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

Oxytocin localization and function in the A1 noradrenergic cell group: ultrastructural and electrophysiological studies

Antibodies to oxytocin and noradrenalin were utilized in an immunocytochemical study of the caudal ventrolateral medulla of the rat brainstem. Noradrenalin was visualized by using antibodies to noradrenalin and by means of a silver-gold intensification of diaminobenzidine, whereas oxytocin could be demonstrated in the same section by using the diaminobenzidine precipitate as a marker. At the light microscopic level, oxytocin fibers were densely distributed around the A1 cell bodies. At the ultrastructural level, oxytocin-containing fibers were seen to terminate synaptically onto noradrenalin-containing neurons. Previous studies have shown that electrical stimulation of A1 neurons selectively activates vasopressin-secreting neurons in the supraoptic nucleus. Therefore, separate electrophysiological studies were set up, in which we observed that oxytocin infusions (100-200 pg) into the A1 area enhanced the activity of 16 out of 19 putative vasopressin-secreting neurons and elicited no response from any of 10 oxytocin-secreting neurons. This finding suggests that some of the parvicellular neurons in the paraventricular nucleus of the hypothalamus, from which the A1 neurons derive their oxytocin innervation, can activate the A1 cell group via this peptidergic neurotransmitter. One of the consequences of A1 neuronal activation is enhanced firing of hypothalamic supraoptic (and paraventricular) vasopressin-secreting neurons, and a consequent rise in plasma vasopressin.

Comparative immunocytochemical study of the catecholaminergic and peptidergic afferent innervation to the dorsal vagal complex in rat and guinea pig

Light and electron microscopic immunocytochemistry was used to study the fine structural organization of the catecholaminergic and hypothalamic peptidergic innervation of the dorsal vagal complex of the medulla oblongata in the rat and guinea pig, the latter of which is known to lack central adrenergic neurons. In the rat, adrenergic fibers immunoreactive to phenylethanolamine-N-methyltransferase were concentrated in the dorsal motor nucleus of the vagus, where they established frequent symmetric synapses with dendrites and perikarya. On the other hand, the density of both oxytocin- and corticotropin-immunoreactive fibers appeared far lower in this nucleus than in the dorsal regions of the nucleus of the tractus solitarius, where they formed asymmetric synapses with small dendrites. In tissue treated for the dual labeling of two neuronal antigens, oxytocin- or corticotropin-reactive fibers were in close contact with adrenergic neurons in this dorsal medullary region. In the guinea pig, unlike the rat, the dorsal motor nucleus of the vagus contained large amounts of oxytocin- and corticotropin-reactive fibers, which formed many symmetric synapses with perikarya and dendrites. Taken together, these data suggest that the control of vagal preganglionic neurons by hypothalamic peptidergic neurons involves a bisynaptic neuronal pathway including adrenergic medullary neurons in the rat, whereas it is direct in the guinea pig, which lacks this adrenergic relay.

The C1 area of rostral ventrolateral medulla: a central site integrating autonomic responses to hemorrhage

Activation of the sympathetic neurons and release of adrenomedullary catecholamines are the principal early reflex responses to hemorrhage. These are initiated by arterial baro- and chemoreceptors, from other cardiopulmonary receptors, and by intracerebral receptors responding to ischemia. A principal gateway for integrating the autonomic responses are a small collection of neurons in a region of the rostral ventrolateral medulla (RVL), containing a cluster of neurons of the C1 adrenergic cell group, the C1 area. Neurons in the C1 area of RVL project exclusively to autonomic nuclei of the spinal cord, are tonically active, and fire with a rhythm linked to the cardiac cycle. They are essential for maintaining resting discharge of sympathetic nerves and, consequently, arterial pressure (AP) and heart rate. They also are critical for reflex changes in AP in the baro- and chemoreceptor, somato-sympathetic (pain), and cerebral ischemic reflexes. Neurons of the C1 area are under tonic excitatory and inhibitory control by pathways from other autonomic centers. They are controlled by a range of neurotransmitters including, gamma aminobutyric acid (GABA), acetylcholine, catecholamines, enkephalin, and several neuropeptides. They also serve as a site of action for the hypotensive actions of several clinically important neurotransmitters. The C1-area of RVL may play a critical role in the autonomic responses to hemorrhage and may be an important target for drugs seeking to treat hemorrhagic shock.

Catecholamine-containing neurons in the sheep brainstem and diencephalon: immunohistochemical study with tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH) antibodies

The present study describes the distribution and morphological characteristics of neurons and nerve fibers containing the catecholamine-synthesizing enzymes, tyrosine hydroxylase and dopamine-beta-hydroxylase, in the sheep brainstem and diencephalon on the basis of immunohistochemical procedures. Neurons and fibers were considered to be dopaminergic if they showed anti-tyrosine hydroxylase immunoreactivity, without corresponding anti-dopamine-beta-hydroxylase immunoreactivity. The structures labeled with both antisera were considered noradrenergic or adrenergic. The distribution of catecholaminergic neurons corresponds to that described by other authors with similar methods in the rat and in primates. The noradrenergic neurons belong to cell groups A1 to A7 and the dopaminergic neurons to cell groups A8 to A15. In almost all studied areas, the catecholaminergic innervation is similar to that observed in the other species. However, the central catecholaminergic systems of the sheep showed some specific characteristics: (1) groups A3 and A4, described in the rat, were not found, (2) group A14 contains fewer neurons than in the rat, (3) group A15 does not contain a dorsal but only a ventral portion, (4) there is a larger dispersion of neurons within each group, especially A6 and A7, than in rodents, and (5) there is a larger noradrenergic innervation of the catecholaminergic groups than in the other species.

Endogenous L-dopa in the rat dorsal vagal complex: an immunocytochemical study by light and electron microscopy

The aim of this work was to examine L-DOPA immunoreactivity (L-DOPA-IR) in the dorsal vagal complex (DVC) of the rat medulla oblongata containing A2/C2 catecholaminergic cell groups, in order to further evaluate the previously proposed hypothesis that various pools of endogenous L-DOPA could be immunocytochemically demonstrated in the mammalian brain. For this purpose, L-DOPA-IR was studied in DVC in comparison with both some other catecholaminergic areas and dopamine immunoreactivity (DA-IR) on adjacent sections of the same brain, by using specific antibodies against glutaraldehyde conjugated L-DOPA and DA. Also, the first preliminary observations of L-DOPA-IR in DVC neurons at the ultrastructural level are reported. The following main results were obtained: (1) bright, intense and homogeneous L-DOPA staining was found in perikarya and proximal neuronal processes situated within the rostrocaudal extension of the DVC; (2) this staining pattern was readily distinct from weak and heterogeneous DA staining; (3) an inverse L-DOPA/DA staining pattern ratio was identified between the DVC and the mesencephalon; (4) L-DOPA-IR at electron microscopic level was roughly similar to that previously observed for DA-IR in mesencephalic cells and their presumptive projections. Although some discrepancies were noticed between L-DOPA staining and data from the literature on tyrosine hydroxylase labeling, our results could not invalidate the hypothesis that, among high L-DOPA/DA ratio containing neurons, some cells in the DVC may contain only L-DOPA.

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.

Excitatory and inhibitory effects of epinephrine on neonatal rat sympathetic preganglionic neurons in vitro

Current and voltage recordings were made from antidromically identified sympathetic preganglionic neurons (SPNs) in transverse thoracolumbar spinal cord slices removed from neonatal rats. When applied by either pressure ejection or superfusion, epinephrine (Epi) caused a slow depolarization or an inward current in 62 SPNs (42%) and a slow hyperpolarization or an outward current in 21 SPNs (14%). The responses persisted in low calcium- or tetrodotoxin-containing media. The Epi-induced depolarization or inward current was associated with increased membrane resistance; it was reduced by membrane hyperpolarization and nullified at a membrane potential of about -100 mV; a clear reversal however was not observed at more negative potential levels. In a number of SPNs the Epi-induced depolarization was accompanied by small inhibitory postsynaptic potentials. The latter were eliminated by a low calcium solution and by the glycine antagonist strychnine, suggesting that they were caused by glycine or a glycine-like substance released from interneurons subsequent to activation by Epi. The Epi-induced hyperpolarization or outward current was associated with decreased membrane resistance, and nullified around -100 mV. The alpha-adrenergic antagonist, dihydroergotamine, and alpha 1-antagonist, prazosin, reversibly blocked the excitatory, whereas the alpha 2-antagonist, yohimbine, abolished the inhibitory response, respectively. It is concluded that Epi acting on alpha 1- and alpha 2-adrenergic receptors depolarizes and hyperpolarizes the rat SPNs by decreasing or increasing membrane conductances to potassium ions.

Distribution of noradrenaline immunoreactivity in the forebrain and midbrain of the lizard Gekko gecko

The distribution of noradrenaline (NA) immunoreactivity in the forebrain and midbrain of the lizard Gekko gecko was studied by means of recently developed antibodies against NA. Noradrenaline-containing cell bodies are found in the hypothalamic periventricular organ and ependymal wall of the infundibular recess of the diencephalon. They are also present in the locus coeruleus and the nucleus of the solitary tract of the brainstem. Noradrenaline-immunoreactive (NAi) fibers and varicosities are widely, but not uniformly, distributed throughout the forebrain and midbrain. In the telencephalon, dense plexuses of NAi fibers are found in the bed nucleus of the medial forebrain bundle, the vertical limb of the nucleus of the diagonal band of Broca, and the caudoventral part of the septal region. The diencephalon, the periventricular preoptic area, the supraoptic nucleus, and, in particular, the medial habenular nucleus are densely innervated by NAi fibers, whereas in the midbrain NAi plexuses are found in the ventral tegmental area, the substantia nigra and its dorsolateral extension (RA8), and in an area ventral to the nucleus interpeduncularis, pars ventralis. Moderately dense plexuses of NAi fibers are found in the small-celled medial cortex, the dorsal cortex, and the midbrain tectum. The remaining forebrain and midbrain areas are generally not or only sparsely innervated by NAi fibers. The distribution of NAi cell bodies and fibers resembles the pattern revealed with antibodies against dopamine-beta-hydroxylase (DBH). A remarkable exception is that the cells in the hypothalamic periventricular organ and ependymal wall of the infundibular recess are immunonegative for DBH. Possible explanations for this discrepancy are discussed. The present study on the distribution of NA immunoreactivity in the brain of Gekko gecko combined with the results of a previous report on the distribution of dopamine in the same species (Smeets et al., '86b) offer the opportunity to differentiate between the two catecholamines in the brain of this vertebrate.

Glucocorticoid receptor-immunoreactivity in C1, C2, and C3 adrenergic neurons that project to the hypothalamus or to the spinal cord in the rat

A combined retrograde transport-double immunohistochemical staining method was used to determine the extent to which rat liver glucocorticoid receptor-immunoreactivity (GR-ir) is contained within phenylethanolamine-N-methyltransferase (PNMT)-ir neurons that project to the paraventricular nucleus of the hypothalamus (PVH) or the spinal cord. The results confirmed that cells in the C1, C2, and C3 adrenergic cell groups each contribute to the adrenergic innervation of the PVH, and indicated that the great majority of retrogradely labeled neurons in each group (80% overall) also express GR-ir. Following injections in the upper thoracic segments of the spinal cord, the bulk of adrenergic neurons that were retrogradely labeled were found in the C1 cell group, though 31% of the total number PNMT-ir cells that could be retrogradely labeled following spinal injections were localized in the C2 and C3 regions. Of these spinally projecting PNMT-ir neurons, 62% displayed GR-ir. The results suggest all three medullary adrenergic cell groups contribute projections to the spinal cord and/or the PVH, and that the capacity to express the GR phenotype is a common, though perhaps not universal, attribute of PNMT-ir neurons. No pronounced differences in the expression GR-ir were observed in adrenergic neurons as a function of their location or efferent projections. Brainstem adrenergic neurons may play a role in integrating neuronal and hormonal controls of adrenal function via ascending and descending projections.

Co-localization of RNAs coding for phenylethanolamine N-methyltransferase and proenkephalin A in bovine and ovine adrenals

A 29-mer oligodeoxyribonucleotide probe, complementary to the coding region of bovine phenylethanolamine N-methyltransferase (PNMT) mRNA was synthesized. Characterization of this probe by Northern blot hybridization showed that it hybridized to a single band in RNA extracted from bovine and ovine adrenal medullae. The molecular size of this hybridized band was approximately 1.0-1.2 kb which is consistent with recently reported data on the molecular weight of bovine PNMT mRNA. In situ hybridization histochemistry was carried out with this probe on bovine and ovine adrenal sections and results compared on adjacent sections with a probe against proenkephalin A (ProEnk A) mRNA synthesized previously. Both showed a similar localization to the outer margin of cells in the adrenal medulla. The results of this study provide strong evidence at the level of mRNA expression that ProEnk A mRNA is expressed preferentially in the adrenaline synthesizing cells within the adrenal medulla. Further, it demonstrates the usefulness of a synthetic oligodeoxyribonucleotide probe for the study of PNMT gene expression.

Differential colocalization of neuropeptide Y- and methionine-enkephalin-Arg6-Gly7-Leu8-like immunoreactivity in catecholaminergic neurons in the rat brain stem

The present study, using a combination of catecholamine (CA) histofluorescence and peptide immunocytochemistry in the same tissue sections, investigated the coexistence of neuropeptide Y (NPY) and methionine-enkephalin-Arg6-Gly7-Leu8 (MEAGL)-like immunoreactivity (LI) in catecholaminergic neurons of colchicine-treated rat brain stems. Of the total number of catecholaminergic neurons in the A1/C1, A2/C2, A3, A4, and A6 regions approximately 83, 28, 98, 76, and 36%, respectively, contained both NPY-LI and CA. Of the total number of catecholaminergic neurons in A1/C1, A2/C2, A3, and A5 regions, approximately 47, 4, 8, and 17%, respectively, contained both MEAGL-LI and CA. Moreover, about 24% of the catecholaminergic neurons in the A1/C1 region contained both NPY- and MEAGL-LI. Neither the noradrenergic neurons (A7) in the pons nor any of the dopaminergic neurons in the midbrain (A8, A9, A10) contained NPY- or MEAGL-LI. Neurons containing both NPY- and MEAGL-like immunoreactive peptides without CA were not found in the rat brain stem. These findings indicate that catecholaminergic neurons in the brain stem of the rat can be subdivided into distinct subgroups on the basis of the coexistence of specific peptides.

Brainstem afferents to the tuberomammillary nucleus in the rat brain with special reference to monoaminergic innervation

Monoaminergic innervation of a histamine-producing cell group, the tuberomammillary nucleus in the posterior hypothalamus, was investigated in the rat by light and electron microscopic immunohistochemical techniques. Immunohistochemical staining of sections of the posterior hypothalamus was demonstrated afferent fibers immunoreactive to tyrosine hydroxylase in ventral and medial subgroups of the tuberomammillary nucleus afferent fibers immunoreactive to tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH), phenyletanolamine-N-methyltransferase (PNMT), and serotonin (5-HT). TH- and DBH-immunoreactive fibers were similar and were evenly and densely distributed throughout the tuberomammillary nucleus. Fibers stained with 5-HT antibodies were also present throughout the tuberomammillary nucleus but exhibited the densest labeling in the dendritic layer adjacent to the glia limitans in the ventral subgroup. Innervation by PNMT-immunoreactive axons was sparse. Electron microscopic analysis of TH-, DBH-, and 5-HT-immunoreactive fibers in the tuberomammillary nucleus revealed vesicle-containing terminal boutons, which formed synapses with dendrites of varying size. Synaptic contacts with nerve cell bodies were not found. Retrograde transport of the fluorescent dye Fast Blue injected into the tuberomammillary nucleus, combined with immunofluorescent staining with anti-TH, anti-DBH, anti-PNMT, and anti-5-HT antibodies, showed that monoaminergic input to the tuberomammillary nucleus originated mainly from the adrenergic and noradrenergic cell groups C1-C3 and A1-A2, respectively, and from the serotoninergic cell groups B5-B9 as designated by Dahlström and Fuxe ('65). Few double-labeled neurons were found in the nucleus locus coeruleus and the dopaminergic cell groups of the rostral brain stem. The present findings suggest that the activity of the histamine-producing neurons of the tuberomammillary nucleus is influenced by monoaminergic neurons in the ventrolateral and dorsomedial medulla oblongata and the raphe nuclei of the rostral brainstem.

Are there bulbospinal catecholaminergic neurones in the guinea pig equivalent to the C1 cell group in the rat and rabbit?

The C1 cell group in the rat is characterized by neurones which contain both adrenaline and phenylethanolamine-N-methyltransferase, and usually also neuropeptide Y (NPY). The former two substances are lacking in Guinea pig brainstem and spinal cord. We have examined the distribution of NPY- and tyrosine hydroxylase-immunoreactivity in the ventrolateral medulla and thoracolumbar intermediate zone of Guinea pig, as well as the distribution of catecholamine-containing neurone somata and spinal terminals visualized after formaldehyde-glutaraldehyde fixation. The results are compared with comparable immunohistochemical data obtained from rats and rabbits. Catecholaminergic neurones in the Guinea pig with locations and terminations that correspond to those of the C1 cell group in rat and its analogue in the rabbit appear to consist of two subgroups, with only the more caudal group containing NPY. The more rostral group requires pretreatment with monoamine oxidase inhibitor to permit visualization of catecholamine fluorescence, a property previously though to be characteristic of adrenergic neurones. This observation raises the possibility that the catecholaminergic cell group in the C1 region of rabbits may not contain adrenaline either.

Inhibition of guinea pig lordosis behavior by the phenylethanolamine N-methyltransferase (PNMT) inhibitor SKF-64139: mediation by alpha noradrenergic receptors

Experiments were undertaken to determine whether the steroid-dependent lordosis response of female guinea pigs is under adrenergic control. In initial experiments, treatment with the centrally active phenylethanolomine N-methyltransferase (PNMT; the enzyme catalyzing methylation of norepinephrine to epinephrine) inhibitor SKF-64139 inhibited lordosis behavior induced by estradiol-17 beta benzoate plus progesterone. SKF-29661, a PNMT inhibitor that does not cross the blood-brain barrier, did not affect lordosis. However, no detectable epinephrine was found in brain or spinal cord of drug- or vehicle-treated guinea pigs. This suggests that epinephrine neuronal systems do not exist in the guinea pig CNS. In agreement with this idea, the inhibitory effects of SKF-64139 on lordosis were found to be primarily attributable to the blockade of alpha noradrenergic receptors rather than to PNMT inhibition. Two lines of evidence support this conclusion. First, using in vitro receptor binding techniques, SKF-64139 was found to have a relatively high affinity for alpha 1 and particularly alpha 2 receptors in guinea pig forebrain. Second, presumably through competitive inhibition of SKF-64139 binding to alpha receptors, treatment with clonidine (an alpha receptor agonist) overrode the inhibitory effects of SKF-64139 on lordosis. Taken together, these findings indicate the possible absence of epinephrine neuronal systems in guinea pig brain and reemphasize the importance of alpha receptors in regulating steroid-dependent lordosis behavior in this species.

PNMT-containing catecholaminergic neurons are not necessarily adrenergic

The intermediolateral cell column (IML) in the spinal cord is densely innervated by the phenylethanolamine-N-methyltransferase (PNMT)-containing neurons of the ventrolateral medulla (C1 cell group). The present study used a sensitive HPLC-EC assay for catecholamines to quantitate epinephrine levels in the region of the spinal cord containing the IML. In dissections of thoracic cord enriched in IML, as well as total thoracic cord, epinephrine levels were below the limit of sensitivity of the assay, indicating that epinephrine levels were less than 0.2 pg/mg tissue. In the region of the IML, epinephrine levels were less than 0.05% of the norepinephrine content. Thus, no epinephrine could be detected in the IML even though the IML contains a dense network of nerve terminals that stain immunohistochemically for PNMT and the other enzymes required for epinephrine biosynthesis. These results suggest that nerve terminals that contain all the enzymes required for epinephrine biosynthesis are not necessarily adrenergic.

Evidence for substance P, serotonin and oxytocin input to medullary catecholamine neurons with diencephalic projections

Using the retrograde transport of horseradish peroxidase (HRP) in combination with two-color immunoperoxidase staining, boutons stained with antisera to substance P (SP), serotonin (5HT) and oxytocin (OX) have been observed in contiguity with neurons in the rostral and caudal medulla that showed immunoreactivity for phenylethanolamine N-methyl transferase (PNMT) and tyrosine hydroxylase (TH), respectively, and which were backfilled with HRP injected into the diencephalon. The juxtaposition of these immunostained structures indicates that SP, 5HT and OX released from fibers in the medulla may affect the activity of adrenergic and noradrenergic medullary neurons that project to the diencephalon. Moreover, the presence of 5HT- and OX-immunoreactive processes in contiguity with medullary CA cells that send fibers to the diencephalon indicates that the raphe nuclei and the paraventricular nucleus of the hypothalamus can directly influence ascending pathways that are known to innervate the hypothalamus and appear to effect changes in vasopressin release.

Ultrastructural localization of phenylethanolamine N-methyltransferase-like immunoreactivity in the rat locus coeruleus

Adrenergic afferents from the rostral ventrolateral medulla are known to modulate the activity of noradrenergic neurons of the locus coeruleus (LC). The light and electron microscopic localization of a polyclonal antiserum directed against the adrenaline synthesizing enzyme, phenylethanolamine N-methyltransferase (PNMT) was used to determine the identity and targets of the adrenergic afferents to the LC of the rat brain. By light microscopy, varicose processes showing intense PNMT-like immunoreactivity (LI) were seen throughout the neuropil surrounding neuronal perikarya which in adjacent sections were shown to contain immunoreactivity for the noradrenaline synthesizing enzyme, dopamine-beta-hydroxylase. Electron microscopy confirmed that these labeled varicose processes were primarily axon terminals. Terminals containing PNMT-LI constituted 30% (141 out of 464) of all identifiable terminals within the LC. These terminals were 0.5-1.8 micron in diameter and contained many small, clear and from 2 to 10 larger dense-core vesicles. The targets of the terminals with PNMT-LI were principally unlabeled (i.e. non-PNMT-containing) perikarya and dendrites. The synaptic junctions on perikarya were rare and exclusively symmetric; whereas, those on proximal (large) dendrites were somewhat more numerous and included symmetric as well as asymmetric membrane specializations. However, the vast majority (85% from a total of 141) of the terminals with PNMT-LI formed asymmetric synaptic junctions on unlabeled distal (small) dendrites and dendritic spines. In rare instances, the PNMT-immunoreactive terminals also formed synaptic junctions with other similarly labeled terminals. These findings provide the first ultrastructural evidence that adrenergic terminals in the LC (1) are one of the more prevalent synaptic inputs to the principally noradrenergic neurons; (2) have both symmetric and asymmetric synaptic specializations conventionally associated with inhibition and excitation, respectively; and (3) may modulate other adrenergic terminals through presynaptic mechanisms. In addition to the varicose processes, light microscopy revealed diffuse PNMT-LI throughout the LC. The ultrastructural correlate of this labeling was seen as patches of peroxidase product within the cytoplasm of a few perikarya and dendrites and throughout the cytoplasm of astrocytes identified by their discrete bundles of microfilaments. The detection of PNMT-LI in cells that are not known to synthesize adrenaline is surprising and suggests either a functional diversity for PNMT or amino acid sequence homologies with related enzymes which are enriched in the LC.

Phenylethanolamine N-methyltransferase-containing neurons in the limbic system of the young rat

Fifteen years ago epinephrine cells were shown to be present in the medulla oblongata of the rat. These cell groups (C1 and C2) were thought to supply the epinephrine innervation in the rest of the central nervous system. In this study I demonstrate the presence of epinephrine-producing neurons in the forebrain of the young rat. Neurons that are immunopositive for phenylethanolamine N-methyltransferase (S-adenosyl-L-methionine:phenylethanolamine N-methyltransferase, EC 2.1.1.29) are present in the central nucleus of the amygdala as well as in the bed nucleus of the stria terminalis. Neurons in the same location are also immunopositive for tyrosine hydroxylase [tyrosine 3-monooxygenase; L-tyrosine, tetrahydrobiopterine:oxygen oxidoreductase (3-hydroxylating), EC 1.14.16.2]. The phenylethanolamine N-methyltransferase immunopositivity disappears by day 35, while a small amount of tyrosine hydroxylase-positive cells still can be found in the adult. In situ hybridization reveals tyrosine hydroxylase mRNA in the above nuclei in both young and adult animals. The number of the positive cells decreases in adulthood. RNA blot-hybridization analysis showed the presence of phenylethanolamine N-methyltransferase mRNA in the amygdala and the bed nucleus of the stria terminalis in the young and in the adult rat brain. Neurons that are immunopositive for phenylethanolamine N-methyltransferase are also present in the human amygdala.

Phenylethanolamine N-methyltransferase-immunoreactive terminals synapse on adrenal preganglionic neurons in the rat spinal cord

Adrenergic neurons in the C1 region in the ventrolateral medulla oblongata send descending axons into spinal cord which terminate in thoracic and upper lumbar segments, overlapping the distribution of sympathetic preganglionic neurons. The present study was undertaken to determine whether adrenergic fibers synapse directly on preganglionic neurons which innervate the adrenal medulla and to examine the ultrastructure of these fibers during development. The ultrastructure and synaptology of adrenergic axons in the intermediolateral nucleus of mid-thoracic spinal cord were studied in 7-, 9-, 24-, 30-, 60-, and 90-day-old rats using immunocytochemical staining for phenylethanolamine N-methyltransferase, the epinephrine-synthesizing enzyme. Phenylethanolamine N-methyltransferase-immunoreactivity was observed in the cytoplasm of unmyelinated axonal varicosities and intervaricose segments in the neuropil of intermediolateral nucleus. Phenylethanolamine N-methyltransferase-immunoreactive synaptic boutons were filled with spherical electron-lucent vesicles and occasional larger dense-core vesicles. These boutons were observed to form symmetrical synaptic contacts with dendritic processes at all ages examined. Asymmetrical synapses on dendrites were also observed in adult rats. Axosomatic synaptic contacts were frequently observed in immature rats, but were never observed in adult rats. To determine whether adrenergic axons synapse on preganglionic neurons which project to the adrenal medulla, adrenal preganglionic neurons were retrogradely labeled with horseradish peroxidase and adrenergic axons were stained for phenylethanolamine N-methyltransferase-immunoreactivity. In young rats, phenylethanolamine N-methyltransferase-immunoreactive boutons were observed to form symmetrical axosomatic and axodendritic synaptic contacts with adrenal preganglionic neurons in intermediolateral nucleus. These contacts had already formed by postnatal day 7, the youngest age studied. In contrast, it was not possible to verify that adrenal preganglionic neurons receive adrenergic innervation in adult rats, since phenylethanolamine N-methyltransferase-immunoreactive boutons were only observed in contact with small diameter dendrites that were not retrogradely labeled by horseradish peroxidase. These studies demonstrate that adrenal preganglionic neurons receive adrenergic synapses prior to the first postnatal week. The initial synapses which form on preganglionic somata and proximal dendrites appear to reorganize late in development. It is suggested that these become more distally located as the dendritic tree matures. More generally, these observations suggest that adrenergic bulbospinal neurons are involved in central regulation of adrenal development and function.

Activation in young rats induced by LY134046, an inhibitor of phenylethanolamine N-methyltransferase

LY134046, a potent, selective inhibitor of rat brain phenylethanolamine N-methyltransferase, was shown to increase activity in 18- and 19-day-old rats. The effects on day 25 were different, with LY134046 causing a decrease in activity. The effects of yohimbine, a selective antagonist of the alpha-2 adrenergic receptor, were markedly different from LY134046, causing a decrease in activity on day 19. These data suggest that epinephrine synthesis may play an inhibitory role in the regulation of activity in young rats.

Adrenergic neurons in sheep brain demonstrated by immunohistochemistry with antibodies to phenylethanolamine N-methyltransferase (PNMT) and dopamine-beta-hydroxylase (DBH): absence of the C1 cell group in the sheep brain

Using immunohistochemistry with specific antisera against dopamine-beta-hydroxylase and phenylethanolamine N-methyltransferase, we present the first description of the adrenergic structures of the sheep medulla oblongata. Dopamine-beta-hydroxylase-immunoreactive perikarya in the sheep brain are localized as described in the rodents (A1 and A2 groups) but their distribution is characterized by only one phenylethanolamine N-methyltransferase immunoreactive cell body group, found in the nucleus tractus solitarius. This group corresponds to the C2 group previously described in the rat, but neither group C1 nor group C3 are found in the sheep with our method. Compared with rodents or primates, this animal presents a different pattern of central adrenergic innervation and could be an alternative model to study the central role of adrenaline in various physiological functions as different as swallowing or reproduction.

Tyrosine hydroxylase-like and dopamine beta-hydroxylase-like immunoreactivity in the gustatory zone of the nucleus of the solitary tract in the hamster: light- and electron-microscopic studies

A quantitative electron-microscopic analysis has been conducted on the neurons within the gustatory zone of the nucleus of the solitary tract of the hamster. The most common group of neurons within the gustatory zone contains both large (X1) and small (X3) members that possess deeply invaginated nuclear profiles. These neurons have somal areas that average 113 micron2 (range 34-281 micron2) and a value of somal area/nuclear area that averages 2.2. Other large and small neurons that have non-invaginated nuclear profiles are also observed. The larger (X2) neurons average 151 micron2 (range 49-487 micron2) and have much cytoplasm and associated membranous organelles that is reflected in a mean value of somal area/nuclear area of 2.6. Members of the X2 group are the largest neurons in the gustatory zone. The smaller (X4) group contains the smallest neurons in the gustatory zone of the nucleus of the solitary tract, averages 50 micron2 (range 16-103 micron2), shows almost no perinuclear cytoplasm and has a mean value of somal area/nuclear area of only 1.5. These findings are consistent with and expand upon the results of similar studies at the light-microscopic level. This grouping has been used to explore the association of tyrosine hydroxylase-like and dopamine beta-hydroxylase-like immunoreactivities with specific populations of neurons that are known to be distributed across the various levels of the gustatory zone. At the light-microscopic level, numerous well-defined and intensely labelled tyrosine hydroxylase-like immunoreactive somata of various morphologies and sizes are observed. Quantification at the electron-microscopic level indicates that 10-15% of the neurons encountered in the dorsal and intermediate levels of the gustatory zone are immunoreactive. The ventral level of the gustatory zone contains few immunoreactive neurons. Tyrosine hydroxylase-like immunoreactive neurons possess either non-invaginated or invaginated nuclear profiles and their somal areas average 106 and 142 micron2, respectively. On the bases of size and ultrastructural features, these immunoreactive somata are assigned to the two groups (X1 and X2) of large neurons within the gustatory portion of the nucleus of the solitary tract. In general, small neurons are not immunoreactive. The distribution of dopamine beta-hydroxylase-like immunoreactivity has also been examined in adjacent sections in order to reveal the presence of any putative noradrenergic neurons in the gustatory zone.(ABSTRACT TRUNCATED AT 400 WORDS)

Immunohistochemical study of the telencephalon of the spiny dogfish, Squalus acanthias

The paucity of experimental data and the differences in telencephalic organization between sharks and other jawed vertebrates have complicated telencephalic comparisons. The distribution of neuropeptides has been extremely useful in recognizing and comparing major subdivisions of the telencephalon among vertebrates. Immunohistochemical techniques were therefore used to study the distribution of substance P (SP), leucin-enkephalin (LENK), and serotonin (5HT), as well as tyrosine hydroxylase (TH), an indicator of catecholamines, in the telencephalon of the spiny dogfish. The distribution of SP and LENK provides a clear distinction between pallial and subpallial portions of the telencephalon. Two regions of the ventrolateral telencephalon, area superficialis basalis and area periventricularis ventrolateralis, exhibit histochemical similarities to the pallidal and striatal subdivisions, respectively, of the basal ganglia in amniotes. Lower densities of LENK+ and SP+ perikarya and fibers occur in the medial pallium and the pars centralis of the dorsal pallium. Similar histochemical traits characterize the sensory thalamorecipient telencephalic structures in amniotes. The lateral pallium in dogfishes is distinguished by the presence of large numbers of TH+ neurons with radially oriented processes. The presence of these distinctive cells also in the medial wall of the rostral telencephalon suggests that the lateral pallium has a medial extension that is situated ventral to the medial pallium. Neurons containing TH were widely distributed in the telencephalon of spiny dogfish and were particularly abundant in the dorsal pallium, olfactory pallium, and area superficialis basalis. It is currently unclear whether these TH+ telencephalic neurons are, in fact, catecholaminergic or merely contain a TH-like substance unrelated to catecholamine synthesis.

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.

Ontogeny of adrenergic fibers in rat spinal cord in relationship to adrenal preganglionic neurons

Adrenergic neurons in the C1 cell group in the rostral ventrolateral medulla oblongata contain epinephrine, as well as its biosynthetic enzyme, phenylethanolamine N-methyltransferase (PNMT). These neurons send axons to regions of the central nervous system known to regulate autonomic function, including the sympathetic preganglionic nuclei of thoracic and upper lumbar spinal cord. Previous studies have shown that PNMT is expressed in neurons located in the medulla oblongata on embryonic day 14; however, the development of the projections from these cells has not been studied. With the aid of high-performance liquid chromatography (HPLC) to determine levels of catecholamines and immunocytochemistry to demonstrate PNMT, the ontogeny of the adrenergic bulbospinal pathway in the embryonic, postnatal, and adult rat has been studied. In addition, the relationship between PNMT-immunoreactive (IR) fibers and retrogradely labeled sympathetic preganglionic neurons projecting to adrenal medulla are described. PNMT-IR fibers were first observed in the caudal medulla oblongata and lateral funiculus of spinal cord on gestational day 15(E15). On E16, PNMT-IR fibers in the thoracic spinal cord were observed in the intermediate gray matter at the level of the lateral horn. Epinephrine was measureable in spinal cord on E20. Both the density of PNMT-IR fibers and the levels of epinephrine increased to a maximum during the second postnatal week and then declined to adult levels. These observations suggest that a period of adrenergic hyperinnervation of spinal sympathetic nuclei occurs during the neonatal period. PNMT-IR terminals in spinal cord were observed, primarily, although not exclusively, in sympathetic nuclei of thoracic cord and parasympathetic nuclei of upper sacral cord. Adrenergic fibers in the intermediolateral nucleus (IML) and the central autonomic nucleus (CAN) dorsal to the central canal were particularly dense during the second postnatal week in both midthoracic and upper sacral segments. In the neonate, a "ladder-like" pattern of PNMT-IR fiber staining was observed which represented transverse fiber bundles connecting IML with CAN and extensive longitundinal fiber bundles along the border of the funiculus in IML. At all spinal levels, adrenergic fibers were also observed adjacent to the ependyma dorsal or lateral to the central canal. The relationship between adrenal preganglionic neurons and PNMT-IR fibers in IML was examined on postnatal days 4, 15, and 60. With retrograde labeling from adrenal medulla, it was demonstrated that PNMT-IR fibers are associated with adrenal preganglionic neurons throughout postnatal development.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

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.

Morphometrical and microdensitometrical studies on phenylethanolamine-N-methyltransferase- and neuropeptide Y-immunoreactive neurons in the rostral medulla oblongata of the adult and old male rat

In the present paper the neuronal systems of the medulla oblongata containing phenylethanolamine-N-methyltransferase- and neuropeptide Y-like immunoreactivity have been characterized in adult (3-month-old) and old (24-month-old) male rats. The phenylethanolamine-N-methyltransferase and neuropeptide Y-immunoreactive neurons have been visualized by means of immunocytochemistry (peroxidase-antiperoxidase technique) and analysed in a quantitative fashion by means of morphometrical (phenylethanolamine-N-methyltransferase- and neuropeptide Y-immunoreactive cell groups) and microdensitometrical (phenylethanolamine-N-methyltransferase-immunoreactive cell groups) approaches developed on the IBAS II image analyser (Zeiss-Kontron). During aging there is (a) a reduction in the area covered by the phenylethanolamine-N-methyltransferase-immunoreactive neuropil for both the C1 and C2 adrenaline cell groups; (b) a reduction in the area covered by the phenylethanolamine-N-methyltransferase-immunoreactive cell bodies, which is highly significant only for the C2 cell group; (c) a decrease in the area covered by the phenylethanolamine-N-methyltransferase-positive cell cluster for both C1 and C2 cell groups; (d) a decrease in the degree of phenylethanolamine-N-methyltransferase immunoreactivity present in the C1 and C2 cell groups; (e) a decay of neuropeptide Y immunoreactivity in the C1 and C2 groups, while the C3 group is unaffected by aging as evaluated by number of phenylethanolamine-N-methyltransferase- and neuropeptide Y-immunoreactive cell body profiles. These results indicate heterogeneities in the responses of the adrenaline-neuropeptide Y cell groups to the aging process. The possible functional consequences of aging-induced changes in the cardiovascular adrenergic neurons are discussed, especially in relation to development of hypertension.

Distribution of catecholaminergic neuronal systems in the canine medulla oblongata and pons

The distribution of catecholamine-containing neurons, fibers, and varicosities in the brainstem of both adult and juvenile dogs was mapped in detail with glyoxylic acid histofluorescence. Four separate groups of catecholamine-fluorescent neurons were identified within the canine medulla and pons in locations comparable to the A1, A2, A5, and A6 regions reported in other species. However, aspects of the pattern and density of the catecholaminergic neuronal systems appeared to be unique to the dog. The A1 neurons of the caudal ventrolateral medulla were much more scattered than in rats or rabbits, but relatively similar to cats. In the A2 region of the dorsomedial medulla, catecholaminergic cells and fibers were uniquely distributed compared to other species: fluorescent neurons were scattered only within the dorsal motor nucleus of the vagus, and a distinctive pattern of fibers and varicosities outlined the nucleus of the solitary tract and dorsal motor nucleus of the vagus. The A5 neurons of the rostral ventrolateral medulla appeared at the rostral limit of the A1 region. Fluorescent A5 cells were more sparse than in rats or primates, and were patterned similarly to cats and rabbits. The canine A6 region contained the most extensive and dense grouping of catecholamine neurons and was similar in pattern to the rabbits but less extensive than that seen in cats or primates. An ascending catecholaminergic fiber pathway was traced through the central tegmental field of the canine medulla and pons, with features similar to the primate. The present study provides the first description of the catecholaminergic neuronal systems of the canine medulla.

Anatomical specificity of noradrenergic inputs to the paraventricular and supraoptic nuclei of the rat hypothalamus

The distribution of neural inputs to the paraventricular (PVH) and supraoptic (SO) nuclei from the regions of the A1, the A2, and the A6 (locus coeruleus) noradrenergic cell groups was investigated by using a plant lectin, Phaseolus vulgaris leucoagglutinin (PHA-L), as an anterogradely transported tracer. An immunofluorescence double-labeling procedure was used to determine the extent to which individual anterogradely labeled fibers and terminals in the PVH and the SO also displayed immunoreactive dopamine-beta-hydroxylase (DBH), a marker for catecholaminergic neurons. The results may be summarized as follows: (1) Projections from the A1 region were found primarily, and in some experiments almost exclusively, in those parts of the magnocellular division of the PVH and the SO known to contain vasopressinergic neurons. (2) Projections from the A2 region were distributed primarily throughout the parvicellular division of the PVH and were most dense in the dorsal medial part, a region known to contain a prominent population of corticotropin-releasing factor (CRF)-immunoreactive neurons. In addition, a less-dense projection to the magnocellular division of the PVH and to the SO was consistently found. (3) Fibers originating from the locus coeruleus were distributed almost exclusively to the parvicellular division of the PVH, with the most prominent input localized to the periventricular zone, a part of the PVH known to contain dopamine-, somatostatin-, and thyrotropin-releasing-hormone-containing neurons. We found no evidence for a projection from A6 to the SO. (4) The majority of fibers originating from the A1, the A2 or the A6 regions contained DBH immunoreactivity, although an appreciable number did not. These results suggest that each of the three brainstem noradrenergic cell groups that contribute to the innervation of the PVH and/or the SO is in a position to modulate the activity of anatomically and chemically distinct groups of neurosecretory neurons.

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.

Catecholaminergic neurons in the ventrolateral medulla and nucleus of the solitary tract in the human

Catecholaminergic neurons in the ventrolateral medulla (VLM) and nucleus of the solitary tract (NTS) are important because of their presumed roles in autonomic regulation, including the tonic and reflex control of arterial pressure, neuroendocrine functions, and the chemosensitivity associated with the ventral medullary surface. However, little is known about the connections of these neurons in the human brain. As a first step in analyzing the functional biochemical anatomy of catecholamine neurons in the human, we used antisera against tyrosine hydroxylase (TH) and phenylethanolamine N-methyltransferase (PNMT) to localize medullary catecholamine-containing neurons and processes in the VLM and the NTS. Cells staining for TH were located throughout the VLM. Most cells staining for TH and PNMT, which are therefore adrenergic, occurred in an area of the VLM probably corresponding to the rostroventrolateral reticular nucleus. Axons of TH-immunoreactive neurons in the VLM projected (1) dorsally, in a series of parallel transtegmental trajectories, toward the dorsomedial reticular formation, the NTS, and vagal motor nucleus, (2) longitudinally, through the central tegmental field, as fascicles running parallel to the neuraxis, (3) ventrolaterally toward the ventral surface (VS) of the rostral VLM where they appeared to terminate, and (4) medially into the raphe, where they arborized. Similar systems of fibers were labeled for PNMT; the longitudinal bundles of PNMT-labeled axons were limited to the principal tegmental bundle and concentrated dorsally. Fibers containing PNMT were also identified in the medullary raphe, on the medullary ventral surface, and contacting intraparenchymal blood vessels. In the NTS, neurons exhibited immunoreactivity to both TH and PNMT: Four principal subgroups of TH-immunoreactive neurons were seen: a ventral, an intermediate, a medial, and a dorsal group. Perikarya containing PNMT were restricted to the dorsolateral aspect of the NTS. Processes containing TH and PNMT immunoreactivity were identified in the medial and dorsolateral NTS; others appeared to project between the NTS and the VLM and within the solitary tract. The presence of catecholaminergic fibers of the VLM interconnecting with the NTS, raphe, intraparenchymal microvessels, VS, and possibly the spinal cord suggests that the autonomic and chemoreceptor functions attributed to these neurons also may apply to the human.

Direct catecholaminergic projection from nucleus tractus solitarii to supraoptic nucleus

To determine whether the supraoptic nucleus (SON) receives a direct projection from catecholamine cells of the nucleus tractus solitarii (NTS), retrograde transport of rhodamine-tagged latex microspheres was combined with a procedure for the fluorescence histochemical visualization of catecholamines. SON tracer injections, made via transpharyngeal approach, retrogradely labelled cells at all levels of NTS, although the majority were located caudal to obex with an ipsilateral predominance. Approximately half of these cells were also identified as catecholaminergic; the relatively caudal level in the dorsomedial medulla of most of these cells suggests that they probably correspond to the A2 catecholamine cell group.

Involvement of central alpha- and beta-adrenoceptors in the pressor response to electrical stimulation of the rostral ventrolateral medulla in rats

1. Electrical stimulation of the C1 area of the rostral ventrolateral medulla in rats elicits an increase in mean arterial pressure (MAP). 2. This increase in MAP is attenuated by intra-hypothalamic and intracisternal administration of the non-selective beta-adrenoceptor antagonist (+/-)-propranolol and the beta 2-selective antagonist ICI 118551. 3. The selective beta 1-antagonist atenolol and (+)-propranolol, which is inactive on beta-adrenoceptors, did not alter the increase in MAP produced by stimulation of the C1 area. 4. The alpha 2-adrenoceptor antagonist idazoxan enhanced the effects of C1 stimulation on MAP when administered either into the posterior hypothalamus or intracisternally. 5. The results indicate that beta 2- and alpha 2-receptors both have a role in the mediation of the rise in MAP during stimulation of the C1 area and that the receptors involved are located both within the hypothalamus and the spinal cord.

Computer-generated rotation analyses reveal a key three-dimensional feature of the nucleus of the solitary tract

The dendritic processes of neurons within the nucleus of the solitary tract are oriented in the horizontal plane and often extend unusually long distances along the long axis of the brainstem. This preferred orientation is not predictable from a knowledge of the cytoarchitectonic organization of their somata within the various subnuclei of the nucleus of the solitary tract. Incoming peripheral afferent fibers, their collaterals and end-terminal ramifications are also oriented in the horizontal plane and are in alignment with the dendrites of second order neurons. These features enable single neurons to be influenced by a variety of widely distributed inputs that are related to vital autonomic functions and ingestional behavior.

Bulbospinal thyrotropin-releasing hormone projections to the intermediolateral cell column: a double fluorescence immunohistochemical-retrograde tracing study in the rat

Whereas the neurochemistry of the peripheral autonomic nervous system has been well characterized, less is known concerning the neurotransmitters utilized by medullary projections onto sympathetic preganglionic neurons residing in the thoracolumbar spinal intermediolateral cell column. Retrograde transport of rhodamine-labeled fluorescent microspheres following discrete microinjection into the thoracic intermediolateral cell column was combined with immunohistochemistry to determine neuroanatomic location of thyrotropin-releasing hormone-immunoreactive neurons which project to the intermediolateral cell column in the rat. The ventromedial group of raphe nuclei including the nucleus raphe pallidus, obscurus, and magnus possessed the greatest number of medullary thyrotropin-releasing hormone-immunoreactive neurons which also contained rhodamine-labeled microspheres. High numbers of intermediolateral cell column-projecting thyrotropin-releasing hormone-immunoreactive neurons were also observed in nucleus reticularis paragigantocellularis lateralis and magnocellularis, the lateral reticular nucleus, and the superficial ventral (arcuate) medullary surface. Despite the observations that nucleus reticularis gigantocellularis, paramedianus, and ventralis pars beta project to the intermediolateral cell column, double-labeled cells were not observed in these nuclei. Furthermore, whereas the nucleus reticularis magnocellularis and gigantocellularis, and the lateral reticular nucleus displayed strong ipsilateral predominance in projecting to the intermediolateral cell column, other medullary reticular and raphe nuclei displayed bilateral projections. The present findings support the hypothesis that thyrotropin-releasing hormone-containing neurons in the ventral medulla project to the intermediolateral cell column, and may influence sympathetic preganglionic neurons.

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)

Immunohistochemistry of tyrosine hydroxylase and phenylethanolamine N-methyltransferase in the human brain stem: description of adrenergic perikarya and characterization of longitudinal catecholaminergic pathways

Using immunocytochemical method in conjunction with antibodies to tyrosine hydroxylase and phenylethanolamine N-methyltransferase, catecholaminergic cell groups and axon pathways are mapped in the human hind brain. Adrenergic perikarya are located mainly in the rostral medulla, as in lower animals, and contribute a subset of axons to the main longitudinal catecholaminergic bundle which runs through the medulla oblongata, pons and midbrain such as the dorsal part of the central nucleus of the medulla oblongata, the parvocellular reticular formation ventromedial to the facial nerve and ventrolateral to the locus coeruleus. Adrenergic terminals are present in the locus coeruleus and other medullary and pontine structures. The locus coeruleus contains only tyrosine hydroxylase-immunoreactive cells and appears to be the source of a discrete dorsal catecholaminergic bundle which runs through the central tegmental field just ventrolateral to the periaqueductal gray of the rostral pons and mesencephalon and which does not contain adrenergic axons. A ventral catecholaminergic bundle arising in the medullary cells does contain a subset of adrenergic axons in the mesencephalic tegmental field. These two longitudinal axon bundles run near each other in the mesencephalic reticular formation. Additional descriptions are provided of catecholaminergic axons near the dorsal and ventral surface of the human medulla.

Brainstem mechanisms in the modulation of the sympathetic baroreflex by piperoxan

Piperoxan (50-100 micrograms/kg) injected into the cisterna magna of anaesthetized dogs increased blood pressure, heart rate and resting rate of sympathetic nerve discharge. The baroreflex curve was shifted to the right with an elevation of the upper plateau (when blood pressure was lowered below resting values, renal sympathetic nerve activity rose to an upper plateau) and with no change in baroreflex sensitivity. Catecholamine depletion, produced by reserpine and alpha-methyl-p-tyrosine, did not change the effects of piperoxan on resting sympathetic nerve activity and on the baroreflex curve. Piperoxan (50 micrograms/kg i.c.) enhanced the rate of renal sympathetic nerve discharge in baroreceptor-denervated dogs. Piperoxan (5 micrograms) injected bilaterally into the nucleus tractus solitarii (NTS) increased blood pressure and resting sympathetic nerve activity with a shift of the sympathetic baroreflex curve to the right and no change in baroreflex sensitivity. Piperoxan (5 micrograms) injected bilaterally into the ventrolateral pressor area did not change blood pressure or the rate of sympathetic discharge. However, the baroreflex curve was shifted to the right with an elevation of the upper plateau level and the baroreflex sensitivity was increased. The present findings suggest that tonically active alpha 2-adrenergic mechanisms located within the NTS regulate resting and reflex sympathetic activity. An alpha 2-adrenergic mechanism in the rostral ventrolateral medulla modulates reflex sympathetic activity but has no influence on resting activity.

Distributions of tyrosine hydroxylase-, dopamine-beta-hydroxylase-, and phenylethanolamine-N-methyltransferase-immunoreactive neurons in the brain of the hamster (Mesocricetus auratus)

Antibodies to the catecholamine synthetic enzymes tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH), and phenylethanolamine-N-methyltransferase (PNMT) were used in an immunohistochemical analysis of the brain of the golden hamster. The distributions and morphological characteristics of neurons displaying immunoreactivity to these enzymes were examined in sets of adjacent sections. Various novel groups of TH-immunoreactive neurons were found. A distinct feature observed in the hamster brain was the presence of a population of magnocellular multipolar neurons in the basal forebrain which displayed intense TH immunoreactivity. These cells were found predominantly in the vertical and horizontal limbs of the nucleus of the diagonal band of Broca and in the lateral preoptic area. Many small TH-positive cells were also found scattered in the deeper layers of the cortex in the hamster. The pericentral divisions of the inferior colliculus contained a large number of TH-immunoreactive neurons, and a few small bipolar cells in the lateral superior olive were also stained. A major cell group was found in the lateral parabrachial nucleus at the level of the locus ceruleus that displayed TH but not DBH immunoreactivity and was obviously separate from the TH- and DBH-positive cells of the locus ceruleus. Additional TH-positive cell groups were found along the seventh nerve, within the medial longitudinal fasiculus, in the nucleus raphe pallidus, and in the pars caudalis of the spinal trigeminal nucleus. The various catecholamine cell groups described by many people in the rat by use of histochemical and immunohistochemical techniques were also present in the hamster brain. These included the noradrenergic, TH- and DBH-immunoreactive cell groups of the pons and medulla. The hamster also displayed groups of medullary neurons displaying immunoreactivity to TH, DBH, and PNMT. These appeared similar in distribution and morphology to the adrenaline cell groups described in the rat. TH-immunoreactive cell groups in the olfactory bulb, hypothalamus, substantia nigra, and ventral tegmental area of the hamster appeared to correspond to the dopaminergic cells groups described in the rat and other species. In addition, as in the rat and cat, numerous TH-positive cells were found in the dorsal motor nucleus of the vagus, the nucleus of the solitary tract, and the area postrema. These observations suggest that catechols may be present in neurons in the cortex, basal forebrain, auditory brainstem, and the parabrachial nucleus of the hamster. These studies also emphasize the need for caution in making generalizations regarding transmitter distributions across species.

Catecholamine-synthesizing neuronal projections to the nucleus tractus solitarii of the rat

The objective of the present study was to determine the location of the neurons that give rise to catecholamine-containing terminals in the nucleus tractus solitarii. This was done by injecting rhodamine-filled latex microspheres into the nucleus tractus solitarii of rats to retrogradely label neuronal cell bodies and by processing sections from the brains of these animals to determine if the labelled neurons were immunoreactive for the catecholamine-synthesizing enzymes, dopamine-beta-hydroxylase (DBH) and phenylethanolamine-N-methyl transferase (PNMT). Approximately 60% of the DBH-immunoreactive neurons that projected to the nucleus tractus solitarii belonged to the A1/C1 cell group, while an additional 20% belonged to the A5 cell group. Thus, these two ventrolateral rhombencephalic cell groups accounted for nearly 80% of the total number of rhodamine-bead-labelled DBH-immunoreactive neurons in this series of experiments. Only a small number of DBH-immunoreactive neurons of the A2/C2 cell group contained rhodamine-filled latex microspheres. Rarely, DBH-immunoreactive neurons in the locus coeruleus and the nucleus subcoeruleus were found to project to the nucleus tractus solitarii. The majority of the PNMT-immunoreactive neurons that projected to the nucleus tractus solitarii belonged to the C1 cell group. Only small numbers of PNMT-immunoreactive neurons of the C2 and C3 groups were found to contain rhodamine-filled latex microspheres. It is concluded that neurons in the ventrolateral medulla and pons, some of which presumably utilize norepinephrine and/or epinephrine as a transmitter, could regulate autonomic function via direct projections to the nucleus tractus solitarii.

Brainstem afferents to the magnocellular basal forebrain studied by axonal transport, immunohistochemistry, and electrophysiology in the rat

Brainstem afferents to the magnocellular basal forebrain were studied by using tract tracing, immunohistochemistry and extracellular recordings in the rat. WGA-HRP injections into the horizontal limb of the diagonal band (HDB) and the magnocellular preoptic area (MgPA) retrogradely labelled many neurons in the pedunculopontine and laterodorsal tegmental nuclei, dorsal raphe nucleus, and ventral tegmental area. Areas with moderate numbers of retrogradely labelled neurons included the median raphe nucleus, and area lateral to the medial longitudinal fasciculus in the pons, the locus ceruleus, and the medial parabrachial nucleus. A few labelled neurons were seen in the substantia nigra pars compacta, mesencephalic and pontine reticular formation, a midline area in the pontine central gray, lateral parabrachial nucleus, raphe magnus, prepositus hypoglossal nucleus, nucleus of the solitary tract, and ventrolateral medulla. A similar but not identical distribution of labelled neurons was seen following WGA-HRP injections into the nucleus basalis magnocellularis. The possible neurotransmitter content of some of these afferents to the HDB/MgPA was examined by combining retrograde Fluoro-Gold labelling and immunofluorescence. In the mesopontine tegmentum, many retrogradely labelled neurons were immunoreactive for choline acetyltransferase. In the dorsal raphe nucleus, some retrogradely labelled neurons were positive for serotonin and some for tyrosine hydroxylase (TH); however, the majority of retrogradely labelled neurons in this region were not immunoreactive for either marker. The ventral tegmental area, substantia nigra pars compacta, and locus ceruleus contained retrogradely labelled neurons which were also immunoreactive for TH. Of the retrogradely labelled neurons occasionally observed in the nucleus of the solitary tract, prepositus hypoglossal nucleus, and ventrolateral medulla, some were immunoreactive for either TH or phenylethanolamine-N-methyltransferase. To characterize functionally some of these brainstem afferents, extracellular recordings were made from antidromically identified cortically projecting neurons, mostly located in the HDB and MgPA. In agreement with most previous studies, about half (48%) of these neurons were spontaneously active. Electrical stimulation in the vicinity of the pedunculopontine tegmental and dorsal raphe nuclei elicited either excitatory or inhibitory responses in 21% (13/62) of the cortically projecting neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Co-localization of neurotensin- and cholecystokinin-like immunoreactivities in catecholamine neurons in the rat dorsomedial medulla

Co-localization of neurotensin and cholecystokinin in tyrosine hydroxylase-containing neurons in the nucleus tractus solitarius of the rat was demonstrated by immunocytochemistry with fluorescent double-staining combined with the peroxidase-antiperoxidase method. Co-localization of neurotensin/tyrosine hydroxylase or cholecystokinin/tyrosine hydroxylase was consistently found in small neurons in the region dorsomedial to the tractus solitarius at the level of the area postrema with high percentages of co-existence: 91.0% tyrosine hydroxylase-immunoreactive neurons contained neurotensin and 91.1% cholecystokinin, suggesting that they represent the same neurons. Accordingly, co-localization of neurotensin and cholecystokinin was assessed on tyrosine hydroxylase-containing neurons bisected into two adjacent sections, and then identified in a certain number of the catecholamine neurons in this region. Furthermore these catecholamine neurons exhibited immunoreactivity for an adrenaline-synthesizing enzyme, phenylethanolamine N-methyltransferase. It was concluded that catecholamine, in particular adrenaline, neurons, characterized by co-localization of neurotensin and cholecystokinin, established a distinct subpopulation in the catecholaminergic system in the dorsomedial medulla of the rat.

Glucocorticoid effects on phenylethanolamine N-methyltransferase (PNMT) in explants of embryonic rat medulla oblongata

Although glucocorticoid hormones have important roles in the development of neurotransmitter systems in cells derived from the neural crest, it is not known whether they have parallel effects on neuronal development in the brain. To address this issue, we have established an in vitro system of fetal medulla oblongata (MO) to follow development of the epinephrine-synthesizing enzyme, phenylethanolamine N-methyltransferase (PNMT). Embryonic MO was explanted from E13 or E18 embryos and maintained for up to 3 weeks. Successful culture of adrenergic neurons was possible only in explants taken from young embryos, since E18 explants failed to develop. In E13 explants, immunoreactivity to both PNMT and tyrosine hydroxylase, the rate limiting enzyme in catecholamine synthesis, was observed. PNMT catalytic activity which was barely detectable at the time of explanation increased markedly during the first week in vitro. To study the effects of glucocorticoids on PNMT development in central neurons, MO explants were grown in glucocorticoid deficient medium in which rat serum from adrenalectomized rats was substituted for human placental serum. Addition of natural glucocorticoids, cortisol or corticosterone, or the mineralcorticoid, deoxycorticosterone, during the third culture week had no effect on PNMT activity. Dexamethasone (DEX), a synthetic glucocorticoid, also had no effect on PNMT during the first or second weeks in culture. However, addition of DEX during the third culture week resulted in a doubling of PNMT activity. However, attempts to block the DEX effect during the third week or to block the increase in PNMT activity during the first week in control cultures with the glucocorticoid receptor antagonist, dexamethasone 21-mesylate, were unsuccessful. These results suggest that PNMT in central neurons does not require glucocorticoids for ontogeny during the embryonic period. This is in contrast to PNMT in adrenal medulla which requires glucocorticoids for normal development during both the embryonic and postnatal periods. More generally, these studies suggest that development of the same neurotransmitter phenotype in brain and periphery may be differentially regulated.

Lack of selectivity between the uptake of [3H]adrenaline and [3H]noradrenaline into rat hypothalamic slices

The uptake of [3H]adrenaline and [3H]noradrenaline into rat hypothalamic slices was compared for determination of whether adrenaline uptake was independent of uptake into noradrenergic neurones. Kinetic analysis revealed a similar high-affinity uptake process for both adrenaline and noradrenaline, with Km and Vmax values within similar ranges. These uptakes were inhibited by desipramine and maprotiline in a dose-dependent manner, but the selective dopamine and 5-hydroxytryptamine uptake inhibitors benztropine and fluoxetine, respectively, were without effect. Competition for uptake sites by unlabelled adrenaline with [3H]adrenaline and [3H]-noradrenaline and by unlabelled noradrenaline with [3H]-adrenaline and [3H]noradrenaline was very similar. Lesioning of the major adrenaline-containing cell group (C1 cell group) decreased the hypothalamic adrenaline concentration but had no effect on hypothalamic [3H]adrenaline or [3H]noradrenaline uptake. The results suggest that exogenous adrenaline is largely taken up by high-affinity sites on noradrenergic nerve terminals.