcacha (Lagostomus maximus), a South American hystricomorph rodent with distinctive reproductive physiology, and to analyze their spatial relationship with GnRH neurons throughout the life cycle. Female plains vizcachas were evaluated during non-pregnancy (ovulating and non-ovulating) and pregnancy (early-, mid-, and late-pregnant). Plasma levels of estradiol (E2), progesterone (P4), and luteinizing hormone (LH) were determined. Astrocytes were assessed by glial fibrillary acidic protein (GFAP) immunohistochemistry in hypothalamic regions involved in reproductive control, including the medial preoptic area (mPOA), arcuate nucleus (ARC), and median eminence (ME). Their spatial relationship with GnRH-immunoreactive neurons and fibers was also analyzed. Pregnancy was associated with marked hormonal changes, including significantly elevated E2 levels and dynamic variations in P4 and LH (p<0.01). Astrocyte distribution was largely conserved across life stages in the mPOA and ME, whereas a significant reduction in GFAP-immunoreactive area was detected in the ARC during early pregnancy. Close appositions between astrocytic processes and GnRH-neurons were observed in ovulating non-pregnant and pseudo-ovulating mid-pregnant animals. In the ME, very intimate contacts between astrocytic processes and GnRH-fibers in the palisade layer were detected exclusively during pregnancy. In conclusion, these findings reveal a steroid-dependent plasticity of hypothalamic astrocytes and support a key role for astrocyte-GnRH neuron interactions in the regulation of reproductive neuroendocrine function during gestation in the plains vizcacha.