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

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

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

Organization of galanin-immunoreactive inputs to the paraventricular nucleus with special reference to their relationship to catecholaminergic afferents

Immunohistochemical and axonal transport techniques were used to characterize the origin and distribution of galanin-immunoreactive inputs to the paraventricular (PVH) and supraoptic (SO) nuclei of the hypothalamus in the rat. In the parvicellular division of the PVH, the most prominent inputs were confined to the anterior and periventricular parts of the nucleus rostrally and the dorsal and ventral medial subdivisions caudally; the galaninergic inputs to the magnocellular division of PVH and SO were very sparse and were preferentially distributed to regions containing predominantly oxytocinergic neurons. A combined retrograde transport-immunohistochemical method was employed to identify sources of these projections. Galanin immunoreactivity was found to coexist with dopamine-beta-hydroxylase (DBH) immunoreactivity in subsets of retrogradely labeled neurons of the A1 and A6 (locus coeruleus) catecholamine cell groups; no evidence was adduced for the presence of galanin in adrenergic (i.e., phenylethanolamine-N-methyltransferase-positive) neurons that project to the PVH. Apart from minor contributions from the mesencephalic raphe nuclei, no other brainstem cell groups contributed to the galaninergic innervation of the PVH. In the forebrain, the most prominent grouping of doubly labeled cells was centered in the rostral part of the dorsomedial nucleus of the hypothalamus (DMH), though significant numbers were also found in the lateral hypothalamic area, the arcuate nucleus, and the medial preoptic area. In experiments designed to define the subnuclear specificity of some galanin-containing inputs to the PVH, iontophoretic deposits of the anterogradely transported plant lectin, Phaseolus vulgaris-leucoagglutinin (PHA-L), were placed in the A1 and A6 cell groups and in the DMH. Sections through the PVH were prepared so as to allow colocalization of anterogradely transported PHA-L and galanin immunoreactivity in individual fibers and varicosities. Consistent with the retrograde transport data, the greatest degree of galanin-PHA-L correspondence was seen after lectin deposits in the DMH, and over 80% of the doubly labeled varicosities were confined to the anterior, periventricular, and medial parvicellular subdivisions of the nucleus. The galanin-containing projection from the locus coeruleus was most circumscribed, with the vast majority of doubly labeled varicosities confined to the periventricular and adjoining aspects of the anterior and medial parvicellular subdivisions.(ABSTRACT TRUNCATED AT 400 WORDS)

Localization of immunoreactive tyrosine hydroxylase in the goldfish brain

This report describes the distribution of tyrosine hydroxylase immunoreactive (TH-ir) structures in the brain of the goldfish (Carassius auratus). The localization of TH-ir cell groups revealed by immunocytochemical techniques is largely in accordance with catecholamine distribution previously reported in teleosts by using monoamine fluorescence; however, in the telencephalon and diencephalon, several new cell groups are elucidated. In the telencephalon, TH-ir cell bodies are observed in the olfactory bulb, area ventralis telencephali, and the central zone of the area dorsalis telencephali. TH-ir fibers and terminals are moderately dense throughout the telencephalon except for a sparse innervation of the area dorsalis, pars medialis. Immunostained cells are present in the suprachiasmatic nucleus and magnocellular and parvicellular components of the preoptic nucleus. Immunoreactive fibers from preoptic cells can be traced caudally in two main tracts to the infundibulum. Dense immunoreactivity around cells in the pituitary provides anatomical support for catecholamine involvement in the neuroendocrine axis probably via preopticohypophysial connections. At middiencephalic levels, immunoreactive cells are present in the ventral thalamus, nucleus pretectalis periventricularis, pars ventralis, and paraventricular organ pars anterioris. In the caudal diencephalon, TH-ir cells are seen within the posterior tuberal nuclei and dorsal to posterior recess. No immunostained cells are observed in the midbrain. In the hindbrain, tyrosine hydroxylase containing cells comprise three groups similar to that described using Falck-Hillarp histofluorescence (Parent et al., '78), i.e., isthmal, central medullary, and medullospinal groups. Tyrosine hydroxylase immunoreactivity is interpreted as evidence for the presence of catecholamines and not only provides an anatomical basis for the functional significance of catecholamines in teleosts, but may be useful in elucidating homologous structures in tetrapod vertebrates, although certain sites of immunoreactivity may prove to be unique to teleosts.

Distribution of acetylcholine and catecholamine neurons in the cat brainstem: a choline acetyltransferase and tyrosine hydroxylase immunohistochemical study

The distribution of acetylcholine neurons in the brainstem of the cat was studied by choline acetyltransferase (ChAT) immunohistochemistry and compared to that of catecholamine neurons examined in the same or adjacent sections by tyrosine hydroxylase (TH) immunohistochemistry. The largest group of ChAT-positive (+) neurons was located in the lateral pontomesencephalic tegmentum within the pedunculopontine tegmental nucleus and the laterodorsal tegmental nucleus rostrally and within the parabrachial nuclei and locus coeruleus nucleus more caudally. TH+ neurons were found to be coextensive and intermingled with ChAT+ neurons in the dorsolateral pontomesencephalic tegmentum, where the number of ChAT+ cells (approximately 18,500) exceeded that of the TH+ cells (approximately 12,000). In the caudal pons, scattered ChAT+ neurons were situated in the ventrolateral tegmentum together with TH+ neurons. In the medulla, numerous ChAT+ cells were located in the lateral tegmental field, where they extended in a radial column from the dorsal motor nucleus of the vagus to the ventrolateral tegmentum around the facial and ambiguus nuclei, occupying the position of preganglionic parasympathetic neurons of the 7th, 9th, and 10th cranial nerves. TH+ cells were also present in this field. Neurons within the general visceral, special visceral, and somatic motor cranial nerve nuclei were all immunoreactive to ChAT. Scattered ChAT+ neurons were also present within the medullary gigantocellular and magnocellular tegmental fields together with a small number of TH+ neurons. Other groups of ChAT+ cells were identified within the periolivary nuclei, parabigeminal nucleus, prepositus hypoglossi nucleus, and the medial and inferior vestibular nuclei. Acetylcholine neurons thus constitute a heterogeneous population of cells in the brainstem, which in addition to including the somatic and visceral efferent systems, comprises many other discrete systems and represents an important component of the brainstem reticular formation. The proximity to and interdigitation with catecholamine neurons within these systems may be of important functional significance.

Study of possible transmitters in the solitary tract nucleus of the cat involved in the carotid sinus baro- and chemoreceptor reflex

By using a multibarrelled microelectrode, the possibility that putative transmitters may influence on the field potential evoked in the solitary tract nucleus by electrical stimulation of the carotid sinus nerve (the NTS response) was examined electrophysiologically in the cat. After iontophoretic application of a selective antagonist to the putative transmitter, it was determined whether or not the NTS response was influenced. Both substance P antagonist and naloxone altered the NTS response recorded in the depressor and apneic (or hypopneic) response zone as well as in the pressor and apneustic (or inspiratory) response zone throughout the rostral, intermediate and commissure regions, suggesting that substance P and opioid peptide may play the role of excitatory transmitters. Under the polarizing cathodal current which may activate inhibitory inputs to the site of the NTS response, bicuculline and prazosin strongly enhanced the NTS response recorded in the pressor and apneustic zone, while naloxone weakly enhanced the NTS response recorded in the depressor and apneic zone. These results suggest that gamma-aminobutyric acid, alpha-adrenergic agonist and opioid peptide may have an inhibitory influence on the NTS response.

Organization of central adrenergic pathways: I. Relationships of ventrolateral medullary projections to the hypothalamus and spinal cord

We studied the organization of projections from the C1 adrenergic and A1 noradrenergic cell groups in the ventrolateral medulla (VLM) to the hypothalamus and the spinal cord by using a combination of retrograde transport of fluorescent tracers and immunocytochemistry. Three issues were addressed. Neurons in the VLM that stain immunohistochemically for phenylethanolamine N-methyltransferase (PNMT) have been assumed to be adrenergic. However, the presence of PNMT-immunoreactive neurons in the hypothalamus that do not stain for tyrosine hydroxylase (TH) prompted us to re-evaluate the VLM by an elution-restaining immunohistochemical procedure. We confirmed that nearly all of the rostral medullary PNMT-immunoreactive neurons also stained for TH. By contrast, in the caudal medulla, very few TH-positive neurons stained for PNMT. Neurons of the C1 group in the rostral VLM project both to the thoracic spinal cord and to the hypothalamus. To determine whether individual C1 neurons send collaterals to the hypothalamus and spinal cord, we injected different-colored fluorescent dyes (diamidino yellow or fast blue) into the thoracic spinal gray matter and either the median preoptic (MnPO) or paraventricular (PVH) nuclei of the hypothalamus. Very few double-labeled neurons were found in the VLM, indicating that hypothalamic and spinal cord projections arise from almost completely independent populations of cells. Approximately half of the neurons projecting to the spinal cord from rostral VLM were not immunoreactive for TH or PNMT, indicating that a substantial part of this projection is noncatecholaminergic. The MnPO and the PVH both receive extensive catecholaminergic inputs from the VLM. We also used fluorescent retrograde tracers to determine whether individual VLM neurons send collaterals to both hypothalamic sites. Approximately 20% of neurons projecting to the MnPO in the rostral two thirds of the VLM also sent collaterials to the PVH, nearly all of these neurons being TH-positive. The collateralization of the VLM catecholaminergic projection to the hypothalamus may provide an anatomical substrate for integration of fore-brain participation in cardiovascular regulation. In contrast, the adrenergic projection from the VLM to the intermediolateral column of the spinal cord arises from a separate population of neurons.

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

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

Descending phenylethanolamine-N-methyltransferase projections to the monkey spinal cord: an immunohistochemical double labeling study

In the present study, we determined that a population of spinally projecting neurons in the monkey brainstem also contained the enzyme phenylethanolamine-N-methyltransferase (PNMT). Following bilateral placements of horseradish peroxidase (HRP) in the cervical spinal cord, brainstem sections containing retrogradely labeled cells were immunohistochemically stained for PNMT. Single labeled PNMT-positive cells were found in a distinctive pattern in the dorsomedial and ventrolateral medulla. A population of double labeled cells was observed in the latter group only. This population was dispersed among other single labeled HRP and single labeled PNMT neurons. Possible functional roles of descending PNMT cells include involvement in sympathetic control of cardiovascular mechanisms and/or tonic descending inhibition of dorsal horn neurons.

Distribution of phenylethanolamine-N-methyltransferase (PNMT)-immunoreactive neurons in the avian brain

The distribution of neurons immunoreactive to tyrosine hydroxylase and phenylethanolamine-N-methyltransferase (PNMT) were described in adjacent sections of the avian medulla oblongata. PNMT-positive neurons were found in two bilaterally symmetrical columns in the ventrolateral and dorsomedial medulla. Within the ventrolateral column, PNMT cells were centered in and around the lateral paragigantocellular and lateral reticular nuclei. In the dorsomedial medulla, PNMT neurons were concentrated within and around the nucleus of the tractus solitarius. The distribution of PNMT-immunoreactive neurons in the avian medulla is similar to those observed in mammals, except there appears to be a greater number of PNMT-positive cells in the bird.

Primate neostriatal neurons containing tyrosine hydroxylase: immunohistochemical evidence

We have detected, in monkey caudate nucleus and putamen, neuronal cell bodies containing tyrosine hydroxylase-like immunoreactivity, as revealed by peroxidase-antiperoxidase immunohistochemistry. Many of these cells are distributed in an outer rim of 1-2 mm throughout the anterior-posterior extent of the neostriatum near its borders with the corona radiata; others are embedded in the adjacent white matter, especially near the ventral putamen and nucleus accumbens. Light and electron microscopy indicate that they are small (8-12 micron), bipolar cells with large nuclei. Such neostriatal neurons, containing tyrosine hydroxylase-like immunoreactivity, number in the tens of thousands.

Responses of adrenocorticotropin and vasopressin to hemorrhage after lesions of the caudal ventrolateral medulla in rats

Hormonal responses to hemorrhage were examined in urethane-anesthetized rats 48 h after electrolytic lesions of the caudal ventrolateral medulla. Bilateral A1-lesions (A1X) inhibited the response of plasma adrenocorticotropin relative either to other lesions (XX) or to sham lesions. A1X inhibited the response of plasma vasopressin relative to XX but not to sham lesions. A1X and XX destroyed similar areas that were dorsal or caudal to A1. No lesion blocked either response completely. A hemodynamic pathway controlling the release of both hormones may pass through A1. However, other pathways may bypass this area.

An immunohistochemical study of the telencephalon of the African lungfish, Protopterus annectens

The telencephalon of the African lungfish, Protopterus annectens, was studied by immunohistochemical techniques in order to identify the major subdivisions of the telencephalon and determine the possible homologues of these subdivisions, if any, in other vertebrates. The distributions of four different neuropeptides (substance P, leucine-enkephalin, avian pancreatic polypeptide, and LANT6), a neurotransmitter (serotonin), and a neurotransmitter-related enzyme that is involved in catecholamine synthesis (tyrosine hydroxylase) were examined. The resultant labeling patterns indicated that the telencephalon of lungfish consists of three major subdivisions--a rostrally and dorsally situated olfactory bulb, a dorsally situated pallial region located caudal to the olfactory bulbs, and a ventrally situated subpallial regions. The dorsal and lateral pallial regions, which both receive secondary olfactory input, are somewhat distinct from one another cytoarchitectonically, but their immunohistochemical labeling characteristics did not differ. Thus, the lateral pallium and the dorsal pallium together appear to constitute an olfactory pallium in lungfishes. The medial pallium was found to consist of three immunohistochemically distinct subdivisions--a dorsal cell group, an intermediate cell group, and a ventral cell group. These medial pallial fields extend throughout the entire rostrocaudal extent of the medial wall of the telencephalon. Although one or more of these medial pallial cell groups may be homologous to specific portions of the medial pallium in land vertebrates, no specific similarities were observed to support any proposed one-to-one correspondences. The possibility that one or more of the medial pallial cell groups of lungfishes correspond to cell groups located in the dorsal pallium of land vertebrates could not be excluded. The subpallium is divided into lateral, medial, and caudal subdivisions. The lateral subdivision appears to be homologous to the basal ganglia of land vertebrates since it contains neuropeptide/neurotransmitter-specific neuronal populations that are characteristic of the striatal and pallidal portions of the basal ganglia of amniotes. The medial subdivision of the subpallium shows the topographic and immunohistochemical characteristics of the septal region and the nucleus accumbens region of the amniote telencephalon. The caudal subpallium does not show any distinctive immunohistochemical labeling characteristics and its possible homologue in land vertebrates is unclear.(ABSTRACT TRUNCATED AT 400 WORDS)

Electrical stimulation of the C1 region of the rostral ventrolateral medulla of the rat increases mean arterial pressure and adrenaline release in the posterior hypothalamus

By using intracerebral dialysis in combination with high performance liquid chromatography and electrochemical detection, extracellular posterior hypothalamic adrenaline, noradrenaline, 3,4-dihydroxyphenylacetic acid and 5-hydroxyindoleacetic acid were measured in the anaesthetized rat and changes in their levels monitored following administration of tranylcypromine and electrical stimulation of the rostral ventrolateral medulla. Tranylcypromine (10 mg/kg i.p.) administration decreased basal extracellular 3,4-dihydroxyphenylacetic acid and 5-hydroxyindole acetic acid levels with a simultaneous increase in adrenaline and noradrenaline levels. Electrical stimulation of the C1 area of the rostral ventrolateral medulla increased (+56.6%) extracellular adrenaline levels in the posterior hypothalamus with a simultaneous increase in mean arterial pressure (+48 mm Hg) compared to prestimulation control values. No change was seen in posterior hypothalamic extracellular levels of noradrenaline, 3,4-dihydroxyphenylacetic acid and 5-hydroxyindole acetic acid during the stimulation period. Electrical stimulation of areas close to but outside the C1 region had no effect on either mean arterial pressure or posterior hypothalamic extracellular levels of the amines or the metabolites. The increase in adrenaline levels in the hypothalamus during stimulation of the C1 region supports the evidence for an adrenergic pathway from the rostral ventrolateral medulla to the hypothalamus and suggests that the increase in mean arterial pressure during electrical stimulation to the C1 region may relate to a specific increase in adrenaline levels.

Function of the ventrolateral medulla in the control of the circulation

The CNS control of the cardiovascular system involves the coordination of a series of complex neural mechanisms which integrate afferent information from a variety of peripheral receptors and produce control signals to effector organs for appropriate physiological responses. Although it is generally thought that these control signals are generated by a network of neural circuits that are widely distributed in the CNS, over the last two decades a considerable body of experimental evidence has accumulated suggesting that several of these circuits involve neurons found on or near the ventral surface of the medulla oblongata. Neurons in the VLM have been shown to be involved in the maintenance of vasomotor tone, in baroreceptor and chemoreceptor (central and peripheral) reflex mechanisms, in mediating the CIR and somatosympathetic reflexes and in the control of the secretion of vasopressin. These physiological functions of VLM neurons have been supported by neuroanatomical and electrophysiological studies demonstrating direct connections with a number of central structures previously implicated in the control of the circulation, including the IML, the site of origin of sympathetic preganglionic axons, and the SON and PVH, the site of origin of neurohypophyseal projecting axons containing AVP. Considerable suggestive evidence has also been obtained regarding the chemical messengers involved in transmitting information from VLM neurons to other central structures. There have been developments suggesting a role for monoamines and neuropeptides in mediating the neural and humoral control of SAP by neurons in the VLM. This review presents a synthesis of the literature suggesting a main role for VLM neurons in the control of the circulation.

A potent excitatory input to the nucleus locus coeruleus from the ventrolateral medulla

Our recent anatomic experiments reveal major innervation of the nucleus locus coeruleus (LC) from the nucleus paragigantocellularis (PGi), located in the rostral ventrolateral medulla. In the present studies, low intensity, single pulse electrical stimulation of the PGi synaptically activated most LC neurons examined (69%), while a smaller percentage of LC cells (20%) exhibited pure inhibitory responses. Pharmacologic experiments suggest that the excitatory response may be mediated by an amino acid transmitter.

Immunohistochemical identification of noradrenaline- and adrenaline- synthesizing neurons in the cat ventrolateral medulla

The distribution and morphology of cell bodies containing the catecholamine biosynthetic enzymes dopamine-beta-hydroxylase (DBH) and phenylethanolamine N-methyltransferase (PNMT) in the ventrolateral medulla (VLM) of the cat were studied immunohistochemically after intracisternal administration of colchicine. Perikarya immunoreactive to DBH were found throughout the VLM extending from approximately the spinomedullary junction to the level of the superior olivary nucleus. In the caudal VLM DBH neurons were found primarily in the region immediately dorsal to the lateral reticular nucleus (LRN), although a few scattered DBH neurons were also found near the ventral surface of the medulla in and around the parvicellular division of the LRN. These DBH neurons in the caudal VLM were generally fusiform, fusiform-bipolar, or multipolar, with a mean somal area of 422 +/- 32 microns2, and with two to four branching processes. In the rostral VLM DBH neurons formed three distinct groups: one group was found in the nucleus paragigantocellularis lateralis in the region just ventromedial to the retrofacial nucleus (RFN) near the ventrolateral surface of the medulla; the second group was found in the region dorsomedial to the rostral aspects of the nucleus ambiguous and the RFN, and the third group was found in the region along the lateral aspect of the superior olivary nucleus. Perikarya immunoreactive to the adrenaline-synthesizing enzyme PNMT were localized to a more restricted region of the VLM that extended from approximately the rostral aspect of the caudal third of the inferior olivary complex (level of the obex) to the caudal pole of the facial nucleus. These PNMT neurons were fusiform or multipolar with a mean somal area of 273 +/- 21 microns2, and with two to five branching processes. The location, size, shape, and numbers of PNMT-immunoreactive neurons corresponded closely to the rostral groups of DBH neurons, with the exception of the group found along the lateral aspect of the superior olivary nucleus. These data indicate that noradrenaline-synthesizing neurons are primarily found in the caudal VLM and in the region near the superior olivary nucleus, whereas catecholamine neurons in the rostral VLM between these two noradrenergic cell groups synthesize adrenaline. As the VLM has previously been shown to have direct connections with spinal cord, brainstem, and hypothalamic areas implicated in cardiovascular and neuroendocrine regulation, this suggests that DBH- and PNMT-synthesizing neurons are components of neuronal circuits involved in these homeostatic mechanisms.

Adrenaline-synthesizing neurons in the medulla of the cat

In this study, the distribution of neurons containing the adrenaline-synthesizing enzyme phenylethanolamine-N-methyltransferase (PNMT) was mapped in the medulla of the cat. Data from recent studies in the rat suggest that the anatomical structure responsible for cardiorespiratory changes that occur following application of neurotransmitters and drugs to Schlaefke's area on the ventral medullary surface is the nucleus reticularis rostroventrolateralis (RVL), which is distinguished from adjacent regions of the reticular formation, in part, by the presence of adrenaline-synthesizing neurons. To determine whether an equivalent adrenergic population is present in the RVL of the cat, we used antibodies raised against bovine adrenal PNMT to map the distribution of adrenaline-synthesizing neurons in the reticular formation. In the ventrolateral medulla, we found that labeled cells extended from the level of the retrofacial nucleus to the calamus scriptorius. The majority of labeled cells were seen in a nucleus designated RVL at the level of the rostral one-third of the inferior olive. In the dorsomedial medulla, cells were labeled in the caudal aspect of the nucleus tractus solitarii (NTS) and were especially dense in the subnucleus gelatinosus and commissural nucleus of the vagus. A few lightly labeled cells were also present in the rostral pole of the area postrema (AP). In contrast to the rat, few or no immunoreactive cells were found in the rostral NTS, medial longitudinal fasciculus, nucleus paragigantocellularis dorsalis, or periventricular gray. Our results are consistent with the notion that an area of the RVL containing adrenergic perikarya is the anatomical structure responsible for cardiovascular changes that occur when chemicals are applied to Schlaefke's area.

In vivo voltammetric monitoring of catecholamine metabolism in the A1 and A2 regions of the rat medulla oblongata

Catecholaminergic metabolism was estimated in A1 and A2 noradrenergic nuclei of the rat medulla oblongata using differential normal pulse voltammetry combined with electrochemically treated carbon fiber microelectrodes. In both areas an oxidation peak appearing at +50 mV was recorded. Electrochemical data and pharmacological experiments indicated that 3,4-dihydroxyphenylacetic acid (DOPAC) synthesized by noradrenergic neurons was the major contributor to this signal. Indeed, alpha-methyl-p-tyrosine, by inhibiting tyrosine hydroxylase, and pargyline, by inhibiting monoamine oxidase, both totally suppressed the peak appearing at +50 mV in A1 and A2 areas. Conversely, FLA-63, an inhibitor of dopamine-beta-hydroxylase, increased it. Moreover, a local and unilateral injection of catecholaminergic neurotoxin (6-hydroxydopamine) in the vicinity of A1 induced a 60% decrease in the peak height. This effect was prevented by pretreatment with desipramine, an inhibitor of noradrenaline reuptake, which is known to protect noradrenergic neurons against the action of 6-hydroxydopamine. Finally, specific drugs acting on alpha-2-noradrenergic receptors (clonidine and piperoxane) modulated the peak height recorded from both structures. Thus, as previously shown in the locus ceruleus, the variations in the extracellular DOPAC levels reflect the metabolic activity of A1 and A2 noradrenergic neurons.

Distribution of PNMT-immunoreactive neurons in the cat medulla oblongata

The distribution and morphology of presumptive adrenaline neurons in the cat medulla oblongata were studied in conjunction with the indirect immunoperoxidase technique utilizing antibody raised against bovine adrenal phenylethanolamine-N-methyltransferase (PNMT), an enzyme which converts noradrenaline to adrenaline. Small PNMT-immunoreactive (IR) perikarya are located in the dorsomedial part of the medulla (C2 group) extending from P17 to P12, and larger ones in the ventrolateral part (C1 group) from P11 to P9 of the caudorostral extent. In the rostral medulla (P11-10), larger cells extended more dorsally in the lateral tegmental field, where only a few catecholamine cells are localized. No midline PNMT-IR cells were identified corresponding to C3 cell group in the rat. Distinct longitudinal PNMT-IR axon bundles can be traced through the dorsal part of the lateral tegmental field. Comments are made on the relative localizations of the PNMT-IR and DBH-IR cells, as well as on species differences in comparison with the results reported in the rat.

A1 noradrenergic neurons tonically inhibit sympathoexcitatory neurons of C1 area in rat brainstem

In rats anesthetized with urethane and paralyzed, bilateral microinjections of kainic acid (KA) into the region of caudal ventrolateral medulla (CVL) containing noradrenergic neurons of the A1 group (A1 area) elicited a decrease followed by an increase in arterial pressure (AP), heart rate (HR) and sympathetic renal nerve activity (RNA). The sympathoinhibitory and sympathoexcitatory effects of KA were prevented by bilateral microinjection of tetrodotoxin into an area of the rostral ventrolateral medulla (RVL) containing C1 adrenergic neurons (the C1 area). In contrast, the autonomic responses were not altered by interruption of the two other principal projections of A1 area neurons, namely to the hypothalamus or to the nucleus tractus solitarii. Bilateral microinjections of tyramine, clonidine, alpha-methylnoradrenaline or histamine into the C1 area elicited a dose-dependent, anatomically specific and reversible decrease in AP, HR and RNA. The effect of tyramine was blocked by previous microinjection of reserpine, 6-hydroxydopamine (6-OHDA), or phentolamine into the C1 area. Pretreatment with phentolamine unveiled a hypertensive effect of alpha-methylnoradrenaline. All effects of alpha-methylnoradrenaline were blocked by pretreatment of the C1 area with phentolamine plus DL-propranolol, whereas those elicited by histamine prevailed. Pretreatment of the C1 area with 6-OHDA abolished all changes in AP and HR elicited by microinjections of KA into the A1 area. We conclude that (1) neurons of the CVL tonically inhibit sympathetic activity, (2) this effect is mediated by an action upon vasomotor neurons of the C1 area of RVL, (3) the inhibition is mediated by noradrenergic projections from A1 neurons into the C1 area, and (4) this tonic sympathoinhibitory effect is independent of the baroreceptor reflex.

Comparative responses of the central adrenaline- and noradrenaline-containing neurons after reserpine injections

The responses of the noradrenaline (NA)- and adrenaline (A)-containing neurons to a reserpine treatment have been studied in the rat brain by using biochemical indices of the neuronal activity. Three days after multiple reserpine injections, tyrosine hydroxylase activity was significantly increased in the locus coeruleus (LC), A1-C1 and C2 regions. No change in this activity was observed in the A2 region. Furthermore, the NA and A endogenous levels were markedly reduced both in NA and A cell bodies and/or terminals, suggesting a reserpine action on NA and A neurons. The NA turnover was unchanged in all the regions analyzed. Conversely, the A turnover was reduced in the LC, A2 and C2 regions and in the nucleus periventricularis of the hypothalamus. This result suggests a different degree of sensitivity and/or response of the NA and A neurons following reserpine administration.

The distribution of tyrosine hydroxylase, dopamine-beta-hydroxylase, and phenylethanolamine-N-methyltransferase immunoreactive neurons in the feline medulla oblongata

The distributions and morphological characteristics of neurons displaying immunoreactivity to the catecholamine synthetic enzymes tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH), and phenylethanolamine-N-methyltransferase (PNMT) were examined in adjacent sections of the feline medulla oblongata. TH-positive neurons were found in two bilaterally symmetrical columns in the ventrolateral and dorsomedial medulla. Within the ventrolateral medulla, TH-positive neurons were found within the lateral reticular formation throughout the entire rostrocaudal extent of the medulla. In the dorsomedial medulla, TH-immunoreactive perikarya were localized to the nucleus of the tractus solitarius including the commissural subnucleus, the dorsal motor nucleus of the vagus, and the area postrema. DBH-positive neurons had distributions and morphologies similar to those of the TH-immunoreactive cells with three exceptions: TH-positive neurons far outnumbered DBH-positive neurons in the area postrema; slightly greater numbers of TH-positive neurons were seen in the commissural nucleus of the tractus solitarius; and, caudal to the obex, only TH-positive neurons were seen within the dorsal motor nucleus of the vagus. PNMT-immunoreactive neurons were found in all the nuclear regions of the medulla where both TH- and DBH-positive neurons were seen. However, the PNMT immunoreactive perikarya had a somewhat more restricted distribution along the rostrocaudal axis. In the ventrolateral medulla, PNMT-positive cells extended rostrally only as far as the retrofacial nucleus and caudally only to the obex. Within the dorsomedial medulla, PNMT immunoreactive cells were found from just rostral to the area postrema to the medullary-spinal cord junction. These findings demonstrate that the distributions of TH, DBH, and PNMT immunoreactive perikarya in the medulla of the cat are generally similar to those seen in the rat insofar as these neurons are arranged in longitudinal columns in both species. However, significant differences exist with regard to the cytoarchitectonic borders within which immunoreactive perikarya can be found and the rostrocaudal extent of the PNMT-positive cell groups in these two species.

Distribution of tyrosine hydroxylase and neuropeptide Y-like immunoreactive neurons in rabbit medulla oblongata, with attention to colocalization studies, presumptive adrenaline-synthesizing perikarya, and vagal preganglionic cells

We studied the distribution, within the rabbit medulla oblongata, of neuronal cell bodies containing either tyrosine hydroxylase or neuropeptide Y-like immunoreactivity. Both avidin-biotin and immunofluorescence procedures were used. Because the two primary antibodies were raised in different species it was possible to perform simultaneous colocalization studies with the immunofluorescence procedure. Tyrosine hydroxylase-containing neurons in the rostral medulla were demonstrated to contain a catecholamine by the colchicine-enhanced FAGLU (formaldehyde-glutaraldehyde) fluorescence histochemical procedure. These neurons are presumably adrenergic, corresponding to the C1 and C2 groups described in the rat. No C3 group was found in the rabbit. The distribution of tyrosine hydroxylase-containing neurons in the caudal medulla was in accordance with previous descriptions of the A1 and A2 groups based on the unenhanced FAGLU procedure. Neuropeptide Y-like immunoreactivity was observed in cell groups corresponding to those already described in the rat, but additional groups were discovered in the rabbit. Some neurons containing neuropeptide Y-like immunoreactivity were observed in nucleus raphe pallidus and these also contained serotonin (5-HT). In the nearby nucleus reticularis gigantocellularis there were occasional neurons that contained neuropeptide Y-like immunoreactivity without any colocalized 5-HT. Neuropeptide Y-like immunoreactivity was also observed in the dorsal motor nucleus of the vagus, rostral to the obex, and these neurons were demonstrated to be true vagal preganglionic cells by colocalization of neuropeptide Y-like immunoreactivity and Fast Blue retrogradely transported from the cervical vagus. We found that neuropeptide Y-like immunoreactivity was colocalized in approximately 75% of the tyrosine hydroxylase-containing neurons in the rostral medulla (C1 and C2 cells). A smaller proportion of the A1 cells also contained this peptide but it was absent from both the most caudal A1 cells and from the A2 cells. Some tyrosine hydroxylase-containing neurons occur in direct apposition to vagal preganglionic cells in both the dorsal motor nucleus of the vagus and the nucleus ambiguous. However, colocalization studies revealed that none of these neurons contained Fast Blue when this dye was retrogradely transported from the cervical vagus. Medullary catecholamine-synthesizing neurons apparently do not contribute axons to the vagus nerve. This finding is consistent with our own studies in the rat but is in contrast to studies in this species published by other workers.

Relationships between catecholaminergic neurons and cholecystokinin-containing neurons in the caudal part of the dorsomedial medulla oblongata of the rat: light and electron microscopic observations by the 'mirror technique'

The 'mirror technique' was used in immuno-electron microscopy to examine the synaptic relationships between neuronal structures containing catecholamines and cholecystokinin (CCK) in the caudal part of the dorsomedial medulla oblongata in the rat, using antisera against tyrosine hydroxylase and CCK. CCK-immunoreactive axon terminals made synaptic contacts with catecholaminergic neurons. Some of these catecholaminergic neurons contained CCK.

Effect of clonidine and gamma-aminobutyric acid on the discharges of medullo-spinal sympathoexcitatory neurons in the rat

Single-unit recordings of 50 pressure-sensitive neurons with axonal projections to the thoracic spinal cord were obtained in the retrofacial portion of nucleus paragigantocellularis lateralis of halothane-anesthetized rats. Two types of cells were distinguished on the basis of their axonal conduction velocities: a slow-conducting (mean 0.6 m/s, group I) and a fast-conducting one (group II, mean 3.3 m/s). Both cell types were completely silenced by elevating mean arterial pressure above 160 mm Hg by means of aortic constriction and exhibited a plateau of high spontaneous activity below 70 mm Hg. Only group I neurons were significantly inhibited by the administration of clonidine in a dose producing 90% of its maximum hypotensive effect (11.5 micrograms/kg, i.v.). Hypotensive doses of clonidine administered into the fourth ventricle also produced a selective inhibition of group I neurons, while the others were unaffected. Iontophoretic applications of clonidine and norepinephrine produced an inhibition of the discharges of group I neurons qualitatively and quantitatively identical to that observed following administration of clonidine by the i.v. or i.c.v. route. Once more, group II cells were unaffected. In contrast, iontophoretically applied gamma-aminobutyric acid exerted a powerful inhibition of both cell types, an effect which was totally prevented or reversed by the gamma-aminobutyric acid antagonist bicuculline. Anatomical experiments were performed to uncover the potential source of catecholaminergic innervation of the area in which recordings were obtained. This area contains a large number of adrenaline-synthesizing neurons and receives a selective noradrenergic input from the A5 pontine group with no contribution from the A1, A2, A6 and A7 brainstem clusters of noradrenergic cells.

Expression and development of phenylethanolamine N-methyltransferase (PNMT) in rat brain stem: studies with glucocorticoids

To study the differentiation of adrenergic (epinephrine-synthesizing) neurons in brain, the initial appearance and ontogeny of phenylethanolamine N-methyltransferase (PNMT), a specific marker of the adrenergic phenotype, were studied with immunocytochemistry and catalytic assay. The appearance of immunoreactivity to dopamine beta-hydroxylase (DBH-IR), an enzyme common to the noradrenergic and adrenergic phenotypes, was also studied. DBH-IR was initially observed on embryonic Day 13 (E13) in cells located on the ventrolateral floor and wall of the rhombencephalon. A day later (E14), PNMT-IR cells and PNMT catalytic activity were observed in the rhombencephalon suggesting that, as in the adrenal gland, noradrenergic expression precedes adrenergic expression. The PNMT-IR cells were presumed to be precursors of C1 neurons since they were located in the ventrolateral medulla oblongata. Cells located in the wall of the medulla which appeared to be migrating ventrally to the C1 group also contained PNMT-IR. On E15, cells which had PNMT-IR processes coursing through the germinal zone were observed dorsally near the fourth ventricle. Although the location of the C1 cell group was apparent when PNMT was initially expressed, the dorsal C2 and C3 adrenergic cell groups were not evident until late in gestation on E19. Even in the term embryo there appeared to be PNMT-IR cells which had not yet reached their final destination. On E14 and E15, PNMT-IR cells were also observed on the floor of the pons just rostral to the pontine flexure. However, these were not observed in older embryos, suggesting that transient expression of PNMT occurs in brain, as well as in the periphery. To determine whether glucocorticoids regulate brain PNMT, we examined the effects of altered glucocorticoid levels. In contrast to PNMT in the sympathetic nervous system, PNMT activity in medulla oblongata was not affected in neonates or adults by the decrease in glucocorticoids following adrenalectomy or hypophysectomy. Conversely, elevation of glucocorticoids by hormonal treatment did not alter PNMT in neonates. Notably, however, treatment of pregnant rats with dexamethasone on E18-E21, but not earlier, increased PNMT activity in the fetal brain stem. These observations suggest that PNMT expression and development is regulated by different factors in cells derived from neural crest and tube. PNMT is expressed earlier in brain than in adrenal and sympathetic ganglia. Further, the development of PNMT in the periphery, but not in the brain, is dependent on maintenance of physiological levels of glucocorticoids.(ABSTRACT TRUNCATED AT 400 WORDS)

Immunohistochemical study of catecholaminergic cell bodies in the rat spinal cord

Immunohistochemistry of three specific synthesizing catecholamine enzymes was used in the rat spinal cord to determine precisely the distribution of catecholaminergic perikarya and the nature of the neurotransmitter they contain. Single and double labeling experiments were performed on cryostat sections from perfused rats. The peroxidase anti-peroxidase (PAP) and the indirect fluorescence techniques were used for labeling spinal catecholaminergic somata and separated into two completely different populations. The first is located in the upper cervical cord and includes three apparently distinct groups: a lateral cluster, of probably a noradrenergic nature, and two central subgroups where noradrenergic and dopaminergic neurons are intermingled. It is likely that these cervical cells represent caudal extensions of the medullary catecholaminergic cell groups. In the remaining cord, only tyrosine hydroxylase immunoreactive cell bodies have been found. Accordingly, this second population is probably dopaminergic. It is present almost exclusively in the first sacral segments, where it is located in the commissural (mostly lateral) grey matter and in the marginal dorsal horn.

Absence of adrenaline neurons in the guinea pig brain: a combined immunohistochemical and high-performance liquid chromatography study

The distributions of catecholamine (CA) neurons in the medulla oblongata of the guinea pig and rat were compared using immunohistochemistry with rabbit antisera against the CA synthesizing enzymes, tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (D beta H) and phenylethanolamine-N-methyltransferase (PNMT). TH and D beta H distributions were similar in the two species. In contrast, the central nervous systems of both normal and colchicine-treated guinea pigs failed to demonstrate immunoreactivity for PNMT, the synthetic enzyme for adrenaline. The concentrations of biogenic amines in the hypothalamus and medulla were determined in guinea pig and rat tissues by high-performance liquid chromatography with electrochemical detection. No adrenaline was detected in the guinea pig brain. Thus it appears that guinea pigs lack central neurons capable of synthesizing adrenaline.

A vasopressor cell group in the rostral dorsomedial medulla of the rabbit

Microinjections of sodium glutamate solution (which excites neuronal cell bodies but not axons of passage) into a circumscribed region within the dorsal reticular formation in the rostral medulla oblongata evoked a large increase in arterial pressure due to wide-spread vasoconstriction. In spontaneously breathing animals, glutamate stimulation of the pressor region did not affect respiratory activity and evoked only a very small and transient increase in electromyographic activity of axial skeletal muscles. The pressor response was not reduced by decerebration or decerebellation, indicating that the pathway connecting the dorsomedial pressor region to the spinal sympathetic outflow is intrinsic to the lower brainstem and spinal cord. Anatomical observations in the present study, combined with those from previous studies, indicate that neurons in this region do not project directly to the spinal cord and do not receive direct afferent inputs from the nucleus tractus solitarius. It is concluded that there exists a circumscribed group of vasopressor neuronal cell bodies within the rostral dorsomedial medulla. The anatomical connections of these neurons, however, are markedly different from those of a previously described group of vasopressor neurons in the rostral ventrolateral medulla, suggesting that the two groups may have different functional roles in cardiovascular regulation.

Projections from the nucleus tractus solitarii to the rostral ventrolateral medulla

Projections from the nucleus tractus solitarii (NTS) to autonomic control regions of the ventrolateral medulla, particularly the nucleus reticularis rostroventrolateralis (RVL), which serves as a tonic vasomotor center, were analyzed in rat by anterograde, retrograde, and combined axonal transport techniques. Autonomic portions of the NTS, including its commissural, dorsal, intermediate, interstitial, ventral, and ventrolateral subnuclei directly project to RVL as well as to other regions of the ventrolateral medulla. The projections are organized topographically. Rostrally, a small cluster of neurons in the intermediate third of NTS, the subnucleus centralis, and neurons in proximity to the solitary tract selectively innervate neurons in the retrofacial nucleus and nucleus ambiguus. Neurons generally located in more caudal and lateral sites in the NTS innervate the caudal ventrolateral medulla (CVL). The RVL, CVL, and nucleus retroambiguus are interconnected. A combined retrograde and anterograde transport technique was developed so as to prove that projections from the NTS to the ventrolateral medulla specifically innervate the region of RVL containing neurons projecting to the thoracic spinal cord or the region of the nucleus containing vagal preganglionic neurons. When the retrograde tracer, fast blue, was injected into the thoracic spinal cord, and wheat germ agglutinin-conjugate horseradish peroxidase (HRP) was injected into the NTS, anterogradely labeled terminals from the NTS surrounded the retrogradely labeled neurons in the RVL and in the nucleus retroambiguus in the caudal medulla. Among the bulbospinal neurons in the RVL innervated by the NTS were adrenaline-synthesizing neurons of the C1 group. When fast blue was applied to the cervical vagus, and HRP was injected into the NTS, anterogradely labeled terminals from the NTS surrounded retrogradely labeled neurons in the rostral dorsal motor nucleus of the vagus, the region of the nucleus ambiguus, the retrofacial nucleus, and the dorsal portion of the RVL, a region previously shown to contain cardiac vagal preganglionic neurons. This combined anterograde and retrograde transport technique provides a useful method for tracing disynaptic connections in the brain. These data suggest that the RVL is part of a complex of visceral output regions in the ventrolateral medulla, all of which receive afferent projections from autonomic portions of the NTS. Bulbospinal neurons in the RVL, in particular the C1 adrenaline neurons, may provide a portion of the anatomic substrate of the baroreceptor and other visceral reflexes.

Evidence that catecholamine-synthesizing perikarya in rat medulla oblongata do not contribute axons to the vagus nerve

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

Sympathoinhibition by A1-noradrenergic neurons is mediated by neurons in the C1 area of the rostral medulla

In anesthetized, paralyzed rats, bilateral microinjections of kainic acid (KA) into an area of caudal ventrolateral medulla containing A1 noradrenergic neurons of the A1 group (A1 area) first reduced and then elevated arterial pressure (AP), heart rate (HR) and sympathetic renal nerve activity. These effects are attributable to initial excitation and then paralysis of local neurons by KA. The microinjection of tetrodotoxin into an area of rostral ventrolateral medulla containing adrenaline neurons of the C1 group (C1 area) and which is innervated by neurons in A1 area abolished all the effects of KA. The pretreatment of the C1 area with 6-hydroxy-dopamine (6-OHDA) also abolished all the effects of KA. In contrast interruption of projections of the A1 area to the hypothalamus or nucleus tractus solitarii had no effects. The latency for response evoked in renal nerve by stimulation of A1 area was about 10 ms longer than that elicited from C1 area. Tyramine microinjected into the C1 area elicited a dose-dependent decrease in AP prevented by local application of desmethylimipramine. We conclude that neurons of the A1 area tonically inhibit sympathetic activity by inhibiting neurons of the C1 area probably by release of NA.

Effects of chronic methamphetamine on the nigral-striatal dopamine system in rat brain: tyrosine hydroxylase immunochemistry and quantitative light microscopic studies

Chronic administration of methamphetamine (20 mg/kg, IP, every 12 hours for 10 days) produced a large decrease in tyrosine hydroxylase staining axons and terminal boutons in the caudate nucleus in rats when examined 60 days following the final methamphetamine injection. This effect was quantitated using the Leitz Data Acquisition and Display System (DADS) revealing that there was a 74% decrease in tyrosine hydroxylase positive processes in the caudate nucleus. Furthermore, this treatment also produced a large decrease in the number of tyrosine hydroxylase positive staining neuronal perikarya in the pars compacta of the substantia nigra. This effect was also quantitative using the Leitz-(DADS) system, revealing a decrease of 89% in tyrosine hydroxylase positive material. These data demonstrate that chronic administration of methamphetamine produces a long-term loss of tyrosine hydroxylase enzyme in both the cell bodies of the substantia nigra and the nerve terminals in the caudate nucleus. Whether this effect is due to the degeneration of the neurons or some metabolic effect remains to be determined.

Distribution of dopamine, noradrenaline and adrenaline in coronal sections of the rat lower brainstem

The concentration of the three major catecholamines (CAs) were determined in 500 micron thick coronal sections of the rat medulla oblongata dissected into microcubes. Noradrenaline (NA) concentrations were always found much higher than the levels of the two other CAs in the same microcube. The highest concentrations of the three CAs were found in the dorso-medial region of the lower brainstem, more exactly in the more caudally located parts of the nucleus tractus solitarii (NTS). In the ventro-lateral region, the CA concentrations were lower and, except for adrenaline (A), did not exhibit any substantial change in their rostro-caudal distribution. Conversely, in the dorso-medial region, there was a clear rostro-caudal pattern of distribution of the three CAs. This distribution was similar for the three amines, since only a small difference (about 500 micron) was found between the maximal NA and A concentrations. Since the three CAs are present in highest concentrations within the same dorso-medial or ventro-lateral groups of microcubes, a microdissection of these two areas seems suitable to study simultaneously the metabolism of the three CAs in the rat lower brainstem. These data also suggest a microdissection procedure to study A metabolism within the C2-C3 A cell bodies and within a region more caudally located, rich in A terminals.

Colocalization of neuropeptide Y immunoreactivity in brainstem catecholaminergic neurons that project to the paraventricular nucleus of the hypothalamus

Immunohistochemical methods were used in the rat to plot the distribution of neuropeptide Y (NPY) immunoreactivity in the paraventricular (PVH) and supraoptic (SO) nuclei of the hypothalamus, and a combined retrograde transport-double immunohistochemical labeling technique was used to determine the extent to which NPY immunoreactivity is coexpressed in brainstem cell groups that stain with antisera to phenylethanolamine-N-methyltransferase (PNMT; a marker for adrenergic neurons) or dopamine-beta-hydroxylase (DBH; a marker for adrenergic and noradrenergic neurons) and also project to the PVH. The results confirm the existence of a major NPY-immunoreactive pathway that is in a position to influence each major class of output neurons in the PVH. Thus, most parts of the parvicellular division receive a dense input that is similar to, though somewhat more extensive than, the one stained by DBH antisera. However, in the magnocellular division catecholaminergic inputs are preferentially associated with vasopressinergic neurons, while NPY-stained fibers tend to be more evenly distributed in regions containing both oxytocinergic and vasopressingergic neurons, and their density appear to be lower than that of DBH-stained fibers. In the SO, only a moderate NPY-stained input was apparent, while, as described previously, DBH-immunoreactive fibers are rather dense and are preferentially distributed in vasopressinergic regions of the nucleus. The results of combined retrograde transport-double immunohistochemical labeling experiments may be summarized as follows: the vast majority of cells in the medulla that were retrogradely labeled after discrete implants of the fluorescent tracer true blue into the PVH, and were PNMT-immunoreactive, also stained for NPY. However, less extensive co-localization was detected in noradrenergic cell groups of the caudal medulla. About 60% of the retrogradely labeled-DBH positive cells in the A1 cell group were also NPY-positive, while those in the caudal part of the nucleus of the solitary tract (the A2 cell group) usually failed to stain with anti-NPY. Similarly, in the locus coeruleus (the A6 cell group) where virtually all retrogradely labeled neurons were DBH-positive, only rarely were triply labeled cells detected. These results suggest that NPY immunoreactivity is extensively co-contained within adrenergic neurons of the C1, C2, and C3 groups that project to the PVH, while the correspondence in noradrenergic cell groups is less complete, and generally limited to a subset of neurons in the A1 cell group.(ABSTRACT TRUNCATED AT 400 WORDS)

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)

The central organization of the vagus nerve innervating the stomach of the rat

We employed the neural tracers cholera toxin-horseradish peroxidase and wheat germ agglutinin-horseradish peroxidase to examine the organization of the afferent and efferent connections of the stomach within the medulla oblongata of the rat. The major finding of this study is that gastric motoneurons of the dorsal motor nucleus (DMN) possess numerous dendrites penetrating discrete regions of the overlying nucleus of the solitary tract (NTS). In particular, dendritic labelling was present in areas of NTS which also received terminals of gastric vagal afferent fibers such as the subnucleus gelatinosus, nucleus commissuralis, and medial nucleus of NTS. This codistribution of afferent and efferent elements of the gastric vagus may provide loci for monosynaptic vagovagal interactions. A small number of dendrites of DMN neurons penetrated the ependyma of the fourth ventricle and a few others entered the ventral aspect of the area postrema, thus making possible the direct contact of preganglionic neurons with humoral input from the cerebrospinal fluid and/or the peripheral plasma. Nucleus ambiguus neurons projecting to the stomach predominantly innervate the forestomach. The dendrites of these cells, when labelled, were generally short, and extended beyond the compact cluster of ambiguus neurons in a ventrolateral direction, parallel to the fascicles of vagal efferent fibers traversing the medulla.

Identification of dopamine-containing cell bodies in the dorsal and median raphe nuclei of the rat brain using tyrosine hydroxylase immunochemistry

Using immunohistochemical methods with antibodies specific to tyrosine hydroxylase, we examined the distribution of dopaminergic cells in the dorsal and median raphe nucleus of the rat brain. Although dopamine-containing cell bodies were previously thought to be almost exclusively confined to the substantia nigra pars compacta, ventral tegmental area, and tuberoinfundibular system, we found numerous cell bodies which stained for tyrosine hydroxylase in the dorsal and median raphe nuclei.

Newly identified GABAergic neurons in regions of the ventrolateral medulla which regulate blood pressure

Glutamic acid decarboxylase (GAD), the enzyme which synthesizes the inhibitory transmitter gamma-aminobutyric acid (GABA), was localized immunocytochemically within cells and processes distributed throughout the ventrolateral medulla. In caudal regions, GAD-stained cells were adjacent to the 'precerebellar' lateral reticular nucleus and partially overlapped the A1 area of norepinephrine synthesizing neurons. The largest number of labeled neurons filled the rostral ventrolateral medulla (RVL), coinciding with and extending beyond the C1 adrenergic area. GAD-positive cells also occupied the nucleus reticularis parvocellularis, raphe magnus (RM) and lateral wings of RM in the region of the pararaphe. Intrinsic GAD-containing cells in the ventrolateral medulla may tonically inhibit sympathoinhibitory neurons in the caudal ventrolateral medulla (CVL) and sympathoexcitatory neurons in the RVL.

Subarachnoid haemorrhage in the rat: effect on the development of vasospasm of selective lesions of the catecholamine systems in the lower brain stem

Intracisternal injection of blood in the rat produces an angiographically demonstrable biphasic vasospasm. Lesioning at the level of the mesencephalon of the ascending catecholamine pathways from locus coeruleus in the pons and the A1 and A2 nuclei in the medulla oblongata prior to cisternal blood injection prevents the development of both acute and late spasm. Selective lesioning in the medulla oblongata of ascending fibres from A1 and A2 also prevents development of spasm, indicating that these nuclei, which project to the hypothalamus-pituitary, are essential for the spasm syndrome. It is suggested that a substance vasospasm is produced by a substance liberated either by the hypothalamus or by the pituitary is involved in the occurrence of spasm.

Ontogeny of phenylethanolamine N-methyltransferase- and tyrosine hydroxylase-like immunoreactivity in presumptive adrenaline neurones of the foetal rat central nervous system

The appearance of phenylethanolamine N-methyltransferase (PNMT)- and tyrosine hydroxylase (TH)-like immunoreactivity (LI) in the foetal rat central nervous system has been investigated. Antibodies raised against PNMT and TH were used in an indirect immunofluorescence method. Attention was focussed on areas containing putative adrenaline-containing nerve cell bodies or fibres and, using an elution-restaining technique, it was possible to analyze whether neurones contained PNMT-LI, TH-LI, or both. PNMT-immunoreactive neurones could first be visualized on day 13 of gestation, in the ventrolateral and dorsal medulla oblongata, and probably corresponding to those of the C1 and C2 groups. The number of positive cell bodies and the intensity of their fluorescent staining in these areas were not dissimilar at this stage to the number and intensity observed at 1 day postnatal, the final age studied. At day 16, PNMT-positive cells were observed for the first time in midline areas of the rostral dorsal medulla oblongata-caudal pons, associated with the medial longitudinal fasciculus. These cells probably composed the C3 cell group. Many PNMT-immunoreactive fibres could be seen at day 13 of gestation, in the medulla, and coursing both in an ascending bundle around the mesencephalic flexure and in a descending bundle toward the spinal cord. The extent of the bundles increased with gestational age, such that dense meshworks of PNMT-immunoreactive varicose fibres were visible ventral to the aqueductus Sylvii, and the periventricular and lateral regions of the hypothalamus by days 18 to 19, and in the paraventricular nucleus, the septum, and the thoracic spinal cord by day 1 after birth. A sparser fibre plexus was observed in the amygdala at day 1 postnatal. In contrast to the explosive appearance of PNMT-immunoreactive cells at day 13 of gestation, the development of TH-LI within these same neurones was much more protracted. Only rarely were TH-LI and PNMT-LI colocalized at day 13, and even at birth TH-LI could not be visualized in 5% of PNMT-immunoreactive cells in the ventrolateral medulla oblongata, and in 50% of those in the dorsal vagal complex. A similar tardy appearance of TH-LI in PNMT-immunoreactive fibres was observed also. It should be emphasized that strongly TH-immunoreactive neurones were found already at gestational day 10.5 in the medulla oblongata, caudal to the PNMT-immunoreactive cells. It is concluded that the expression of enzymes involved in the synthesis of adrenaline is not unitarily controlled, and may be partly dependent on other than epigenetic factors.(ABSTRACT TRUNCATED AT 400 WORDS)

Inputs from the A1 noradrenergic region to hypothalamic paraventricular neurons in the rat

Electrical stimulation of the rat A1 noradrenergic region produced excitation (77%) of the activity of putative vasopressin (VP)-secreting neurons in the paraventricular nucleus (PVN) and produced excitation (4%), inhibition (26%) and excitation-inhibition (11%) of the activity of PVN neurons that were not antidromically identified by neurohypophysial stimulation. The excitatory response of putative VP-secreting neurons was blocked by microiontophoretically applied phentolamine, an alpha-adrenoceptor antagonist, but not by timolol, a beta-adrenoceptor antagonist. The inhibitory response of unidentified PVN neurons, on the other hand, was blocked by timolol, but not by phentolamine.

Response of phasically firing paraventricular neurons to A1 noradrenergic region stimulation and its attenuation by adrenoceptor antagonists

In urethane-anesthetized rats electrical stimulation of the A1 noradrenergic region in the ventrolateral medulla produced excitatory (27%), excitatory-inhibitory (24%), or inhibitory (34%) responses of spontaneous activity of phasically firing units in the paraventricular nucleus (PVN) of the hypothalamus. The latency of excitatory responses was significantly shorter in those followed by inhibition, suggesting the existence of two distinct excitatory pathways. The latency of inhibitory responses, however, was not different between primary and postexcitatory inhibitory responses. Effects of alpha- and beta-adrenoceptor antagonists on responses of phasically firing PVN units to stimulation of the A1 region were tested. The excitatory responses that were not followed by inhibition were significantly attenuated by intraperitoneal phenoxybenzamine, whereas the other responses were not affected. Both primary and postexcitatory inhibitory responses were significantly attenuated by intravenous propranolol, whereas neither type of excitatory response was affected. These results suggest that the medullary (A1 region) inputs to phasically firing PVN units are mediated by alpha-adrenergic (excitatory), beta-adrenergic (inhibitory), and nonaminergic (excitatory) pathways.

The alpha-adrenergic receptor: radiohistochemical analysis of functional characteristics and biochemical differences

The partial agonist [3H]para-aminoclonidine was used to label alpha 2-adrenergic binding sites in intact sections of the rat central nervous system using in vitro labeling receptor autoradiographic techniques. The distribution of alpha 2-agonist binding sites closely parallels the reported distribution of noradrenergic and adrenergic cell groups and their terminal fields, particularly the projections of the medullary catecholamine neurons. This distribution of alpha 2 binding sites confirms physiological studies which indicate that the anti-hypertensive actions of alpha 2-agonist compounds are mediated centrally in medullary and spinal centers involved in the control of parasympathetic and sympathetic outflow. Further, the high concentrations of alpha 2 binding sites in pontine and limbic areas such as the locus coeruleus, parabrachial nucleus, dorsal raphe, hypothalamus, amygdala, bed nucleus of the stria terminalis, septum and entorhinal cortex offer an anatomical basis for understanding the anxiolytic and antidepressant actions of drugs like clonidine. The antagonists [3H]prazosin and [3H]WB4101 were used to study the distribution of alpha 1-adrenergic binding sites in the rat forebrain and biochemical studies were performed to analyze the marked differences that were initially seen in the distribution of [3H]prazosin and [3H]WB4101 binding sites. Several pieces of evidence derived from both biochemical and autoradiographic studies suggest that [3H]prazosin and [3H]WB4101 act at distinctly different binding sites. However, both sites may represent components of an alpha 1-adrenergic receptor-effector complex since a high degree of overlap was seen in the binding site distribution of these two ligands and since kinetic interactions could be demonstrated in at least one region of the brain, the hippocampus. Differences noted in the relative displacements of [3H]prazosin and [3H]WB4101 binding in various forebrain regions could reflect differences in the coupling efficiency of the [3H]prazosin and [3H]WB4101 component of the hypothesized complex. Further, in some regions, [3H]WB4101 labeled a binding site that is different from the alpha 1-receptor. Thus, [3H]prazosin and [3H]WB4101 binding sites seen in forebrain regions such as lamina V of the cortex, thalamic nuclei and dorsal raphe probably represent alpha 1-adrenergic receptors and confirm electrophysiological and biochemical studies which demonstrate that adrenergic transmission in these regions can be mediated through an alpha 1-receptor.

The somatostatin systems of the guinea-pig brainstem

The tetradecapeptide somatostatin has been shown to have a widespread distribution in the rat brain. Except for its role in the inhibition of growth hormone secretion, the function of this molecule in the remainder of the central nervous system is unknown. To address this problem, the distribution of somatostatin-like immunoreactivity in the guinea-pig brainstem was examined systematically. Of 116 nuclei and/or areas, 34 nuclei had somatostatin neurons, 32 did not have any immunoreactivity and the remainder had immunoreactive fibers and/or terminals. Cranial nerve motor nuclei--somatic, branchiomeric and visceral--did not contain somatostatin neurons; somatostatin fibers were present in all nuclei with the exception of the somatic motor nuclei which innervate the ocular muscles. Of the cranial nerve sensory nuclei--both somatic and visceral--somatostatin neurons were present only in the somatic nuclei nervi spinal trigeminal caudalis, interpolaris and oralis; all of these nuclei, however, contained substantial numbers of immunoreactive fibers. Somatostatin neurons and fibers were also present in the spinal somatic sensory nuclei cuneatus medialis and gracilis. Of the cranial nerve special somatic sensory nuclei, somatostatin neurons were present in two vestibular nuclei--spinalis and medialis--and in the ventral cochlear nucleus. Not all of these nuclei contained somatostatin fibers. Of the nuclei related to the auditory system, somatostatin neurons were present only in the dorsal and ventral trapezoid nuclei and in the cortex of the inferior colliculus. In nuclei of the visual system in the brainstem, somatostatin neurons were present only in the superior colliculus. Of the raphe nuclei, four had somatostatin neurons--magnus, obscurus, pallidus and superior centralis; somatostatin fibers were present in all raphe nuclei. Of 24 nuclei in the reticular formation, 12 had somatostatin neurons--most notably nuclei gigantocellularis and paragigantocellularis--and only two nuclei, paranigralis and sagulum, did not contain any immunoreactive fibers. In the cerebellum, somatostatin fibers and terminals were restricted to the deep cerebellar nuclei. Of the 11 nuclei projecting to the cerebellum, five contained somatostatin neurons and the majority received somatostatin fibers. Of the limbic system nuclei, somatostatin neurons were confined to the central grey at both pontine and mesencephalic levels. Somatostatin neurons were present in the substantia nigra--compactus and lateralis, but not in reticularis--and absent from the nucleus ruber.(ABSTRACT TRUNCATED AT 400 WORDS)

Immunohistochemical mapping of galanin-like neurons in the rat central nervous system

Using an antiserum generated in rabbits against synthetic galanin (GA) and the indirect immunofluorescence method, the distribution of GA-like immunoreactive cell bodies and nerve fibers was studied in the rat central nervous system (CNS) and a detailed stereotaxic atlas of GA-like neurons was prepared. GA-like immunoreactivity was widely distributed in the rat CNS. Appreciable numbers of GA-positive cell bodies were observed in the rostral cingulate and medial prefrontal cortex, the nucleus interstitialis striae terminalis, the caudate, medial preoptic, preoptic periventricular, and preoptic suprachiasmatic nuclei, the medial forebrain bundle, the supraoptic, the hypothalamic periventricular, the paraventricular, the arcuate, dorsomedial, perifornical, thalamic periventricular, anterior dorsal and lateral thalamic nuclei, medial and central amygdaloid nuclei, dorsal and ventral premamillary nuclei, at the base of the hypothalamus, in the central gray matter, the hippocampus, the dorsal and caudoventral raphe nuclei, the interpeduncular nucleus, the locus coeruleus, ventral parabrachial, solitarii and commissuralis nuclei, in the A1, C1 and A4 catechaolamine areas, the posterior area postrema and the trigeminal and dorsal root ganglia. Fibers were generally seen where cell bodies were observed. Very dense fiber bundles were noted in the septohypothalamic tract, the preoptic area, in the hypothalamus, the habenula and the thalamic periventricular nucleus, in the ventral hippocampus, parts of the reticular formation, in the locus coeruleus, the dorsal parabrachial area, the nucleus and tract of the spinal trigeminal area and the substantia gelatinosa, the superficial layers of the spinal cord and the posterior lobe of the pituitary. The localization of the GA-like immunoreactivity in the locus coeruleus suggests a partial coexistence with catecholaminergic neurons as well as a possible involvement of the GA-like peptide in a neuroregulatory role.

The central neural connections of the area postrema of the rat

We applied the neuroanatomical tracers cholera toxin-horseradish peroxidase and wheat germ agglutinin-horseradish peroxidase to investigate the neural connections of the area postrema (AP) in the rat. We find that the AP projects to the nucleus of the solitary tract (NTS) and dorsal motor nucleus of the vagus bilaterally both rostral and caudal to obex; the nucleus ambiguus; the dorsal aspect of the spinal trigeminal tract and nucelus and the paratrigeminal nucleus; the region of the ventrolateral medullary catecholaminergic column; the cerebellar vermis; and a cluster of structures in the dorsolateral pons which prominently include a discrete set of subnuclei in the lateral parabrachial nucleus. The major central afferent input to the area postrema is provided by a group of neurons in the paraventricular and dorsomedial hypothalamic nuclei whose collective dendrites describe a horizontally oriented plexus which encircles the parvocellular nucleus of the hypothalamus bilaterally. In addition, the caudal NTS may project lightly to the AP. The lateral parabrachial nucleus provides a very light input as well. These connections, when considered in the context of the known vagal afferent input and reduced blood-brain barrier of AP, place this structure in a unique position to receive and modulate ascending interoceptive information and to influence autonomic outflow as well.