Tryptophan hydroxylase activity and 5-hydroxytryptamine-immunoreactive cells in the superior cervical ganglion of hydrocortisone-treated neonatal rats

Early postnatal glucocorticoid injections led to a large increase in the number of 5-hydroxytryptamine(5-HT)-immunoreactive small cells in the rat superior cervical ganglion. Tryptophan hydroxylase (TPH) activity in ganglia from animals treated with glucocorticoids was not significantly different from saline-injected controls. Both 5-HT immunoreactivity and TPH activity were decreased in ganglia from animals treated with glucocorticoid and the TPH inhibitor parachlorophenylalanine, but not in animals treated with 5-HT uptake inhibitor fluoxetine. These results suggest that 5-HT is synthesized in the small intensely fluorescent (SIF) cells.

Evidence for retrograde degeneration of epinephrine neurons in Alzheimer's disease

Alzheimer's disease (AD) is associated with a progressive loss of locus ceruleus neurons. These noradrenergic neurons receive a major afferent projection from epinephrine neurons in epinephrine cell groups in the brainstem. The epinephrine neurons have a specific enzymatic marker, phenylethanolamine N-methyltransferase (PNMT), which allows them to be identified chemically and immunohistochemically. We have previously reported a decrease in PNMT in brains of patients with AD. We now report that the decrease in PNMT activity in projections to the locus ceruleus is not due to the loss of epinephrine neurons, although up to 33% of these neurons are atrophic. The decrease in presynaptic PNMT does, however, correlate with the loss of postsynaptic locus ceruleus neurons in brains from AD patients. The percentage of degenerating neurons in the epinephrine nuclei also correlates significantly with the amount of loss of locus ceruleus neurons in AD. In addition, there is a 55% decrease in mitogen activity, a nonspecific measure of growth or maintenance factors, in dialysed locus ceruleus extracts from the AD patients compared to those from control subjects. The mitogen activity in the locus ceruleus was significantly correlated with PNMT activity and with the density of locus ceruleus neurons in all cases examined. These findings provide evidence for the hypothesis that retrograde degeneration is a mechanism of neuronal degeneration in AD and suggest that trophic factors may play a role in this process.

Tyrosine hydroxylase-containing neurons in the supraoptic and paraventricular nuclei of the adult human

We have studied the distribution of tyrosine hydroxylase-containing neurons in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) of the adult human hypothalamus. Large numbers of these neurons were seen in these hypothalamic nuclei; approximately 40% of all the cells within the SON and PVN were immunoreactive for tyrosine hydroxylase (TH-ir). Most of these cells were magnocellular. Their distribution was compared to that of arginine-vasopressin-immunoreactive (AVP-ir) cells. In the SON a greater proportion of magnocellular TH-ir cells was found caudally compared to AVP-ir cells. In the PVN the magnocellular TH-ir cells were larger in mean diameter compared to AVP-ir cells. In double-immunofluorescence experiments some TH-ir cells contained oxytocin immunoreactivity but none contained AVP-ir. In the adult human a large number of PVN and SON magnocellular cells appear to synthesize a catecholamine. A subclass of these neurons also synthesize oxytocin but most cells are distinct from the classically described neurosecretory neurons.

Biochemical evidence for presence of dopamine beta-hydroxylase in rat retina

Previously, we demonstrated immunocytochemically that certain phenylethanolamine N-methyltransferase neurons in the inner nuclear layer of rat retina contain other catecholamine synthesizing enzymes, including tyrosine hydroxylase and aromatic-L-amino acid decarboxylase but not dopamine beta-hydroxylase (DBH), the norepinephrine biosynthetic enzyme. In the present study by using a sensitive radioenzymatic assay for DBH we demonstrated the presence of DBH enzymatic activity in retinal extracts. Immunocytochemical studies, however, failed to demonstrate DBH-immunoreactive perikarya even in animals pretreated with colchicine, an inhibitor of axonal transport. Probably causes for these discrepant findings are discussed.

Distribution of monoamine-synthesizing neurons in the human medulla oblongata

We have employed immunohistochemical and morphometric procedures to study the distribution of monoamine-synthesizing neurons in the medulla oblongata of the adult human, utilizing antibodies to tyrosine hydroxylase (TH), phenylethanolamine N-methyltransferase (PNMT), and phenylalanine hydroxylase (PH8). In the human brain, the antigen with which PH8 reacts occurs within neurons that presumably synthesize serotonin (Haan et al., '87). Neurons containing these antigens were mapped and counted in successive coronal sections with the aid of a computer-assisted procedure. The results indicate that monoamine-synthesizing neurons are distributed in the human brain in patterns broadly similar to those described for other species. TH-immunoreactive cells extended caudorostrally for approximately 32 mm commencing at the spinomedullary junction and ending 8 mm caudal to the pontomedullary junction. In coronal sections these TH-immunoreactive neurons were seen in the lateral medulla dorsal to the inferior olive extending in a continuous band to the dorsomedial medulla. Above the obex the majority of these cells apparently synthesize adrenaline since many PNMT-immunoreactive cells were also found in this region. There were few or no PNMT-immunoreactive cells caudal to the obex, indicating that the TH-immunoreactive cells in this region synthesize either noradrenaline or dopamine. Approximately 65% of these TH-immunoreactive neurons contained melanin pigment, whereas few or no PNMT-immunoreactive cells contained melanin pigment. PH8-immunoreactive cells extended throughout the rostrocaudal extent of the medulla oblongata (approximately 40 mm). In coronal sections the majority were found in the medullary raphe nuclei. However, many cells throughout the rostrocaudal extent of the medulla were found laterally intermingled with catecholamine-synthesizing neurons. Occasional neurons in the lateral medulla appeared to contain both PH8- and TH-immunoreactivity.

The distribution of neuropeptide Y-like immunoreactive neurons in the human medulla oblongata

We have described the distribution of neuropeptide Y-like immunoreactive neurons in the medulla oblongata of the adult human. The majority of neuropeptide Y-like immunoreactive cells were found in four regions of the medulla: the ventrolateral reticular formation, the dorsomedial medulla, the secondary sensory nuclei and the rostral raphe nuclei. The morphology of neuropeptide Y-like immunoreactive cells varied in each of these regions. In the ventrolateral reticular formation, the labelled neurons were round and pigmented caudal to the obex but elongated and non-pigmented rostral to the obex; in the dorsomedial medulla, they were triangular and pigmented caudal to but not rostral to the obex; in the secondary sensory nuclei, they were multipolar, non-pigmented and significantly smaller than in the other areas; in the rostral raphe nuclei, they were bipolar and non-pigmented. Colocalization studies revealed that many neuropeptide Y-like immunoreactive cells also synthesize monoamines, consistent with conclusions based on a quantitative comparison of their distributions. Neuropeptide Y-like immunoreactivity was present in about 25% of presumed noradrenaline-synthesizing cells in the caudal ventrolateral medulla (corresponding to the A1 region); about 50% of adrenaline- and 70% of presumed serotonin-synthesizing cells in the rostral ventrolateral medulla (C1 and B2-3 regions); 90-100% of presumed noradrenaline-synthesizing cells in the dorsomedial medulla at and above the obex (A2 region); about 50% of adrenaline-synthesizing cells in the rostral dorsomedial medulla (C2 region); about 5% of presumed serotonin-synthesizing cells in the rostral raphe nuclei (B2-3 region). The largest of these groups was the presumed serotonin-synthesizing cells that contained neuropeptide Y-like immunoreactivity in the rostral ventrolateral medulla. This is the first report of such a cell group in the medulla of any mammal, and emphasizes the neuroanatomical differences between humans and other species.

Gamma-aminobutyric acid in the medial rat nucleus accumbens: ultrastructural localization in neurons receiving monosynaptic input from catecholaminergic afferents

Neurons containing gamma-aminobutyric acid (GABA) in the medial portion of the adult rat nucleus accumbens were characterized with respect to their ultrastructure, sites of termination, and catecholaminergic input. Antisera against GABA-conjugates and the catecholamine-synthesizing enzyme, tyrosine hydroxylase (TH), were localized within single sections by means of peroxidase-antiperoxidase (PAP) and immunoautoradiographic labeling methods. Peroxidase reaction product indicating GABA-like immunoreactivity (GABA-LI) was seen in medium-size (15-20 microns) perikarya containing either round and unindented or invaginated nuclear membranes. The cells with invaginated nuclei were few in number and usually exhibited more intense peroxidase reaction product in sections collected at the same distance from the surface of the tissue. Reaction product for GABA was also detected in proximal (1.5-3.0 microns) dendrites, axons, and terminals. Terminals with GABA-LI formed symmetric junctions on perikarya, proximal dendrites, and dendritic spines of neurons that usually lacked detectable immunoreactivity. Many of the GABAergic terminals also were apposed directly to other unlabeled terminals and to terminals exhibiting either peroxidase labeling for GABA or immunoautoradiographic labeling for TH. Many of the unlabeled terminals associated with the GABAergic axons formed asymmetric junctions on dendritic spines. From 138 TH-labeled, principally dopaminergic terminals that were examined in the medial nucleus accumbens, 4% were associated with the somata of GABAergic neurons and another 14% formed symmetric junctions with proximal dendrite showing GABA-LI. The remaining TH-immuno-reactive terminals either lacked recognizable densities or formed symmetric synapses on unlabeled dendrites and spines. A few of the unlabeled dendrites, as well as those containing GABA-LI, received symmetric synapses from both catecholaminergic and GABAergic terminals. We conclude that in the medial portion of the rat nucleus accumbens, GABA is localized to two morphologically distinct types of neurons, one or both of which receive monosynaptic input from catecholaminergic afferents, and that GABAergic terminals form symmetric synapses on other principally non-GABAergic neurons. The results also support earlier physiological evidence showing that GABA may modulate the output of other GABAergic and non-GABAergic neurons through presynaptic associations.

Ultrastructural characterization of substance P-like immunoreactive neurons in the rostral ventrolateral medulla in relation to neurons containing catecholamine-synthesizing enzymes

Substance P (SP) and catecholamines, particularly adrenaline, have been implicated in cardiovascular responses mediated by neurons in the rostral ventrolateral medulla (RVL). Immunoperoxidase labeling of an antiserum against SP and/or immunoautoradiographic localization of catecholamine (tyrosine hydroxylase-TH)- or adrenaline (phenylethanolamine N-methyltransferase-PNMT)-synthesizing enzymes were examined histologically to determine the cellular basis for a functional interaction involving either synaptic or intracellular relations between these putative transmitters in the adult rat RVL. Peroxidase labeling for SP was localized in perikarya, dendrites, and axon terminals. Most of these perikarya were located medial and ventral to those labeled with TH or PNMT within the same section. However, as others have previously demonstrated by light microscopy, colocalization of SP-like immunoreactivity (SPLI) and PNMT was seen in a few perikarya of colchicine treated animals. Both single- and dual-labeled perikarya contained abundant dense core vesicles. The terminals with SPLI were 0.4-1.4 micron in diameter and contained a few mitochondria, a large population of small, clear vesicles, and from three to 11 large dense core vesicles. In some cases the terminals were seen in continuity with more proximal processes of neurons in the RVL. These terminals formed synapses with a few perikarya and many dendrites, some of which also contained SPLI. In the material dually labeled for TH and SP, terminals with SPLI (n = 32) formed synaptic junctions primarily with TH-labeled dendrites (69%); the remainder were with TH-labeled perikarya (6%) or with unlabeled dendrites (25%). The axosomatic junctions were exclusively symmetric, whereas the majority of axodendritic junctions were primarily asymmetric on small dendrites (0.8-1.0 micron in diameter) or dendritic spines. In sections dually labeled for PNMT and SP, the terminals containing SPLI (n = 37) formed synaptic associations with PNMT-labeled perikarya (11%), PNMT-immunoreactive dendrites (59%), or with perikarya and dendrites lacking PNMT immunoreactivity (30%). The axosomatic junctions were all symmetric and most often associated with the spinous portion of the soma. The axodendritic junctions were primarily asymmetric and were found both on the spinous portion of the PNMT-labeled dendrites. In addition, both TH- and PNMT-labeled somata and dendrites received symmetric and asymmetric contacts from terminals lacking SPLI.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of dopamine on tyrosine hydroxylase in cultured rat adrenal medulla

Explants of rat adrenal medulla were cultured in defined medium for up to 22 hr. Addition of dopamine to the medium led to a diminution in the activity of tyrosine hydroxylase (tyrosine 3-monooxygenase; EC 1.14.16.2) in the tissue. The enzyme activity was inversely proportional to the concentration of dopamine in the culture medium. The extent of loss of tyrosine hydroxylase, as measured by immunochemical titration, corresponded to the degree of loss in enzyme activity under the same conditions. The decreased amount of enzyme protein was due to a decrease in the rate of synthesis of tyrosine hydroxylase. However, this effect was not specific in that the relative rate of tyrosine hydroxylase synthesis was not decreased. Metabolites of dopamine when added to the medium did not affect tyrosine hydroxylase activity. Two other adrenal medullary enzymes, monoamine oxidase (EC 1.4.3.4) and acid phosphatase (EC 3.1.3.2), were not affected by addition of dopamine to the medium. The results indicate that elevated cytoplasmic levels of dopamine decrease the concentration of tyrosine hydroxylase by inhibiting protein synthesis.

5-Hydroxytryptamine and catecholamines in developing sympathetic cells of the rat

Appearance of 5-hydroxytryptamine (5-HT) in developing sympathetic cells of prenatal rats was studied using the indirect immunofluorescence method. In consecutive sections, tyrosine hydroxylase (TH) immunoreactivity was considered as a marker for catecholamine-synthesizing cells in general, while phenylethanolamine N-methyltransferase (PNMT) immunoreactivity was used as an indicator of adrenaline synthesis. 5-HT immunoreactivity was observed for the first time in 12.5-day-old embryos in developing sympathetic chain ganglia. On day 13.5, 5-HT-immunoreactive cells were first seen on the preaortic region and on day 14.5 in the developing adrenal gland. Comparison with consecutive sections stained for TH revealed that all TH-immunoreactive cells were also 5-HT-immunoreactive. During later development, however, 5-HT immunoreactivity was retained by some cell types in each sympathetic tissue. In the ganglia, most developing principal nerve cells gradually lost their 5-HT immunoreactivity, while all so-called small intensely fluorescent (SIF) cells remained intensely 5-HT-immunoreactive. In the adrenal medulla, all catecholamine-containing cells showed 5-HT immunoreactivity until day 16.5. The first adrenaline-synthesizing cells appeared at this stage. Occasionally on day 16.5 and constantly on day 17.5 noradrenaline cell islets were distinguished among adrenaline cells. The adrenaline cells retained intense 5-HT immunoreactivity, while the noradrenaline cells were non-reactive to it. In the main retroperitoneal paraganglion, two noradrenaline cell populations were distinguished from day 15.5, one being 5-HT-immunoreactive and the other non-reactive. A third population appeared in this tissue at the time of birth, consisting of adrenaline-synthesizing cells which were also 5-HT-immunoreactive. These results indicate that the 3 sympathetic tissues undergo similar developmental changes: 5-HT immunoreactivity occurs in conjunction with the initiation of catecholamine synthesis and appears first in all catecholamine cells. During maturation it is confined to certain subpopulations in each tissue, i.e. the SIF cells and some principal nerve cells of the ganglion, the adrenaline cells of the adrenal medulla, the adrenaline cells and some noradrenaline cells of the paraganglionic tissue.

Characterization of the catalytic domain of bovine adrenal tyrosine hydroxylase

Mild trypsin proteolysis of tyrosine hydroxylase (TH) produces a 34 kDa fragment which is catalytically active. To determine the structure of the trypsin-digested tyrosine hydroxylase (tTH) relative to the native enzyme and to regulatory phosphorylation sites, bovine adrenal tTH was purified to homogeneity and the sequence of 17 amino acids from the N-terminus was determined. These data indicate that the N-terminus of tTH corresponds to amino acid 158. Thus the catalytic region is contained within the central region of enzyme approximately 17 kDa from the N-terminal and 5 kDa from the C-terminal and does not include phosphorylation sites located in the N-terminus. This region of TH shares a high degree of homology with phenylalanine hydroxylase and tryptophan hydroxylase and thus reflects a selective conservation of regions required for catalysis in contrast to the non-homologous regulatory sites. Activation by proteolysis corresponds to an increase in affinity for both substrate and cofactor indicating that the region removed by proteolysis imposes additional constraints on substrate and cofactor binding. These data are consistent with the model that the catalytic core of TH is contained within a 34 kDa region in the highly conserved central portion of the molecule whereas the non-homologous N-terminus regulates cofactor binding and directs substrate specificity.

Substance P in the rat nucleus accumbens: ultrastructural localization in axon terminals and their relation to dopaminergic afferents

Dual labeling electron microscopic immunocytochemistry was used to investigate the cellular substrate for functional interactions between substance P (SP) and dopamine in the rat nucleus accumbens. Coronal vibratome sections from acrolein-fixed brains were sequentially processed for the localization of: (1) a rat monoclonal antiserum against SP identified by the peroxidase--anti-peroxidase immunocytochemical method, and (2) a rabbit polyclonal antiserum against tyrosine hydroxylase (TH) identified by immunoautoradiography. The monoclonal rat antiserum recognized principally SP, but also exhibited cross-reactivity with certain other tachykinins such as substance K. Terminals showing SP-like immunoreactivity (SPLI) were 0.2-1.5 microns in diameter and contained numerous small (30-40 nm), round vesicles; one or more large (80-150 nm), dense-core vesicles; and an occasional membrane-bound multivesicular body. From a total of 114 SP-labeled terminals that were quantitatively analyzed, 30.1% formed symmetric synapses with dendrites; whereas only 8% formed asymmetric junctions with dendritic spines. Terminals showing SPLI also occasionally formed junctions with dendrites receiving synaptic input from other terminals that were similarly labeled for the peptide or from terminals immunoautoradiographically labeled for TH. In contrast to the low frequency of postsynaptic relationships, 39.8% of the terminals containing SPLI showed close associations with other unlabeled or TH-labeled terminal or preterminal axons. The axonic contacts were characterized by equally spaced membranes that were not separated by glial processes. Within the terminals containing SPLI, vesicles were located near the axonic contacts; whereas vesicles in unlabeled terminals were located more distally with respect to these appositions. We conclude that in the rat nucleus accumbens SP or a closely related tachykinin subserves principally inhibitory functions at postsynaptic sites as indicated by the prominence of symmetric junctions. The abundance of axonic associations and sparsity of convergent input from TH- and SP-labeled terminals at closely spaced sites on dendrites supports the concepts that a SP-like tachykinin also may modulate the release of dopamine through direct or indirect presynaptic mechanisms. The possibility that there may be more extensive postsynaptic associations through convergence at widely spaced sites on common neurons is discussed.

Possible mechanism of action of SKF 64139 in vivo on rat adrenal and brain phenylethanolamine N-methyltransferase activity

SKF 64139, a specific inhibitor of the epinephrine-synthesizing enzyme, phenylethanolamine N-methyltransferase (PNMT), has been widely used as a pharmacological tool for studying the characteristics of epinephrine-containing neurons. However, the mechanism of action of this drug on PNMT in vivo has not been fully elucidated. In the present study, we traced changes of PNMT activity in rat adrenal glands and medulla oblongata between 1 and 48 hr after intraperitoneal injection of SKF 64139 (50 mg/kg body wt). Within 1 hr, enzyme activity in both tissues decreased to 10% of the respective control value. However, starting at 4 hr, activity gradually recovered from the inhibition and completely returned to the respective control level by 48 hr. Removal of the inhibitor by dialysis substantially restored the adrenal enzyme activity in 1, 2 and 4 hr groups and completely returned it to control levels in 18 and 48 hr groups. A similar pattern also seemed to hold with brain extracts. The profiles of immunotitration curves, using dialyzed tissue extracts and specific antibodies to bovine adrenal PNMT, clearly indicate that, even after dialysis, a substantial amount of inactive enzyme was present in tissue extracts from 1, 2 and 4 hr groups. In contrast, by 18 hr a very small amount of inactive enzyme was present. Throughout the experimental periods there was no noticeable differences among the control and the experimental groups in the number or intensity of immunocytochemical stained neurons with PNMT antibodies of the C1 area of ventrolateral medulla. Judging from the data obtained by dialysis, immunochemical titration and immunocytochemical staining, recovery of PNMT activity following its inhibition by SKF 64139 was not due to irreversible inhibition of the enzyme followed by new enzyme synthesis. Instead, reversible binding of inhibitor to PNMT and its release were responsible for recovery. PNMT from the 1, 2 and 4 hr groups resisted further in vitro inhibition by SKF 64139 because the residual inhibitor was probably still bound to the enzyme.

Distribution of substance P-like immunoreactive neurons in the human medulla oblongata: co-localization with monoamine-synthesizing neurons

The raphe nuclei also contained SP-like immunoreactivity (up to 30%) while few monoamine-synthesizing neurons in the lateral and dorsomedial medulla contained SP-like immunoreactivity (approximately 5% of presumed serotonin-, noradrenaline-, and adren- the adult human. The majority of SP-like immunoreactive neurons were found in four main regions: the lateral medulla, the dorsomedial medulla, the spinal trigeminal nucleus, and the raphe nuclei. The morphology of immunoreactive cells varied according to the region in which they were found. In contrast to previous studies, we found large numbers (90,000) of SP-like immunoreactive neurons throughout the adult human medulla oblongata. The distribution of these SP-like immunoreactive neurons appears to be significantly different from those described in the rat and cat. These results were compared to the distributions of monoamine-synthesizing and neuropeptide Y (NPY)-like immunoreactive neurons in the human medulla previously reported (Halliday et al.: Neuroscience, in press, 1988a; J. Comp. Neurol., in press, 1988b). Colocalization studies revealed that many presumed serotonin-synthesizing neurons in the raphe nuclei also contained SP-like immunoreactivity (up to 30%) while few monoamine-synthesizing neurons in the lateral and dorsomedial medulla contained SP-like immunoreactivity (approximately 5% of presumed serotonin-, noradrenaline-, and adrenaline-synthesizing neurons). The distributions of SP- and NPY-like immunoreactive neurons were similar, although SP-like immunoreactive neurons were concentrated in the lateral regions of the same structures. We have found that the distributions of monoamine-synthesizing, NPY-, and SP-like immunoreactive neurons significantly overlap, particularly in the lateral medulla of the adult human. There is a large increase in the number of these cells in this region compared to other species, emphasizing the neuroanatomical differences between humans and other species.

Do tyrosine hydroxylase-immunoreactive neurons in the ventrolateral arcuate nucleus produce dopamine or only L-dopa?

Dopamine (DA) was early demonstrated in the arcuate nucleus by means of the formaldehyde-induced histofluorescence method. In the present study we have investigated the distribution of cell bodies in the arcuate nucleus with antisera against tyrosine hydroxylase (TH), aromatic L-amino acid decarboxylase (AADC) and DA. The results indicate that TH-immunoreactive cells in the dorsomedial part of the arcuate nucleus also contain immunoreactivity for both AADC and DA. However, TH-positive cells in the ventrolateral arcuate nucleus lacked AADC- and DA-immunoreactivity with the sensitivity of the present methods. The findings raise the question whether the ventrolateral cells synthesize L-DOPA or DA as endproducts.

Ultrastructural localization of beta-adrenergic receptor-like immunoreactivity in the cortex and neostriatum of rat brain

We sought to quantitatively examine the processes containing beta-adrenergic receptor-like immunoreactivity (beta-AR-LI) in the cerebral cortex and neostriatum using a previously characterized rabbit antiserum to frog erythrocyte beta-ARs under optimized immunolabeling conditions. Quantitative assessments of the laminar distribution of beta-AR-LI in the cortex was achieved by computer-assisted image analysis of immunoautoradiographs and by quantitative electron microscopic analysis of peroxidase-antiperoxidase (PAP) labeling in aldehyde-fixed sections and unfixed synaptosomes. In the somatosensory and anterior cingulate cortical areas, light microscopy of aldehyde-fixed sections immunolabeled by the PAP method revealed small (0.5-1.0 micron) punctate processes in all layers. In the deeper layers, rims of immunoreactivity around the plasmalemma of a population of neuronal perikarya and processes were also observed. By immunoautoradiography, labeling was seen in distinct, laminar distributions resembling the reported autoradiographic patterns using radioligands. By electron microscopy, the immunoreactive profiles in all cortical layers were primarily thick and thin postsynaptic densities (PSDs), comprising 4% of all identifiable PSDs in fixed sections and 12% in unfixed synaptosomal preparations. Also labeled were saccules of smooth endoplasmic reticulum and pinocytotic vesicles in dendrites, glial processes and lightly myelinated axons. In the neostriatum, the density of autoradiographic immunoreactivity was equivalent to the heavily labeled laminae of the cerebral cortex. Immunoreactivity detectable by light microscopy included punctate processes and rims of perikarya, as was seen in the cerebral cortex. The PAP reaction was shown by electron microscopy to be localized to the cytoplasmic surface of plasmalemma of a few proximal dendrites, but was most prominently associated with PSDs of dendritic spines. Preadsorption of the antiserum with a partially purified beta-AR preparation abolished all detectable immunoreactivity. These results provide further support for the specificity of the antiserum for beta-ARs, and are the first quantitative ultrastructural evidence for association of beta-AR-LI with PSDs in the cerebral cortex. The neostriatum, whose major catecholaminergic innervation is dopaminergic, and not noradrenergic, is also confirmed to exhibit high levels of beta-AR-LI within subcellular structures analogous to those seen in the cerebral cortex.(ABSTRACT TRUNCATED AT 400 WORDS)

Serotonin axon terminals in the ventral tegmental area of the rat: fine structure and synaptic input to dopaminergic neurons

The serotoninergic (5-hydroxytryptamine, 5-HT) innervation of the rat ventral tegmental area (VTA) was examined by light and electron microscopic radioautography following intraventricular infusion of [3H]5-HT. The [3H]5-HT labeled processes were characterized with respect to their regional distribution, ultrastructure and relationships with all neurons, including dopaminergic neurons, identified in the same sections using immunocytochemistry for the localization of the catecholamine-synthesizing enzyme, tyrosine hydroxylase (TH). By light microscopy, [3H]5-HT labeled axons and axonal varicosities were detected throughout the interfascicular nucleus and ventral portion of the VTA. By electron microscopy, [3H]5-HT-labeled axons were found to be mainly small and unmyelinated, although a few showed several lamellae of myelin. The labeled varicosities measured 0.6 micron in mean diameter and contained many small, round or flattened agranular vesicles and a few large granular vesicles. More than 18% showed synaptic specializations in single thin sections. Most of these synapses were asymmetric and established on dendritic shafts. Based on the probability of seeing such synaptic specializations in single thin sections, it was estimated that as many as 50% of the labeled 5-HT terminals formed synaptic contacts in the VTA. In dually labeled light microscopic sections, [3H]5-HT-accumulating processes often appeared adjacent to TH-immunoreactive perikarya and proximal dendrites. Electron microscopy demonstrated that terminals with radioautographic labeling for 5-HT formed conventional synapses both with TH-labeled and unlabeled dendrites in the VTA. Many additional 5-HT terminals lacking recognizable synaptic densities were directly apposed to TH-labeled dendrites and were isolated from the rest of the neuropil by thin glial leaflets. These results suggest that 5-HT neurons innervate both dopaminergic and non-dopaminergic neurons in the VTA and may influence mesocortical and mesolimbic efferent systems through synaptic as well as non-synaptic mechanisms.

Neurons in the area postrema are the only catecholamine-synthesizing cells in the medulla or pons with projections to the rostral ventrolateral medulla (C1-area) in the rabbit

We have identified, in the rabbit medulla and pons, neurons which project to the C1-region of the rostral ventrolateral medulla. By combining tyrosine hydroxylase immunohistochemistry with retrograde transport of Fluoro-Gold we determined whether any of the retrogradely labelled neurons synthesize catecholamines. The only doubly labelled cells were located in the area postrema. No other group of catecholamine-synthesizing neurons in either the medulla or the pons was found to project to the C1-area of the rostral ventrolateral medulla. Pharmacological agents which lower arterial pressure by stimulating adrenoceptors in the rostral ventrolateral medulla may act on receptors which are not innervated by catecholamine-synthesizing perikarya located outside the C1-region.

Phenylethanolamine N-methyltransferase activity is decreased in Alzheimer's disease brains

Phenylethanolamine N-methyltransferase (PNMT) is the rate-limiting enzyme involved in the synthesis of epinephrine and a specific marker for epinephrine neurons. We have previously described the stability of this enzyme in a variety of pre- and postmortem conditions in human brain autopsy specimens and demonstrated its presence in areas of the human brain that are associated with memory and attention. We now report on 5 patients with Alzheimer's disease (AD) who had a decrease in PNMT activity of 37 to 48% in areas of the brain affected by the disease but not in the cerebellum, an area of the brain unaffected by the disease. The degree of decrease in PNMT activity in the hippocampus correlated significantly with the degree of dementia. We have provided direct immunochemical evidence that the decrease in PNMT activity in AD is due to the loss of this specific enzyme protein.

A single gene codes for aromatic L-amino acid decarboxylase in both neuronal and non-neuronal tissues

We have sought to determine whether aromatic L-amino acid decarboxylase which functions as a neurotransmitter biosynthetic enzyme in neuronal cells can be distinguished from an enzyme with similar activity found in peripheral tissues where no neurotransmitters are synthesized. Aromatic L-amino acid decarboxylase was purified to electrophoretic homogeneity from bovine adrenal medulla, and highly specific antibodies were produced. In addition, a DNA clone complementary to aromatic L-amino acid decarboxylase mRNA was isolated by immunological screening of a lambda gt11 cDNA expression library. We have used these antibodies and cDNA probes for biochemical, immunochemical, and molecular analyses. A single form of aromatic L-amino acid decarboxylase is detected in rat and bovine tissue. Specifically, aromatic L-amino acid decarboxylase protein is biochemically and immunochemically indistinguishable in brain, liver, kidney, and adrenal medulla. Hybridization to aromatic L-amino acid decarboxylase cDNA identifies a single mRNA species of 2.3 kilobase pairs in rat tissue. Furthermore, Southern blot analysis reveals that a single gene codes for aromatic L-amino acid decarboxylase.

Ibotenic acid-induced lesions of striatal target and projection neurons: ultrastructural manifestations in dopaminergic and non-dopaminergic neurons and in glia

The cytological changes elicited by central microinjections of the excitotoxin, ibotenic acid (IBO) were examined in the adult rat striatonigral system using electron microscopic immunocytochemistry. The chemical markers included tyrosine hydroxylase (TH), a biosynthetic enzyme in dopaminergic neurons, and glial fibrillary acidic protein (GFAP). Both short (1-7 day) and long (30-60 days) term effects were evaluated at the site of IBO-injections in the striatum and more distally in the substantia nigra, which both contributes afferents and receives efferents from the striatum. In the neostriatum at every survival period examined, TH-labeled axonal processes appeared equally numerous in the control and IBO-injected hemispheres. However, the TH-labeled axons in the striatum ipsilateral to the IBO-injection were slightly enlarged, and generally lacked synaptic densities. In the early period the remaining neuropil showed signs of edema and contained perikarya and dendrites with vacuolar or dense cytoplasm as well as intact, unlabeled terminals. Numerous astrocytes, and apparently demyelinated axons were more commonly seen at the 7 day period. At 30 and 60 days, bundles of myelinated axons, unlabeled axon terminals, and astrocytes containing a variety of cytosomes and other cytoplasmic inclusions were in close apposition to TH-labeled axon terminals. These results suggest that the dopaminergic terminals may serve neuromodulatory functions with respect to glia or other afferent axons remaining after IBO-injections in the striatum. In the substantia nigra, homolateral to the injection, a dense type of degeneration was seen in a few perikarya and dendrites at 7 days of survival. At this stage, electron dense anterograde degeneration also was seen in terminals contacting both TH-labeled and unlabeled dendrites. The secondary long term changes in nuclear groups located distal to the primary lesion are characteristic of certain types of progressive human neuropathological disorders.

Immunocytochemical colocalization of histamine, histidine decarboxylase, 5-hydroxytryptamine and tyrosine hydroxylase in the superior cervical ganglion of the rat

The coexistence of histamine, histidine decarboxylase (the enzyme synthesizing histamine), 5-hydroxytryptamine and tyrosine hydroxylase (the rate-limiting enzyme in catecholamine synthesis), was studied in the rat superior cervical ganglion with the indirect immunofluorescence method. Possible colocalization was examined by staining consecutive sections with two different antibodies, or alternatively in the same section by eluting the first antibody with a mild solution containing potassium permanganate and sulphuric acid, and by staining the same section with another antibody. It was shown that tyrosine hydroxylase immunoreactivity was found both in large principal nerve cells and in small cells, which on the basis of their size and high nucleus-cytoplasm ratio corresponded to small intensely fluorescent (SIF) cells. Histamine, histidine decarboxylase and 5-hydroxytryptamine immunoreactivities were observed only in SIF cells. Those SIF cells which were immunoreactive for histamine, histidine decarboxylase or 5-hydroxytryptamine also contained tyrosine hydroxylase immunoreactivity. On the other hand, all tyrosine hydroxylase-immunoreactive SIF cells were also immunoreactive for histidine decarboxylase or 5-hydroxytryptamine. Some of the SIF cells, which were non-reactive for histamine, were immunoreactive for tyrosine hydroxylase.

Phenylethanolamine N-methyltransferase-containing neurons in the rostral ventrolateral medulla of the rat. I. Normal ultrastructure

The electron microscopic localization of the adrenaline-synthesizing enzyme, phenylethanolamine N-methyltransferase (PNMT) was examined in the rostral ventrolateral medulla (RVL) of adult rats. The brains were fixed by perfusion with 3.75% acrolein and 2.0% paraformaldehyde in phosphate buffer. Coronal Vibratome sections through the RVL were immunocytochemically labeled using a rabbit polyclonal antiserum to PNMT and the peroxidase-antiperoxidase method. A semi-quantitative ultrastructure analysis revealed that the perikarya constituted 9% of the total immunoreactive profiles observed in the RVL. The labeled somata were large (18-24 microns) and were characterized by an indented nucleus and abundant cytoplasm with numerous mitochondria. An average of 136.8 +/- 11.6 mitochondria were present per 100 microns2 cytoplasm, which is 38% greater than the numbers found for PNMT-immunoreactive neurons in the nucleus of the solitary tract. Moreover, the labeled somata were often found in direct apposition to the basal lamina of small capillaries and neighboring astrocytic processes. The remaining labeled profiles were neuronal processes of which 72% were dendrites. Both the PNMT-labeled somata and dendrites received primarily symmetric contacts from unlabeled axon terminals. Only a few axons and terminals containing immunoreactivity for PNMT were observed. The axons were both unmyelinated and myelinated. The PNMT-immunoreactive terminals were characterized by a mixed population of vesicles and by the formation of synaptic junctions with both unlabeled dendrites and PNMT-labeled perikarya and dendrites. The ultrastructural morphology and proximity to blood vessels and glia suggest a high metabolic activity and possibly a chemosensory function of PNMT neurons in the RVL. The existence of myelinated and unmyelinated axons could imply that PNMT-containing neurons have different conduction velocities in efferent pathways to the spinal cord or other brain regions. Furthermore, the multiple types of synaptic interactions between labeled and unlabeled axons and dendrites support the concept that adrenergic neurons modulate and are modulated by neurons containing the same or other putative transmitters in the RVL.