Regulation of neuropeptide expression in sympathetic neurons. Paracrine and retrograde influences

Ischemia-reperfusion myocardial infarction induces remodeling of left cardiac-projecting stellate ganglia neurons

Neurons in the stellate ganglion (SG) provide sympathetic innervation to the heart, brown adipose tissue (BAT), and other organs. Sympathetic innervation to the heart becomes hyperactive following myocardial infarction (MI). The impact of MI on the morphology of cardiac sympathetic neurons is not known, but we hypothesized that MI would stimulate increased cell and dendritic tree size in cardiac neurons. In this study, we examined the effects of ischemia-reperfusion MI on sympathetic neurons using dual retrograde tracing methods to allow detailed characterization of cardiac- and BAT-projecting neurons. Different fluorescently conjugated cholera toxin subunit B (CTb) tracers were injected into the pericardium and the interscapular BAT pads, respectively. Experimental animals received a 45-min occlusion of the left anterior descending coronary artery and controls received sham surgery. One week later, hearts were collected for assessment of MI infarct and SGs were collected for morphological or electrophysiological analysis. Cardiac-projecting SG neurons from MI mice had smaller cell bodies and shorter dendritic trees compared with sham animals, specifically on the left side ipsilateral to the MI. BAT-projecting neurons were not altered by MI, demonstrating the subpopulation specificity of the response. The normal size and distribution differences between BAT- and cardiac-projecting stellate ganglion neurons were not altered by MI. Patch-clamp recordings from cardiac-projecting left SG neurons revealed increased spontaneous excitatory postsynaptic currents despite the decrease in cell and dendritic tree size. Thus, increased dendritic tree size does not contribute to the enhanced sympathetic neural activity seen after MI.NEW & NOTEWORTHY Myocardial infarction (MI) causes structural and functional changes specifically in stellate ganglion neurons that project to the heart, but not in cells that project to brown adipose fat tissue.

Potential Crosstalk between the PACAP/VIP Neuropeptide System and Endoplasmic Reticulum Stress-Relevance to Multiple Sclerosis Pathophysiology

Multiple sclerosis (MS) is an immune-mediated disorder characterized by focal demyelination and chronic inflammation of the central nervous system (CNS). Although the exact etiology is unclear, mounting evidence indicates that endoplasmic reticulum (ER) stress represents a key event in disease pathogenesis. Pituitary adenylate cyclase-activating peptide (PACAP) and vasoactive intestinal peptide (VIP) are two structurally related neuropeptides that are abundant in the CNS and are known to exert neuroprotective and immune modulatory roles. Activation of this endogenous neuropeptide system may interfere with ER stress processes to promote glial cell survival and myelin self-repair. However, the potential crosstalk between the PACAP/VIP system and ER stress remains elusive. In this review, we aim to discuss how these peptides ameliorate ER stress in the CNS, with a focus on MS pathology. Our goal is to emphasize the importance of this potential interaction to aid in the identification of novel therapeutic targets for the treatment of MS and other demyelinating disorders.

Pancreatic sympathetic innervation disturbance in type 1 diabetes

Pancreatic sympathetic innervation can directly affect the function of islet. The disorder of sympathetic innervation in islets during the occurrence of type 1 diabetes (T1D) has been reported to be controversial with the inducing factor unclarified. Several studies have uncovered the critical role that sympathetic signals play in controlling the local immune system. The survival and operation of endocrine cells can be regulated by immune cell infiltration in islets. In the current review, we focused on the impact of sympathetic signals working on islets cell regulation, and discussed the potential factors that can induce the sympathetic innervation disorder in the islets. We also summarized the effect of interference with the islet sympathetic signals on the T1D occurrence. Overall, complete understanding of the regulatory effect of sympathetic signals on islet cells and local immune system could facilitate to design better strategies to control inflammation and protect β cells in T1D therapy.

Changes in the Neurochemical Coding of the Anterior Pelvic Ganglion Neurons Supplying the Male Pig Urinary Bladder Trigone after One-Sided Axotomy of Their Nerve Fibers

The present study investigated the effect of unilateral axotomy of urinary bladder trigone (UBT)-projecting nerve fibers from the right anterior pelvic ganglion (APG) on changes in the chemical coding of their neuronal bodies. The study was performed using male pigs with immunohistochemistry and quantitative real-time PCR (qPCR). The animals were divided into a control (C), a morphological (MG) or a molecular biology group (MBG). APG neurons supplying UBT were revealed using the retrograde tracing technique with Fast Blue (FB). Unilateral axotomy resulted in an over 50% decrease in the number of FB+ neurons in both APG ganglia. Immunohistochemistry revealed significant changes in the chemical coding of FB+ cells only in the right ganglion: decreased expression of dopamine-B-hydroxylase (DBH)/tyrosine hydroxylase (TH) and up-regulation of the vesicular acetylcholine transporter (VAChT)/choline acetyltransferase (ChAT), galanin (GAL), vasoactive intestinal polypeptide (VIP) and brain nitric oxide synthase (bNOS). The qPCR results partly corresponded with immunofluorescence findings. In the APGs, genes for VAChT and ChAT, TH and DBH, VIP, and NOS were distinctly down-regulated, while the expression of GAL was up-regulated. Such data may be the basis for further studies concerning the plasticity of these ganglia under experimental or pathological conditions.

Effect of partial hysterectomy on the neurons of the paracervical ganglion (PCG) of the pig

Autonomic neurons innervating uterine horn is probably the only nerve cell population capable of periodical physiological degeneration and regeneration. One of the main sources of innervation of the uterus is paracervical ganglion (PCG). PCG is a unique structure of the autonomic nervous system. It contains components of both the sympathetic and parasympathetic nervous system. The present study examines the response of neurons of PCG innervating uterine horn to axotomy caused by partial hysterectomy in the domestic pig animal model. The study was performed using a neuronal retrograde tracing and double immunofluorescent staining for tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DβH), choline acetyltransferase (ChAT), vesicular acetylcholine transporter (VAChT), neuronal nictric oxide synthase (nNOS), galanin, neuropeptide Y (NPY), vasoactive intestinal peptide (VIP), pituitary adenylate cyclase-activating peptide (PACAP), somatostatin and substance P (SP). Our study showed that virtually all neurons of the porcine PCG innervating uterine horn are adrenergic and we did not confirm that PCG is the source of cholinergic fibers innervating uterine horn of the pig. After axotomy there was a decrease in expression of catecholamine-synthesizing enzymes (TH, DβH) and a strong increase in the galanin expression. The increase of the number of NPY-IR neurons in the ganglia after axotomy was observed. There were no changes in the expression of other studied substances in the PCG neurons innervating the uterine horn, what was often found in rodents studies. This indicates that neurons can respond to damage in a species-specific way.

Atf3 mutant mice show reduced axon regeneration and impaired regeneration-associated gene induction after peripheral nerve injury

Axon injury in the peripheral nervous system (PNS) induces a regeneration-associated gene (RAG) response. Atf3 (activating transcription factor 3) is such a RAG and ATF3's transcriptional activity might induce ‘effector’ RAGs (e.g. small proline rich protein 1a (Sprr1a), Galanin (Gal), growth-associated protein 43 (Gap43)) facilitating peripheral axon regeneration. We provide a first analysis of Atf3 mouse mutants in peripheral nerve regeneration. In Atf3 mutant mice, facial nerve regeneration and neurite outgrowth of adult ATF3-deficient primary dorsal root ganglia neurons was decreased. Using genome-wide transcriptomics, we identified a neuropeptide-encoding RAG cluster (vasoactive intestinal peptide (Vip), Ngf, Grp, Gal, Pacap) regulated by ATF3. Exogenous administration of neuropeptides enhanced neurite growth of Atf3 mutant mice suggesting that these molecules might be effector RAGs of ATF3's pro-regenerative function. In addition to the induction of growth-promoting molecules, we present data that ATF3 suppresses growth-inhibiting molecules such as chemokine (C-C motif) ligand 2. In summary, we show a pro-regenerative ATF3 function during PNS nerve regeneration involving transcriptional activation of a neuropeptide-encoding RAG cluster. ATF3 is a general injury-inducible factor, therefore ATF3-mediated mechanisms identified herein might apply to other cell and injury types.

Changes in Somatostatin-Like Immunoreactivity in the Sympathetic Neurons Projecting to the Prepyloric Area of the Porcine Stomach Induced by Selected Pathological Conditions

The aim of the present study was to define changes in the expression of somatostatin (SOM) in the sympathetic perikarya innervating the porcine stomach prepyloric area during acetylsalicylic-acid-induced gastritis (ASA) and experimentally induced hyperacidity (HCL) and following partial stomach resection (RES). On day 1, the stomachs were injected with neuronal retrograde tracer Fast Blue (FB). Animals in the ASA group were given acetylsalicylic acid orally for 21 days. On the 22nd day after FB injection, partial stomach resection was performed in RES animals. On day 23, HCL animals were intragastrically given 5 ml/kg of body weight of a 0.25 M aqueous solution of hydrochloric acid. On day 28, all pigs were euthanized. Then, 14-μm thick cryostat sections of the coeliac-superior mesenteric ganglion (CSMG) complexes were processed for routine double-labelling immunofluorescence. All pathological conditions studied resulted in upregulation of SOM-like (SOM-LI) immunoreactivity (from 14.97 ± 1.57% in control group to 33.72 ± 4.39% in the ASA group, to 39.02 ± 3.65% in the RES group, and to 29.63 ± 0.85% in the HCL group). The present studies showed that altered expression of SOM occurs in sympathetic neurons supplying the prepyloric area of the porcine stomach during adaptation to various pathological insults.

NGF and Its Receptors in the Regulation of Inflammatory Response

There is growing interest in the complex relationship between the nervous and immune systems and how its alteration can affect homeostasis and result in the development of inflammatory diseases. A key mediator in cross-talk between the two systems is nerve growth factor (NGF), which can influence both neuronal cell function and immune cell activity. The up-regulation of NGF described in inflamed tissues of many diseases can regulate innervation and neuronal activity of peripheral neurons, inducing the release of immune-active neuropeptides and neurotransmitters, but can also directly influence innate and adaptive immune responses. Expression of the NGF receptors tropomyosin receptor kinase A (TrkA) and p75 neurotrophin receptor (p75NTR) is dynamically regulated in immune cells, suggesting a varying requirement for NGF depending on their state of differentiation and functional activity. NGF has a variety of effects that can be either pro-inflammatory or anti-inflammatory. This apparent contradiction can be explained by considering NGF as part of an endogenous mechanism that, while activating immune responses, also activates pathways necessary to dampen the inflammatory response and limit tissue damage. Decreases in TrkA expression, such as that recently demonstrated in immune cells of arthritis patients, might prevent the activation by NGF of regulatory feed-back mechanisms, thus contributing to the development and maintenance of chronic inflammation.

Myocardial Infarction Causes Transient Cholinergic Transdifferentiation of Cardiac Sympathetic Nerves via gp130

Sympathetic and parasympathetic control of the heart is a classic example of norepinephrine (NE) and acetylcholine (ACh) triggering opposing actions. Sympathetic NE increases heart rate and contractility through activation of β receptors, whereas parasympathetic ACh slows the heart through muscarinic receptors. Sympathetic neurons can undergo a developmental transition from production of NE to ACh and we provide evidence that mouse cardiac sympathetic nerves transiently produce ACh after myocardial infarction (MI). ACh levels increased in viable heart tissue 10-14 d after MI, returning to control levels at 21 d, whereas NE levels were stable. At the same time, the genes required for ACh synthesis increased in stellate ganglia, which contain most of the sympathetic neurons projecting to the heart. Immunohistochemistry 14 d after MI revealed choline acetyltransferase (ChAT) in stellate sympathetic neurons and vesicular ACh transporter immunoreactivity in tyrosine hydroxylase-positive cardiac sympathetic fibers. Finally, selective deletion of the ChAT gene from adult sympathetic neurons prevented the infarction-induced increase in cardiac ACh. Deletion of the gp130 cytokine receptor from sympathetic neurons prevented the induction of cholinergic genes after MI, suggesting that inflammatory cytokines induce the transient acquisition of a cholinergic phenotype in cardiac sympathetic neurons. Ex vivo experiments examining the effect of NE and ACh on rabbit cardiac action potential duration revealed that ACh blunted both the NE-stimulated decrease in cardiac action potential duration and increase in myocyte calcium transients. This raises the possibility that sympathetic co-release of ACh and NE may impair adaptation to high heart rates and increase arrhythmia susceptibility.

SIGNIFICANCE STATEMENT

Sympathetic neurons normally make norepinephrine (NE), which increases heart rate and the contractility of cardiac myocytes. We found that, after myocardial infarction, the sympathetic neurons innervating the heart begin to make acetylcholine (ACh), which slows heart rate and decreases contractility. Several lines of evidence confirmed that the source of ACh was sympathetic nerves rather than parasympathetic nerves that are the normal source of ACh in the heart. Global application of NE with or without ACh to ex vivo hearts showed that ACh partially reversed the NE-stimulated decrease in cardiac action potential duration and increase in myocyte calcium transients. That suggests that sympathetic co-release of ACh and NE may impair adaptation to high heart rates and increase arrhythmia susceptibility.

Alterations of neurochemical expression of the coeliac-superior mesenteric ganglion complex (CSMG) neurons supplying the prepyloric region of the porcine stomach following partial stomach resection

The purpose of the present study was to determine the response of the porcine coeliac-superior mesenteric ganglion complex (CSMG) neurons projecting to the prepyloric area of the porcine stomach to peripheral neuronal damage following partial stomach resection. To identify the sympathetic neurons innervating the studied area of stomach, the neuronal retrograde tracer Fast Blue (FB) was applied to control and partial stomach resection (RES) groups. On the 22nd day after FB injection, following laparotomy, the partial resection of the previously FB-injected stomach prepyloric area was performed in animals of RES group. On the 28th day, all animals were re-anaesthetized and euthanized. The CSMG complex was then collected and processed for double-labeling immunofluorescence. In control animals, retrograde-labelled perikarya were immunoreactive to tyrosine hydroxylase (TH), dopamine β-hydroxylase (DβH), neuropeptide Y (NPY) and galanin (GAL). Partial stomach resection decreased the numbers of FB-positive neurons immunopositive for TH and DβH. However, the strong increase of NPY and GAL expression, as well as de novo-synthesis of neuronal nitric oxide synthase (nNOS) and leu5-Enkephalin (LENK) was noted in studied neurons. Furthermore, FB-positive neurons in all pigs were surrounded by a network of cocaine- and amphetamine-regulated transcript peptide (CART)-, calcitonin gene-related peptide (CGRP)-, and substance P (SP)-, vasoactive intestinal peptide (VIP)-, LENK- and nNOS- immunoreactive nerve fibers. This may suggest neuroprotective contribution of these neurotransmitters in traumatic responses of sympathetic neurons to peripheral axonal damage.

Neuropeptide Y in the adult and fetal human pineal gland

Neuropeptide Y was isolated from the porcine brain in 1982 and shown to be colocalized with noradrenaline in sympathetic nerve terminals. The peptide has been demonstrated to be present in sympathetic nerve fibers innervating the pineal gland in many mammalian species. In this investigation, we show by use of immunohistochemistry that neuropeptide Y is present in nerve fibers of the adult human pineal gland. The fibers are classical neuropeptidergic fibers endowed with large boutons en passage and primarily located in a perifollicular position with some fibers entering the pineal parenchyma inside the follicle. The distance from the immunoreactive terminals to the pinealocytes indicates a modulatory function of neuropeptide Y for pineal physiology. Some of the immunoreactive fibers might originate from neurons located in the brain and be a part of the central innervation of the pineal gland. In a series of human fetuses, neuropeptide Y-containing nerve fibers was present and could be detected as early as in the pineal of four- to five-month-old fetuses. This early innervation of the human pineal is different from most rodents, where the innervation starts postnatally.

VGLUTs in Peripheral Neurons and the Spinal Cord: Time for a Review

Vesicular glutamate transporters (VGLUTs) are key molecules for the incorporation of glutamate in synaptic vesicles across the nervous system, and since their discovery in the early 1990s, research on these transporters has been intense and productive. This review will focus on several aspects of VGLUTs research on neurons in the periphery and the spinal cord. Firstly, it will begin with a historical account on the evolution of the morphological analysis of glutamatergic systems and the pivotal role played by the discovery of VGLUTs. Secondly, and in order to provide an appropriate framework, there will be a synthetic description of the neuroanatomy and neurochemistry of peripheral neurons and the spinal cord. This will be followed by a succinct description of the current knowledge on the expression of VGLUTs in peripheral sensory and autonomic neurons and neurons in the spinal cord. Finally, this review will address the modulation of VGLUTs expression after nerve and tissue insult, their physiological relevance in relation to sensation, pain, and neuroprotection, and their potential pharmacological usefulness.

Axotomy-induced changes in the chemical coding pattern of colon projecting calbindin-positive neurons in the inferior mesenteric ganglia of the pig

The present study examines the response of colon-projecting neurons localized in the inferior mesenteric ganglia (IMG) to axotomy in the pig animal model. In all animals (n = 8), a median laparotomy was performed under anesthesia and the retrograde tracer Fast Blue was injected into the descending colon wall. In experimental animals (n = 4), the descending colon was exposed and the bilateral caudal colonic nerves were identified and severed. All animals were euthanized and the inferior mesenteric ganglia were harvested and processed for double-labeling immunofluorescence for calbindin-D28k (CB) in combination with either tyrosine hydroxylase (TH), neuropeptide Y (NPY), somatostatin (SOM), vasoactive intestinal polypeptide (VIP), nitric oxide synthase (NOS), Leu-enkephalin (LENK), substance P, vesicular acetylcholine transporter, or galanin. Immunohistochemistry revealed significant changes in the chemical coding pattern of injured inferior mesenteric ganglion neurons. In control animals, Fast Blue-positive neurons were immunoreactive to TH, NPY, SOM, VIP, NOS, LENK, and CB. In the experimental group, the numbers of TH-, NPY-, and SOM-expressing neurons were reduced, whereas the number of neurons immunoreactive to LENK was increased. Our data indicate that the colon-projecting neurons of the porcine IMG react to the axotomy in a similar, but not an identical manner in a comparison to other species, especially rodents. Further studies are needed to elucidate the detailed factors/mechanisms involved in the response to nerve injury.

Downstream effector molecules in successful peripheral nerve regeneration

The robust axon regeneration that occurs following peripheral nerve injury is driven by transcriptional activation of the regeneration program and by the expression of a wide range of downstream effector molecules from neuropeptides and neurotrophic factors to adhesion molecules and cytoskeletal adaptor proteins. These regeneration-associated effector molecules regulate the actin-tubulin machinery of growth-cones, integrate intracellular signalling and stimulatory and inhibitory signals from the local environment and translate them into axon elongation. In addition to the neuronally derived molecules, an important transcriptional component is found in locally activated Schwann cells and macrophages, which release a number of cytokines, growth factors and neurotrophins that support neuronal survival and axonal regeneration and that might provide directional guidance cues towards appropriate peripheral targets. This review aims to provide a comprehensive up-to-date account of the transcriptional regulation and functional role of these effector molecules and of the information that they can give us with regard to the organisation of the regeneration program.

Some lumbar sympathetic neurons develop a glutamatergic phenotype after peripheral axotomy with a note on VGLUT₂-positive perineuronal baskets

Glutamate is the main excitatory neurotransmitter in the nervous system, including in primary afferent neurons. However, to date a glutamatergic phenotype of autonomic neurons has not been described. Therefore, we explored the expression of vesicular glutamate transporter (VGLUT) types 1, 2 and 3 in lumbar sympathetic chain (LSC) and major pelvic ganglion (MPG) of naïve BALB/C mice, as well as after pelvic nerve axotomy (PNA), using immunohistochemistry and in situ hybridization. Colocalization with activating transcription factor-3 (ATF-3), tyrosine hydroxylase (TH), vesicular acetylcholine transporter (VAChT) and calcitonin gene-related peptide was also examined. Sham-PNA, sciatic nerve axotomy (SNA) or naïve mice were included. In naïve mice, VGLUT(2)-like immunoreactivity (LI) was only detected in fibers and varicosities in LSC and MPG; no ATF-3-immunoreactive (IR) neurons were visible. In contrast, PNA induced upregulation of VGLUT(2) protein and transcript, as well as of ATF-3-LI in subpopulations of LSC neurons. Interestingly, VGLUT(2)-IR LSC neurons coexpressed ATF-3, and often lacked the noradrenergic marker TH. SNA only increased VGLUT(2) protein and transcript in scattered LSC neurons. Neither PNA nor SNA upregulated VGLUT(2) in MPG neurons. We also found perineuronal baskets immunoreactive either for VGLUT(2) or the acetylcholinergic marker VAChT in non-PNA MPGs, usually around TH-IR neurons. VGLUT(1)-LI was restricted to some varicosities in MPGs, was absent in LSCs, and remained largely unaffected by PNA or SNA. This was confirmed by the lack of expression of VGLUT(1) or VGLUT(3) mRNAs in LSCs, even after PNA or SNA. Taken together, axotomy of visceral and non-visceral nerves results in a glutamatergic phenotype of some LSC neurons. In addition, we show previously non-described MPG perineuronal glutamatergic baskets.

Enteric neural crest differentiation in ganglioneuromas implicates Hedgehog signaling in peripheral neuroblastic tumor pathogenesis

Peripheral neuroblastic tumors (PNTs) share a common origin in the sympathetic nervous system, but manifest variable differentiation and growth potential. Malignant neuroblastoma (NB) and benign ganglioneuroma (GN) stand at opposite ends of the clinical spectrum. We hypothesize that a common PNT progenitor is driven to variable differentiation by specific developmental signaling pathways. To elucidate developmental pathways that direct PNTs along the differentiation spectrum, we compared the expression of genes related to neural crest development in GN and NB. In GNs, we found relatively low expression of sympathetic markers including adrenergic biosynthesis enzymes, indicating divergence from sympathetic fate. In contrast, GNs expressed relatively high levels of enteric neuropeptides and key constituents of the Hedgehog (HH) signaling pathway, including Dhh, Gli1 and Gli3. Predicted HH targets were also differentially expressed in GN, consistent with transcriptional response to HH signaling. These findings indicate that HH signaling is specifically active in GN. Together with the known role of HH activity in enteric neural development, these findings further suggested a role for HH activity in directing PNTs away from the sympathetic lineage toward a benign GN phenotype resembling enteric ganglia. We tested the potential for HH signaling to advance differentiation in PNTs by transducing NB cell lines with Gli1 and determining phenotypic and transcriptional response. Gli1 inhibited proliferation of NB cells, and induced a pattern of gene expression that resembled the differential pattern of gene expression of GN, compared to NB (p<0.00001). Moreover, the transcriptional response of SY5Y cells to Gli1 transduction closely resembled the transcriptional response to the differentiation agent retinoic acid (p<0.00001). Notably, Gli1 did not induce N-MYC expression in neuroblastoma cells, but strongly induced RET, a known mediator of RA effect. The decrease in NB cell proliferation induced by Gli1, and the similarity in the patterns of gene expression induced by Gli1 and by RA, corroborated by closely matched gene sets in GN tumors, all support a model in which HH signaling suppresses PNT growth by promoting differentiation along alternative neural crest pathways.

Substance P is involved in the cutaneous blood flow increase response to sympathetic nerve stimulation in persistently inflamed rats

Changed vascular functions have been reported in several pathological conditions, such as chronic regional pain syndrome, obstructive vascular disease, and inflammation. Our previous experiments also showed that electrical stimulation of the lumbar sympathetic trunk (sympathetic stimulation: SS), which normally induces a decrease in blood flow (BF), caused a BF increase in about half of the measured sites in rats persistently inflamed with complete Freund's Adjuvant (AI rats). We also showed that the BF-increase response was only partially suppressed by the alpha1 antagonist at a higher dosage, suggesting the involvement of nonadrenergic mechanisms. We hypothesize that nonadrenergic mechanisms mediating vasodilatation might involve a vasodilating neuropeptide such as substance P (SP) that is released from sympathetic nerve terminals. In this experiment, we conducted an examination using an NK-1 receptor antagonist to determine whether SP plays any role in changed response to SS in AI rats, and also an immunohistochemical examination of whether SP is expressed in the lumbar sympathetic nerve ganglia (SG) of AI rats. The administration of an NK-1 receptor antagonist, CP-96,345, significantly reduced the BF-increase response to SS in AI rats, but its inactive enantiomer, CP-96,344, had no effect. Immunohistochemistry for SP revealed that SP-ir positive SG neurons (mean 13 neurons/rat) were found in 5 of 8 AI rats, whereas only one neuron was stained in 8 control rats. These results suggest that NK-1 receptor activation is involved in the BF-increase response to SS, and that this activation is in part mediated by SP from lumbar SG that was synthesized de novo in inflamed animals.

Neural plasticity after peripheral nerve injury and regeneration

Injuries to the peripheral nerves result in partial or total loss of motor, sensory and autonomic functions conveyed by the lesioned nerves to the denervated segments of the body, due to the interruption of axons continuity, degeneration of nerve fibers distal to the lesion and eventual death of axotomized neurons. Injuries to the peripheral nervous system may thus result in considerable disability. After axotomy, neuronal phenotype switches from a transmitter to a regenerative state, inducing the down- and up-regulation of numerous cellular components as well as the synthesis de novo of some molecules normally not expressed in adult neurons. These changes in gene expression activate and regulate the pathways responsible for neuronal survival and axonal regeneration. Functional deficits caused by nerve injuries can be compensated by three neural mechanisms: the reinnervation of denervated targets by regeneration of injured axons, the reinnervation by collateral branching of undamaged axons, and the remodeling of nervous system circuitry related to the lost functions. Plasticity of central connections may compensate functionally for the lack of specificity in target reinnervation; plasticity in human has, however, limited effects on disturbed sensory localization or fine motor control after injuries, and may even result in maladaptive changes, such as neuropathic pain, hyperreflexia and dystonia. Recent research has uncovered that peripheral nerve injuries induce a concurrent cascade of events, at the systemic, cellular and molecular levels, initiated by the nerve injury and progressing throughout plastic changes at the spinal cord, brainstem relay nuclei, thalamus and brain cortex. Mechanisms for these changes are ubiquitous in central substrates and include neurochemical changes, functional alterations of excitatory and inhibitory connections, atrophy and degeneration of normal substrates, sprouting of new connections, and reorganization of somatosensory and motor maps. An important direction for ongoing research is the development of therapeutic strategies that enhance axonal regeneration, promote selective target reinnervation, but are also able to modulate central nervous system reorganization, amplifying those positive adaptive changes that help to improve functional recovery but also diminishing undesirable consequences.

The neuropoietic cytokine family in development, plasticity, disease and injury

Neuropoietic cytokines are well known for their role in the control of neuronal, glial and immune responses to injury or disease. Since this discovery, it has emerged that several of these proteins are also involved in nervous system development, in particular in the regulation of neurogenesis and stem cell fate. Recent data indicate that these proteins have yet more functions, as key modulators of synaptic plasticity and of various behaviours. In addition, neuropoietic cytokines might be a factor in the aetiology of psychiatric disorders.

Participation of vasoactive intestinal polypeptide in ovarian steroids production during the rat estrous cycle and in the development of estradiol valerate-induced polycystic ovary

Vasoactive intestinal polypeptide (VIP) stimulates estradiol and progesterone release from ovarian granulosa cellsin vitro. Very little information is available as to the role VIP plays in the control of steroid secretion during reproductive cyclicity and in ovarian pathologies involving altered steroid secretion. In this study, we determined the involvement of VIP in regulating ovarian androgen and estradiol release during estrous cyclicity and estradiol valerate (EV)-induced polycystic ovarian development in rats. Our findings show that androgen and estradiol release from ovaries obtained during different stages of rat estrous cycle mimic cyclic changes in steroid release observedin vivowith maximal release occurring during late proestrus. VIP increased androgen release from ovaries of all cycle stages except late proestrus and estradiol release from all cycle stages. Increases in VIP-induced androgen and estradiol release were maximal at early proestrus. Inclusion of saturating concentrations of androstenedione increased magnitude of VIP-induced estradiol release at diestrus and estrus but not proestrus. Magnitude of VIP-induced androgen and estradiol release tended to be greater in the ovaries from EV-treated rats with polycystic ovary compared with estrous controls. At the tissue level, ovarian VIP concentration was cycle stage dependent with highest level seen in diestrus. Maximum concentration of VIP was found in EV-treated rats. Changes in VIP were inversely related to changes in ovarian nerve growth factor, a neuropeptide involved in ovarian androgen secretion. These results strongly suggest that intraovarian VIP participates in the control of estradiol secretion during the rat estrous cycle and possibly in the maintenance of increased ovarian estradiol secretory activity of EV-treated rats.

Bone morphogenetic protein down-regulation of neuronal pituitary adenylate cyclase-activating polypeptide and reciprocal effects on vasoactive intestinal peptide expression

Among bone morphogenetic proteins (BMPs), the decapentaplegic (Dpp; BMP2, BMP4) and glass bottom boat (Gbb/60A; BMP5, BMP6, BMP7) subgroups have well-described functions guiding autonomic and sensory neuronal development, fiber formation and neurophenotypic identities. Evaluation of rat superior cervical ganglia (SCG) post-ganglionic sympathetic neuron developmental regulators identified that selected BMPs of the transforming growth factor beta superfamily have reciprocal effects on neuronal pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) expression. Dpp and Gbb/60A BMPs rapidly down-regulated PACAP expression, while up-regulating other sympathetic neuropeptides, including PACAP-related VIP. The suppressive effects of BMP on PACAP mRNA and peptide expression were potent, efficacious and phosphorylated mothers against decapentaplegic homolog (Smad) signaling-dependent. Axotomy of SCG dramatically increases PACAP expression, and the possibility that abrogation of inhibitory retrograde target tissue BMP signaling may contribute to this up-regulation of sympathetic neuron PACAP was investigated. Replacement of BMP6 to SCG explant preparations significantly blunted the injury-induced elevated PACAP expression, with a concomitant decrease in sympathetic PACAP-immunoreactive neuron numbers. These studies suggested that BMPs modulate neuropeptide identity and diversity by stimulating or restricting the expression of specific peptidergic systems. Furthermore, the liberation of SCG neurons from target-derived BMP inhibition following axotomy may be one participating mechanism associated with injury-induced neuropeptidergic plasticity.

A neuroinductive biomaterial based on dopamine

Chemical messengers such as neurotransmitters play an important role in cell communication, differentiation, and survival. We have designed and synthesized a bioactive biomaterial that derived its biological activity from dopamine. The resultant biodegradable polymer, PCD, has pendent groups bearing dopamine functionalities. Image analysis demonstrated that nerve growth factor-primed rat pheochromocytoma cells (PC12) and explanted rat dorsal root ganglions attached well and displayed substantial neurite outgrowth on the polymer surface. Furthermore, PCD promoted more vigorous neurite outgrowth in PC12 cells than tissue culture polystyrene, laminin, and poly(d-lysine). The histogram of neurite length of PC12 cells showed distinctive patterns on PCD that were absent on the controls. A subset of PC12 cells displayed high filopodium density on PCD. The addition of dopamine in culture medium had little effect on the differentiation of PC12 cells on tissue culture polystyrene. Tyrosine, the precursor of dopamine, did not exhibit this ability to impart specific bioactivity to an analogous polymer. Thus, the dopamine functional group is likely the origin of the inductive effect. PCD did not cause nerve degeneration or fibrous encapsulation when implanted immediately adjacent to the rat sciatic nerves. This work is a step toward creating a diverse family of bioactive materials using small chemical messengers as monomers.

Switching mature retinal ganglion cells to a robust growth state in vivo: gene expression and synergy with RhoA inactivation

The inability of mature CNS neurons to regenerate injured axons has been attributed to a loss of inherent growth potential of cells and to inhibitory signals associated with myelin and the glial scar. The present study investigated two complementary issues: (1) whether mature CNS neurons can be stimulated to alter their gene expression profile and switch into a strong growth state; and (2) whether inactivating RhoA, a convergence point for multiple inhibitory signals, is sufficient to produce strong regeneration even without activating the growth state of neurons. In the mature rat, retinal ganglion cells (RGCs) normally fail to regenerate axons through the injured optic nerve but can be stimulated to do so by activating macrophages in the eye (e.g., by lens injury). To investigate underlying changes in gene expression, we retrogradely labeled RGCs with a fluorescent dye, performed optic nerve surgery with or without lens injury, and 4 d later, dissociated retinas, isolated RGCs by fluorescence-activated cell sorting, and examined their profiles of gene expression using microarrays. To investigate the effects of inactivating RhoA, we transfected RGCs with adeno-associated viruses carrying a gene for C3 ribosyltransferase. Our results show that, with appropriate stimulation, mature CNS neurons can undergo dramatic changes in gene expression comparable with those seen in regenerating neurons of the PNS, and that RhoA inactivation by itself results in moderate regeneration, and strongly potentiates axon regeneration through the mature optic nerve when the growth state of neurons is activated.

Myocardial infarction stimulates galanin expression in cardiac sympathetic neurons

Cardiac ischemia-reperfusion alters sympathetic neurotransmission in the heart, but little is known about its effect on neuropeptide expression in sympathetic neurons. Ischemia followed by reperfusion induces the production of inflammatory cytokines in the heart, including interleukin-6 and cardiotrophin-1. These cytokines and related molecules inhibit the expression of neuropeptide Y (NPY), and stimulate the expression of vasoactive intestinal peptide (VIP), substance P (SubP), and galanin (GAL) in cultured sympathetic neurons. Therefore, we quantified NPY, VIP, SubP, and GAL mRNA in neurons of the stellate ganglia 1 week after ischemia-reperfusion to determine if neuropeptide expression was altered in cardiac sympathetic neurons. NPY, VIP, and SubP mRNAs were unchanged compared to unoperated control animals, but GAL mRNA was increased significantly. The increased GAL mRNA was not accompanied by elevated GAL peptide content in the stellate ganglia. Galanin content was increased significantly in the heart, however, indicating that elevated GAL mRNA led to increased peptide production. GAL content was increased in the left ventricle below the coronary artery ligation, but was not increased significantly in the atria or the base of the heart above the ligation. The buildup of GAL specifically in the damaged left ventricle is consistent with previous reports that GAL is transported to regenerating nerve endings after axon damage.

Increased expression of nitric oxide synthase in cultured neurons from adult rat colonic submucous ganglia

Neuronal plasticity in the enteric nervous system (ENS) is probably a key step in intestinal adaptation during growth, maturation and ageing as well as in several pathophysiological situations. Studies on cultured myenteric neurons have revealed an increased vasoactive intestinal peptide (VIP) expression in neuronal nitric oxide synthase (NOS)-expressing neurons. In addition, both VIP and nitric oxide (NO) promote survival of cultured myenteric neurons. The aim of the present study was to investigate possible changes in the expression of VIP and NOS in cultured submucous neurons from adult rat large intestine. Submucous neurons were cultured as explants or as dissociated neurons for 3 and 8 days. Immunocytochemistry was used to determine the proportions of neurons containing VIP or NOS in preparations of uncultured controls (reflects the conditions in vivo) and in cultured explants of submucosa and dissociated submucous neurons. In situ hybridization was used to determine changes in the expressions of NOS and VIP mRNA. The relative number of NOS-expressing neurons increased significantly during culturing. The percentage of all neurons expressing NOS was 22% in controls, while approximately 50% of the cultured submucous neurons expressed NOS. VIP-expressing neurons constituted approximately 80% of all submucous neurons in controls as well as in cultured explants or dissociated neurons. Studies on coexistence revealed that the VIP-containing neurons were the ones that started to express NOS during culture. The induced expression of NOS in cultured adult submucous neurons indicates that nitric oxide, possibly in cooperation with VIP, is important for neuronal adaptation, maintenance and survival.

A calcium-initiated signaling pathway propagated through calcineurin and cAMP response element-binding protein activates proenkephalin gene transcription after depolarization

Essential components of a signal-transduction pathway regulating activity-dependent neuropeptide gene transcription have been identified. Proenkephalin (PEnk) gene activation after depolarization of chromaffin cells with 40 mM KCl was blocked by the voltage-sensitive calcium-channel blocker methoxyverapamil (D600) (30 microM) and by calcineurin inhibition with 100 nM cyclosporin A or ascomycin but not by inhibiting new protein synthesis with 0.5 microg/ml cycloheximide. KCl-induced elevation of PEnk mRNA was distinct from activation of the PEnk gene by either cAMP or protein kinase C. Twenty-five micromolar forskolin- and 100 nM phorbol 12-myristate 13-acetate-induced elevations of PEnk mRNA were cycloheximide-sensitive and were not blocked by cyclosporin A or ascomycin. KCl stimulated Ser-133 phosphorylation of cAMP response element-binding protein (CREB) in chromaffin cells, and CREB phosphorylation was blocked by both ascomycin and D600. A reporter gene containing 193 bases of the PEnk gene 5' flank driving luciferase gene expression (pENK12-Luc) transfected into chromaffin cells was transcriptionally activated by KCl depolarization. Activation was blocked by both ascomycin and D600 and required an intact CREB binding site (ENKCRE2). An oligonucleotide containing the PEnk cAMP response element-2 was gel-shifted by both unstimulated and potassium-stimulated chromaffin cell nuclear extracts into a prominent complex supershifted by CREB antibodies. Finally, stimulation of transcription of the pENK12-Luc reporter by KCl in chromaffin cells was blocked by coexpression of the CREB antagonist A-CREB but not by the AP-1 antagonist A-Fos. Stimulus-transcription coupling after depolarization in chromaffin cells occurs via calcineurin-dependent activation of CREB, a pathway distinct from cAMP- or protein kinase C-initiated signaling and independent of immediate early gene regulation.

Infarction alters both the distribution and noradrenergic properties of cardiac sympathetic neurons

Regional changes occur in the sympathetic innervation of the heart after myocardial infarction (MI), including loss of norepinephrine (NE) uptake and depletion of neuronal NE. This apparent denervation is accompanied by increased cardiac NE spillover. One potential explanation for these apparently contradictory findings is that the sympathetic neurons innervating the heart are exposed to environmental stimuli that alter neuronal function. To understand the changes that occur in the innervation of the heart after MI, immunohistochemical, biochemical, and molecular analyses were carried out in the heart and stellate ganglia of control and MI rats. Immunohistochemistry with panneuronal markers revealed extensive denervation in the left ventricle (LV) below the infarct, but sympathetic nerve fibers were retained in the base of the heart. Western blot analysis revealed that tyrosine hydroxylase (TH) expression (normalized to a panneuronal marker) was increased significantly in the base of the heart and in the stellate ganglia but decreased in the LV below the MI. NE transporter (NET) binding sites, normalized to total protein, were unchanged, except in the LV, where [3H]nisoxetine binding was decreased. TH mRNA was increased significantly in the left and right stellate ganglia after MI, while NET mRNA was not. In the base of the heart, increased TH coupled with no change in NET may explain the increase in extracellular NE observed after MI. Coupled with substantial denervation in the LV, these changes likely contribute to the onset of cardiac arrhythmias.

Induction of neuropeptide gene expression and blockade of retrograde transport in facial motor neurons following local peripheral nerve inflammation in severe combined immunodeficiency and BALB/C mice

Peripheral nerve inflammation is a common clinical problem that accompanies nerve injury and several diseases including Guillain-Barre syndrome and acute and chronic inflammatory demyelinating polyneuropathy. To determine if neuropeptides are induced in motor neurons after inflammation and to study the mechanisms involved, a nerve cuff soaked in complete Freund's adjuvant (CFA) was applied locally to the facial nerve of Balb/C mice. This procedure resulted in an influx of lymphocytes and macrophages to the affected area and a blockade of retrograde axonal transport distal, but not proximal, to the site of application. The same treatment resulted in a strong ipsilateral induction of pituitary adenylyl cyclase activating peptide (PACAP) gene expression in motor neurons in the facial motor nucleus. Because the changes could have occurred due to the loss of target-derived factors or to the production of new factors by immune cells, we studied the effect of the inflammatory stimulus on PACAP mRNA in mice with severe combined immunodeficiency (SCID). As expected, SCID mice showed a severely reduced influx of T-lymphocytes but not macrophages to the peripheral nerve. Moreover, although retrograde transport distal to the inflammation site was blocked similarly in control and SCID mice, the number of motor neurons expressing PACAP mRNA after CFA application was significantly reduced in SCID mice. The data indicate that the induction of PACAP mRNA during nerve inflammation requires the involvement of lymphocytes. However, because the induction of PACAP gene expression was only partially blocked in SCID mice, macrophages, loss of target-derived factors, or other mechanisms may also contribute to the upregulation of PACAP gene expression in motor neurons after nerve inflammation.

Rapid electrical and delayed molecular signals regulate the serum response element after nerve injury: convergence of injury and learning signals

Axotomy elicits changes in gene expression, but little is known about how information from the site of injury is communicated to the cell nucleus. We crushed nerves in Aplysia californica and the sciatic nerve in the mouse and found short- and long-term activation of an Elk1-SRF transcription complex that binds to the serum response element (SRE). The enhanced short-term binding appeared rapidly and was attributed to the injury-induced activation of an Elk1 kinase that phosphorylates Elk1 at ser383. This kinase is the previously described Aplysia (ap) ERK2 homologue, apMAPK. Nerve crush evoked action potentials that propagated along the axon to the cell soma. Exposing axons to medium containing high K(+), which evoked a similar burst of spikes, or bathing the ganglia in 20 microM serotonin (5HT) for 20 min, activated the apMAPK and enhanced SRE binding. Since 5HT is released in response to electrical activity, our data indicate that the short-term process is initiated by an injury-induced electrical discharge that causes the release of 5HT which activates apMAPK. 5HT is also released in response to noxious stimuli for aversive learning. Hence, apMAPK is a point of convergence for injury signals and learning signals. The delay before the onset of the long-term SRE binding was reduced when the crush was closer to the ganglion and was attributed to an Elk1 kinase that is activated by injury in the axon and retrogradely transported to the cell body. Although this Elk1 kinase phosphorylates mammalian rElk1 at ser383, it is distinct from apMAPK.

Increased expression of vasoactive intestinal polypeptide in cultured myenteric neurons from adult rat small intestine

Adult neurons possess the ability to adapt to a changing environment. Loss of target-derived neurotrophic factors due to axotomy or isolation by culturing is known to induce changes in neuropeptide expression in several types of peripheral neurons. The aim of the present study was to investigate changes in the expression of vasoactive intestinal polypeptide (VIP) and nitric oxide synthase (NOS) in cultured myenteric ganglia and dissociated neurons. Myenteric ganglia and neurons from rat small intestine were dissociated and cultured for up to 21 days. Immunocytochemistry was used to determine the total number of neurons and the proportions of subpopulations containing VIP or NOS or both in preparations of whole mounts (controls used to determine the conditions in vivo), myenteric ganglion culture and dissociated myenteric neuronal culture. In situ hybridization was used to determine changes in the expressions of NOS and VIP mRNA. The relative number of VIP-expressing neurons increased significantly during culturing. The percentage of all neurons expressing VIP was 3.6+/-0.3% in whole mounts, 22-24% in cultured myenteric ganglia, and up to 35% in cultured dissociated neurons. NOS-expressing neurons constituted approximately 30-40% of all neurons in whole mounts as well as in cultured ganglia or dissociated neurons. A dramatic increase in NOS/VIP-containing neurons were detected in cultured neurons irrespective of whether they were arranged in ganglia or dissociated, as compared to whole mount preparations. This suggests that the NOS-containing neurons are the ones that increase their VIP expression. The induced expression of VIP in cultured adult myenteric neurons indicates that VIP is important for neuronal adaptation, maintenance and survival.

Peripheral tachykinin receptors as potential therapeutic targets in visceral diseases

More than 10 years of intensive preclinical investigation of selective tachykinin (TK) receptor antagonists has provided a rationale to the speculation that peripheral neurokinin (NK)-1, -2 and -3 receptors may be involved in the pathophysiology of various human diseases at the visceral level. In the airways, despite promising effects in animal models of asthma, pilot clinical trials with selective NK-1 or -2 receptor antagonists in asthmatics have been ambiguous, whereas the potential antitussive effects of NK-1, -2 or -3 antagonists have not yet been verified in humans. In the gastrointestinal (GI) tract, irritable bowel syndrome (IBS) and pancreatitis are appealing targets for peripherally-acting NK-1 and -2 antagonists, respectively. In the genito-urinary tract, NK-1 receptor antagonists could offer some protection against nephrotoxicity and cytotoxicity induced by chemotherapeutic agents, whereas NK-2 receptor antagonists appear to be promising new agents for the treatment of neurogenic bladder hyperreflexia. Finally, there is preclinical evidence for hypothesising an effect of NK-3 receptor antagonists on the cardiovascular disturbance that characterises pre-eclampsia. Other more speculative applications are also mentioned.

Distribution and regulation of galanin receptor 1 messenger RNA in the forebrain of wild type and galanin-transgenic mice

To learn more about molecular alterations in the brain that occur as a consequence of either the chronic excess or absence of peptide neurotransmitters, we examined the impact of genetically manipulating the neuropeptide galanin on the expression of one of its cognate receptors, galanin receptor 1. First, we examined the distribution of galanin receptor 1 messenger RNA in the mouse forebrain, and found it to be abundantly expressed in many brain regions, including in numerous hypothalamic and other forebrain regions associated with neuroendocrine function. The distribution of galanin receptor 1 messenger RNA in the mouse was similar to previous reports in the rat, with additional expression noted in the caudate putamen and in several midbrain regions. Next, using quantitative in situ hybridization, we measured cellular levels of galanin receptor 1 messenger RNA in the brains of mice that either overexpress galanin (galanin transgenic) or lack a functional galanin gene (galanin knockout). We report that relative to wild-type controls, the expression of galanin receptor 1 messenger RNA was increased in discrete areas of the brain in galanin-transgenic mice, but that depletion of galanin/noradrenergic innervation to the hypothalamus with the neurotoxin 6-hydroxydopamine did not alter levels of galanin receptor 1 messenger RNA. We also report that levels of galanin receptor 1 messenger RNA were not different between galanin-knockout and wild-type mice. These results suggest that compensatory adjustments in the expression of cognate receptors represent one mechanism by which the developing nervous system attempts to maintain homeostasis in response to overexpression of a peptidergic transmitter. However, the lack of significant changes in galanin receptor 1 messenger RNA in galanin-knockout mice suggests that developmentally programmed levels of receptor expression are maintained even in the complete absence of ligand.

D2 Dopamine receptor blockade results in sprouting of DA axons in the intact animal but prevents sprouting following nigral lesions

Recently it was demonstrated that sprouting of dopaminergic neurons and a microglial and astrocyte response follows both partial lesions of the substantia nigra pars compacta and blockade of the D2 dopamine receptor. We therefore studied the effects of the combination of these two treatments (lesioning and D2 dopamine receptor blockade). Haloperidol administration caused a 57% increase in dopaminergic terminal tree size (measured as terminal density per substantia nigra pars compacta neuron) and an increase of glia in the striatum. Following small to medium nigral lesions (less than 60%), terminal tree size increased by 51% on average and returned density of dopaminergic terminals to normal. In contrast, administration of haloperidol for 16 weeks following lesioning resulted in reduced dopaminergic terminal density and terminal tree size (13%), consistent with absent or impaired sprouting. Glial cell numbers increased but were less than with lesions alone. When haloperidol was administered after the striatum had been reinnervated through sprouting (16-32 weeks after lesioning), terminal tree size increased up to 150%, similar to the effect of haloperidol in normal animals. By examining the effect of administering haloperidol at varying times following a lesion, we concluded that a switch in the effect of D2 dopamine receptor blockade occurred after dopaminergic synapses began to form in the striatum. We postulate that when synapses are present, D2 dopamine receptor blockade results in increased terminal density, whereas prior to synapse formation D2 dopamine receptor blockade causes attenuation of a sprouting response. We speculate that D2 dopamine receptors located on growth cones 'push' neurites toward their targets, and blockade of these receptors could lead to attenuation of sprouting.

Testosterone and nerve growth factor have distinct but interacting effects on structure and neurotransmitter expression of adult pelvic ganglion cells in vitro

Circulating testosterone has potent effects on the structure and function of many pelvic ganglion cells in adult rats in vivo. However not all androgen-sensitive pelvic neurones possess androgen receptors and testosterone effects may therefore be indirect, by an action on the target organs. Here we have examined if testosterone influences neuronal structure in vitro in pelvic ganglion cells cultured from adult male rats. We have also used multiple label immunofluorescence to monitor the expression of transmitter-synthesising enzymes and peptides under various culture conditions. Testosterone was a more potent stimulant of noradrenergic soma growth in culture than nerve growth factor. Whereas nerve growth factor increased the number, branching and length of neurites, testosterone stimulated growth of a small number of very short processes, each of which bore numerous short protrusions. Testosterone also impeded the longer neurite growth induced by nerve growth factor. Many pelvic ganglion cells altered their expression of transmitters/neuropeptides under different culture conditions. In particular, under control conditions or during nerve growth factor treatment, vasoactive intestinal peptide was up-regulated in noradrenergic and cholinergic neurones; testosterone impeded this up-regulation in noradrenergic neurones. Choline acetyltransferase immunoreactivity could only be visualised when nerve growth factor was present in the cultures, and cholinergic neurones showed less neurite outgrowth than noradrenergic neurones under all culture conditions. Nerve growth factor did not stimulate levels of this enzyme as strongly if testosterone was present. This study has shown that testosterone has potent effects on the structure of many pelvic ganglion cells in vitro. It is possible that these effects are mediated indirectly, e.g. by stimulating glial-derived substances, however our results suggest that the effects are not mediated by nerve growth factor. The results also show that testosterone influences some of the actions of nerve growth factor, suggesting that there may be complex interactions between steroid signalling and neurotrophic factors in maintaining neuronal structure and function in vivo.

Galanin and galanin receptor expression in neuroblastic tumours: correlation with their differentiation status

Neuroblastoma and its benign differentiated counterpart, ganglioneuroma, are paediatric neuroblastic tumours arising in the sympathetic nervous system. Their broad spectrum of clinical virulence is mainly related to heterogeneous biologic background and tumour differentiation. Neuroblastic tumours synthesize various neuropeptides acting as neuromodulators. Previous studies suggested that galanin plays a role in sympathetic tissue where it could be involved in differentiation and development. We investigated the expression and distribution of galanin and its three known receptors (Gal-R1, Gal-R2, Gal-R3) in 19 samples of neuroblastic tumours tissue by immunohistochemistry, in situ hybridization and fluorescent-ligand binding. This study provides clear evidence for galanin and galanin receptor expression in human neuroblastic tumours. The messengers coding for galanin, Gal-R1 and -R3 were highly expressed in neuroblastoma and their amount dramatically decreased in ganglioneuroma. In contrast, Gal-R2 levels remained unchanged. Double labelling studies showed that galanin was mainly co-expressed with its receptors whatever the differentiation stage. In neuroblastic tumours, galanin might promote cell-survival or counteract neuronal differentiation through the different signalling pathways mediated by galanin receptors. Finally, our results suggest that galanin influences neuroblastoma growth and development as an autocrine/paracrine modulator. These findings suggest potential critical implications for galanin in neuroblastic tumours development.

Growth and neurotrophic factors regulating development and maintenance of sympathetic preganglionic neurons

The functional anatomy of sympathetic preganglionic neurons is described at molecular, cellular, and system levels. Preganglionic sympathetic neurons located in the intermediolateral column of the spinal cord connect the central nervous system with peripheral sympathetic ganglia and chromaffin cells inside and outside the adrenal gland. Current knowledge is reviewed of the development of these neurons, which share their origin with progenitor cells, giving rise to somatic motoneurons in the ventral horn. Their connectivities, transmitters involved, and growth factor receptors are described. Finally, we review the distribution and functions of trophic molecules that may have relevance for development and maintenance of preganglionic sympathetic neurons.

Neurotrophins, but not depolarization, regulate substance P expression in the developing optic tectum

Neurotransmitter expression can be regulated by both activity and neurotrophins in a number of in vitro systems. We examined whether either of these factors was likely to play a role in the in vivo optic nerve-dependent regulation of a substance P-like immunoreactive (SP-ir) population of cells in the developing optic tectum of the frog. In contrast to our previous results with the adult system, blocking tectal cell responses to glutamate release by retinal ganglion cells with 6-cyano-7-nitroquinoxaline-2,3 dione (CNQX) did not affect the percent of SP-ir cells in the developing tectum. Treatment with d-(-)-2-amino-5-phosphonovaleric acid (d-AP-5) was also ineffective in this regard, although both it and CNQX treatment disrupted visual map topography. Chronic treatment with brain-derived neurotrophic factor (BDNF) and neurotrophin-4/5 (NT-4/5) produced increases in SP-ir cells in the treated lobes of normal animals, which were significant in the case of NT-4/5. Both substances also prevented the decrease of SP cells that would otherwise occur in the deafferented lobe of unilaterally optic nerve-transected tadpoles. These changes in the percent of SP-ir cells occurred without any detectable changes in the overall number of tectal cells. NGF had no effect on SP expression. Nor did it affect topographic map formation, which was disrupted by treatment with either BDNF or NT-4/5. Our results demonstrate that different mechanisms regulate SP expression in the developing and adult tectum. They indicate that neurotrophin levels in the developing optic tectum may selectively regulate a specific neuropeptide-expressing population of cells.

Functional implications of neurotransmitter expression during axonal regeneration: serotonin, but not peptides, auto-regulate axon growth of an identified central neuron

We studied the regenerative properties of one of two electrically coupled molluscan neurons, the serotonergic cerebral giant cells (CGCs) of Lymnaea stagnalis, after axotomy. The CGCs play a crucial role in feeding behavior, and when both cells are disconnected from their target neurons, animals no longer feed. When one CGC was permanently disconnected from its targets and the other was reversibly damaged by a nerve crush, the latter one regenerated over a period of 2 weeks to reform functional synapses with specific target neurons. At the same time, recovery of the feeding behavior was observed. After the crush, neuropeptide gene expression in the CGC was downregulated to approximately 50%. Serotonin synthesis, on the other hand, remained unaffected, suggesting that serotonin might have an active role in regeneration. In primary neuron culture, CGCs failed to extend neurites in the presence of serotonin; in cells that extended neurites in the absence of serotonin, focally applied serotonin, but not neuropeptides, induced growth cone collapse. Using serotonin-sensitive sniffer cells, we show that CGC neurites and growth cones release serotonin in culture. Finally, both the spontaneous and stimulation-induced release of serotonin from CGCs in culture resulted in growth cone collapse responses that could be blocked by the serotonin receptor antagonist methysergide. Our data suggest that auto-released serotonin is inhibitory to CGC neurite outgrowth in vitro. During regeneration in vivo, serotonin release might fine-tune axon guidance and branching by inducing local collapse responses in extending neurites.

Distribution and regulation of substance P-related peptide in the frog visual system

Modulation of visual signal activity has consequences for both signal processing and for activity-dependent structuring mechanisms. Among the neuromodulatory agents found in visual areas are substance P (SP)-related peptides. This article reviews what is known about these substances in the amphibian retina and optic tectum with special emphasis on the leopard frog, Rana pipiens. It is found that the distribution of these SP-related peptides is remarkably similar to that seen in mammals. This suggests that study of model amphibian systems may significantly enhance our understanding of how neuropeptides contribute to visual system function and organization.

Cholecystokinin-8 promotes recovery of sympathectomy induced by 6-hydroxydopamine in adult mice

We used an experimental model of sympathetic neuropathy to investigate the effects of intraperitoneal cholecystokinin-8 (CCK-8) administration on the recovery of injured peripheral neurones. After treatment of adult mice with 6-hydroxydopamine (6-OHDA), which known to induce peripheral sympathectomy, nerve growth factor (NGF) in peripheral tissue first increased and then rapidly decreased to baseline levels. Following this observation, sympathectomised mice were treated with CCK-8 starting when the NGF levels lowered toward the control value. Our results show that injections with 8 nmol/kg of CCK-8 promote not only recovery of noradrenergic innervation but also NGF and neuropeptide Y (NPY) synthesis in peripheral tissue. This latter observation suggests that the effect of CCK-8 might be mediated through the stimulation of NGF synthesis.

RISK-1: a novel MAPK homologue in axoplasm that is activated and retrogradely transported after nerve injury

Sensory neurons (SNs) of Aplysia are widely used to study the molecular correlates of learning. Among these is the activation of an Aplysia (ap) MAPK that phosphorylates the transcription factor apC/EBPbeta. Because crushing the axons of the SNs induces changes similar to learning, we tested the hypothesis that apMAPK is a point of convergence on the pathways for learning and injury. One event in common is long-term hyperexcitability (LTH), and LTH was induced in the SNs after intrasomatic injection of active vertebrate extracellular signal-regulated kinase 1 (ERK1; as an apMAPK surrogate). Nerve crush activated an axoplasmic kinase at the site of injury that phosphorylated apC/EBPbeta. Surprisingly, this was not apMAPK, but a kinase that was recognized by antibodies to vertebrate ERKs and to doubly phosphorylated, activated ERKs. The activated kinase was transported to the cell body and nucleus and its arrival was concurrent with an injury-induced increase in apC/EBPbeta mRNA and protein. We call this retrogradely transported kinase RISK-1. RISK-1 initiated the binding of apC/EBPbeta to the ERE enhancer site in vitro and an increase in ERE-binding was detected in injured neurons containing active RISK-1. Thus, Aplysia neurons contain two MAPK homologues, one of which is a late acting retrogradely transported injury signal.

Regulation of vasoactive intestinal peptide receptor expression in developing nervous systems

Vasoactive intestinal peptide (VIP) is a 28-amino acid peptide that has several functions, including the regulation of water and electrolyte secretion, hormone and cytokine release, bronchodilitation, and neurogenesis. VIP effects are mediated by specific G-protein coupled receptors. Three distinct receptor subtypes, with differing affinity for VIP, have been cloned and characterized as receptors 1 and 2 (VPAC1 and VPAC2) and pituitary adenylate cyclase activating polypeptide receptor (PAC1). Our laboratory has demonstrated that upregulation of VPAC1 in SK-N-SH neuroblastoma cells results in marked shift in cell type to the glial lineage with a corresponding loss of neuronal lineage and suppression of xenograft tumor growth. To understand the molecular mechanisms responsible for regulation of the VPAC1 gene in neuronal lineage, we have cloned and sequenced 2.6-kb of the 5'-flanking sequences of the human VPAC1 gene. Sequence analysis demonstrated that the human VPAC1 promoter sequence contains putative binding sites for several known transcription factors, including Sp1, NFkB, and cETS-1. To study the temporal and spatial expression pattern of human VPAC1 promoter sequences, we have generated transgenic mice expressing the bacterial beta-galactosidase gene under the control of the 2.6-kb 5'-flanking and promoter sequence of the human VPAC1 gene. Transgene expression was detected in brain, spinal cord, and lung in 14-day-old animals. Taken together, these results demonstrate that VPAC1 may play an important role in the nervous system, and suggest a role for VIP in neuronal differentiation.

Regulation of chromogranin biosynthesis by neurotrophic growth factors in neuroblastoma cells

Polypeptide growth factors secreted from the target tissue determine the choice of transmitter synthesis in the innervating nerves. We have investigated whether they also influence the expression of chromogranins and neuropeptide Y, components co-stored with the neurotransmitters within large dense-core vesicles. IMR-32 and SH-SY5Y human neuroblastoma cells were treated for up to six days with various neurotrophic growth and differentiation factors. For chromogranins A and B, no significant changes at the mRNA level were observed and for chromogranin A this was confirmed at the protein level. The expression of secretogranin II/pro-secretoneurin mRNA, however, was considerably enhanced in both cell lines after basic fibroblast growth factor treatment. In IMR-32 cells we determined a fast and continuous induction, whereas the up-regulation in SH-SY5Y cells was more delayed. A transient elevation of secretogranin II/pro-secretoneurin mRNA levels was seen in SH-SY5Y cells in response to epidermal growth factor. In these cells we also measured the amounts of secretogranin II/pro-secretoneurin protein which were increased by both growth factors. In addition to the above described changes in secretogranin II/pro-secretoneurin biosynthesis we extended and confirmed data available on neuropeptide Y. We found a qualitatively similar pattern of biosynthesis regulation as for secretogranin II/pro-secretoneurin, indicating that the ultimately increased expression of the two proteins may be characteristic of the phenotypic differentiation after growth factor treatment. Moreover, this finding of a concomitant regulation further emphasizes the concept of secretogranin II/pro-secretoneurin being a neuropeptide precursor from which the functional peptide secretoneurin is proteolytically liberated.

Positive injury signals induce growth and prolong survival in Aplysia neurons

Injury to a peripheral nerve initiates changes that can lead to regeneration of the damaged axons. How information about a distant injury is communicated to the cell body is not clear. Using the nervous system of Aplysia californica, we tested the idea that some of this information is conveyed via positive injury signals-axoplasmic proteins that are activated at the injury site and transported to the cell soma. We collected these proteins by crushing pedal nerves and then placing a ligation proximal to the ligation. The contralateral nerves were ligated as controls. Twenty h later, axoplasm was extruded from the nerve segment just distal to the ligation on the crushed nerves (cr/lig) and on the control nerves (lig). The total proteins were rhodaminated and injected into the cytoplasm of neurons in vitro to look for nuclear import. Punctate fluorescence was detected in the nucleus of all seven neurons injected with the cr/lig axoplasm. Only two of five neurons injected with lig axoplasm had any fluorescence. Equal amounts of cr/lig and lig axoplasm were then injected directly into the cell bodies of neurons maintained in vitro. The cells injected with cr/lig axoplasm exhibited renewed growth and significantly longer survival: 25.9 +/- 2.1 days (mean +/- SEM: n = 22) relative to the cells injected with lig axoplasm (15.3 +/- 1.2 days; n = 14) and to those that were not injected (12.2 +/- 1.7 days; n = 24). Fractionation of the cr/lig axoplasm indicated that different factors are responsible for growth and survival.