Changes In Tyrosine Hydroxylase Research Articles

Evidence for developmental dopaminergic alterations in the human immunodeficiency virus-1 transgenic rat

Neurologic impairments associated with human immunodeficiency virus (HIV) infection in pediatric patients may affect quality of life, and can develop despite antiretroviral therapy (ART). Behavioral changes observed in clinical studies of HIV-infected children suggest alterations in dopaminergic neurotransmission. Findings from our model of choice, the HIV-1 transgenic rat, reveal a significant increase in phosphorylated tyrosine hydroxylase protein expression and a decrease in dopamine transporter mRNA, without changes in tyrosine hydroxylase (TH) or dopamine transporter (DAT) protein or in more general markers of protein and gene expression levels in the HIV-1 transgenic rat midbrain. Thus these findings suggest selective vulnerability of the dopamine system in developing brains to HIV-1 infection.

Selective vulnerability of the striatal subregions of C57BL/6 mice to paraquat

Paraquat (PQ) is a strong redox agent that contributes to the formation of reactive oxygen species (ROS) and induces toxicity of the nigrostriatal dopaminergic system. In this study, we investigated the effect of PQ on the dopaminergic system of four striatal subregions. Male C57BL/6 mice (aged 7 weeks and 23–25 g) were used for this study. The mice were administrated with normal saline or PQ (10 mg/kg i.p.) twice weekly for three consecutive weeks, and we evaluated changes in body weight and the performance of motor coordination. We also measured changes in tyrosine hydroxylase (TH) immunoreactivity, dopamine (DA) and its metabolites, reduced glutathione (GSH), and oxidized glutathione (GSSG) in the striatum. The body weight gain of PQ-treated mice was lower than that of control mice 2 weeks after PQ administration, and this lowering effect was sustained until 4 weeks after PQ administration. In the rota-rod test, PQ had a significant effect on the time it took mice to fall from the rotating rod at 2 weeks after injection as compared to the control rats, and the effect was sustained up to 4 weeks after PQ administration. Additionally, the densities of TH-positive fibers were reduced in dorsal regions of both the striata and ventral subregion of the caudal striatum (RD, CD and CV subregions). The DA level however, decreased in four subregions of the striata. The rate of DA oxidation and O-methylation increased in the RD subregion. After PQ administration, GSH levels were significantly reduced in the RD and CV subregions, but GSSG levels in the RD and CD subregions increased compared to the control rats. The ratio of GSH/GSSG also decreased in the RD and CD subregions. We found that repeated PQ injection altered DA metabolism through the generation of oxidative stress in the striatum, and although the RD subregion showed the most prominent change, the dorsal region of the striatum may be more sensitive to PQ exposure.

Identification by hydrogen/deuterium exchange of structural changes in tyrosine hydroxylase associated with regulation.

The activity of tyrosine hydroxylase is regulated by reversible phosphorylation of serine residues in an N-terminal regulatory domain and catecholamine inhibition at the active site. Catecholamines such as dopamine bind very tightly to the resting enzyme; phosphorylation of Ser40 decreases the affinity for catecholamines by 3 orders of magnitude. The effects of dopamine binding and phosphorylation of Ser40 on the kinetics of deuterium incorporation into peptide bonds were examined by mass spectrometry. When dopamine is bound, three peptic peptides show significantly slower deuterium incorporation, 35-41 and 42-71 in the regulatory domain and 295-299 in the catalytic domain. In the phosphorylated enzyme, peptide 295-299 shows more rapid incorporation of deuterium, while 35-41 and 42-71 can not be detected. These results are consistent with tyrosine hydroxylase existing in two different conformations. In the closed conformation, the regulatory domain lies across the active site loop containing residues 295-298; this is stabilized when dopamine is bound in the active site. In the open conformation, the regulatory domain has moved out of the active site, allowing substrate access; this conformation is favored by phosphorylation of Ser40.

Paraquat induces alternation of the dopamine catabolic pathways and glutathione levels in the substantia nigra of mice

The herbicide paraquat (PQ) is a strong redox agent that participates in the formation of reactive oxygen species (ROS) and induces toxicity in the nigrostriatal dopaminergic system. In this study, we investigated the effect of PQ on dopamine (DA) and glutathione levels in the substantia nigra (SN) of mice. Male C57BL/6 mice (aged 7 weeks and 23-25 g) were used for this study. The mice were treated with normal saline (vehicle) and PQ (10 mg/kg, i.p.) twice weekly for three consecutive weeks. We measured changes in tyrosine hydroxylase (TH) immunoreactivity, DA and its metabolites, and glutathione (reduced and oxidized) in the SN. After repeated PQ administration, the density of TH-positive neurons in the substantia nigra pars compacta (SNpc) decreased as compared to the control. Levels of DA and homovanillic acid (HVA) decreased significantly in the PQ-treated mice (p<0.05), but levels of 3,4-dihydroxyphenylacetic acid (DOPAC) and 3-methoxytyramine (3-MT) did not change. The rate of DA oxidation increased significantly in the SNpc, whereas the O-methylation pathway remained unchanged. Levels of reduced glutathione (GSH) in the SNpc decreased more in the PQ group than in the control group, while levels of oxidized glutathione (GSSG) increased in same region. We propose that repeated PQ injection induces dopaminergic neurotoxicity through generation of oxidative stress, and that this toxicity is related to the decline of GSH in the SNpc. The neurotoxic mechanism may specifically involve enhancement of the oxidative pathway of DA metabolism through coupling with the antioxidant GSH system of the SN.

Diencephalo-telencephalic changes of tyrosine hydroxylase in rats and grass frogs after sleep deprivation

Based on sleep deprivation-produced changes of electrographic parameters of the wakefulness-sleep cycle (WSC) in rats and frogs (Rana temporaria), dynamics of activity of tyrosine hydroxylase, the key enzyme of dopamine synthesis, was studied immunohistochemically in substantia nigra and nigrostriatal pathway in rats and in striatum, paraventricular organ, and extrahypothalamic pathways in frogs. Changes in dynamics of tyrosine hydroxylase in rats and in frogs are revealed after the 6-h sleep deprivation and after 2 h of postdeprivation sleep. This allows determining the degree of participation of corticostriatal neuroregulatory and hypothalamo-pituitary neurosecretory systems and their role in regulation of WSC. Possible evolutionary peculiarities of morphofunctional differences in homoiothermal and poikilothermal animals are discussed.

Tissue Plasminogen Activator Is Not Involved in Methamphetamine-Induced Neurotoxicity

To investigate the role of tissue plasminogen activator (tPA) in methamphetamine (METH)-induced dopaminergic neurotoxicity, we compared the changes in tyrosine hydroxylase (TH) and dopamine transporter (DAT) levels in the striatum after repetitive treatment of METH at 4 mg/kg among wild-type, tPA-deficient (tPA−/−), and protease activated receptor-1–deficient (PAR-1−/−) mice. METH treatment caused a marked decrease in TH and DAT levels in the striatum of those mice with a similar magnitude. No difference in METH-induced abnormal behavior and hyperthermia was observed among the three types of mice. These results suggest that neither tPA nor PAR-1 is involved in METH-induced dopaminergic neurotoxicity in vivo.

Age-related changes in the catecholaminergic neurons of the mesopontine tegmentum in the rat

Immunohistochemistry and computer assisted image analysis were used to examine the age-related changes in tyrosine hydroxylase- (TH-) immunoreactivity in substantia nigra (SN), ventral tegmental area (VTA), locus ceruleus (LC) and dopamine-betahyroxylase- (DBH-) immunoreactivity in LC and subceruleus nuclei of the rat. The findings in 3-month-old rats were compared with 28-month-old rats. In SN TH-positive neurons were concentrated in pars compacta and to a lesser extent - in pars lateralis. In VTA the TH-positive neurons were present over the entire area. In LC the immunoreactive perikarya were densely arranged and superimposed, but in subceruleus nuclei they were less numerous and individual cells were clearly discernible. The DBHimmunoreaction distinctly demonstrated the noradrenergic LC and subceruleus neurons. The results indicate of only subtle signs of cell loss in the dopaminergic neuronal population of SN and VTA, whilst the cell loss of the noradrenergic neurons in LC and subceruleus nuclei is evident. On the other hand, considerable age-related dendritic alterations were observed in all catecholaminergic nuclei. Cross-sectional area and optical density (OD) of the TH-immunoreactive neurons in SN, VTA and LC, and of the DBH-immunoreactive neurons in LC and subceruleus nuclei were investigated. In aging the cross-sectional area decreased statistically and OD of the neurons in SN decreased with 13%. In VTA the cross-sectional area did not change its dimensions, while the OD increased with 19%. In LC and subceruleus nuclei the cross-sectional area decreased with 36% and the OD of the neurons decreased with 16%. In conclusion, the most resistant to age-related changes catecholaminergic region in the rat is the VTA, followed by the pars compacta of SN. Rodent LC is a very vulnerable region. Biomedical Reviews 2007; 18: 45-58.

Neurotoxic‐related changes in tyrosine hydroxylase, microglia, myelin, and the blood‐brain barrier in the caudate‐putamen from acute methamphetamine exposure

Changes in the histological morphology of the caudate-putamen (CPu) were determined after a high-dose methamphetamine (METH) exposure in an effort to elucidate whether BBB disruption plays a role in CPu neurotoxicity. This was accomplished by evaluating the tyrosine hydroxylase immunoreactivity (TH-IR), isolectin B4 reactivity, Black Gold II (BG-II) and Fluoro-Jade C (FJ-C) staining, and immunoreactivity to mouse immunoglobulin G (IgG-IR) in adult male mice at 90-min, 4-h, 12-h, 1-day, and 3-day post-METH exposure. The IgG-IR indicated that the BBB was only modestly altered in the CPu at time points after neurodegeneration occurred and dependent on hyperthermia and status epilepticus. The modest CPu IgG-IR changes observed in the perivascular areas indicated that immunoglobulins were present on some CPu microglia 1 day or more after METH. The first signs of CPu damage were swellings in the TH-IR axons, myelin damage, and a few degenerating neurons at 4-h post-METH. The loss of TH-IR was dependent on hyperthermia but not seizures or CPu neurodegeneration, and the TH-IR was virtually absent throughout the CPu within 12 h. Surprisingly, signs of FJ-C labeling (degenerating) axons in the CPu were seen only in the regions of pronounced somatic neurodegeneration and independent of TH-IR loss. Microglial activation did not occur until 1 day or more post-METH. In summary, a major BBB disruption within the CPu does not directly contribute to neurotoxicity in this single high-dose METH exposure. However, seizure activity produced or exacerbated by amygdalar BBB disruption can significantly increase CPu somatic neurodegeneration (but not affect dopamine (DA) terminal damage). The time course of microglial activation indicates a response to the neurodegeneration, myelin damage, and/or damaged DA terminals after loss of TH-IR.

Experimental change on dopaminergic neurons in striatum of Parkinson disease rats.

Parkinson's disease (PD) is a common neurodegenerative disorder characterized by selective and progressive demise of dopamine-containing neurons in the midbrain. In this study, we observe the expression of c-Jun in the striatum of rats with 6-hydroxydopamine (6-OHDA)-lesions after apomorphine (APO) intraperitoneal injection (ip) in substantia nigra compacta (SNc), and to study the mechanism of the rotations behavior. The 6-OHDA was unilaterally injected into rat right SNC. The APO- induced abnormal rotations were investigated on the 1st, 4th, 7th, 14th, 21st days after lesion, respectively. Meanwhile dopaminergic degeneration and c-Jun expression were observed with microscope. Nissl's body staining and immunohistochemical method (ABC) were employed to study the changes of tyrosine hydroxylase (TH) and c-Jun in DA neurons. We found that the number of dopaminergic neurons decreased gradually in the lesioned site and those neurons' electron-microscopic structure was severe damaged. There were over 75% of dopaminergic neurons lost, contralateral rotations over 7 turns per minute and c-Jun expressing in the ipsilateral striatum. Dopaminergic neurons deletion may be linked to upregulation of c-Jun.

Neuroprotection in Parkinson models varies with toxin administration protocol

Numerous factors contribute to substantia nigra pars compacta (SNc) dopamine (DA) neuron death in Parkinson's disease (PD), thus complicating the search for effective neuroprotective agents for this disease. Although the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mouse has been widely used for assessing neuroprotective agents for PD, the pathological processes resulting from MPTP exposure can vary greatly depending upon the MPTP administration protocol. This study assessed the degree to which the neuroprotective efficacy of particular agents may depend upon the MPTP administration protocol (i.e. acute vs. subacute toxin administration). Endpoints analysed were changes in tyrosine hydroxylase (TH) and NeuN cell numbers in the SNc, striatal DA and metabolite levels, and striatal TH+ fiber density. The efficacy of putative neuroprotective agents [i.e. LIGA 20, nicotinamide and pramipexole (PPX)] varied depending upon the MPTP administration protocol. LIGA 20 spared striatal DA levels in both MPTP models, while nicotinamide was only effective in the acute toxin administration model and PPX was only effective in the subacute model. In both MPTP models, LIGA 20 and nicotinamide significantly spared DAergic neurons; PPX only spared DAergic neurons in the subacute model. Only acute MPTP-treated mice that received nicotinamide had a significant sparing of striatal DAergic fibers. These results underscore the need to assess putative neuroprotective agents for PD in multiple animal models using multiple endpoints. This strategy may better identify compounds with broad neuroprotective/neurorestorative profiles that may be more likely to be clinically effective.

Rifampicin attenuates the MPTP-induced neurotoxicity in mouse brain

Rifampicin, an antibacterial drug, is highly effective in the treatment of tuberculosis and leprosy. Recently, it has been reported to have neuroprotective effects in in vitro and in vivo models. This study was designed to elucidate its neuroprotective effects against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurotoxicity (known as an in vivo mouse model of Parkinson's disease). Mice were injected intraperitoneally (i.p.) with MPTP (10 mg/kg) four times at 1- h intervals, and brains were analyzed 3 or 7 days later. Rifampicin at 20 mg/kg (i.p., twice) had protective effects against MPTP-induced neuronal damage (immunohistochemical changes in tyrosine hydroxylase) in both the substantia nigra and striatum. Rifampicin also protected against the MPTP-induced depletions of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA) in the striatum. The maximal concentrations of rifampicin between 30 and 240 min after a single rifampicin injection (20 mg/kg, i.p.) were 2.6 μM (at 30 min) in plasma and 0.77 μM (at 60 min) in striatum. Next, the effects of rifampicin on oxidative stress [lipid peroxidation in mouse brain homogenates and free radical-scavenging activity against diphenyl- p-picrylhydrazyl (DPPH)] were evaluated to clarify the underlying mechanism. At 1 μM or more, rifampicin significantly inhibited both lipid peroxidation in the striatum and free radical production. These findings suggest that in mice, rifampicin can reach brain tissues at concentrations sufficient to attenuate MPTP-induced neurodegeneration in the nigrostriatal dopaminergic neuronal pathway, and that an inhibitory effect against oxidative stress may be partly responsible for its observed neuroprotective effects.

Role of PKC in regulation of Fos and TH expression after naloxone induced morphine withdrawal in the heart

We previously demonstrated that morphine withdrawal induced hyperactivity of the heart by activation of noradrenergic pathways innervating the left and right ventricle, as evaluated by noradrenaline (NA) turnover and Fos expression. The present study was designed to investigate the role of protein kinase C (PKC) in this process, by estimating whether pharmacological inhibition of PKC would attenuate morphine withdrawal induced Fos expression and changes in tyrosine hydroxylase (TH) immunoreactivity levels and NA turnover in the left and right ventricle. Dependence on morphine was induced on day 8 by an injection of naloxone. Morphine withdrawal induced Fos expression and increased TH levels and NA turnover in the right and left ventricle. Infusion of calphostin C, a selective PKC inhibitor, did not modify the morphine withdrawal-induced increase in NA turnover and TH levels. However, this inhibitor produced a reduction in the morphine withdrawal-induced Fos expression. The results of the present study provide new information on the mechanisms that underlie morphine withdrawal-induced up-regulation of Fos expression in the heart and suggest that TH is not a target of PKC during morphine withdrawal at heart levels.

Regeneration of the abdominal postganglionic sympathetic system

The abdominal sympathetic system is unique in that its postganglionic axons do not directly innervate gastrointestinal smooth muscle layers but exert their effects through the enteric nervous system. The purpose of the present study was to examine the ability of neurons in abdominal sympathetic ganglia to regenerate after axonal injury and to determine whether reinnervation occurs after the removal of ganglia. Axons from the celiac ganglion and superior mesenteric ganglion complex (CG/SMG) of adult female BALB/c mice were crushed or the ganglion complex was removed. Immunohistochemistry, western blotting and in situ hybridization were performed to examine the changes in tyrosine hydroxylase (TH) and growth-associated protein 43 (GAP-43) in the duodenum and the sympathetic ganglia. Terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling and injection of the tracer dye, fluorogold were also performed. After crushing the nerve, TH in the duodenum disappeared and reappeared within 90 days. In the CG/SMG, TH decreased and increased as in the duodenum, while the expression of GAP-43 changed in the opposite direction. Nerve crushing caused cell death to limited number of neurons in the CG/SMG. The removal of CG/SMG decreased TH in the duodenum and stomach, but 180 days later TH-positive innervation was recovered. Fluorogold injection revealed that the inferior mesenteric ganglion reinnervated the stomach. Therefore, postganglionic sympathetic nerves in the abdomen are able to regenerate and reinnervation occurs even after the removal of sympathetic ganglia.

Role of PKC‐α,γ isoforms in regulation of c‐Fos and TH expression after naloxone‐induced morphine withdrawal in the hypothalamic PVN and medulla oblongata catecholaminergic cell groups

We previously demonstrated that morphine withdrawal induced hyperactivity of the hypothalamus-pituitary-adrenocortical axis by activation of noradrenergic pathways innervating the hypothalamic paraventricular nucleus (PVN), as evaluated by Fos expression and corticosterone release. The present study was designed to investigate the role of protein kinase C (PKC) in this process by estimating changes in PKCalpha and PKCgamma immunoreactivity, and whether pharmacological inhibition of PKC would attenuate morphine withdrawal-induced c-Fos expression and changes in tyrosine hydroxylase (TH) immunoreactivity levels in the PVN and nucleus tractus solitarius/ ventrolateral medulla (NTS/VLM). Dependence on morphine was induced in rats by 7 day s.c. implantation of morphine pellets. Morphine withdrawal was induced on day 8 by an injection of naloxone. The protein levels of PKCalpha and gamma were significantly down-regulated in the PVN and NTS/VLM from the morphine-withdrawn rats. Morphine withdrawal induced c-Fos expression in the PVN and NTS/VLM, indicating an activation of neurons in those nuclei. TH immunoreactivity was increased in the NTS/VLM after induction of morphine withdrawal, whereas there was a decrease in TH levels in the PVN. Infusion of calphostin C, a selective protein kinase C inhibitor, produced a reduction in the morphine withdrawal-induced c-Fos expression. Additionally, the changes in TH levels in the PVN and NTS/VLM were significantly modified by calphostin C. The present results suggest that activated PKC in the PVN and catecholaminergic brainstem cell groups may be critical for the activation of the hypothalamic-pituitary adrenocortical axis in response to morphine withdrawal.

Oestradiol-dependent and -independent modulation of tyrosine hydroxylase mRNA levels in subpopulations of A1 and A2 neurones with oestrogen receptor (ER)alpha and ER beta gene expression.

Oestradiol (E2) induces luteinizing hormone-releasing hormone (LHRH) hypersecretion, thereby triggering LH surge release in ovariectomized (OVX) rats. Neural signals responsible for the surge are marked by a morning increase in LHRH gene expression and an afternoon increase in LHRH release. Evidence suggests that subpopulations of noradrenergic neurones may be responsible for one or both of these signals. To further investigate this issue, we examined effects of E2 on the activity of A1 and A2 noradrenergic neurones, as reflected in changes in tyrosine hydroxylase (TH) mRNA expression, on the day of LH surge release. We then used dual-label in situ hybridization to determine whether E2-induced changes occurred primarily in A1 and A2 subdivisions wherein most noradrenergic neurones expressed oestrogen receptor (ER)alpha and/or ER beta mRNA. We found that in all subdivisions, levels of TH mRNA were higher in E2- than oil-treated rats at 12.00 h. These differences resulted from a decline in TH mRNA expression in oil-treated rats, as well as a rise in levels in E2-treated rats between 10.00 h and 12.00 h. During the afternoon, TH mRNA expression in most A1 and A2 subdivisions peaked at 14.00 h when LH surge release began. However, in all but the middle and caudal A2 subdivisons, levels were similar in E2-treated and control rats at this time. This was attributable to a widespread increase in TH mRNA expression between 12.00 h and 14.00 h in OVX rats. There was no evidence that E2 induced changes in TH mRNA expression preferentially in regions wherein most neurones contained ER alpha or ER beta mRNA. Our findings suggest that E2 activation of middle and caudal A2 neurones, in conjunction with the widespread E2-independent activation of noradrenergic neurones in other subdivisions, may play a role in the induction of LH surge release.

Tyrosine hydroxylase and dopamine transporter expression in residual dopaminergic neurons: potential contributors to spontaneous recovery from experimental Parkinsonism.

1-Methyl-4-phenyl-1,2,3,6-tetrahyrdropyridine (MPTP)-exposed cats develop severe Parkinsonism that spontaneously resolves in 4-6 weeks. The present study examined the extent to which compensatory changes in tyrosine hydroxylase (TH) and dopamine transporter (DAT) gene and protein expression may underlie this behavioral recovery. In normal cats, TH and DAT protein levels were higher in the dorsal vs. ventral striatum. Expression of DAT and TH mRNA was higher in substantia nigra pars compacta (SNc) than in the ventral tegmental area (VTA). In symptomatic parkinsonian animals, DAT and TH protein levels were significantly decreased in all striatal areas studied. TH and DAT mRNA expression in residual SNc neurons were decreased a mean 32% and 38%, respectively. DAT gene expression in residual VTA neurons in symptomatic animals was decreased 30% whereas TH gene expression was unaffected. In spontaneously recovered cats, TH protein levels were significantly higher than the levels in symptomatic cats only in the ventral striatum, whereas no increase in DAT protein levels were observed in any striatal area. Residual neurons in most ventral mesencephalic regions of recovered cats had increased TH mRNA expression but not increased DAT gene expression, compared with symptomatic animals. Thus, increased TH protein and mRNA and suppression of DAT protein and mRNA expression in the striatum and ventral mesencephalon were associated with functional recovery from MPTP-induced parkinsonism.

Prevention of Neurotoxin Damage of 6-OHDA to Dopaminergic Nigral Neuron by Subthalamic Nucleus Lesions

Object: To investigate the possibility that subthalamic nucleus (STN) ablation could prevent the toxicity of the selective dopaminergic neurotoxin 6-hydroxydopamine (6-OHDA). Methods: Sixty rats were divided into 6 groups (n = 10). The control group received a unilateral microinjection of 6-OHDA into the right ventral tegmental area (VTA) and the right median forebrain bundle (MFB). Group 1 received an administration of kainic acid (KA) into the right STN and, 1-week later, an injection of 6-OHDA in the right VTA and MFB. Groups 2–5 received an injection of 6-OHDA in the right VTA and MFB, 1 h, 2 h, 3 days, and 7 days before KA in the right STN respectively. Four weeks later, the changes of tyrosine hydroxylase (TH)-positive (dopaminergic) neurons in the SNc were investigated with immunocytochemical and morphometrical methods. Results: The number of TH-positive cells in the SNc on the injected side of treated groups (groups 1–5) and control group were 71.46 ± 6.84, 57.07 ± 5.54, 51.09 ± 4.85, 12.68 ± 2.67, 4.15 ± 1.60 and 3.40 ± 1.54/slice, which decreased to 96.7, 72.9, 69.8, 17.2, 5.6 and 4.4% of the non-injected side, respectively. The number of TH-positive neurons in groups 1–4 significantly increased in comparison with the controls (p < 0.05, 0.01). In group 5, there were no remarkable differences in contrast to the number of TH-positive neurons of the controls (p > 0.05). The difference in the number of TH-positive neurons between groups 1–5 was statistically significant (p < 0.01). Conclusion: The results indicate that STN ablation can provide antiglutamate-based neuroprotection of the dopaminergic nigrostriatal pathway against 6-OHDA toxicity.

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 vitrostudies 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 PCBsin vivoby 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 vivoexposure to a PCB mixture can produce changes in second messenger systems that are similar to those observed afterin vitroexposure 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.

Changes in Tyrosine Hydroxylase and Substance P Immunoreactivity in the Cat Carotid Body Following Chronic Hypoxia and Denervation

Long-term hypoxia elicits functional changes in the cat carotid body which are manifest as altered chemosensitivity in response to hypoxia. Previous studies have suggested that these functional adjustments may be mediated by changes in neurotransmitter levels in chemosensory type I cells. Neurotransmitter metabolism in the carotid body has also been shown to be regulated by the neural innervation to the organ. The present study using the cat carotid body demonstrates profound changes in the levels of immunoreactivity of the catecholamine-synthesizing enzyme, tyrosine hydroxylase, and the neuropeptide, substance P, in response to a two-week exposure to hypoxia (10% O 2 in 90% N 2). Furthermore, these changes were modulated both by sensory and sympathetic denervation of the organ. For TH, the intensity of immunostaining in type I cells was markedly increased by long-term hypoxia in both normal and chronic carotid sinus nerve-denervated carotid bodies, but this effect was blocked following chronic sympathectomy. Substance P immunoreactivity in type I cells was dramatically attenuated by hypoxia in both intact and chronic carotid sinus nerve-denervated preparations, but this effect was reduced following chronic sympathectomy. Tyrosine hydroxylase- and substance P-positive axon terminals were observed to innervate type I cells. These axons were also present in chronically sympathectomized preparations, but they disappeared following chronic carotid sinus nerve-denervation suggesting that they very likely arise from sensory neurons in the petrosat ganglion. Our data indicate that chronic chemoreceptor stimulation by hypoxia elicits multiple neurochemical adjustments in the cat carotid body. These changes suggest that catecholaminergic enzymes and neuropeptides play a significant role in the adaptive mechanisms of chemoreceptor function which occur in response to chronic physiological stimulation. Furthermore, the data suggest that neurotrophic mechanisms may influence neurotransmitter metabolism in chemosensory type I cells.

Photo-dynamic tissue oxidation, a novel technique for controlling neuronal transmission

Unilateral injections of the serotonin, 5,7-dihydroxytryptamine (DHT), at various points along the 5-HT pathway to the forebrain produce a turning syndrome associated with alterations of dopamine synthesis in the ipsilateral striatum. Unilateral injections of DHT into theSN produced an ipsilateralincrease in striatal dopamine (DA) turnover andcontralateral rotation in response to amphetamine or apomorphine. Injection of DHT into theMFB produced an ipsilateraldecrease in striatal DA turnover and tyrosine hydroxylase (TOH) activity, andipsilateral rotation in response to amphetamine or apomorphine. After the injection of DHT into the SN or MFB, there was a significant correlation between the rates of drug-induced rotation, the decrease in cortical 5-HT turnover, and the change in striatal DA turnover, suggesting that the unilateral change in DA turnover (and, presumably, the increased stimulation of DA receptors) is causally linked to turning. Injection of DHT into the zones of the striatum and GP richest in 5-HT terminals produced the same responses as the MFB-lesioned rats: ipsilateral rotation and a decrease in striatal TOH activity. Injection of DHT into the area of the striatum richest in DA terminals failed to produce rotation or a significant change in TOH activity.We suggest that 5-HT neurons from the raphe nuclei exert a tonic inhibition on the nigrostriatal pathway at the level of the SN through direct synapses on DA neurons, whereas their neostriatal terminals have an indirect effect on DA terminals, perhaps via interaction with cholinergic and GABA-ergic neurons.