The influence of catecholamine on the migration of gonadotropin-releasing hormone-producing neurons in the rat foetuses

atecholamines (CA) play an important role inthe regulation of GnRH neurons in adults, and it is probablethat they control GnRH-neuron development. Migration ofGnRH neurons was evaluated in male and female rats at the17th embryonic day (E17) and E21, following the dailytreatment of their pregnant mothers from the 11th to the16th and 20th day of gestation witha-methyl-para-tyrosine(aMPT), an inhibitor of catecholamine synthesis. High-performance liquid chromatography with electrochemicaldetection (HPLC-ED) was used to specify theaMPT-induced CA depletion. There was a 50–70% decrease indopamine and noradrenaline content in the nose and in thebrain ofaMPT-treated foetuses, proving the efficacy of thispharmacological model. Immunohistochemistry was usedto evaluate the percentage (%) of GnRH neurons alongtheir migration pathway from the vomeronasal organ(VNO) in the nose to the septo-preoptic area in the fore-brain which is considered as an index of neuron migration.Special attention was paid to the topographic relationshipsof GnRH neurons with catecholaminergic fibres. Thesewere observed in apposition with GnRH neurons in theentrance to the forebrain. In CA-deficient foetuses, thepercentage of GnRH neurons located in the rostral regionsextending from the VNO to the septum was greater than incontrols. However, no statistically significant differencewas found in the forebrain which extended from the septumto the retrochiasmatic area. In conclusion, these data sug-gest that endogenous catecholamines stimulate the GnRHneuron migration in ontogenesis

Expression précoce de la tyrosine hydroxylase dans l'épithélium olfactif et respiratoire chez le foetus de mouton (Ovis aries)

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Prolonged Neurogenesis during Early Development of Gonadotropin-Releasing Hormone Neurones in Sheep <i>(Ovis aries):</i> In vivo and in vitro Studies

International audienceGonadotropin-releasing hormone (GnRH) neurons involved in controlling the reproductive function in vertebrates are derived from the olfactory placode. However, in the sheep and the rat species, GnRH-immunoreactive (GnRH-IR) neurons could not be detected in the olfactory region during the earliest phase of GnRH system development. Using in situ hybridization (ISH) and immunohistochemistry (IHC) in sheep embryos ranging from 26 to 53 days' gestational age (G26-G53), the present work confirmed that GnRH expression could not be detected during the earliest steps of migration. The first ISH+ cells were detected in the nasal septum and at the entrance of the telencephalon at G33 stage. [(3)H]-thymidine pulses applied to in vitro olfactory explant cultures showed that GnRH neuron precursor cells have an extended multiplication period corresponding to G26-G36 before entering the neuronal differentiation process. Therefore, the lack of GnRH neuron detection during the early phase of development in the sheep compared to the mouse and other vertebrates represents a major difference in the early development of GnRH neurons. In the mouse, GnRH neuron precursors have a limited multiplication period in the vomeronasal pit and only postmitotic neurons start migration, whereas in the sheep embryo, the multiplication period is extended to about 10 days as demonstrated in olfactory explant cultures

Tyrosine hydroxylase expression in the olfactory/respiratory epithelium in early sheep fetuses (Ovis aries)

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Early development of GnRH neurons in sheep embryo. In vivo and in vitro studies

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