Influence of peripheral inflammation on the postnatal maturation of primary sensory neuron phenotype in rats

The influence of early peripheral inflammation upon the postnatal developme nt of rat primary sensory neuron subtypes was investigated. Lumbar dorsal r oot ganglia (DRG) were immunostained for calcitonin gene-related peptide (C GRP), neurofilament (NF200), and isolectin B4 (IB4) binding. Proportions of each subpopulation were measured at postnatal day (P) 0, P3, P7, and P21 i n normal pups and in those that had received a unilateral hindpaw carrageen an injection at P1. The effects were compared with those following a simila r injury in adults. Both the IB4 (positive [+ve]) and NF200+ve cell populat ions increased postnatally (IB4+ve: 23 +/- 1.6% to 32.6 +/- 1.3%; NF200+ve: 33.8 +/- 1.2% to 43.3 +/- 1.9%), whereas the population of CGRP+ve cells s tayed the same. After neonatal inflammation, the rise in IB4+ve binding occ urred earlier but was the same as that in controls by P21. The CGRP+ve popu lation increased at 2 and 6 days after carrageenan in neonates, because of an increase in both small CGRP/IB4 and larger CGRP/NF200 double-labeled cel ls, but was normal by 3 weeks. Carrageenan in adults caused an increase in CGRP/IB4 cells only. The effects of peripheral inflammation differ in neona tal and adult DRG. Neonatal inflammation causes CGRP upregulation in both s mall and large cells and accelerates the postnatal increase in IB4 binding. These effects might influence subsequent central development.