Proneurogenic and microglial modulatory properties of botulinum neurotoxin in the hippocampus of aging experimental mice

BACKGROUND: Botulinum neurotoxin (BoNT) is widely recognized as an effective therapeutic agent for managing various neurological disorders, characterized by motor impairments and neuromuscular deficits. BoNT works by modulating the release of acetylcholine at the neuromuscular junction. Recently, BoNT has been shown to enhance spatial memory and attenuate anxiety in experimental aging animals. While neurogenesis in the hippocampus contributes to cognitive properties, BoNT treatment could potentially influence the regulation of adult neurogenesis. As aging-associated microglial activation impairs neurogenesis, the anti-inflammatory properties of BoNT could be associated with the modulation of microglial activity, thereby enhancing cognitive function. AIM: To investigate the neurogenic and microglial modulatory properties of BoNT in the hippocampus of aging experimental mice. METHODS: Experimental aging mice were administered BoNT and after four weeks, the animals were sacrificed. The brains were subjected to cryosections followed by immunohistochemical analysis to quantify doublecortin (DCX)-positive immature neurons, bromodeoxyuridine (BrdU)-neuronal nuclei (NeuN) double positive newly matured neurons and ionized calcium-binding adapter molecule 1 (Iba1)-positive microglia in the hippocampal dentate gyrus. In parallel, an additional set of animals was used to evaluate BoNT-mediated alterations in key inflammatory markers such as cyclooxygenase (COX)-2, and nitric oxide (NO) in hippocampal tissues. RESULTS: The results revealed a significant increase in the number of DCX-positive immature neurons and BrdU-NeuN positive differentiated neurons in the hippocampus of the BoNT-treated group compared to the control. This enhancement in neurogenesis was accompanied by a marked reduction in the activated form of microglial cells, coupled with decreased mRNA expression of COX-2 and reduced NO levels in the hippocampus of BoNT-treated animals. CONCLUSION: This study validates the proneurogenic and anti-neuroinflammatory properties of BoNT, which may underlie its procognitive effects. Hence, BoNT could be a promising therapeutic agent for treating various neurocognitive disorders.