Phenylethanolamine-N-methyltransferase and dopamine-beta-hydroxylase alterations in young spontaneously hypertensive rats

Descending adrenergic input to the primate spinal cord and its possible role in modulation of spinothalamic cells

The present study focuses on 3 different aspects of the descending adrenergic system in the primate: (1) the distribution of adrenergic fibers and terminals in the spinal cord, (2) the source of this input and (3) the possible physiological effects of this system on spinal nociceptive processing. Antibodies to the enzyme phenylethanolamine-N-methyltransferase (PNMT) were employed to map the distribution of epinephrine-containing axonal profiles in the primate spinal cord. Smooth longitudinally oriented fibers were localized to the outer edge of the lateral funiculus. PNMT-containing axonal enlargements were distributed to the superficial dorsal horn, intermediate gray matter and the region surrounding the central canal at all spinal cord levels. PNMT-immunostained profiles were also observed in the intermediolateral cell column. A double labeling study employing retrograde transport of HRP from the spinal cord and PNMT immunohistochemistry identified a small population of HRP-PNMT-labeled neurons in the 'C1' region at the levels of the medulla and ponto-medullary junction. Thus, these cells are a probable source of adrenergic input to the spinal cord. Electrophysiological studies demonstrated that iontophoresis of epinephrine onto identified primate spinothalamic tract neurons in the lumbar dorsal horn resulted in inhibition of the glutamate-induced firing of these cells. The data from these studies support the hypothesis that adrenergic (PNMT-containing) cells in the caudal brainstem project to all levels of the cord and may contribute to descending modulation of nociceptive processing at these levels.

Alpha 2-adrenergic binding sites in the medulla oblongata of tree shrews demonstrated by in vitro autoradiography: species related differences in comparison to the rat

Alpha 2-adrenergic binding sites in the medulla oblongata of tree shrews and rats were detected and quantified by in vitro-autoradiography with the alpha 2-antagonist 3H-rauwolscine (3H-RAUW). The autoradiographic pattern of the radioligand binding in the tree shrew medulla oblongata resembles that which has been described by others for the human myelencephalon. This pattern coincides well with the occurrence of catecholaminergic structures detected by immunocytochemistry with antibodies against phenylethanolamine-N-methyltransferase and tyrosine hydroxylase. In contrast to the rat, where only the nucleus tractus solitarii and the nucleus dorsalis nervi vagi were labeled, five discrete nuclei specifically bound 3H-RAUW in tree shrews. The highest number of binding sites was detected in the nucleus dorsalis nervi vagi (nX; Bmax: 333 fmoles/mg) and the nucleus tractus solitarii (NTS; 311 fmoles/mg), followed by the nucleus nervi hypoglossi (nXII; 297 fmoles/mg), the nucleus reticularis parvocellularis (FRS; 230 fmoles/mg), and the area of the catecholamine cell groups A1 and C1 (area C1; 202 fmoles/mg). Maximal binding in the two labeled nuclei of the rat was 158 fmoles/mg. The discrete nuclei of the two species also showed different affinities for 3H-RAUW with Kd ranging from 0.17 to 0.83 nM in tree shrews and 1.80 to 1.95 nM in rats. Competition experiments revealed that the radioligand bound specifically to alpha 2-binding sites. In the tree shrew, nX, nXII and the area C1, also have a relatively high affinity for the alpha 1-antagonist prazosin which is a quality of the adrenoceptor subtype alpha 2B. Furthermore, in the area C1, 3H-RAUW binding was inhibited by the dopamine antagonist haloperidol. There are thus species related as well as regional differences with respect to the number, the affinity, and the pharmacological properties of alpha 2-binding sites in the medulla oblongata. In tree shrews, alpha 2-adrenoceptors can be autoradiographically quantified in regions which are not labeled in the rat, although former data predicted the existence of such receptors, e.g., in the area of the adrenaline cell group C1.

Distribution of phenylethanolamine N-methyltransferase cell bodies, axons, and terminals in monkey brainstem: an immunohistochemical mapping study

Adrenaline (epinephrine) is an important candidate transmitter in descending spinal control systems. To date intrinsic spinal adrenergic neurons have not been reported; thus adrenergic input is presumably derived from brainstem sites. In this regard, the localization of adrenergic neurons in the brainstem is an important consideration. Maps of adrenergic cell bodies and to a lesser extent axons and terminal fields have been made in various species, but not in monkeys. Thus, the present study concerns the organization of adrenergic systems in the brainstem of a monkey (Macaca fascicularis) immunohistochemically mapped by means of an antibody to the enzyme phenylethanolamine N-methyltransferase (PNMT). PNMT-immunostained cell bodies are distributed throughout the medulla in two principal locations. One concentration of labeled cells is in the dorsomedial medulla and includes the nucleus of the solitary tract (NTS), the dorsal motor nucleus of the vagus (X), and an area ventral to X in a region of the reticular formation (RF) known as the central nucleus dorsalis (CnD) of the medulla. A few scattered cells are observed in the periventricular gray just ventral to the IVth ventricle and on midline in the raphe. The second major concentration of PNMT-immunostained cells is located in the ventrolateral RF, lateral and dorsolateral to the inferior olive (IO), including some cells in the rostral part of the lateral reticular nucleus (LRN). Terminal fields are located in the NTS, X, area postrema (AP), and the floor of the IVth ventricle in the medulla and pons. A light terminal field is also observed in the raphe, particularly raphe pallidus (RP). A heavy terminal field is present in locus coeruleus (LC). Fibers labeled for PNMT form two major fiber tracts. One is in the dorsomedial RF extending as a well-organized bundle through the medulla, pons, and midbrain. A second tract is located on the ventrolateral edge of the medulla and caudal pons. Fibers in this tract appear to descend to the spinal cord. A comparison with maps of other catecholamine neurons in primates is discussed, confirming that the distribution of the adrenergic system in monkeys is similar to that described in the human.

Persistent hypotensive effect of L-dopa given early during development to rats with inherited stress-induced arterial hypertension

A long-lasting decrease of the basal and stress-induced arterial blood pressure was obtained in rats with inherited emotional stress-induced arterial hypertension by means of injections of the dopamine precursor L-DOPA during early development (21-25 days after birth). The restoring effect of L-DOPA was produced through enhancement of synthesis of the brain noradrenaline and, perhaps, adrenaline. The effect was associated with a normalization of the response of the brain adrenergic system to noradrenaline and, presumably, with increase of tyrosine hydroxylase activity in the cortex and hindbrain.

Anatomy of the adrenergic system in the medulla oblongata of the tree shrew: PNMT immunoreactive structures within the nucleus tractus solitarii

The adrenergic system in the medulla oblongata of tree shrews was investigated by immunocytochemistry with an antibody against phenylethanolamine-N-methyltransferase. Two groups of adrenergic cells, which are equivalent to those of other species, were detected: Group C1 in the ventrolateral medulla and group C2 in the dorsomedial medulla. Adrenergic cells in C1 are located around the lateral reticular nucleus or between its subdivisions. They are mostly multipolar with branched processes. In group C2, some immunoreactive cell bodies smaller than those in C1 and many nerve terminals are found in the motor nucleus of the vagus, but most of the adrenergic cells and fibers are observed in the nucleus tractus solitarii. The cytoarchitecture of this nucleus resembles that described before for the rhesus monkey. In contrast to the rat, the subnucleus gelatinosus, which according to other authors receives cardiac and gastric afferents, is a prominent structure in immunocytochemically as well as conventionally stained sections. Adrenergic cell bodies and their fibers form a ring around this nucleus, but no immunoreactive structures are found within it. In the dorsomedial part of the nucleus tractus solitarii, adrenergic neurons are accumulated. They are often located in close proximity to blood vessels. Elongated immunoreactive neurons in the medial subdivision of the nucleus also seem to project in the direction of the dorsal area. Our data give new information about the adrenergic system in the medulla oblongata, especially in the nucleus tractus solitarii of the tree shrew, a species that provides a useful model of a small primate brain.

Distribution of neurons containing phenylethanolamine N-methyltransferase in medulla and hypothalamus of rat

Neurons immunocytochemically labeled with the adrenaline-synthesizing enzyme phenylethanolamine N-methyltransferase were mapped in the brain of rat pretreated with colchicine. In medulla, immunoreactive cells in the C1 and C2 groups were distributed in a more complex manner than described previously. C1 neurons were identified in the reticular formation of ventrolateral medulla and were organized into two populations: (1) a cell column extending throughout the ventrolateral medulla, and lying ventral to the ambiguus cell group and either dorsal to the precerebellar lateral reticular nucleus or interposed between its two subdivisions; (2) a rostral cell cluster forming medial to the column at caudal levels and enlarging close to and in parallel with the ventral surface of the rostral ventrolateral medulla. A large proportion of cells and processes of the rostral cell group were oriented medially and ventromedially. processes of C1 neurons were traced dorsally toward the nucleus tractus solitarii, dorsal motor nucleus, and principal tegmental adrenergic bundle, ventrally toward the ventral surface, laterally toward the trigeminal complex, and medially or ventromedially toward the raphe. C2 neurons were located in the dorsomedial medulla and were subdivided into four distinct populations: (1) neurons in the rostral nucleus paragigantocellularis pars dorsalis (NGCd) and medial longitudinal fasciculus (MLF) were contiguous and similar in size and shape, with their long diameters oriented horizontally or diagonally along several axes; (2) neurons of the periventricular gray were located in a cytoarchitecturally undefined area dorsal to the MLF; these cells were ovoid, smaller, and organized more compactly than those in the NGCd-MLF; (3) a cell group in the rostromedial nucleus tractus solitarii (NTS) and dorsal motor nucleus overflowed caudally into the intermediate thirds of both structures; and (4) a parvicellular group in the NTS was compactly organized in the dorsolateral NTS and was best developed at the level of the area postrema. Processes of C2 neurons were generally directed sagitally, medially, and laterally along the ventricular floor and ventrally or medially toward the raphe; other fibers arborized and terminated within the NTS and dorsal motor nucleus. In the medulla, local processes were traced from C1 and C2 neurons directly into respective ventral and dorsal parts of the medullary raphe and surrounding intraparenchymal blood vessels. Fibers from these neurons were also followed, respectively, onto the ventral subpial surface and the floor of the fourth ventricle.(ABSTRACT TRUNCATED AT 400 WORDS)

Brain, spinal cord and adrenal catecholamine concentrations in neonate rats of the Lyon hypertensive strain

The catecholamine concentrations were determined in brain parts, spinal cord and adrenals of neonate hypertensive rats of the Lyon strain (LH), compared to normotensive (LN) and low-blood-pressure (LL) control rats. In adrenals of LH rats, noradrenaline and adrenaline concentrations are increased, and 3,4-dihydroxyphenylacetic acid (DOPAC) concentration decreased. At the central level, the DOPAC concentration and the ratio DOPAC/dopamine are decreased in the mesencephalon and the forebrain of LH rats. These results suggest that neonate LH rats exhibit a decreased activity in central dopaminergic neurons, and an enhanced maturation of the adrenals.

Rat medulla oblongata. II. Dopaminergic, noradrenergic (A1 and A2) and adrenergic neurons, nerve fibers, and presumptive terminal processes

The aim of this study was to determine the anatomical relationships between catecholaminergic neurons and cytoarchitectonically defined nuclei in the caudal medulla oblongata. Previous studies have demonstrated the existence of noradrenergic cell bodies (designated as the A1 and A2 cell groups) in the caudal medulla oblongata of the rat (Dahlström and Fuxe, '64), including the nTS. There is no information currently available with regard to details of the distribution of these noradrenergic neurons in the functionally distinct subnuclei of the medulla oblongata. In this study the location of catecholamine-synthesizing enzymes was examined in the serial sections of the caudal medulla oblongata of the rat: tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH), and phenylethanolamine N-methyl transferase (PNMT). The immunoperoxidase method of Sternberger ('79) was used to demonstrate the location of immunoreactive neurons, nerve fibers, and presumptive terminal processes. This was followed by Nissl staining of the same sections to localize accurately the immunoreactivity. Noradrenergic neurons (TH- and DBH-positive and PNMT-negative) were localized in a number of subnuclei of the nucleus of the tractus solitarius (nTS), the area postrema (ap), and in the dorsal motor nucleus of the vagus (dmnX). The distribution of these noradrenergic cells was different at different rostrocaudal levels. In addition, adrenergic neurons (TH-, DBH-, and PMNT-positive) were identified dorsal to the tractus solitarius (TS), in the dorsal strip region (ds), the periventricular region (PVR), the dorsal parasolitarius region (dPSR), and the dmnX (rostral to obex). In addition, dopaminergic neurons (TH-positive and DBH- and PNMT-negative) were found in the ap and dmnX. The A1 cell group in the ventrolateral medulla consisted almost exclusively of noradrenergic neurons (TH- and DBH-positive and PNMT-negative). These results indicate that in the rat the A2 cell group is a mixed population of catecholaminergic neurons that are localized in well-defined regions of the dorsal medulla oblongata. The distribution of these neurons is very specific both in terms of rostrocaudal levels and cytoarchitectonic subdivisions of regions of the medulla known to be involved in central autonomic control. This supports the hypothesis that monoaminergic neurons in the dorsal medulla play important roles in the central regulation of visceral function.

Adrenergic neurons in human brain demonstrated by immunohistochemistry with antibodies to phenylethanolamine-N-methyltransferase (PNMT): discovery of a new group in the nucleus tractus solitarius

Adrenaline neurons in human brain were demonstrated by immunohistochemistry using antibody to phenylethanolamine-N-methyltransferase (PNMT), the final enzyme in the pathway of adrenaline synthesis, using fixed frozen sections and a highly sensitive free floating technique which utilizes metallization. Small densely packed PNMT-immunoreactive neurons were observed to form a nucleus lying just ventrolateral to the area postrema and in the dorsal part of the nucleus tractus solitarius. Larger adrenergic neurons were also present in and around the lateral reticular nucleus and in relationship with the dorsal motor nucleus of the vagus in regions equivalent to the C1 and C2 groups in rats. Longitudinally oriented PNMT-positive axons constitute a subset of tyrosine hydroxylase-immunoreactive axons in the dorsomedial reticular formation.

Specific decrease of secretin/VIP-stimulated adenylate cyclase in the heart from the Lyon strain of hypertensive rats

The cardiac adenylate cyclase activity of genetically hypertensive rats from the Lyon strain (LH) was compared to that of Lyon normotensive rats (LN) and that of low blood pressure Lyon rats (LL). The major finding was a 30-35% decrease of secretin- and VIP-stimulated adenylate cyclase activity in cardiac membranes of LH rats that was already obvious in 5 week-old prehypertensive animals: this alteration was apparently specific for the cardiac secretin/VIP-stimulated adenylate cyclase activity, the same activity in membranes from brain, anterior pituitary, and liver being similar in LH, LN and LL rats. It is tempting to conclude that a selective alteration of functional cardiac secretin/VIP receptors in LH rats reflects a local hyperactivity of the sympathetic adrenergic system.

Effects of chronic ethanol feeding on sympathetic innervated organs: temporal sequence of biochemical, functional, and trophic changes

In noradrenergic nerves as well as in effector organs of the sympathetic nervous system, chronic ethanol feeding induced biochemical, functional, and trophic changes. The time sequence of modifications in the activities of tyrosine hydroxylase, phenylethanolamine-N-methyl transferase, monoamine oxidase, endogenous norepinephrine levels, as well as the neuronal uptake mechanism and secretory responses to norepinephrine in the submaxillary gland of the rat, confirms that the effects of chronic ethanol administration are related to an increase in sympathetic tone.

Distribution of tyrosine hydroxylase, dopamine-beta-hydroxylase and phenylethanolamine-N-methyltransferase activities in coronal sections of the rat lower brainstem

The activities of the three major catecholamines synthesizing enzymes were determined on supernatants from microcubes dissected out from 500 microns thick coronal sections of the rat lower brainstem. The microcubes exhibiting significant or high enzymatic activities represented only one-third of the microcubes analyzed and were generally localized either in the dorso-medial or in the ventro-lateral region of the lower brainstem. In the ventro-lateral region, referred to as the A1-C1 region, the rostro-caudal distribution of the enzymatic activities exhibited a small difference between the maximal TH and DBH activities and the maximum PNMT activity located 500 microns more rostrally. Conversely, in the dorso-medial region, referred to as the A2-C2 region, there was a much larger rostro-caudal difference (about 1500 microns) between the peaks of TH and DBH activities and the more rostral peak of PNMT activity. Such a distribution suggests a separation between the adrenaline (A) and the noradrenaline (NA) containing neurons within the dorso-medial region. According to the results of this study, a preferential microdissection of the A versus NA neurons seems possible in the A2-C2 region of the rat medulla oblongata.

Distribution of dopamine-, noradrenaline-, and adrenaline-containing cell bodies in the rat medulla oblongata: demonstrated by the immunocytochemical localization of catecholamine biosynthetic enzymes

The immunocytochemical localization of the biosynthetic enzymes--tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH), and phenylethanolamine-N-methyltransferase (PNMT)--was used to determine the cytological features and precise neuroanatomical location of catecholaminergic neurons in the medulla oblongata of rat. Perikarya labeled with TH were detected in two bilaterally symmetrical columns located in the ventrolateral and dorsomedial medulla. The distribution and the number of neuronal perikarya containing TH were the same as those containing DBH, except in the dorsal motor nucleus of the vagus at the level of the area postrema where the number of neurons immunocytochemically labeled for TH was considerably greater than those labeled for DBH. The detection of perikarya which show immunoreactivity for TH, used in the biosynthesis of dopamine, noradrenaline, and adrenaline, but not DBH, which converts dopamine to noradrenaline, suggests the existence of dopamine-synthesizing neurons in the medulla. Perikarya labeled with PNMT, used in the biosynthesis of adrenaline, were localized in more restricted regions corresponding to rostral subsets of the dorsal and ventral groups labeled for TH and DBH. Counts of neurons immunocytochemically labeled for TH or PNMT were obtained in order to determine the relative ratio of neurons which contain the enzymes necessary for the synthesis of dopamine, noradrenaline, or adrenaline at various levels of the medulla. At the most caudal levels no PNMT labeled neurons were detected. Further rostral, PNMT-labeled neurons were first detected in the ventrolateral medulla. At the level of the area postrema, the number of PNMT-labeled neurons in the ventrolateral medulla was approximately half of the number of cells showing immunoreactivity for TH. In contrast, few PNMT-labeled cells were detected in the dorsomedial medulla at the level of the area postrema compared to many neurons labeled for TH. At rostral medullary levels, in both the ventrolateral and the dorsomedial regions, the number of neurons labeled for TH and PNMT was essentially the same. Thus most, if not all, of the catecholaminergic neurons in the rostral medulla have PNMT, necessary for the synthesis of adrenaline.

Serum dopamine-beta-hydroxylase activity in a new strain of spontaneously hypertensive rats

The serum dopamine-beta-hydroxylase (DBH) activity is higher in 5-week-old rats of the Lyon Hypertensive strain than in rats of the Lyon Normotensive strain. This difference disappears in older animals when the hypertension is developed, while the DBH activity decreases in the both strains.

Urinary excretion of catecholamines and metabolites in the Lyon strain of genetic hypertensive rats

Urinary catecholamines (Norepinephrine : NE, Epinephrine : E) methoxylated amines (Metanephrine : MN, Normetanephrine : NMN) and 3-methoxy-4-hydroxyphenylglycol (MHPG) have been studied in the Lyon hypertensive strain of rats (LHS) and their normotensive controls (LNS) at three ages (5, 9 and 21 weeks) characteristic of the development of hypertension. In 5-week-old rats, increased excretion of E, MN, NMN and early elevation of the ratio E/E+NE were observed, thus suggesting a sympatho-adrenal hyperactivity, with accelerated maturation of E secretion. At adult age, the excretion of most adrenergic metabolites was similar in the two strains of rats. However, the data from adult LHS are difficult to interpret because of a potential renal impairment at this age. Furthermore, there was a positive correlation between systolic blood pressure and urinary catecholamines at 5 weeks and 9 weeks of age but not at 21 weeks. It is suggested that the early sympathoadrenal hyperactivity, which disappears with age, may be related to the onset of hypertension in the Lyon strain of hypertensive rats.

Regional changes in phenylethanolamine-N-methyltransferase of rat brain during development

The changes of phenylethanolamine-N-methyltransferase (PNMT, EC 2.1.1.28), the enzyme that catalyzes the final step in the biosynthesis of adrenaline, were studied during the development of several regions of rat brain. PNMT is present in medulla oblongata-pons, hypothalamus, cerebellum, and midbrain five days before birth, and a progressive increase in the enzyme activity is observed during development. The adult levels are attained between 15 and 20 days, depending on the region. The increases in PNMT activity in the rostral regions are higher than in the caudal regions. PNMT attains adult levels earlier than tyrosine hydroxylase and dopamine-beta-hydroxylase. The apparatus for adrenaline synthesis seems to be mature at three weeks after birth in the medulla oblongata-pons, which contains the cell bodies of adrenaline-containing neurons. In the other regions the adult levels of enzyme activity are attained at 15 days after birth.