TrkB Expression at the Neuromuscular Junction is Reduced During Ageing - a Review Summary of Findings This experiment looked at the expression of two types of tyrosine kinase B - the full length TrkB and truncated TrkB. These receptors were looked at in ageing tissues. The experiment hypothesised that there was less expression of TrkB in soleus muscles of 24-month-old mice when compared with the muscles of 3 and 12 month of mice. TrkB receptors are co-localised with ACh receptors; their main responsibility is stabilising structure and modifying synaptic transmission throughout the central nervous system. Both the structure and function of the neuromuscular junction are impacted by TrkB signalling via the brain-derived neurotrophic factor (BDNF) and neurotropin-4/5 (NT-4/5). The expression of both ligands and the receptor of TrkB at the neuromuscular junction is innervation dependent. During the ageing process, the postsynaptic AChR area expands and presynaptic nerve terminals are lost; this leads to the denervation of the soleus muscle fibres. Overall, the experiment found that TrkB expression is reduced during the normal ageing process; this reduction is associated with age-related alterations of the neuromuscular structure. Experimental Approach The experiment began by euthanising mice aged 3, 12 and 24 months old, and then removing their soleus muscles. These removed muscles were immunolabelled with a diluted rabbit polyclonal anti- TrkB. This enabled the scientists to view extracellular concentrations of both the full length and truncated TrkB. The immunolabelled samples were imaged under the microscope to show whether the anti-TrkB antibody wash was successful and the visible AChR's were manually counted. Next, mRNA was isolated from the middle third of the muscle to allow for RNA extraction using real-time reverse transcription quantitative PCR. Finally, the percentage overlap of ACh receptors versus TrkB was calculated. Discussion The experiment proved their hypothesis and backed their conclusions with evidence, which showed that there was a lower expression of TrkB in the 24-month-old mice, when compared with the 3- and 12-month-old mice. The loss of TrkB expression aligned with changes in the structure of ACh receptors. However, the sample sizes were not kept at a constant number, and this difference has not been explained throughout the article. The changes were in the number of mice per age group and the number of neuromuscular junctions taken. Furthermore, there was no control group of mice. A control group could have been used to explain why there were increased levels of TrkB, despite changes in mRNA expression. Despite the adaptations to the experiment that could be made, the overall hypothesis could be met and evidenced.