Age-dependent changes in the neurochemical properties of sensory neurons

Sensory neurons represent a heterogenous population of neurons with different morphological, receptor, and immunohistochemical characteristics. The majority of large neurons with myelinated Aδ-fibers contain the neurofilament protein 200 kDa (NF200); some small afferent neurons can bind to isolectin B4 (IB4). Sensory neurons also may contain different types of tyrosine kinases (TrkA, B, and C) and neurotrans-mitters. Neuropeptides are generally located in small and medium-sized neurons. The proportion of neurons containing TrkA decreases and the percentage of NF200-, IB4-, substance P- and CGRP-positive neurons increases during early development. The growth and development of different types of sensory neurons is controlled by neurotrophins.