5‐Hydroxytryptamine Distribution Alteration in Both Neuron and Synapse of Tg( <scp>SOD1</scp> * <scp>G93A</scp> )1gur Mice: A Potential Intervention Candidate Strategy for Amyotrophic Lateral Sclerosis

AIMS: Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease; the precise pathogenesis of sporadic ALS (sALS) has not yet been elucidated up to now. Previous studies revealed that the abnormal alterations of some non-motor neurons (non-MN) were a potential pathogenesis of sALS. Therefore, this study aims to search the potential evidences of non-MN in the pathogenesis of ALS via exploring potential relationships between 5-hydroxytryptamine (5-HT) neurons and the development of ALS. METHODS: We employed fluorescent immunohistochemistry to investigate the altered distribution patterns of 5-HT and tryptophan hydroxylase 2 in the spinal cord and brainstem of Tg(SOD1*G93A)1Gur (TG) and wild-type (WT) mice. Additionally, we used western blot to analyze the expression levels of 5-hydroxytryptamine receptor 1A (5-HTR1A) and 5-HTR2A. RESULTS: Our findings revealed that 5-HT synapses were primarily distributed in the funiculus lateralis, anterior horn, posterior horn, central lateral column, and the area around the central canal of cervical, thoracic, and lumbar segments, and raphe nucleus as well as lateral paragigantocellular nucleus, and gradually reduced following age increase in WT mice. However, 5-HT synapses in the spinal cord and 5-HT neurons in the brainstem gradually increased following the progression of disease and presented a significantly negative correlation between the increased distribution of 5-HT synapses and neurons and the reduction of neural cell number (positively correlated with the increase in neural cell death) at the onset and/or progression stage of TG mice. 5-HTR1A significantly increased, while 5-HTR2A significantly decreased at the onset stage of TG mice. CONCLUSION: Our study speculated that the distribution changes of 5-HT synapses in the spinal cord and 5-HT neurons in the brainstem play a potential protective role in the pathogenesis of sALS through a compensatory 5-HT increase.