Aromatic L-amino acid decarboxylase-immunoreactive structures in human midbrain, pons, and medulla

The objective of the present study was to determine with precision the localization of neurons and fibers immunoreactive (ir) for aromatic L-amino acid decarboxylase (AADC), the second-step enzyme responsible for conversion of L-dihydroxyphenylalanine (L-DOPA) to dopamine (DA) and 5-hydroxytryptophan (5-HTP) to serotonin (5-hydroxytryptamine: 5-HT) in the midbrain, pons, and medulla oblongata of the adult human brain. Intense AADC immunoreactivity was observed in a large number of presumptive 5-HT neuronal cell bodies distributed in all of the raphe nuclei, as well as in regions outside the raphe nuclei such as the ventral portions of the pons and medulla. Moderate to strong immunoreaction was observable in presumptive DA cells in the mesencephalic reticular formation, substantia nigra, and ventral tegmental area of Tsai, as well as in presumptive noradrenergic (NA) cells, which were aggregated in the locus coeruleus and dispersed in the subcoeruleus nuclei. In the medulla oblongata, immunoreaction of moderate intensity was distributed in the mid and ventrolateral portions of the intermediate reticular nucleus, which constitutes the oblique plate of A1/C1 presumptive adrenergic and/or NA neurons. The dorsal vagal AADC-ir neurons were fewer in number and stained more weakly than cells immunoreactive for tyrosine hydroxylase (TH). AADC immunoreactivity was not identified in an aggregate of TH-ir neurons lying in the gelatinous subnucleus of the solitary nucleus, a restricted region just rostroventral to the area postrema. Nonaminergic AADC-positive neurons (D neurons), which are abundant in the rat and cat midbrain, pons, and medulla, were hardly detectable in homologous regions in the human brain, although they were clearly distinguishable in the forebrain.

Dopamine-beta-hydroxylase and tyrosine hydroxylase immunoreactive neurons in the human brainstem

Immunohistochemistry of dopamine-beta-hydroxylase in the human hind brain indicates that neuronal cell bodies containing the antigen form prominent populations in the nucleus tractus solitarius and nearby medial and dorsal edge of the medial vestibular nucleus. They are frequent in and around the periphery of the dorsal motor nucleus of the vagus and in an oblique band extending from that region to the ventrolateral aspect of the reticular formation, where they are most numerous at the mid medullary levels. Dopamine-beta-hydroxylase immunoreactive neurons are also closely packed in the nuclei coeruleus and subcoeruleus. Concomitant immunohistochemistry for tyrosine hydroxylase demonstrates small numbers of neuronal cell bodies that are reactive only for this antigen, and which do not contain detectable dopamine-beta-hydroxylase. Such neurons are present in the nucleus tractus solitarius, the pontine lateral parabrachial nucleus and within the core of the rostral pontine reticular formation. Some medullary and pontine axon bundles similarly stain for tyrosine hydroxylase but not for dopamine-beta-hydroxylase. These differential staining patterns suggest, among other possibilities, that in humans some neurons of the caudal brainstem are dopamine (if they contain the second step catecholamine synthesizing enzyme, aromatic L-aminoacid decarboxylase) rather than noradrenaline or adrenaline containing catecholamine neurotransmitters.

The internal organization of the human solitary nucleus

The present study examines the topography and cytoarchitecture of the solitary nucleus (Sol). Three human medulla oblongatae were serially sectioned and alternate sections were reacted for the enzyme acetylcholinesterase or stained with cresyl violet. The 10 component subnuclei of Sol were identified on the basis of their acetylcholinesterase reactivity and cytoarchitecture. These subnuclei are the paracommissural, commissural, gelatinosus, medial, ventral, ventrolateral, dorsal, dorsolateral, intermediate, and interstitial. Cytoarchitecturally, Sol is characterised by an abundance of small cells of varied morphology but also features some medium to large cells as well as pigmented neurons which are differentially distributed across the subnuclei. From spaced serial sections, the outlines of the subnuclei and the entire Sol were used to create three-dimensional computer reconstructions to display the position and extent of each component subnucleus. Our results show that the internal architecture of the human solitary nucleus is similar to that of rodents and carnivores, though there are some notable species differences.

Parkinson's disease: an immunohistochemical study of Lewy body-containing neurons in the enteric nervous system

We performed immunohistochemical analysis of specimens from three autopsied patients with Parkinson's disease, using antibodies to tyrosine hydroxylase (TH), vasoactive intestinal polypeptide (VIP), somatostatin, met-enkephalin, leu-enkephalin and substance P in an attempt to reveal the types of neurons that contain Lewy bodies (LBs) in the paravertebral and celiac sympathetic ganglia and in the enteric nervous system of the alimentary tract. In the sympathetic ganglia, almost all LB-containing neuronal cell bodies and processes were immunoreactive for TH. In the alimentary tract, however, most LBs were found in the VIP-immunoreactive (VIP-IR) neuronal cell bodies and processes. In spite of the significant presence of TH-IR neuronal cell bodies and processes in the alimentary tract, LB-containing TH-IR neuronal elements were rarely encountered. These findings indicate that in the alimentary tract, the VIP neuron system is mainly involved in the disease process of Parkinson's disease.

Tyrosine hydroxylase-immunoreactive intrinsic neurons in the Auerbach's and Meissner's plexuses of humans

We carried out an immunohistochemical study of the Auerbach's and Meissner's plexuses of the human alimentary tract, using antiserum against tyrosine hydroxylase (TH), a rate-limiting enzyme of the catecholamine-synthesizing pathway. TH-immunoreactive intrinsic neuronal cell bodies were observed in both plexuses in almost all parts of the alimentary tract, being most frequent in the Auerbach's plexus of the lower esophagus.

Esthesioneuroblastoma: a nasal catecholamine-producing tumor of neural crest origin. Demonstration of tyrosine hydroxylase-immunoreactive tumor cells

An esthesioneuroblastoma in a 16-year-old male was studied ultrastructurally and immunohistochemically, using antiserum against tyrosine hydroxylase (TH), a rate-limiting enzyme in the catecholamine-synthesizing pathway. Tumor cells were fairly uniform in appearance, showing scanty eosinophilic cytoplasm and round to oval hyperchromatic nuclei, and were arranged in nests and cords of various sizes. Ultrastructurally, individual tumor cells had well-developed cell organelles including polyribosomes, microtubules, intermediate filaments, centrioles, Golgi apparatus and mitochondria. Secretory-like granules were occasionally found, predominantly in the cell processes. Immunohistochemically, many tumor cells were shown to be immunoreactive for TH. This finding strongly suggested that the present tumor was capable of producing catecholamines and that it might be derived from certain sympathetic neuronal cell nests in the superior nasal cavity.

The occurrence of catecholamine neurons in a parietal lobe ganglioglioma

A parietal lobe ganglioglioma in a 2-year-old girl was investigated ultrastructurally and immunohistochemically, using antiserum against tyrosine hydroxylase (TH), a rate-limiting enzyme of the catecholamine (CA)-synthesizing pathway. The tumor was composed essentially of neuronal and astrocytic cells. Ultrastructurally, numerous dense core vesicles measuring between 56 nm and 136 nm (mean, 90 nm) in diameter were observed in the neuronal cytoplasm and processes. The fact that the TH immunohistochemistry revealed many positive neuronal cells in the tumor tissue was of considerable interest. The implications and possible significance of the presence of CA neurons in this ganglioglioma are discussed.

Paragangliomas of the craniocervical region. An immunohistochemical study on tyrosine hydroxylase

An immunohistochemical study on tyrosine hydroxylase (TH), a rate-limiting enzyme in the catecholamine synthesizing pathway, was made on three craniocervical region paragangliomas, two of which showed metastases to the cervical lymph nodes. In all of the original tumors, the majority of tumor cells showed positive immunostaining for TH of variable intensity in their cytoplasm regardless of their cytological features such as cellular and nuclear pleomorphism. The finding suggests that most tumor cells are capable of production of catecholamines and are derived from chief cells in the normal paraganglia. In cervical lymph nodes, however, no positive immunostaining for TH was observed in metastatic tumor cells, in contrast with the findings in the original tumors. The absence of TH immunoreactivity in metastatic tumor cells appears to be noteworthy in considering their malignant potential. Application of the TH immunohistochemistry to further cases appears important for the better understanding of this neoplasm, a catecholamine-producing tumor.