Brain-derived neurotrophic factor (BDNF) affects somatotrophic axis activity in sheep

Brain-derived neurotrophic factor (BDNF), a growth protein factor belonging to the neurotrophin peptide family, participates in mechanisms that promote differentiation and survival of developing neurons. Moreover, BDNF is involved in processes related to neuronal neuroplasticity and neuroprotective mechanisms, such as the stimulation of nerve growth and the formation of synaptic connections between nerve cells (Peiris et al., 2004). Brain-derived neurotrophic factor mRNA is located in several areas of the brain; for example, in the neocortex, hippocampus, medulla oblongata and hypothalamus. In the mediobasal hypothalamus (MBH), BDNF immunoreactive material has been identified in the paraventricular (PVN), arcuate (ARC), ventromedial (VMN) or dorsomedial (DMN) nuclei, as well as in the median eminence (ME) (Unger et al., 2007; Cordeira et al., 2010). The presence of tyrosine kinase receptor isoform B (TrkB), which is a specific receptor for BDNF, ABSTRACT. Brain-derived neurotrophic factor (BDNF) is a growth protein factor belonging to the neurotrophin peptide family that is involved in the regulation of several activities of the central nervous system. However, its effects on the activity of the somatotrophic axis in ruminants have not yet been determined. The present study aimed to verify the research hypothesis, which assumed that BDNF can modulate key hormones of the somatotrophic axis in sheep. The experiment involved sexually mature Polish Merino sheep (n = 24). The animals were divided into three groups, and the following intracerebroventricular infusions were performed: control group received Ringer-Locke solution (480 μl/day), BDNF10 – BDNF at a dose of 10 μg/480 μl/day and BDNF60 – BDNF at a dose of 60 μg/480 μl/day. Blood samples were collected on days 0 and 3 of infusions. After the experiment, the animals were slaughtered and selected structures of the hypothalamus, pituitaries and plasma samples were stored for Real-Time reverse transcription-polymerase chain reaction (Real-Time RT-PCR) and radioimmunoassay analysis. It was revealed that central BDNF administration induced a dose-dependent increase in growth hormone relasing hormone (GHRH) mRNA expression in the mediobasal hypothalamus of sheep. Moreover, central BDNF administration increased growth hormone (GH) mRNA expression in the pituitary and the GH pulse amplitude, which, consequently, increased the mean GH concentration in the blood plasma. These observations suggest the up-regulation of the somatotrophic axis activity in female sheep after BDNF infusion. So, it can be stated that BDNF is involved in the modulation of key hormones co-creating the somatotrophic axis in mature sheep. Received: 27 July 2021 Revised: 19 October 2021 Accepted: 26 October 2021