Repeated allergen exposure induces neural plasticity of adult neurons in lower airway parasympathetic ganglia

Abstract

We tested whether repeated allergen challenge induces neural plasticity of principle neurons in lower airway parasympathetic ganglia. We used single and double (24 h apart) antigen aerosol challenge (0.05, 0.1, 0.3% ovalbumin, 5 minutes each) of sensitized guinea pigs and analyzed tissue from each of these groups 24 and 48 hours after exposure. At all time points, there was increased eosinophils (42–89%) compared to control level of 24±5 eosinophils/mm2. In the guinea pig trachea, there are two distinct populations of parasympathetic neurons: cholinergic and nonadrenergic, noncholinergic (NANC) neurons, the latter synthesize nitric oxide (NO) and VIP. There was no change in cholinergic phenotype at any time point but VIP levels decreased at 24 and 48 hrs after a double allergen challenge. 48 hours after a double allergen challenge: 13% of NANC neurons were immunoreactive for the cholinergic marker, ChAT; there was an increase in dendritic growth in cholinergic neurons from an average total dendritic length per neuron of 878±104μm to 1023±113μm (n = 6), and we observed neurotrophin-3 immunostaining, but not other neurotrophins, in infiltrating cells in the lower airways (n = 4). These results provide evidence that, at longer periods following repeated allergen challenge, there is plasticity of neurons in lower airway parasympathetic ganglia. Funding: JHU Woodrow Wilson Fellowship (JP); NIH-NHLBI (BJU).