Evidence for the existence of putative dopamine-, adrenaline- and noradrenaline-containing vagal motor neurons in the brainstem of the rat

Quantification of brainstem norepinephrine relative to vocal impairment and anxiety in the Pink1-/- rat model of Parkinson disease

Vocal communication impairment and anxiety are co-occurring and interacting signs of Parkinson Disease (PD) that are common, poorly understood, and under-treated. Both vocal communication and anxiety are influenced by the noradrenergic system. In light of this shared neural substrate and considering that noradrenergic dysfunction is a defining characteristic of PD, tandem investigation of vocal impairment and anxiety in PD relative to noradrenergic mechanisms is likely to yield insights into the underlying disease-specific causes of these impairments. In order to address this gap in knowledge, we assessed vocal impairment and anxiety behavior relative to brainstem noradrenergic markers in a genetic rat model of early-onset PD (Pink1-/-) and wild type controls (WT). We hypothesized that 1) brainstem noradrenergic markers would be disrupted in Pink1-/-, and 2) brainstem noradrenergic markers would be associated with vocal acoustic changes and anxiety level. Rats underwent testing of ultrasonic vocalization and anxiety (elevated plus maze) at 4, 8, and 12 months of age. At 12 months, brainstem norepinephrine markers were quantified with immunohistochemistry. Results demonstrated that vocal impairment and anxiety were increased in Pink1-/- rats, and increased anxiety was associated with greater vocal deficit in this model of PD. Further, brainstem noradrenergic markers including TH and α1 adrenoreceptor immunoreactivity in the locus coeruleus, and β1 adrenoreceptor immunoreactivity in vagal nuclei differed by genotype, and were associated with vocalization and anxiety behavior. These findings demonstrate statistically significant relationships among vocal impairment, anxiety, and brainstem norepinephrine in the Pink1-/- rat model of PD.

Unexpected Roles for the Second Brain: Enteric Nervous System as Master Regulator of Bowel Function

At the most fundamental level, the bowel facilitates absorption of small molecules, regulates fluid and electrolyte flux, and eliminates waste. To successfully coordinate this complex array of functions, the bowel relies on the enteric nervous system (ENS), an intricate network of more than 500 million neurons and supporting glia that are organized into distinct layers or plexi within the bowel wall. Neuron and glial diversity, as well as neurotransmitter and receptor expression in the ENS, resembles that of the central nervous system. The most carefully studied ENS functions include control of bowel motility, epithelial secretion, and blood flow, but the ENS also interacts with enteroendocrine cells, influences epithelial proliferation and repair, modulates the intestinal immune system, and mediates extrinsic nerve input. Here, we review the many different cell types that communicate with the ENS, integrating data about ENS function into a broader view of human health and disease. In particular, we focus on exciting new literature highlighting relationships between the ENS and its lesser-known interacting partners.

Vagally mediated effects of brain stem dopamine on gastric tone and phasic contractions of the rat

Dopamine (DA)-containing fibers and neurons are embedded within the brain stem dorsal vagal complex (DVC); we have shown previously that DA modulates the membrane properties of neurons of the dorsal motor nucleus of the vagus (DMV) via DA1 and DA2 receptors. The vagally dependent modulation of gastric tone and phasic contractions, i.e., motility, by DA, however, has not been characterized. With the use of microinjections of DA in the DVC while recording gastric tone and motility, the aims of the present study were 1) assess the gastric effects of brain stem DA application, 2) identify the DA receptor subtype, and, 3) identify the postganglionic pathway(s) activated. Dopamine microinjection in the DVC decreased gastric tone and motility in both corpus and antrum in 29 of 34 rats, and the effects were abolished by ipsilateral vagotomy and fourth ventricular treatment with the selective DA2 receptor antagonist L741,626 but not by application of the selective DA1 receptor antagonist SCH 23390. Systemic administration of the cholinergic antagonist atropine attenuated the inhibition of corpus and antrum tone in response to DA microinjection in the DVC. Conversely, systemic administration of the nitric oxide synthase inhibitor nitro-l-arginine methyl ester did not alter the DA-induced decrease in gastric tone and motility. Our data provide evidence of a dopaminergic modulation of a brain stem vagal neurocircuit that controls gastric tone and motility.NEW & NOTEWORTHY Dopamine administration in the brain stem decreases gastric tone and phasic contractions. The gastric effects of dopamine are mediated via dopamine 2 receptors on neurons of the dorsal motor nucleus of the vagus. The inhibitory effects of dopamine are mediated via inhibition of the postganglionic cholinergic pathway.

Central nervous system control of gastrointestinal motility and secretion and modulation of gastrointestinal functions

Although the gastrointestinal (GI) tract possesses intrinsic neural plexuses that allow a significant degree of autonomy over GI functions, the central nervous system (CNS) provides extrinsic neural inputs that regulate, modulate, and control these functions. While the intestines are capable of functioning in the absence of extrinsic inputs, the stomach and esophagus are much more dependent upon extrinsic neural inputs, particularly from parasympathetic and sympathetic pathways. The sympathetic nervous system exerts a predominantly inhibitory effect upon GI muscle and provides a tonic inhibitory influence over mucosal secretion while, at the same time, regulates GI blood flow via neurally mediated vasoconstriction. The parasympathetic nervous system, in contrast, exerts both excitatory and inhibitory control over gastric and intestinal tone and motility. Although GI functions are controlled by the autonomic nervous system and occur, by and large, independently of conscious perception, it is clear that the higher CNS centers influence homeostatic control as well as cognitive and behavioral functions. This review will describe the basic neural circuitry of extrinsic inputs to the GI tract as well as the major CNS nuclei that innervate and modulate the activity of these pathways. The role of CNS-centered reflexes in the regulation of GI functions will be discussed as will modulation of these reflexes under both physiological and pathophysiological conditions. Finally, future directions within the field will be discussed in terms of important questions that remain to be resolved and advances in technology that may help provide these answers.

Distribution of dopamine receptors D1- and D2-immunoreactive neurons in the dorsal motor nucleus of vagus in rats

The dorsal motor nucleus of vagus (DMV) plays an important role in the regulation of gastrointestinal function. Dopamine (DA) exerts potent neuromodulatory effects on the motoneurons in the DMV via dopamine receptors (DRs). However, the distribution of DRs and their neurochemical phenotypes in the DMV are unclear. In the present study, the distribution of DRs D1- and D2-immunoreactive (IR) neurons and their neurochemical phenotypes in the DMV of rats were investigated using a double-labeling immunofluorescence technique combined with confocal microscopy. The results indicated that a considerable quantity of D1 and D2 was expressed throughout the DMV. A large amount of choline acetyltransferase (ChAT)-IR and a few tyrosine hydroxylase (TH)-IR neurons were observed in the DMV. Nearly all of the neurons were also D1-IR and D2-IR. In conclusion, the present study demonstrates the wide distribution of D1 and D2 in the cholinergic and catecholaminergic neurons in the DMV of rats. The DRs might play an important role in the regulation of DA on the activity of cholinergic and catecholaminergic neurons in the DMV.

CXCR4 receptors in the dorsal medulla: implications for autonomic dysfunction

The chemokine receptor, CXCR4, plays an essential role in guiding neural development of the CNS. Its natural agonist, CXCL12 [or stromal cell-derived factor-1 (SDF-1)], normally is derived from stromal cells, but is also produced by damaged and virus-infected neurons and glia. Pathologically, this receptor is critical to the proliferation of the HIV virus and initiation of metastatic cell growth in the brain. Anorexia, nausea and failed autonomic regulation of gastrointestinal (GI) function cause morbidity and contribute to the mortality associated with these disease states. Our previous work on the peripheral cytokine, tumor necrosis factor-alpha, demonstrated that similar morbidity factors involving GI dysfunction are attributable to agonist action on neural circuit elements of the dorsal vagal complex (DVC) of the hindbrain. The DVC includes vagal afferent terminations in the solitary nucleus, neurons in the solitary nucleus (NST) and area postrema, and visceral efferent motor neurons in the dorsal motor nucleus (DMN) that are responsible for the neural regulation of digestive functions from the oral cavity to the transverse colon. Immunohistochemical techniques demonstrate a dense concentration of CXCR4 receptors on neurons throughout the DVC and the hypoglossal nucleus. CXCR4-immunoreactivity is also intense on microglia within the DVC, though not on the astrocytes. Physiological studies show that nanoinjection of SDF-1 into the DVC produces a significant reduction in gastric motility in parallel with an elevation in the numbers of cFOS-activated neurons in the NST and DMN. These results suggest that this chemokine receptor may contribute to autonomically mediated pathophysiological events associated with CNS metastasis and infection.

Central nervous system distribution of the transcription factor Phox2b in the adult rat

Phox2b is required for development of the peripheral autonomic nervous system and a subset of cranial nerves and lower brainstem nuclei. Phox2b mutations in man cause diffuse autonomic dysfunction and deficits in the automatic control of breathing. Here we study the distribution of Phox2b in the adult rat hindbrain to determine whether this protein is selectively expressed by neurons involved in respiratory and autonomic control. In the medulla oblongata, Phox2b-immunoreactive nuclei were present in the dorsal vagal complex, intermediate reticular nucleus, dorsomedial spinal trigeminal nucleus, nucleus ambiguus, catecholaminergic neurons, and retrotrapezoid nucleus (RTN). Phox2b was expressed by both central excitatory relays of the sympathetic baroreflex (nucleus of the solitary tract and C1 neurons) but not by the inhibitory relay of this reflex. Phox2b was absent from the ventral respiratory column (VRC) caudal to RTN and rare within the parabrachial nuclei. In the pons, Phox2b was confined to cholinergic efferent neurons (salivary, vestibulocochlear) and noncholinergic peritrigeminal neurons. Rostral to the pons, Phox2b was detected only in the oculomotor complex. In adult rats, Phox2b is neither a comprehensive nor a selective marker of hindbrain autonomic pathways. This marker identifies a subset of hindbrain neurons that control orofacial movements (dorsomedial spinal trigeminal nucleus, pontine peritrigeminal neurons), balance and auditory function (vestibulocochlear efferents), the eyes, and both divisions of the autonomic efferent system. Phox2b is virtually absent from the respiratory rhythm and pattern generator (VRC and dorsolateral pons) but is highly expressed by neurons involved in the chemical drive and reflex regulation of this oscillator.

Dopamine effects on identified rat vagal motoneurons

Catecholaminergic neurons of the A2 area play a prominent role in brain stem vagal circuits. It is not clear, however, whether these neurons are noradrenergic or adrenergic, i.e., display tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DbetaH) immunoreactivity (-IR) or dopaminergic (i.e., TH- but not DbetaH-IR). Our aims were to investigate whether a subpopulation of neurons in the A2 area was dopaminergic and, if so, to investigate the effects of dopamine (DA) on the membrane of gastric-projecting vagal motoneurons. We observed that although the majority of A2 neurons were both TH- and DbetaH-IR, a small percentage of nucleus tractus solitarius neurons were TH-IR only, suggesting that DA itself may play role in these circuits. Whole cell recordings from thin brain stem slices showed that 71% of identified gastric-projecting motoneurons responded to DA (1-300 microM) with either an excitation (28%) or an inhibition (43%) of the membrane; the remaining 29% of the neurons were unresponsive. The DA-induced depolarization was mimicked by SK 38393 and prevented by pretreatment with SCH 23390. Conversely, the DA-induced inhibition was mimicked by bromoergocryptine and prevented by pretreatment with L741626. When tested on the same neuron, the effects of DA and NE were not always similar. In fact, in neurons in which DA induced a membrane depolarization, 77% were inhibited by NE, whereas 75% of neurons unresponsive to DA were inhibited by NE. Our data suggest that DA modulates the membrane properties of gastric-projecting motoneurons via D1- and D2-like receptors, and DA may play different roles than norepinephrine in brain stem vagal circuits.

Brain–adipose tissue cross talk

While investigating the reversible seasonal obesity of Siberian hamsters, direct sympathetic nervous system (SNS) postganglionic innervation of white adipose tissue (WAT) has been demonstrated using anterograde and retrograde tract tracers. The primary function of this innervation is lipid mobilization. The brain SNS outflow to WAT has been defined using the pseudorabies virus (PRV), a retrograde transneuronal tract tracer. These PRV-labelled SNS outflow neurons are extensively co-localized with melanocortin-4 receptor mRNA, which, combined with functional data, suggests their involvement in lipolysis. The SNS innervation of WAT also regulates fat cell number, as noradrenaline inhibits and WAT denervation stimulates fat cell proliferationin vitroandin vivorespectively. The sensory innervation of WAT has been demonstrated by retrograde tract tracing, electrophysiological recording and labelling of the sensory-associated neuropeptide calcitonin gene-related peptide in WAT. Local injections of the sensory nerve neurotoxin capsaicin into WAT selectively destroy this innervation. Just as surgical removal of WAT pads triggers compensatory increases in lipid accretion by non-excised WAT depots, capsaicin-induced sensory denervation triggers increases in lipid accretion of non-capsaicin-injected WAT depots, suggesting that these nerves convey information about body fat levels to the brain. Finally, parasympathetic nervous system innervation of WAT has been suggested, but the recent finding of no WAT immunoreactivity for the possible parasympathetic marker vesicular acetylcholine transporter (VAChT) argues against this claim. Collectively, these data suggest several roles for efferent and afferent neural innervation of WAT in body fat regulation.

Appetitive sensitization by amphetamine does not reduce its ability to produce conditioned taste aversion to saccharin

Previous exposure to amphetamine attenuates its ability to induce conditioned taste aversion (CTA). Because amphetamine, unlike emetic agents like LiCl, possesses appetitive properties that sensitize when it is administered repeatedly, the present study assessed the contribution of sensitization to this US-pre-exposure effect (US-PEE). It was found that not all sensitizing regimens of systemic amphetamine injections produce a US-PEE. In addition, previous exposure to amphetamine in the VTA, where it acts to induce sensitization but not CTA, did not produce a US-PEE. It is concluded that amphetamine sensitization alone does not modulate this drug's ability to produce CTA. Implications of these findings for anatomically based associative and non-associative models of CTA and the US-PEE are discussed.

Brainstem circuits regulating gastric function

Brainstem parasympathetic circuits that modulate digestive functions of the stomach are comprised of afferent vagal fibers, neurons of the nucleus tractus solitarius (NTS), and the efferent fibers originating in the dorsal motor nucleus of the vagus (DMV). A large body of evidence has shown that neuronal communications between the NTS and the DMV are plastic and are regulated by the presence of a variety of neurotransmitters and circulating hormones as well as the presence, or absence, of afferent input to the NTS. These data suggest that descending central nervous system inputs as well as hormonal and afferent feedback resulting from the digestive process can powerfully regulate vago-vagal reflex sensitivity. This paper first reviews the essential "static" organization and function of vago-vagal gastric control neurocircuitry. We then present data on the opioidergic modulation of NTS connections with the DMV as an example of the "gating" of these reflexes, i.e., how neurotransmitters, hormones, and vagal afferent traffic can make an otherwise static autonomic reflex highly plastic.

Melanocortin-4 receptor mRNA is expressed in sympathetic nervous system outflow neurons to white adipose tissue

Energy balance results from the coordination of multiple pathways affecting energy expenditure and food intake. Candidate neuropeptides involved in energy balance are the melanocortins. Several species, including Siberian hamsters studied here, decrease and increase food intake in response to stimulation and blockade of the melanocortin 4-receptor (MC4-R). In addition, central application of the MC3/4-R agonist melanotan-II decreases body fat (increases lipolysis) beyond that accounted for by its ability to decrease food intake. Because an increase in the sympathetic nervous system drive to white adipose tissue (WAT) is the principal initiator of lipolysis, we tested whether the sympathetic outflow circuitry from brain to WAT contained MC4-R mRNA expressing cells. This was accomplished by labeling the sympathetic outflow to inguinal WAT using the pseudorabies virus (PRV), a transneuronal retrograde viral tract tracer, and then processing the brain for colocalization of PRV immunoreactivity with MC4-R mRNA, the latter assessed by in situ hybridization. MC4-R mRNA was impressively colocalized in PRV-labeled cells (approximately greater than 60%) in many brain areas across the neuroaxis, including those typically implicated in lipid mobilization (e.g., hypothalamic paraventricular, suprachiasmatic, arcuate and dorsomedial nuclei, lateral hypothalamic area), as well as those not traditionally identified with lipolysis (e.g., preoptic area, subzona incerta of the lateral hypothalamus, periaqueductal gray, solitary nucleus). These data provide compelling neuroanatomical evidence that could underlie a direct central modulation of the sympathetic outflow to WAT by the melanocortins through the MC4-Rs resulting in changes in lipid mobilization and adiposity.

New developments in tracing neural circuits with herpesviruses

Certain neurotropic viruses can invade the nervous system of their hosts and spread in chains of synaptically connected neurons. Consequently, it is possible to identify entire hierarchically connected circuits within an animal. In this review, we discuss the use of neurotropic herpesviruses as neuronal tract tracers. Although a variety of tract tracing viruses are available, each with its own unique infection characteristics, we focus on the widespread use of attenuated strains of pseudorabies virus (PRV), a swine herpesvirus with a broad host range. In particular, we focus on new applications of PRV for tract tracing including use of multiple infections by PRV reporter viruses to test for circuit convergence/divergence within the same animal. We provide examples of these combined application techniques within the context of an animal model to study the naturally occurring reversal of seasonal obesity in Siberian hamsters.

Epidermal growth factor A61G polymorphism and cardiac autonomic control in adults

The authors examined the relationship between functional epidermal growth factor gene A61G polymorphism and cardiac autonomic control in a sample of 75 young adults. Heart rate, preejection period, and respiratory sinus arrhythmia were measured continuously during rest and a set of challenging tasks. The functional G allele of the epidermal growth factor gene was associated with lower heart rate F(5,32), 6.92, p = 0.014, eta2 = 0.19, and higher respiratory sinus arrhythmia F(5,32), 4.71, p = 0.038, eta2 = 0.14, among women during the rest, but was not related to with cardiovascular reactivity for challenges in women or in men. The present findings suggest that epidermal growth factor A61G polymorphism is associated with cardiac control in women.

Autonomic ganglionic neurones in rabbits with differing resistance to emotional stress

The aim of the present study was to evaluate the reactions of autonomic neurones of the nodose ganglion of the vagus nerve, and the stellate and superior cervical ganglia in rabbits under emotional stress, and to correlate these reactions with the individual variations in responses to the stressor. Emotional stress was induced in immobilized adult male Chinchilla rabbits by electrical stimulation of the ventromedial hypothalamus and skin. During the experiment (3 hours) arterial blood pressure (BP) was recorded. Metabolic activities of the stellate and superior cervical sympathetic ganglia and nodose ganglion were measured as contents of biogenic amines and their synthesizing and degrading enzymes, neuronal size and dry mass and total RNA; these corresponded to the changes in BP. One group of rabbits showed small fluctuations of BP throughout the experiment and were defined as resistant to stress, whereas in the other group (predisposed to stress) BP progressively decreased. In the former, there was a smaller increase of sympathetic and nodose ganglia metabolic activity than in the latter, in which changes included reduced neuronal dry mass, increased RNA content compared with controls, and reduced tyrosine hydroxylase activity and increased norepinephrine content compare with controls and stress- resistant rabbits. The predisposed rabbits showed earlier and greater increases in circulating norepinephrine concentrations than the resistant rabbits, indicating sustained sympathetic activation. The data indicate that the ganglia of the sympathetic nervous system are part of a major mechanism of BP regulation under acute experimental emotional/painful stress. The nodose ganglion participates in the maintenance of stable cardiovascular function in extreme conditions.

The origin of catecholaminergic nerve fibers in the subdiaphragmatic vagus nerve of rat

It is known that the vagus nerve contains catecholaminergic fibers. However, the origin of these fibers has not been systematically examined. In this study, we addressed this issue using retrograde tracing from the subdiaphragmatic vagus nerve combined with immunocytochemistry. The cervical and thoracic sympathetic trunk ganglia, the nodose ganglia and the dorsal motor nucleus of the vagus nerve were examined following injection of Fluoro-Gold or cholera toxin horseradish peroxidase conjugate into the trunks of the subdiaphragmatic vagus nerve of rats. Numerous retrogradely labeled neurons were seen in the nodose ganglion and the dorsal motor nucleus of the vagus nerve. Very few labeled neurons were found in the sympathetic ganglia (less than 0.06% of the neurons in either superior cervical ganglion or cervicothoracic ganglion were retrogradely labeled). Double labeling with immunofluoresence for catecholamine synthesizing enzymes revealed that: (1) 92% of all Fluoro-Gold retrogradely labeled tyrosine hydroxylase immunoreactive neurons were found in parasympathetic sources (75% in the dorsal motor nucleus of the vagus nerve and 17% in the nodose ganglia), and only 8% in the cervicothoracic sympathetic ganglia; (2) 12% of the retrogradely labeled catecholaminergic neurons in the dorsal motor nucleus of the vagus nerve were also dopamine-beta-hydroxylase immunopositive neurons; (3) 70% of the retrogradely labeled neurons in the sympathetic ganglia were tyrosine hydroxylase immunopositive and 54% of these catecholaminergic neurons contained dopamine-beta-hydroxylase, while 30% of the retrogradely labeled neurons were non-catecholaminergic neurons. These results indicate that catecholaminergic fibers in the abdominal vagus nerve are primarily dopaminergic and of parasympathetic origin, and that only an extremely small number of these fibers, mostly noradrenergic in nature, arise from postganglionic sympathetic neurons.

Catecholamines in rabbit nodose ganglion following exposure to an acute emotional stressor

The aim of the present investigation was to examine catecholamine content and the activities of catecholamine synthesizing and degrading enzymes in the nodose ganglia of rabbits with different patterns of arterial blood pressure during exposure to an acute emotional stressor. The stress protocol involved exposure of immobilized adult male rabbits to electrical stimulation of the ventromedial hypothalamus and the skin for 3 hours. Stress-resistant rabbits that had small fluctuations in arterial pressure during exposure to the stressor had significant reductions in levels ofnorepinephrine (NE) in the nodose ganglion during the 3 hours of stress exposure. In contrast, stress-sensitive rabbits that had progressive decreases in arterial pressure exhibited significant elevations in nodose ganglion content of NE, dopamine (DA) and dihydroxyphenylacetic acid (DOPAC) throughout the period of stress. Tyrosine hydroxylase (TH) activity was changed during the course of the experiment while monoamine oxidase (MAO) activity was unaffected by stress exposure. The changes in nodose ganglion catecholamine content of stress-sensitive and stress-resistant rabbits suggest that the nodose ganglion plays an important role in the maintenance of cardiovascular homeostasis during exposure of animals to an acute emotional stressor.

Interaction between parasympathetic and sympathetic nerves in prevertebral ganglia: morphological evidence for vagal efferent innervation of ganglion cells in the rat

Vagal efferent preganglionic neurons were anterogradely labeled by injecting either DiI or DiA, fluorescent lipophilic carbocyanine dyes, into the dorsal motor nucleus of the vagus of the rat. All neurons of the peripheral nervous system (outside the blood-brain barrier) were then fluorescently counterstained in vivo by injecting Fluorogold (Fluorochrome, Inc., Englewood, CO) intraperitoneally. The upper abdominal prevertebral ganglia, including the numerous microganglia associated with the periarterial plexuses of the celiac and superior mesenteric arteries, were identified and dissected in formalin-fixed tissue under ultraviolet light and stereomicroscopic guidance. In 14 of 15 animals analyzed (93%), labeled vagal efferent fibers were found to penetrate into both the left and right celiac ganglia and the superior mesenteric ganglion, as well as into some of the associated microganglia. These projections formed varicose terminal-like structures, highly suggestive of synaptic contacts surrounding individual ganglion cells. In about half the animals, such vagal innervation was also seen in the left and right suprarenal ganglia. The specificity of vagal efferent labeling was confirmed by control experiments, which included injections in vagotomized animals and direct selective labeling of vagal afferents from the nodose ganglia. It is concluded that vagal efferent preganglionics innervate principal ganglion cells of prevertebral ganglia. These vagal contacts may either directly modulate the postganglionic outflow or else gate some or all of the potential modulatory inputs to these postganglionic neurons, thus allowing the vagal system to exert a more selective influence on sympathetic outflow. Finally, the use of laser scanning confocal microscopy and the in toto Fluorogold staining method for investigations of the peripheral nervous system are discussed.

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 C8 spinal rats and subsequently, transneuronally-labelled 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-beta-hydroxylase (DBH), phenylethanolamine-N-methyltransferase (PNMT), and histidine decarboxylase. 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.(ABSTRACT TRUNCATED AT 250 WORDS)

Opioid peptide gene expression in the nucleus tractus solitarius of rat brain and increases induced by unilateral cervical vagotomy: implications for role of opioid neurons in respiratory control mechanisms

Neurons expressing messenger RNA encoding the opioid peptide precursors, preproenkephalin and preprodynorphin were localized in the medulla oblongata of the rat by in situ hybridization of specific DNA oligonucleotide probes. Neurons containing preproenkephalin messenger RNA were found throughout the medullary reticular formation in the gigantocellular and paragigantocellular reticular nuclei, the parvicellular and lateral reticular nuclei; commissural, medial and ventrolateral subnuclei in the nucleus tractus solitarius and the nucleus of the spinal trigeminal tract. Labelled cells were also concentrated in the more medial regions of the area postrema. In contrast, neurons containing preprodynorphin messenger RNA had a more restricted distribution and were detected in the commissural and ventrolateral nucleus tractus solitarius and nucleus of the spinal trigeminal tract, especially in the more dorsal regions. Expression of preproenkephalin and preprodynorphin messenger RNA was also examined in the dorsal vagal complex of rats that had undergone a unilateral nodose ganglionectomy or cervical vagotomy. Twenty-four hours after both cervical vagotomy and nodose ganglionectomy, there was a specific 1.5-2-fold elevation in preproenkephalin and preprodynorphin messenger RNA levels in the ventrolateral subnucleus of the contralateral nucleus tractus solitarius relative to levels in the ipsilateral nucleus tractus solitarius and in the nucleus tractus solitarius of sham-operated animals. Previous immunohistochemical studies demonstrating the co-localization of enkephalin and dynorphin in the ventrolateral nucleus tractus solitarius suggest that these changes occurred in the same population of neurons. In light of the suggested role of the ventrolateral nucleus tractus solitarius as a central respiratory centre and the activation of the intact pulmonary afferents that innervate this area following a unilateral vagotomy (which increases inspiration volume and expiratory time by affecting the Hering-Breuer reflex), our results suggest a specific involvement of enkephalin- and dynorphin-containing neurons in the ventrolateral nucleus tractus solitarius in central respiratory control mechanisms.

Dopamine antagonists act on central, but not peripheral, receptors to inhibit sham and real feeding

We examined the relative contribution of dopamine (DA) receptors in the brain and periphery in the control of sham and real feeding of sucrose solutions. Intraperitoneal (IP) administration of pimozide, an antagonist of peripheral and brain DA receptors, suppressed both sham and real feeding in a dose-related manner. In contrast, IP injections of domperidone, a DA antagonist restricted to peripheral receptors, had no effect on either sham or real feeding. The inability of domperidone to influence sucrose intake did not result from a lack of biological activity of the drug because the identical doses of domperidone that failed to alter eating significantly inhibited gastric acid secretion. The results implicate central, but not peripheral, DA receptors in the control of the ingestion of palatable foods and also suggest that sham feeding is more sensitive to DA antagonism than real feeding.

Substance P- and tyrosine hydroxylase-containing neurons in the human dorsal motor nucleus of the vagus nerve

The aim of this study was to provide a comprehensive account of the topography, morphology, and frequencies of the substance P- and tyrosine hydroxylase-containing neurons in the human dorsal motor nucleus of the vagus nerve. The morphology of immunoreactive neurons was studied and the variations of the cell distributions were presented by three-dimensional computer reconstructions. Three types of substance P-like immunoreactive neurons were identified. They were predominantly located in the dorsointermediate, centrointermediate, caudointermediate, and caudal division of the dorsal motor nucleus of the vagus nerve. The morphology of substance P-like immunoreactive neurons varied according to the subnuclei in which they were found. Three types of tyrosine hydroxylase-like immunoreactive neurons were identified, mainly in the periphery of the dorsal motor nucleus of the vagus nerve, including the medial fringe, ventrointermediate, and dorsointermediate subnuclei of the 10. Many cells throughout the ventrointermediate subnucleus of the dorsal motor nucleus of the vagus nerve are seen ventrally to intermingle with the tyrosine hydroxylase neurons of the intermediate reticular zone. Computer reconstructions provided a three-dimensional view of the positions of substance P- and tyrosine hydroxylase-like immunoreactive neurons within the subdivisions of the dorsal motor nucleus of the vagus nerve. The uneven distribution of substance P- and tyrosine hydroxylase-like immunoreactive neurons within the subdivisions suggests an involvement of these substances in some, but not all, autonomic functions of the dorsal motor nucleus of the vagus nerve.

Effect of cervical vagotomy on catecholaminergic neurons in the cranial division of the parasympathetic nervous system

This study provides evidence of catecholaminergic neurons in the cranial division of the parasympathetic nervous system. Presumptive catecholaminergic preganglionic neurons in the dorsal motor nucleus of the vagus (DMX) were revealed by a clearcut depletion of intracellular catecholamine-synthesizing enzyme immunoreactivity induced by unilateral cervical vagotomy and identified on tissues immunocytochemically processed for tyrosine hydroxylase (TH), dopamine beta-hydroxylase (D beta H) or phenylethanolamine N-methyltransferase (PNMT). This experimental design was essential because of the recent failure in two species to reproduce data previously obtained in double-label (combined immunocytochemical-retrograde transport) studies. Vagotomy data confirmed three spatially-segregated populations of catecholaminergic visceromotor neurons in the DMX. These cell bodies were morphologically identical to preganglionic neurons observed on alternate tissues stained for Nissl substance or immunostained for choline acetyltransferase (ChAT), the enzyme biosynthesizing acetylcholine. Neurons in the central and medial DMX demonstrated fall-off of TH-like immunoreactivity (LI) ipsilateral to the vagotomy at levels caudal to the obex. This cell group is assumed to be predominantly dopaminergic since relatively few neurons at this level of the DMX expressed D beta H-LI and none were immunostained for PNMT. A second population of immunoreactive neurons, concentrated in the rostral-lateral region of the DMX, was depleted of D beta H-LI on the ipsilateral side but did not express PNMT. These visceromotor neurons may, therefore, biosynthesize noradrenaline and belong to the rostral pole of the A2 area. A third population of presumptive adrenergic vagal dorsomotor neurons in the rostral-medial DMX was depleted of TH-, D beta H- and PNMT-LI at levels of the ipsilateral nucleus anterior to obex. Patterns of depletion of cytoplasmic enzyme-immunoreaction product were identical in all cases irrespective of the site of the transection or the postoperative survival period. Quantitative analysis demonstrated statistically significant loss of immunolabeled neurons in rostral and caudal subgroups of the DMX on the side ipsilateral to the vagotomy. It is concluded that catecholaminergic processes in the vagus nerve, as previously identified by the aldehyde-induced histofluorescence method, may partly arise from the lower brainstem.

Distribution of GAP-43 mRNA in the adult rat brain

Regional distribution of gene expression of the axonal growth-associated protein, GAP-43, was studied in adult rat brains by in situ hybridization autoradiography to determine the features of mature neuronal populations that synthesize GAP-43 protein. Such synthesis appears to correlate with axonal growth during maturation and regrowth after axotomy. In most adult neurons, the sharp decline in GAP-43 gene expression implies a reduced capacity for axonal growth. Neurons capable of extending axonal knobs in the absence of injury may indicate a "plasticity" underlying dynamic processes of interaction between neurons and their synaptic targets. Antisense and sense (control) riboprobes were used on serial sections in the three principal axes, and the magnitude of hybridization signal was examined to determine regional patterns. GAP-43 mRNA levels are pronounced in diverse neuronal groups including the locus coeruleus, raphé nn., dopaminergic nigral and ventral tegmental nn., mitral cells, hippocampal CA3, inferior olivary n., vagal motor n. and other parasympathetic preganglionic neurons, select thalamic midline and intralaminar nn., several specific nn. of the hypothalamus and basal forebrain, the granular layer of cerebellar cortex, the infragranular neocortex, and the granular olfactory paleocortex; there is a substantial range in the magnitude of expression. Regions revealing minimal signal include most thalamic sensory relay nuclei, the granule neurons of the olfactory bulb and dentate gyrus, and the caudate and putamen. Possible concomitants of GAP-43 expression include regulation of ion flux and neurotransmitter release. Those neurons with long, extensively dispersed and numerous synaptic connections display the strongest signals and may possess the greatest propensity for continuous growth and turnover of their axon terminals, in contrast to short-axon and specific projection neurons exhibiting minimal levels. These data may enable inferring which populations display normal or experimentally induced axonal growth.

Organization of presumptive catecholamine-synthesizing neurons in the canine medulla oblongata

Immunocytochemical methods were used to identify cells and processes containing two major catecholamine (CA)-biosynthetic enzymes in areas of the canine medulla implicated in autonomic control. Antisera were employed against tyrosine hydroxylase (TH) and phenylethanolamine N-methyltransferase (PNMT). These enzymes respectively catalyze the conversions of tyrosine to L-DOPA and noradrenaline to adrenaline. Immunocytochemical studies laid the groundwork for subsequent investigations in conscious dog in which we characterized an area of cardiovascular control in the rostral ventrolateral medulla (RVLM). In the anatomical studies, previously unidentified neuronal somata and processes were demonstrated in the canine medulla. Presumptive adrenergic (CI) neurons in the canine RVLM were subjacent to the nucleus ambiguous (NA) and most numerous at a level where the compact and semicompact divisions of NA merged. In contrast to their distribution in rodents, C1 neurons were skewed caudally and did not extend rostrally to the caudal pole of the facial nucleus. C1 neurons were also relatively less concentrated in the RVLM. A large number of C1 neurons extended dorsally into the lateral tegmental field (LTF). Most C1 neurons in the LTF (like those in the A1 area) were aligned with catecholaminergic (TH- and PNMT-ir) processes traversing the intermediate reticular zone. Since the numbers and locations of TH- and PNMT-ir neurons in the C1 area of the RVLM and rostral LTF were virtually identical on adjacent sections, it can be implicitly inferred that the enzymes are co-localized to the same somata and that these neurons are capable of biosynthesizing adrenaline. The C1 and A5 areas were clearly separated by a transitional zone, sparsely populated by TH-ir somata (1-2 cells per section), where the facial nucleus and rostral pole of the NA pars compacta (NAc) occupied the same level. A5 neurons were more abundant and complexly organized than suggested by previous CA-histofluorescence data. In addition, a new parvicellular subgroup was identified and composed of neurons containing TH but not PNMT. In contrast to other species, the A1 cell group was not confined to the VLM. A large number of A1 neurons extended into the caudal LTF and were situated between the nucleus tractus solitarii-motor vagal complex (NTS-X) and caudal VLM (CVLM). In contrast to previous reports, presumptive adrenergic (TH- and PNMT-ir) cell groups were more densely represented in the C2-3 areas of the canine NTS and dorsomedial reticular formation.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Preprogalanin mRNA is increased in vagal motor neurons following axotomy

Expression of preprogalanin and tyrosine hydroxylase mRNA was examined in the rat dorsal vagal complex following nodose ganglionectomy and cervical vagotomy, using in situ hybridization of specific 35S-labelled oligonucleotides. Seven days after unilateral cervical vagotomy (and nodose ganglionectomy), neurons in the ipsilateral dorsal motor nucleus of the vagus and nucleus ambiguus expressed 6- to 10-fold increased levels of preprogalanin mRNA. In contrast, tyrosine hydroxylase mRNA was no longer expressed by cells of the dorsal motor nucleus of the vagus after the lesion. These results demonstrate that changes in the expression of the galanin and tyrosine hydroxylase genes occur in vagal motor neurons following lesion of their axons. More generally, these results, and those from other laboratories, demonstrate that specific alterations of neuropeptide and neurotransmitter production, are part of the reactive process activated by nerve injury.

Identification of vagal efferent fibers and putative target neurons in the enteric nervous system of the rat

The stomach and small intestine receive an efferent innervation from the dorsal motor nucleus of the vagus (DMX). The current experiments were undertaken as a partial test of the hypothesis that the CNS innervates only a small number of command neurons in a restricted number of enteric ganglia. The anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) was injected into the DMX by iontophoresis, and 10-21 days later PHA-L was visualized in the bowel by immunofluorescence. Varicose vagal efferent fibers, labeled by PHA-L, were found in the myenteric plexus as far distally as the ileo-colic junction. PHA-L-labeled varicose axons were rare in comparison to nonlabeled fibers, entered a minority of myenteric ganglia, and contacted a small proportion of the neurons. Ganglia thus innervated by vagal efferent fibers were more numerous in the stomach than in the small intestine. Within the stomach, these ganglia were common in the antrum than in the corpus and none were found in the wall of the rumen. Innervated ganglia in the small intestine became progressively more sparse distally. No PHA-L-labeled axons were observed in the submucosal plexus, thus raising the possibility that vagal modulation of secretomotor responses involves an intermediate synapse in the myenteric plexus. Nonvaricose bundles of PHA-L-labeled fibers were also observed. These bundles appeared to utilize the connectives of the myenteric plexus as a pathway within which to descend within the bowel. Vagal efferent bundles were found to pass through the pyloric sphincter to enter the small intestine from the stomach; thus vagal fibers can reach the distal intestine by an intraenteric route that is not lesioned by crushing mesenteric nerves. The existence of this pathway affects the interpretation of experiments seeking to utilize such lesions to distinguish intrinsic from extrinsic neurites. Possible target neurons of the vagal efferent innervation were identified by simultaneously demonstrating the immunoreactivities of 5-hydroxytryptamine (5-HT), vasoactive intestinal polypeptide (VIP), enkephalin (ENK), galanin (GAL), and tyrosine hydroxylase (TH) along with that of PHA-L. Vagal terminals in the myenteric plexus appeared selectively to contact 5-HT- and, to a significantly lesser extent, VIP-, but not ENK- or GAL-immunoreactive neurons. Apparent vagal innervation of 5-HT-immunoreactive neurons was significantly more common in the duodenum, where a majority of the 5-HT-immunoreactive cells were encircled by varicose PHA-L-labeled axons, than in the stomach.(ABSTRACT TRUNCATED AT 400 WORDS)

Catecholaminergic parasympathetic efferents within the dorsal motor nucleus of the vagus in the rat: a quantitative analysis

Catecholaminergic vagal motor neurones were identified within the dorsal motor nucleus of the vagus, by retrograde tracing of True blue from the stomach followed by immunocytochemistry using antibodies directed against tyrosine hydroxylase. Presumed dopaminergic efferents were largely confined to caudal regions, where they averaged as much as 30% of the labelled efferents. Most but not all of these were also identified on the basis of acetylcholinesterase histochemistry.

Epinephrine in mammalian brain

1. Epinephrine is widely distributed in brains of various species throughout phylogeny but maintains its localization to hypothalamus and brainstem/medulla in all species studied. 2. A general decrease in brain epinephrine content is observed phylogenetically beyond fishes with wide variation within species. 3. The cellular localization of epinephrine forming enzyme is dissociated from epinephrine stores in hypothalamus where epinephrine appears to be primarily a hormone. 4. Three proposed functional pools of epinephrine are described. Synthesis of a hormonal pool and a second, perhaps nonfunctional, pool co-stored in noradrenergic terminals in the forebrain occurs extraneuronally and is probably inhibited acutely in the presence of high corticosteroids due to inhibition of uptake 2. Synthesis of epinephrine in the neuronal pool found primarily in the medulla may be enhanced due to increased PNMT activity in the presence of elevated corticosteroids. 5. Phylogenetic and pharmacological data suggest that epinephrine may play an important role in tonic regulation of the level of arousal, reward and sensitivity to environmental stimuli in mammals.

Are there epinephrine neurons in rat brain?

The present model of epinephrine containing and PNMT containing neurons in rat brain (and by extension other species) implies that epinephrine is primarily a postsynaptic metabolite of norepinephrine in forebrain due to the probable postsynaptic localization of PNMT. As a result the most physiologically relevant pool is found in extracellular space with the bulk of tissue epinephrine found co-stored in noradrenergic terminals. Changes in the extracellular pool of epinephrine are effected by changes in the extracellular norepinephrine concentration as in times of increased release, reuptake blockade or inhibition of degradation. alpha 2-Adrenergic receptors associated with cells not necessarily in synaptic contact with the noradrenergic terminal containing epinephrine could be stimulated through this extracellular pool. The majority of PNMT containing cells in the brainstem/medulla appear to also contain other catecholamine biosynthetic enzymes. The present model suggests that epinephrine formed in these neurons is primarily used as a co-transmitter with norepinephrine formed in these same terminals. The balance of norepinephrine to epinephrine found in vesicles in these terminals would be a function of intraneuronal PNMT activity, MAO activity and reuptake which would be the major regulator of intraneuronal norepinephrine concentrations. The literature is reviewed in these contexts, questioning the existence of classical epinephrine neurons. Evidence is presented in support of a model for postsynaptic synthesis of epinephrine in the forebrain, especially during times of high norepinephrine release. The classic model of compartmentalization of biosynthetic enzymes is used in support of a co-transmitter role of epinephrine in the brainstem/medulla. Epinephrine is considered a unique metabolite of norepinephrine with important pharmacological actions and a receptor subtype in brain which monitors and regulates its formation. Epinephrine is recognized by the uptake system on noradrenergic terminals and vesicles and can therefore compete for storage in these noradrenergic neurons. Based on the distribution of PNMT and its association with major noradrenergic fiber tracts, epinephrine can be considered a site-selective metabolite of physiological and neuronal importance. Due to the compartmentalization of synthetic enzymes, it is probably not a classical neurotransmitter in the central nervous system, although it may be the primary catecholamine neurotransmitter in some medullary neurons.

Immunohistochemical evidence for the coexistence of cholinergic and catecholaminergic phenotypes in neurones of the vagal motor nucleus in the adult rat

Catecholaminergic nerve cell bodies have been recently identified in the rat spinal cord. They lie in the rostral cervical segments and at the lumbosacral junction. Among them, many are located in parasympathetic areas. This finding led us to investigate the interactions between these catecholaminergic neurones and the cholinergic ones. To address this question, we performed sequential immunocytochemical detection of choline acetyltransferase (ChAT) and tyrosine hydroxylase (TH) in the same sections. We could then identify the co-expression of both TH and ChAT-like immunoreactivities (LI) in some perikarya of the cervical spinal cord and medulla oblongata. Such cells are located in the caudal extension of the dorsal motor nucleus of the vagus nerve (DMNX) as well as in the caudal part of the medullary DMNX itself. Such a co-expression of TH-LI and ChAT-LI could not be found in the lumbosacral region, another parasympathetic territory where cell bodies displaying TH-LI were intermingled with those containing ChAT-LI. This is one of the first demonstrations of the co-existence of catecholaminergic and cholinergic phenotypes in some neurones of the adult mammalian nervous system. These observations also support the presence of catecholaminergic efferents within the vagus nerve.

Effects of systemic and intracranial amphetamine injections on behavior in the open field: a detailed analysis

Systemic injections of amphetamine result in profound changes in the behavior of animals in an open field. There is an increase in activity, certain species-typical behaviors are produced, and there is a tendency for any elicited behavior to be repeated in a stereotyped way. The present study examined the contributions of dopamine terminal regions to these effects in rats by microinjecting amphetamine directly into one of six discrete sites (medial frontal cortex, nucleus accumbens, anteromedial caudate nucleus, ventrolateral caudate nucleus, amygdala, or the region surrounding the area postrema) and making detailed behavioral observations. This data was compared with the behavior of systemically injected rats that were also observed in the open field. An observer recorded the occurrence of twelve categories of behavior and recorded photocell beam interruptions during five post-injection observation periods. The results confirmed and extended previous accounts of the behavior of systemically injected rats, adding increased snout contact with the environment as an additional effect of amphetamine. Intracranial injections produced changes in activity level from several of the injection sites but there was no increase in the species-typical behaviors associated with stereotypy. Changes in the occurrence of some recorded behaviors were produced by injections into most of the sites and these data are presented in detail.

Changes in cerebrospinal fluid homovanillic acid in children with Ondine's curse

The cerebrospinal fluid (CSF) concentrations of three acid monoamine metabolites, two purines, and a group of amino acids were determined in two children with chronic central alveolar hypoventilation (Ondine's curse). The levels of all assayed neuroactive substances, metabolites, and amino acids, with one exception, were normal compared to an age-matched group of neurologically healthy children. The levels of the dopamine metabolite homovanillic acid in the children with Ondine's curse were approximately 2.4 times higher than expected for age range. The present findings may indicate a link between central nervous system dopamine activity and chronic central alveolar hypoventilation. Among other possible explanations, the changes seen might represent a primary alteration in dopamine activity or may reflect a change in dopamine turnover resulting from the chronic hypoventilation.

Contributions of dopamine terminal areas to amphetamine-induced anorexia and adipsia

Systemic injections of amphetamine produce both anorexia and adipsia. Evidence suggests that it is the stimulation of activity by the drug in both noradrenergic and dopaminergic synapses that mediate these effects. The present study examined the contributions of dopamine terminal regions to these effects in rats by microinjecting amphetamine directly into one of six discrete sites (medial frontal cortex, nucleus accumbens, anteromedial caudate nucleus, ventrolateral caudate nucleus, amygdala, or the region surrounding the area postrema) and observing the effects of the injections on eating or drinking. The rats were mildly deprived of either food or water and following microinjection of either amphetamine or saline, were given access to food or water. Injections of amphetamine into either the nucleus accumbens or amygdala caused both anorexia and adipsia but no effects were observed from the other sites. It is suggested that the amphetamine's action on these two sites contributes to the anorexia and adipsia that are observed after systemic injection of the drug. Possible behavioral mechanisms for the effects are discussed.

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

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

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

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

Immunohistochemical study of catecholaminergic cell bodies in the rat spinal cord

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

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

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

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.