Fyn interacts with and regulates the function of many neurotransmitter receptors in the brain and mediates effects of neurotrophins.261 For example, Fyn colocalizes with and mediates adenosine-induced transactivation of Trk-A and Trk-B neurotrophin receptors in vitro.262 Fyn also interacts directly with 5-HT6 receptors through its SH3 domain, and this interaction increases Fyn activity via an unknown mechanism.263 In addition, serotonin-dependent activation of ERK is mediated by Fyn,263 indicating cross-talk between Fyn and ERK signal transduction pathways. Fyn directly interacts with the α7 nACh receptor and may contribute to neuroprotection induced by nicotinic receptor stimulation.264 In addition, Fyn can increase NMDA receptor activity by phosphorylating the NR2B subunit of NMDA receptors, which may modulate susceptibility to seizures265 and underlie BDNF-induced increases in NMDA receptor function.266
