Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.14.16.2 (tyrosine hydroxylase)
 14,760 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

This study examines the ultrastructural relationships established by the nigrostriatal dopaminergic and the corticostriatal afferent fibers with neuropeptide Y (NPY)-containing neurons in the rat striatum. By means of dual immunolabeling procedures using peroxidase conjugated F(ab) fragments and 125I-labeled protein A, direct appositions and morphologically defined synaptic contacts of the symmetrical type were visualized between tyrosine hydroxylase-labeled nerve terminals and NPY-labeled neurons. After deafferentation of the striatum from its cortical input direct appositions and asymmetrical synaptic contacts were evidenced between characteristic degenerative boutons and NPY-positive neurons in the striatum. These results suggest that striatal NPY interneurons undergo direct influence from both nigrostriatal dopaminergic and corticostriatal neuronal systems.
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PMID:Ultrastructural correlates of functional relationships between nigral dopaminergic or cortical afferent fibers and neuropeptide Y-containing neurons in the rat striatum. 276 90

Numerous studies indicate that gamma-aminobutyric acid (GABA) can either hyperpolarize or depolarize hippocampal pyramidal and granule cells. While the inhibitory action of GABA may occur directly on these cells, the excitatory action may be mediated by interactions of GABAergic neurons with each other or with catecholaminergic afferents. We sought to examine the cellular basis for these interactions and their relative frequency. Thus, the ultrastructural morphology of GABAergic neurons and their relation to terminals exhibiting immunoreactivity for the catecholamine-synthesizing enzyme tyrosine hydroxylase (TH) were examined in the rat hippocampal formation using combined immunoautoradiographic and peroxidase-antiperoxidase labeling methods. By light microscopy, GABAergic perikarya and processes codistributed most noticeably with TH-containing processes in the hilus of the dentate gyrus (DG) and in strata lucidum, radiatum, and lacunosum-moleculare of the CA3 region of the hippocampus. Thus, these regions were examined further by electron microscopy. In the ultrastructural analysis, GABA-like immunoreactivity (GABA-LI) was detected in neuronal perikarya, dendrites, axons, and axon terminals. The GABA-containing perikarya were large, ovoid (20-40 microns in diameter), and contained abundant cytoplasm and an indented nucleus with one nucleolus. Synaptic junctions on the perikarya and dendrites with GABA-LI were both symmetric and asymmetric. Approximately equal numbers of TH-labeled terminals (19% of 133 in DG; 39% of 26 in CA3) and GABA-containing terminals (19% DG, 15% CA3) formed synapses with GABA-labeled perikarya. The remainder of the presynaptic terminals (62% DG, 46% CA3) were unlabeled, i.e., contained unidentified transmitters. Terminals with GABA-LI (0.5-1.6 microns) contained numerous small clear vesicles and from 0 to 2 large dense-core vesicles. The types of associations formed by terminals with GABA-LI were remarkably similar in the DG and hippocampus proper despite differences in intrinsic cell type and function. Terminals with GABA-LI formed associations with unlabeled perikarya and dendrites (24% of 151 in DG, 25% of 75 in CA3) and synapses with GABA-containing perikarya and dendrites (18% DG, 5% CA3). Additionally, GABAergic terminals converged upon the same perikarya or dendrite as a TH-containing terminal (15% DG, 21% CA3) and were in direct apposition to TH-labeled terminals (19% DG, 20% CA3). The remaining GABAergic terminals (24% DG, 28% CA3) were without any apparent synaptic relations. In both the DG and CA3, the junctions formed by GABAergic terminals were symmetric. Terminals showing colocalization of GABA-LI and TH-I were also detected although rarely.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:GABAergic neurons in the rat hippocampal formation: ultrastructure and synaptic relationships with catecholaminergic terminals. 279 31

In adult rats with a unilateral 6-hydroxydopamine-induced destruction of the nigrostriatal dopamine (DA) pathway, grafts of embryonic substantia nigra can establish a new dopaminergic terminal fiber plexus in the previously denervated neostriatum and compensate for some of the behavioral deficits induced by the nigrostriatal lesion. In the present study the synaptic connections of the ingrowing DA fibers from the graft were analyzed ultrastructurally, using immunocytochemical localization of tyrosine hydroxylase (TH), in animals whose lesion-induced motor asymmetry had been completely compensated for by the nigral grafts. In two of the animals, horseradish peroxidase-wheatgerm agglutinin conjugate was injected into the graft in order to trace possible reciprocal afferent connections to the graft from the host striatum. TH-immunoreactive axons from the graft were seen to make abundant symmetric synapses with neuronal elements in the host neostriatum. Between 85 and 90% of these synapses were on dendritic shafts and spines, and the rest were on neuronal perikarya. Two principal targets were identified: dendrites of spiny neurons, the majority of which are likely to be striatal projection neurons; and the cell bodies of giant neurons, most (or perhaps all) of which are known to be cholinergic interneurons. The synapses made on dendritic spines, which constituted about 40% of all TH-positive synapses formed by the TH-positive neurons in the graft, resembled those seen in normal animals, both in that they made contacts with spine necks and in that they invariably were associated with an asymmetric TH-negative synapse contacting the spine head. The innervation of the giant cell perikarya, which constituted about 6% of all TH-positive synapses found, was strikingly abnormal in that the graft-derived TH-positive fibers formed dense pericellular "baskets" selectively around the giant cell bodies. Such arrangements were never seen in the normal striatum, nor did they occur in the intact contralateral striatum in the grafted animals. It is proposed that this apparent dopaminergic hyperinnervation from the graft could provide a powerful inhibition of the cholinergic interneurons in the reinnervated host striatum, and that such an inhibitory mechanism could assist in the graft-induced functional recovery by potentiating the functional effects of DA synapses terminating on the spiny efferent neurons. This dual innervation may thus help to explain why restoration of only a small proportion of the striatal DA innervation by the graft is sufficient to induce complete compensation of, e.g., motor asymmetry in the lesioned rats.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Efferent synaptic connections of grafted dopaminergic neurons reinnervating the host neostriatum: a tyrosine hydroxylase immunocytochemical study. 285 78

A pre-embedding immunostaining procedure was developed using ferritin and peroxidase to enable simultaneous electron microscopic localization of two antigens in the same tissue section. This method was used to study the anatomic relationship between glutamic acid decarboxylase (GAD) immunoreactive axons and tyrosine hydroxylase (TH) - containing neurons of the rat arcuate nucleus. The findings provide ultrastructural evidence that GAD-immunoreactive terminals establish symmetric (Gray II) synapses on TH-reactive neurons.
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PMID:Application of avidin-ferritin and peroxidase as contrasting electron-dense markers for simultaneous electron microscopic immunocytochemical labelling of glutamic acid decarboxylase and tyrosine hydroxylase in the rat arcuate nucleus. 286 85

After unilateral injections of wheat germ agglutinin-horseradish peroxidase into the rat caudate-putamen, a few retrogradely labeled neurons were found in the contralateral pars compacta of the substantia nigra. These contralaterally projecting nigral cell bodies also immunoreacted positively to a specific tyrosine hydroxylase antiserum. We conclude that crossed catecholaminergic nigrostriatal projections may contribute to the reciprocal regulation exerted by the two nigrostriatal dopaminergic systems.
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PMID:Evidence for crossed catecholaminergic nigrostriatal projections by combining wheat germ agglutinin-horseradish peroxidase retrograde transport and tyrosine hydroxylase immunocytochemistry. 286 49

The fine structure of the tyrosine hydroxylase (TH) immunoreactive neurons of the hypothalamic arcuate nucleus was examined by means of immunocytochemistry [peroxidase-antiperoxidase (PAP) method], utilizing an antibody against TH. Immunolabeled axon terminals were observed infrequently and were located predominantly in the lateral region, whereas numerous labeled perikarya and dendrites were found throughout the nucleus. The labeled terminals, containing primarily clear and occasionally dense core vesicles, were never observed in synaptic contact. On the other hand, unlabeled axon terminals were frequently seen synapsing on labeled dendrites. In addition, the labeled dendrites were often seen in direct apposition to other neuronal elements such as both labeled and unlabeled perikarya. In contrast, unlabeled dendrites were never seen apposed to labeled perikarya. Labeled dendrites also occurred in direct contact with one another and with unlabeled dendrites. Moreover, numerous labeled dendrites were encountered along tanycytic processes. Dendrites engaged in tanycytic appositions were occasionally partially encompassed by thin sheaths emanating from the tanycytic process. The extensive contact made by the labeled dendritic profiles on both labeled perikarya and dendrites suggests that tubero-infundibular dopaminergic (TIDA) cells may communicate with each other by means of dendritic release of dopamine. The presence of appositions between labeled dendrites and both unlabeled perikarya and dendrites suggests that the TIDA system also influences other neuronal populations through its dendrites. Finally, the dendrotanycytic relationship suggests that the TIDA system may play some role in the regulation of tanycytic function.
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PMID:The fine structural organization of tyrosine hydroxylase immunoreactive neurons in rat arcuate nucleus. 286 61

The histological organization of the filum terminale of the spinal cord in Rana catesbeiana and Rana pipiens was characterized to determine if this region possessed an organized neuropil or whether it was merely a glial remnant that persisted after absorption of the larval tail. The excised filum was maintained in vitro. Intracellular electrophysiological recording was performed with horseradish peroxidase injection. Tyrosine hydroxylase and serotonin distribution were revealed by immunocytochemical methods. Astroglia were the dominant cell type and displayed an elaborate variety of forms. The mean membrane potential was logarithmically related to the extracellular potassium concentration but displayed a sub-Nernstian slope. Oligodendroglia were also seen, as well as ependyma that extended from the central canal to the pial surface. Neuronal activity was revealed by occasional intracellular penetration of elements that displayed spontaneous excitatory postsynaptic or action potentials. The major evidence for the presence of neurons was the demonstration of tyrosine hydroxylase (TH) immunoreactivity in a large population of cerebrospinal fluid-contacting neurons that abutted the ventral half of the central canal. The axons of these cells entered a ventral bundle and ascended the cord; some fibers left this tract and apparently terminated on large arcuate neurons within the filum. Serotoninergic fibers were primarily confined to a subpial location at the dorsal midline. We conclude that the filum terminale of the frog has a sparse but functional neuropil that is organized around the central canal and supported by a profusion of elaborate glial forms.
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PMID:Organization of the filum terminale in the frog. 286 65

Two different antigens in the same ultrathin section of brain tissue can be revealed by 'double immunocytochemistry' in which one antigen is detected by horseradish peroxidase and the other by silver intensification of colloidal gold (SIG) adsorbed to Protein A. By means of this procedure it has been possible to show that GABAergic axon terminals (containing glutamate decarboxylase) are in synaptic contact with the cell bodies and dendrites of dopaminergic neurons (containing tyrosine hydroxylase) in the substantia nigra of the rat. Thus, several of the physiological and pharmacological effects of GABA and GABAergic drugs in this part of the brain are likely to be mediated by a direct action via postsynaptic GABAergic receptors located on dopaminergic nigrostriatal neurons.
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PMID:GABA axons in synaptic contact with dopamine neurons in the substantia nigra: double immunocytochemistry with biotin-peroxidase and protein A-colloidal gold. 286 17

We attempted to confirm reports that medullary catecholamine-synthesizing neurons in the rat contribute axons to the vagus nerve. Vagal preganglionic neurons in the medulla were identified by the retrograde intra-axonal transport of Fast Blue from the cervical vagus. Catecholamine-synthesizing neurons were identified using a specific antibody against tyrosine hydroxylase. A rhodamine-labelled second antibody was used to ensure that Fast Blue and tyrosine hydroxylase could be viewed entirely independently. We did not find any medullary neurons which contained both tyrosine hydroxylase and Fast Blue. Although further investigations by other laboratories are necessary, we believe that previous studies, using punctate versus diffuse horseradish peroxidase staining to doubly label neurons may have produced false positive results.
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PMID:Evidence that catecholamine-synthesizing perikarya in rat medulla oblongata do not contribute axons to the vagus nerve. 286 12

We surveyed retinas of Raja erinacea, Mustelus canis, and Squalus acanthias for neurotransmitter substances by using antisera directed against the substances themselves or against their synthesizing enzymes. Both the peroxidase-antiperoxidase (PAP) and indirect fluorescent techniques were employed to visualize the primary antisera. In all three species positive results were obtained with antisera directed against tyrosine hydroxylase (TOH), glutamic acid decarboxylase (GAD), serotonin (5-HT), and leucine enkephalin (Lenk). Antisera directed against glucagon, neurotensin, beta-endorphin, vasoactive intestinal peptide, or bombesin failed to show any specific staining. Immunoreactivity was located in amacrine, interplexiform, and horizontal cells as well as in axons of the optic fiber layer. The four antisera labelled different amacrine cell classes, distinguished on the bases of perikaryal morphology and the distribution of cell processes in the inner plexiform layer (IPL). Amacrine cells that labelled with the same marker were seen to have different morphologies in the species studied. Thus, TOH-like immunoreactivity was distributed in layers 1, 3, and 5 of the IPL in Mustelus but only in layers 1 and 3 in Raja retina. GAD-like immunoreactivity was found diffusely over all layers of the IPL in Raja, but in Mustelus it was confined primarily to layers 1, 3, and 5 of the IPL. Lenk- and 5-HT-like immunoreactivities showed similar species variations. Two neurochemical classes of interplexiform cell were identified in this study. In Mustelus GAD-like and Lenk-like immunoreactive interplexiform cells were seen whereas in Raja only GAD-positive interplexiform cells were detected. In squalus no unequivocal demonstration of any interplexiform cell was made with these antisera. The GAD antiserum also labelled a subset of the horizontal cells in the dorsal retina of Raja. TOH and 5-HT-antisera labelled axons in the optic fiber layer of all three species but reactive ganglion cell perikarya were not identified.
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PMID:Retinal neurochemistry of three elasmobranch species: an immunohistochemical approach. 286 65


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