Odor-Induced, Activity-Dependent Transneuronal Gene InductionIn Vitro: Mediation by NMDA Receptors

Abstract

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. THpositive 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.

Transcription Factor KLF7 Is Important for Neuronal Morphogenesis in Selected Regions of the Nervous System

“…Primary OSNs were prepared and cultured as described previously (51). Cells were fixed for 10 min in 4% paraformaldehyde, and antibodies were blocked for 30 min in 2% normal goat serum-0.2% Triton X-100; primary and secondary antibodies were incubated for 12 h at 4°C and for 1 h at room temperature, respectively.…”

Plasticity in the Olfactory System: Lessons for the Neurobiology of Memory

“…Activation of D2 receptors in the olfactory bulb reduces transmitter release from olfactory receptor axons, effectively reducing the gain of afferent input (Wachowiak and Cohen 1999;Ennis and others 2001). Conversely, a reduction in olfactory stimulation (odor deprivation) causes an N-methyl-D-aspartate (NMDA) receptordependent (Puche and Shipley 1999) decrease in dopamine expression in these neurons (Cho and others 1996), which effectively enhances the responsiveness of mitral cells to subsequent stimulation (Wilson and Sullivan 1995). Thus, as with piriform cortical afferents, recent levels of odor stimulation can be remembered and adjusted for through a presynaptic regulation of transmitter release.…”

Odorant-Induced Activation of Extracellular Signal-Regulated Kinase/Mitogen-Activated Protein Kinase in the Olfactory Bulb Promotes Survival of Newly Formed Granule Cells

“…There are several published methods for culturing OB neurons (Currie and Dutton, 1980;Trombley and Westbrook, 1990;Carlson et al, 1997;Puche and Shipley, 1999;Osako et al, 2000;Muramoto et al, 2001), which lead to differences in cellular organization and morphology of cultured cells. Furthermore, because these cultured cells were generally used for single-cell activity in electrophysiological and/or optical recordings, the biochemical responses of granule cells in culture remain unknown.…”