Distribution and morphology of gonadotropin-releasing hormone neurons in the hypothalamus of an induced ovulator – The llama (Lama glama)

• Published in: General and comparative endocrinology 2018-07, Vol.263, p.43-50
• Main Authors: Carrasco, Rodrigo A., Singh, Jaswant, Adams, Gregg P.
• Format: Article
• Language: English
• Subjects: Gonadotropin-releasing hormone; Hypothalamus; Median eminence Llamas; Neurons
• ISSN: 0016-6480; 1095-6840
• DOI: 10.1016/j.ygcen.2018.04.011

•GnRH neurons are present in the hypothalamus of llamas.•GnRH neurons are predominantly located in the medio-basal hypothalamus.•GnRH axons are directed towards the median eminence.•GnRH axons can be detected in the posterior pituitary. Gonadotropin-releasing hormone (GnRH) is a decapeptide involved in the regulation of reproduction in all mammals, but the distribution of GnRH neurons within the brain varies widely among species. The objective of the present study was to characterize the number and distribution of GnRH neurons in the hypothalamus and preoptic area of llamas, an induced ovulator. The brains of female llamas (n = 4) were fixed, frozen and sectioned serially every 50 µm in the transverse (coronal) plane. Every 10th section was stained for immunohistochemical detection of GnRH-positive neuron cell bodies and fibers by incubation with 3,3′-diaminobenzidine. The number of counted immunoreactive cells ranged from 222 to 250 (≈241 ± 13 cells in the preoptic area and hypothalamus per animal) and were localized in the medio-basal hypothalamus (44.3%), anterior hypothalamus (27%), preoptic area (14.9%), diagonal band of Broca/medial septum (13.4%), and mammillary area (0.5%). The immunoreactive cells were not localized in specific hypothalamic nuclei, but rather appeared to be distributed diffusely. The highest concentration of immunoreactive neuron fibers was in the median eminence (P