Microscopic Study of Nervous System Plasticity: Interactions of Sympathetic Nerves with Neurons of Intraocular Hippocampal Transplants.

Functional interactions of sympathetic fibers innervating the iris with the neurons of central origin in intraocular transplants of the rat hippocampus were studied by optic, confocal, and electron microscopy. After formaldehyde fixation, fluorescent dye Dil was applied to the upper cervical ganglion; the dye migrated to the transplant by lateral diffusion via axons. Sympathetic nerves labeled with fluorescent dye grew into the neurotransplants along perivascular membranes of blood vessels. In addition, some fluorescent axons were identified in the transplant parenchyma. Electron microscopy showed large bundles of the peripheral type axons in the vascular adventitia and Schwann-axonal complexes in the transplant neuropil. Autonomic axons formed synaptic contacts with transplanted neurons.

Dense Intra-adipose Sympathetic Arborizations Are Essential for Cold-Induced Beiging of Mouse White Adipose Tissue.

Efferent signals from the central nervous system represent a key layer of regulation of white adipose tissue (WAT). However, the mechanism by which efferent neural signals control WAT metabolism remains to be better understood. Here, we exploit the volume fluorescence-imaging technique to visualize the neural arborizations in mouse inguinal WAT at single-fiber resolution. The imaging reveals a dense network of sympathetic arborizations that had been previously undetected by conventional methods, with sympathetic fibers being in close apposition to > 90% of adipocytes. We demonstrate that these sympathetic fibers originate from the celiac ganglia, which are activated by cold challenge. Sympathetic-specific deletion of TrkA receptor or pharmacologic ablation by 6-hydroxydopamine abolishes these intra-adipose arborizations and, as a result, cold-induced beiging of inguinal WAT. Furthermore, we find that local sympathetic arborizations function through beta-adrenergic receptors in this beiging process. These findings uncover an essential link connecting efferent neural signals with metabolism of individual adipocytes.

Overexpression of Sarcoendoplasmic Reticulum Calcium ATPase 2a Promotes Cardiac Sympathetic Neurotransmission via Abnormal Endoplasmic Reticulum and Mitochondria Ca2+ Regulation.

Reduced cardiomyocyte excitation-contraction coupling and downregulation of the SERCA2a (sarcoendoplasmic reticulum calcium ATPase 2a) is associated with heart failure. This has led to viral transgene upregulation of SERCA2a in cardiomyocytes as a treatment. We hypothesized that SERCA2a gene therapy expressed under a similar promiscuous cytomegalovirus promoter could also affect the cardiac sympathetic neural axis and promote sympathoexcitation. Stellate neurons were isolated from 90 to 120 g male, Sprague-Dawley, Wistar Kyoto, and spontaneously hypertensive rats. Neurons were infected with Ad-mCherry or Ad-mCherry-hATP2Aa (SERCA2a). Intracellular Ca2+ changes were measured using fura-2AM in response to KCl, caffeine, thapsigargin, and carbonylcyanide-p-trifluoromethoxyphenylhydrazine to mobilize intracellular Ca2+ stores. The effect of SERCA2a on neurotransmitter release was measured using [3H]-norepinephrine overflow from 340 to 360 g Sprague-Dawley rat atria in response to right stellate ganglia stimulation. Upregulation of SERCA2a resulted in greater neurotransmitter release in response to stellate stimulation compared with control (empty: 98.7±20.5 cpm, n=7; SERCA: 186.5±28.41 cpm, n=8; P<0.05). In isolated Sprague-Dawley rat stellate neurons, SERCA2a overexpression facilitated greater depolarization-induced Ca2+ transients (empty: 0.64±0.03 au, n=57; SERCA: 0.75±0.03 au, n=68; P<0.05), along with increased endoplasmic reticulum and mitochondria Ca2+ load. Similar results were observed in Wistar Kyoto and age-matched spontaneously hypertensive rats, despite no further increase in endoplasmic reticulum load being observed in the spontaneously hypertensive rat (spontaneously hypertensive rats: empty, 0.16±0.04 au, n=18; SERCA: 0.17±0.02 au, n=25). In conclusion, SERCA2a upregulation in cardiac sympathetic neurons resulted in increased neurotransmission and increased Ca2+ loading into intracellular stores. Whether the increased Ca2+ transient and neurotransmission after SERCA2A overexpression contributes to enhanced sympathoexcitation in heart failure patients remains to be determined.

Pulmonary Artery Denervation Attenuates Pulmonary Arterial Remodeling in Dogs With Pulmonary Arterial Hypertension Induced by Dehydrogenized Monocrotaline.

OBJECTIVES: This study aimed to investigate sympathetic nerve (SN) ultrastructural changes and hemodynamic and pulmonary artery (PA) pathological improvements by pulmonary arterial denervation (PADN) in animals with pulmonary arterial hypertension (PAH), as well as the underlying mechanisms. BACKGROUND: SN overactivity plays a role in PAH. Previous studies have reported short-term improvements in pulmonary arterial pressure (PAP) and cardiac function by PADN, but PA remodeling and the associated mechanisms remain unclear. METHODS: Forty dogs were randomly (ratio of 1:3) assigned to the control (intra-atrial injection of N-dimethylacetamide, 3 mg/kg) and test (intra-atrial injection of dehydrogenized-monocrotaline, 3 mg/kg) groups. After 8 weeks, the animals in the test group with a mean PAP >25 mm Hg (n = 20) were randomized (ratio of 1:1) into the sham and PADN groups. At 14 weeks, the hemodynamics, medial wall thickness and PA muscularization, and messenger ribonucleic acid expression of genes in lung tissues were measured. Another 35 PAH dogs were used to measure the SN conduction velocity, electron microscopic assessment, and nerve distribution. RESULTS: PADN induced significant SN demyelination and axon loss and slowed SN conduction velocity over time, with resulting profound reductions in the mean PAP (23.5 ± 2.3 mm Hg vs. 33.7 ± 5.8 mm Hg), pulmonary vessel resistance (3.5 ± 2.3 Wood units vs. 7.7 ± 1.7 Wood units), medial wall thickness (22.3 ± 3.3% vs. 30.4 ± 4.1%), and full muscularization (40.3 ± 9.3% vs. 57.1 ± 5.7%) and increased nonmuscularization (29.8 ± 6.1% vs. 12.9 ± 4.9%) compared with the Sham group (all p < 0.001). PADN inhibited the messenger ribonucleic acid expression of genes correlated with inflammation, proliferation, and vasoconstriction. CONCLUSIONS: PADN induces permanent SN injury and subsequent improvements in hemodynamics and PA remodeling in animals with PAH through mechanisms that may be experimentally and clinically beneficial.

Differential toxicities of intraneurally injected mercuric chloride for sympathetic and somatic motor fibers: an ultrastructural study.

BACKGROUND/PURPOSE: Mercury is a well-known neurotoxin but the susceptibility of autonomic nerves to mercury poisoning in vivo has seldom been studied. Our previous studies have shown that the hypoglossal nerve in hamsters contains somatic motor and postganglionic sympathetic fibers. The aim of this study was to investigate the ultrastructural changes in the nervous system following intraneural injection of mercuric chloride into the hypoglossal nerve in hamsters. METHODS: Six adult hamsters were used in this study. After anesthesia, the digastric muscle on the right side was removed and the trunk of the hypoglossal nerve was exposed. Two microliters of mercuric chloride aqueous solution was injected into the main trunk of the hypoglossal nerve at the bifurcation. The contralateral hypoglossal nerve was kept intact and used as the normal control. Animals were allowed to survive for 1 or 3 days and were prepared for ammonium sulfide histochemistry and electron microscopy. RESULTS: Three days after injection of mercuric chloride solution, almost all unmyelinated sympathetic fibers in the hypoglossal nerve trunk were lost, whereas myelinated somatic axons were spared. Although mercury deposition in the myelin sheaths of neuronal processes was observed in the hypoglossal nucleus, the neuronal somas were intact. By contrast, degenerated neuronal processes and mercury deposition in neuronal somas were frequently found in the superior cervical ganglia. CONCLUSION: This study demonstrated an undue susceptibility of sympathetic fibers to mercury intoxication. The mechanisms that underlie the selective reaction of sympathetic fibers to mercury warrant further investigation.

A new organellar complex in rat sympathetic neurons.

Membranous compartments of neurons such as axons, dendrites and modified primary cilia are defining features of neuronal phenotype. This is unlike organelles deep to the plasma membrane, which are for the most part generic and not related directly to morphological, neurochemical or functional specializations. However, here we use multi-label immunohistochemistry combined with confocal and electron microscopy to identify a very large (approximately 6 microns in diameter), entirely intracellular neuronal organelle which occurs singly in a ubiquitous but neurochemically distinct and morphologically simple subset of sympathetic ganglion neurons. Although usually toroidal, it also occurs as twists or rods depending on its intracellular position: tori are most often perinuclear whereas rods are often found in axons. These 'loukoumasomes' (doughnut-like bodies) bind a monoclonal antibody raised against beta-III-tubulin (SDL.3D10), although their inability to bind other beta-III-tubulin monoclonal antibodies indicate that the responsible antigen is not known. Position-morphology relationships within neurons and their expression of non-muscle heavy chain myosin suggest a dynamic structure. They associate with nematosomes, enigmatic nucleolus-like organelles present in many neural and non-neural tissues, which we now show to be composed of filamentous actin. Loukoumasomes also separately interact with mother centrioles forming the basal body of primary cilia. They express gamma tubulin, a microtubule nucleator which localizes to non-neuronal centrosomes, and cenexin, a mother centriole-associated protein required for ciliogenesis. These data reveal a hitherto undescribed organelle, and depict it as an intracellular transport machine, shuttling material between the primary cilium, the nematosome, and the axon.

Anatomy of synaptic circuits controlling the activity of sympathetic preganglionic neurons.

Sympathetic preganglionic neurons (SPN) are critical links in the sympathetic neural circuitry that controls every organ in the body. All sympathetic outflow to the periphery comes from SPN, which send their axons from thoracic and upper lumbar spinal segments to innervate post-ganglionic neurons in sympathetic ganglia and chromaffin cells in the adrenal medulla. Despite over 30 years of study, we still do not have a sufficiently detailed understanding of the synaptic circuits through which these important neurons receive information from other central sites. We know that there is direct synaptic input to SPN from both supraspinal and intraspinal neurons, but not sensory neurons. Ultrastructural studies support functional evidence that amino acids are the primary fast-acting transmitters controlling SPN activity and indicate that an amino acid transmitter occurs in every synaptic input to an SPN. In addition, axons that synapse on SPN contain neuropeptides and monoamines, which would co-exist with and be released with the amino acids. Receptors and transporters for transmitters have also been localized in SPN inputs. Light and electron microscopic observations suggest that there are qualitative and/or quantitative differences in the neurochemical types and origins of axons, which provide synaptic input to SPN that supply different targets or have different functions. However, more research is required before it can be confirmed that SPN receive projection- or function-specific patterns of innervation. This information is likely to be important if we are to understand how the central nervous system differentially regulates sympathetic outflow to different target tissues.

Ultrastructural changes of posterior lingual glands after hypoglossal denervation in hamsters.

Posterior lingual glands consist of two sets of minor salivary glands that serve important functions in oral physiology. To investigate the hypothesis that the hypoglossal nerve provides sympathetic innervation to the posterior lingual glands, we examined ultrastructural changes in the glands following hypoglossal denervation. In the posterior deep lingual glands (of von Ebner), the serous acinar cells showed a decrease in the number of secretory granules and an increase in lipofuscin accumulation. The ratios of cells containing lipofuscin granules were 11.39, 36.49 and 50.46%, respectively, of the control, 3- and 7-day post-axotomy glands (P < 0.001). Intraepithelial phagocytotic activity was increased. The mucous acinar cells in the posterior superficial lingual glands (of Weber) also showed degenerative changes after hypoglossal denervation. One week after nerve transection, marked cytoplasmic vacuolation and fragmentation of organelles were frequently observed. Degenerative changes were also found in unmyelinated axons associated with the glands. We provide the first evidence of the structural and functional connections between the sympathetic component of the hypoglossal nerve and posterior lingual glands.

Investigation of close interactions between sympathetic neural fibres and the follicular dendritic cells network in the mouse spleen.

In this study, co-localization between sympathetic neural fibres and the follicular dendritic cells (FDCs) network was observed within the mouse spleen by confocal technology. Immunohistochemical techniques were used to reveal the rare interactions between the FDCs network and sympathetic neural fibres. We estimated the frequency of three kinds of close interactions which could be defined as overlaps, contacts or neural fibres closer than 10 microm from a FDCs network. Using these estimates, a comparison was made between five uninfected mouse strains exhibiting the same Prnpa genotype but showing different incubation periods when inoculated with primary bovine spongiform encephalopathy (BSE)-infected brain. In prion disease, infectivity is generally detected in the spleen much earlier than in the brain, especially after peripheral inoculation. The way by which the infectious agent reaches the central nervous system is still unclear. From the five mouse strains, we obtained differences in the proportion of splenic FDCs networks with close interactions. Our work suggests that the percentage of splenic FDCs networks with at least one sympathetic neural fibre in close vicinity may influence the length of incubation period.

[Comparative analysis of vasomotor responses and sympathetic innervation of feed arteries from locomotor and respiratory muscles in a rat].

The characteristics of feeding arteries of diaphragm and medial gastrocnemius (with a diameter of 200-250 micron) were studied. The registration of the mechanical activity of ring preparations under isometric conditions revealed that diaphragm arteries, like arteries of other muscles with a high content of slow muscle fibers, are highly sensitive to adrenoceptor agonists and acetylcholine. The differences in endothelium-dependent relaxation between diaphragm and gastrocnemius arteries are preserved in the presence of L-NAME and diclofenac. Responses to serotonin in diaphragm and gastrocnemius arteries are similar. At the same time, the high density of innervation is characteristic of diaphragm artery only, while in other slow muscles it is low. The density of adrenergic fibers plexus in the diaphragm artery is much higher than in the gastrocnemius artery. The results suggest that the properties of small arteries of diaphragm are determined not only by the oxidative capacity of diaphragm muscle fibers but also by the belonging of the diaphragm to respiratory musculature.

[Sympathetic and parasympathetic centers of the brain and spinal marrow of rats during exposure to +Gz].

Structural transformations in the dorsal vagal complex and intermediolateral nucleus due to +G, loads were studied in white outbred male rats centrifuged according to the standard procedure (P.S.Paschenko, 1995). Methods of investigation included light and electron microscopy, morphometric analysis and statistical analysis. Acute exposure to +Gz loads resulted in essentially reactive changes in the centers under study. At the same time, regular exposure to this extreme factor led to cumulation of destructive changes. The peculiar structure of the centers governs uniqueness of disorders which may unbalance the autonomous regulation of organism functions.

Wide distribution and subcellular localization of histamine in sympathetic nervous systems of different species.

Previous studies have demonstrated that histamine (HA) acts as a neurotransmitter in the cardiac sympathetic nervous system of the guinea pig. The aim of the current study was to examine whether HA widely exists in the sympathetic nervous systems of other species and the subcellular localization of HA in sympathetic terminals. An immunofluorescence histochemical multiple-staining technique and anterograde tracing method were employed to visualize the colocalization of HA and norepinephrine (NE) in sympathetic ganglion and nerve fibers in different species. Pre-embedding immunoelectron microscopy was used to observe the subcellular distribution of HA in sympathetic nerve terminals. Under the confocal microscope, coexistence of NE and HA was displayed in the superior cervical ganglion and celiac ganglion neurons of the mouse and dog as well as in the vas deferens, mesenteric artery axon, and varicosities of the mouse and guinea pig. Furthermore, colocalization of NE and HA in cardiac sympathetic axons and varicosities was labeled by biotinylated dextranamine injected into the superior cervical ganglion of the guinea pig. By electron microscopy, HA-like high-density immunoreactive products were seen in the small vesicles of the guinea pig vas deferens. These results provide direct cellular and subcellular morphological evidence for the colocalization of HA and NE in sympathetic ganglion and nerve fibers, and support that HA is classified as a neurotransmitter in sympathetic neurons.

Ultrastructural evidence for selective noradrenergic innervation of CNS vagal projections to the fundus of the rat.

We reported pharmacological data suggesting that stimulation of the vago-vagal reflex activates noradrenergic neurons in the hindbrain that inhibit dorsal motor nucleus of the vagus (DMV) neurons projecting to the fundus, but not to the antrum [Ferreira Jr., M., Sahibzada, N., Shi, M., Panico, W., Neidringhaus, M., Wasserman, A., Kellar, K.J., Verbalis, J., Gillis, R.A., 2002. CNS site of action and brainstem circuitry responsible for the intravenous effects of nicotine on gastric tone. J. Neurosci. 22, 2764-2779.]. The purpose of this study was to use an ultrastructural approach to test the hypothesis that noradrenergic terminals form synapses with DMV fundus-projecting neurons, but not with DMV antrum-projecting neurons. A retrograde tracer, CTbeta-HRP, was injected into the gastric smooth muscle of either the fundus or the antrum of rats. Animals were re-anesthetized 48 h later and perfusion-fixed with acrolein and paraformaldehyde. Brainstems were processed histochemically for CTbeta-HRP, and immunocytochemically for either DbetaH or PNMT by dual-labeling electron microscopic methods. Most cell bodies and dendrites of neurons that were retrogradely labeled from the stomach occurred at the level of the area postrema. Examination of 482 synapses on 238 neurons that projected to the fundus revealed that 17.4+/-2.7% (n=4) of synaptic contacts were with DbetaH-IR terminals. Of 165 fundus-projecting neurons, 4.4+/-1.5% (n=4) formed synaptic contacts with PNMT-IR terminals. In contrast, the examination of 384 synapses on 223 antrum-projecting neurons revealed no synaptic contact with DbetaH-IR terminals. These data provide proof that norepinephrine containing nerve terminals synapse with DMV fundus-projecting neurons but not with DMV antrum-projecting neurons. These data also suggest that brainstem circuitry controlling the fundus differs from circuitry controlling the antrum.

Morphology and ultrastructure of the sympathetic celiac ganglion neurons projecting to the cardia and pylorus of the rat stomach.

The stomach receives sympathetic projections from the celiac ganglion. To determine what kinds of neurons in the celiac ganglion project to the cardia or the pylorus of the stomach, we injected the retrograde tracer Fluoro-Gold into the cardia and the retrograde tracer cholera toxin subunit b into the pylorus of the same animal. A few neurons (about 10%) innervating the cardia sent collateral projections to the pylorus. Ultrastructural observations revealed that the celiac ganglion contained oval, medium-sized to large neurons. They had a dark cytoplasm containing numerous free ribosomes, rough endoplasmic reticulum, mitochondria, lysosomes, several Golgi apparatuses, and an oval nucleus. The axon terminals were small and usually contacted thin processes extending from the dendrites or the soma. About half of the terminals contained round vesicles, while the rest contained pleomorphic vesicles. Both types of terminals made asymmetric synaptic contacts. We then retrogradely labeled the neurons projecting to the cardia and the pylorus with wheat germ agglutinin conjugated horseradish peroxidase to examine their ultrastructural characteristics. The neurons projecting to the cardia (33.3x22.4 microm) were similar to the neurons projecting to the pylorus (33.4x24.7 microm) in their size and ultrastructural appearance. The neurons not projecting to the stomach (40.4x28.0 microm) were significantly larger than the neurons projecting to the cardia or the pylorus. Only a few axosomatic terminals were found on the neurons projecting to the cardia (1.6 per somatic profile), the pylorus (1.3) or the neurons not projecting to the stomach (0.9). These results provide morphological bases for the sympathetic motor neurons innervating the stomach.

The effects of age and streptozotocin diabetes on the sympathetic innervation in the rat penis.

The objective was to describe the changes in catecholamine levels, noradrenaline (NA) release and the ultrastructural and immunohistochemical changes in the sympathetic nerves in the penis of STZ-diabetic rats. Amines were measured using HPLC. Nerves were studied using immunocytochemistry for tyrosine hydroxylase, and electron microscopy. Diabetic animals were compared with age-matched controls. The concentration of penile NA increases at least 2.5-fold after about 10 weeks of hyperglycaemia, is maintained for over 40 weeks. The rate of release of NA in the diabetics also increases approximately by fourfold. Immunohistochemical staining for tyrosine hydroxylase showed either no change or an increase in the levels of the enzyme around the central arteries and the outer coverings of the corpus cavernosum. Cavernosal nerves show increased intensity of staining for tyrosine hydroxylase, and the presence of dilated nerve fibres and engorged endings. The axons of the dorsal nerve of the diabetic penis have a smaller cross-sectional area that is most marked in unmyelinated axons. In the diabetic penis, the nerve endings appear to contain significantly more NA than the controls, and the turnover of noradrenaline is increased substantially. There is immunocytochemical evidence of an increase in staining for tyrosine hydroxylase, suggesting an increase in synthetic activity. These results are discussed in relation to the existing literature on the role of amines in normal and disordered erectile function. In particular, the increased concentration and turnover of NA in the diabetic rat contrasts with the fall in NA in cavernosal blood described during normal erection in humans.

Cocaine- and amphetamine-regulated transcript peptide and sympatho-adrenal axis.

Cocaine- and amphetamine-regulated transcript peptide (CART) is constitutively expressed in discrete regions of the mammalian central and peripheral nervous system. Immunohistochemical studies reveal a well-defined network of CART-immunoreactive (irCART) neurons organized along the sympatho-adrenal axis. Sympathetic preganglionic neurons, but not parasympathetic preganglionic neurons, in the lateral horn area are CART-positive; which in turn innervate postganglionic neurons in the paravertebral and prevertebral sympathetic ganglia as well as the adrenal medulla. A population of chromaffin cells in the adrenal medulla is CART-positive; whereas, postganglionic neurons are not. Sympathetic preganglionic neurons themselves are contacted by irCART cell processes arising from neurons in the arcuate nucleus, the retrochiasmatic nucleus and the rostral ventrolateral medulla. Results from several recent studies suggest CART directly excites neurons along the sympathetic neural axis or indirectly by potentiating the action of glutamate on NMDA receptors, as evidenced by an elevation of blood pressure and heart rate following intracerebroventricular, intracisternal or intrathecal administration of the peptide to anesthetized rats or conscious rabbits.

Evidence that estrogen directly and indirectly modulates C1 adrenergic bulbospinal neurons in the rostral ventrolateral medulla.

Blood pressure in women increases after menopause, and sympathetic tone in female rats decreases with estrogen injections in the rostral ventrolateral medulla (RVLM) region that contains bulbospinal C1 adrenergic neurons and is involved in blood pressure control. We investigated the anatomical and physiological basis for estrogen effects in the RVLM. Neurons with alpha- or beta-subtypes of estrogen receptor (ER) immunoreactivity (-ir) overlapped in distribution with tyrosine hydroxylase (TH)-containing C1 neurons. Immunoelectron microscopy revealed that ERalpha- and ERbeta-ir had distinct cellular and subcellular distributions. ERalpha-ir was most commonly in TH-lacking profiles, many of which were axons and peptide-containing afferents that contacted TH-containing dendrites. ERalpha-ir was also in some TH-containing dendrites. ERbeta-ir was most frequently in TH-containing somata and dendrites, particularly on endoplasmic reticula, mitochondria, and plasma membranes. In whole-cell patch clamp recordings from isolated bulbospinal RVLM neurons, 17beta-estradiol dose-dependently reduced voltage-gated Ca(++) currents, especially the long-lasting (L-type) component. This inhibition was reversed by washing or prevented by adding the non-subtype-selective ER antagonist ICI182780. An ERbeta-selective agonist, but not an ERalpha-selective agonist, reproduced the Ca(++) current inhibition. The data indicate that estrogens can modulate the function of RVLM C1 bulbospinal neurons either directly, through extranuclear ERbeta, or indirectly through extranuclear ERalpha in selected afferents. Moreover, Ca(++) current inhibition may underlie the decrease in sympathetic tone evoked by local 17beta-estradiol application. These findings provide a structural and functional basis for the effects of estrogens on blood pressure control and suggest a mechanism for the modulation of cardiovascular function by estrogen in women.

Increased close appositions between corticospinal tract axons and spinal sympathetic neurons after spinal cord injury in rats.

Treatments for spinal cord injury may promote new spinal cord synapses. However, the potential for new synapses between descending somatomotor and spinal sympathetic neurons has not been investigated. We studied rats with intact spinal cords and rats after a chronic, bilateral, dorsal spinal hemisection. We identified sympathetically related spinal neurons by transynaptic, retrograde transport of renally injected pseudorabies virus. We counted retrogradely labeled sympathetic preganglionic neurons (SPN) and putative sympathetic interneurons (IN) that, under light microscopy, appeared closely apposed by anterogradely labeled axons of the corticospinal tract (CST) and by axons descending from the well-established sympathetic regulatory region in the rostral ventrolateral medulla (RVLM). Spinal sympathetic neurons that were closely apposed by CST axons were significantly more numerous in lesioned rats than in unlesioned rats. CST axons closely apposed 5.4% of SPN and 10.3% of IN in rats with intact spinal cords, and 38.0% of SPN and 37.3% of IN in rats with chronically lesioned spinal cords. Further, CST appositions in SCI rats consisted of many more varicosities than those in uninjured rats. SPN and IN closely apposed by axons from the RVLM were not more numerous in lesioned rats. However, RVLM axons apposed many more SPN than IN in both control and lesioned rats. Therefore, RVLM sympathoexcitation may be mediated largely by direct synapses on SPN. Although we have not determined the functional significance of close appositions between the CST and spinal sympathetic neurons, we suggest that future studies of spinal cord repair and regeneration include an evaluation of potential, new, somatic-autonomic interactions.

Ultrastructural identification of a sympathetic component in the hypoglossal nerve of hamsters using experimental degeneration and horseradish peroxidase methods.

We employed experimental degeneration, tract-tracing with wheatgerm agglutinin conjugated with horseradish peroxidase (WGA-HRP) and electron microscopy to explore the postganglionic sympathetic fibers in the hypoglossal nerve of hamsters. Quantitative results of normal untreated animals at the electron microscopic level showed the existence of unmyelinated fibers, which made up about 20% of the total fibers in the nerve, being more numerous on the left side. The nerve fibers were preferentially distributed at the periphery of the nerve. Following superior cervical ganglionectomy, most of the unmyelinated fibers underwent degenerative changes. Tract-tracing studies showed that some of the unmyelinated fibers were labeled by WGA-HRP injected into the superior cervical ganglion (SCG). It is suggested that the unmyelinated fibers represent the postganglionic sympathetic fibers originated from the SCG.

Extracellular signal-regulated kinases regulate dendritic growth in rat sympathetic neurons.

NGF activates several signaling cascades in sympathetic neurons. We examined how activation of one of these cascades, the ERK/MAP (extracellular signal-regulated kinase/mitogen-activated protein) kinase pathway, affects dendritic growth in these cells. Dendritic growth was induced by exposure to NGF and BMP-7 (bone morphogenetic protein-7). Exposure to NGF increased phosphorylation of ERK1/2. Unexpectedly, two MEK (MAP kinase kinase) inhibitors (PD 98059 and U 0126) enhanced dendritic growth, and a ligand, basic FGF, that activates the ERK pathway inhibited the growth of these processes. The enhancement of dendritic growth by PD 98059 was associated with an increase in the number of axo-dendritic synapses, and it appeared to represent a specific morphogenic effect because neither axonal growth nor cell survival was affected. In addition, increased dendritic growth was not observed after exposure to inhibitors of other signaling pathways, including the phosphatidylinositol-3-kinase inhibitor LY 294002. Dendritic growth was also increased in cells transfected with dominant-negative mutants of MEK1 and ERK2 but not with dominant-negative mutants of MEK5 and ERK5, suggesting that ERK1/2 is the primary mediator of this effect. Exposure to BMP-7 induces nuclear translocation of Smad1 (Sma- and Mad-related protein 1), and PD 98059 treatment potentiated nuclear accumulation of Smad-1 induced by BMP-7 in sympathetic neurons, suggesting a direct enhancement of BMP signaling in cells treated with an MEK inhibitor. These observations indicate that one of the signaling cascades activated by NGF can act in an antagonistic manner in sympathetic neurons and reduce the dendritic growth induced by other NGF-sensitive pathways.