Depolarizing influences regulate preprotachykinin mRNA in sympathetic neurons.

Abstract

We have been studying mechanisms regulating neurotransmitter plasticity in sympathetic neurons. Neurons of the rat superior cervical ganglion (SCG) synthesize multiple putative transmitters, including the peptide substance P (SP). We have now examined steady-state levels of the mRNA encoding preprotachykinin (PPT), the SP precursor. A cloned cDNA probe was used to examine regulation mRNA levels in culture and in vivo. In RNA gel blot experiments, a single band (1.1 kilobases long) was observed in all cases in which an RNA was detected. A low level of PPT mRNA was detected by RNase protection assay in uncultured ganglia, suggesting that the low levels of SP previously observed in the normal ganglion in vivo are synthesized locally. When ganglia were maintained in culture, with consequent denervation, the steady-state level of PPT mRNA increased by 25-fold over the first 24 hr, and the high level was maintained for at least 7 days. RNase protection experiments indicated that the major message in the SCG is the 18-PPT mRNA, encoding both SP and neurokinin A peptide regions. Accumulation of the PPT mRNA in cultured ganglia was sharply inhibited by the depolarizing agent veratridine, and this effect was blocked by tetrodotoxin. Therefore, one form of neuronal plasticity, change in neurotransmitter metabolism, is regulated at least in part by altering steady-state levels of specific mRNA. More generally, extracellular signals may contribute to neuronal plasticity through changes in gene expression.Multiple lines of evidence indicate that continuous functional change in the nervous system governs such varied processes as sensory perception, motor behavior, learning, and memory. A central problem in neuroscience concerns the mechanisms through which neural activity alters the functional state of neuron ensembles. Analysis at the level of single neurons has been particularly fruitful in identifying activitydependent processes. For example, activity influences diverse properties, including neuronal morphology (1), the propensity to generate subsequent action potentials (2), synaptic ultrastructure (2), the mix of co-localized transmitters that are released (3), and the synthesis of neurotransmitters.The regulation of transmitter metabolism has attracted wide interest, since these signals are prime agents of neural communication. Moreover, the realization that single neurons use multiple transmitters has vastly expanded our appreciation of the potential for mutability at the neuronal level. Recent studies indicate that activity may differentially alter concentrations of individual co-localized transmitters.

Phenotypic plasticity in adult sympathetic neurons: changes in neuropeptide expression in organ culture.

“…USA 89 (1992) neonatal ganglia, it appears to have some similarities with the increase in VIP-IR in adult ganglion. For example, in both cases there are increases in peptide content, in the number of immunostained neurons, and in the level ofthe corresponding mRNA (31). In addition, however, there are interesting differences between the two peptides.…”

Localization, regulation and functions of neurotransmitters and neuromodulators in cervical sympathetic ganglia

“…PPT mRNA was increased 25-fold in the explanted SCG. This effect could be inhibited by the depolarizing agent, veratridine, indicating a suppressive effect of physiological impulse activity on PPT synthesis (Roach et al, 1987). As with VIP, the elevation of SP immunoreactivity after axotomy is prevented by dexamethasone which also blocks SP expression induced by interleukin-lp (IL-1p; Hart et al, 1991;Kessler et al, 1993) or lipopolysaccharide (Shadiack et al, 1994).…”

“…Multiple preprotachykinin (PPT) mRNAs arise from a single gene through alternate splicing of primary transcripts (Krause et al, 1987). Detection of low levels of PPT mRNA in the rat SCG (Roach et al, 1987) indicated that SP can be synthesized within sympathetic ganglia.…”

Effect of potassium-induced depolarization on somatostatin gene expression in cultured fetal rat cerebrocortical cells

“…Recent studies have shown that membrane depolarization causes not only rapid alterations in protein phosphorylation (Nairn et al, 1985), but also activation of new programs of gene expression in neuronal-type cells (Greenberg et al, 1985(Greenberg et al, , 1986Morgan and Curran, 1986;Black et al, 1987;Saffen et al, 1988;Bartel et al, 1989). Moreover, an increase in mRNA has been measured with stimuli causing the activation of Ca2+ and Na+ channels and membrane depolarization Morgan and Curran, 1986;Naranjo et al, 1986;Roach et al, 1987;Von Dreden et al, 1988). Genes regulated by depolarization include those that encode neuropeptides and neurotransmitter biosynthetic enzymes (Morris et al, 1988;Van Mguyen et al, 1990;Lu et al, 199 1).…”