Aging mice inhibited the activation of BDNF–TrkB signaling pathway and showed hippocampal-dependent cognitive impairment in relative to adult animals, with the reduced transcription and expression of synaptic protein markers, such as growth-associated protein 43 (GAP43), synaptophysin (SYN), post-synaptic density protein 95 (PSD95), including decreased synapse density, and PSD thickness. The gene discussed is GAP43; the disease is Cognitive impairment.