Alpha-synuclein expression in oxytocin neurons of young and old bovine brains

Understanding of central nervous system mechanisms underlying age-related infertility remains limited. Fibril alpha-synuclein, distinct from its monomeric form, is implicated in age-related diseases. Notably, fibril alpha-synuclein spreads among neurons, similar to prions, from damaged old neurons in cortex and hippocampus to healthy neurons. However, less is known whether alpha-synuclein propagates into oxytocin neurons, which play crucial roles in reproduction. We compared alpha-synuclein expression in the oxytocin neurons in suprachiasmatic nucleus (SCN), supraoptic nucleus (SON), paraventricular hypothalamic nucleus (PVN), and posterior pituitary (PP) gland of healthy heifers and aged cows to determine its role in age-related infertility. We analyzed mRNA and protein expression, along with Congo red histochemistry and fluorescent immunohistochemistry for oxytocin and alpha-synuclein, followed by confocal microscopy with Congo red staining. Both mRNA and protein expressions of alpha-synuclein were confirmed in the bovine cortex, hippocampus, SCN, SON, PVN, and PP tissues. Significant differences in alpha-synuclein mRNA expressions were observed in the cortex and hippocampus between young heifers and old cows. Western blots showed five bands of alpha-synuclein, probably reflecting monomers, dimers, and oligomers, in the cortex, hippocampus, SCN, SON, PVN, and PP tissues, and there were significant differences in some bands between the young heifers and old cows. Bright-field and polarized light microscopy did not detect obvious amyloid deposition in the aged hypothalami; however, higher-sensitive confocal microscopy unveiled strong positive signals for Congo red and alpha-synuclein in oxytocin neurons in the aged hypothalami. alpha-synuclein was expressed in oxytocin neurons, and some differences were observed between young and old hypothalami.