[Induction of growth-associated protein-43 expression in airway afferent nerves of guinea pigs by allergic airway inflammation].

OBJECTIVE: To investigate the mechanisms underlying sensitization of airway sensory nerves induced by allergic airway inflammation.

METHODS: Thirty-nine guinea pigs were divided randomly into three groups including group A (saline sensitized/challenged guinea pigs, n = 9), group B [ovalbumin (OVA) sensitized/saline challenged guinea pigs, n = 9], group C (OVA sensitized/challenged guinea pigs, n = 21). In group C, animals were subdivided into three groups with group C1 (treated by one OVA challenge, n = 6), group C2 (treated by 3 consecutive days OVA challenges, n = 6), group C3 (treated by 5 consecutive days OVA challenges, n = 9). The guinea pigs were sensitized by intraperitoneal injection of 0.5 ml saline (group A) or 0.5 ml 10% OVA (group B and C) on day 0 and challenged via the airway with saline (group A and B) or 1% OVA (group C) for 30 min on days 10, 11, 12, 13, and 14 by ultrasonic nebulization. The expression patterns of growth-associated protein-43 (GAP-43) in the airway nerve endings, the nodose and jugular ganglion neurons and the distribution relationships of GAP-43 with substance P (SP) and glial cell line-derived neurotrophic factor (GDNF) receptor components c-RET in the nodose and jugular ganglion neurons in guinea pig after allergic airway inflammation were studied using immunofluorescence double-labeling with laser confocal scanning microscopy, and Western blot.

RESULTS: By morphological study, after 2 hours following 5 consecutive days OVA challenge, GAP-43 immunoreactivity (IR) positive nerve endings were observed in the large bronchi, distributing network-like in the submucosa, a few nerve endings extending between the epithelia in the guinea pig airways. A substantial amount of GAP-43 IR neurons were found in the nodose and jugular ganglion, and GAP-43 IR co-localized with SP were predominantly in the nodose ganglion neurons, but in the jugular ganglion neurons, GAP-43 IR and c-RET IR were co-localized predominantly. By Western blot, GAP-43 protein levels (A) were 0.38 +/- 0.04, 0.41 +/- 0.03, 0.49 +/- 0.05, 0.79 +/- 0.08, 0.76 +/- 0.04 in group A, B, C1, C2, C3 respectively, after 2 hours following 1, 3, 5 d challenged. GAP-43 protein levels were increased significantly in the nodose and jugular ganglion after 2 hours following the first OVA challenged (0.49 +/- 0.05, P < 0.05) when compared with that in group B, after 3 consecutive days OVA challenge treatment, GAP-43 protein expression levels (0.79 +/- 0.08) were increased more significantly (P < 0.01), compared with that in group B and reached the levels of GAP-43 of group C3 (0.76 +/- 0.04, P > 0.05).

CONCLUSION: These data indicate that GAP-43 protein expression in airway afferent neurons including SP peptidergic neurons in the nodose ganglion and GDNF responsive neurons in the jugular ganglion in guinea pigs can be induced by allergic airway inflammation.