GnRH neurones population in the diencephalon of the coypu (Myocastor coypus)

Abstract

The goal of this study was to investigate the distribution and morphology of neurones that synthesise and store gonadotrophin releasing factor (GnRH) in the diencephalon of the coypu (Myocastor coypus), a South American rodent of the hystricomorpha suborder. For this purpose the encephalon of three mature male coypus were fixed by intra-arterial perfusion, using a paraformaldehyde and picric acid solution. The hypothalamic blocks were cut with freezing microtome to obtain 40µm thick coronal sections. The slides were exposed to an ultrasound antigen retrieval process in order to unmask hidden antigens. These sections were then processed using an immunohistochemical technique to show the GnRH neurones, using a monoclonal antibody (LRH 13). One group of serial sections was stained with cresyl violet (Nissl techniques) while the other sections were stained using Küver Barrera´s method (luxol fast blue and cresyl violet), to show the nuclei and nervous tracts of the hypothalamus under microscopic observation. Morphometric and quantitative analysis of neuronal bodies were performed using an image analyser. GnRH immunoreactive neurones were bipolar and long. The total number of neuronal bodies for this species was estimated at 1072 ± 27. All the cells were located in the rostral hypothalamus, mainly in the preoptic area. A few neurones were also observed in the bed nucleus of the stria terminalis and hypothalamic preoptic medial nucleus. The immunoreactive fibres were observed in the external layer of the median eminence. According to the data obtained we inferred that the distribution of the GnRH neurones of the coypu mainly coincides with that of other rodents such as the rat.