Aminergic and cholinergic systems in the dorsolateral pontine tegmentum

Topographic relationship between cholinergic and aminergic neuronal somata has been studied in the dorsolateral pontine tegmentum by using three histochemical techniques, acetylcholinesterase (AchE) histochemistry in rats having received systemic injection of diisopropylfluorophosphate, choline acetyltransferase (CAT) immunohistochemistry and catecholamine fluorescence histochemistry. Based on comparing the data obtained from these different techniques, it seems evident that all noradrenergic neurons contain AchE. The remaining population of AchE-containing somata appears to correspond with CAT-containing, therefore, cholinergic neuronal cell bodies. No AchE-positive perikarya were detected in neuronal structures other than cholinergic and aminergic neurons. In addition, coexistence of noradrenaline and acetylcholine in a single cell seems improbable, at least, in the dorsolateral pontine tegmentum.     

Localization of enkephalinergic neurons in the dorsolateral pontine tegmentum projecting to the spinal cord of the cat

The dorsolateral pontine tegmentum of the cat is known to contain enkephalinergic neurons, with most of the enkephalin co-contained in the catecholaminergic neurons; however, enkephalinergic cells projecting to the spinal cord have not been identified. This study employs retrograde transport of horseradish peroxidase in combination with methionine-enkephalin or tyrosine hydroxylase immunocytochemistry to 1) determine the locations of pontospinal enkephalinergic neurons and 2) compare these with the locations of pontospinal catecholaminergic neurons. Pontospinal enkephalinergic neurons were observed in the nuclei locus coeruleus and subcoeruleus and the K?lliker-Fuse nucleus. A high concentration of these neurons was evident in the K?lliker-Fuse nucleus when compared to the nuclei locus coeruleus and subcoeruleus (P less than .01). Both the enkephalinergic and catecholaminergic neurons projecting to the spinal cord were located in the same general areas of the dorsolateral pontine tegmentum and there was no significant difference in the mean diameters of these two neuronal types (P greater than .05). Quantitative data concerning the pontospinal enkephalinergic neurons correlated well with previous data on pontospinal catecholaminergic neurons (Reddy et al., Brain Res. 491:144-149, '89). A majority of the descending neurons from the dorsolateral pontine tegmentum contain enkephalin (72-80%) and catecholamine (80-87%). The observations suggest that enkephalin is contained in many of the pontospinal catecholaminergic neurons.     

Descending projections from the dorsolateral pontine tegmentum to the paramedian reticular nucleus of the caudal medulla in the cat.

We examined whether the dorsolateral pontine cholinergic cells project to the paramedian reticular nucleus (PRN) of the caudal medulla. In 3 cats, wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) was injected into the PRN and we noted cells in the dorsolateral pons that contained the HRP reaction product, cells that were immunolabeled for choline acetyltransferase (ChAT), and cells that contained the HRP reaction product and were ChAT positive. We found cholinergic projections from the pedunculopontine tegmental and laterodorsal tegmental nuclei to the PRN. This finding is consistent with studies indicating a cholinoceptive region in the medial medulla mediating suppression of muscle tone. Our results demonstrate that this medullary region has monosynaptic input from pontine neurons implicated in generating the atonia of rapid eye movement sleep.     

The pigmented subpeduncular nucleus: a neuromelanin-containing nucleus in the human pontine tegmentum

Summary A nuclear gray is found in the human pontine tegmentum close to the lower circumference of the superior cerebellar peduncle and is located within the pedunculo-lemniscal trigone. It is mainly characterized by the presence of medium-sized neuromelanin-containing neurons and, therefore, referred to as the pigmented subpeduncular nucleus. Three basic neuronal types occur within the boundaries of the nucleus. Scattered among the neuromelanin-containing type I nerve cells are type II cells with lipofuscin deposits and type III neurons devoid of any pigmentation. In cases of Alzheimer-type dementia, the pigmented subpeduncular nucleus shows severe changes. Neurofibrillary tangles can frequently be found within the somata of both the melanin-laden and the lipofuscin-containing neurons. In contrast, the non-pigmented nerve cells remain devoid of such pathological filaments. Furthermore, large numbers of neuropil threads are scattered throughout the nuclear gray.Supported by grants from the Deutsche Forschungsgemeinschaft     

Ultrastructure of endomorphin-1 immunoreactivity in the rat dorsal pontine tegmentum: evidence for preferential targeting of peptidergic neurons in Barrington's nucleus rather than catecholaminergic neurons in the peri-locus coeruleus

Endomorphins are opioid tetrapeptides that have high affinity and selectivity for mu-opioid receptors (muORs). Light microscopic studies have shown that endomorphin-1 (EM-1) -containing fibers are distributed within the brainstem dorsal pontine tegmentum. Here, immunoelectron microscopy was conducted in the rat brainstem to identify potential cellular interactions between EM-1 and tyrosine hydroxylase (TH) -labeled cellular profiles in the locus coeruleus (LC) and peri-LC, an area known to contain extensive noradrenergic dendrites of LC neurons. Furthermore, sections through the rostral dorsal pons, from colchicine-treated rats, were processed for EM-1 and corticotropin releasing factor (CRF), a neuropeptide known to be present in neurons of Barrington's nucleus. EM-1 immunoreactivity was identified in unmyelinated axons, axon terminals, and occasionally in cellular profiles resembling glial processes. Within axon terminals, peroxidase labeling for EM-1 was enriched in large dense core vesicles. In sections processed for EM-1 and TH, approximately 10% of EM-1-containing axon terminals (n=269) targeted dendrites that exhibited immunogold-silver labeling for TH. In contrast, approximately 30% of EM-1-labeled axon terminals analyzed (n = 180) targeted CRF-containing somata and dendrites in Barrington's nucleus. Taken together, these data indicate that the modulation of nociceptive and autonomic function as well as stress and arousal responses attributed to EM-1 in the central nervous system may arise, in part, from direct actions on catecholaminergic neurons in the peri-LC. However, the increased frequency with which EM-1 axon terminals form synapses with CRF-containing profiles in Barrington's nucleus suggests a novel role for EM-1 in the modulation of functions associated with Barrington's nucleus neurons such as micturition control and pelvic visceral function.     

Localization of reward-relevant neurons in the pontine tegmentum: a moveable electrode mapping study

Monopolar moveable stimulation electrodes were implanted in male adult rats in order to map the reward substrate in the pontine tegmentum. Electrodes were implanted 6 mm below the surface of the skull and subsequently lowered by steps of 0.16 or 0.32 mm. Each bar press in a Skinner box delivered a train (0.4 s in duration) of cathodal rectangular pulses of fixed intensity (200 microA) and width (0.1 ms). Self-stimulation was recorded from zero to maximum performance by varying the number of pulses per train. The rewarding effectiveness of the stimulation at each positive site was inferred by determining the frequency threshold. Out of 476 sites that were sampled, 137 supported self-stimulation. Eighty-one percent of the positive sites (111 out of 137) were located within 1 mm of the midline. Of the 181 sites that were sampled in the region posterior to the caudal end of the dorsal raphe, only 9 sites (less than 5%) supported self-stimulation. These results suggest that the majority of neurons that constitute the brainstem reward substrate either originate from and/or terminate in the rostral pons.     

Role of Barrington's nucleus in micturition

Barrington's nucleus is a central component of the micturition circuit. This nucleus projects axons to the sacral parasympathetic nucleus, where preganglionic neurons innervating the urinary bladder are located. To clarify the functional role of this nucleus, the firing properties of Barrington's neurons that project axons to the spinal cord were examined. Based on these studies, a model begins to emerge that places Barrington's nucleus in the micturition pathway that is involved in increasing bladder pressure rapidly and strongly, while also maintaining high bladder pressure. In addition, Barrington's neurons are suggested to have another role, that is, increasing the probability of micturition contraction by activating a spinal excitatory pathway or disinhibiting a spinal inhibitory mechanism. In contrast to the excitatory role of Barrington's nucleus, this nucleus does not seem to trigger bladder relaxation.     

Direct projections from the dorsolateral pontine tegmentum to pudendal motoneurons innervating the external urethral sphincter muscle in the rat

Direct projections from the dorsolateral pontine tegmentum to pudendal motoneurons innervating the external urethral sphincter and the external anal sphincter muscles were examined in the rat by the tract-tracing methods utilizing retrograde transport of cholera toxin B subunit and anterograde transport of biotinylated dextran amine. The dorsolateral pontine tegmental region, corresponding to the micturition reflex center of Barrington, was confirmed to send bilaterally, with an ipsilateral dominance, projection fibers to the spinal parasympathetic nucleus (inferior intermediolateral nucleus). The micturition reflex center of Barrington, however, did not seem to send many projection fibers to the ventral horn of the lumbosacral cord segments, whereas the region immediately ventral to the micturition reflex center of Barrington was found to send bilaterally, with a contralateral dominance, projection fibers to the dorsolateral group of pudendal motoneurons in both the male and female rats. In the female rat, the dorsolateral group of pudendal motoneurons are comprised primarily of motoneurons that innervate the external urethral sphincter muscle. The dorsomedial group of pudendal motoneurons, which contain motoneurons that innervate the external anal sphincter and the bulbocavernosus muscles, did not seem to receive major projections from the dorsolateral pontine tegmental regions. It was also observed that the locus coeruleus sent some projection fibers bilaterally to the spinal parasympathetic nucleus but only a few to the ventral horn of the lumbosacral cord segments. Thus, the present results indicate that the dorsolateral group of pudendal motoneurons containing those innervating the external urethral sphincter muscle receive pontospinal projection fibers mainly from the dorsolateral pontine tegmental region immediately ventral to the micturition reflex center of Barrington. © 1995 Wiley-Liss, Inc.     

Corticotropin-releasing factor (CRF) immunoreactivity in the dorsolateral pontine tegmentum: further studies on the micturition reflex system

A cluster of neurons in the pontine tegmentum thought to correspond with the micturition reflex center was retrogradely labeled following the injection of the fluorescent tracer True Blue into the sacral spinal cord. Simultaneous immunofluorescence staining indicated that these neurons display corticotropin-releasing factor (CRF)-like immunoreactivity. Also, CRF-positive varicose fibers were detected in the intermediolateral column of the sacral cord. The results indicate the presence of CRF or a CRF-like peptide in a descending projection to the spinal cord that may be involved in regulating the micrutition reflex.     

Barrington's nucleus: Neuroanatomic landscape of the mouse “pontine micturition center”

Barrington's nucleus (Bar) is thought to contain neurons that trigger voiding and thereby function as the “pontine micturition center.” Lacking detailed information on this region in mice, we examined gene and protein markers to characterize Bar and the neurons surrounding it. Like rats and cats, mice have an ovoid core of medium‐sized Bar neurons located medial to the locus coeruleus (LC). Bar neurons express a GFP reporter for Vglut2, develop from a Math1/Atoh1 lineage, and exhibit immunoreactivity for NeuN. Many neurons in and around this core cluster express a reporter for corticotrophin‐releasing hormone (Bar^CRH). Axons from Bar^CRH neurons project to the lumbosacral spinal cord and ramify extensively in two regions: the dorsal gray commissural and intermediolateral nuclei. Bar^CRH neurons have unexpectedly long dendrites, which may receive synaptic input from the cerebral cortex and other brain regions beyond the core afferents identified previously. Finally, at least five populations of neurons surround Bar: rostral‐dorsomedial cholinergic neurons in the laterodorsal tegmental nucleus; lateral noradrenergic neurons in the LC; medial GABAergic neurons in the pontine central gray; ventromedial, small GABAergic neurons that express FoxP2; and dorsolateral glutamatergic neurons that express FoxP2 in the pLC and form a wedge dividing Bar from the dorsal LC. We discuss the implications of this new information for interpreting existing data and future experiments targeting Bar^CRH neurons and their synaptic afferents to study micturition and other pelvic functions.     

Benign cyst of the paramedian pontine tegmentum

A benign ovoid cyst, without an epithelial lining, localized in the paramedian pontine tegmentum, was examined by computed tomography (CT) and magnetic resonance imaging (MRI) (25×15×15 mm) and successfully operated upon. The one-and-a-half syndrome (horizontal gaze palsy to the right and paralysis of adduction of the right eye) and ipsilateral peripheral VII nerve palsy dominated the clinical picture. Fenestration, 5 mm in diameter, of the cyst wall through the floor of the IV ventricle was performed and 2.6 ml of clear, colorless fluid was evacuated. Inspection of the cyst, using the operating microscope, revealed a smooth, white, glistening cavity with no evidence of other pathological tissue. Duraplasty was performed with allogenic pericardium. Neurological symptoms improved immediately after surgery. Light and electron microscopy of the cyst wall revealed a fibrillar astroglial network and fragments of ependyma at the ventricular side of the biopsy.Presented at the 12th Congress of the European Society for Paediatric Neurosurgery, Warsaw 1990     

Novel role for the pontine micturition center, Barrington's nucleus: evidence for coordination of colonic and forebrain activity

This report provides evidence for a novel role of Barrington's nucleus, considered the pontine micturition center, in regulation of colonic function. Barrington's activation elicited increases in colonic intraluminal pressure that were eliminated by scopolamine and intrathecal lidocaine, suggesting an impact of Barrington's neurons on colonic activity via projections to lumbosacral parasympathetic neurons. Consistent with this, Barrington's neurons were transsynaptically labeled from the distal colon by pseudorabies virus and several of these were also retrogradely labeled from the locus coeruleus, which projects extensively to the forebrain. Thus, Barrington's nucleus is strategically positioned to coordinate colonic and forebrain activity. Dysfunctions within this divergent system may underlie the frequent comorbidity of colonic and psychiatric symptoms.     

Localization of rabbit laryngeal motoneurons in the nucleus ambiguus

The localization of rabbit laryngeal motoneurons in nucleus ambiguus was investigated using injection of a fluorescent labeling substance, i.e., nuclear yellow, into the individual laryngeal muscles. The nucleus ambiguus of the rabbit comprises four subnuclei, CoG, SGm, SGl, and DiG. The CoG is a group of compactly arranged neurons, and is situated in the rostral one-half of the nucleus. The SG, situated in its rostral one-third, is scattered around the CoG, with a subdivision into SGm and SGl. These subdivisions are medial and lateral to the CoG, respectively. The DiG is formed by diffusely arranged neurons, and is located in the caudal two-thirds of the nucleus. All labeled motoneurons were found in the ipsilateral nucleus ambiguus. The motoneurons supplying the cricothyroid muscle, which is innervated by the superior laryngeal nerve, were present in the SGm, with a clear rostralward segregation from the other motoneurons. The motoneurons supplying the muscles innervated by the inferior laryngeal nerve were located in the DiG, where they displayed a rostrocaudal myotopical arrangement in the order posterior cricoarytenoid, thyroarytenoid, and lateral cricoarytenoid. The posterior cricoarytenoid motoneurons were intermingled with the thyroarytenoid motoneurons in the rostral two-thirds of the DiG, and the former tended to be concentrated more rostrally than the latter. The lateral cricoarytenoid motoneurons were confined to the most caudal one-third of the DiG.     

Projections of the locus coeruleus and adjacent pontine tegmentum in the cat.

The projections of the locus coeruleus and adjacent pontine tegmentum have been studied using anatomical and physiological methods in the cat. Axonal trajectories were traced using either the Fink-Heimer I method following electrolytic lesions, or the autoradiographic method after injection of tritiated proline into the nucleus. Results with both methods were similar. Axons of locus noeruleus neurons ascended ipsilaterally through the mesencephalon lateral to the medial longitudinal fasiculus, ventrolateral to the central gray. In the caudal diencephalon, the ascending fibers entered the centrum medianum-parafascicular complex where they diverged into two fascicles: a dorsal fascicle which terminated in the intralaminar nuclei of the thalamus, and a ventral fascicle which gave off fibers to the ventrobasal complex and reticular nucleus of the thalamus while continuing centrolaterally into the lateral hypothalamus medial to the internal capsule. Fibers of the ventral fascicle ascended in the lateral hypothalamus and zona incerta and were traced through the preoptic region into the septum. Fibers could not be consistently traced to the cerebral cortex, and were not seen at all in the cerebellum. Throughout the ascending course of the path from the locus coeruleus, axons were given off to the pretectal area, the medial and lateral geniculate nuclei and the amygdala; fibers passed contralaterally through the posterior commissure, the midline thalamus, and the supraoptic commissure. Fibers descending from the locus coeruleus surrounded the intramedullary portion of the facial nerve and further caudally were observed ventrolateral to the hypoglossal and dorsal vagal nuclei. The axonal trajectories visualized with degeneration and autoradiographic methods followed closely those previously shown for reticular formation neurons, but were also similar to locus coeruleus projections revealed by histofluorescence methods. After injections of horseradish peroxidase into the centrum medianum-parafascicular complex, lateral hypothalamus or preoptic region, labeled neurons were located in the locus coeruleus, nucleus subcoeruleus, and lateral parabrachial nucleus. Reticular formation neurons were not labeled. Neurons in locus coeruleus and adjacent pontine tegmentum could be antidromically activated by stimulation in the rostral midbrain or caudal diencephalon. Our data indicate that both adrenergic and non-adrenergic neurons of the dorsolateral pontine tegmentum have similar projections.     

Connections of Barrington's nucleus to the sympathetic nervous system in rats

Barrington's nucleus (BN) has been considered a pontine center related exclusively to the control of pelvic parasympathetic activity. The present study demonstrates an anatomical linkage between BN and autonomic outflow to visceral targets innervated exclusively by the sympathetic division of the autonomic nervous system. Temporal analysis of infection after injection of pseudorabies virus (PRV), a retrograde transynaptic tracer, into two sympathetically innervated organs, the spleen and the kidney, revealed the presence of infected neurons in BN at early post-inoculation survival intervals. Immunohistochemical localization of PRV after spleen injections showed that a small subpopulation of BN neurons became labeled in a time frame coincident with the appearance of infected neurons in other brain regions known to project to sympathetic preganglionic neurons (SPNs) in the thoracic spinal cord; a larger number of infected neurons appeared in BN at intermediate intervals after PRV injections into the spleen or kidney. Coinjection of the retrograde tracer Fluoro-Gold i.p. and PRV into the spleen demonstrated that parasympathetic preganglionic neurons in the caudal medulla or lumbo-sacral spinal cord were not infected, indicating that infected BN neurons were not infected via a parasympathetic route. Thus, BN neurons become infected after PRV injections into the spleen or kidney either directly through BN projections to SPNs, or secondarily via BN projections to infected pre-preganglionic neurons. These results demonstrate an anatomical linkage, either direct or indirect, between BN and sympathetic activity. Because BN receives numerous inputs from diverse brain regions, the relation of BN with both branches of the autonomic nervous system suggests that this nucleus might play a role in the integration of supraspinal inputs relevant to the central coordination of sympathetic and parasympathetic activity.     

Afferent projections related to attack sites in the pontine tegmentum

Attack by a cat on a rat was elicited by electrical stimulation of the ventral parabrachial nucleus or the paralemniscal pontine reticular formation. The attack was quiet and it differed from similar behavior elicited at other sites in that the cat not only bit the rat but struck it with its paw.Horseradish peroxidase was deposited at the attack sites. Cells sending projections to the attack sites were located in gyrus proreus, anterior, central, and medial amygdala, the bed nucleus of the stria terminalis, lateral, dorsal and perifornical hypothalamus, as well as the central gray matter, superior colliculus, midbrain reticular formation, locus coeruleus, nucleus of the lateral lemniscus, and nucleus interpositus. Additional sites of cells of origin appeared with less regularity. This distribution of sites correlates well with the sites from which attack can be elicited or modulated.     

Spinal projections from the lower brain stem in the cat as demonstrated by the horseradish peroxidase technique. II. projections from the dorsolateral pontine tegmentum and raphe nuclei

The descending projections to the spinal cord arising from the dorsolateral pontine tegmentum and brain stem raphe nuclei have been investigated by means of the horseradish peroxidase (HRP) technique. Particular attention was taken to clarify the cells of origin and the funicular trajectory of these spinal projections.After injections of HRP into the spinal cord, a significant number of HRP labeled neurons were observed in the following dorsolateral pontine tegmental structures: (1) an area ventral to the nucleous cuneiformis; (2) principal locus coeruleus; (3) locus coeruleus α; (4) locus subcoeruleus; (5) Kölliker-Fuse nucleus; and (6) nucleus parabrachialis lateralis. As a rule, the projections are ipsilateral and the descending fibers course in the ventral part of the lateral funiculus.As concerns the raphe-spinal projections, we have demonstrated that the nucleus raphe dorsalis also sends axons to the cervical segment of the spinal cord. Furthermore, in accord with previous reports, HRP labeled cells were also identified in the nucleus raphe magnus, pallidus and obscurus, but not in the nucleus raphe centralis superior and pontis.On the whole the present study further clarified the organization of spinal projections from the dorsolateral pons and raphe nuclei and provided some additional anatomical data for the physiology of the tegmentospinal and raphe-spinal projections.     

Cytoarchitecture of serotonin-synthesizing neurons in the pontine tegmentum of the human brain

We have employed immunohistochemical and morphometric procedures to study serotonin-synthesizing (PH8-immunoreactive) neurons in the pontine reticular formation of the adult human. PH8-immunoreactive neurons were found in three cytoarchitectural regions: the median raphe nucleus (MnR), oral pontine reticular nucleus (PnO), and supralemniscal region (group B9). On the basis of cell size, morphology, and position, it was possible to distinguish distinct subgroups within the MnR (dorsal, midline, and paramedian cell clusters) and within the PnO (dorsal and central cell clusters), whereas within the B9 there were no distinct cell clusters. We have estimated that there are approximately 125,000 PH8-immunoreactive neurons in the human pontine tegmentum; 64,400 in the MnR, 30,700 in PnO and 29,000 in B9. The large numbers of serotonin-synthesizing neurons in the human pontine tegmentum contrasts with their relative paucity in nonprimate species such as rats and cats. Nonhuman primates also have large numbers of pontine serotonergic neurons but the morphology of these neurons and their spatial arrangement is significantly different in humans. These results are discussed with respect to the possible projections and functions of these neurons in humans.