Distribution Of Tyrosine Hydroxylase Research Articles

A role for dopamine in control of the hypoxic ventilatory response via D2 receptors in the zebrafish gill.

Dopamine is a neurotransmitter involved in oxygen sensing and control of reflex hyperventilation. In aquatic vertebrates, oxygen sensing occurs in the gills via chemoreceptive neuroepithelial cells (NECs), but a mechanism for dopamine in autonomic control of ventilation has not been defined. We used immunohistochemistry and confocal microscopy to map the distribution of tyrosine hydroxylase (TH), an enzyme necessary for dopamine synthesis, in the gills of zebrafish. TH was found in nerve fibers of the gill filaments and respiratory lamellae. We further identified dopamine active transporter (dat) and vesicular monoamine transporter (vmat2) expression in neurons of the gill filaments using transgenic lines. Moreover, TH- and dat-positive nerve fibers innervated NECs. In chemical screening assays, domperidone, a D2 receptor antagonist, increased ventilation frequency in zebrafish larvae in a dose-dependent manner. When larvae were confronted with acute hypoxia, the D2 agonist, quinpirole, abolished the hyperventilatory response. Quantitative polymerase chain reaction confirmed expression of drd2a and drd2b (genes encoding D2 receptors) in the gills, and their relative abundance decreased following acclimation to hypoxia for 48h. We localized D2 receptor immunoreactivity to NECs in the efferent gill filament epithelium, and a novel cell type in the afferent filament epithelium. We provide evidence for the synthesis and storage of dopamine by sensory nerve terminals that innervate NECs. We further suggest that D2 receptors on presynaptic NECs provide a feedback mechanism that attenuates the chemoreceptor response to hypoxia. Our studies suggest that a fundamental, modulatory role for dopamine in oxygen sensing arose early in vertebrate evolution.

Focused Ultrasound Promotes the Delivery of Gastrodin and Enhances the Protective Effect on Dopaminergic Neurons in a Mouse Model of Parkinson’s Disease

Parkinson’s disease (PD) is the second most common chronic neurodegenerative disease globally; however, it lacks effective treatment at present. Focused ultrasound (FUS) combined with microbubbles could increase the efficacy of drug delivery to specific brain regions and is becoming a promising technology for the treatment of central nervous system diseases. In this study, we explored the therapeutic potential of FUS-mediated blood–brain barrier (BBB) opening of the left striatum to deliver gastrodin (GAS) in a subacute PD mouse model induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). The concentration of GAS in the left hemisphere was detected by ultra-high performance liquid chromatography electrospray Q-Orbitrap mass spectrometry (UHPLC/ESI Q-Orbitrap) and the distribution of tyrosine hydroxylase (TH) neurons was detected by immunohistochemical staining. The expression of TH, Dopamine transporter (DAT), cleaved-caspase-3, B-cell lymphoma 2 (Bcl-2), brain-derived neurotrophic factor (BDNF), postsynaptic density protein 95 (PSD-95), and synaptophysin (SYN) protein were detected by western blotting. Analysis showed that the concentration of GAS in the left hemisphere of PD mice increased by approximately 1.8-fold after the BBB was opened. FUS-mediated GAS delivery provided optimal neuroprotective effects and was superior to the GAS or FUS control group. In addition, FUS enhanced GAS delivery significantly increased the expression of Bcl-2, BDNF, PSD-95, and SYN protein in the left striatum (P < 0.05) and reduced the levels of cleaved-caspase-3 remarkably (P = 0.001). In conclusion, the enhanced delivery by FUS effectively strengthened the protective effect of GAS on dopaminergic neurons which may be related to the reinforcement of the anti-apoptotic activity and the expression of synaptic-related proteins in the striatum. Data suggests that FUS-enhanced GAS delivery may represent a new strategy for PD treatment.

Spinal Dopaminergic Mechanisms Regulating the Micturition Reflex in Male Rats with Complete Spinal Cord Injury.

Traumatic spinal cord injury (SCI) often causes micturition dysfunction. We recently discovered a low level of spinally-derived dopamine (DA) that regulates recovered bladder and sphincter reflexes in SCI female rats. Considering substantial sexual dimorphic features in the lower urinary tract, it is unknown if the DA-ergic mechanisms act in the male. Histological analysis showed a similar distribution of tyrosine hydroxylase (TH)+ neurons in the lower cord of male rats and the number increased following thoracic SCI. Subsequently, focal electrical stimulation in slices obtained from L6/S1 spinal segments of SCI rats elicited detectable DA release with fast scan cyclic voltammetry. Using bladder cystometrogram and external urethral sphincter (EUS) electromyography in SCI male rats, intravenous (i.v.) administration of SCH 23390, a D1-like receptor (DR1) antagonist, induced significantly increased tonic EUS activity and a trend of increased residual volume, whereas activation of these receptors with SKF 38393 did not influence the reflex. Meanwhile, blocking spinal D2-like receptors (DR2) with remoxipride had no effect but stimulating these receptors with quinpirole elicited EUS bursting to increase voiding volume. Further, intrathecal delivery of SCH 23390 and quinpirole resulted in similar responses to those with i.v. delivery, respectively, which indicates the central action regardless of delivery route. In addition, metabolic cage assays showed that quinpirole increased the voiding frequency and total voiding volume in spontaneous micturition. Collectively, spinal DA-ergic machinery regulates recovered micturition reflex following SCI in male rats; spinal DR1 tonically suppress tonic EUS activity to enable voiding and activation of DR2 facilitates voiding.

Dopaminergic neuronal development in the embryonic mesencephalon of mouse

This study presents neuronal migration pattern of dopamine (DA) neurons generated in separate regions occupying the ventral mesencephalic territory. A single pulse 5-bromodeoxyuridine (BrdU) was administered at embryonic day (E)10-E15. Distribution of tyrosine hydroxylase (TH) positive cells was determined at E13-postnatal day 0 (P0) by immunohistochemistry. BrdU positive cells labeled at E10 were spread out uniformly in the mesencephalon from E13 to E15, migrating through dorsal and ventral routes at E17 and P0. TH expression labeled at E10 was observed at E13 in the ventromedial region and clearly formed in the ventral tegmental area (VTA) at E15. At E17, TH expression in the substantia nigra (SN) was observed in the ventrolateral region, spreading more outward of the mesencephalon at P0. Generation of TH-positive cells labeled at E13 was also observed in VTA and SN of the mesencephalon at E17 and P0. The expression of these cells labeled after E15 was markedly decreased. These results demonstrated that an almost complete primary structure of DA neuron was formed at the early embryonic stage in the ventral mesencephalon, showing the most active neuronal migration was occurred at E13-E17. Keywords: development, dopaminergic neuron, mesencephalon, neuronal migration

Differences in behavior between surface and cave Astyanax mexicanus may be mediated by changes in catecholamine signaling.

Astyanax mexicanus is a teleost fish that is in the process of allopatric speciation. Ancestral Astyanax are found in surface rivers and derived blind forms are found in cave systems. Adaptation to life in nutrient poor caves without predation includes the evolution of enhanced food seeking behaviors and loss of defensive responses. These behavioral adaptations may be mediated by changes in catecholaminergic control systems in the brain. We examined the distribution of tyrosine hydroxylase, a conserved precursor for the synthesis of the catecholamines dopamine and noradrenaline, in the brains of surface and cave Astyanax using immunohistochemistry. We found differences in tyrosine hydroxylase staining in regions that are associated with nonvisual sensory perception, motor control, endocrine release, and attention. These differences included significant increases in the diameters of tyrosine hydroxylase immunoreactive soma in cave Astyanax in the olfactory bulb, basal telencephalon, preoptic nuclei, ventral thalamus, posterior tuberculum, and locus coeruleus. These increases in modulation by dopamine and noradrenaline likely indicate changes in behavioral control that underlie adaptations to the cave environment.

Distribution of tyrosine-hydroxylase-immunoreactive neurons in the hypothalamus of tree shrews.

The tree shrew (Tupaia belangeri chinensis) is the closest living relative of primates. Yet, little is known about the anatomical distribution of tyrosine hydroxylase (TH)-immunoreactive (ir) structures in the hypothalamus of the tree shrew. Here, we provide the first detailed description of the distribution of TH-ir neurons in the hypothalamus of tree shrews via immunohistochemical techniques. TH-ir neurons were widely distributed throughout the hypothalamus of tree shrew. The majority of hypothalamic TH-ir neurons were found in the paraventricular hypothalamic nucleus (PVN) and supraoptic nucleus (SON), as was also observed in the human hypothalamus. In contrast, rare TH-ir neurons were localized in the PVN and SON of rats. Vasopressin (AVP) colocalized with TH-ir neurons in the PVN and SON in a large number of neurons, but oxytocin and corticotropin-releasing hormone did not colocalize with TH. In addition, colocalization of TH with AVP was also observed in the other hypothalamic regions. Moreover, TH-ir neurons in the PVN and SON of tree shrews expressed other dopaminergic markers (aromatic l-amino acid decarboxylase and vesicular monoamine transporter, Type 2), further supporting that TH-ir neurons in the PVN and SON were catecholaminergic. These findings provide a detailed description of TH-ir neurons in the hypothalamus of tree shrews and demonstrate species differences in the distribution of this enzyme, providing a neurobiological basis for the participation of TH-ir neurons in the regulation of various hypothalamic functions.

Dapagliflozin improves left ventricular remodeling and aorta sympathetic tone in a pig model of heart failure with preserved ejection fraction

BackgroundHeart failure with preserved ejection fraction (HFpEF) is a difficult disease with high morbidity and mortality rates and lacks an effective treatment. Here, we report the therapeutic effect of dapagliflozin, a sodium-glucose cotransporter 2 inhibitor (SGLT2i), on hypertension + hyperlipidemia-induced HFpEF in a pig model.MethodsHFpEF pigs were established by infusing a combination of deoxycorticosterone acetate (DOCA) and angiotensin II (Ang II), and Western diet (WD) feeding for 18 weeks. In the 9th week, half of the HFpEF pigs were randomly assigned to receive additional dapagliflozin treatment (10 mg/day) by oral gavage daily for the next 9 weeks. Blood pressure, lipid levels, echocardiography and cardiac hemodynamics for cardiac structural and functional changes, as well as epinephrine and norepinephrine concentrations in the plasma and tissues were measured. After sacrifice, cardiac fibrosis, the distribution of tyrosine hydroxylase (TH), inflammatory factors (IL-6 and TNF-α) and NO-cGMP-PKG pathway activity in the cardiovascular system were also determined.ResultsBlood pressure, total cholesterol (TC), triglyceride (TG) and low-density lipoprotein (LDL) were markedly increased in HFpEF pigs, but only blood pressure was significantly decreased after 9 weeks of dapagliflozin treatment. By echocardiographic and hemodynamic assessment, dapagliflozin significantly attenuated heart concentric remodeling in HFpEF pigs, but failed to improve diastolic function and compliance with the left ventricle (LV). In the dapagliflozin treatment group, TH expression and norepinephrine concentration in the aorta were strongly mitigated compared to that in the HFpEF group. Moreover, inflammatory cytokines such as IL-6 and TNF-α in aortic tissue were markedly elevated in HFpEF pigs and inhibited by dapagliflozin. Furthermore, the reduced expression of eNOS and the PKG-1 protein and the cGMP content in the aortas of HFpEF pigs were significantly restored after 9 weeks of dapagliflozin treatment.Conclusion9 weeks of dapagliflozin treatment decreases hypertension and reverses LV concentric remodeling in HFpEF pigs partly by restraining sympathetic tone in the aorta, leading to inhibition of the inflammatory response and NO-cGMP-PKG pathway activation.

The expression of tyrosine hydroxylase and DARPP-32 in the house crow (Corvus splendens) brain.

Birds of the family Corvidae which includes diverse species such as crows, rooks, ravens, magpies, jays, and jackdaws are known for their amazing abilities at problem-solving. Since the catecholaminergic system, especially the neurotransmitter dopamine, plays a role in cognition, we decided to study the distribution of tyrosine hydroxylase (TH), the rate-limiting enzyme in the synthesis of catecholamines in the brain of house crows (Corvus splendens). We also studied the expression of DARPP-32 (dopamine and cAMP-regulated phosphoprotein), which is expressed in dopaminoceptive neurons. Our results demonstrated that as in other avian species, the expression of both TH and DARPP-32 was highest in the house crow striatum. The caudolateral nidopallium (NCL, the avian analogue of the mammalian prefrontal cortex) could be differentiated from the surrounding pallial regions based on a larger number of TH-positive "baskets" of fibers around neurons in this region and greater intensity of DARPP-32 staining in the neuropil in this region. House crows also possessed distinct nuclei in their brains which corresponded to song control regions in other songbirds. Whereas immunoreactivity for TH was higher in the vocal control region Area X compared to the surrounding MSt (medial striatum) in house crows, staining in RA and HVC was not as prominent. Furthermore, the arcopallial song control regions RA (nucleus robustus arcopallialis) and AId (intermediate arcopallium) were strikingly negative for DARPP-32 staining, in contrast to the surrounding arcopallium. Patterns of immunoreactivity for TH and DARPP-32 in "limbic" areas such as the hippocampus, septum, and extended amygdala have also been described.

Memantine ameliorates depressive-like behaviors by regulating hippocampal cell proliferation and neuroprotection in olfactory bulbectomized mice

Our previous study suggested that the non-competitive N-methyl-d-aspartate receptor antagonist memantine (MEM) inhibits dopamine (DA) reuptake and turnover by inhibiting brain monoamine oxidase. Clinical studies have reported that MEM may improve depressive symptoms; however, specific mechanisms underlying this effect are unclear. We performed emotional behavior, tail suspension, and forced swimming tests to examine whether MEM has antidepressant effects in olfactory bulbectomized (OBX) mice, an animal model of depression. Subsequently, we investigated the effects of MEM on the distribution of tyrosine hydroxylase (TH), altered microglia morphometry, and astrocyte and cell proliferation in the hippocampus with immunohistochemistry. We also investigated MEM effects on the levels of norepinephrine (NE), DA, and their metabolites with high performance liquid chromatography, and of neurotrophic, proinflammatory, and apoptotic molecules in the hippocampus with western blotting. Forty-two days after surgery, OBX mice showed depressive-like behaviors, as well as decreased levels of monoamines, reduced cell proliferation, and lower levels of TH, phospho(p)-TH (ser31 and ser40), p-protein kinase A (PKA), p-DARPP-32, p-ERK1/2, p-CREB, brain-derived neurotrophic factor (BDNF), doublecortin, NeuN, and Bcl-2 levels. In contrast, the number of activated microglia and astrocytes and the levels of Iba1, GFAP, p-IκB-α, p-NF-κB p65, TNF-α, IL-6, Bax, and cleaved caspase-3 were increased in the hippocampus. These changes (except for those in NE and Bax) were reversed with chronic administration of MEM. These results suggest that MEM-induced antidepressant effects are associated with enhanced hippocampal cell proliferation and neuroprotection via the PKA-ERK-CREB-BDNF/Bcl-2-caspase-3 pathway and increased DA levels.

Three-dimensional distribution of tyrosine hydroxylase, vasopressin and oxytocin neurones in the transparent postnatal mouse brain.

Over the years, advances in immunohistochemistry techniques have been a critical step in detecting and mapping neuromodulatory substances in the central nervous system. The better quality and specificity of primary antibodies, new staining procedures and the spectacular development of imaging technologies have allowed such progress. Very recently, new methods permitting tissue transparency have been successfully used on brain tissues. In the present study, we combined whole-mount immunostaining for tyrosine hydroxylase (TH), oxytocin (OXT) and arginine vasopressin (AVP), with the iDISCO+ clearing method, light-sheet microscopy and semi-automated counting of three-dimensionally-labelled neurones to obtain a (3D) distribution of these neuronal populations in a 5-day postnatal (P5) mouse brain. Segmentation procedure and 3D reconstruction allowed us, with high resolution, to map TH staining of the various catecholaminergic cell groups and their ascending and descending fibre pathways. We show that TH pathways are present in the whole P5 mouse brain, similar to that observed in the adult rat brain. We also provide new information on the postnatal distribution of OXT and AVP immunoreactive cells in the mouse hypothalamus, and show that, compared to AVP neurones, OXT neurones in the supraoptic (SON) and paraventricular (PVN) nuclei are not yet mature in the early postnatal period. 3D semi-automatic quantitative analysis of the PVN reveals that OXT cell bodies are more numerous than AVP neurones, although their immunoreactive soma have a volume half smaller. More AVP nerve fibres compared to OXT were observed in the PVN and the retrochiasmatic area. In conclusion, the results of the present study demonstrate the utility and the potency of imaging large brain tissues with clearing procedures coupled to novel 3D imaging technologies to study, localise and quantify neurotransmitter substances involved in brain and neuroendocrine functions.

Tyrosine hydroxylase-immunoreactivity and its relations with gonadotropin-releasing hormone and neuropeptide Y in the preoptic area of the guinea pig

The present study examines the distribution of tyrosine hydroxylase (TH) immunoreactivity and its morphological relationships with neuropeptide Y (NPY)- and gonadoliberin (GnRH)-immunoreactive (IR) structures in the preoptic area (POA) of the male guinea pig. Tyrosine hydroxylase was expressed in relatively small population of perikarya and they were mostly observed in the periventricular preoptic nucleus and medial preoptic area. The tyrosine hydroxylase-immunoreactive (TH-IR) fibers were dispersed troughout the whole POA. The highest density of these fibers was observed in the median preoptic nucleus, however, in the periventricular preoptic nucleus and medial preoptic area they were only slightly less numerous. In the lateral preoptic area, the density of TH-IR fibers was moderate. Two morphological types of TH-IR fibers were distinguished: smooth and varicose. Double immunofluorescence staining showed that TH and GnRH overlapped in the guinea pig POA but they never coexisted in the same structures. TH-IR fibers often intersected with GnRH-IR structures and many of them touched the GnRH-IR perikarya or dendrites. NPY wchich was abundantly present in the POA only in fibers showed topographical proximity with TH-IR structures. Althoug TH-IR perikarya and fibers were often touched by NPY-IR fibers, colocalization of TH and NPY in the same structures was very rare. There was only a small population of fibers which contained both NPY and TH. In conclusion, the morphological evidence of contacts between TH- and GnRH-IR nerve structures may be the basis of catecholaminergic control of GnRH release in the preoptic area of the male guinea pig. Moreover, TH-IR neurons were conatcted by NPY-IR fibers and TH and NPY colocalized in some fibers, thus NPY may regulate catecholaminergic neurons in the POA.

Differential activation and tyrosine hydroxylase distribution in the hippocampal, pallial and midbrain brain regions in response to cognitive performance in Indian house crows exposed to abrupt light environment

Disruption of the cyclic feature of the day-night environment can cause negative effects on daily activity and advanced brain functions such as learning, memory and decision-making behaviour. These functions in songbirds, including corvids, involve the hippocampus, pallium and midbrain, as revealed by ZENK (a neuronal activation marker) and tyrosine hydroxylase (TH) expressions. TH is rate-limiting marker enzyme of the biosynthesis of dopamine, widely implicated in learning and memory. Here, we measured ZENK and TH immunoreactivity in the hippocampal, pallial and midbrain regions in response to cognitive performance (learning-memory retrieval) tests in Indian house crows (Corvus splendens) exposed to constant light environment (LL) with controls on 12h light:12h darkness. Along with the decay of circadian rhythm in activity behaviour, LL caused a significant decline in the cognitive performance. There was also a decrease under LL in the activity of neurons in the hippocampus, medial and central caudal nidopallium, and hyperpallium apicale, which are widely distributed with TH-immunoreactive fibres. Further, under LL, TH- immunoreactive neurons were reduced in number in midbrain dopamine synthesis sites, the venteral tegmental area (VTA) and substantia nigra (SN), with a negative correlation of co-localized ZENK/TH- immunoreactive cells on errors during the association tasks. These results show decreased activity of learning and memory neural systems, and underscore the role of dopamine in reduced cognitive performance of diurnal corvids with disrupted circadian rhythms under an abrupt light environment.

Histologic validation of locus coeruleus MRI contrast in post-mortem tissue

The locus coeruleus (LC) noradrenergic system regulates arousal and modulates attention through its extensive projections across the brain. LC dysfunction has been implicated in a broad range of neurodevelopmental, neurodegenerative and psychiatric disorders, as well as in the cognitive changes observed during normal aging. Magnetic resonance imaging (MRI) has been used to characterize the human LC (elevated contrast relative to surrounding structures), but there is limited understanding of the factors underlying putative LC contrast that are critical to successful biomarker development and confidence in localizing nucleus LC. We used ultra-high-field 7T magnetic resonance imaging (MRI) to acquire T1-weighted microscopy resolution images (78μm in-plane resolution) of the LC from post-mortem tissue samples. Histological analyses were performed to characterize the distribution of tyrosine hydroxylase (TH) and neuromelanin in the scanned tissue, which allowed for direct comparison with MR microscopy images. Our results indicate that LC-MRI contrast corresponds to the location of neuromelanin cells in LC; these also correspond to norepinephrine neurons. Thus, neuromelanin appears to serve as a natural contrast agent for nucleus LC that can be used to localize nucleus LC and may have the potential to characterize neurodegenerative disease.

Tyrosine hydroxylase protein expression in ventral nerve cord of Neotropical freshwater crab.

Given the importance of catecholamines in coordinating physiological and behavioral responses in brachyurans, the present study was designed to investigate the distribution of tyrosine hydroxylase (TH)-positive cells and fibers in the ventral nerve cord of Dilocarcinus pagei the Neotropical freshwater crab. TH immunoreactivity was visualized in adult crabs of both sexes, during the intermolt period. We found TH-positive cells that have not been previously described in brachyurans. Specifically, we found a pair of TH-positive cells in the ventral region of the thoracic ganglion, and in ventral and dorsal regions of the abdominal (pleonic) ganglion, suggesting catecholaminergic modulation of claws' function and abdominal structures. In addition, great population of TH-positive cells was observed in the subesophageal ganglion, indicating conservation during evolution of catecholamines in this ganglion of decapods. Dopamine is present in cells and fiber tracts of brachyuran ventral nerve cord, projecting to endocrine, cardiac and digestive structures, suggesting widespread modulation and control of physiological functions and behavior. Dopamine plays a central role in movement and psychiatric disorders in humans. Information on dopaminergic function in the nervous system of invertebrates should improve the understanding of its function in more complex systems, such as human beings.

Distribution of adrenergic and cholinergic nerve fibres within intrinsic nerves at the level of the human heart hilum

The disbalance between adrenergic (sympathetic) and cholinergic (parasympathetic) cardiac inputs facilitates cardiac arrhythmias, including the lethal ones. In spite of the fact that the morphological pattern of the epicardiac ganglionated subplexuses (ENsubP) has been previously described in detail, the distribution of functionally distinct axons in human intrinsic nerves was not investigated thus far. Therefore, the aim of the present study was to quantitatively evaluate the distribution of tyrosine hydroxylase (TH)- and choline acetyltransferase (ChAT)-positive axons within intrinsic nerves at the level of the human heart hilum (HH), since they are of pivotal importance for determining proper treatment options for different arrhythmias. Tissue samples containing the intrinsic nerves from seven epicardiac subplexuses were obtained from nine human hearts without cardiac pathology and processed for immunofluorescent detection of TH and ChAT. The nerve area was measured and the numbers of axons were counted using microphotographs of nerve profiles. The densities of fibres were extrapolated and compared between subplexuses. ChAT-immunoreactive (IR) fibres were evidently predominant (>56%) in nerves of dorsal (DRA) and ventral right atrial (VRA) ENsubP. Within both left (LC) and right coronary ENsubP, the most abundant (70.9 and 83.0%, respectively) were TH-IR axons. Despite subplexal dependence, ChAT-IR fibres prevailed in comparatively thinner nerves, whereas TH-IR fibres in thicker ones. Morphometry showed that at the level of HH: (i) LC subplexal nerves were found to be the thickest (25 737 ± 4131 μm(2)) ones, whereas the thinnest (2604 ± 213 μm(2)) nerves concentrated in DRA ENsubP; (ii) the density of ChAT-IR axons was highest (6.8 ± 0.6/100 μm(2)) in the ventral left atrial nerves and lowest (3.2 ± 0.1/100 μm(2)) in left dorsal ENsubP and (iii) the density of TH-IR fibres was highest (15.9 ± 2.1/100 μm(2)) in LC subplexal nerves and lowest (4.4 ± 0.3/100 μm(2)) in VRA nerves. (i) The principal intrinsic adrenergic neural pathways in the human heart proceed via both coronary ENsubP that supply cardiac ventricles and (ii) the majority of cholinergic nerve fibres access the human heart through DRA and VRA ENsubP and extend towards the right atrium, including the region of the sinuatrial node.

Zebrafish Tyrosine Hydroxylase 2 Gene Encodes Tryptophan Hydroxylase

The primary pathological hallmark of Parkinson disease (PD) is the profound loss of dopaminergic neurons in the substantia nigra pars compacta. To facilitate the understanding of the underling mechanism of PD, several zebrafish PD models have been generated to recapitulate the characteristics of dopaminergic (DA) neuron loss. In zebrafish studies, tyrosine hydroxylase 1 (th1) has been frequently used as a molecular marker of DA neurons. However, th1 also labels norepinephrine and epinephrine neurons. Recently, a homologue of th1, named tyrosine hydroxylase 2 (th2), was identified based on the sequence homology and subsequently used as a novel marker of DA neurons. In this study, we present evidence that th2 co-localizes with serotonin in the ventral diencephalon and caudal hypothalamus in zebrafish embryos. In addition, knockdown of th2 reduces the level of serotonin in the corresponding th2-positive neurons. This phenotype can be rescued by both zebrafish th2 and mouse tryptophan hydroxylase 1 (Tph1) mRNA as well as by 5-hydroxytryptophan, the product of tryptophan hydroxylase. Moreover, the purified Th2 protein has tryptophan hydroxylase activity comparable with that of the mouse TPH1 protein in vitro. Based on these in vivo and in vitro results, we conclude that th2 is a gene encoding for tryptophan hydroxylase and should be used as a marker gene of serotonergic neurons.

Alterations in TH- and ChAT-immunoreactive neurons in the DMV and gastric dysmotility in an LPS-induced PD rat model

To study movement disorder in Parkinson's disease (PD), an animal model of PD can be created by injecting lipopolysaccharide (LPS) into the substantia nigra of rats. In addition to body movement disorders, patients with PD often experience gastrointestinal (GI) dysfunction, such as gastroparesis. However, the underlying mechanism of these disorders remains unclear. The dorsal motor nucleus of vagus (DMV) is a well-known visceral nucleus that regulates GI function. The present study investigated alterations in DMV neurons and gastric motility in rats with LPS-induced PD (LPS-PD rats). Gastric motility was recorded using a strain gauge force transducer in vivo. The distributions of tyrosine hydroxylase (TH)- and choline acetyltransferase (ChAT)-positive neurons in the DMV were determined using immunofluorescence and confocal laser microscopy. Our results indicated that in LPS-PD rats, the number of neurons in the substantia nigra, including neurons with TH immunoreactivity, was markedly reduced, although glial cell proliferation was clearly observed. However, enhanced TH immunoreactivity and decreased ChAT immunoreactivity were found in the DMV. Furthermore, weakened gastric motility was recorded in anesthetized LPS-PD rats. In conclusion, rats with LPS-induced PD exhibited gastric dysmotility with an alteration in DMV neurons. This PD model may be used to study autonomic nervous system disorders that are often observed in patients with early-stage PD.

Neuromelanin in Substantia Nigra Neurons Lacking Tyrosine Hydroxylase

Immunocytochemical studies of the distribution of tyrosine hydroxylase (TH), the key enzyme in catecholamine synthesis, in neurons of the substantia nigra of human brains (n = 7) were performed, with identification of the locations of melanin in the same cells. The results showed that the substantia nigra contains three types of neurons: neurons containing TH and neuromelanin, neurons containing only neuromelanin, and neurons containing neither TH nor neuromelanin. The existence of a population of neuromelanin-containing neurons lacking TH (accounting for 7–30% of cells) is assessed from the point of view of the involvement of catecholamines and TH in neuromelanin synthesis.

Transient Appearance of Tyrosine Hydroxylase Immunoreactive Cells in the Midline Epithelial Seam of the Human Fetal Secondary Palate

Transient immunoreactivity for tyrosine hydroxylase, which mediates the conversion of the amino acid L-tyrosine to dihydroxyphenylalanine, in the midline epithelial seam between the bilateral palatal shelves was investigated in human fetuses. Horizontal or frontal paraffin sections of two human fetuses at 9 and 15 weeks of gestation were used to examine the distribution of tyrosine hydroxylase-immunoreactive cells in regions of the entire head other than the brain. Immunohistochemical staining for S100 protein, calretinin, cytokeratin 14, and vimentin was examined using adjacent or near sections. Tyrosine hydroxylase-immunoreactive cells were large and densely distributed in the midline epithelial seam at the site of palatal fusion in fetuses at 9 weeks but not in fetuses at 15 weeks, in which the midline epithelial seam had already disappeared. No expression of S100 protein, calretinin, or vimentin was detected, but the midline epithelial seam was positive for cytokeratin 14. Tyrosine hydroxylase immunoreactivity was not detected in epithelia during the process of palatal fusion in mice from E 14.0 to 15.0. These findings indicate that tyrosine hydroxylase-immunoreactive cells in the midline epithelial seams are nonneural epithelial cells and suggest that the tyrosine hydroxylase is a novel factor involved in normal palatal formation, especially the fate of the midline epithelial seam in humans.

Differential hypothalamic tyrosine hydroxylase distribution and activation by light in adult mice reared under different light conditions during the suckling period

In mammals, early light experience during a critical period within the first 3 weeks of postnatal development has long-lasting effects on circadian locomotor activity behaviour and neuropeptide expression in the suprachiasmatic nucleus (SCN) of the hypothalamus, site of the principal pacemaker. Dopamine is thought to be involved in the modulation of photic input within the SCN and in tadpoles, the expression of tyrosine hydroxylase (TH), a rate-limiting enzyme in the synthesis of dopamine, in the SCN is altered by previous light history. We thus hypothesised that dopaminergic neurons may be important for the development of the adapted responses to light that we have previously observed. To test this, we raised mice in either constant darkness, 12:12 h light-dark cycles or constant light during the first 3 weeks after birth, and later examined the expression of TH and FOS in the hypothalamus of these mice as adults, both in the dark and after exposure to a light pulse. We found that early light experience affects TH and FOS expression, both baseline levels and in response to a light pulse, in brain areas which are directly connected to the SCN, and are associated with the circadian control of neuroendocrine function. Therefore, our results suggest that the long-lasting alterations induced by early light environment on several hypothalamic nuclei may be relayed through the SCN, and that TH-expressing cells may play a role in conveying/establishing these alterations. These data suggest a role of early light experience in the regulation of future hormonal homeostasis and circadian behaviour.