Catecholamine cell groups of the cat medulla oblongata

Neuroactive substances in the dorsal vagal complex of the medulla oblongata: nucleus of the tractus solitarius, area postrema, and dorsal motor nucleus of the vagus

The distributions of classical and putative neurotransmitters within somata and fibres of the dorsal vagal complex are reviewed. The occurrence within the dorsal medulla oblongata of receptors specific for some of these substances is examined, and possible functional correlations of the specific neurochemicals with respect to their distribution within the dorsal vagal complex are discussed. Many of the known transmitters and putative transmitters are represented in the dorsal vagal complex, particularly within various subnuclei of the nucleus of the solitary tract, the main vagal afferent nucleus. In a few cases, some of these have been examined in detail, particularly with respect to their possible mediation of cardiovascular or gastrointestinal functions. For example, the catecholamines, substance P and angiotensin II in the nucleus of the solitary tract have all been strongly implicated as playing a role in the central control of cardiovascular function. Other neurotransmitters or putative transmitters may be involved as well, but probably to a lesser extent. Similarly, the roles in the dorsal vagal complex of dopamine, the endorphins and cholecystokinin in control of the gut have been studied in some detail. Future investigations of the distributions of and electrophysiological parameters of neurotransmitters at the cellular level should provide much needed clues to advance our knowledge of the correlations between anatomical distributions of specific neurochemicals and physiological functions mediated by them.

Distribution and morphology of putative catecholaminergic and serotonergic neurons in the medulla oblongata of a sub-adult giraffe, Giraffa camelopardalis

The current study details the nuclear parcellation and appearance of putative catecholaminergic and serotonergic neurons within the medulla oblongata of a sub-adult giraffe, using immunohistochemistry for tyrosine hydroxylase and serotonin. We hypothesized that the unusual phenotype of the giraffe, this being the long neck and potential axonal lengthening of these neurons, may pose specific problems in terms of the efficient functioning of these systems, as several groups of catecholaminergic and serotonergic neurons, especially of the medulla, are known to project to the entire spinal cord. This specific challenge may lead to observable differences in the nuclear parcellation and morphology of these systems in the giraffe. Our personal observations in the giraffe reveal that, as with other Artiodactyls, the spinal cord extends to the caudal end of the sacral vertebrae. Within the giraffe medulla we found evidence for five putative catecholaminergic (neurons containing tyrosine hydroxylase) and five serotonergic nuclei. In terms of both morphological appearance of the neurons and nuclear parcellation we did not find any evidence for features that may be considered affected by the phenotype of the giraffe. The nuclear parcellation and appearance of both the putative catecholaminergic and serotonergic systems in the medulla of the giraffe studied are strikingly similar to that seen in previous studies of other Artiodactyls. We interpret these findings in terms of a growing literature detailing order specific phylogenetic constraints in the evolution of these neuromodulatory systems.

Differentiation of lamina I spinomedullary and spinothalamic neurons in the cat

We characterized spinomedullary neurons that project to the ventrolateral portion of the medulla that receives lamina I terminations in two sets of experiments in the cat. First, their distribution was examined using single unilateral iontophoretic injections of cholera toxin subunit B. The injection sites were characterized by microelectrode recordings from nociceptive- and thermoreceptive-specific units, indicative of lamina I input. The spinomedullary neurons were symmetrically distributed bilaterally, predominantly (63-69%) in lamina I but also in laminae V-VIII and the thoracic lateral horn (intermediolateral cell column). In horizontal sections, spinomedullary lamina I neurons included all three main morphological types described earlier. Second, spinomedullary and spinothalamic neurons were compared in retrograde double-labeling experiments. Different combinations of tracers were injected in the right thalamus and the left or right ventrolateral medulla (guided by recordings). The numbers of spinomedullary and spinothalamic neurons on the left side were comparable, and the segmental and laminar distributions were similar, except that a greater proportion of spinomedullary neurons originated from thoracic segments. However, the proportion of double-labeled neurons was consistently approximately 1%, indicating that spinomedullary and spinothalamic pathways arise from separate subpopulations. Spinomedullary neurons were more ventrally located within lamina I than spinothalamic neurons. A significantly greater proportion of spinomedullary neurons had fusiform somata (49% vs. 36%). These observations indicate that lamina I is the major source of spinal input to this portion of the ventrolateral medulla, that the projection includes several morphological types of inputs, and that this projection is distinct from the spinothalamic projection. These findings are consistent with the concept that lamina I projections constitute an ascending homeostatic afferent pathway relating the physiological condition of the body.

Nucleus retroambiguus projections to the periaqueductal gray in the cat

The nucleus retroambiguus (NRA) of the caudal medulla is a relay nucleus by which neurons of the mesencephalic periaqueductal gray (PAG) reach motoneurons of pharynx, larynx, soft palate, intercostal and abdominal muscles, and several muscles of the hindlimbs. These PAG-NRA-motoneuronal projections are thought to play a role in survival behaviors, such as vocalization and mating behavior. In the present combined antero- and retrograde tracing study in the cat, we sought to determine whether the NRA, apart from the neurons projecting to motoneurons, also contains cells projecting back to the PAG. After injections of WGA-HRP in the caudal and intermediate PAG, labeled neurons were observed in the NRA, with a slight contralateral preponderance. In contrast, after injections in the rostral PAG or adjacent deep tectal layers, no or very few labeled neurons were present in the NRA. After injection of [(3)H]leucine in the NRA, anterograde labeling was present in the most caudal ventrolateral and dorsolateral PAG, and slightly more rostrally in the lateral PAG, mainly contralaterally. When the [(3)H]leucine injection site extended medially into the medullary lateral tegmental field, labeling was found in most parts of the PAG as well as in the adjoining deep tectal layers. No labeled fibers were found in the dorsolateral PAG, and only a few were found in the rostral PAG. Because the termination pattern of the NRA fibers in the PAG overlaps with that of the sacral cord projections to the PAG, it is suggested that the NRA-PAG projections play a role in the control of motor functions related to mating behavior.

Precollicular decerebration reduces the pressor responses evoked by stimulation of rostral pons but not medulla in cats

In 30 cats under chloralose (40 mg/kg) and urethane (400 mg/kg) anesthesia, the ponto-medullary region involved in cardiovascular integration were stimulated by rectangular pulses (0.5 ms, 80 or 5 Hz, 100 to 200 microA) and/or by microinjection of sodium glutamate (Glu, 0.25-0.5 M, 70-200 nl). Changes of systemic arterial blood pressure (SAP) and renal sympathetic nerve activity (RNA) following stimulation were compared before and after precollicular decerebration. Precollicular decerebration itself resulted in an immediate but brief (5 to 15 min) hypotension with a decrease in SAP ranging from 40 to 100 mmHg. Stimulation of the lateral tegmental field (FTL) produced depressor responses. After precollicular decerebration, the stimulation induced depressor responses were either abolished or converted to mild pressor responses. Stimulation of the dorsal gigantocellular tegmental field-periventricular grey (dFTG-PVG) produced pressor responses. These responses were abolished after precollicular decerebration without exception. On the other hand, precollicular decerebration did not reduce pressor responses produced by stimulation of the ventrolateral medulla (VLM) and the dorsal medulla (DM). In 7 additional cats killed with an overdose of pentobarbital, the brain stem were processed for dopamine beta-hydroxylase (DBH). The pressor areas of the VLM and DM were DBH positive, indicating the presence of norepinephrine, while the dFTG-PVG and FTL were not. These findings suggest that the depressor mechanism of the FTL and the pressor mechanism of the dFTG, but not of the VLM or DM depend on actions of the brain structures rostral to superior colliculi.

Serotoninergic innervation of the dorsal column nuclei and its relation to cytoarchitectonic subdivisions: an immunohistochemical study in cats and monkeys (Aotus trivirgatus)

The serotoninergic innervation of the dorsal column nuclei (DCN) was investigated in cats and owl monkeys (Aotus trivirgatus) with immunohistochemical methods. A dense network of serotonin-immunoreactive fibers was present in the reticular regions of DCN in cats, and in the pars triangularis of the cuneate nucleus and the peripheral and caudal regions of the gracile nucleus in owl monkeys. The cat's cluster regions and the monkey's rotund regions were more sparsely innervated. Electron microscopic examination showed that the labeled fibers were thin and unmyelinated. Vesicle-containing, terminal-like structures were small. They were in contact with dendrites, other terminals and cell bodies, but synapses were rare. The results demonstrate that the serotoninergic projection to the DCN in both cats and owl monkeys is heterogeneously distributed in a pattern that is faithfully related to the cytoarchitectonic subdivisions of the DCN. The densely innervated reticular regions in the DCN of cats and the corresponding regions in monkeys are predominantly involved in the processing of sensory information to the cerebellum, either directly, or indirectly through projections to the inferior olive, pontine gray, tectum, pretectum, red nucleus, or zona incerta. Thus, the present findings suggest that the serotoninergic innervation of the DCN is primarily related to the DCN's involvement in motor functions.

Dopaminergic neurons in the cat dorsal motor nucleus of the vagus, demonstrated by dopamine, AADC and TH immunohistochemistry

In the rostral part of the dorsal motor nucleus of the vagus of the cat, neurons do not contain histochemically detectable catecholamines, even though many perikarya contain both intense aromatic L-amino acid decarboxylase (AADC) immunoreactivity and strong monoamine oxidase enzymatic activity. Similarly located perikarya have distinct immunoreactivities to tyrosine hydroxylase (TH) and dopamine after treatment with colchicine. Since inhibition of monoamine oxidase fails to reveal dopamine in these cells, its absence in non-colchicine-treated animals cannot be due to rapid deamination. It appears that dopamine is synthesized by TH and AADC in dorsal motor vagal cells and is then rapidly transported from the perikarya.

[The nucleus tractus solitarius: neuroanatomic, neurochemical and functional aspects]

The nucleus tractus solitarii (NTS) has long been considered as the first central relay for gustatory and visceral afferent informations only. However, data obtained during the past ten years, with neuroanatomical, biochemical and electrophysiological techniques, clearly demonstrate that the NTS is a structure with a high degree of complexity, which plays, at the medullary level, a key role in several integrative processes. The NTS, located in the dorsomedial medulla, is a structure of small size containing a limited number of neurons scattered in a more or less dense fibrillar plexus. The distribution and the organization of both the cells and the fibrillar network are not homogeneous within the nucleus and the NTS has been divided cytoarchitectonically into various subnuclei, which are partly correlated with the areas of projection of peripheral afferent endings. At the ultrastructural level, the NTS shows several complex synaptic arrangements in form of glomeruli. These arrangements provide morphological substrates for complex mechanisms of intercellular communication within the NTS. The NTS is not only the site of vagal and glossopharyngeal afferent projections, it receives also endings from facial and trigeminal nerves as well as from some renal afferents. Gustatory and somatic afferents from the oropharyngeal region project with a crude somatotopy within the rostral part of the NTS and visceral afferents from cardiovascular, digestive, respiratory and renal systems terminate viscero-topically within its caudal part. Moreover the NTS is extensively connected with several central structures. It projects directly to multiple brain regions by means of short connections to bulbo-ponto-mesencephalic structures (parabrachial nucleus, motor nuclei of several cranial nerves, ventro-lateral reticular formation, raphe nuclei...) and long connections to the spinal cord and diencephalic and telencephalic structures, in particular the hypothalamus and some limbic structures. The NTS is also the recipient of several central afferent inputs. It is worth to note that most of the structures that receive a direct projection from the NTS project back to the nucleus. Direct projections from the cerebral cortex to the NTS have also been identified. These extensive connections indicate that the NTS is a key structure for autonomic and neuroendocrine functions as well as for integration of somatic and autonomic responses in certain behaviors. The NTS contains a great diversity of neuroactive substances. Indeed, most of the substances identified within the central nervous system have also been detected in the NTS and may act, at this level, as classical transmitters and/or neuromodulators.(ABSTRACT TRUNCATED AT 400 WORDS)

Aromatic L-amino acid decarboxylase-immunohistochemistry in the cat lower brainstem and midbrain

By indirect immunohistochemistry, the present study examined the distribution of neuronal structures in the cat medulla oblongata, pons, and midbrain, showing immunoreactivity to aromatic L-amino acid decarboxylase (AADC), which catalyzes the conversion of L-3, 4-dihydroxyphenylalanine (L-DOPA) to dopamine, and 5-hydroxytryptophan to serotonin (5HT). With simultaneous and serial double immunostaining techniques, immunoreactivity to this enzyme was demonstrated in most of the catecholaminergic and serotonergic neurons. We could also demonstrate AADC-IR cell bodies that do not contain tyrosine hydroxylase (TH-) or 5HT-immunoreactivity (called "D-type cells") outside such monoaminergic cell systems. At the medullo-spinal junction, very small D-type cells were found within and beneath the ependymal layer of the 10th area of Rexed surrounding the central canal. D-type cells were localized in the caudal reticular formation, nucleus of the solitary tract, a dorsal aspect of the lateral parabrachial nucleus, and pretectal areas as have been reported in the rat. Furthermore, the present study describes, in the cat brainstem, new additional D-type cell groups that have not been reported in the rat. Dense or loose clusters of D-type cells were localized in the external edge of the laminar trigeminal nucleus, dorsal motor nucleus of the vagus, external cuneate nucleus, nucleus praepositus hypoglossi, central, pontine, and periaqueductal gray, superficial layer of the superior colliculus, and area medial to the retroflexus. D-type cells were loosely clustered in the lateral part of the central tegmental field dorsal to the substantia nigra, extending dorsally in the medial division of the posterior complex of the thalamus and medial side of the brachium of the inferior colliculus. They extended farther rostrodorsally along the medial side of the nucleus limitans and joined with the pretectal cell group. Almost all these cells were very small and ovoid to round with 1-2 short processes with the exception of dorsal motor vagal cells. AADC-IR axons were clearly identified in the vagal efferent nerves, longitudinal medullary pathway, dorsal tegmental bundle rostral to the locus coeruleus. Serotonergic axons were identified not only in the central tegmentum field and lateral side of the central superior nucleus, but also in the ventral surface of the medulla oblongata. We describe principal densely stained fiber plexuses in the cat brainstem. The findings of the present study provide a morphological basis for neurons that decarboxylate endogenous and exogenous L-DOPA, 5HTP, and other aromatic L-amino acids.

Serotonergic innervation of the lateral cervical nucleus: an immunohistochemical study in cats and monkeys (Aotus trivirgatus)

A serotonergic input to the lateral cervical nucleus of cats and monkeys (Aotus trivirgatus) was demonstrated with immunohistochemical methods. In both species, the lateral cervical nucleus was found to contain a network of serotonin-immunoreactive fibers. However, the density of labeled fibers was greater in the monkeys than in the cats. Most labeled fibers were thin and had irregularly spaced varicosities. Electron microscopic examination showed that labeled varicosities were in apposition with dendrites, neuronal somata and unlabeled terminals, but synapses were rare. The results demonstrate that the lateral cervical nucleus receives a serotonergic innervation, as is the case with other somatosensory relay structures such as the spinal dorsal horn and the dorsal column nuclei. The presence of a serotonergic innervation suggests that the transmission of somatosensory information through the lateral cervical nucleus is modulated by a descending pathway. However, its effect on the response properties of neurons in the lateral cervical nucleus is unknown.

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.

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.

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.

Norepinephrine throughout the spinal cord of the cat: I. Normal quantitative laminar and segmental distribution

Norepinephrine (NE) concentrations were measured by radioenzymatic assay in microdissected individual laminae of each segment of the cat spinal cord. Norepinephrine was detected in all areas of the spinal gray matter and showed more than a 7-fold difference in concentration between the laminae with the highest and lowest NE. The cervical, thoracic, and lumbosacral spinal regions showed significant interlaminar differences in NE. Intersegmental changes in NE were seen within single laminae of the thoracic and lumbosacral spinal cord, but not in the cervical spinal cord. A significant rostral to caudal, increasing regional gradient of NE was observed from the cervical to lumbosacral spinal cord in laminae I-III, V, VI, VII, and IX. In the intermediolateral cell column (IML), epinephrine concentrations were 2 to 5% of NE. Neither neurotransmitter showed a significant intersegmental variation in the IML. These data should prove useful in further defining the precise role of NE in specific regions of the spinal cord that mediate sensory, motor, autonomic, or propriospinal functions.

The effects of noradrenaline on neurones in the rat dorsal motor nucleus of the vagus, in vitro

1. Intracellular recordings were made from vagal motoneurones identified by antidromic stimulation in the dorsal motor nucleus of the vagus (d.m.v.) in slice preparations of rat medulla oblongata. 2. Noradrenaline (NA) applied by perfusion (0.01 microM to 1 mM) depolarized 55%, hyperpolarized 32% and produced a biphasic response (hyperpolarization followed by depolarization) in 9% of the d.m.v. neurones tested. 3. The NA effects persisted after complete elimination of synaptic inputs during perfusion with Ca2+-free high-Mg2+ solution, and therefore probably resulted from a direct action on the postsynaptic membranes. 4. The NA depolarization was blocked by prazosin and the NA hyperpolarization by yohimbine, but neither was blocked by propranolol or timolol. Phenoxybenzamine blocked both responses. The results indicate that NA depolarization is mediated by alpha 1-adrenoceptors and hyperpolarization by alpha 2-adrenoceptors. 5. The neurones which were depolarized by NA were also hyperpolarized by NA when the alpha 1-adrenoceptors were blocked by prazosin (all of seven neurones tested). This result suggests that most vagal motoneurones in the d.m.v. have both alpha 1-and alpha 2-adrenoceptors. 6. The NA depolarization was accompanied by a decrease in membrane conductance and the hyperpolarization by an increase in membrane conductance, both of which were measured under manual-clamp conditions. 7. The reversal potentials for the NA responses were around -85 mV in normal Ringer solution, and shifted as predicted by the Nernst equation when the extracellular K+ concentration was changed. 8. The inhibitory postsynaptic potentials evoked by focal electrical stimulation on the slice surface of the commissural part of the nucleus of the tractus solitarius (n.t.s.), which contains an A2 catecholaminergic cell group, were abolished by yohimbine. 9. The results suggest that NA modulates vagal output by decreasing or increasing the K+ conductance of d.m.v. neurones through alpha 1- or alpha 2-adrenoceptors. In addition, the A2 noradrenergic cell group within the n.t.s. may send inhibitory inputs to the d.m.v.

Overlap in the distribution of cholinergic and catecholaminergic neurons in the upper brainstem of the ferret

The distribution of catecholaminergic and cholinergic neurons in the upper brainstem of the ferret were mapped by staining immunohistochemically two adjacent series of sections of brainstem for tyrosine hydroxylase and choline acetyltransferase, respectively. As in other species, large numbers of tyrosine-hydroxylase-positive neurons are localized in the ventral tegmental area (A10), the substantia nigra (A9), and in A8. Tyrosine-hydroxylase-positive neurons in the dorsolateral pontine tegmentum (A4, A6, and A7--the locus coeruleus complex) of the ferret are rather diffusely distributed, as has been observed in other carnivore species such as the cat and the dog, but unlike the cat, these cells in the ferret display a relative uniformity in size and morphology. Choline-acetyltransferase-positive neurons which extend in the ferret's pedunculopontine tegmental nucleus and ventral parabrachial area (Ch5) are relatively large cells that stain intensely for choline acetyltransferase, and their dendrites form prominent bundles in regions where unstained fibre tracts are prevalent. Choline-acetyltransferase-positive neurons distributed in the laterodorsal tegmental nucleus (Ch6) are smaller than the cholinergic cells of Ch5, and they stain less intensely for choline acetyltransferase. Rostrally, there is little overlap between the catecholaminergic cell groups A8, A9, and A10 and the cholinergic cell groups of Ch5 and Ch6. Caudally, the Ch5 neurons extend some considerable extent into the locus coeruleus complex. In the region of overlap, no cells with staining for both tyrosine hydroxylase and choline acetyltransferase were observed, as was ascertained with a double staining method employing a combination of tyrosine hydroxylase immunofluorescence and choline acetyltransferase peroxidase-antiperoxidase immunohistochemistry. In conclusion, the ferret has a typically carnivore pattern for the distribution of catecholaminergic cells in the upper brainstem, and there is a significant overlap between the catecholaminergic and cholinergic cell groups in the dorsolateral pontine tegmentum.

Localization of tyrosine hydroxylase-immunoreactive neurons in the cat hypothalamus, with special reference to fluorescence histochemistry

The present study examines the distribution and morphological characteristics of neurons containing immunoreactivity of tyrosine hydroxylase in the cat hypothalamus. We used the indirect immunoperoxidase technique on vibratome sections. Tyrosine hydroxylase-immunoreactive cell bodies were widely distributed in discrete regions of the cat hypothalamus. Several principal cell groups were identified. They were seen in the posterior and dorsal hypothalamic areas, zona incerta, dorsomedial and lateral hypothalamic areas, arcuate nucleus, periventricular nucleus, paraventricular nucleus, and an area of the tuber cinereum and preoptic area. These cells presented two different morphological characteristics; small with two to three short processes and medium to large, multipolar with three to five long dendritic trees. The atlas is presented in twelve cross-sectional drawings of the cat hypothalamus from the level A8.5 to A15 of the Horsley-Clarke stereotaxic planes. We also examined the distribution of hypothalamic catecholamine fluorescent neurons by using the aqueous aldehyde method in combination with glyoxylic acid applied to vibratome sectioned tissues, which improves sensitivity. Comments are made on the relative localizations of the tyrosine hydroxylase-immunoreactive and aldehyde-induced histofluorescent cells, as well as on species differences between the cat, rat, and mouse.

Afferent connections and spinal projections of the pressor region in the rostral ventrolateral medulla of the cat

Following microinjection of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) into the pressor region of the rostral ventrolateral medulla of the cat, the medulla, pons and hypothalamus were examined for retrogradely labelled cell bodies, while the thoracolumbar segments of the spinal cord were examined for anterogradely labelled axons. Dense groups of labelled cells were found in the following areas: (1) the nucleus of the solitary tract, particularly the medial, ventrolateral and commissural subnuclei; (2) the ambiguous complex and immediately surrounding area; (3) the Kölliker-Fuse nucleus in the pons; (4) the paraventricular nucleus and lateral hypothalamic area. In the spinal cord, labelled axons formed a band extending throughout the dorsolateral and ventrolateral funiculi at thoracic segments, while terminal labelling was observed in the intermediolateral nucleus and to a lesser extent the central autonomic area, but not in other parts of the grey matter. The findings are discussed in relation to the role of the rostral ventrolateral medulla in cardiovascular regulation, particularly the baroreceptor reflex.

Visualization of tyrosine hydroxylase-immunoreactive neurons in the cat dorsal motor vagal cells after treatment with parachlorophenylalanine

We examined tyrosine hydroxylase-immunoreactive (TH-IR) neuronal structures in the cat dorsal motor nucleus of the vagus (DMV) and its adjacent regions. We identified only a few in the caudal part of the DMV and no TH-IR cells at all in its rostral portion. However, after treatment with parachlorophenylalanine (PCPA), numerous TH-IR perikarya were visualized in the DMV. Comments are made on the central catecholamine regulation and the possible influence of serotonin afferents on this nucleus.

Distribution of two types of monoamine oxidase-containing neurons in the cat medulla oblongata demonstrated by an improved histochemical method

The topographic distribution of cells containing monoamine oxidase, the enzyme which deaminates amines, was studied in the cat medulla oblongata. By means of enzyme histochemistry using a new coupled peroxidation method, monoamine oxidase activity was demonstrated in the somata, dendrites and fibers. Type A monoamine oxidase, inhibited by clorgyline but not deprenyl, were localized in the cells distributed in the ventrolateral and dorsomedial medulla where catecholaminergic neurons are present. Type B monoamine oxidase-positive cell bodies were identified in the regions containing serotonergic neurons. Furthermore, we found an intense activity of type A monoamine oxidase in many cells of the dorsal motor nucleus of the vagus of the rostrocaudal extent, and more rostrally in the nucleus parvocellularis where few or no aminergic neurons have been described.

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.

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.

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.

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.

Rat medulla oblongata. III. Adrenergic (C1 and C2) neurons, nerve fibers and presumptive terminal processes

The goal of this study was to define the cytoarchitectonic relationships between the catecholaminergic cell groups (the C1 and C2) in the rostral medulla oblongata of the rat. Immunocytochemistry was combined with Nissl staining to determine the nuclear boundaries in this region of the brain stem. In addition, the morphological characteristics of neurons in the C1 and C2 cell groups were determined and the relationship between these populations of neurons and their caudaul counterparts (A1 and A2 cell groups) was established (Kalia et al., '85a). The results indicate that the C1 and C2 cell groups are distributed over a wide region of the rostral medulla. The location of these adrenergic neurons is related to a number of nuclear groups in this region. This finding was remarkably consistent in all the animals studied in this series. In addition, adrenergic nerve fibers were found to be distributed over a large region of the medullary reticular formation. There was homogeneity in the morphology of the C1 and C2 cell groups. These rostrally located adrenergic neurons did not share morphological features in common with the recently described (Kalia et al., '85a) caudally located adrenergic neurons in the dorsal region of the nucleus of the tractus solitarius. These striking anatomical features of the adrenergic C1 and C2 cell groups support the proposal that adrenergic neurons in the rostral medulla oblongata play an important role in the integration of visceral functions (Fuxe et al., '80).

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

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

The central distribution of vagal catecholaminergic neurons which project into the abdomen in the rat

A double labeling technique employing retrograde labeling of vagal neurons with horseradish peroxidase from injections into the stomach wall and immunocytochemistry for dopamine-beta-hydroxylase revealed catecholaminergic neurons in the medulla oblongata which project into the abdomen. The great majority of such neurons were located in the dorsal motor nucleus of the vagus, particularly in its rostral third.

Ultrastructure of the dorsal motor nucleus of the vagus nerve in monkey with a comparison of synaptology in monkey and cat

Neurons of the dorsal motor nucleus of the vagus nerve were studied following injections of horseradish peroxidase into the vagus nerve in a monkey (Macaca fascicularis). In frozen sections, the dorsal motor nucleus appeared to be completely filled by labeled medium-sized (20-30 micron in long axis) neurons. Labeled dendrites from these neurons often extended outside the borders of the nucleus into the nucleus of the tractus solitarius. In 1 micron thick plastic sections and ultrathin sections of the dorsal motor nucleus, two distinct types of neurons were observed with the light and electron microscope. Medium-sized neurons with abundant cytoplasm and an oval nucleus were retrogradely labeled with HRP, while small (10-15 micron in long axis) neurons with a paucity of organelles and an invaginated nucleus remained unlabeled. Medium-sized neurons outnumbered the small neurons by approximately five to one. The synaptic organization of the dorsal motor nucleus in monkey was studied and compared with that in cat. The porportions of different types of axosomatic synapses were similar in both species. Terminals containing round vesicles and making symmetrical or asymmetrical contact with the postsynaptic structure were more common than synaptic terminals containing pleomorphic vesicles. In both species, there was a slightly greater synaptic density on the medium-sized neurons than on the small neurons. The synaptic density in the monkey dorsal nucleus was greatest on the smallest dendrites in the neuropil and least on the somata.

Distribution of catecholamines in the brain stem and spinal cord of the lizard Varanus exanthematicus: an immunohistochemical study based on the use of antibodies to tyrosine hydroxylase

Antibodies to tyrosine hydroxylase were used to study the distribution of nerve cells, fibers and terminals, containing catecholamines, in the lizard Varanus exanthematicus, by means of the indirect immunofluorescence technique. Tyrosine hydroxylase-containing cell bodies occurred in the hypothalamus, the ventral and dorsal tegmentum mesencephali, the substantia nigra, the isthmic reticular formation, in and ventrolaterally to the locus coeruleus, in the nucleus tractus solitarii and in a lateral part of the nucleus reticularis inferior. In addition tyrosine hydroxylase-containing cell bodies were found throughout the spinal cord, ventral to the central canal. Tyrosine hydroxylase-immunoreactive terminal areas in the brain stem were seen in the nucleus interstitialis of the fasciculus longitudinalis medialis, the nucleus raphes superior, the locus coeruleus, several parts of the reticular formation and the nucleus descendens nervi trigemini. Ascending catecholaminergic pathways could be traced from the ventral mesencephalic tegmentum as well as from the dorsal isthmic tegmentum rostralwards, through the lateral hypothalamus. These pathways correspond to the mesostriatal and isthmocortical projections respectively, as described in mammals. Furthermore, ascending catecholaminergic fibers could be traced from the catecholaminergic cell groups in the medulla oblongata to the isthmus, where they intermingle with the locus coeruleus neurons. These pathways correspond to the medullohypothalamic projection and to the dorsal periventricular system in mammals. Descending catecholaminergic fibers to the spinal cord pass via the dorsomedial part of the lateral funiculus, and mainly terminate in the dorsal horn. The results obtained in the present study have been placed in a comparative perspective, which illustrates the constancy of catecholaminergic innervation throughout phylogeny.

Chemical anatomy of the brain

The development of sensitive histochemical-neuroanatomical techniques has made it possible to analyze the content of specific compounds in single nerve cells and their processes. In consequence, it has been possible to construct detailed maps of the distribution of various types of neurons on the basis of their transmitter substance. There are now many examples of neurons containing both a classical transmitter and a peptide. In some instances the peptides seem to support the action of the classical transmitters. This interaction may have applications in the prevention and treatment of nervous disease states.

A lectin horseradish peroxidase study of the origin of ascending fibers in the medial forebrain bundle of the rat. The lower brainstem

The origins of projections within the medial forebrain bundle from the lower brainstem were examined with the horseradish peroxidase technique. Labeled cells were found in at least 15 lower brainstem nuclei following injections of a conjugate or horseradish peroxidase and wheat germ agglutinin at various levels of the medial forebrain bundle. Dense labeling was observed in the following cell groups (from caudal to rostral): A1 (above the lateral reticular nucleus); A2 (mainly within the nucleus of the solitary tract); a distinct group of cell trailing ventrolaterally from the medial longitudinal fasciculus at the level of the rostral pole of the inferior olive; raphe magnus; nucleus incertus; dorsolateral tegmental nucleus (of Castaldi); locus coeruleus; nucleus subcoeruleus; caudal part of the dorsal (lateral) parabrachial nucleus; and raphe pontis. Distinct but light labeling was seen in raphe pallidus and obscurus, nucleus prepositus hypoglossi, nucleus gigantocellularis pars ventralis, and the ventral (medial) parabrachial nucleus. Sparse labeling was observed throughout the medullary and caudal pontine reticular formation. Several lower brainstem nuclei were found to send strong projections along the medial forebrain bundle to very anterior levels of the forebrain. They were: A1, A2, raphe magnus (rostral part), nucleus incertus, dorsolateral tegmental nucleus, raphe pontis and locus coeruleus. With the exception of the locus coeruleus, attention has only recently been directed to the ascending projections of most of the nuclei mentioned above. Evidence was reviewed indicating that fibers from lower brainstem nuclei with ascending medial forebrain bundle projections distribute to widespread regions of the forebrain. It is concluded from the present findings that several medullary cell groups are capable of exerting a direct effect on the forebrain and that the medial forebrain bundle is the major ascending link between the lower brainstem and the forebrain.

Direct pathway from neurons in the ventrolateral medulla relaying cardiovascular afferent information to the supraoptic nucleus in the cat

In chloralose anesthetized cats experiments were done to electrophysiologically identify neurons in the ventrolateral medulla (VLM) which relay cardiovascular afferent information directly to the supraoptic nucleus (SON). Action potentials elicited antidromically by electrical stimulation of the SON were recorded from 69 histologically verified single units in the VLM. Single units responded with latencies corresponding to conduction velocities of 7.8 +/- 0.6 m/s. Of these units 26 were excited orthodromically by stimulation of the buffer nerves; 12 responded to stimulation of only the carotid sinus nerve, 7 responded to stimulation of only the aortic depressor nerve, and 7 responded to both buffer nerves. The axons of VLM units that responded to buffer nerves conducted at a significantly slower velocity than those of non-responsive units (5.7 +/- 0.4 and 9.1 +/- 0.8 m/s, respectively). These data provide electrophysiological evidence of two different populations of VLM neurons which project directly to the SON, and suggest that the direct pathway from the VLM to the SON is involved in the release of vasopressin by SON neurons during activation of baroreceptor and chemoreceptor afferent fibers.

Lateral reticular regions and the descending control of dorsal horn neurones of the cat: selective inhibition by electrical stimulation

In barbiturate-anaesthetized cats, brainstem sites were electrically stimulated while studying the synaptic responses of lumbar dorsal horn neurones. The excitation of these neurones by impulses in unmyelinated primary afferents was selectively inhibited by stimulation of the ventrolateral medulla in the region of the caudal lateral reticular nucleus. The significance of this inhibition was heightened by the finding that stimulus currents producing inhibition from this area were less effective in the raphé region and not effective at intervening or dorsal sites. Bilateral lesions of the inhibition-producing ventrolateral sites reduced tonic descending inhibition of the responses of dorsal horn neurones to impulses in C fibres. The lateral reticular regions of the medulla may thus exert a considerable control over the transmission of nociceptive information in the cat spinal cord.

Origin of the hypotensive and sympathoinhibitory effect of morphinomimetic agents

In vagotomized dogs, lesions of the lateral reticular nucleus (LRN) region did not change arterial blood pressure and sympathetic nerve activity. The hypertensive and tachycardic responses elicited by section of both carotid sinus nerves and both vagus nerves were not altered. However the sympathoinhibitory component of the baroreflex arc was attenuated. These lesions also abolished the hypotensive and sympathoinhibitory effects of fentanyl (10 micrograms/kg i.v.). In debuffered dogs, bilateral lesions of the LRN regions attenuated the effects of fentanyl (20 micrograms/kg i.v.) on arterial blood pressure and splanchnic discharges. Microinfusion of naloxone into the LRN reduced the effects of fentanyl (10 micrograms/kg) administered intravenously. Microinfusion of [D-Ala2,Met5]enkephalinamide (0.1-1 microgram) into the LRN region produced a dose dependent decrease in arterial blood pressure and sympathetic nerve activity. Lesions of the nucleus ambiguus (NA) region also reduced the effects of fentanyl. In contrast, lesions placed in the ventral median reticular formation or above the NA were ineffective in changing the sympathoinhibitory effect of fentanyl. These results indicate that the lateral reticular formation ventral to the nucleus ambiguus including the lateral reticular nucleus region is involved in the sympathoinhibitory effect of morphinomimetic agents.

Atlas of catecholamine perikarya, varicosities and pathways in the brainstem of the cat

By application of a modified glyoxylic acid--paraformaldehyde histofluorescence technique, catecholamine perikarya, varicosities, and pathways were delineated within the brainstem of kittens that were either untreated, pretreated pharmacologically, or injected intracerebrally with 6-OHDA. Three principle catecholamine cell groups were identified within the medulla and pons; the dorsomedial medullary cell group, the dorsolateral pontine cell group, and a ventrolateral cell group extending from the medulla into the pons. Induced axonal accumulation of catecholamines with intracerebral 6-OHDA injections revealed a major longitudinal catecholamine bundle which courses in a dorsolateral position through the entire brainstem tegmentum. The dorsomedial medullary and dorsolateral pontine cell groups contribute ascending and descending fibers to this bundle. Axons of the ventrolateral pontomedullary cells also feed into the bundle at successive levels through radially coursing transverse fibers. Via this major dorsolateral conduit and its ventrally and medially coursing tributaries, catecholamine fibers and terminals are distributed to multiple nuclei through the brainstem. The regions of the catecholamine cell groups and the serotonin raphe nuclei all receive a dense catecholamine innervation. Varicosities are also dense in the visceral cranial nerve nuclei, moderately dense in most somatic spinal and cranial nerve motor nuclei, and moderate to light in sensory cranial nerve and relay nuclei. The lateral and ventromedial reticular formation are moderately innervated by varicose catecholamine fibers that traverse these regions. The longitudinal catecholamine bundle continues caudally into the lateral funiculus to descend into and innervate the spinal cord. Rostrally it continues into the tegmental fascicles of the midbrain to ascend into and innervate the diencephalon and there join the medial forebrain bundle to ascend into the telencephalon. Thus, the catecholamine neurons utilize this dorsolateral longitudinal bundle to distribute collaterals to multiple bulbar nuclei and to travel beyond the brainstem to innervate the spinal cord and forebrain.

Projections of upper structure to the spinal cardioacceleratory center in cats: an HRP study using a new microinjection method

We studied, with the horseradish peroxidase (HRP) method, the supraspinal structure projections to the cardioacceleratory center in the intermediolateral nucleus (ILN) of T3-4 segments of the cat spinal cord. A fiber-filled double-barrel coaxial electrode was devised. The inner barrel electrode, filled with 3 M NaCl solution, was used for stimulating intraspinal structures to determine the cardioacceleratory center. The outer barrel electrode with an Agar stop, filled with a 20% HRP solution, was used for injecting HRP by pulses of positive electric current. In every experiment, HRP was injected into 3 points within the cardioacceleratory center at intervals of 1 mm. Out of 36 experiments, 10 showed that the HRP injection sites were centered in and almost confined to the ILN, and the population of the HRP-labeled cells was not less than 50. Some 1146 HRP-labeled cells were thus identified. They were distributed in the medulla oblongata (72.1%), pons (10.2%), midbrain (8.5%) and hypothalamus (9.2%). They were concentrated in the medullary reticular formation (37.8%), median raphe (26.9%) and pontine reticular formation (10.2%). Contrary to expectation, the HRP-labeled cells were few in the nucleus tractus solitarii (3.7%), paraventricular hypothalamic area (3.3%) and nucleus locus coeruleus (none).

Human brainstem catecholamine neuronal anatomy as indicated by immunocytochemistry with antibodies to tyrosine hydroxylase

Immunocytochemistry based on antibodies to tyrosine hydroxylase is used to identify catecholaminergic neurons in the human brain stem. An atlas is provided and the distribution of structures compared with that in other animals and with biochemical and catecholamine fluorescent data from humans. Broad agreement of results increases the confidence with which tyrosine hydroxylase-like immunoreactivity can be used to trace catecholaminergic pathways in human postmortem material. As compared to most studies of other animals there are striking increases in populations of upper pontine and mesencephalic catecholaminergic neurons in the human. Distinct cytoarchitectonic features, consistent differences in tyrosine hydroxylase immunoreactive staining intensity and regional variations in substance P innervation indicate complexity within the substantia nigra. Human catecholaminergic neurons are prominent in the midline of the ventral tegmentum and the upper parts of the central tegmental tracts. A bundle of tyrosine hydroxylase-immunoreactive axons runs between the latter regions and a cluster of smaller catecholaminergic neurons which lie in the oblique band of axons joining ventrolateral and dorsomedial medullary catecholaminergic groups. There are more catecholaminergic neurons within and closely related to the superior cerebellar peduncles than have been described in other species. Anatomically, the central compact nucleus of the locus coeruleus appears to be related to several nearby catecholaminergic cell groups. The data provided are being used as a basis for neuropathologic studies of human neurological diseases.

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

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

The organization of noradrenergic pathways from the brainstem to the paraventricular and supraoptic nuclei in the rat

Axonal transport and immunohistochemical methods have been used to clarify the organization of pathways from noradrenergic and adrenergic cell groups in the brainstem to the paraventricular (PVH) and supraoptic (SO) nuclei of the hypothalamus. First, the location of such cells was determined with a combined retrograde tracer-immunofluorescence method. The fluorescent tracer, True Blue, was injected into the PVH or the SO, and sections through the brainstem were stained with anti-(rat) DBH, a specific marker for noradrenergic and adrenergic neurons. It was found that, after injections in the PVH, doubly labeled neurons were confined almost exclusively to 3 cell groups, the A1 region of the ventral medulla, which contained a majority of such cells, the A2 region in the dorsal vagal complex, and the locus coeruleus (A6 region). After injections centered in the SO an even greater proportion of doubly labeled cells were found in the A1 region, although some were also found in the A2 and A6 regions. The topography of doubly labeled cells indicates that these projections arise primarily from noradrenergic neurons, although adrenergic cells in both the C1 and the C2 groups probably contribute as well. Because well over 80% of the retrogradely labeled cells in these three regions were also DBH-positive, we next placed injections of [3H]amino acids into each of them in different groups of animals, and traced the course and distribution of the ascending (presumably DBH-positive) projections to the PVH and SO in the resulting autoradiograms. Injections centered in the A1 region labeled a substantial projection to most parts of the parvocellular division of the PVH, and was most dense in the dorsal and medial parts. In addition, terminal fields were labeled on those parts of the magnocellular division of the PVH, and of the SO, in which vasopressinergic cell bodies are concentrated. Injections centered in the A2 region also labeled a projection to the parvocellular division of the PVH that was topographically similar, but less dense, than that from the A1 region. In contrast, [3H]amino acid injections centered in the locus coeruleus labeled a moderately dense projection to the PVH that was limited to the medialmost part of the parvocellular division. Neither the A2 nor the A6 cell groups project to the magnocellular parts of PVH, or to the SO. The autoradiographic material, and additional double-labeling experiments, were used to identify and to characterize projections that interconnect the A1, A2 and A6 regions, as well as possible projections from these cell groups to the spinal cord. These results may be summarized as follows: a substantial projection from the nucleus of the solitary tract to the A1 region was identified, but this pathway does not arise from catecholaminergic neurons in the A2 cell group. DBH-stained cells in the A1 region project back to the dorsal vagal complex, as well as quite massively to the locus coeruleus (A6 region)...

Immunohistochemical localization of putative neurotransmitters within the feline nucleus tractus solitarii

With the aid of immunohistochemical techniques the distribution of substance P, met-enkephalin, serotonin, somatostatin, alpha-melanocyte stimulating hormone, neurotensin and neurophysin immunoreactivities were mapped throughout the rostro-caudal extent of the cat's nucleus tractus solitarii. Three of the putative neurotransmitters (substance P, enkephalin and serotonin) were found to be widely distributed as varicose fibers and punctate structures. The densities of their immunoreactivities were plotted in a range from very dense, dense, moderate, occasional, to none, at different levels of the nucleus of the solitary tract. Substance P immunoreactivity was the most varied and dense of all the neurotransmitters studied. Its accumulations ranged from very dense in the lateral, dense in portions of the parvocellular and lateral, moderate in medial and commissural and occasional in ventrolateral and portions of the parvocellular subdivisions. Both the enkephalin and serotonin immunoreactivities had patterns similar to that of substance P immunoreactivity, although their amounts were not as great. Following colchicine treatment neurons containing substance P and enkephalin immunoreactivity were found in many subdivisions of the nucleus of the solitary tract. Somatostatin, alpha-melanocyte stimulating hormone, neurotensin and neurophysin immunoreactivities were present in the nucleus of the solitary tract as isolated varicose fibers scattered throughout the nucleus. Immunoreactive neurons were not found for these putative neurotransmitters after colchicine treatment. The presence of substance P immunoreactivity within subdivisions which receive visceral afferent input is discussed in relation to the role of substance P as a possible transmitter of the afferent limb of the vagus nerve. The distribution of enkephalin and serotonin immunoreactivities in the nucleus of the solitary tract reflect their involvement in the regulation or modulation of cardiovascular and respiratory functions. While the significance of somatostatin, alpha-melanocyte stimulating hormone, neurotensin and neurophysin immunoreactivities within the nucleus of the solitary tract is not understood at present, these substances might possibly play a role in visceral functions.

The location of brainstem neurones tonically inhibiting dorsal horn neurones of the cat

In an investigation of the origin of tonic descending inhibition of dorsal horn neurones by impulses in unmyelinated primary afferents, brainstem regions were electrolytically lesioned. With each neurone studied, tonic descending inhibition was measured before and after brainstem lesions by cooling a segment of spinal cord cephalic to the recording site. Such inhibition was not reduced by lesions of areas which, when stimulated, produce analgesia. These included the periaqueductal grey and the raphé areas of the midbrain and pons-medulla. Tonic descending inhibition was reduced by bilateral lesions of the ventrolateral caudal medulla in the region of the lateral reticular nuclei. Lateral reticular areas may have a functional role in the control of pain.

Efferent projections of the A1 catecholamine cell group in the rat: an autoradiographic study

Efferent connections of the region of the A1 catecholamine cell group were investigated by the anterograde autoradiographic method in rats, some of which had been pretreated with intraventricular injections of 6-hydroxydopamine (6-OHDA). Spinal projections were further studied by combining histofluorescence and horseradish peroxidase staining in the same sections. Projections from the A1 region ascend through the lateral hypothalamus to the bed nucleus of the stria terminalis, the medial preoptic area, and several hypothalamic nuclei: the dorsomedial nucleus, the dorsal hypothalamic area, the paraventricular and supraoptic nuclei, and the median eminence. These projections are predominantly ipsilateral. Since they are sensitive to 6-OHDA, they presumably arise from catecholamine cells of the A1 group. Other pathways are not noticeably affected by 6-OHDA. These include projections through the reticular formation to the contralateral nucleus ambiguus, the ipsilateral facial nucleus, and the Kölliker-Fuse nuclei, the parabrachial nuclei and the periaqueductal gray on both sides, as well as the intralaminar nuclei of the thalamus. These pathways probably do not arise from the A1 group, although a minor noradrenergic component cannot be ruled out. Spinal projections extend to the intermediolateral cell column and the ventral horn, and especially to the phrenic motor nucleus. However, these projections arise almost exclusively from non-catecholamine cells. Only a small minority of the fluorescent A1 cells are retrogradely labeled after injections of HRP into the upper thoracic spinal cord. They lie at the level of the pyramidal decussation. Likewise only a few fluorescent cells of the A2 group are labeled. Although the A1 and A2 groups were long thought to be principal sources of spinal norepinephrine, a review of the literature shows that this belief was based on equivocal evidence.

Olivary afferents from the raphe nuclei as studied with retrograde transport of horseradish peroxidase

The afferent projection to the olive from the raphe nuclei in the cat has been studied in animals where microinjections of horseradish peroxidase have been made into the inferior olive from a ventral approach. Retrogradely labelled cells were present in the three caudal most raphe nuclei: the nucleus raphe pallidus, obscurus and magnus. The retrogradely labelled cells are of all sizes, and there appears to be a higher concentration of cells on the side ipsilateral to the injection. The observations demonstrate that all three major subdivisions of the olive--the medial accessory, the dorsal accessory and the principal olive--all receive efferent raphe fibres. No retrogradely labelled cells were present in the other raphe nuclei. The findings are discussed and related to other tracer studies dealing with olivary afferents from the raphe complex.

Selective retrograde transport of 3H-serotonin in vagal afferents

A new serotonergic afferent vagal component has been demonstrated in the cat by radioautography. Twenty-four hours after a bilateral injection of tritiated serotonin (3H-5-HT) into the area of the nucleus of the solitary tract (NST), heavily and lightly labelled cell bodies were observed in the nodose ganglia. After unilateral injections of 3H-5-HT into the same area, labelled ganglionar cell bodies were found in the ipsilateral nodose ganglion. Some were also found in the contralateral one, suggesting a serotonergic crossed fibers component. Dense clusters of silver grains, depicting typical labelling of neuronal varicosities, were observed in the NST. After destruction of the serotonergic terminals with 5,7-dihydroxytryptamine, followed by injection of 3H-5-HT, the number of labelled cell bodies decreased dramatically in the ipsilateral nodose ganglia and the clusters of silver grains disappeared in the NST. After ligature or section of the supranodose vagal nerve, following injection of 3H-5-HT into the NST, no radioautographic reaction was observed in the homolateral nodose ganglia. The present study demonstrates the existence of a peripheral serotonergic system in vagal afferents. The physiological implications of this new serotonergic visceral pathway remain to be studied.