Quantitation of changes in gene expression of norepinephrine biosynthetic enzymes in rat stellate ganglia induced by stress

Effect of a single and repeated stress exposure on gene expression of catecholamine biosynthetic enzymes in brainstem catecholaminergic cell groups in rats

Brainstem catecholaminergic neurons significantly participate in the regulation of neuroendocrine system activity, particularly during stressful conditions. However, so far the precise quantitative characterisation of basal and stress-induced changes in gene expression and protein levels of catecholaminergic biosynthetic enzymes in these neurons has been missing. Using a quantitative reverse transcription-polymerase chain reaction method, we investigated gene expression of catecholamine biosynthetic enzymes in brainstem noradrenergic and adrenergic cell groups in rats under resting conditions as well as in acutely and repeatedly stressed animals. For the first time, we described quantitative differences in basal levels of catecholamine biosynthetic enzyme mRNA in brainstem catecholaminergic ascending and descending projecting cell groups. Moreover, we found and defined some differences among catecholaminergic cell groups in the time-course of mRNA levels of catecholaminergic enzymes following a single and especially repeated immobilisation stress. The data obtained support the assumption that brainstem catecholaminergic cell groups represent a functionally differentiated system, which is highly (but specifically) activated in rats exposed to stress. Therefore, potential interventions for the treatment of stress-related diseases need to affect the activity of brainstem catecholaminergic neurons not uniformly but with some degree of selectivity.

Treadmill exercise does not change gene expression of adrenal catecholamine biosynthetic enzymes in chronically stressed rats

ABSTRACT Chronic isolation of adult animals represents a form of psychological stress that produces sympatho-adrenomedullar activation. Exercise training acts as an important modulator of sympatho-adrenomedullary system. This study aimed to investigate physical exercise-related changes in gene expression of catecholamine biosynthetic enzymes (tyrosine hydroxylase, dopamine-ß-hydroxylase and phenylethanolamine N-methyltransferase) and cyclic adenosine monophosphate response element-binding (CREB) in the adrenal medulla, concentrations of catecholamines and corticosterone (CORT) in the plasma and the weight of adrenal glands of chronically psychosocially stressed adult rats exposed daily to 20 min treadmill running for 12 weeks. Also, we examined how additional acute immobilization stress changes the mentioned parameters. Treadmill running did not result in modulation of gene expression of catecholamine synthesizing enzymes and it decreased the level of CREB mRNA in the adrenal medulla of chronically psychosocially stressed adult rats. The potentially negative physiological adaptations after treadmill running were recorded as increased concentrations of catecholamines and decreased morning CORT concentration in the plasma, as well as the adrenal gland hypertrophy of chronically psychosocially stressed rats. The additional acute immobilization stress increases gene expression of catecholamine biosynthetic enzymes in the adrenal medulla, as well as catecholamines and CORT levels in the plasma. Treadmill exercise does not change the activity of sympatho-adrenomedullary system of chronically psychosocially stressed rats.

Stress-triggered changes in peripheral catecholaminergic systems

The sympathetic nervous system not only regulates cardiovascular and metabolic responses to stress but also is altered by stress. The sympathoneural and sympathoadrenomedullary systems are modified by different metabolic pathways and have different responses to short- and to long-term stressors. Stress also induces nonneuronal catecholamine enzymes, primarily through corticosteroids. Catecholamine synthetic enzymes are induced by different pathways in response to short- and long-term acting stressors, like cold exposure or immobilization, and differently in the sympathetic ganglia and the adrenal medulla. However, a long-term exposure to one stressor can increase the response to a second, different stressor. Tyrosine hydroxylase gene transcription increases after only 5min of immobilization through phosphorylation of CREB, but this response is short lived. However, repeated stress gives a longer-lived response utilizing transcription factors such as Egr-1 and Fra-2. Glucocorticoids and ACTH also induce sympathoneural enzymes leading to distinct patterns of short-term and long-lived activation of the sympathetic nervous system. Nonneuronal phenylethanolamine N-methyltransferase (PNMT) develops early in the heart and then diminishes. However, intrinsic cardiac adrenergic cells remain and nonneuronal PNMT is present in many cells of the adult organism and increases in response to glucocorticoids. Both stress-induced and administered glucocorticoids induce fetal PNMT and hypertension. Human stressors such as caring for an ill spouse or sleep apnea cause a persistent increase in blood norepinephrine, increased blood pressure, and downregulated catecholamine receptors. Hypertension is associated with a loss of slow-wave sleep, when sympathetic nerve activity is lowest. These findings indicate that stress-induced alteration of the sympathetic nervous system occurs in man as in experimental animals.

Effect of immobilization stress on gene expression of catecholamine biosynthetic enzymes in heart auricles of socially isolated rats

Chronic stress is associated with the development of cardiovascular diseases. The sympathoneural system plays an important role in the regulation of cardiac function both in health and disease. In the present study, the changes in gene expression of the catecholamine biosynthetic enzymes tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH) and phenylethanolamine N-methyltransferase (PNMT) and protein levels in the right and left heart auricles of naive control and long-term (12 weeks) socially isolated rats were investigated by Taqman RT-PCR and Western blot analysis. The response of these animals to additional immobilization stress (2 h) was also examined. Long-term social isolation produced a decrease in TH mRNA level in left auricles (about 70%) compared to the corresponding control. Expression of the DBH gene was markedly decreased both in the right (about 62%) and left (about 81%) auricles compared to the corresponding control, group-maintained rats, whereas PNMT mRNA levels remained unchanged. Exposure of group-housed rats to acute immobilization for 2 h led to a significant increase of mRNA levels of TH (about 267%), DBH (about 37%) and PNMT (about 60%) only in the right auricles. Additional 2-h immobilization of individually housed rats did not affect gene expression of these enzymes in either the right or left auricle. Protein levels of TH, DBH and PNMT in left and right heart auricles were unchanged either in both individually housed and immobilized rats. The unchanged mRNA levels of the enzymes examined after short-term immobilization suggest that the catecholaminergic system of the heart auricles of animals previously exposed to chronic psychosocial stress was adapted to maintain appropriate cardiovascular homeostasis.

Immobilization stress elevates intron-containing transcripts for tyrosine hydroxylase in rat superior cervical ganglia indicating transcriptional activation

While both the adrenal medulla and sympathetic nervous system are important in mediating the catecholaminergic response to stress, there are crucial differences in the mechanism. Stress elevates tyrosine hydroxylase (TH) protein and mRNA levels in both the adrenal medulla and sympathetic ganglia. In the adrenal medulla, transcription of the TH gene is rapidly induced with immobilization (IMO) stress. Here, we examine whether IMO also increases TH transcription in the superior cervical ganglia (SCG). Quantitative real-time reverse transcription polymerase chain reaction was used to determine the changes in TH mRNA and in transcripts containing intron 2. As expected in the adrenal medulla following repeated IMO TH mRNA and intron containing transcripts were elevated about 5-fold. In the SCG, a significant increase in TH mRNA was observed following repeated 2 h IMO for 2 or 6 days, but not with single IMO. The intron 2 containing transcripts were elevated about 50% above controls with even single IMO, and were at similarly elevated levels after the 2nd or 6th repeated daily IMO. The results indicate, for the first time, that transcriptional mechanisms are involved in mediating the IMO stress triggered elevation in TH gene expression in the SCG.

Catecholaminergic systems in stress: structural and molecular genetic approaches

Stressful stimuli evoke complex endocrine, autonomic, and behavioral responses that are extremely variable and specific depending on the type and nature of the stressors. We first provide a short overview of physiology, biochemistry, and molecular genetics of sympatho-adrenomedullary, sympatho-neural, and brain catecholaminergic systems. Important processes of catecholamine biosynthesis, storage, release, secretion, uptake, reuptake, degradation, and transporters in acutely or chronically stressed organisms are described. We emphasize the structural variability of catecholamine systems and the molecular genetics of enzymes involved in biosynthesis and degradation of catecholamines and transporters. Characterization of enzyme gene promoters, transcriptional and posttranscriptional mechanisms, transcription factors, gene expression and protein translation, as well as different phases of stress-activated transcription and quantitative determination of mRNA levels in stressed organisms are discussed. Data from catecholamine enzyme gene knockout mice are shown. Interaction of catecholaminergic systems with other neurotransmitter and hormonal systems are discussed. We describe the effects of homotypic and heterotypic stressors, adaptation and maladaptation of the organism, and the specificity of stressors (physical, emotional, metabolic, etc.) on activation of catecholaminergic systems at all levels from plasma catecholamines to gene expression of catecholamine enzymes. We also discuss cross-adaptation and the effect of novel heterotypic stressors on organisms adapted to long-term monotypic stressors. The extra-adrenal nonneuronal adrenergic system is described. Stress-related central neuronal regulatory circuits and central organization of responses to various stressors are presented with selected examples of regulatory molecular mechanisms. Data summarized here indicate that catecholaminergic systems are activated in different ways following exposure to distinct stressful stimuli.

Stress-induced alterations in catecholamine enzymes gene expression in the hypothalamic dorsomedial nucleus are modulated by caudal brain and not hypothalamic paraventricular nucleus neurons

The hypothalamic dorsomedial nucleus (DMN) represents an important coordinate center for regulation of autonomic and neuroendocrine systems, especially during stress response. The present study was focused on the gene expression of catecholamine-synthesizing enzymes and the protein levels of tyrosine hydroxylase in DMN, both in control and stressed rats. Moreover, pathways modulating the gene expression of tyrosine hydroxylase in DMN during immobilization (IMO) stress were also investigated. Gene expressions of all catecholamine-synthesizing enzymes were detected in DMN samples. While the levels of tyrosine hydroxylase and phenylethanolamine N-methyltransferase mRNA were increased in IMO rats, aromatic L-amino acid decarboxylase and dopamine-beta-hydroxylase mRNA remained unchanged. Tyrosine hydroxylase protein levels were significantly elevated in the DMN only after repeated IMO stress. Postero-lateral deafferentations of the DMN, or transections of the ascending catecholaminergic pathways originating in the lower brainstem abolished the IMO-induced increase of tyrosine hydroxylase gene expression in the DMN. Nevertheless, postero-lateral deafferentations of the hypothalamic paraventricular nucleus (PVN), which separate the DMN from the PVN, had no effect on IMO-induced elevation of tyrosine hydroxylase mRNA in the DMN. The present data indicate that certain DMN neurons synthesize mRNA of catecholamine enzymes. The stress-induced increase of tyrosine hydroxylase and phenylethanolamine N-methyltransferase mRNA in DMN neurons indicates the involvement of these catecholaminergic neurons in stress response. The gene expression of tyrosine hydroxylase in DMN is modulated by lower brainstem and/or spinal cord, but not by PVN afferents.

Stress-induced catecholaminergic function: transcriptional and post-transcriptional control

This review summarizes knowledge on the effects of stress on two catecholamine biosynthetic enzymes, tyrosine hydroxylase (TH) and phenylethanolamine N-methyltransferase (PNMT). Information is presented on differential responses of the enzymes to a variety of stressors as well as differential responses of the enzymes localized to the central nervous system vs. peripheral nervous system and tissues. Changes in mRNA and protein or activity are described, including species- and stressor-specific effects. While temporal changes in these parameters may differ for the particular stressor or enzyme, in general, maximal changes in mRNA and protein content occur at 6-8 and 24 h after stressor exposure, respectively. Elevation of TH and PNMT transcriptional activators prior to mRNA induction and nuclear run-on assays show that stress activates the genes encoding these enzymes. Yet, extents of induction of mRNA, protein and enzyme activity are often discordant depending on the stress, its duration and repetition of exposure. The extremes are concordant changes in mRNA and protein/activity vs. highly elevated mRNA with no change in protein/activity. Post-transcriptional and/or post-translational regulatory influences that may contribute to the complex effects of stress on TH, PNMT and the stress hormone epinephrine are explored.

Gene expression of phenylethanolamine N-methyltransferase in corticotropin-releasing hormone knockout mice during stress exposure

AIMS

Epinephrine (EPI) synthesizing enzyme phenylethanolamine N-methyltransferase (PNMT, EC 2.1.1.28) is primarily localized in the adrenal medulla (AM). We have recently described existence of the PNMT gene expression in cardiac atria and ventricles and in sympathetic ganglia of adult rats and mice. The aim of the present work was to study regulation of the PNMT gene expression in corticotropin-releasing hormone knockout mice (CRH KO) and matched control wild-type mice (WT) under normal and stress conditions.

METHODS

Levels of the PNMT mRNA were determined by RT-PCR; PNMT immunoprotein and protein of transcription factor EGR-1 by Western Blot. Plasma EPI and corticosterone (CORT) levels were determined by radioenzymatic and RIA methods. Immobilization (IMMO) was used as a stressor.

RESULTS

Stress-induced increases in the PNMT mRNA and protein levels observed in WT mice were almost completely absent in CRH KO mouse adrenal medulla, stellate ganglia, and cardiac atria, while ventricular PNMT mRNA elevation was not CRH-dependent. Plasma EPI and CORT levels were markedly reduced in CRH KO compared to WT mice both before and after the stress. Levels of EGR-1, crucial transcription factor for regulation of the PNMT were highly increased in stressed WT and CRH KO mice in cardiac areas, but not in the adrenal medulla.

CONCLUSIONS

Data show that the CRH deficiency can markedly prevent immobilization-triggered induction of the PNMT mRNA and protein levels in the adrenal medulla and stellate ganglia. Reduced plasma epinephrine and corticosterone levels and adrenal medullary EGR-1 protein levels in CRH knockout versus WT mice during stress indicate that the HPA axis plays a crucial role in regulation of the PNMT gene expression in these organs. Cardiac atrial PNMT gene expression with stress is also dependent on intact HPA axis. However, in cardiac ventricles, especially after the single stress exposure, its expression is not impaired by CRH deficiency. Since cardiac EGR-1 protein levels in CRH KO mice are also not affected by the single stress exposure, we propose existence of different regulation of the PNMT gene expression, especially in the cardiac ventricles.Overall, our findings reveal that the PNMT gene expression is regulated through the HPA in both sympathoadrenal system and the heart and also via EGR-1 in the adrenal medulla, but apparently not in the heart. Regulation of the PNMT gene expression in various compartments of heart includes both corticosterone-dependent and independent mechanisms.

Identification of phenylethanolamine N-methyltransferase gene expression in stellate ganglia and its modulation by stress

Phenylethanolamine N-methyltransferase (PNMT, EC 2.1.1.28) is the terminal enzyme of the catecholaminergic pathway converting noradrenaline to adrenaline. Although preferentially localized in adrenal medulla, evidence exists that PNMT activity and gene expression are also present in the rat heart, kidney, spleen, lung, skeletal muscle, thymus, retina and different parts of the brain. However, data concerning PNMT gene expression in sympathetic ganglia are still missing. In this study, our effort was focused on identification of PNMT mRNA and/or protein in stellate ganglia and, if present, testing the effect of stress on PNMT mRNA and protein levels in this type of ganglia. We identified both PNMT mRNA and protein in stellate ganglia of rats and mice, although in much smaller amounts compared with adrenal medulla. PNMT gene expression and protein levels were also increased after repeated stress exposure in stellate ganglia of rats and wild-type mice. Similarly to adrenal medulla, the immobilization-induced increase was probably regulated by glucocorticoids, as determined indirectly using corticotropin-releasing hormone knockout mice, where immobilization-induced increase of PNMT mRNA was suppressed. Thus, glucocorticoids might play an important role in regulation of PNMT gene expression in stellate ganglia under stress conditions.

Effect of Lesion of A5 and A7 Brainstem Noradrenergic Areas or Transection of Brainstem Pathways on Sympathoadrenal Activity in Rats During Immobilization Stress

Both A5 and A7 brainstem noradrenergic cell groups innervate dorsal horns of the spinal cord. Moreover, A5 cell group directly innervates sympathetic preganglionic neurons. Thus, A5 and A7 noradrenergic neurons could modulate the sympathoadrenal system (SAS) activity. We investigated the role of A5 and A7 noradrenergic cell groups in regulation of the SAS activity under control and stressful conditions. We evaluated the effect of electrolytical lesions of A5 or A7 cell groups and also the effect of bilateral brainstem cuts interrupting brainstem pathways on tyrosine hydroxylase gene expression in A5 and A7 areas and on the SAS activity measured by plasma epinephrine and norepinephrine levels. We have found that immobilization stress increases activity of the A5 and A7 brainstem areas and also levels of the gene expression of tyrosine hydroxylase, the rate-limiting catecholamine biosynthetic enzyme. Immobilization of sham-operated and brainstem pathways transected or A5 or A7 lesioned animals induced a similar, highly significant increase in plasma epinephrine and norepinephrine levels in both sham-operated and A5 or A7 destroyed or transected groups. Our data suggest that both A5 and A7 noradrenergic cell groups are activated during immobilization stress. However, transection of brainstem pathways innervating A5 and A7 neurons or lesion of A5 or A7 cell groups is not sufficient enough for changes in immobilization stress-induced activation of the SAS. We suggest that neither A5 and A7 noradrenergic neurons nor the transected brainstem pathways represent structures crucial for an activation of the SAS during immobilization stress. We hypothesize that during regulation of the stress response, various areas and pathways are involved and the elimination just one of them might be compensated by the remained intact areas and pathways.

Ethanol consumption increases rat stress hormones and adrenomedullary gene expression

Numerous reports document altered drinking behavior following acute stressors but few describe physiological responses to acute stress of chronic ethanol consuming subjects. We tested rats' responses to 120-min foot restraint immobilization (Immo) after 1 week of liquid diet containing 5% wt/vol ethanol (ethanol-fed). Controls consumed isocaloric liquid diet ad libitum (adlib-fed) or in amounts equal to that of ethanol-fed subjects on the previous day (pair-fed). Each rat was implanted with a tail artery cannula on day 7 to allow remote blood collection before and during Immo on day 8. Plasma epinephrine (Epi); norepinephrine (NE); corticosterone (Cort); prolactin (PRL); adrenomedullary gene expression of catecholamine biosynthetic enzymes tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH), and phenylethanolamine-N-methyl transferase (PNMT); and TH protein levels were measured. Ethanol-fed rats had two to threefold higher basal plasma Epi and NE and tended to have increased Cort compared to adlib-fed or pair-fed rats. Immo increased Epi and NE in ethanol-fed rats more than twofold above those observed in controls, and also increased Cort more in ethanol-fed than in control rats. PRL was marginally affected. Ethanol potentiated the normal immobilization-induced increase in adrenomedullary TH, DBH, and PNMT messenger RNA (mRNA). TH protein increased only in ethanol-fed rats. Increased plasma catecholamine levels, adrenomedullary gene expression, and TH protein concentration in nonimmobilized ethanol-fed rats strongly suggest that ethanol consumption was itself a stressor, which potentiated the subsequent response to acute Immo. Moreover, the observed interaction of ethanol and stress on plasma catecholamine levels illustrates the importance of minimizing additional stressful stimuli when investigating ethanol's physiological effects.

Identification of the aromatic L-amino acid decarboxylase gene expression in various mice tissues and its modulation by immobilization stress in stellate ganglia

Despite of the fact that the impact of various stressful stimuli on catecholamine biosynthetic enzyme gene expression, activity and immunoreactive protein has been intensively studied, less is known about the aromatic L-amino acid decarboxylase (AADC), the enzyme, which catalyzes decarboxylation of L-dihydroxyphenylalanine to dopamine. We focused on the identification of AADC mRNA and immunoprotein in various mice tissues and detected both in selected mice neuronal tissues (adrenal medulla, sympathetic stellate and cervical ganglia) and also in non-neuronal tissues (liver, spleen, kidney and all four parts of the heart). Surprisingly, although we failed to detect AADC mRNA in mice thymus, lungs and abdominal fat, we found presence of the AADC immunoprotein in lungs as well as in the abdominal fat. We also tested the hypothesis, whether single or repeated immobilization stress can affect the AADC mRNA or immunoprotein levels in mice stellate ganglia. We revealed that single immobilization stress exposure did not affect the AADC mRNA or immunoprotein levels, while repeated immobilization stress produced significant elevation of both, AADC mRNA and immunoprotein levels in stellate ganglia. The aromatic L-amino acid decarboxylase is generally not considered to be limiting in regulation of the catecholamine biosynthesis. However, our data suggest a possible participation of this enzyme in the regulation of catecholamine biosynthesis in stellate ganglia of repeatedly stressed mice.

Localization and regulation of phenylethanolamine N-methyltransferase gene expression in the heart of rats and mice during stress

Recently we have described the existence of phenylethanolamine N-methyltransferase (PNMT) mRNA in the heart of adult rats. In this study, we report the first data on distribution of the PNMT protein in rat hearts, which follows the distribution of PNMT mRNA (high levels in the atria and low levels in ventricles). The main aim of this study was to determine the localization of the PNMT mRNA in the heart and to examine whether gene expression of this enzyme is affected by immobilization (IMO) stress in a time-dependent manner. PNMT mRNA levels were detected in all seven studied parts of the heart (atria without and with intramural ganglion cells, ventricles, and septum), with the highest levels in the left atrium and its ganglionic part. Both Southern blot and sequencing verified the specificity of PNMT detected by RT-PCR. Single IMO for 2-h increased gene expression of PNMT, as determined by both RT-PCR and Real-Time PCR in the right and left atria. Surprisingly, the ganglionic parts of the atria did not respond to stress stimulation. Peak levels of PNMT mRNA were found in the 3-h interval after the IMO terminated, and also 24 h after the first or sixth IMO. Expression of aromatic L-amino acids decarboxylase and dopamine-beta-hydroxylase has also been detected in the heart of control and stressed rats. In the atria, the effect of stress is clearly modulated by glucocorticoids, since in mice with corticotrophin-releasing hormone knocked out gene the immobilization-induced increase in the PNMT mRNA levels seen in wild-type animals was abolished. Thus, our data have shown that gene expression of the PNMT is localized, not predominantly in cardiac ganglion cells, but in a wide range in atrial cardiomyocytes. Mechanism responsible for the regulation of stress-induced increase of PNMT gene expression in cardiac atria is clearly dependent on the presence of glucocorticoids.

Modulation of catecholamine-synthesizing enzymes in the rat heart by repeated immobilization stress

Stress is one of the major risk factors responsible for the increased incidence of a number of common life-threatening disorders, predominantly of cardiovascular origin. The aim of the present study was to establish the effect of repeated immobilization stress on gene expression and protein levels of aromatic L-amino acid decarboxylase (AADC) and phenylethanolamine N-methyltransferase (PNMT) in cardiac left and right atria. In the process of repeated immobilization, rats were immobilized 2 h daily for 7 days and killed 3 h after the last immobilization. Gene expression was determined by regular and real-time reverse transcription with subsequent polymerase chain reaction, and protein levels were determined by Western blot analysis. In cardiac atria, we identified mRNA for AADC and PNMT. Repeated immobilization stress did not affect AADC mRNA levels. However, repeated immobilization significantly increased PNMT mRNA levels compared with unstressed control animals. No further increase was observed compared with adapted control rats (rats immobilized six times for 2 h daily and decapitated 24 h after the sixth immobilization). AADC protein levels corresponded with mRNA levels of this enzyme. However, we were not able to detect PNMT immunoreactive protein. The observed elevation in the gene expression of PNMT mRNA levels in the heart may be involved in the increased risk of cardiovascular diseases with stress.

Quantitative evaluation of catecholamine enzymes gene expression in adrenal medulla and sympathetic Ganglia of stressed rats

Stress-induced changes in mRNA levels of tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH), and phenylethanolamine N-methyltransferase (PNMT) have been expressed as relative arbitrary units compared with a control group. The aim of this study was to quantify basal and stress-induced levels of TH, DBH, and PNMT mRNAs in rat adrenal medulla (AM) and stellate ganglia (SG) by the RT-competitive PCR method using corresponding competitors of known concentration. In rats stressed by immobilization (IMO) once for 2 h, the concentration of mRNAs was determined in various intervals after the end of stress stimulus. In SG, the basal concentration of TH mRNA was 0.017 amol/ng of total RNA, which is approximately 30 times lower than in the AM (0.460 amol/ng RNA). The basal concentration of DBH mRNA in SG was 2.60 amol/ng of total RNA, which is about 150 times more than TH mRNA in SG but only two times less than DBH mRNA in the AM in which PNMT mRNA is present in the highest concentration. After a single 2-h IMO, the peak elevation of TH and DBH mRNA concentration in SG occurred 24 h after the termination of stress stimulus, when their AM mRNA concentrations were already at control values. Presence of PNMT mRNA levels in the SG, of control and stressed rats has been demonstrated for the first time. Repeated IMO (7 days, 2 h daily) did not produce further increase in the mRNA concentrations compared with the elevated values found in adapted control groups. Levels of TH protein were significantly increased only after repeated IMO in SG and AM. Thus, our data show for the first time the exact concentrations of TH, DBH, and PNMT mRNA in SG and AM of rats under control and stress conditions. The lowest concentration of TH mRNA in the AM and SG supports the hypothesis that tyrosine hydroxylation is the rate-limiting step in catecholamine biosynthesis.

Molecular regulation of gene expression of catecholamine biosynthetic enzymes by stress: sympathetic ganglia versus adrenal medulla

Stress induces tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH) gene expression in sympathetic ganglia and adrenal medulla (AM). However, distinct molecular mechanisms appear to regulate these genes in these locations. The elevation of TH mRNA in response to single immobilization stress (IMO) in AM is robust, but transient, while the induction of TH and DBH mRNAs in sympathetic ganglia is slower and more long lasting. Injections of adrenocorticotropic hormone (ACTH) elicited induction of TH and DBH gene expression in rat sympathetic ganglia, but not in AM. The superior cervical (SCG) and stellate (StG) ganglia, but not AM, were found to express mRNA for the MC-2 receptor, the major ACTH responsive receptor in adrenal cortex. IMO led to increase in MC-2 receptor mRNA levels in SCG. Thus, ACTH, via the MC-2 receptor, may be directly involved in the stress-elicited regulation of norepinephrine biosynthesis in sympathetic ganglia. The signaling pathways triggered by IMO differed in these locations. In AM, IMO triggered activation of the MAP kinase, JNK, and induction of AP1 factors, Egr1 and phosphorylation of CREB. In contrast in the SCG, with IMO we did not observe changes in JNK and little binding to the AP1 motif of the TH promoter. However, there was an increase in CREB binding to the CRE site of the TH promoter. The results reveal differential mechanisms of regulation of catecholamine biosynthetic enzymes by stress in two components of the sympathoadrenal system and should provide basis for possible selective pharmacologic interventions.

Environmental light conditions alter gene expression of rat catecholamine biosynthetic enzymes and Neuropeptide Y: differential effect in superior cervical ganglia and adrenal gland

The hypothalamic suprachiasmatic nuclei (SCN) comprise the main site in the brain involved in the control of the homeostatic mechanism which respond to environmental daily light changes. The sympathetic nervous system and hypothalamic releasing or inhibiting factors mediate the SCN control of a number of peripheral organs and tissues. In this work we analyzed the involvement of two environmental light conditions, constant light (LL) and constant dark (DD) for 20 days, on the expression of mRNAs for catecholamines biosynthetic enzymes and neuropeptide Y (NPY) genes in rat superior cervical ganglia (SCG) and adrenal gland. The results of Northern blot analysis show that LL exposure reduces mRNA levels for tyrosine hydroxylase (TH) the rate limiting catecholamine biosynthetic enzyme and also of dopamine beta-hydroxylase (DBH) as well as for NPY in SCG to about half the levels in control animals. In contrast, exposure of the rats to DD did not elicit any change in the SCG. In the adrenal gland, both, LL and DD conditions increased the TH, DBH as well as phenylethanolamine N-methyltransferase (PNMT) mRNA levels. Under the same conditions, adrenal NPY mRNA levels were decreased by either LL or DD. The results show, for the first time, that prolonged changes in environmental light can alter the gene expression of catecholamine biosynthetic enzymes and of NPY. There was differential response in SCG and adrenal gland.

Social hierarchy affects gene expression for catecholamine biosynthetic enzymes in rat adrenal glands

Social stressors, like other stressors, are powerful activators of the sympathoadrenomedullary system. Differential housing (single vs. group) and social defeat of rats is known to alter the activity of catecholamine-synthesizing enzymes in the medulla. The present studies examined the effect of 70 days of triad (3 rats per large cage) and individual housing of male rats on adrenal mRNA levels of tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH) and phenylethanolamine-N-methyltransferase (PNMT) and on TH protein levels. Behavioral ratings carried out at the triad formation indicated that dominant rats exhibited mostly offensive aggressive behaviors. By contrast, subordinate rats expressed primarily defensive behaviors, while the subdominant rats displayed intermediate levels of these behaviors. Overall, compared with single housing, triad housing resulted in lower gene expression for TH, DBH and PNMT and lower TH protein in the adrenals. Within triads, gene expression for these enzymes and TH protein concentration were higher in subordinate compared with dominant and subdominant rats. The dominant rats tended to have the lowest gene expression of these enzymes. These data indicate that in rodents, individual housing and a subject's social rank have a differential impact on the regulation of catecholamine biosynthesis already during the process of gene expression of catecholamine biosynthetic enzymes in the adrenals.