Catecholamine Cell Research Articles

A1 catecholamine cell group: fine structure and synaptic input from the nucleus of the solitary tract.

Preembedding immunoperoxidase staining methods were used to characterize tyrosine hydroxylase-immunoreactive (TH-ir) elements in the caudal ventrolateral medulla, and to determine the extent to which neurons of the A1 cell group are directly innervated by projections of the nucleus of the solitary tract (NTS). TH-ir neurons in the A1 region were medium-sized and multipolar. They possessed rounded nuclei with infrequent invaginations, well-developed Golgi apparati, high cytoplasmic densities of mitochondria, and a low to moderate tendency for rough endoplasmic reticulum (RER) to align in parallel stacks. A1 cell bodies were commonly juxtaposed to TH-positive and TH-negative neurons, myelinated profiles, glia and/or vascular elements, but close membrane appositions were only seen with glial elements. Synaptic input to A1 neurons was predominantly asymmetric, provided virtually exclusively by non-TH-ir terminals, and directed principally to dendritic shafts; A1 somata are relatively sparsely innervated. In a second experiment, silver-intensified immunogold localization of TH-ir was combined with immunoperoxidase labeling for anterogradely transported Phaseolus vulgaris-leucoagglutinin (PHA-L), following tracer injections in the caudal aspect of the medial division of the NTS. These experiments revealed a small proportion of PHA-L-labeled axon terminals that made asymmetric contacts with dendritic shafts of TH-ir neurons. These results suggest that the fine structure and synaptic input of A1 neurons are somewhat distinct from that of rostrally situated C1 catecholamine cells. In addition, while they document a direct NTS-A1 projection that may participate in the interoceptive control of vasopressin secretion, the bulk of ventrolaterally directed projections from the caudomedial NTS contact noncatecholaminergic elements in the A1 region, some of which may correspond to so-called depressor neurons implicated in the baroreflex control of sympathetic outflow and vasopressin secretion.

Development of catecholamine systems in the brain of the lizard Gallotia galloti

For a better insight into general and derived traits of developmental aspects of catecholaminergic (CA) systems in amniotes, we have studied the development of these systems in the brain of a lizard, Gallotia galloti, with tyrosine hydroxylase (TH)- and dopamine (DA) immunohistochemical techniques. Two main groups of TH-immunoreactive (THi) perikarya appear very early in development: one group in the midbrain which gives rise to the future ventral tegmental area, substantia nigra and retrorubral cell groups, and another group in the tuberomammillary hypothalamus. Somewhat later in development, TH/DA-immunoreactive cells are observed in the thalamus, rostrodorsal hypothalamus and spinal cord, and, with another delay, in the suprachiasmatic nucleus, the periventricular organ, and the pretectal posterodorsal nucleus. CA cell groups that appear rather late in development include the cells in the olfactory bulb, the locus coeruleus and the caudal brainstem. As expected, the development of immunoreactive fibers stays behind that of the cell bodies, but reaches the adult-like pattern just prior to hatching. The present study revealed considerable variation in the relation between the state of cytodifferentiation and first expression of TH/DA immunoreactivity between CA cell groups. Catecholamine cells in the midbrain and tuberomammillary hypothalamus are still migrating, immature (absence of dendrites) and express only TH immunoreactivity at the time of first detection. Cells which appear at later developmental stages lie already further away from the ventricle, possess two or more dendritic processes, and generally express both TH- and DA immunoreactivity.

Detection and Regulation of Tyrosine Hydroxylase mRNA in Catecholaminergic Terminal Fields: Possible Axonal Compartmentalization

Reverse transcriptase coupled with nested polymerase chain reaction amplification (RT/nested-PCR) was used to detect mRNA encoding tyrosine hydroxylase, the rate-limiting enzyme in catecholamine biosynthesis, in adult rat cerebellum, striatum, and pituitary neurointermediate lobe (NIL). These regions receive catecholaminergic innervation from the locus coeruleus, substantia nigra, and arcuate and periventricular nuclei of the hypothalamus, respectively, but are devoid of catecholamine-synthesizing cells. The RT/ nested-PCR products, which were generated using primers located on different exons of the tyrosine hydroxylase gene, indicate that the tyrosine hydroxylase mRNA detected is devoid of introns and, hence, is processed. These findings raise the possibility that tyrosine hydroxylase mRNA may be axonally transported. Using the same RT/nested-PCR protocol, we were unable to detect mRNA encoding dopamine β-hydroxylase, a different catecholaminergic biosynthetic enzyme, in either cerebellum, striatum, or NIL pituitary tissue. Thus, the detection of tyrosine hydroxylase mRNA in catecholamine terminal regions is biochemically specific. We were unable to detect tyrosine hydroxylase mRNA in optic nerve, indicating some degree of anatomical specificity as well. Expression of tyrosine hydroxylase mRNA in the cerebellum was markedly increased by subcutaneous administration of the catecholamine-depleting agent, reserpine, suggesting that tyrosine hydroxylase mRNA in catecholamine terminal regions may be functionally important. This finding also indirectly supports the hypothesis that tyrosine hydroxylase mRNA can be axonally transported since the ability of reserpine to induce expression of this transcript in conventional catecholamine cell groups is considered secondary to catecholamine depletion, and cerebellar cells do not synthesize catecholamines. Finally, lesions of the nigro-striatal pathway significantly decreased levels of tyrosine hydroxylase mRNA in the striatum, providing strong additional support for this hypothesis.

Connectivity of the lobus parolfactorius of the domestic chicken (Gallus domesticus): an anterograde and retrograde pathway tracing study.

In 1-week-old domestic chicks, the connectivity of the lobus parolfactorius (LPO), part of the avian basal ganglia, was investigated using Phaseolus vulgaris leucoagglutinin and horseradish peroxidase for anterograde and retrograde pathway tracing, respectively. Tyrosine hydroxylase immunocytochemistry was applied in combination with Phaseolus lectin to assess the overlap between LPO efferents and diencephalic and mesencephalic catecholamine centres. Anterograde projections from LPO were detected in the hyperstriatum, neostriatum, and paleostriatum. Intranuclear connections were also apparent within the LPO. Descending LPO efferents innervated the lateral mammillary and intramedial nuclei and the dorsomedial thalamic complex. Fibres from LPO were observed in the tectal gray, substantia nigra, area ventralis tegmentalis of Tsai, and the adjacent nucleus mesencephalicus profundus. Further caudally, projections from LPO reached the nucleus papillioformis, locus coeruleus, and subcoeruleus ventralis. LPO efferents were coextensive with tyrosine hydroxylase-positive cells in the nuclei mamillaris lateralis and intramedialis of the hypothalamus, area ventralis tegmentalis, substantia nigra, locus coeruleus, and subcoeruleus ventralis of mesencephalic and pontine tegmentum. Close contacts between LPO fibres and catecholamine cells were visible in the nigra and the area ventralis tegmentalis. Retrograde labelling from LPO was found in the archistriatum, dorsomedial thalamic complex, nuclei lateralis anterior and superficialis parvicellularis thalami, substantia nigra, central gray, area ventralis tegmentalis of Tsai, and locus coeruleus and in cells dorsal to the decussation of brachium conjunctivum. Reciprocal connections were verified between the LPO and the following areas: dorsomedial thalamic complex, central gray, substantia nigra, area ventralis of Tsai, and locus coeruleus.

Expression of fos-like protein in brain following sustained hypertension and hypotension in conscious rabbits

The purpose of this study was to examine comprehensively and quantitatively the effects of sustained hypertension and hypotension on neuronal expression of Fos, the protein product of the proto-oncogene c- fos, in the brain of conscious rabbits. Hypertension or hypotension was produced by continuous intravenous infusion of phenylephrine or nitroprusside, at a rate sufficient to increase or decrease, respectively, arterial pressure by 20–30 mmHg, maintained for a period of 60 min. In comparison with a sham control group of rabbits that were infused with the vehicle solution alone, hypertension induced a significant increase in Fos immunoreactivity in the area postrema, the nucleus tractus solitarii, the caudal and intermediate ventrolateral medulla, the lateral parabrachial nucleus and the central nucleus of the amygdala. Double-labelling for tyrosine hydroxylase and Fos immmunoreactivity showed that few (approximately 5%) of the Fos-positive neurons in the caudal and intermediate ventrolateral medulla in this group of animals were also positive for tyrosine hydroxylase. Hypotension also produced a significant increase in Fos immunoreactivity in the above regions, as well as in the rostral ventrolateral medulla, the A5 area, the locus coeruleus and subcoeruleus, the paraventricular nucleus, the supraoptic nucleus, the arcuate nucleus and the medial preoptic area. Approximately 65% of neurons in the rostral, intermediate and caudal ventrolateral medulla that expressed Fos following hypotension were also positive for tyrosine hydroxylase. Similarly, in the pons, approximately 75% of Fos-positive cells in the locus coeruleus, subcoeruleus and A5 area were positive for tyrosine hydroxylase. In the hypothalamus, 92% of Fos-positive neurons in the supraoptic nucleus, and 37% of Fos-positive neurons in the paraventricular nucleus, were immunoreactive for vasopressin. Our results demonstrate that hypertension and hypotension induce reproducible and specific patterns of Fos expression in the brainstem and forebrain. The distribution patterns and chemical characteristics of Fos-positive neurons following sustained hypertension or hypotension are significantly different. In particular, hypotension, but not hypertension, caused Fos expression in many tyrosine hydroxylasepositive cells within all pontomedullary catecholamine cell groups.

Ontogeny of catecholamine systems in the central nervous system of anuran amphibians: An immunohistochemical study with antibodies against tyrosine hydroxylase and dopamine

To get more insight into developmental aspects of catecholamine systems in vertebrates, in particular anuran amphibians, these systems were studied immunohistochemically in embryos and larvae of Xenopus laevis and Rana ridibunda. Antisera against tyrosine hydroxylase (TH) and dopamine (DA) revealed that catecholamine systems are already present at early embryonic stages. The first dopamine group to be detected was found ventral to the central canal of the spinal cord of Xenopus, soon followed by DA cell groups in the posterior tubercle, the hypothalamic periventricular organ, the accompanying cell group of the periventricular organ, and the suprachiasmatic nucleus. Although weakly TH-immunoreactive cells were found in the olfactory bulb at about the same embryonic stages, DA immunoreactivity was not detected until premetamorphic stage 49. Dopamine cell groups in the caudal brainstem, midbrain, and pretectum appeared at late premetamorphic and prometamorphic stages, whereas the preoptic group was first observed at the metamorphic climax stage. Rana showed an almost similar timetable of development of catecholamine cell groups, except for the caudal brainstem group which was already present at the end of the embryonic period. When compared with previous studies by means of formaldehyde-induced fluorescence technique, it becomes clear that TH/DA immunohistochemistry enables an earlier detection of catecholamine cell groups and fiber systems in anuran amphibians. The present study also revealed that the DA-immunoreactive cells of the hypothalamic periventricular organ never stained with the TH antiserum during development, thus supporting their putatively DA accumulating nature. Another notable result is the site of origin and rather late appearance of the midbrain dopaminergic cell group. It is suggested that the latter cell group only partly corresponds to the ventral tegmental area and substantia nigra of amniotes.

C-Fos expression in hypothalamic neurosecretory and brainstem catecholamine cells following noxious somatic stimuli

Noxious somatic stimuli elicit vasopressin secretion, an effect thought to result from activation of a facilitatory input from Al catecholamine cells of the medulla oblongata. To better characterize the Al cell response and effects on other neuroendocrine Al projection targets, particularly within the paraventricular nucleus, we have now mapped c-fos expression in neurochemically identified catecholamine and neurosecretory cells following a noxious somatic stimulus. Unilateral hind paw pinch significantly increased c-fos expression in contralateral Al cells whereas other brainstem catecholamine cell groups were unaffected. Expression of c-fos was also increased in the supraoptic nucleus, this effect being more pronounced for vasopressin than oxytocin neurosecretory cells and, as with Al cells, primarily on the side contralateral to the stimulated paw. In contrast, the increase in the paraventricular nucleus was greater in oxytocin rather than in vasopressin cells. Additionally there was a significant rise in c-fos expression in medial parvocellular paraventricular nucleus cells of noxiously stimulated animals. Notably, the majority of tuberoinfundibular corticotropin-releasing factor cells are located in this medial parvocellular zone. These results are consistent with and expand on those previously reported from electrophysiological and anatomical studies. The finding of differing neurosecretory cell responses between supraoptic and paraventricular nuclei has interesting implications with regard to the afferent control of neurosecretory cell activity. For example, the substantially greater activation of supraoptic versus paraventricular nucleus vasopressin cells, despite being innervated by the same medullary noradrenergic cell group, raises the possibility of a differential input or differences in responsiveness. Furthermore, the activation of paraventricular nucleus parvocellular cells is consistent with suggestions that the Al cell group provides an excitatory input to this population.

CNS monoamine cell groups projecting to pancreatic vagal motor neurons: a transneuronal labeling study using pseudorabies virus

The CNS monoamine cell groups that project to the pancreatic parasympathetic preganglionic neurons were identified with the use of the viral retrograde transneuronal labeling method. Pseudorabies virus (PRV) was injected into the pancreas of C 8 spinal rats and subsequently, transneuronally-labeled central monoamine neurons were mapped in brain tissue sections that had been stained by an immunohistochemical procedure that allowed for the visualization of PRV products and biogenic amine neurotransmitter enzymes or serotonin (5-HT) in the same neuron. The enzymes studied were tyrosine hydroxylase (TH), dopamine-β-hydroxylase (DBH), phenylethanolamine- N-methyltransferase (PNMT), and histidine decar☐ylase. Pancreatic vagal motor neurons originate exclusively from the dorsal vagal motor nucleus and some of these may be dopamine neurons because they were TH immunopositive, but DBH and PNMT immunonegative. Transneuronally labeled aminergic neurons were found throughout the medulla oblongata. The adrenergic inputs arose from the C1, C2, and C3 cell groups. Noradrenergic inputs originated predominantly from the A5 cell group, with lesser contributions from the A1 and A2 cell groups as well as from the area postrema. None of the other CNS catecholamine cells were labeled, except for some weakly staining TH-immunoreactive neurons, presumably dopaminergic, in the paraventricular hypothalamic nucleus (PVN). The greatest number of 5-HT neurons that innervate the pancreatic vagal motor neurons come from the gigantocellular reticular nucleus, pars alpha with lesser inputs from the raphe magnus, obscurus, and pallidus nuclei. None of the CNS histaminergic cell groups were labeled. In conclusion, the present study demonstrates that pancreatic vagal motor neurons receive inputs from adrenergic, noradrenergic, and 5-HT neurons of the lower brainstem and from a potential dopaminergic input from the PVN.

The projections of noradrenergic neurons in the A5 catecholamine cell group to the spinal cord in the rat: anatomical evidence that A5 neurons modulate nociception

Brainstem noradrenergic neurons located in the A5, A6, and A7 catecholamine cell groups provide the entire noradrenergic innervation of the spinal cord. We have previously demonstrated that noradrenergic neurons in the A6 and A7 cell groups innervate the ventral and dorsal horns, respectively. Since the specific spinal cord terminations of the A5 cell group have not been clearly delineated, the present experiments were designed to trace the projections from this noradrenergic cell group to the spinal cord, using the anterograde tracer Phaseolus vulgaris-leucoag-glutinin (PHA-L) in combination with dopamine-β-hydroxylase immunocytochemistry. The results of these experiments indicate that A5 noradrenergic neurons project ipsilaterally through the dorsolateral funiculus in cervical, thoracic, and lumbar segments. In cervical segments, these axons terminate primarily in the ipsilateral deep dorsal horn (laminae IV–VI) and the intermediate zone (lamina VII). In thoracic segments, the intermediolateral cell column is heavily innervated by A5 axons. In lumbar segments, the concentration of A5 axons is more diffuse and more widely distributed than that in cervical and thoracic segments. Although there is a higher density of axons in the deep dorsal horn and the intermediate zone, there are also scattered axons in the dorsal and ventral horns. The innervation of these regions of the spinal cord by A5 neurons provides anatomical support for the conclusion that these noradrenergic neurons are involved in modulating cardiovascular reflexes and nociceptive transmission in the spinal cord.

Distribution, parabrachial region projection, and coexistence of neuropeptide and catecholamine cells of the nucleus of the solitary tract in the pigeon.

The chemical nature of the cells of the nucleus of the solitary tract (NTS) that project to the parabrachial nucleus (PB) was investigated in the pigeon by the use of fluorescent bead retrograde tracer and immunofluorescence for the detection of substance P (SP), leucine-enkephalin (LENK), cholecystokinin (CCK), neurotensin (NT), somatostatin (SS), and tyrosine hydroxylase (TH). Cells immunoreactive for CCK were located in subnuclei lateralis dorsalis pars anterior (LDa) and medialis superficialis pars posterior, and caudal NTS (cNTS); 22-26.5% of these cells were double-labeled bilaterally. Immunoreactive SP cells were found in ventral NTS subnuclei; 24-25% of these cells were double-labeled bilaterally. Cells immunoreactive for LENK and NT were concentrated in the anterior NTS; 5.5-7.5% of the LENK cells were double-labeled bilaterally, while 11% (ipsilateral) and 21% (contralateral) of the NT immunoreactive cells were double-labeled. Many SS immunoreactive cells were found in peripherally located subnuclei; 5.5-6.5% of these cells were double-labeled bilaterally. Catecholamine cells were distributed in LDa, peripheral subnuclei, and cNTS; 23% of these cells were double-labeled ipsilaterally and 8.5% contralaterally. A two-color double-labeling immunofluorescence technique revealed many cells immunoreactive for both NT and LENK, only a rare cell immunoreactive for both SS and SP, and no cells immunoreactive for both TH and SP. Cells immunoreactive for SP, CCK, NT, and TH are major contributors to NTS projections to PB. The confinement of these substances to specific NTS subnuclei, which receive visceral sensory information from specific organs, may contribute to the chemical encoding of ascending visceral information.

Projections from the commissural subnucleus of the solitary tract onto catecholamine cell groups of the ventrolateral medulla

Efferent projections of the commissural subnucleus of the solitary tract (COM) to the ventrolateral medulla were studied in the cat using anterograde labeling with biocytin combined with dopamine β-hydroxylase immunohistochemistry. COM neurons were observed to send their axons densely to the areas of distribution of respiration-related neurons in the ventrolateral medulla, e.g. ventral respiratory group, Bötzinger complex. Axon terminals from COM neurons were further found in the areas of distribution of catecholamine neurons (C1 and A1 cell groups), that were distributed in the close vicinity of the reported respiration-related areas in the ventrolateral medulla. Putative synaptic contacts of axon terminals from COM neurons with catecholamine neurons were often observed in the C1 area.

Presence of a dynorphin-like peptide in a restricted subpopulation of catecholaminergic neurons in rat nucleus tractus solitarii

Immunofluorescence colocalization techniques were used to examine the extent of coexistence of the endogenous opioid peptide dynorphin with catecholamines and the related opioid peptide enkephalin within neurons of the rat medulla oblongata. Immunoreactivities for dynorphin and the catecholamine-synthesizing enzyme tyrosine hydroxylase were found to coexist within a limited subpopulation of A2 catecholamine cells, localized to the medial nucleus of the nucleus tractus solitarii. Colocalization of the two opioid peptides was found mainly within perikarya situated in the medial and ventrolateral nuclei of the nucleus tractus solitarii. Triple-labeling studies revealed only rare cases of catecholamine/dynorphin/enkephalin coexistence. These data demonstrate that dynorphin is present within a restricted subpopulation of catecholamine neurons in the dorsal medulla oblongata. In addition, the content of either of the opioids enkephalin or dynorphin appears to distinguish subsets of medullary catecholamine neurons.

Antinociception induced by microinjection of substance p into the A7 catecholamine cell group in the rat

Stimulation of neurons in the ventromedial medulla produces antinociception that is mediated in part by indirect activation of pontospinal noradrenergic neurons. Substance P-containing neurons located in the ventromedial medulla project to the A7 catecholamine cell group and may serve as an excitatory link between these two cell groups. Thus, the antinociception induced by stimulation of the neurons in ventromedial medulla may be mediated by substance P released from these projections which activates spinally projecting noradrenergic neurons in the A7 cell group. This hypothesis was tested by determining whether microinjection of various doses of substance P into the A7 cell group of the rat could induce antinociception. The results indicated that substance P induced dose-dependent antinociception that was more pronounced in the hindlimb ipsilateral to the microinjections. This observation is consistent with anatomical observations that noradrenergic A7 neurons project predominantly to the ipsilateral spinal cord dorsal horn. Moreover, the antinociceptive effects of substance P microinjection appear to be mediated at least in part by activation of spinally projecting noradrenergic neurons in the A7 cell group, because intrathecal injections of the alpha-2 noradrenergic antagonists yohimbine and idazoxan blocked these antinociceptive effects. The results of these experiments support the hypothesis that the antinociception induced by stimulation of neurons in the ventromedial medulla is mediated in part by activation of substance P-containing neurons that project to, and activate, spinally projecting noradrenergic neurons located in the A7 catecholamine cell group.

Rostrocaudal differences in morphology and neurotransmitter content of cells in the subretrofacial vasomotor nucleus

The rostral ventrolateral medulla (RVLM) contains sympathoexcitatory neurons that exert a powerful control over the sympathetic outflow to the cardiovascular system. In the cat there is a concentration of such neurons (but not neurons subserving other functions) within a narrow longitudinal column in the RVLM termed the subretrofacial (SRF) nucleus. Furthermore, it has been suggested that there are subgroups of cells, located at different rostrocaudal levels of the SRF nucleus, that preferentially or exclusively control different vascular beds (e.g. in the kidney and hindlimb). The aim of this study was to map quantitatively the rostrocaudal distribution within the nucleus of different cell types, defined according to morphological and/or chemical criteria, and to correlate this with the regional vasomotor effects (in hindlimb and kidney) evoked by stimulation of SRF cells at the corresponding rostrocaudal levels. SRF cells were highly heterogeneous with respect to both their morphology and chemical properties. They varied greatly in size (equivalent diameter ranging from 10–40 μm) as well as in shape and orientation. An immunohistochemical examination using the avidin-biotin procedure revealed that many SRF cells (estimated 57% of all SRF cells) were immunoreactive for tyrosine hydroxylase (TH, a marker of catecholamine cells). In addition, there were SRF cells immunoreactive for neuropeptide Y (NPY, 11% of total), enkephalin (ENK, 16% of total), and serotonin (5HT, 10% of total), but not for substance P, galanin or somatostatin. Different cell types, defined according to their morphology and/or chemical properties, were unevenly distributed throughout the nucleus. In the most caudal part of the SRF nucleus, virtually all cells were TH-positive, and the large majority (estimated 80%) were NPY-positive, suggesting that many cells at this level contained both TH and NPY. In contrast, in the most rostral part of the SRF nucleus, only 30% of cells were TH-positive, and no NPY-positive cells were observed. Both 5HT- and ENK-positive cells were found throughout the rostrocaudal extent of the nucleus, but predominantly within its rostral part. Furthermore, TH-positive cells in the rostral SRF nucleus were on average significantly larger (mean equivalent diameter 18–43% greater) than TH/NPY-positive cells in the caudal part of the nucleus, but smaller than 5HT- or ENK-positive cells at the same level. Overall, rostral cells (regardless of their chemical type) were larger than caudal cells within the SRF nucleus (mean equivalent diameter 13–28% greater). Talking into account both morphological and chemical properties, a minimum of four distinct cell subgroups in the SRF nucleus could be defined: caudal TH/NPY-positive cells, rostral TH-positive (but NPY-negative) cells, 5HT-positive cells (possibly also containing ENK), and cells that were not immunoreactive for any of these compounds. Large (> 100%) increases in blood pressure and iliac vascular resistance were elicited by microinjection of picomolar amounts of sodium glutamate into sites throughout the entire rostrocaudal extent of the SRF nucleus. In contrast, large or moderate (> 50%) increases in renal sympathetic nerve activity were evoked only from sites within the most rostral part of the nucleus. Correlation of the functional and immunohistochemical data indicates that NPY/TH-positive cells in the caudal SRF nucleus contribute to the regulation of the hindlimb but not the renal vascular bed. Secondly, they suggest that both catecholamine

Antinociception induced by electrical stimulation of spinally projecting noradrenergic neurons in the A7 catecholamine cell group of the rat

Recent anatomical evidence indicates that the pontine A7 catecholamine cell group provides the major noradrenergic innervation of the spinal cord dorsal horn (laminae I–IV). The experiments described in this report were designed to determine if these neurons modulate nociception at the level of the spinal cord. To this end, the antinociceptive effect of electrical stimulation applied at various sites along several tracks through the dorsolateral pontine tegmentum was determined in lightly anesthetized rats. The latency of the withdrawal response of the hind feet to noxious radiant thermal stimulation applied to the dorsal surface was used as a measure of nociception. The results indicated that the most potent and consistent antinociception was produced at sites near the A7 cell group. In addition, intrathecal injection of α-noradrenergic antagonists blocked the antinociception produced by electrical stimulation at sites near the A7 group. These observations indicate that the antinociception produced by stimulation near the A7 cell group was mediated by spinally projecting noradrenergic neurons. The results of these experiments provide evidence that pontospinal noradrenergic neurons located in the A7 cell group are important components of the descending neuronal system that modulates nociception.

Organization of amygdaloid projections to brainstem dopaminergic, noradrenergic, and adrenergic cell groups in the rat

The distribution of amygdaloid axons in the various brainstem dopaminergic, noradrenergic and adrenergic cell groups was examined. This was accomplished by means of the Phaseolus vulgaris leucoagglutinin lectin (PHA-L) anterograde tracing technique combined with glucose-oxidase immunocytochemistry to catecholamine markers (i.e., tyrosine hydroxylase, dopamine beta hydroxylase and phenylethanolamine N-methyltransferase). Injections of PHA-L in the medial part of the central amygdaloid nucleus resulted in axonal and terminal labeling in most catecholamine cell groups in the brainstem. Amygdaloid terminals appeared to contact catecholaminergic cells in several brainstem regions. The most heavily innervated catecholaminergic cells were the A9 (lateral) and A8 dopaminergic cell groups and the C2/A2 adrenergic/noradrenergic cell groups in the nucleus of the solitary tract. The medial pan of the A9 and adjacent A10 dopaminergic cell groups was moderately innervated. A moderate innervation by amygdaloid terminals was observed on rostral locus coeruleus noradrenergic cells (A6 rostral) and adrenergic cells of the rostral ventrolateral medulla (C1). Noradrenergic cells of the A5, main body of the locus coeruleus (A6), A7 and subcoeruleus were sparsely innervated. Amygdaloid axons were not observed on noradrenergic neurons of the A4 cell group, area postrema and A1 cells of the ventrolateral medulla. The results demonstrate that the amygdala primarily innervates the dopaminergic cells of midbrain (i.e., A8 and lateral A9 cells) and the adrenergic cells (C2) and noradrenergic (A2) cells in the nucleus of the solitary tract. The possible functional significance of amygdaloid innervation of catecholaminergic cells is discussed.

Is there a dopaminergic projection from the A11 catecholamine cell group to the amygdala?

The dopaminergic nature of the pathway from the subparafascicular thalamic nucleus and its adjacent region to the amygdala was reexamined by means of retrograde fluorescent tracers coupled with tyrosine hydroxylase (TH) immunofluorescence. After injecting a small amount of tracer into the amygdala, retrogradely labeled cells were found in the subparafascicular thalamic nucleus and its adjacent periventricular region. TH immunofluorescence showed that these labeled cells completely lacked TH immunoreactivity. Similar results were obtained when a larger amount of tracer was applied to the amygdala. The present study, in contrast to the previous report describing the dopaminergic innervation of the amygdala by the cells in and around the subparafascicular area (A11 catecholamine cell group), indicates that the A11 cell group does not contribute to a dopaminergic input to the amygdala.

Light microscopic radioautographic localization of somatostatin binding sites in the brainstem of the rat

The distribution of somatostatin binding sites was investigated by light microscopic radioautography in the brainstem of the rat following in vitro labeling with 125I-Tyr 0-DTrp 8-somatostatin 14. Moderate to high labeling densities were detected within the superior colliculus, the locus coeruleus and subcoeruleus, the parabrachial complex, the nucleus of the solitary tract and the dorsal motor nucleus of the vagus. Most of the white matter was devoid of specific somatostatin binding except for fibers of the glossopharyngeal nerve and the spinal trigeminal tract. In most of the labeled areas, 125I-somatostatin binding was evenly distributed between neuropil and perikarya. In a few instances, however, the binding clearly predominated over nerve cell bodies: namely in the dorsal motor nucleus of the vagus and in the pontine and medullary tegmentum. In the latter two regions, the labeled neurons were identified in adjacent sections by tyrosine hydroxylase immunohistochemistry as belonging to the A5 and A1 catecholamine cell groups, respectively. These findings, together with the confirmed association of somatostatin binding sites with noradrenergic neurons in the locus coeruleus, suggest that interactions with catecholaminergic systems may represent a major mode of action for somatostatin in the brainstem.

Brainstem Reticular Nuclei that Project to the Cerebellum in Rats A Retrograde Tracer Study; pp. 39–53

The nuclear origins of projections from the brainstem reticular formation to the cerebellum were examined using four retrograde tracer substances: horseradish peroxidase, wheat germ agglutinin-horseradish peroxidase conjugate, Fluoro-Gold, and rhodamine beads. Tracer injections were made into each of the three major longitudinal zones of the cerebellar cortex (vermis, paravermal hemisphere, and lateral hemisphere) as well as into the various deep cerebellar nuclei. Counts of retrogradely labeled cells were done on a large sample of select cases. The data generated by these cell counts indicate that the strongest reticulocerebellar projections arise from the three specialized pre-cerebellar reticular nuclei: the lateral reticular nucleus, the medullary paramedian reticular nucleus, and the reticulotegmental nucleus. The presumed noradrenergic locus coeruleus (A6 cell group) was also densely packed with retrogradely labeled neurons. However, strong reticulocerebellar projections also arose from other presumed catecholamine cell groups such as those in the ventrolateral medulla (the A1/C1 complex) and the caudal pons (A5). Substantial cerebellar projections originated from most of the various presumed serotonergic brainstem raphe cell groups (particularly raphe obscurus in the medulla), as well as from the presumed cholinergic Ch5 cell group (the pedunculopontine pars compact us nucleus). Labeled cells were also seen in several nonaminergic isodendritic reticular nuclei thought to be involved in visuomotor activity (e.g. paragigantocellularis dorsalis, raphe interpositus, and the pontine dorsomedial tegmental area), as well as in the lateral reticular zone of the medulla and lower pons (reticularis dorsalis and parvocellularis). Tracer injections into the deep nuclei produced relatively greater numbers of labeled neurons in large-celled medial reticular nuclei associated with skeletomotor activity, such as gigantocellularis. magnocellularis, and pontis caudalis. Reticular nuclei conspicuous in their lack of projections to the cerebellum included reticularis ventralis in the medulla, pontis oralis, and both subdivisions of the midbrain reticular formation (cuneiformis and subcuneiformis). As a whole, the various isodendritic reticular nuclei project most strongly to midline cerebellar structures (vermal cortex or fastigial nuclei), less strongly to the paravermal cortex or interposed nuclei, and least strongly to the lateral cortex or dentate nucleus. Within individual reticular nuclei, the morphology of labeled neurons is identical to that reported previously by this laboratory subsequent to spinal or cortical HRP injections, thus strengthening this laboratory's hypothesis that the various brainstem reticular nuclei can be distinguished on the basis of neuronal morphology.

The projection of noradrenergic neurons in the A7 catecholamine cell group to the spinal cord in the rat demonstrated by anterograde tracing combined with immunocytochemistry

Noradrenergic neurons located in the A5, A7 and locus coeruleus/subcoeruleus (LC/SC) catecholamine cell groups innervate all levels of the spinal cord. However, the specific spinal cord terminations of these neurons have not been clearly delineated. This study determined the spinal cord terminations of the A7 catecholamine cell group using the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) in combination with dopamine-β-hydroxylase (DBH) immunocytochemistry. In addition, the spinal cord projections of A7 neurons were examined by measuring the reduction in the density of DBH-immunoreactive axons in specific regions of the spinal cord after a unilateral electrolytic lesion of the A7 cell group. The results of these experiments indicate that noradrenergic neurons in the A7 cell group project primarily in the ipsilateral dorsolateral funiculus and terminate most heavily in the dorsal horn (laminae I–IV).