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Triiodothyronine Exerts a Trophic Action on Rat Sensory Neuron Survival and Neurite Outgrowth through Different Pathways
Author(s) -
Walter I. Barakat
Publication year - 1996
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1111/j.1460-9568.1996.tb01229.x
Subject(s) - neurite , neuron , sensory neuron , nerve growth factor , biology , neurotrophin , neuroscience , neurotrophic factors , microbiology and biotechnology , sensory system , in vitro , receptor , biochemistry
Apart from several growth factors which play a crucial role in the survival and development of the central and peripheral nervous systems, thyroid hormones can affect different processes involved in the differentiation and maturation of neurons. The present study was initiated to determine whether triiodothyronine (T 3 ) affects the survival and neurite outgrowth of primary sensory neurons in vitro. Dorsal root ganglia (DRG) from 19‐day‐old embryos or newborn rats were plated in explant or dissociated cell cultures. The effect of T 3 on neuron survival was tested, either in mixed DRG cell cultures, where neurons grow with non‐neuronal cells, or in neuron‐enriched cultures where non‐neuronal cells were eliminated at the outset. T 3 , in physiological concentrations, promoted the growth of neurons in mixed DRG cell cultures as well as in neuron‐enriched cultures without added nerve growth factor (NGF). Since neuron survival in neuron‐enriched cultures cannot be promoted by endogenous neurotrophic factors synthesized by non‐neuronal cells, the increased number of surviving neurons was due to a direct trophic action of T 3 . Another trophic effect was revealed in this study: T 3 sustained the neurite outgrowth of sensory neurons in DRG explants. The stimulatory effect of T 3 on nerve fibre outgrowth was considerably reduced when non‐neuronal cell proliferation was inhibited by the antimitotic agent cytosine arabinoside, and was completely suppressed when the great majority of non‐neuronal cells were eliminated in neuron‐enriched cultures. These results indicate that the stimulatory effect of T 3 on neurite outgrowth is mediated through non‐neuronal cells. It is conceivable that T 3 up‐regulates Schwann cell expression of a neurotrophic factor, which in turn stimulates axon growth of sensory neurons. Together, these results demonstrate that T 3 promotes both survival and neurite outgrowth of primary sensory neurons in DRG cell cultures. The trophic actions of T 3 on neuron survival and neurite outgrowth operate under two different pathways.