BDNF and allergic respiratory disease: Since AVPNs themselves are known to synthesize BDNF (Zaidi et al., 2005), and BDNF has been well-recognized to be able to cause upregulation of NKCC1 and/or downregulation of KCC2 (Coull et al., 2005; Choe et al., 2015; Tang et al., 2015), our results suggest that in airway allergy, both BDNF paracrine from activated microglia in the NA and BDNF autocrine from AVPNs might be involved in the alteration of NKCC1/KCC2 expression in putative AVPNs, which subsequently leads to enhanced excitatory response of AVPNs to inhibitory neurotransmitters.