The Journal of Neuroscience, February 15, 1999, 19(4):1359-1370
Odor-Induced, Activity-Dependent Transneuronal Gene Induction
In Vitro: Mediation by NMDA Receptors
A. C.
Puche and
M. T.
Shipley
Department of Anatomy and Neurobiology, Program in Neuroscience,
School of Medicine, University of Maryland, Baltimore, Maryland 21201
Expression of tyrosine hydroxylase (TH) by juxtaglomerular (JG)
neurons of the olfactory bulb (OB) requires innervation of the bulb by
olfactory receptor neurons (ORNs). ORN lesion selectively downregulates
TH in JG neurons. In reversible odor deprivation, TH expression is
downregulated as the naris is closed and then upregulated upon naris
reopening. The mechanism or mechanisms regulating this dependence are
unknown. TH expression could be regulated by trophic factor release
and/or synaptic activity from ORN terminals. We investigated TH
expression in cocultures of dissociated postnatal rat OB cells and
embryonic olfactory neuroepithelium (OE) slice explants. TH-positive
neurons in control dissociated OB cell cultures alone comprise only a
small fraction of the total population of cells present in the culture.
However, when OE slice explants are cocultured with dispersed OB cells,
there is a mean 2.4-fold increase in the number of TH-positive neurons.
ORNs in vivo use glutamate as a neurotransmitter. Broad
spectrum excitatory amino acid antagonists (kyurenic acid) or selective
antagonists of the NMDA receptor (APV) both prevent induction of TH
expression in OE-OB cocultures. Furthermore, pulse application of NMDA
stimulates TH expression in OB neurons in the absence of OE. In
vitro, OB TH neurons express NMDA receptors, suggesting that
NMDA stimulation is acting directly on TH neurons. Exposure of OE
explants to natural odorants results in upregulation of TH, presumably
through increased ORN activity, which could be blocked by APV. These
findings indicate that odorant-stimulated glutamate release by ORN
terminals regulates TH expression via NMDA receptors on JG dopaminergic neurons.
Key words:
dopamine; tyrosine hydroxylase; neurotransmitters; olfactory; activity-dependent; glutamate
Copyright © 1999 Society for Neuroscience 0270-6474/99/1941359-12$05.00/0