Journal of Neuroscience, Vol 11, 3991-4002, Copyright © 1991 by Society for Neuroscience
A catecholaminergic sensory neuron phenotype in cranial derivatives of the neural crest: regulation by cell aggregation and nerve growth factor
DM Katz
Department of Neurosciences, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106.
Tyrosine hydroxylase (TH) is transiently detectable in cells distributed
throughout cranial sensory ganglia during early stages of gangliogenesis
[embryonic day (E) 10.5-15.5]. Although TH cells appear in embryonic
ganglia of both neural crest and placode origin, mature cranial sensory
neurons that express catecholaminergic properties are restricted to placode
derivatives. The mechanism(s) underlying the loss of TH expression in
crest-derived sensory ganglia is unknown, and the present study was
undertaken to define the temporal regulation of this phenotype. Our data
indicate that transient TH cells belong to a large subset of primary
sensory neurons that exhibit the capability to express TH throughout
development. The lack of TH expression after E15.5 appears to be due to
modulation of this catecholaminergic potential. The phenotype reappears,
however, when E16.5 and older ganglia are dissociated in culture into
single cells, suggesting that factors associated with cell aggregation
modulate TH expression. In support of this hypothesis, sensory neurons
grown at high cell density exhibit lower levels of TH expression than
low-density cultures. The decrease in TH levels seen at high density was
associated with changes in sensory neuron morphology that are
characteristic of ganglion cell maturation in vivo; therefore, modulation
of TH expression may be only one facet of a more general program of sensory
neuron differentiation associated with cell aggregation in developing
ganglia. In contrast to the effects of cell aggregation, treatment with NGF
increased the proportion of TH cells in dissociate cultures of E14.5 and
E16.5 cranial sensory ganglia. Our findings indicate that sensory
transmitter phenotype may be modulated by multiple factors during
gangliogenesis, including cellular interactions intrinsic to the developing
ganglionic microenvironment.