Immunohistochemical Localization of Some Neurotrophic Factors and Their Receptors in the Rat Carotid Body

The carotid body (CB) is a small neural crest-derived organ that registers oxygen and glucose levels in blood and regulates ventilation. The most abundant cell type in the CB glomeruli is glomus or type I cells, which is enveloped by processes of sustentacular or type II cells. Growth and neurotrophic factors have been established as signaling molecules played an important role in the development of the CB. To gain insight whether these signaling molecules are present in the adult rat CB, we examined the expression and cellular localization of some neurotrophic factors and their corresponding receptors in this organ by immunohistochemistry. The results showed the presence of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF) as well as p75NTR, tyrosine kinase A receptor (TrkA), tyrosine kinase B receptor (TrkB) and GDNF family receptor alpha1 (GFRα1) in the adult CB. At the light-microscopical level, the immunoreactivity for NGF and both its low-affinity (p75) and high-affinity (TrkA) receptors was detected in the majority of glomus cells and also in a subset of sustentacular cells. BDNF and its receptors, p75 and TrkB, were observed in the glomus cells, too. Remarkably, the immunohistochemical analysis revealed that the neuron-like glomus cells, but not the glial-like sustentacular cells, expressed GDNF and GFRα1. Taken together with prior results, it can be inferred that neurotrophins may be involved in the CB cell differentiation and survival in adulthood, and may exert a potent glomic protective action as well. It is also presumable that GDNF production by glomus cells plays a pivotal role in permitting long-term viability of CB grafts, which permits their potential applicability in cell therapy as a promising tool in neurodegenerative disorders.