Segment-specific pattern of sympathetic preganglionic projections in the chicken embryo spinal cord is altered by retinoids

Sympathetic preganglionic neurons exhibit segment-specific projections. Preganglionic neurons located in rostral spinal segments project rostrally within the sympathetic chain, those located in caudal spinal segments project caudally, and those in midthoracic segments project either rostrally or caudally in segmentally graded proportions. Moreover, rostrally and caudally projecting preganglionic neurons are skewed toward the rostral and caudal regions, respectively, of each midthoracic segment. The mechanisms that establish these segment-specific projections are unknown. Here we show that experimental manipulation of retinoid signaling in the chicken embryo alters the segment-specific pattern of sympathetic preganglionic projections and that this effect is mediated by the somitic mesoderm. Application of exogenous retinoic acid to a single rostral thoracic somite decreases the number of rostrally projecting preganglionic neurons at that level. Conversely, disrupting endogenous synthesis of retinoic acid in a single caudal thoracic somite increases the number of rostrally projecting preganglionic neurons at that level. The number of caudally projecting neurons does not change in either case, indicating that the effect is specific for rostrally projecting preganglionic neurons. These results indicate that the sizes of the rostrally and caudally projecting populations may be independently regulated by different factors. Opposing gradients of such factors along the longitudinal axis of the thoracic region of the embryo could be sufficient, in combination, to determine the segment-specific identity of preganglionic projections.     

A study of a highly specific pyroglutamyl aminopeptidase type-II from the membrane fraction of bovine brain

The purpose of these experiments was to define the topography of cuneate and spinal projections to the forelimb representation in the rostral dorsal accessory olive (rDAO). We were interested in determining whether the spinal and cuneate inputs constitute a homogeneous afferent source, and whether there is evidence that they serve different functional roles. We were also interested in determining whether the somatotopy of rDAO is the result of a point-to-point projection from its afferent sources, or whether the projection suggests a reorganization of afferents at the olive. Single unit recording was used to identify specific regions of rDAO, and the topography of inputs to the identified regions was determined by using wheat germ agglutinin-horseradish peroxidase (WGA-HRP) as a tracer. The results from retrograde tracing were confirmed by using WGA-HRP as an anterograde tracer from input sources. The cuneate and spinal neurons providing input to rDAO constitute two distinct neural populations. One consists of cells in the caudal cuneate nucleus and lamina VI of the rostral two cervical segments, the other consists of cells in the rostral cuneate nucleus. The cells in the caudal cuneate nucleus and the rostral cervical segments are large, multipolar neurons that form a single column of rDAO input cells. The column of cells projects to the contralateral rDAO in a topographic fashion with rostral regions of the column projecting to rostral rDAO, which contains cells that respond to somatosensory stimulation of the contralateral shoulder, trunk, and proximal forelimb. Caudal regions of the column project to caudal rDAO, which contains cells that respond to stimulation of the distal forelimb. Despite this topography, there is a large degree of overlap in the terminations from neighboring regions of the input column, indicating that a major reorganization occurs at the rDAO. The projection from the rostral cuneate nucleus arises from small neurons that project bilaterally to rDAO, and the input from the rostral cuneate nucleus lacks a clear topography. We propose that input from the cell column is responsible for the somatosensory sensitivity of rDAO neurons, whereas input from rostral cuneate is most likely modulatory, probably inhibitory, in nature.     

Spinal cord segments mediating tonic sympathetic nerve discharge to the kidney in the anesthetized cat

According to anatomical data, preganglionic neurons projecting to the kidney via sympathetic ganglia occupy a wide range of adjacent segments in the thoracolumbar spinal cord, from Th7 to L2. Since, however, the majority of preganglionic neurons is silent at resting states, the active segments indeed transmitting sympathetic activity, at rest, may be different. In the present experiments, the spontaneous sympathetic activity was recorded before and after the sympathetic trunk and white rami (WR) Th8-L3 were cut in a sequential manner. The step-by-step changes in the power of renal nerve discharge were estimated and used for mapping tonic renal outflow to the spinal cord. We found that powerful activity comprising 70-95% of the power of control recordings remained after eliminating the input from Th1-Th12, indicating that thoracic spinal cord including segments that contain the largest number of cells projecting to renal postganglionic neurons contributes relatively weakly to tonic renal nerve activity. It appeared that resting sympathetic nerve discharge was predominantly maintained by the caudalmost division of the renal preganglionic neuron population since the largest decrease in nerve power occurred after severing WR Th13, L1, and L2. These findings suggest that the 'active segmental map' of preganglionic neurons controlling a certain organ at rest does not necessarily match the distribution of the total population of neurons projecting to the same effector.     

GABA- and glutamate-immunoreactive synapses on sympathetic preganglionic neurons projecting to the superior cervical ganglion

Our previous work suggests that virtually all of the synapses on sympathetic preganglionic neurons projecting to the rat adrenal medulla are immunoreactive for either the inhibitory amino acid, gamma-aminobutyric acid (GABA) or the excitatory amino acid, L-glutamate. To investigate whether or not this is true for other groups of sympathetic preganglionic neurons, and to determine whether or not the proportion of inputs containing each type of amino acid neurotransmitter is the same for different groups of sympathetic preganglionic neurons, we retrogradely labelled rat and rabbit sympathetic preganglionic neurons projecting to the superior cervical ganglion and used post-embedding immunogold on ultrathin sections to localise GABA- and glutamate-immunoreactivity. The cell bodies and dendrites of both rat and rabbit sympathetic preganglionic neurons projecting to the superior cervical ganglion received synapses and direct contacts from nerve fibres immunoreactive for GABA and from nerve fibres immunoreactive for glutamate. In the rat, GABA was present in 48.9% of the inputs to sympathetic preganglionic neurons projecting to the superior cervical ganglion, and glutamate was present in 51.7% of inputs. Double immunogold labelling for glutamate and GABA on the same section, as well as labelling of consecutive serial sections for the two antigens, indicated that GABA and glutamate occur in separate populations of nerve fibres that provide input to rat sympathetic preganglionic neurons projecting to the superior cervical ganglion. We now have shown that GABA or glutamate is present in virtually all of the inputs to sympathetic preganglionic neurons projecting to the superior cervical ganglion and in essentially all of the inputs to sympathetic preganglionic neurons supplying the adrenal medulla. These findings are consistent with the hypothesis that all fast synaptic transmission in central autonomic pathways may be mediated by either excitatory or inhibitory amino acids. Furthermore, we showed a statistically significant difference in the proportion of glutamate-immunoreactive inputs between sympathetic preganglionic neurons projecting to the superior cervical ganglion and sympathoadrenal neurons (data from Llewellyn-Smith et al. [Llewellyn-Smith, I.J., Phend, K.D., Minson, J.B., Pilowsky, P.M., Chalmers, J.P., 1992. Glutamate immunoreactive synapses on retrogradely labelled sympathetic neurons in rat thoracic spinal cord. Brain Res. 581, 67-80]), with preganglionics supplying the adrenal medulla receiving more excitatory inputs than those supplying the superior cervical ganglion. This increased excitatory input to sympathoadrenal neurons may explain the predominant activation of these neurons following baroreceptor unloading.     

Localization of NADPH diaphorase in the thoracolumbar and sacrococcygeal spinal cord of the dog

The distribution of NADPH-d activity and NOS-immunoreactivity in the spinal cord of the dog was studied to evaluate the role of nitric oxide in lumbosacral afferent and spinal autonomic pathways. At all levels of the spinal cord examined, NADPH-d staining and NOS-immunoreactivity were present in neurons and fibers in the superficial dorsal horn, dorsal commissure and in neurons around the central canal. Sympathetic preganglionic neurons in the rostral lumbar segments identified by choline acetyl transferase (ChAT) immunoreactivity exhibited prominent NADPH-d and and NOS-immunoreactive staining; whereas the ChAT-immunoreactive parasympathetic preganglionic neurons in the sacral segments were not stained. The most prominent NADPH-d activity in the sacral segments occurred in fibers extending form Lissauer's tract through lamina I along the lateral edge of the dorsal horn to the region of the sacral parasympathetic nucleus. These fibers were prominent in the S1-S3 segments but not in adjacent segments (L5-L7 and Cx1 or in thoracolumbar segments. The NADPH-d fibers were not NOS-immunoreactive, but did overlap with a prominent fiber bundle containing vasoactive intestinal polypeptide immunoreactivity in the sacral spinal cord. These results indicate that nitric oxide may function as a transmitter in thoracolumbar sympathetic preganglionic neurons, but not in sacral parasympathetic preganglionic neurons. The functional significance of the NADPH-d positive, NOS-negative fiber bundle on the lateral edge of the sacral dorsal horn remains to be determined. However, based on anatomical studies in other species it seems reasonable to speculate that the fiber tract represents, in part, visceral afferent projections to the sacral parasympathetic nucleus.     

Descending projections from the spinal and mesencephalic nuclei of the trigeminal nerve to the spinal cord in the cat. A study with the horseradish peroxidase technique

Descending projections from the spinal (Vsp) and the mesencephalic nuclei (Vme) of the trigeminal nerve to the spinal cord were studied by means of the retrograde horseradish peroxidase technique in the cat. The number of labeled neurons was largest in the case of high cervical injections and decreased as the injections were placed caudally. Small laminae III and IV neurons of the nucleus caudalis (Vc) were labeled ipsilaterally following injections placed as caudally as the middle cervical segments (C4-C5). Lamina I (marginal) neurons of the Vc were labeled ipsilaterally after injections at the middle thoracic level (T6) but those of C1 were labeled after lumbar injections (L3). Lamina V neurons of C1 and the medullary counterparts were labeled bilaterally after injections placed caudally to thoracic segments. A few small neurons were labeled in the ipsilateral nucleus interpolaris (Vi) after injections placed as caudally as the middle cervical segments (C6). Among the subdivisions of the Vsp, the labeled neurons were most numerous in the nucleus oralis (Vo). They were medium-sized and large, and appeared bilaterally, with an ipsilateral predominance at the level of the superior olive. The great majority projected to the cervical segments but a few also projected to the lower cervical to the thoracic segments (C8-T9). Neurons of the Vme projected ipsilaterally to the upper cervical segments (C1-C3). No projections were found from the principal sensory nucleus. The present study suggests that the trigeminospinal projections of the Vsp and the Vme are composed of various cells of origin and thereby subserve not only the trigeminospinal reflex but other unknown functions.     

Differential spinal projections from the forelimb areas of the rostral and caudal subregions of primary motor cortex in the cat

We used anterograde transport of WGA-HRP to examine the topography of corticospinal projections from the forelimb areas within the rostral and caudal motor cortex subregions in the cat. We compared the pattern of these projections with those from the somatic sensory cortex. The principal finding of this study was that the laminar distribution of projections to the contralateral gray matter from the two motor cortex subregions was different. The rostral motor cortex projected preferentially to laminae VI-VIII, whereas caudal motor cortex projected primarily to laminae IV-VI. Confirming earlier findings, somatic sensory cortex projected predominantly to laminae I-VI inclusive. We found that only rostral motor cortex projected to territories in the rostral cervical cord containing propriospinal neurons of cervical spinal segments C3-4 and, in the cervical enlargement, to portions presumed to contain Ia inhibitory interneurons. We generated contour maps of labeling probability on averaged segmental distributions of anterograde labeling for all analyzed sections using the same algorithm. For rostral motor cortex, heaviest label in the dorsal part of lamina VII in the contralateral cord was consistently located in separate medial and lateral zones. In contrast, no consistent differences in the mediolateral location of label was noted for caudal motor cortex. To summarize, laminae I-III received input only from the somatic sensory cortex, while laminae IV-V received input from both somatic sensory and caudal motor cortex. Lamina VI received input from all cortical fields examined. Laminae VII-IX received input selectively from the rostral motor cortex. For motor cortex, our findings suggest that projections from the two subregions comprise separate descending pathways that could play distinct functional roles in movement control and sensorimotor integration.     

Oxytocin innervation of spinal preganglionic neurons projecting to the superior cervical ganglion in the rat

The paraventricular nucleus of the hypothalamus is a major integrative nucleus for relaying information from the suprachiasmatic nucleus to the autonomic system. The precise pathway by which this information can influence autonomic functions, such as melatonin synthesis in the pineal gland, is not clear. In the present study, we used a retrograde tracer injected in the superior cervical ganglion to identify spinal preganglionic neurons. One of the main neurotransmitters present in descending projections of the paraventricular nucleus of the hypothalamus, oxytocin, was detected with immunocytochemistry to visualise possible contacts with the neurons located in the intermediolateral column of the spinal cord and projecting to the superior cervical ganglion. Although many appositions could be seen at the light-microscopic level, this abundance could not be confirmed at the electron-microscopic level. The implications of these observations for the overall timing message received by the spinal preganglionic neurons are discussed.     

How to manage chest pain in patients with normal coronary angiograms

Sympathetic nerve activity is maintained after high spinal injury through circuits that remain in question. We evaluated patterns of c-fos gene induction as a monitor of spinal neurons responding to high spinal cord transection in the rat. Rats were anesthetized with isofluorane. Lower cervical or upper thoracic spinal segments were exposed, immersed in warm mineral oil and transected. Spinal cords were exposed but not transected in anesthetized controls. After 2.5 h, spinalized and control rats were perfused for immunocytochemistry. Cervical and thoracolumbar spinal segments and dorsal root ganglia were sectioned coronally. Tissues were incubated in primary, polyclonal antisera raised in rabbit or sheep against a peptide sequence unique to the N-terminal domain of Fos, and processed immunocytochemically. Neurons were induced to express Fos-like immunoreactivity (FLI), bilaterally, in the spinal gray, but not in primary sensory ganglia. Spinal cord transection induced neurons to express FLI in thoracic laminae I, IIo (outer substantia gelatinosa), Vre (lateral reticulated division), VII (lamina intermedia) and X, and the intermediolateral cell column. Lamina VIII was also labeled in spinal-injured but not in control animals. Immunolabeled nuclei were prominent in lumbar segments and were concentrated in the medial third of laminae I and IIo, and in laminae VII and X. Few cells were labeled in upper cervical or sacral segments. FLI was sparse in the spinal gray of controls and expressed mainly within the dorsal root entry zone of upper thoracic segments. Patterns of c-fos gene expression were site-specific and correlated with laminae that respond predominantly to noxious stimulation and that contain sympathetic interneurons. Laminae that are responsive to non-noxious stimuli and activated by walking, IIi, nucleus proprius, medial V and layer VI were not induced to express FLI. We conclude that neurons in specific spinal laminae that process high threshold afferents and that harbor neurons with sympathetic nerve-related activity are activated selectively by spinal cord transections. We hypothesize that peripheral afferents processed by spinal-sympathetic circuit neurons may regulate sympathetic discharge in the absence of supraspinal drive.     

Ascending propriospinal afferents to area X (substantia grisea centralis) of the spinal cord in the rat

Area X (the tenth area) of the spinal cord is a region surrounding the central canal and extending throughout the spinal cord length. Using anterograde and retrograde labeling techniques, ascending propriospinal projections to area X were examined in the rat. For anterograde tracing of axons, biotinylated dextran was injected into middle-thoracic, lumbar, or sacral-caudal segments. Unilateral injections resulted in bilateral labeling of terminals in area X of all segments rostral to the injections. The distribution of labeled terminals was conspicuous in regions dorsal and lateral to the central canal. The labeled axons were derived from the ventrolateral and the lateral cord. They coursed through lamina VII, giving off terminal axons. While giving off terminal axons in area X, they coursed further rostrally or caudally along the central canal or crossed over the central canal to terminate in the contralateral area X. Possible cells of origin of these ascending afferents were examined after injections of wheat germ agglutinin-horseradish peroxidase into regions surrounding the central canal (area X) at the cervical or thoracic level. Retrogradely labeled neurons were consistently seen in area X, and laminae VII and VIII of the thoracic and lumbar segments. The present study shows that ascending propriospinal axons project to area X of all spinal levels rostral to the cells of origin and suggests that some of these afferents may originate from neurons in area X and laminae VII and VIII. Based on previous data, it is surmised that area X functions, through these intricate interconnections, as a site for integration or modulation of somatic or nociceptive and visceroceptive sensation.     

Brainstem origin of preganglionic cardiac motoneurons in the muskrat

The muskrat, and aquatic rodent with a brisk and reliable diving response, shows a remarkable bradycardia after nasal stimulation. However, the medullary origin of cardiac preganglionic motoneurons is unknown in this species. We injected fat pads near the base of the heart of muskrats with a WGA-HRP solution to label retrogradely preganglionic parasympathetic neurons that project to the cardiac plexi. Results showed that the preponderance of labeled neurons was in ventrolateral parts of the medulla from 1.5 mm caudal to the obex to 2.0 mm rostral. Eighty-nine percent of the labeled neurons were located bilaterally in the external formation of the nucleus ambiguus, 5.6% were in the lateral extreme of the dorsal motor nucleus of the vagus nerve and 5.3% were found in the intermediate area in between these two nuclei. Although controversy still exists concerning the medullary origin of preganglionic cardiac motoneurons, our results from muskrats agree with those from most other species where preganglionic cardiac motoneurons were located just ventral to the nucleus ambiguus.     

Descending projections from the nucleus raphe obscurus to pudendal motoneurons in the male rat

Previous physiological and behavioral studies have shown that the nucleus raphe obscurus (nRO) modulates pelvic floor reflex function (Yamanouchi and Kakeyama [1992] Physiol. Behav. 51:575-579; Beattie et al. [1996] Soc. Neurosci. Abstr. 22:722.4; Holmes et al. [1997] Brain Res. 759:197-204). In the present study, small injections of fluorescent tracers were used to investigate direct descending projections from the rostral and caudal portions of the brainstem nRO to retrogradely labeled pudendal motoneurons (MN) in the male rat. The caudal nRO projects into the ventral and lateral funiculi of the spinal cord, with arborizations in the thoracic intermediolateral cell column; in laminae VII, IX, and X of the lumbosacral cord; and in the sacral parasympathetic nucleus (SPN). Many identified external anal sphincter and ischiocavernosus MNs appeared to be in direct apposition with fibers originating from the caudal nRO; and more than half of the bulbospongiosus MNs that were identified appeared to receive such descending input. In addition to the nRO spinal autonomic and pudendal motoneuronal targets, projections were observed to regions of the intermediate gray that contain interneurons organizing the pelvic floor reflexes and to MN pools that are involved in functionally related somatic activities. Finally, several neurons in the lumbar enlargement were labeled retrogradely with FluoroRuby after injections into the nRO and the immediately adjacent reticular formation. Thus, the nRO may be in a position to modulate the coordinated actions of autonomic preganglionic and functionally related skeletal MN activity involved in sexual and eliminative reflex functions.     

Identification of lamina V and VII interneurons presynaptic to adrenal sympathetic preganglionic neurons in rats using a recombinant herpes simplex virus type 1

Although indirect evidence suggests that the control of sympathetic preganglionic neurons is mediated to a great extent through interneurons, little is known about the location, morphology or neurotransmitter phenotype of such interneurons. This limitation seriously impedes our understanding of spinal synaptic circuits crucial to control of arterial pressure and other visceral functions. We used a highly neurotropic, minimally cytopathic recombinant herpes simplex virus type-1 to study spinal "sympathetic" interneurons labelled by trans-synaptic transport of the virus from the adrenal gland in rats. Approximately 120-320 infected neurons/rat were identified by immunocytochemical detection of the viral antigen. We distinguished between virus-infected preganglionic neurons and infected interneurons by (i) their location within the spinal laminae, (ii) their size and shape and (iii) the presence or absence of immunoreactivity for the acetylcholine-synthesizing enzyme, choline acetyltransferase, a marker of sympathetic preganglionic neurons. Virus-labelled sympathetic preganglionic neurons were found within the known spinal preganglionic nuclei. Non-cholinergic, virus-labelled neurons were located throughout lamina VII and in the ventral portion of lamina V. These putative interneurons were found in the major spinal preganglionic nuclei, usually intermingled with the preganglionic neurons. Sometimes, they were located in clusters separate from the preganglionic neurons. The interneurons were approximately 15 microm in diameter, smaller than the average preganglionic neuron (diameter=25 microm), and had a few fine processes emanating from them. These non-cholinergic interneurons constituted approximately one-half of the population of virus-infected neurons. In summary, with the use of a recombinant herpes simplex virus, we identified a large number of non-cholinergic interneurons close to, or intermingled with, adrenal sympathetic preganglionic neurons. The neurotransmitter phenotype of these neurons remains to be determined but they likely integrate much of the supraspinal and primary afferent inputs to spinal preganglionic neurons that control arterial pressure and other visceral functions.     

Segmental and propriospinal projection systems of frog lumbar interneurons

Spinal interneuronal networks have been implicated in the coordination of reflex behaviors and limb postures in the spinal frog. As a first step in defining these networks, retrograde transport of horseradish peroxidase (HRP) was used to examine the anatomical organization of interneuronal circuitry in the lumbar spinal cord of the frog. Following neuronal degeneration induced by spinal transection and section of the dorsal and ventral roots, HRP was placed at different locations in the spinal cord and the positions of labeled neuronal cell bodies plotted using a Eutectics Neuron Tracing System. We describe four spinal interneuronal systems, three with cell bodies located in the lumbar cord and one with descending projections to the lumbar cord. Interneurons with cell bodies located in the lumbar cord include: (1) Lumbar neurons projecting rostrally. Those projecting to thoracic segments tended to be located in the lateral and ventrolateral gray and in the lower two-thirds of the dorsal horn, with projections that were predominantly uncrossed. Those projecting to the brachial plexus and beyond were located in the dorsal part of the dorsal horn (uncrossed) and in the lateral, ventrolateral, and ventromedial gray (crossed). (2) Lumbar neurons with segmental projections within the lumbar cord. These neurons, which were by far the most numerous, had both uncrossed and crossed projections and were distributed throughout the dorsal, lateral, ventrolateral, and ventromedial gray matter. (3) Lumbar neurons projecting to the sacral cord. This population, which arose mainly from the dorsal horn and lateral or ventrolateral gray, was much smaller than in the other systems. Neuronal density of some of these populations of lumbar interneurons appeared to vary with rostrocaudal level. Finally, a population of neurons with cell bodies in the brachial and thoracic segments that projects to the lumbar cord is described. The most rostral of these neurons were multipolar cells with uncrossed projections, while those with crossed projections were confined almost exclusively to the ventral half of the cord. The distribution of spinal interneurons reported here will provide guidance for future studies of the role of interneuronal networks in the control of movements using the spinal frog as a model system.     

Dynorphin mRNA expression in dorsal horn neurons after traumatic spinal cord injury: temporal and spatial analysis using in situ hybridization

Dynorphin, an endogenous opioid, may contribute to secondary nervous tissue damage following spinal cord injury. The temporal and spatial distribution of preprodynorphin (PPD) mRNA expression in the injured rat spinal cord was examined by in situ hybridization. Rats were subjected to traumatic spinal cord injury at the T13 spinal segment using the weight-drop method. Motor function of these rats was evaluated by their ability to maintain their position on an inclined plane. Two double-labeling experiments revealed that increased PPD mRNA and dynorphin peptide expression were found exclusively in dorsal horn neurons. Neurons exhibiting an increase in the level of PPD mRNA were concentrated in the superficial laminae and the neck of dorsal horn within several spinal segments from the epicenter of the injury at 24 and 48 h after injury. A number of neurons showing increased PPD mRNA were found in gray matter adjacent to the injury areas. Segments caudal to the injury site exhibited a long-lasting elevation of PPD mRNA in neurons, compared to the rostral segments. The number of neurons expressing PPD mRNA in each rat was significantly positively correlated with its motor dysfunction. These findings suggest that increased expression of dynorphin mRNA and peptide in dorsal horn neurons occurs after traumatic spinal cord injury. This also supports the hypothesis that the dynorphin has a pathological role in secondary tissue damage and neurological dysfunction after spinal cord injury.     

Electrophysiological evidence for oxytocin receptors on sympathetic preganglionic neurones--an in vitro study on the neonatal rat

The action of oxytocin (0.01-1 microM) on sympathetic preganglionic neurones was studied by intracellular recording in slices of neonatal rat thoracic spinal cord. In 85% of the cells superfusion induced a slow tetrodotoxin-insensitive depolarization accompanied by the appearance or increase in frequency of repetitive discharges. Oxytocin also caused some cells to switch from silent neurones to spontaneously active ones. These effects were reversibly blocked by a specific oxytocin antagonist.     

Physiologic basis of pulmonary edema during intestinal reperfusion

The ventrolateral portion of the intermediate reticular formation of the medulla (ventrolateral medulla, VLM), including the C1/A1 groups of catecholaminergic neurons, is thought to be involved in control of sympathetic cardiovascular outflow, cardiorespiratory interactions, and reflex control of vasopressin release. As all these functions are affected in patients with multiple systems atrophy (MSA) with autonomic failure, we sought to test the hypothesis that catecholaminergic (tyrosine hydroxylase [TH]-positive) neurons of the VLM are depleted in these patients. Medullas were obtained at autopsy from 4 patients with MSA with prominent autonomic failure and 5 patients with no neurological disease. Patients with MSA had laboratory evidence of severe adrenergic sudomotor and cardiovagal failure. Tissue was immersion fixed in 2% paraformaldehyde at 4 degrees C for 24 hours and cut into 1-cm blocks in the coronal plane from throughout the medulla. Serial 50-microm sections were collected and one section every 300 microm was stained for TH. There was a pronounced depletion of TH neurons in the rostral VLM in all cases of MSA. There was also significant reduction of TH neurons in the caudal VLM in 3 MSA patients compared with 3 control subjects. In 2 MSA cases and in 2 control subjects, the thoracic spinal cord was available for study. There was also depletion of TH fibers and sympathetic preganglionic neurons (SPNs) in the 2 MSA cases examined. Thus, depletion of catecholaminergic neurons in the VLM may provide a substrate for some of the autonomic and endocrine manifestations of MSA.     

Frequency and clinical correlates of occlusive lesions of cerebral arteries in Japanese patients without stroke. Evaluation by MR angiography

BACKGROUND: In order to provide a morphological basis for the understanding of the role of nitric oxide (NO) in autonomic preganglionic neurons, the present study was designed to clarify the localization and distribution of nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) activity, a marker of NO synthase, in the rabbit spinal cord. METHODS: 11 Chinchilla rabbits of both sexes were used in this study. Animals were kept under conditions of controlled light and heat regimens. NADPH-d activity was examined by histochemical methods. RESULTS: The presence of NADPH-d activity in the spinal cord was detected in the dorsal horn, around the central canal (lamina X) and in autonomic preganglionic neurons. Focused on the latter, there was a prominent NADPH-d activity between T1 and L5 segments in the intermediate zone and less intensive NADPH-d staining between S1 and S3 segments. Differences between the two parts of the autonomic system were seen in the arrangement (periodical in sympathetic, and continuous in parasympathetic), in the length of neuronal processes length (shorter in sacral preganglionic neurons) and in their localization (both are seen in the intermediolateral nucleus, but neurons of the sympathetic autonomic system can be found also medially towards the central canal, whilst those of the parasympathetic system were not). CONCLUSIONS: The present results suggest that NO can be used as a transmitter in preganglionic neurons and can be involved in autonomic and sensory processes. (Fig. 10, Ref. 37.)     

Barosensitive neurons in the rostral ventrolateral medulla of the rat in vivo: morphological properties and relationship to C1 adrenergic neurons

The aim of this study, conducted in anaesthetized rats, was to examine the morphology of barosensitive neurons in the rostral ventrolateral medulla and their immunoreactivity for a catecholamine synthesizing enzyme, tyrosine hydroxylase. Thirty neurons displaying inhibitory postsynaptic potentials following stimulation of the aortic depressor nerve were intracellularly labelled with Lucifer Yellow or Neurobiotin. Some of these neurons could be excited antidromically from the second thoracic segment of the spinal cord, with conduction velocities of spinal axons ranging from 1.9 to 7.2 m/s. The filled somas were found immediately caudal to the facial nucleus and ventral or ventromedial to compact formation of the nucleus ambiguus. Some dendrites reached the ventral medullary surface. Axons usually projected dorsomedially and then made a sharp rostral and/or caudal turn. The caudally projecting axon could, in some cases, be followed to the first cervical segment of the spinal cord. Seven cells issued fine axon collaterals on the ipsilateral side. These were identified mainly in two areas: in the rostral ventrolateral medulla (or immediately dorsomedial to that region), and within the dorsal vagal complex. Seven of 27 examined cells (26%) were tyrosine hydroxylase-immunoreactive and were classified as C1 adrenergic neurons. No clear relationship was found between the presence or absence of adrenergic phenotype and the morphology of filled cells. However, the amplitude of aortic nerve-evoked inhibitory postsynaptic potentials was significantly larger in tyrosine hydroxylase-positive neurons. Possible reasons for the low percentage of barosensitive cells with tyrosine hydroxylase immunoreactivity found in this study, in comparison with previously published estimates, are discussed. This is the first study describing the morphology of neurons in this part of the medulla identified as barosensitive in vivo, and directly demonstrating adrenergic phenotype in a subset of these neurons.     

Effects of chemical disinfectants on the surface characteristics and color of denture resins

Previous research has demonstrated that anorectal contractions in the rat are modulated by activation of spinal autonomic circuits. In the present study, anterograde tracing of descending pathways originating from the caudal nucleus raphe obscurus (nRO) revealed that this nucleus projects to cells within the intermediolateral (IML) cell column of the thoracic cord and the sacral parasympathetic nucleus (SPN). These anatomical studies suggested that the nRO may influence the regulation of spinal reflexes of the pelvic floor. In a second set of experiments, acute rat preparations were used to investigate changes in anorectal motility during electrical stimulation of the nRO. Anorectal contractions were measured by a fluid-filled manometer. Electrical stimulation of the nRO significantly reduced spontaneous anorectal activity when compared to baseline contractions recorded for 1 min prior to stimulation. Stimulation sites outside the nRO did not affect anorectal contractions when compared to either (a) the 1-min pre-stimulation baseline for that site or (b) the 1-min stimulation period for sites within the nRO. Stimulation of caudal portions of the nRO were more likely than the rostral nRO to reduce anorectal contractions. Given that the SPN contains preganglionic neurons which may be involved in control of anorectal contractions (mediated via the pelvic nerve), the studies presented here suggest a functional role for nRO regulation of preganglionic motoneurons innervating the distal gut of the rat.