KCNQ2 and KCNQ3 potassium channel subunits: molecular correlates of the M-channel

The M-current regulates the subthreshold electrical excitability of many neurons, determining their firing properties and responsiveness to synaptic input. To date, however, the genes that encode subunits of this important channel have not been identified. The biophysical properties, sensitivity to pharmacological blockade, and expression pattern of the KCNQ2 and KCNQ3 potassium channels were determined. It is concluded that both these subunits contribute to the native M-current.

The neurotrophins BDNF, NT-3, and NGF display distinct patterns of retrograde axonal transport in peripheral and central neurons

The pattern of retrograde axonal transport of the target-derived neurotrophic molecule, nerve growth factor (NGF), correlates with its trophic actions in adult neurons. We have determined that the NGF-related neurotrophins, brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3), are also retrogradely transported by distinct populations of peripheral and central nervous system neurons in the adult. All three 125I-labeled neurotrophins are retrogradely transported to sites previously shown to contain neurotrophin-responsive neurons as assessed in vitro, such as dorsal root ganglion and basal forebrain neurons. The patterns of transport also indicate the existence of neuronal populations that selectively transport NT-3 and/or BDNF, but not NGF, such as spinal cord motor neurons, neurons in the entorhinal cortex, thalamus, and neurons within the hippocampus itself. Our observations suggest that neurotrophins are transported by overlapping as well as distinct populations of neurons when injected into a given target field. Retrograde transport may thus be predictive of neuronal types selectively responsive to either BDNF or NT-3 in the adult, as first demonstrated for NGF.

Novel roles for neurotrophins are suggested by BDNF and NT-3 mRNA expression in developing neurons

The results of our in situ hybridization experiments demonstrate that sensory neurons, sympathetic neurons, and motoneurons express brain-derived neurotrophic factor and/or neurotrophin-3 mRNAs during development in mouse. In accordance with previous data, we also find neurotrophins in the targets of sensory neurons (skin) and motoneurons (muscle) and the neurotrophin receptors p75, trkA, and trkB in sensory and sympathetic ganglia. These results suggest that neurotrophins have roles other than being target-derived factors that support neuron survival during developmental cell death (neurotrophic hypothesis), but may be transported in an orthograde fashion in neurons and released from axon terminals. We discuss several novel roles for neurotrophins, including autocrine/paracrine regulation of neuron survival, regulation of Schwann cell activity, and neuron to target signaling.

An enzyme-linked immunoassay for nerve growth factor (NGF): a tool for studying regulatory mechanisms involved in NGF production in brain and in peripheral tissues

A sensitive enzyme-linked immunosorbent assay (ELISA) for nerve growth factor (NGF) has been developed. The sensitivity of this assay (0.1 pg/well) permits the quantification of endogenous immunoreactive NGF in the peripheral nervous system and the CNS. Studies on the regulatory mechanisms involved in NGF production indicate that, in addition to neurally mediated mechanisms, other stimuli, e.g., inflammation, significantly contribute to NGF production.

Relationship between levels of nerve growth factor (NGF) and its messenger RNA in sympathetic ganglia and peripheral target tissues

We have developed a sensitive assay for the quantification of nerve growth factor mRNA (mRNANGF) in various tissues of the mouse using in vitro transcribed RNANGF. Probes of both polarities were used to determine the specificity of the hybridization signals obtained. Comparison of NGF levels with its mRNA revealed that both were correlated with the density of sympathetic innervation. Thus, vas deferens contained high levels of both NGF and mRNANGF, whereas skeletal muscle levels were barely detectable, indicating that in peripheral tissues NGF levels are primarily regulated by the quantity of mRNANGF and not by the rate of processing of NGF precursor to NGF. However, although superior cervical ganglia contained the highest levels of NGF, its mRNA was barely detectable. Thus, the high levels of NGF in sympathetic ganglia result from retrograde axonal transport rather than local synthesis. The quantity of NGF found in the submandibular glands of female animals was three orders of magnitude higher than expected from their mRNA levels. This observation is discussed in the context of the difference between the mechanism of storage and exocytosis of exocrine glands versus the constitutive release from other tissues.

Common origin and developmental dependence on c-ret of subsets of enteric and sympathetic neuroblasts

c-ret encodes a tyrosine kinase receptor that is necessary for normal development of the mammalian enteric nervous system. Germline mutations in c-ret lead to congenital megacolon in humans, while a loss-of-function allele (ret.k-) causes intestinal aganglionosis in mice. Here we examine in detail the function of c-ret during neurogenesis, as well as the lineage relationships among cell populations in the enteric nervous system and the sympathetic nervous system that are dependent on c-ret function. We report that, while the intestine of newborn ret.k- mice is devoid of enteric ganglia, the esophagus and stomach are only partially affected; furthermore, the superior cervical ganglion is absent, while more posterior sympathetic ganglia and the adrenal medulla are unaffected. Analysis of mutant embryos shows that the superior cervical ganglion anlage is present at E10.5, but absent by E12.5, suggesting that c-ret is required for the survival or proliferation of sympathetic neuroblasts. In situ hybridization studies, as well as direct labelling of cells with DiI, indicate that a common pool of neural crest cells derived from the postotic hindbrain normally gives rise to most of the enteric nervous system and the superior cervical ganglion, and is uniquely dependent on c-ret function for normal development. We term this the sympathoenteric lineage. In contrast, a distinct sympathoadrenal lineage derived from trunk neural crest forms the more posterior sympathetic ganglia, and also contributes to the foregut enteric nervous system. Overall, our studies reveal previously unknown complexities of cell lineage and genetic control mechanisms in the developing mammalian peripheral nervous system.

Involvement of the ubiquitin-proteasome system in the early stages of wallerian degeneration

Local axon degeneration is a common pathological feature of many neurodegenerative diseases and peripheral neuropathies. While it is believed to operate with an apoptosis-independent molecular program, the underlying molecular mechanisms are largely unknown. In this study, we used the degeneration of transected axons, termed "Wallerian degeneration," as a model to examine the possible involvement of the ubiquitin proteasome system (UPS). Inhibiting UPS activity by both pharmacological and genetic means profoundly delays axon degeneration both in vitro and in vivo. In addition, we found that the fragmentation of microtubules is the earliest detectable change in axons undergoing Wallerian degeneration, which among other degenerative events, can be delayed by proteasome inhibitors. Interestingly, similar to transected axons, degeneration of axons from nerve growth factor (NGF)-deprived sympathetic neurons could also be suppressed by proteasome inhibitors. Our findings suggest a possibility that inhibiting UPS activity may serve to retard axon degeneration in pathological conditions.

Cellular localization of nerve growth factor synthesis by in situ hybridization

A very sensitive and specific method for in situ hybridization has been developed. This method detects low copy numbers of mRNA(NGF) transcripts in both tissue sections and cultured cells using 35S-labelled cRNA and oligonucleotide probes. In order to reduce the high nonspecific background occurring with 35S-labelled probes, prehybridization in the presence of non-labelled thio alpha UTP at pH 5.5 proved to be essential, together with a series of additional changes in the standard procedures for in situ hybridization. With this improved method it was possible to demonstrate that in tissues densely innervated by sensory (whisker pad) or both sympathetic and sensory (iris) fibers, NGF is synthesized not only by Schwann cells ensheathing these fibers, but also--and even to a much larger extent--by the target cells of the sensory and sympathetic neurons, i.e. epithelial cells, smooth muscle cells and fibroblasts. Moreover, in the sciatic nerve of newborn rats (where the mRNA(NGF) levels are 15 X higher than in adults) it was demonstrated that all Schwann cells have the capacity to express mRNA(NGF), not just those ensheathing the axons of NGF-responsive neurons.

The distribution of oxytocin- and neurophysin-stained fibers in the spinal cord of the rat and monkey

Immunohistochemical methods have been used to describe the distribution of neurophysin I- and oxytocin-stained fibers in the spinal cord. In albino rats of either sex, such fibers descend through the dorsal part of the lateral funiculus to the caudal end of the cord. Fibers leave the lateral funiculus to innervate the marginal zone of the dorsal horn at all levels, and the intermediolateral column at thoracic, lumbar and sacral levels. Some fibers course medially through the intermediate gray to end in the central gray, which is innervated at all levels, and also appears to be innervated by fibers descending in the central gray itself. A semiquantitative analysis shows that the density of terminal fields in the intermediolateral column, marginal zone, and central gray varies significantly at different levels. The intermediolateral column is preferentially innervated between T1-T3, T9-T11, and T13-L2. The nucleus intercalatusspinalis and the dorsal commissural nucleus (between T13 and L2), both of which contain preganglionic neurons, are densely innervated. In the monkey (Macaca fascicularis), neurophysin I- and oxytocin-stained fibers descend through the lateral funiculus to the filum terminale, where some of them enter the pia-arachnoid surrounding the filum. The intermediolateral column is not innervated between T1-T3, is sparsely innervated at sacral levels, and is moderately innervated between T4 and L3; the greatest density of fibers occurs at L3. At most levels, few if any fibers are found in the central gray and marginal zone; the central gray is sparsely innervated between T8 and L2 at S2, and between Co3-Co6, and the marginal zone contains a small number of fibers in the region of S2 and Co6. Neurophysin I- and oxytocin-stained fibers were also found in the intermediolateral column, marginal zone, and central gray of homozygous Brattleboro, spontaneously hypertensive, and Egyptian sand rats. The results suggest that the paraventriculo-spinal pathway is particularly related to specific groups of sympathetic and parasympathetic preganglionic neurons, and to the marginal zone, whick is involved in the relay of ascending nociceptive information through the spinothalamic tract.

Artemin is a vascular-derived neurotropic factor for developing sympathetic neurons

Artemin (ARTN) is a member of the GDNF family of ligands and signals through the Ret/GFRalpha3 receptor complex. Characterization of ARTN- and GFRalpha3-deficient mice revealed similar abnormalities in the migration and axonal projection pattern of the entire sympathetic nervous system. This resulted in abnormal innervation of target tissues and consequent cell death due to deficiencies of target-derived neurotrophic support. ARTN is expressed along blood vessels and in cells nearby to sympathetic axonal projections. In the developing vasculature, ARTN is expressed in smooth muscle cells of the vessels, and it acts as a guidance factor that encourages sympathetic fibers to follow blood vessels as they project toward their final target tissues. The chemoattractive properties of ARTN were confirmed by the demonstration that sympathetic neuroblasts migrate and project axons toward ARTN-soaked beads implanted into mouse embryos.

Products of endocytosis and autophagy are retrieved from axons by regulated retrograde organelle transport

Cellular homeostasis in neurons requires that the synthesis and anterograde axonal transport of protein and membrane be balanced by their degradation and retrograde transport. To address the nature and regulation of retrograde transport in cultured sympathetic neurons, I analyzed the behavior, composition, and ultrastructure of a class of large, phase-dense organelles whose movement has been shown to be influenced by axonal growth (Hollenbeck, P. J., and D. Bray. 1987. J. Cell Biol. 105:2827-2835). In actively elongating axons these organelles underwent both anterograde and retrograde movements, giving rise to inefficient net retrograde transport. This could be shifted to more efficient, higher volume retrograde transport by halting axonal outgrowth, or conversely shifted to less efficient retrograde transport with a larger anterograde component by increasing the intracellular cyclic AMP concentration. When neurons were loaded with Texas red-dextran by trituration, autophagy cleared the label from an even distribution throughout the neuronal cytosol to a punctate, presumably lysosomal, distribution in the cell body within 72 h. During this process, 100% of the phase-dense organelles were fluorescent, showing that they contained material sequestered from the cytosol and indicating that they conveyed this material to the cell body. When 29 examples of this class of organelle were identified by light microscopy and then relocated using correlative electron microscopy, they had a relatively constant ultrastructure consisting of a bilamellar or multilamellar boundary membrane and cytoplasmic contents, characteristic of autophagic vacuoles. When neurons took up Lucifer yellow, FITC-dextran, or Texas red-ovalbumin from the medium via endocytosis at the growth cone, 100% of the phase-dense organelles became fluorescent, demonstrating that they also contain products of endocytosis. Furthermore, pulse-chase experiments with fluorescent endocytic tracers confirmed that these organelles are formed in the most distal region of the axon and undergo net retrograde transport. Quantitative ratiometric imaging with endocytosed 8-hydroxypyrene-1,3,6-trisulfonic acid showed that the mean pH of their lumena was 7.05. These results indicate that the endocytic and autophagic pathways merge in the distal axon, resulting in a class of predegradative organelles that undergo regulated transport back to the cell body.

Nerve growth factor receptor and choline acetyltransferase colocalization in neurons within the rat forebrain: response to fimbria-fornix transection

Although it is well known that magnocellular cholinergic basal forebrain neurons are trophically responsive to nerve growth factor (NGF) and contain NGF receptors (NGFr), the exact distribution of forebrain NGFr-immunoreactive neurons and the degree to which cholinergic neurons are colocalized with them have remained in question. In this study we employed a very sensitive double-labelling method and examined in the same tissue section the distribution and cellular features of NGFr-positive and choline acetyltransferase (ChAT)-immunolabelled neurons within the rat basal forebrain. Throughout this region the majority of magnocellular basal forebrain neurons were immunoreactive for both NGFr and ChAT. However, a small percentage of neurons in the ventral portion of the vertical limb of the diagonal band of Broca were immunoreactive only for NGFr, whereas a larger population of magnocellular neurons in the substantia innominata exhibited only ChAT immunoreactivity. No NGFr-immunoreactive cells were found associated with ChAT-positive neurons in the striatum, neocortex, or hippocampus, and no single-labelled NGFr-immunoreactive neurons were found outside the basal forebrain area, except for a large number of positive-labelled cells along the ventricular walls of the third ventricle. In addition to its function in maintaining the normal integrity of the basal forebrain and cholinergic, peripheral sympathetic, and neural-crest-derived sensory neurons, NGF may also have a role in the growth of these neurons after damage to the nervous system. To examine this postulate the hippocampus was denervated of its septal input and examined 8 weeks later. Two populations of neurons were found to have undergone collateral sprouting--namely, the midline magnocellular cholinergic neurons of the dorsal hippocampus and the sympathetic noradrenergic neurons of the superior cervical ganglion. Both of these neuronal populations also stained strongly for NGFr. In contrast, the small intrinsic cholinergic neurons of the hippocampus exhibited neither sprouting response nor staining for NGFr. In view of these results, we suggest that the differing sprouting responses demonstrated by these three neuronal populations may be due to their responsiveness to NGF, as indicated by the presence or absence of NGF receptors.

Parkinson's disease: an immunohistochemical study of Lewy body-containing neurons in the enteric nervous system

We performed immunohistochemical analysis of specimens from three autopsied patients with Parkinson's disease, using antibodies to tyrosine hydroxylase (TH), vasoactive intestinal polypeptide (VIP), somatostatin, met-enkephalin, leu-enkephalin and substance P in an attempt to reveal the types of neurons that contain Lewy bodies (LBs) in the paravertebral and celiac sympathetic ganglia and in the enteric nervous system of the alimentary tract. In the sympathetic ganglia, almost all LB-containing neuronal cell bodies and processes were immunoreactive for TH. In the alimentary tract, however, most LBs were found in the VIP-immunoreactive (VIP-IR) neuronal cell bodies and processes. In spite of the significant presence of TH-IR neuronal cell bodies and processes in the alimentary tract, LB-containing TH-IR neuronal elements were rarely encountered. These findings indicate that in the alimentary tract, the VIP neuron system is mainly involved in the disease process of Parkinson's disease.

Endogenous levels of nerve growth factor (NGF) are altered in experimental diabetes mellitus: a possible role for NGF in the pathogenesis of diabetic neuropathy

Sympathetic and neural-crest derived sensory neurons consisting of unmyelinated and small myelinated fibers are known to be affected at an early stage in diabetes mellitus (DM). Since these peripheral neurons need nerve growth factor (NGF) for their development and maintenance of function in adulthood, changes in endogenous NGF levels could be of relevance for the pathogenesis of diabetic neuropathy (DNP). Using an improved two-site enzyme immunoassay for NGF, we have investigated whether endogenous NGF levels are altered in Sprague-Dawley rats with DM induced by a single injection of streptozotocin (STZ). STZ-treated rats are known to develop in many respects equivalents to neuropathic complications observed in human DM. We found in some sympathetically innervated target organs decreased NGF contents by maximally 56%: transiently in the iris 2 weeks and in the ventricle 12-24 weeks after DM induction and permanently in the submandibular gland already 3 days after DM induction. Several weeks after onset of DM, NGF content was increased by maximally 145-300% in most peripheral targets investigated, such as in iris, cardiac atrium and ventricle, spleen, prostate gland, and vas deferens. This is suggestive for an impaired NGF removal by NGF-sensitive neurons in diabetic rats. Moreover, NGF levels were decreased to minimally 42.6 +/- 4% of control in the NGF-transporting sciatic nerve. NGF levels began to decrease not before 3 weeks after DM induction and remained decreased with 54.0 +/- 5% of control even after 6 months duration of DM. About the same time (i.e., 2 weeks after induction of DM) NGF levels began to decrease in the superior cervical ganglion (where the sympathetic perikarya are located) to minimally 53.2 +/- 4% of control 12 weeks after DM induction. No altered NGF levels were observed during a 3-month duration of DM in the terminal ileum and sensory trigeminal ganglion. Since NGF exerts its neurotrophic action in the perikarya after its retrograde transport from the NGF-producing periphery, our results are consistent with the hypothesis that an alteration in NGF levels may play a role in the pathogenesis of DNP as far as sympathetic neurons are concerned. Thus, our results suggest that DM influences the production and/or transport of endogenous NGF and consequently, that a deprivation of this neurotrophic factor may account for some of the functional deficits known to occur in DNP, such as impaired catecholaminergic transmitter synthesis. This hypothesis possibly opens the way for new concepts in the therapy of DNP.

Control of noradrenergic differentiation and Phox2a expression by MASH1 in the central and peripheral nervous system

Mash1, a mammalian homologue of the Drosophila proneural genes of the achaete-scute complex, is transiently expressed throughout the developing peripheral autonomic nervous system and in subsets of cells in the neural tube. In the mouse, targeted mutation of Mash1 has revealed a role in the development of parts of the autonomic nervous system and of olfactory neurons, but no discernible phenotype in the brain has been reported. Here, we show that the adrenergic and noradrenergic centres of the brain are missing in Mash1 mutant embryos, whereas most other brainstem nuclei are preserved. Indeed, the present data together with the previous results show that, except in cranial sensory ganglia, Mash1 function is essential for the development of all central and peripheral neurons that express noradrenergic traits transiently or permanently. In particular, we show that, in the absence of MASH1, these neurons fail to initiate expression of the noradrenaline biosynthetic enzyme dopamine beta-hydroxylase. We had previously shown that all these neurons normally express the homeodomain transcription factor Phox2a, a positive regulator of the dopamine beta-hydroxylase gene and that a subset of them depend on it for their survival. We now report that expression of Phox2a is abolished or massively altered in the Mash1−/− mutants, both in the noradrenergic centres of the brain and in peripheral autonomic ganglia. These results suggest that MASH1 controls noradrenergic differentiation at least in part by controlling expression of Phox2a and point to fundamental homologies in the genetic circuits that determine the noradrenergic phenotype in the central and peripheral nervous system.

The NGF-inducible SCG10 mRNA encodes a novel membrane-bound protein present in growth cones and abundant in developing neurons

We have characterized and sequenced cDNA clones corresponding to the neural-specific SCG10 mRNA. The predicted amino acid sequence is novel and not strongly homologous to that of any known polypeptide. The protein is encoded by two mRNAs that differ in their choice of polyadenylation site. Immunocytochemical localization experiments using an affinity-purified antibody (against an SCG10-TrpE fusion protein) reveal accumulations of punctate staining in the perinuclear cytoplasm, axons, and growth cones of cultured neurons. SCG10 levels are maximal in the embryonic CNS but are dramatically reduced in the adult. Preliminary cell fractionation experiments suggest that the protein is tightly associated with membranes but is not itself an integral membrane protein. The apparent localization and timing of expression of the SCG10 protein are reminiscent of GAP-43, but the sequences of the two polypeptides are unrelated. Cross-hybridizing mRNAs and antigenically related proteins are found in several nonneuronal cell lines that do not express SCG10.

Antagonist discrimination between ganglionic and ileal muscarinic receptors

The effects of four antagonists on the depolarization of isolated superior cervical ganglia and the contraction of isolated ileal segments of the rat were compared. pA2 values estimated from Schild plots indicated significantly higher affinities of stercuronium (x100) and pirenzepine (x23) and a significantly lower affinity of 4-diphenylacetoxy-N-methylpiperidine methiodide (x0.39) for the ganglion than for the ileum. The affinities of N-methylscopolamine for the two tissues were not significantly different. It is concluded that the two types of muscarinic receptor are not identical.

Selective retrograde transsynaptic transfer of a protein, tetanus toxin, subsequent to its retrograde axonal transport

The fate of tetanus toxin (mol wt 150,000) subsequent to its retrograde axonal transport in peripheral sympathetic neurons of the rat was studied by both electron microscope autoradiography and cytochemistry using toxin-horseradish peroxidase (HRP) coupling products, and compared to that of nerve growth factor (NGF), cholera toxin, and the lectins wheat germ agglutinin (WGA), phytohaemagglutinin (PHA), and ricin. All these macromolecules are taken up by adrenergic nerve terminals and transported retrogradely in a selective, highly efficient manner. This selective uptake and transport is a consequence of the binding of these macromolecules to specific receptive sites on the nerve terminal membrane. All these ligands are transported in the axons within smooth vesicles, cisternae, and tubules. In the cell bodies these membrane compartments fuse and most of the transported macromolecules are finally incorporated into lysosomes. The cell nuclei, the parallel golgi cisternae, and the extracellular space always remain unlabeled. In case the tetanus toxin, however, a substantial fraction of the labeled material appears in presynaptic cholinergic nerve terminals which innervate the labeled ganglion cells. In these terminals tetanus toxin-HRP is localized in 500-1,000 A diam vesicles. In contrast, such a retrograde transsynaptic transfer is not at all or only very rarely detectable after retrograde transport of cholera toxin, NGF, WGA, PHA, or ricin. An atoxic fragment of the tetanus toxin, which contains the ganglioside-binding site, behaves like intact toxin. With all these macromolecules, the extracellular space and the glial cells in the ganglion remain unlabeled. We conclude that the selectivity of this transsynaptic transfer of tetanus toxin is due to a selective release of the toxin from the postsynaptic dendrites. This release is immediately followed by an uptake into the presynaptic terminals.

AKAP150 signaling complex promotes suppression of the M-current by muscarinic agonists

M-type (KCNQ2/3) potassium channels are suppressed by activation of G(q/11)-coupled receptors, thereby increasing neuronal excitability. We show here that rat KCNQ2 can bind directly to the multivalent A-kinase-anchoring protein AKAP150. Peptides that block AKAP150 binding to the KCNQ2 channel complex antagonize the muscarinic inhibition of the currents. A mutant form of AKAP150, AKAP(DeltaA), which is unable to bind protein kinase C (PKC), also attenuates the agonist-induced current suppression. Analysis of recombinant KCNQ2 channels suggests that targeting of PKC through association with AKAP150 is important for the inhibition. Phosphorylation of KCNQ2 channels was increased by muscarinic stimulation; this was prevented either by coexpression with AKAP(DeltaA) or pretreatment with PKC inhibitors that compete with diacylglycerol. These inhibitors also reduced muscarinic inhibition of M-current. Our data indicate that AKAP150-bound PKC participates in receptor-induced inhibition of the M-current.

Rapid accumulation of inositol phosphates in isolated rat superior cervical sympathetic ganglia exposed to V1-vasopressin and muscarinic cholinergic stimuli

An accumulation of 3H-labelled inositol phosphates is observed when prelabelled rat superior cervical sympathetic ganglia are exposed to [8-arginine]vasopressin or to muscarinic cholinergic stimuli. The response to vasopressin is much greater than the response to cholinergic stimuli. The response to vasopressin is blocked by a V1-vasopressin antagonist, and oxytocin is a much less potent agonist than vasopressin. Vasopressin causes no increase in the cyclic AMP content of ganglia. These ganglia therefore appear to have functional V1-vasopressin receptors that are capable of activating inositol lipid breakdown, but no V2-receptors coupled to adenylate cyclase. The first [3H]inositol-labelled products to accumulate in stimulated ganglia are inositol trisphosphate and inositol bisphosphate, suggesting that the initiating reaction in stimulated inositol lipid metabolism is a phosphodiesterase-catalysed hydrolysis of phosphatidylinositol 4,5-bisphosphate (and possibly also phosphatidylinositol 4-phosphate). This response to exogenous vasopressin occurs in ganglia incubated in media of reduced Ca2+ concentration. The physiological functions of the V1-vasopressin receptors of these ganglia remain unknown.

Degeneration of cardiac sympathetic nerve begins in the early disease process of Parkinson's disease

Decreased cardiac uptake of meta-iodobenzylguanidine (MIBG) on [(123)I] MIBG myocardial scintigraphy has been reported in the early stages of Parkinson's disease (PD), which suggests involvement of the cardiac sympathetic nerve in the early disease process of PD. For confirmation, we immunohistochemically examined cardiac tissue, sympathetic ganglia and medulla oblongata of 20 patients with incidental Lewy body disease (ILBD), which is thought to be a presymptomatic stage of PD, and 10 control subjects, using antibodies against tyrosine hydroxylase (TH) and neurofilament (NF). Immunoreactive nerve fibers of fascicles in the epicardium were well preserved in 10 of the 20 patients with ILBD and in the control subjects. In contrast, TH-immunoreactive nerve fibers had nearly disappeared in six subjects and were moderately decreased in four of the 20 patients with ILBD. Neuronal cell loss in the dorsal vagal nucleus and the sympathetic ganglia was not detectable in any of the ILBD patients examined. These findings suggest that degeneration of the cardiac sympathetic nerve begins in the early disease process of PD and that it occurs before neuronal cell loss in the dorsal vagal nucleus.

Neuronal and nonneuronal expression of neurotrophins and their receptors in sensory and sympathetic ganglia suggest new intercellular trophic interactions

Nerve growth factor promotes the survival of populations of sensory and sympathetic neurons. Although ganglia have been used for classical assays of neurotrophin action, knowledge is incomplete regarding the spatial arrangements through which neurotrophins are delivered to responsive cells within the ganglia and their attached nerve trunks. Whereas populations of ganglionic neurons may be capable of responding to a particular neurotrophin in vitro, the spectrum of receptor components and neurotrophins expressed by the various neuronal and nonneuronal cells comprising the ganglia in adult rats remains to be elucidated in vivo. Brain-derived neurotrophic factor (BDNF) mRNA was expressed by a population of small to medium sized neurons in all sensory ganglia except in the mesencephalic nucleus of the trigeminal nerve. Interestingly, BDNF immunoreactivity was detected in a more widespread population of neurons of these ganglia, as well as in scattered satellite cells of both sensory and sympathetic ganglia. These nonneuronal cells also expressed mRNA encoding a truncated form of the BDNF receptor, trkBtrunc, and full-length transcripts of trkB appeared to be confined to neuronal populations. Several other components of neurotrophin receptors (low-affinity neurotrophin receptor, trk, and trkC) were prominently expressed by different populations of neuronal cells in sympathetic and sensory ganglia, but they were not detected in nonneuronal cells. Neither nerve growth factor nor neurotrophin-3 mRNAs were detected in these ganglia. Unexpectedly, BDNF and trkBtrunc expression was detected in oligodendrocytes myelinating the central processes of sensory neurons. Schwann cells did not express detectable quantities of either entity, thereby establishing a dramatic boundary delineated by neurotrophin/neurotrophin receptor expression that coincided with the interface between the oligodendroglia of the central nervous system (CNS) and Schwann cells of the peripheral nervous system (PNS). Localization of BDNF expression to an additional population of nonneuronal cells--satellite cells within sensory and sympathetic ganglia--suggest a more extensive role for neurotrophic factors than originally encompassed by the target-derived neurotrophic-factor-concept paradigm. These data support the hypothesis of a possible autocrine or paracrine trophic interaction between populations of neuronal and nonneuronal cells in the peripheral nervous system. BDNF expression in oligodendrocytes but not in Schwann cells at the CNS/PNS junction may provide an additional means of maintaining cell-appropriate connections in the nervous system.

Localization of ATP-gated P2X receptor immunoreactivity in rat sensory and sympathetic ganglia

The distribution of P2X1, P2X2, P2X3, P2X4, P2X5 and P2X6 receptors, a family of ATP-gated cation channels, in rat trigeminal, dorsal root, nodose, superior cervical, and coeliac ganglia was studied immunohistochemically. It was found that polyclonal antibodies for the six P2X receptor subtypes could label over 90% of neurones in these ganglia to different intensities. There was also considerable variation in intensity of immunoreactivity in individual neurones within each ganglion. In dorsal root and trigeminal ganglia expression of the P2X3 receptor was much higher than for the other five subtypes. P2X3 immunoreactivity was much more intense in the small-diameter neurones than in the large-diameter neurones. In nodose ganglion, both P2X2 and P2X3 antibodies labelled the neurones intensely. In sympathetic superior cervical and coeliac ganglia, immunoreactivity to five P2X receptor subtypes were detected (exception, P2X5), with P2X2, P2X4 and P2X6 showing higher intensity. Low level expression of P2X3 receptor in sympathetic ganglia indicates that this receptor subtype is not limited to the sensory ganglia where it was highly expressed. The results have demonstrated that both sensory and sympathetic ganglia express a variety of P2X receptor subtypes and that different subtypes are expressed to different levels and by different subpopulations of neurones.