Assay of tyrosine hydroxylase by coupled decarboxylation of DOPA formed from 1- 14 C-L-tyrosine

Silver nanoparticles compromise neurodevelopment in PC12 cells: critical contributions of silver ion, particle size, coating, and composition

BACKGROUND

Silver exposures are rising because of the increased use of silver nanoparticles (AgNPs) in consumer products. The monovalent silver ion (Ag+) impairs neurodevelopment in PC12 cells and zebrafish.

OBJECTIVES AND METHODS

We compared the effects of AgNPs with Ag+ in PC12 cells for neurodevelopmental end points including cell replication, oxidative stress, cell viability, and differentiation. First, we compared citrate-coated AgNPs (AgNP-Cs) with Ag+, and then we assessed the roles of particle size, coating, and composition by comparing AgNP-C with two different sizes of polyvinylpyrrolidone-coated AgNPs (AgNP-PVPs) or silica nanoparticles.

RESULTS

In undifferentiated cells, AgNP-C impaired DNA synthesis, but to a lesser extent than an equivalent nominal concentration of Ag+, whereas AgNP-C and Ag+ were equally effective against protein synthesis; there was little or no oxidative stress or loss of viability due to AgNP-C. In contrast, in differentiating cells, AgNP-C evoked robust oxidative stress and impaired differentiation into the acetylcholine phenotype. Although the effects of AgNP-PVP showed similarities to those of AgNP-C, we also found significant differences in potencies and differentiation outcomes that depended both on particle size and coating. None of the effects reflected simple physical attributes of nanoparticles, separate from composition or coating, as equivalent concentrations of silica nanoparticles had no detectable effects.

CONCLUSIONS

AgNP exposure impairs neurodevelopment in PC12 cells. Further, AgNP effects are distinct from those of Ag+ alone and depend on size and coating, indicating that AgNP effects are not due simply to the release of Ag+ into the surrounding environment.

Maternal social stress during late pregnancy affects hypothalamic-pituitary-adrenal function and brain neurotransmitter systems in pig offspring

Maternal stress in pregnant sows may induce long-lasting alterations in the behavior, physiology, and immunity of their offspring. The aim of the present study was to investigate the consequences of repeated social stress during late gestation on determinants of the hypothalamic-pituitary-adrenal axis and on hippocampal neurotransmitter profiles in pig offspring. All pregnant gilts were housed in pairs. Each Stress gilt was mixed with an unfamiliar gilt twice a week between days 77 and 105 of gestation (n=18). Control gilts were housed in stable pairs over the same period (n=18). Plasma cortisol and corticosteroid binding globulin (CBG) were measured in 1 male and 1 female per litter in a basal situation on postnatal days (PND) 4, 26, and 60 and in a stressful situation at PND 28 (2 d after weaning) and 62 (2 d after relocation to a new building). Prenatal stress had no effect on plasma cortisol, but it decreased CBG at PND 26. Brain and adrenals were collected from 1 female per litter after weaning or relocation at PND 28 and PND 62. Adrenals were additionally collected at PND 4. Glucocorticoid receptor binding in the hippocampus and hypothalamus was not affected by prenatal treatment. However, prenatal stress increased the expression of 11beta-hydroxysteroid dehydrogenase type 1 mRNA in the hippocampus after weaning (P<0.05) and after relocation (P=0.08). In addition, prenatally stressed piglets showed an increased 5-hydroxyindole-3-acetic acid to 5-hydroxytryptamine ratio in the hippocampus after weaning and increased hippocampal c-fos mRNA expression and noradrenaline concentration after relocation (P<0.05). Prenatal stress also increased the relative adrenal weight at PND 4 and the cell density in the cortex and the medulla at PND 28, whereas no difference was found for activities of catecholamine-synthesising enzymes in the medulla. Overall, our data indicate that repeated social stress during pregnancy has long-lasting consequences on hypothalamic-pituitary-adrenal axis and hippocampal neurotransmitter activity in the offspring of pigs.

Benzo[a]pyrene impairs neurodifferentiation in PC12 cells

Animal studies indicate neurobehavioral anomalies after prenatal exposure to benzo[a]pyrene (BaP). In order to determine if BaP directly affects neurodevelopment, we compared its effects to those of the organophosphate insecticide, chlorpyrifos (CPF), in undifferentiated and differentiating neuronotypic PC12 cells, evaluating indices of cell replication, cell number, neurite outgrowth and phenotypic differentiation. Unlike CPF, BaP did not inhibit DNA synthesis in undifferentiated cells. In cells undergoing nerve growth factor-induced differentiation, CPF reduced cell numbers (assessed by DNA content) whereas BaP increased them, suggesting a delay in the transition between cell replication and differentiation. Indices of cell enlargement (total protein/DNA) and neurite outgrowth (membrane protein/DNA) also showed opposite effects of CPF (increases) and BaP (decreases). We directly confirmed BaP impairment of neurodifferentiation by measuring markers for the two neurotransmitter phenotypes expressed by PC12 cells: tyrosine hydroxylase (dopamine phenotype) and choline acetyltransferase (acetylcholine phenotype). BaP significantly reduced both markers in differentiating cells, with a preferentially greater effect on the acetylcholine phenotype. Our results indicate that low, non-toxic levels of BaP can impair neurodifferentiation, resulting in excess cell numbers at the expense of the emergence of neurotransmitter phenotypes. BaP thus has direct actions on developing neuronal cells that could contribute to the adverse neurodevelopmental effects seen with in vivo exposures.

Myocardial catecholamines and their biosynthetic enzymes in various human heart diseases

Myocardial noradrenaline (NA) content, together with the activities of the enzymes tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH) was measured in biopsy specimens taken during cardiac surgery from patients with various heart diseases. Fluorescence histochemical studies were also performed on comparable specimens. The mean NA content in patients with symptomatic ischaemic heart disease (IHD) was significantly higher than that in patients with valvular heart disease (VHD), atrial septal defect (ASD) or congestive heart failure (CHF). The lowest mean NA content was found in patients with CHF. The activities of TH and DBH were highest in the IHD group, although the differences between IHD and VHD groups were not significant. Histochemical investigations of adrenergic structures showed less fluorescence intensity in the CHF than in the other 3 groups. On the other hand, the density of the adrenergic nerve net and the size and number of varicosities were greatest in patients suffering from IHD. The significance of these results is discussed in relation to the pathophysiological mechanisms underlying these various disease conditions. In IHD the high myocardial NA content creates local conditions for excessive NA release into the myocardial interstitium at the onset of ischaemia, which is known to result in several adverse local consequences.

Auricular tyrosine hydroxylase and dopamine-beta-hydroxylase activities and noradrenaline content in ischaemic heart disease

Assessments were made of the tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH) activities as well as the noradrenaline (NA) content of samples excised from right auricular tissue during cardiac surgery on a total of 55 patients with ischaemic heart disease (IHD), valvular heart disease (VHD), uncomplicated atrial septal defect (ASD) or congestive heart failure (CHF). The NA content was significantly higher in the IHD group than in the other three groups. The TH activity was highest in the IHD group although the difference was statistically significant only compared with the ASD and CHF groups. The DBH activity was also highest in the IHD group, but again the difference was statistically significant only compared with the ASD and CHF groups. In the whole material there was a significant positive correlation between the NA content and TH or DBH activity, as well as between TH and DBH activity. In the IHD group there was a significant positive correlation between heart volume and TH activity. The results suggest that at least compared with ASD and CHF, the sympathetic tone is relatively high in IHD, possibly involving an enhanced NA turnover.

Is fipronil safer than chlorpyrifos? Comparative developmental neurotoxicity modeled in PC12 cells

Fipronil, a GABA(A) receptor antagonist, is replacing many insecticide uses formerly fulfilled by organophosphates like chlorpyrifos. Few studies have addressed the potential for fipronil to produce developmental neurotoxicity. We compared the neurotoxicity of fipronil and chlorpyrifos in undifferentiated and differentiating neuronotypic PC12 cells, evaluating indices of cell replication, cell number, differentiation, and viability for short- and long-term exposures. Fipronil inhibited DNA and protein synthesis in undifferentiated PC12 cells and evoked oxidative stress to a greater extent than did chlorpyrifos, resulting in reduced cell numbers even though cell viability was maintained. In differentiating cells, fipronil displayed an even lower threshold for disruption of development, reducing cell numbers without impairing cell growth, and promoting emergence of neurotransmitter phenotypes; superimposed on this effect, the phenotypic balance was shifted in favor of dopamine as opposed to acetylcholine. Differentiation also enhanced the susceptibility to fipronil-induced oxidative stress, although antioxidant administration failed to provide protection from cell loss. At low concentrations maintained for prolonged periods, fipronil had a biphasic effect on cell numbers, increasing them slightly at low concentrations, implying interference with apoptosis, while nevertheless reducing cell numbers at higher concentrations. Our results suggest that fipronil is inherently a more potent disruptor of neuronal cell development than is chlorpyrifos. The neurodevelopmental effects are not predicated on GABA(A) antagonist properties, since PC12 cells lack the GABA(A) receptor. If fipronil is intended to provide greater safety than chlorpyrifos, then this will have to entail advantages from factors that are yet unexamined: exposure, persistence, pharmacokinetics.

Developmental neurotoxicity of perfluorinated chemicals modeled in vitro

BACKGROUND

The widespread detection of perfluoroalkyl acids and their derivatives in wildlife and humans, and their entry into the immature brain, raise increasing concern about whether these agents might be developmental neurotoxicants.

OBJECTIVES

We evaluated perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA), perfluorooctane sulfonamide (PFOSA), and perfluorobutane sulfonate (PFBS) in undifferentiated and differentiating PC12 cells, a neuronotypic line used to characterize neurotoxicity.

METHODS

We assessed inhibition of DNA synthesis, deficits in cell numbers and growth, oxidative stress, reduced cell viability, and shifts in differentiation toward or away from the dopamine (DA) and acetylcholine (ACh) neurotransmitter phenotypes.

RESULTS

In general, the rank order of adverse effects was PFOSA > PFOS > PFBS approximately PFOA. However, superimposed on this scheme, the various agents differed in their underlying mechanisms and specific outcomes. Notably, PFOS promoted differentiation into the ACh phenotype at the expense of the DA phenotype, PFBS suppressed differentiation of both phenotypes, PFOSA enhanced differentiation of both, and PFOA had little or no effect on phenotypic specification.

CONCLUSIONS

These findings indicate that all perfluorinated chemicals are not the same in their impact on neurodevelopment and that it is unlikely that there is one simple, shared mechanism by which they all produce their effects. Our results reinforce the potential for in vitro models to aid in the rapid and cost-effective screening for comparative effects among different chemicals in the same class and in relation to known developmental neurotoxicants.

Antiapoptotic and trophic effects of dominant-negative forms of dual leucine zipper kinase in dopamine neurons of the substantia nigra in vivo

There is extensive evidence that the mitogen-activated protein kinase (MAPK) signaling cascade mediates programmed cell death in neurons. However, current evidence that the mixed linage kinases (MLKs), upstream in this cascade, mediate cell death is based, in the in vivo context, entirely on pharmacological approaches. The compounds used in these studies have neither complete specificity nor selectivity among these kinases. Therefore, to better address the molecular specificity of the MLKs in mediating neuron death, we used dominant-negative constructs delivered by AAV (adenoassociated virus) vector transfer. We assessed effects in a neurotoxin model of parkinsonism, in which neuroprotection by pharmacologic MLK inhibition has been reported. We find that two dominant-negative forms of dual leucine zipper kinase (DLK) inhibit apoptosis and enhance long-term survival of dopamine neurons, but a dominant negative of MLK3 does not. Interestingly, the kinase-dead form of DLK not only blocks apoptosis but also has trophic effects on dopamine neurons. Although the MAPK cascade activates a number of downstream cell death mediators, we find that inhibition of DLK correlates closely with blockade of phosphorylation of c-jun and prevention of cell death. We conclude that DLK acts primarily through c-jun phosphorylation to mediate cell death in this model.

Screening for developmental neurotoxicity using PC12 cells: comparisons of organophosphates with a carbamate, an organochlorine, and divalent nickel

BACKGROUND

In light of the large number of chemicals that are potential developmental neurotoxicants, there is a need to develop rapid screening techniques.

OBJECTIVES

We exposed undifferentiated and differentiating neuronotypic PC12 cells to different organophosphates (chlorpyrifos, diazinon, parathion), a carbamate (physostigmine), an organochlorine (dieldrin), and a metal (divalent nickel; Ni2+) and examined indices of cell replication and differentiation for both short- and long-term exposures.

RESULTS

In undifferentiated cells, all the agents inhibited DNA synthesis, with the greatest effect for diazinon, but physostigmine eventually produced the largest deficits in the total number of cells after prolonged exposure. The onset of differentiation intensified the adverse effects on DNA synthesis and changed the rank order in keeping with a shift away from noncholinergic mechanisms and toward cholinergic mechanisms. Differentiation also worsened the effects of each agent on cell number after prolonged exposure, whereas cell growth was not suppressed, nor were there any effects on viability as assessed with trypan blue. Nevertheless, differentiating cells displayed signs of oxidative stress from all of the test compounds except Ni2+, as evidenced by measurements of lipid peroxidation. Finally, all of the toxicants shifted the transmitter fate of the cells away from the cholinergic phenotype and toward the catecholaminergic phenotype.

CONCLUSIONS

These studies point out the feasibility of developing cell-based screening methods that enable the detection of multiple end points that may relate to mechanisms associated with developmental neurotoxicity, revealing some common targets for disparate agents.

Chlorpyrifos affects phenotypic outcomes in a model of mammalian neurodevelopment: critical stages targeting differentiation in PC12 cells

The organophosphate insecticide chlorpyrifos (CPF) adversely affects mammalian brain development through multiple mechanisms. To determine if CPF directly affects neuronal cell replication and phenotypic fate, and to identify the vulnerable stages of differentiation, we exposed PC12 cells, a model for mammalian neurodevelopment, to CPF concentrations spanning the threshold for cholinesterase inhibition (5-50 microM) and conducted evaluations during mitosis and in early and mid-differentiation. In undifferentiated cells, exposure to 5 microM CPF for 1-3 days reduced DNA synthesis significantly without eliciting cytotoxicity. At the same time, CPF increased the expression of tyrosine hydroxylase (TH), the enzymatic marker for the catecholamine phenotype, without affecting choline acetyltransferase (ChAT), the corresponding marker for the cholinergic phenotype. Upon exposure to nerve growth factor (NGF), PC12 cells developed neuritic projections in association with vastly increased TH and ChAT expression accompanying differentiation into the two phenotypes. CPF exposure begun at the start of differentiation significantly reduced ChAT but not TH activity. In contrast, when CPF was added in mid-differentiation (4 days of NGF pretreatment), ChAT was unaffected and TH was increased slightly. Thus, CPF exerts stage-specific effects, reducing DNA synthesis in the undifferentiated state, impairing development of the cholinergic phenotype at the start of differentiation, and promoting expression of the catecholaminergic phenotype both in undifferentiated and differentiated cells. CPF administration in vivo produces deficits in the number of neurons and cholinergic function, and because we were able to reproduce these effects in vitro, our results suggest that CPF directly influences the phenotypic fate of neuronal precursors.

Behavior, physiology, and performance of bulls mixed at the onset of finishing to form uniform body weight groups

In some production settings, beef bulls are mixed at the beginning of the finishing period to obtain homogeneous groups to facilitate finishing and to produce more homogeneous carcasses. Given the stress induced by mixing, we questioned whether this practice was profitable. Sixty-four young bulls were finished in groups of four over 8 mo. They were either mixed or unmixed and had either homogeneous vs. heterogeneous BW at the beginning of finishing. Behavioral traits (social behavior following mixing and general activities during the finishing period), stress measurements (cortisol concentration, adrenal weight, catecholamine-synthesizing enzyme activity, and pain sensitivity), and production traits (growth rate, homogeneity, feed efficiency, and carcass measurements) were evaluated. Bulls reacted to the mixing with increased frequency of social interactions (agonistic interactions: 17.9 in mixed vs. 1.2 in unmixed bulls, P < 0.001; sexual interactions: 9.6 vs. 1.7, P < 0.001; nonagonistic interactions: 5.25 vs. 3.1, P < 0.05). Agonistic and sexual interactions were more frequent between bulls of homogeneous BW (P < 0.05). Throughout the finishing period, the synchronization of activity tended to be lower between mixed bulls (P = 0.09). At slaughter, the activity of tyrosine hydroxylase, a catecholamine-synthesizing enzyme, was increased in mixed bulls (1.52 vs. 1.16 nmol.h(-1).mg(-1), P < 0.05), which may indicate chronic stress. No differences were noted in ADG or carcass traits among treatments. The variability of BW within groups increased in groups that were initially homogeneous, whereas it decreased in groups that were initially heterogeneous. In conclusion, mixing young beef bulls at the beginning of the finishing period did not have detrimental effects on health and production, but mixing induced stress, perhaps due to decreased cohesion within groups. Thus, we failed to confirm the proposed benefit of mixing bulls to homogenize their BW at the onset of finishing because BW homogeneity within groups was not maintained throughout the finishing period.

Gender-specific effects of prenatal stress on emotional reactivity and stress physiology of goat kids

The aims of this study were to investigate the effects of maternal stress during pregnancy on the emotional reactivity, the hypothalamo-pituitary-adrenocortical (HPA) axis, and the sympatho-adrenomedullary (SAM) system of goat offspring according to their gender, and to investigate the role of maternal cortisol in prenatal stress effects. Goats were exposed to ten transports in isolation or ten ACTH injections (0.125 IU/kg body weight) during the last third of pregnancy. Control goats remained undisturbed. No effect of repeated transport during the last third of pregnancy was found on basal cortisol concentrations of the offspring. However, an increase in phenylethanolamine N-methyl transferase activity in the adrenals was observed in prenatally stressed kids compared to control kids (P = 0.031). In the presence of novelty, prenatally stressed female kids were more active (P = 0.049) than control females; they also showed more signs of arousal (P = 0.039) and tended to explore more of their environment (P = 0.053) in reaction to a startling stimulus. On the contrary, prenatally stressed male kids tended to be less active (P = 0.051) than control male kids but showed more signs of distress (P = 0.047) in the presence of novelty. Intermediate effects were found on the emotional reactivity to novelty of kids born from dams given injections of ACTH. In conclusion, transport stress in pregnant goats affects the sympatho-adrenomedullary system and the emotional reactivity of their offspring in a gender-specific manner. Moreover, the effects of prenatal transport and ACTH injections showed some similarities but differed in some critical details.

Effect of novel stressors on tyrosine hydroxylase gene expression in the adrenal medulla of repeatedly immobilized rats

The activity of the sympathetic-adrenomedullary system in rats submitted to novel stressors after prior repeated or chronic stress exposure is poorly understood. The purpose of the present work was to investigate changes in adrenomedullary (AM) tyrosine hydroxylase (TH) gene expression after a single or long-term repeated exposure of rats to immobilization stress (IMMO; 42 times), as well as in repeatedly immobilized rats (41 times) exposed once to various novel heterotypic stressors. Cold exposure for 5 h, administration of insulin (INS, 51U), or 2-deoxyglucose (2DG, 500 mg/kg) were used as novel stressors. A single exposure to cold, INS, or 2DG produced transient increases in TH mRNA levels in AM. Animals exposed to repeated homotypic IMMO stress showed permanently increased TH mRNA levels, TH activity, and protein levels; however, an exposure of such animals to heterotypic novel stressors did not induce any further changes. Thus the observed differences in TH mRNA levels in the AM of control rats and long-term repeatedly IMMO rats suggest that an adaptation to this stressor is displayed by a permanently increased TH gene expression, TH activity, and protein level. The exposure of repeatedly IMMO rats to a single episode of novel stressor does not induce exaggerated responses in TH gene expression, as some other stressors do. The mechanism of this finding could involve a central regulation and/or adrenomedullary signaling pathway(s), leading to additional modifications or accumulation of transcription factors. The precise mechanism(s) of this phenomenon remains to be elucidated.

Tyrosine hydroxylase activity in the endocrine pancreas: changes induced by short-term dietary manipulation

BACKGROUND: Tyrosine hydroxylase (TH) activity and its possible participation in the control of insulin secretion were studied in pancreatic islets of adult Wistar rats fed a standard commercial diet (SD) or carbohydrates alone (CHD) for one week. TH activity, norepinephrine (NE) content, and glucose-induced insulin secretion were assessed. Blood glucose and insulin levels were measured at the time of sacrifice. RESULTS: CHD rats had significantly higher blood glucose and lower insulin levels than SD rats (114.5 PlusMinus; 6.7 vs 80.7 PlusMinus; 7.25 mg/dl, p < 0.001; 20.25 PlusMinus; 2.45 vs 42.5 PlusMinus; 4.99 &mgr;U/ml, p < 0.01, respectively). Whereas TH activity was significantly higher in CHD isolated islets (600 PlusMinus; 60 vs 330 PlusMinus; 40 pmol/mg protein/h; p < 0.001), NE content was significantly lower (18 PlusMinus; 1 vs 31 PlusMinus; 5 pmol/mg protein), suggesting that TH activity would be inhibited by the end-products of catecholamines (CAs) biosynthetic pathway. A similar TH activity was found in control and solarectomized rats (330 PlusMinus; 40 vs 300 PlusMinus; 80 pmol/mg protein/h), suggesting an endogenous rather than a neural origin of TH activity. CHD islets released significantly less insulin in response to glucose than SD islets (7.4 PlusMinus; 0.9 vs 11.4 PlusMinus; 1.1 ng/islet/h; p < 0.02). CONCLUSIONS: TH activity is present in islet cells; dietary manipulation simultaneously induces an increase in this activity together with a decrease in glucose-induced insulin secretion in rat islets. TH activity - and the consequent endogenous CAs turnover - would participate in the paracrine control of insulin secretion.

Effect of diazinon on behavior of Japanese medaka (Oryzias latipes) and gene expression of tyrosine hydroxylase as a biomarker

This paper reports on the development of a biomarker used to monitor abnormal behaviors caused by diazinon in Japanese medaka (Oryzias latipes) as a model organism. Tyrosine hydroxylase (TH) activity in tissues was measured and the TH enzyme production in specific organs using a in situ cytochemical technique was monitored. These data were comparatively analyzed with those from semi-quantitative RT-PCR utilizing medaka TH gene that could be a potential biomarker for neuronal modulations and behaviors. For monitoring experiments at behavioral and molecular biological levels, the fish were treated under different sublethal conditions of diazinon (O, O-diethyl O-[6-methyl-2-(1-methylethyl)-4-pyrimidinyl] phosphorothioate) and their behavioral responses were observed. There were no significant differences in activity of TH head and body portions when the fish were exposed to lower concentrations (0.5-10 ppb) of diazinon including control treatment (0 ppb) for 24 hr. In temporal change of TH activity at 100 ppb diazinon treatment, however, the activity of body portion appeared to be inhibited during the first 30 min exposure but later seemed to recover slightly after 1 hr. TH appeared to be expressed mainly in the olfactory bulb, midbrain and brain stem regions as assessed by in situ immunohistochemistry. The treatment (1000 ppb) significantly suppressed TH protein production in the olfactory bulb, midbrain and brain stem regions. In kidney from the body portion the higher concentration treatment (1000 ppb) caused little suppression compared with the control. The RT-PCR showed that a production of TH mRNA transcript was significantly inhibited at 5 ppm diazinon treatment in the body portion. It was concluded that a suppression of TH activity would be one of the causes for the abnormal behaviors of the medaka that could be quantitatively monitored using an image processing system. This study provides molecular and neurobehavioral bases of a biomonitoring system for toxic chemicals using a model organism such as fish.

Regulation of tyrosine hydroxylase gene expression by muscarinic agonists in rat adrenal medulla

Tyrosine hydroxylase (TH) gene expression in the adrenal medulla is regulated by numerous stimuli via transsynaptic mechanisms. The adrenal chromaffin cell receptors that mediate this transsynaptic response remain unidentified. In this report we demonstrate that the muscarinic acetylcholine receptor agonist bethanechol stimulates the TH gene transcription rate in both innervated and denervated adrenal glands. Hence, this muscarinic response is not dependent on transsynaptic influences, suggesting that agonist occupation of adrenal chromaffin cell muscarinic receptors is sufficient to activate intracellular signaling pathways that stimulate the TH gene. When bethanechol is administered repeatedly over a 3-h interval (four injections spaced 1 h apart), TH mRNA levels are increased two- to threefold at 6 and 12 h after the initial injection of drug. It is surprising that this induction of TH mRNA does not lead to increases in TH activity or TH protein level. These results are consistent with the hypothesis that both transcriptional and posttranscriptional mechanisms must be regulated to induce TH protein and that muscarinic agonists activate only a subset of these mechanisms.

Simultaneous measurement of tyrosine hydroxylase activity and phosphorylation in bovine adrenal chromaffin cells

A method for simultaneous measurement of tyrosine hydroxylase (TH) activation and phosphorylation in permeabilised and intact bovine adrenal chromaffin cells (BACCs) was established. Permeabilised cells were stimulated with cyclic AMP (1--10 microM) in the presence of [32P]ATP and L-[carboxyl-(14)C]tyrosine. Intact BACCs were preincubated with 32P(i) for 3 h and stimulated with forskolin (1--5 microM) in the presence of L-[carboxyl-(14)C]tyrosine. On stimulation each well was covered with a sealed 'chimney' fitted with a small plastic cup containing 300 microl of 1.0 M NaOH that trapped the 14CO(2) released. TH activity was determined by measuring 14C radioactivity. TH phosphorylation was measured in the same cells by separating the solubilized proteins on SDS PAGE followed by autoradiography and/or HPLC analysis. It was found that H89, a protein kinase A inhibitor, significantly blocked both TH phosphorylation and activation in response to cyclic AMP in permeabilised cells. However, in intact cells, H89 was effective only in respect to forskolin-stimulated TH activity and did not block the forskolin-stimulated TH phosphorylation of Ser-40. The reason(s) for this lack of correlation between TH activation and phosphorylation is presently not understood.

Characterization of the rat adrenal medulla cultured in vitro

A wide variety of experimental animal models have been used to investigate the mechanisms of synthesis, storage, and release of catecholamines. Whereas in vivo experimental models are situated at one end of the spectrum, cell culture models are situated at the other end. In the present study, we have characterized various aspects of the rat adrenal medulla cultured in vitro as a whole tissue, aiming to establish a new experimental model in between in vivo animal models and cell culture models. We adapted a bottle rotator system commonly used for culturing rodent whole embryos. Changes in histology, activities and mRNA levels of catecholamine-synthesizing enzymes, and concentrations of catecholamines in the adrenal medulla were studied. In addition, the effects of cholinergic stimulation on catecholamine release from the adrenal medulla were examined. Overall the results indicate that various aspects of the adrenal medulla become stable after 4 d of culture and the adrenal medulla at this stage releases catecholamines in response to cholinergic stimulation. The whole adrenal medulla culture system may be a useful tool for investigating catecholamine-related functions dependent on intercellular reactions or communications.

Repeated exposure of adult rats to Aroclor 1254 causes brain region-specific changes in intracellular Ca2+ buffering and protein kinase C activity in the absence of changes in tyrosine hydroxylase

Polychlorinated biphenyls (PCBs) are ubiquitous environmental contaminants, some of which may be neurotoxic. In vitro studies from this laboratory indicated that noncoplanar PCBs perturbed intracellular signal transduction mechanisms including Ca2+ homeostasis, receptor-mediated inositol phosphate production, and translocation of protein kinase C (PKC). In the present study, we examined the effects of PCBs in vivo by dosing adult male Long-Evans rats orally with Aroclor 1254 (0, 10, or 30 mg/kg/day; 5 days/week for 4 weeks) in corn oil. At 24 h after the last dose, rats were tested for motor activity in a photocell device for 30 min. Immediately, the rats were euthanized, blood was collected for thyroid hormone analysis, and brains were removed, dissected into regions (cerebellum, frontal cortex, and striatum), and subcellular fractions were obtained for neurochemical analysis. Following Aroclor 1254 treatment, body weight gain in the high-dose group was significantly lower than the control and low-dose groups. Horizontal motor activity was significantly lower in rats dosed with 30 mg/kg Aroclor 1254. Ca2+ buffering by microsomes was significantly lower in all three brain regions from the 30 mg/kg group. In the same dose group, mitochondrial Ca2+ buffering was affected in cerebellum but not in cortex or striatum. Similarly, total cerebellar PKC activity was decreased significantly while membrane-bound PKC activity was significantly elevated at 10 and 30 mg/kg. PKC activity was not altered either in cortex or the striatum. Neurotransmitter levels in striatum or cortex were slightly altered in PCB-exposed rats compared to controls. Furthermore, repeated oral administration of Aroclor 1254 to rats did not significantly alter forebrain tyrosine hydroxylase immunoreactivity or enzymatic activity. Circulating T4 (total and free) concentrations were severely depressed at both doses in Aroclor 1254-exposed rats compared to control rats, suggesting a severe hypothyroid state. These results indicate that (1) in vivo exposure to a PCB mixture can produce changes in second messenger systems that are similar to those observed after in vitro exposure of neuronal cell cultures; (2) second messenger systems seem to be more sensitive than alterations in neurotransmitter levels or tyrosine hydroxylase involved in dopamine synthesis during repeated exposure to PCBs; and (3) the observed motor activity changes were independent of changes in striatal dopamine levels.

Comparison of the neuroendocrine responses to stress in outbred, inbred and F1 hybrid rats

In order to study the genetic factors involved in the neuroendocrine responses to stress, we have compared the intensity of the hypothalamic-pituitary-adrenal (HPA) axis and sympathetic nervous system activation following a 60 minute-restraint stress or after a 10 minute-exposure to a novel environment in three rat strains : outbred Wistar, inbred Brown Norway and Fischer 344, and F1 hybrid Brown Norway x Fischer 344 rats. The basal activity of the HPA axis did not differ between the four groups of rats whereas Brown Norway rats had the lowest release of corticosterone following restraint stress. Although differences in plasma adrenocorticotropic hormone failed to reach significance after exposure to a novel environment, the lowest level of corticosterone was found in Brown Norway rats. This lower release of corticosterone in Brown Norway rats has probably an adrenal origin as suggested by the ratios of corticosterone to ACTH levels following exposure to a novel environment: 632 +/- 222, 200 +/- 45, 636 +/- 89, 258 +/- 65 in Wistar, Brown Norway, Fischer 344 and F1 hybrids, respectively. This trait was dominant over the "adrenal responsive" phenotype of the Fischer 344 rat strain. In response to novelty, the lowest levels of prolactin and renin activity were found in plasma of Brown Norway and Wistar rats and the highest in Fischer 344 and F1 hybrid Brown Norway x Fischer 344 rats, the "high response" phenotype of the Fischer 344 strain being dominant. No strain-related difference was found in plasma glucose and either adrenal tyrosine hydroxylase or phenylethanolamine N-methyl transferase activity. Taken together, these data suggest that 1) genetic factors might contribute to the interindividual differences in neuroendocrine responses to stress and 2) subsets of these responses are controlled by specific genetic factors.

Estrogens influence growth, maturation, and amyloid beta-peptide production in neuroblastoma cells and in a beta-APP transfected kidney 293 cell line

During development in vivo and in vitro, estrogens: a) increase brain excitability, particularly in limbic structures; b) are responsible for the maturation and cyclicity of limbic-hypothalamic interrelations; c) enhance myelinogenesis; and d) may act with NGF to stimulate neurite formation. In senescence, estrogen administration would improve memory in postmenopausal women. The absence or low levels of estrogens after menopause would increase prevalence of Alzheimer's dementia (AD) more in women than men, irrespective of age or ethnicity. In the present study, addition of 17-beta estradiol to cultured human neuroblastoma cells affected growth slightly, but stimulated cell maturation as shown by increased tyrosine hydroxylase activity. The extracellular deposition in brain tissue and around blood vessels of the amyloid beta-peptide (A beta), a 4.3 kD fragment of the larger integral membrane protein, beta-amyloid precursor protein (beta-APP), is considered an important characteristic of AD. We investigated whether 17-beta estradiol may influence the formation of the A beta (thus the abnormal accumulation of amyloid proteins) in neuroblastoma cells and in a beta-APP transfected human kidney 293 cell line. Two doses of 17 beta-estradiol were added to the cultures of both cell lines. Cells were grown until confluence, metabolically labeled with 35S-methionine, immunoprecipitated with the rabbit antiserum R1282, gel electrophoresed and autoradiographed in order to compare levels of A beta under the different estradiol concentrations. While in neuroblastoma cells, levels of A beta were only slightly reduced after estradiol and a dose-effect relationship with the hormone could not be demonstrated, in the 293 cells, A beta band intensity decreased as concentration of estradiol increased. These data support the role of estrogen in normal and abnormal brain metabolism and suggest potential hormonal interventions which may reduce or prevent the formation of amyloid deposits occur in AD.

Pb-induced alterations in tyrosine hydroxylase activity in rat brain

Our previous studies have shown that exposure to low levels of Pb results in significant reductions in dopamine (DA) and its metabolites (3,4-dihyroxyphenylacetic acid, DOPAC and homovanillic acid, HVA) in nucleus acumbens (NA). This area of brain receives dopaminergic projections from the ventral tegmentum and is considered vital in manifestation of many behavioral responses. Similarly, basal and K(+)-induced release of DA was found significantly reduced in the Pb-exposed rats as compared to the controls in this brain region. Additional studies indicated that acute infusion of Pb in nucleus acumbens caused significant release of DA. Based on these observations it was postulated that the reductions in DA contents and in the basal and stimulus-induced release of DA in NA were manifestations of attenuated dopaminergic activity in this brain region. However, the mechanism of this attenuation is not yet clear. Studies reported here were designed to evaluate the role of a key regulatory enzyme in biosynthesis of DA, i.e. tyrosine hydroxylase (TH) in Pb-induced reductions in dopaminergic activity. The results of these studies indicated that 50 and 500 ppm Pb produced 22.8 and 56% inhibition of TH activity in vitro respectively, and that the enzyme activity was reduced to 43% in rats exposed to 50 ppm lead for 30 days as compared to the controls. The alterations in TH activity in Pb-exposed animals were further confirmed by Western blot analysis. Collectively, these results suggest that Pb-induced inhibition of TH activity in rat brain may contribute to the reductions in dopaminergic activity observed in Pb-exposed animals.

Effects of continuous and intermittent cold (SART) stress on sympathoadrenal system activity in rats

We compared sympathoadrenal responses to intermittent cold (SART) stress (in which cold exposure is interrupted by 4-hourly intervals daily at room temperature) with those to continuous cold (-3 degrees C) stress. Plasma levels of dihydroxyphenylalanine (DOPA), catecholamines and their metabolites as well as tyrosine hydroxylase (TH) activities in sympathetically innervated tissues were examined in rats exposed to each stressor for 1 day or for 5 days. Neither SART nor continuous exposure to cold for 1 day or 5 days altered plasma epinephrine (EPI) levels. However, norepinephrine (NE) and dihydroxyphenylglycol (DHPG) levels increased markedly during exposure to these stressors. On the first day of SART or continuous cold stress, NE levels were increased similarly, but the increments in DHPG levels were greater during SART stress. Since DHPG is formed in neurons, neural reuptake of NE may be more enhanced on the first day of SART stress than on the first day of continuous cold stress. After 5 days of SART stress plasma NE levels were significantly higher than those found after 5 days of continuous cold exposure. Plasma levels of DHPG were elevated to the same extent in both 5 days SART- and continuously cold-stressed rats, whereas plasma levels of methoxyhydroxyphenylglycol (MHPG) increased only by 5 days SART stress. Even at 1 h after the removal from 5 days SART stress, increased plasma levels of NE, DHPG and MHPG were still evident. These results suggest that 5 days SART stress elevates extraneuronal O-methylation of DHPG, and that NE turnover is more greatly increased by SART stress than by continuous cold stress. Plasma levels of DOPA, dopamine, dihydroxyphenylacetic acid and homovanillic acid also increased after either SART or continuous cold stress for 1 day and 5 days. Adrenal TH activities were significantly increased in rats exposed to SART or continuous cold stress for 1 day and 5 days, but in brown fat TH activity was elevated only in rats exposed to 5 days of continuous cold. Both SART and continuous cold stress are selective and potent stimuli for activation of the sympathoneural system, apparently without significant adrenomedullary EPI release. The increase of TH activity in the brown fat pad as well as of plasma NE and its metabolites is probably a result of adaptation to cold. It appears that even short intervals of return to a normal environmental temperature, as in SART, are sufficient to diminish sympathetic adaptation to cold.

Tyrosine hydroxylase in the cerebral ganglia of the American cockroach (Periplaneta americana L.): an immunohistochemical study

We have investigated the distribution of tyrosine-hydroxylase-like immunoreactivity in the cerebral ganglia of the American cockroach, Periplaneta americana. Groups of tyrosine-hydroxylase-immunoreactive cell bodies occur in various parts of the three regions of the cerebral ganglia. In the protocerebrum, single large neurons or small groups of neurons are located in the lateral neuropil, adjacent to the calyces, and in the dorsal portion of the pars intercerebralis. Small scattered cell bodies are found in the outer layers of the optic lobe, and clusters of larger cell bodies can be found in the deutocerebrum, medial and lateral to the antennal glomeruli. Thick bundles of tyrosine-hydroxylase-positive nerve fibers traverse the neuropil in the proto- and deutocerebrum and innervate the glomerular and the non-glomerular neuropil with fine varicose terminals. Dense terminal patterns are present in the medulla and lobula of the optic lobe, the pars intercerebralis, the medial tritocerebrum, and the area surrounding the antennal glomeruli, the central body and the mushroom bodies. The pattern of tyrosine-hydroxylase-like immunoreactivity is similar to that previously described for catecholaminergic neurons, but it is distinctly different from the distribution of histaminergic and serotonergic neurons.

An HSV-1 vector expressing tyrosine hydroxylase causes production and release of L-dopa from cultured rat striatal cells

In this report we demonstrate that a defective herpes simplex virus type one (HSV-1) vector can express enzymatically active tyrosine hydroxylase in cultured striatal cells that are thereby converted into L-DOPA-producing cells. A human tyrosine hydroxylase cDNA (form II) was inserted into an HSV-1 vector (pHSVth) and packaged into virus particles using an HSV-1 strain 17 mutant in the immediate early 3 gene (either ts K or D30EBA) as helper virus. Cultured fibroblasts were infected with pHSVth and 1 day later tyrosine hydroxylase immunoreactivity and tyrosine hydroxylase enzyme activity were observed. The tyrosine hydroxylase enzyme activity directed the production of L-DOPA. pHSVth infection of striatal cells in dissociated cell culture resulted in expression of tyrosine hydroxylase RNA and tyrosine hydroxylase immunoreactivity. Release of L-DOPA and low levels of dopamine were observed from cells in pHSVth-infected striatal cultures. Expression of tyrosine hydroxylase and release of catecholamines were maintained for at least 1 week after infection.

Sustained tyrosine phosphorylation of p140trkA in PC12h-R cells responding rapidly to NGF

The PC12h cell, a subclone of PC12 cells, has considerable activities of tyrosine hydroxylase (TH) and choline acetyltransferase (ChAT) and shows an NGF-induced increase in both enzyme activities. The TH activity and its inducibility by NGF in PC12h cells were stably maintained in the passage of > 200 generations whereas the ChAT activity was not. We isolated a new cell line, PC12h-R (originally clone 8), from a long-term culture of PC12h cells. PC12h-R cells still showed the considerable TH activity, but not the ChAT activity, and maintained the inducibility of TH activity by NGF. Thus, the responses of PC12h-R cells to NGF were similar to those of chromaffin cells and sympathetic neurons. PC12h-R cells were found to extend neurites and differentiate into sympathetic neuron-like cells in response to NGF much more rapidly than PC12h cells. In addition, PC12h-R cells showed sustained NGF-induced tyrosine phosphorylation of p140trkA and several cellular proteins, including 42-, 44- and 54-kDa proteins, in comparison with PC12h cells. We suggest that the NGF-induced sustained tyrosine phosphorylation signal in PC12h-R cells may be correlated closely with their rapid NGF-induced differentiation into neuron-like cells.

Induction of tyrosine hydroxylase gene expression by a nonneuronal nonpituitary-mediated mechanism in immobilization stress

Stress stimulates the sympathoadrenal system, causing activation of the catecholamine biosynthetic enzymes. Here we examine the changes of gene expression of tyrosine hydroxylase (TH; EC 1.14.16.2), the initial enzyme of catecholamine biosynthesis, with stress. A single immobilization of rats led to a large transient elevation in TH mRNA and a small elevation in TH immunoreactive protein and activity. Repeated daily immobilizations triggered more sustained changes in TH mRNA levels. After two immobilizations, the levels remained elevated even 3 days later. The rise in TH mRNA was followed by increased immunoreactive protein but only a small elevation in activity. With seven repeated immobilizations, the animals did not appear to adapt and still manifested a further rise in TH mRNA. TH activity was markedly elevated and returned to control levels 7 days after the immobilization. The rise in TH mRNA with a single immobilization occurred even in adrenals of hypophysectomized rats that underwent splanchnic nerve section. Immobilization for 30 min was sufficient to increase TH mRNA. The effect was abolished by the transcriptional inhibitor actinomycin D. Mobility gel-shift assays revealed increased binding of c-Fos and c-Jun to the AP-1 transcription factor site after a single immobilization, and the binding was not further elevated with repeated stress. This study shows that a single immobilization can activate TH gene expression by a nonneuronal nonpituitary-mediated pathway associated with increased binding of AP-1 transcription factors.

Increased cell-cell contact stimulates the transcription rate of the tyrosine hydroxylase gene in rat pheochromocytoma PC18 cells

Cell aggregation is one of several environmental cues that influence the expression of neurotransmitter phenotype during development. The expression of the catecholaminergic phenotype is increased in rat pheochromocytoma cells cultured at high density. In the present study we have investigated whether this cell density-mediated effect on the catecholaminergic phenotype is due to the stimulation of the tyrosine hydroxylase gene. When rat pheochromocytoma PC18 cells are cultured at high density (2 x 10(5) cells/cm2), tyrosine hydroxylase enzymatic activity and tyrosine hydroxylase protein increase two- to threefold over that observed in cells cultured at low density (1 x 10(4) cells/cm2). This increase in tyrosine hydroxylase protein observed in high-density cultures is fully accounted for by a preceding increase in tyrosine hydroxylase mRNA levels. The relative transcription rate of the tyrosine hydroxylase gene, measured using a nuclear run on assay, is two- to threefold greater in PC18 cells cultured at high density than in cells cultured at low density. Using flow cytometry, we have determined that in high-density cultures, there are approximately twice as many cells in the G0-G1 phases of the cell cycle compared with the number of G0-G1 cells observed in low-density cultures. However, when G0-G1 cells are isolated by cellular elutriation, tyrosine hydroxylase gene transcription rate remains two- to threefold greater in G0-G1 cells from high-density cultures than in G0-G1 cells from low-density cultures. These results indicate that increased cell-cell contact stimulates the transcription rate of the tyrosine hydroxylase gene, resulting in the subsequent increased expression of tyrosine hydroxylase mRNA and protein.

Pituitary adenylate cyclase activating polypeptide (PACAP) potently enhances tyrosine hydroxylase (TH) expression in adrenal chromaffin cells

In primary cultured bovine adrenal chromaffin cells (BACC), pituitary adenylate cyclase activating polypeptide 1-38 (PACAP) produced a dose related increase in tyrosine hydroxylase (TH) Vmax when measured 48 hours after the beginning of the treatment; a significant increase was observed with 0.5 nM and the maximal induction of close to 2.5-fold was found with 0.1 microM PACAP. The potency of PACAP was nearly 3 orders of magnitude greater than forskolin and VIP in inducing TH activity. These effects were preceded by an increase in TH mRNA levels, that started 2 hours after treatment and peaked 12 hours later. The presence of the phosphodiesterase inhibitor HL 725 further increased the stimulation of TH activity by PACAP, indicating that this activation was mediated via a cascade of events initiated by cAMP. Nicotine (1 microM) failed to increase TH activity significantly, however, when added in association with PACAP, a statistically significant increase of TH was elicited with peptide concentrations 5 times lower (0.1 nM) than the threshold dose of the peptide. The stimulation of nicotinic receptors facilitates the TH induction elicited by PACAP.

Induction of cholinergic and adrenergic differentiation in N-18 cells by differentiation agents and DNA demethylating agents

Effects of various differentiating agents and DNA demethylating agents on the expression of choline acetyltransferase (ChAT) and tyrosine hydroxylase (TH), marker enzymes for cholinergic and adrenergic differentiation, respectively, were examined in N-18 neuroblastoma cells. Retinoic acid (RA) and a medium conditioned over C6-glioma cells (GCM), which have been shown to enhance the ChAT activity of PC12 cells, NG108-15 cells and fetal rat brain cells, did not induce ChAT activity of N-18 cells. Treatment of the cells with the DNA demethylating agents alone also did not affect ChAT activity. But after pretreatment of the cells with the DNA demethylating agents, ChAT activity of N-18 cells was greatly increased by either RA or GCM. TH activity of N-18 cells was enhanced by forskolin, an activator of adenylate cyclase. The pretreatment of the cells with the DNA demethylating agents greatly enhanced the induction of TH activity by forskolin. Levels of ChAT and TH messenger RNA were altered in accordance with changes in ChAT and TH activities. Possible mechanisms of the actions of the demethylating agents on cholinergic and adrenergic differentiation are discussed.

Neurochemical characterization of the alterations in the noradrenergic afferents to the cerebellum of adult rats exposed to X-irradiation at birth

A single dose of x-irradiation was applied on the cephalic end of newborn rats, and the alterations in the noradrenergic afferents to the cerebellum were studied 180 days later. A net increase in the noradrenaline content of cerebellum was found (122% of nonirradiated controls). The response of noradrenaline content to reserpine injection (0.9 mg/kg, i.p.) was similar in exposed and control rats. Likewise, the 3H release induced by Ro 4-1284 from cerebellar cortex slices labeled with [3H]noradrenaline was unmodified by x-rays, although a mild increase in the spontaneous efflux of 3H was found. The retention of 3H by the slices was reduced in exposed animals (58% of controls). Both the in vitro activity of tyrosine hydroxylase and the accumulation of L-3,4-dihydroxyphenylalanine (L-DOPA) were not significantly different between x-treated rats and controls. In contrast, monoamine oxidase activity was markedly reduced in x-irradiated cerebellum (38% of controls). The x-ray-induced decrease in cerebellar weight (-60%) resulted in marked increases in noradrenaline concentration (223%), tyrosine hydroxylase activity per milligram of protein (206%), and 3H retention (50%). The accumulation of L-DOPA per gram of tissue was also increased at every time considered. These data indicate that x-irradiation at birth produces a cerebellar loss not completely shared by the noradrenergic afferents, and a permanent imbalance between the noradrenergic afferent input and its target cells might eventually result.(ABSTRACT TRUNCATED AT 250 WORDS)

Retinoic acid induces cholinergic differentiation of cultured newborn rat sympathetic neurons

Many studies provide evidence that retinoic acid (RA), an endogenous derivative of vitamin A, plays a role in the development of the nervous system. We now report that RA controls the neurotransmitter phenotype of post-mitotic rat sympathetic neurons in cell culture. RA added to the culture medium increased the specific activity of choline acetyltransferase (ChAT) and the level of acetylcholine (ACh). Concomitantly, RA reduced the specific activities of two catecholamine synthetic enzymes, tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH) and the level of norepinephrine (NE). After a 2 week treatment with 5 microM RA, ChAT was increased by 5-10 fold, whereas TH and DBH were decreased by 10-15 fold and 2-3 fold, respectively, as compared to sympathetic neurons grown in the absence of RA. The modulation of the activity of the three enzymes was dose-dependent and followed a similar time course. The decrease of TH expression was demonstrated to be due to a decreased number of TH molecules.

Recovery of hippocampal dentate granule cell responsiveness to entorhinal cortical input following norepinephrine depletion

Hippocampal dentate granule cell responsivity to excitatory input from entorhinal perforant path fibers was examined in the chronic rabbit preparation following norepinephrine (NE) depletion induced with the neurotoxin DSP4. To examine granule cell responsivity as a function of perforant path activation, constant low frequency stimulation (0.1 Hz) was applied to the perforant path using an ascending intensity series. To examine granule cell responsivity to more complex patterns of stimulation, a train of impulses, with a random interstimulus interval (Poisson distribution; mean frequency of 2 Hz), was applied to the perforant path. Both single impulse and random interval impulse stimulation revealed that NE depletion increased the average amplitude of the perforant path-granule cell population spike. The random interval impulse stimulation revealed that NE depletion also increased the magnitude and duration of second order inhibitory interactions. These changes were transient, however, and recovered over the 21 day test period. Hippocampal NE levels were reduced an average of 80% between 23 and 38 days post-DSP4. The activity of the rate-limiting enzyme for NE synthesis, tyrosine hydroxylase (TH), was reduced an average of 60%. That NE levels were reduced to a greater extent than was TH activity is suggestive of increased NE synthesis within the remaining nerve terminals. Such an increase in NE synthesis may reflect a compensatory response underlying the functional recovery of electrophysiological responsiveness following partial NE depletion.

Vasoactive intestinal polypeptide-related peptides modulate tyrosine hydroxylase gene expression in PC12 cells through multiple adenylate cyclase-coupled receptors

We investigated the receptor mechanisms by which vasoactive intestinal polypeptide (VIP) and related peptides exert their effects on tyrosine hydroxylase (TH) gene expression. VIP, secretin, and peptide histidine isoleucine (PHI) each produced increases in TH gene expression, as measured by increases in TH mRNA levels and TH activity. The concentrations at which the effects of these peptides were maximal differed for TH activity and TH mRNA. Moreover, maximal increases in TH activity were 130-140% of control, whereas maximal increases in TH mRNA were 250% of control. The concentration dependence of the increases in TH mRNA in response to the three peptides was analyzed by fitting the data to nonlinear regression models that assume either one or two components to the response. The data for secretin fit best to a model that assumes a single component to the increase in TH mRNA levels. The data derived for PHI and VIP fit best to models that assumed two components to the TH mRNA response. These data suggested that there may be more than one receptor or signal transduction mechanism involved in the response to the various peptides. We examined whether the peptides exerted their effects through common or multiple second messenger systems. The ability of maximally active concentrations of these peptides to stimulate increases in TH mRNA was not additive, indicating that the peptides work through a common receptor or signal transduction pathway. Each peptide stimulated increases in protein kinase A (PKA) activity. Secretin and VIP were ineffective in increasing TH mRNA levels in a PKA-deficient mutant PC12 cell line (A126-1B2). Moreover, the adenylate cyclase antagonist 2',5'-dideoxyadenosine prevented the increase in TH mRNA produced by each peptide. Thus, each peptide requires an intact cyclic AMP second messenger pathway to produce changes in TH gene expression, suggesting that the complex pattern of response to VIP and PHI revealed by concentration-response analysis was due to the actions of these peptides at multiple receptors. To evaluate this possibility, we examined the effect of several peptide receptor antagonists on the increase in TH gene expression elicited by VIP, PHI, and secretin. The secretin antagonist secretin (5-27) (20 microM) had no significant effect on VIP or PHI stimulation of TH gene expression, but reduced the effect of secretin. The VIP antagonist VIP (10-28) (20 microM) reduced the effect of VIP on increasing TH mRNA, but had no significant effect on the response of TH mRNA to secretin or PHI.(ABSTRACT TRUNCATED AT 400 WORDS)

Regulation of the chromaffin granule catecholamine transporter in cultured bovine adrenal medullary cells: stimulus-biosynthesis coupling

The transsynaptic induction of the monoamine transporter present on the membrane of chromaffin granules was studied in primary cultures of dissociated bovine adrenomedullary cells submitted to a chronic secretory stimulation. The amount of the vesicular monoamine transporter was assayed by binding of the specific ligand [3H]-dihydrotetrabenazine. After several days of incubation in the presence of high potassium, the concentration of [3H]-dihydrotetrabenazine binding sites was increased by a 1.5-2.5 factor. This increase was smaller in the presence of the cholinergic agonist carbachol. The long-term inductions of the vesicular monoamine transporter, of tyrosine hydroxylase, and of acetylcholinesterase were of similar magnitude. Under the same conditions, we found no variation in either the activities of other catecholamine biosynthetic enzymes (dopamine beta-hydroxylase and DOPA decarboxylase), or in metabolic enzymes such as lactate dehydrogenase and cytochrome c oxidase, and a decrease in the cellular content of chromogranin A and cytochrome b-561. The induction of the vesicular monoamine transporter was inhibited by the calcium channel antagonists, fluspirilene and nifedipine, and was increased by the agonist Bay K 8644. It was abolished by cycloheximide and actinomycin D. These results indicate that calcium entry into chromaffin cells increases the synthesis of the vesicular monoamine transporter, presumably by transcriptional activation. Elevation of intracellular cyclic AMP concentration or activation of protein kinase C also induced an increase in the expression of the vesicular monoamine transporter. Our results confirm that components of storage vesicle membranes are differentially regulated in response to secretory stimulation, as are several cytosolic or intravesicular soluble proteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of Tyrosine Hydroxylase and Dopamine ?-Hydroxylase mRNA Levels in Rat Adrenals by a Single and Repeated Immobilization Stress

Adrenal catecholamines are known to mediate many of the physiological consequences of the "fight or flight" response to stress. However, the mechanisms by which the long-term responses to repeated stress are mediated are less well understood and possibly involve alterations in gene expression. In this study the effects of a single and repeated immobilization stress on mRNA levels of the adrenal catecholamine biosynthetic enzymes, tyrosine hydroxylase and dopamine beta-hydroxylase, were examined. A repeated 2-hr daily immobilization for 7 consecutive days markedly elevated both tyrosine hydroxylase and dopamine beta-hydroxylase mRNA levels (about six- and fourfold, respectively). In contrast, tyrosine hydroxylase but not dopamine beta-hydroxylase mRNA levels were elevated immediately following a single immobilization. The elevation in tyrosine hydroxylase mRNA with a single immobilization was as high as with seven daily repeated immobilizations. This elevation was not sustained and returned toward control values 24 hr later. Both tyrosine hydroxylase and dopamine beta-hydroxylase mRNA levels were elevated immediately following two daily immobilizations to levels similar to those observed after seven immobilizations and were maintained 24 hr later. The results indicate that both tyrosine hydroxylase and dopamine beta-hydroxylase mRNA levels are elevated by stress; however, the mechanism and/or timing of their regulation are not identical.

Effects of 6-hydroxydopamine lesions of the prefrontal cortex on tyrosine hydroxylase activity in mesolimbic and nigrostriatal dopamine systems

The effects of prefrontal cortical dopamine depletion on subcortical dopamine function in the rat were examined. 6-Hydroxydopamine lesions of the dopaminergic innervation of the prefrontal cortex did not alter concentrations of dopamine or its metabolite 3,4-dihydroxyphenylacetic acid in either the striatum or nucleus accumbens. Similarly, the activity of the catecholamine biosynthetic enzyme tyrosine hydroxylase in the striatal complex was not changed in animals with prefrontal cortical lesions. Animals sustaining neurotoxic lesions of the prefrontal cortex were challenged with haloperidol in order to activate submaximally tyrosine hydroxylase activity. The magnitude of the haloperidol-induced increase in enzyme activity in the nucleus accumbens was significantly greater in lesioned subjects than in control animals. These data suggest that lesions of the prefrontal cortical dopamine innervation do not result in significant alterations in basal dopaminergic function in the striatal complex. However, lesions of the dopaminergic innervation of the prefrontal cortex significantly increase the responsiveness of mesolimbic dopamine afferents to pharmacological challenge.