210 C
decrease in TH and an increase in VIP neurons [6,37,38], the current data are consistent with a role for endogenous
NGF in vivo to maintain normal neurotransmitter pheno- type in nodose petrosal ganglia neurons. These data,
coupled with the presence of TrkA mRNA and of the
125
retrograde transport of I-NGF by vagal afferent neurons,
indicate an important role for NGF in the functions including maintenance of normal transmitter phenotype
of these visceral afferent neurons. Moreover, these data coupled with the well established insensitivity of develop-
ing nodose ganglion neurons to the survival promoting actions of NGF at a time when the neurons do require
trophic support [14], suggest a developmental change in the responsiveness of these neurons. Our data also demon-
strate differences in the response between mature placode-
Fig. 4. Bar graphs showing the numbers of NF-200-ir neurons per 1000
derived visceral afferent and neural crest-derived DRG
cells plated in each well in dissociated, enriched 5-day cultures of
neurons. In distinction to the NGF-induced alterations in
nodose petrosal ganglia in the absence of neurotrophin control, and the
TH- and VIP-ir in nodose petrosal ganglia neurons; in
presence of 100 ng ml of NGF, NT-3 or NT-4.
adult DRG neurons in culture, NGF 50 ng ml increases SP- and CGRP-ir but does not alter VIP-ir in culture
mature DRG neurons do not have TH [17,23]. Verge et al. [33] showed however that NGF infusion reduced the
4. Discussion numbers of VIP-ir neurons in the DRG after injury. In
sympathetic neurons of the superior cervical ganglion, The data presented here demonstrate that specific neuro-
NGF increases the expression of TH and but does not alter trophins NGF and NT-3 influence the numbers of
VIP [19,39]. neurons labeled for TH and VIP in nodose petrosal
The mechanism through which NGF alters the numbers ganglia cultures. That the effects are mediated by actions
of TH and VIP neurons is not known. One possibility is of the neurotrophin is verified by the ability of the
that NGF is acting directly through TrkA receptors on precipitating antibodies to prevent or attenuate the actions
specific cultured nodose and petrosal ganglion neurons. of the neurotrophins. The neurotrophin-induced changes
Although we have preliminary evidence for the presence of are likely due to changes in the content of the neurochemi-
TrkA mRNA in cultured NG PG neurons Zhuo, Verdier- cals within neurons and are unlikely to be due to altera-
Pinard and Helke, unpublished data, we do not know if tions in neuronal survival. This is based on our data
the TrkA mRNA containing neurons are those in which the demonstrating an absence of effect of any of the neuro-
content of TH or VIP is altered. Moreover, we did not find trophins tested on the numbers of NF-200 immunoreactive
TH-positive neurons of intact nodose and petrosal ganglia neurons present after 5 days in culture. Moreover, it was
that co-expressed TrkA [9]. NGF is also a ligand for p75 previously shown that the mature visceral sensory neurons
and nearly all nodose ganglion neurons contain p75 do not require exogenous neurotrophins for survival
[32,34,36]. Thus, the roles of neuronal TrkA and p75, [11,15,16]. However, we cannot rule out the possibility
remain to be defined in this system. Likewise, the possi- that specific survival effects on a small subset of neurons
bility that a non-neuronal cell type e.g., fibroblasts expressing a specific agent contributes to an observed
remaining in these neuronally-enriched cultures responds change in immunoreactive neurons. The proposed changes
to the addition of NGF with the secretion of a factor that in content of immunoreactive agents within the neurons of
secondarily alters neuronal phenotype requires additional the cultured nodose and petrosal ganglia may reflex
studies. neurotrophin-induced changes in TH and or VIP mRNA
Whereas NT-3 up to 150 ng ml does not affect peptide content and subsequent synthesis of TH and or VIP.
expression in newborn DRG [23], we found that NT-3 did However, it is also possible that the neurotrophins either
affect the numbers of VIP-ir neurons in the mature nodose directly or indirectly affect post translational processing,
petrosal ganglia cultures. In contrast, in DRG neurons and or stability of the products within the neurons.
NT-3 was shown to upregulate neuropeptide Y but not VIP In this study, exogenous NGF increased the TH-ir and
in an in vivo model of neural injury where VIP was already decreased VIP-ir neurons in the nodose petrosal ganglia
significantly upregulated [27]. cultures. Given that in vivo NGF is a retrogradely trans-
The opposite actions of NGF and NT-3 on the numbers ported target-derived neurotrophin, and that loss of contact
of VIP-ir neurons are intriguing and potentially significant. with target either through vagotomy or inhibition of
If additional studies verify that these actions result from axonal transport in the cervical vagus nerve results in a
changes in VIP mRNA, it would represent directionally
C .J. Helke, D. Verdier-Pinard Brain Research 884 2000 206 –212
211
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