Increased transcription of the tyrosine hydroxylase gene in individual locus coeruleus neurons following footshock stress

doi:10.1016/S0306-4522(00)00352-3

Neuroscience

Volume 101, Issue 1, 27 October 2000, Pages 131-139

https://doi.org/10.1016/S0306-4522(00)00352-3 Get rights and content

Abstract

Footshock-evoked change in transcriptional activity of tyrosine hydroxylase in neurons of the locus coeruleus was examined using an intron-specific in situ hybridization histochemical technique. A significant increase in the cellular concentration of tyrosine hydroxylase primary transcripts was found in locus coeruleus neurons 3 h following 30 min of intermittent footshock. However, the footshock-induced increase in tyrosine hydroxylase transcription was not homogeneously expressed in locus coeruleus neurons. Similarly, administration of the α₂-adrenergic receptor antagonist idazoxan produced a significant increase in the cellular concentration of tyrosine hydroxylase primary transcripts that was heterogeneously distributed among locus coeruleus neurons. Both footshock and idazoxan significantly increased the regional levels of tyrosine hydroxylase messenger RNA in the locus coeruleus. The time-course of changes in tyrosine hydroxylase transcription rate and messenger RNA levels in the locus coeruleus was examined after a 15 min exposure to footshock. A robust increase in tyrosine hydroxylase transcription rate was found at the end of 15 min of footshock, which remained elevated for 6 h and was back to the control levels by 24 h. In contrast, in response to a 15 min period of footshock tyrosine hydroxylase messenger RNA concentrations in the locus coeruleus did not increase until 6 h and remained elevated at 24 h.

These findings demonstrate that transcription of the tyrosine hydroxylase gene in locus coeruleus neurons in response to footshock stress occurs rapidly, is sustained for many hours and is heterogeneously distributed. These data also suggest that the increase in tyrosine hydroxylase messenger RNA following footshock is mediated, at least in part, by an increase in tyrosine hydroxylase gene transcription.

Section snippets

Animals

Male Sprague–Dawley rats (225–250 g; Zivic Laboratories; Zelienople, PA) were housed two per cage at 22–23°C and were provided with food (Purina Rodent Chow, Ralston-Purina, St Louis, MO) and water ad libitum. The room was maintained on a 12 h light/dark cycle, with lights on 07.00–19.00. All experiments were performed during the light phase. All rats were gently handled on a daily basis for at least one week preceding the experiment. All experiments were conducted in a fashion so as to minimize

Effects of footshock on tyrosine hydroxylase gene transcription in locus coeruleus neurons

A 30 min period of intermittent footshock evoked a 6.3-fold increase in the average levels of TH primary transcript in LC neurons as measured 3 h after the onset of the shock period (F_2,2395 =36.38, P<0.0001, Table 1).

The results of the cellular analysis of TH primary transcript levels in individual LC neurons from control rats and following footshock are illustrated by the frequency distribution histograms in Fig. 1A. Under baseline conditions, a low level of TH primary transcript expression

Discussion

The present study used a sensitive intron-specific in situ hybridization method to quantify the cellular concentrations of TH primary transcripts, reflecting the rate of TH gene transcription, in LC neurons following acute footshock stress. Acute footshock induced a rapid, robust and sustained increase in TH gene transcription in LC neurons, but this was not uniformly expressed in all LC neurons. The increase in TH transcription was followed by a delayed elevation in TH mRNA levels.

Conclusions

We suggest that the increase in TH mRNA levels in LC neurons following stress is dependent, at least in part, on an increase in the transcriptional activity of the TH gene. The stress-induced elevation in TH gene transcription in LC neurons occurs with a rapid onset, sustained activity and a heterogeneous cellular pattern of expression. Overall, our findings reveal unique cellular and molecular characteristics of LC neurons that raise some fundamental questions regarding the impact of stress on

Acknowledgements

We thank Dr Allan Sampson and Sungyoung Auh for their assistance with the statistical analyses and Sandra Best and Heather Murphy for their technical assistance. This study was supported in part by USPHS grants MH29670, MH45156, MH00058 and MH51159.

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Citation Excerpt :
Discrepancies between changes in TH transcription rate, TH mRNA levels and/or TH protein levels have been reported in many studies. For instance, Chang et al. (2000) have reported long-term increases in TH mRNA in locus coeruleus, which are associated with only short-term increases in TH transcription rate. Similar results have been observed in the adrenal medulla after reserpine administration (Alterio et al., 2001) and in locus coeruleus after nicotine administration (Sun et al., 2004).
Polycytosine-binding proteins (PCBPs) are RNA-binding proteins that participate in post-transcriptional control pathways. Among the diverse functions of these proteins is the interaction with a 27 nucleotide pyrimidine-rich domain within the 3′UTR of tyrosine hydroxylase (TH) mRNA. Mutations to this domain result in decreased stability of TH mRNA and loss of cAMP-mediated activation of TH mRNA translation. PCBPs are hypothesized to play key roles in these regulatory mechanisms. In order to further test this hypothesis, we examined the tissue distribution of PCBPs in catecholaminergic cells. Initial studies demonstrated that proteins from catecholaminergic tissues bind to TH mRNA 3′UTR sequences and these proteins have an apparent Mr of ∼44 kDa, which is close to the molecular sizes for PCBPs. Fluorescent immunohistochemistry and confocal microscopy was used to analyze the distribution of PCBP isoforms in TH-positive cells of the rat midbrain, locus coeruleus, and adrenal gland. Our results suggest that: (1) PCBP2 is the predominant isoform in TH-positive cells of the rat midbrain; (2) PCBP3 is the predominant isoform in TH-positive cells of the locus coeruleus; and (3) PCBP1 is the predominant isoform in the adrenal medulla. The localization of PCBP proteins to TH-positive cells in these catecholaminergic tissues is consistent with the hypothesis that PCBPs play a role in the regulation of TH expression.

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Increased transcription of the tyrosine hydroxylase gene in individual locus coeruleus neurons following footshock stress

Abstract

Section snippets

Animals

Effects of footshock on tyrosine hydroxylase gene transcription in locus coeruleus neurons

Discussion

Conclusions

Acknowledgements

Prog. Brain Res.

Prog. Brain Res.

Brain Res. Bull.

J. Neurosci. Meth.

Biochem. biophys. Res. Commun.

Brain Res.

Neuroscience

Life Sci.

Biol. Psychiatry

Molec. Brain Res.

Brain Res.

Pharmac. Biochem. Behav.

Neurosci. Biobehav. Rev.

Brain Res.

Biol. Cell

Molec. Brain Res.

Brain Res.

Single unit response of noradrenergic neurons in locus coeruleus of freely moving cats I. Acutely presented stressful and non-stressful stimuli

J. Neurosci.