ABSTRACT
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.