Changes in expression of peptides in rat facial motoneurons after facial nerve crushing and resection

Reduced Gene Expression of KCC2 Accelerates Axonal Regeneration and Reduces Motor Dysfunctions after Tibial Nerve Severance and Suturing

Gamma-aminobutyric acid and glycine (GABA/Gly) are predominantly inhibitory neurotransmitters in the mature central nervous system; however, they mediate membrane potential depolarization during development. These differences in actions depend on intracellular Cl- concentrations ([Cl-]i), which are primarily regulated by potassium chloride cotransporter 2 (KCC2). After nerve injury, KCC2 expression markedly decreases and GABA/Gly mediate depolarization. Following nerve regeneration, KCC2 expression recovers and GABA/Gly become inhibitory, suggesting that KCC2 reduction and GABA/Gly excitation may be crucial for axonal regeneration. To directly clarify their involvement in regeneration, we analyzed recovery processes after tibial nerve severance and suturing between heterozygous KCC2 knockout mice (HT), whose KCC2 levels are halved, and their wild-type littermates (WT). Compared with WT mice, the sciatic functional index-indicating lower limb motor function-was significantly higher until 28 days after operation (D28) in HT mice. Furthermore, at D7, many neurofilament-positive fibers were elongated into the distal part of the sutured nerve in HT mice only, and myelinated axonal density was significantly higher at D21 and D28 in HT animals. Electron microscopy and galanin immunohistochemistry indicated a shorter nerve degeneration period in HT mice. Moreover, a less severe decrease in choline acetyltransferase was observed in HT mice. These results suggest that nerve degeneration and regeneration proceed more rapidly in HT mice, resulting in milder motor dysfunction. Via similar microglial activation, nerve surgery may reduce KCC2 levels more rapidly in HT mice, followed by earlier increased [Cl-]i and longer-lasting GABA/Gly excitation. Taken together, reduced KCC2 may accelerate nerve regeneration via GABA/Gly excitation.

Slow progression of sciatic nerve degeneration and regeneration after loose ligation through microglial activation and decreased KCC2 levels in the mouse spinal cord ventral horn

Peripheral nerve injury affects motor functions. To reveal the mechanisms underlying motor dysfunction and recovery after nerve compression, which have not been precisely examined, we investigated the temporal relationship among changes in motor function, nerve histopathology, and marker molecule expression in the spinal cord after loose ligation of the mouse sciatic nerve. After ligation, sciatic motor function suddenly declined, and axons gradually degenerated. During degeneration, galanin was localized in motor neuron cell bodies. Then, in the ventral horn, microglia were activated, and expression of choline acetyltransferase (ChAT), a synthetic enzyme of acetylcholine, and potassium chloride co-transporter 2 (KCC2), which shifts the action of γ-amino butyric acid (GABA) and glycine to inhibitory, decreased. Motor function recovery was insufficient although axonal regeneration was complete. ChAT levels gradually recovered during axonal regeneration. When regeneration was nearly complete, microglial activation declined, and KCC2 expression started to increase. The KCC2 level sufficiently recovered when axonal regeneration was complete, suggesting that the excitatory action of GABA/glycine may participate in axonal regeneration. Furthermore, these changes proceeded slower than those after severance, suggesting that loose ligation, compression, may mediate slower progression of degeneration and regeneration than severance, and these changes may cause the motor dysfunction and its recovery.

Neuropeptides Involved in Facial Nerve Regeneration

Neuropeptides and neurotransmitters act as intermediaries to transmit impulses from one neuron to another via a synapse. These neuropeptides are also related to nerve degeneration and regeneration during nerve damage. Although there are various neuropeptides, three are associated with neural regeneration in facial nerve damage: calcitonin gene-related peptide (CGRP), galanin, and pituitary adenylyl cyclase-activating peptide (PACAP). Alpha CGRP in facial motoneurons is a signaling factor involved in neuroglial and neuromuscular interactions during regeneration. Thus, it may be a marker for facial nerve regeneration. Galanin is a marker of injured axons rather than nerve regeneration. PACAP has various effects on nerve regeneration by regulating the surrounding cells and providing neurotrophic factors. Thus, it may also be used as a marker for facial nerve regeneration. However, the precise roles of these substances in nerve generation are not yet fully understood. Animal studies have demonstrated that they may act as neuromodulators to promote neurotrophic factors involved in nerve regeneration as they appear early, before changes in the injured cells and their environment. Therefore, they may be markers of nerve regeneration.

Changes in the expression and localization of signaling molecules in mouse facial motor neurons during regeneration of facial nerves

After injury, peripheral axons usually re-extend toward their target, and neuronal functions recover. Previous studies have reported that expression of various molecules are transiently altered in motor neurons after nerve injury, but the time course of these changes and their relationship with functional recovery have not been clearly demonstrated. We used the mouse facial nerve transection and suturing model, and examined the changes in expression of five molecules, choline acetyl transferase (ChAT), galanin, calcitonin gene-related protein (CGRP), gephyrin, and potassium chloride co-transporter 2 (KCC2) in the facial motor neurons after surgery until recovery. Number of ChAT-positive neurons was markedly decreased at days 3 and 7, and recovered to the normal level by day 60, when facial motor functions recovered. Localization of two neuropeptides, CGRP and galanin, was increased in the perikarya and axons during regeneration, and returned to the normal levels by days 60 and 28, respectively. Expression of two postsynaptic elements of γ-amino butyric acid synapses, gephyrin and KCC2, was decreased at days 3 and 7, and recovered by day 60. These results suggest that ChAT, CGRP, and KCC2 may be objective indicators of regeneration, and altering their expression may be related to the functional recovery and axonal re-extension.

Response of the GABAergic System to Axotomy of the Rat Facial Nerve

The responses of inhibitory neurons/synapses to motoneuron injury in the cranial nervous system remain to be elucidated. In this study, we analyzed GABA_A receptor (GABA_AR) and GABAergic neurons at the protein level in the transected rat facial nucleus. Immunoblotting revealed that the GABA_ARα1 protein levels in the axotomized facial nucleus decreased significantly 5-14 days post-insult, and these levels remained low for 5 weeks. Immunohistochemical analysis indicated that the GABA_ARα1-expressing cells were motoneurons. We next examined the specific components of GABAergic neurons, including glutamate decarboxylase (GAD), vesicular GABA transporter (VGAT) and GABA transporter-1 (GAT-1). Immunoblotting indicated that the protein levels of GAD, VGAT and GAT-1 decreased transiently in the transected facial nucleus from 5 to 14 days post-insult, but returned to the control levels at 5 weeks post-insult. Although GABA_ARα1 protein levels in the transected nucleus did not return to their control levels for 5 weeks post-insult, the administration of glial cell line-derived neurotrophic factor at the cut site significantly ameliorated the reductions. Through these findings, we verified that the injured facial motoneurons suppressed the levels of GABA_ARα1 protein over the 5 weeks post-insult, presumably due to the deprivation of neurotrophic factor. On the other hand, the levels of the GAD, VGAT and GAT-1 proteins in GABAergic neurons were transiently reduced in the axotomized facial nucleus at 5-14 days post-insult, but recovered at 4-5 weeks post-insult.

■ REVIEW : LIF, NGF, and the Cell Body Response to Axotomy

Adult peripheral neurons can regenerate after axonal damage. Large changes in gene expression occur in the cell bodies of these axotomized neurons, including decreases in expression of a number of proteins used for synaptic transmission and increases in expression of a number of proteins involved in regeneration. The signals that trigger these changes are just beginning to be elucidated. One characteristic of axotomized sympathetic, sensory, and motor neurons is that they increase expression of two neuropeptides, vasoactive intestinal peptide and galanin. These peptides may play important roles in the survival and regeneration of axotomized neurons deprived of their target-derived trophic factors. Recent studies have demonstrated two important signals in the induction of these peptides in sympathetic neurons: one is the release of leukemia inhibitory factor (LIF) by non-neuronal cells in the vicinity of the injured neurons and the other, the removal of target-derived nerve growth factor (NGF). Furthermore, there is a synergistic interaction between these two events whereby the removal of NGF alters the responsiveness of neurons to LIF. Future efforts will hopefully determine the extent to which LIF and NGF signal other aspects of the cell body response and the mechanisms that underlie these actions. NEUROSCIENTIST 3:176-185, 1997

The pros and cons of growth factors and cytokines in peripheral axon regeneration

Injury to a peripheral nerve induces a complex cellular and molecular response required for successful axon regeneration. Proliferating Schwann cells organize into chains of cells bridging the lesion site, which is invaded by macrophages. Approximately half of the injured neuron population sends out axons that enter the glial guidance channels in response to secreted neurotrophic factors and neuropoietic cytokines. These lesion-associated polypeptides create an environment that is highly supportive for axon regrowth, particularly after acute injury, and ensure that the vast majority of regenerating axons are directed toward the distal nerve stump. Unfortunately, most neurotrophic factors and neuropoietic cytokines are also strong stimulators of axonal sprouting. Although some of the axonal branches will withdraw at later stages, the sprouting effect contributes to the misdirection of reinnervation that results in the lack of functional recovery observed in many patients with peripheral nerve injuries. Here, we critically review the role of neuronal growth factors and cytokines during axon regeneration in the peripheral nervous system. Their differential effects on axon elongation and sprouting were elucidated in various studies on intraneuronal signaling mechanisms following nerve lesion. The present data define a goal for future therapeutic strategies, namely, to selectively stimulate a Ras/Raf/ERK-mediated axon elongation program over an intrinsic PI3K-dependent axonal sprouting program in lesioned motor and sensory neurons. Instead of modulating growth factor or cytokine levels at the lesion site, targeting specific intraneuronal molecules, such as the negative feedback inhibitors of ERK signaling, has been shown to promote long-distance regeneration while avoiding sprouting of regenerating axons until they have reached their target areas.

gp130 cytokines are positive signals triggering changes in gene expression and axon outgrowth in peripheral neurons following injury

Adult peripheral neurons, in contrast to adult central neurons, are capable of regeneration after axonal damage. Much attention has focused on the changes that accompany this regeneration in two places, the distal nerve segment (where phagocytosis of axonal debris, changes in the surface properties of Schwann cells, and induction of growth factors and cytokines occur) and the neuronal cell body (where dramatic changes in cell morphology and gene expression occur). The changes in the axotomized cell body are often referred to as the "cell body response." The focus of the current review is a family of cytokines, the glycoprotein 130 (gp130) cytokines, which produce their actions through a common gp130 signaling receptor and which function as injury signals for axotomized peripheral neurons, triggering changes in gene expression and in neurite outgrowth. These cytokines play important roles in the responses of sympathetic, sensory, and motor neurons to injury. The best studied of these cytokines in this context are leukemia inhibitory factor (LIF) and interleukin (IL)-6, but experiments with conditional gp130 knockout animals suggest that other members of this family, not yet determined, are also involved. The primary gp130 signaling pathway shown to be involved is the activation of Janus kinase (JAK) and the transcription factors Signal Transducers and Activators of Transcription (STAT), though other downstream pathways such as mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) may also play a role. gp130 signaling may involve paracrine, retrograde, and autocrine actions of these cytokines. Recent studies suggest that manipulation of this cytokine system can also stimulate regeneration by injured central neurons.

Cholecystokinin B-type receptors mediate a G-protein-dependent depolarizing action of sulphated cholecystokinin ocatapeptide (CCK-8s) on rodent neonatal spinal ventral horn neurons

Reports of cholecystokinin (CCK) binding and expression of CCK receptors in neonatal rodent spinal cord suggest that CCK may influence neuronal excitability. In patch-clamp recordings from 19/21 ventral horn motoneurons in neonatal (PN 5-12 days) rat spinal cord slices, we noted a slowly rising and prolonged membrane depolarization induced by bath-applied sulfated CCK octapeptide (CCK-8s; 1 microM), blockable by the CCK B receptor antagonist L-365,260 (1 microM). Responses to nonsulfated CCK-8 or CCK-4 were significantly weaker. Under voltage clamp (V H -65 mV), 22/24 motoneurons displayed a CCK-8s-induced tetrodotoxin-resistant inward current [peak: -136 +/- 28 pA] with a similar time course, mediated via reduction in a potassium conductance. In 29/31 unidentified neurons, CCK-8s induced a significantly smaller inward current (peak: -42.8 +/- 5.6 pA), and I-V plots revealed either membrane conductance decrease with net inward current reversal at 101.3 +/- 4.4 mV (n = 16), membrane conductance increase with net current reversing at 36.1 +/- 3.8 mV (n = 4), or parallel shift (n = 9). Intracellular GTP-gamma-S significantly prolonged the effect of CCK-8s (n = 6), whereas GDP-beta-S significantly reduced the CCK-8s response (n = 6). Peak inward currents were significantly reduced after 5-min perfusion with N-ethylmaleimide. In isolated neonatal mouse spinal cord preparations, CCK-8s (30-300 nM) increased the amplitude and discharge of spontaneous depolarizations recorded from lumbosacral ventral roots. These observations imply functional postsynaptic G-protein-coupled CCK B receptors are prevalent in neonatal rodent spinal cord.

The axotomy-induced neuropeptides galanin and pituitary adenylate cyclase-activating peptide promote axonal sprouting of primary afferent and cranial motor neurones

The neuropeptides galanin and pituitary adenylate cyclase-activating peptide (PACAP) are markedly up-regulated in response to peripheral nerve lesion. Both peptides are involved in neuronal differentiation and neurite outgrowth during development. In this study, we investigated the effects of galanin and PACAP on axonal elongation and sprouting by adult rat sensory neurones in vitro and facial motor neurones in vivo. Dissociated rat dorsal root ganglion neurones were plated on laminin substrate and analysed morphometrically. Both the mean axonal length and the number of branch points significantly increased in the presence of galanin or PACAP (2-5 microm). Effects on axonal collateralization were investigated in the rat facial nerve lesion model by direct application of the peptides to collagen-filled conduits entubulating the transected facial nerve stumps. Triple retrograde labelling of brainstem neurones confirmed that the peptides potently induce axonal sprouting of cranial motor neurones. The number of neurones regenerating into identified rami of the facial nerve increased up to fivefold. Biometrical analysis of whisking behaviour revealed that galanin and PACAP impaired the functional outcome when compared with vehicle-treated animals 8 weeks after surgery. In conclusion, although galanin and PACAP have been established as neurotrophic molecules with respect to axonal development and regeneration, their potential as treatments for peripheral nerve lesions appears limited because of the extensive stimulation of collateral axon branching. These branches are misrouted towards incorrect muscles and cause impairment in their coordinated activity.

Differential expression of calcitonin gene-related peptide (CGRP) and choline acetyltransferase (ChAT) in the axotomized motoneurons of normoxic and hypoxic rats

We employed a double injury model (axotomy along with hypoxia) to determine how nerve injury and hypoxic insult would affect the expression of calcitonin gene-related peptide (CGRP) and choline acetyltransferase (ChAT) in the hypoglossal nucleus (HN) and nucleus ambiguus (NA). Adult rats were subjected to unilateral vagus and hypoglossal nerve transection, following which half of the animals were kept in an altitude chamber (PO2=380 Torr). The immunoexpression of CGRP and ChAT (CGRP-IR/ChAT-IR) were examined by quantitative immunohistochemistry at 3, 7, 14, 30 and 60 days post-axotomy. The results revealed that CGRP-IR in the HN was increased at 3 days but decreased to basal levels at 7 days following nerve injury. The decline was followed by a second rise in CGRP-IR at 30 days post-axotomy, followed again by a return to basal levels at 60 days. In the NA, CGRP-IR was up-regulated at 3 days and remained increased for up to 60 days after nerve injury. Animals treated with a double injury showed a greater CGRP-IR than normoxic group in both nuclei at all post-axtomized periods. In contrast to CGRP, ChAT-IR was markedly reduced in the HN and NA at 3 days reaching its nadir at 14 days following nerve injury. Hypoxic animals showed a stronger reduction of ChAT-IR in both nuclei at all post-axtomized periods. Results of cell counting showed that neuronal loss was somewhat obvious in hypoxic HN than that of normoxic ones. The present results suggest that up-regulation of CGRP-IR may exert its trophic effects while down-regulation of ChAT-IR may correlate with the poor neurotransmission within the injured neurons. It is speculated that the enhanced expression of CGRP-IR and the pronounced reduction of ChAT-IR in hypoxic rats may result from a drastic shift of intracellular metabolic pathways, which in turn could lead to more metabolic loading to the severely damaged neurons following the double insult.

The facial nerve axotomy model

Experimental models such as the facial nerve axotomy paradigm in rodents allow the systematic and detailed study of the response of neurones and their microenvironment to various types of challenges. Well-studied experimental examples include peripheral nerve trauma, the retrograde axonal transport of neurotoxins and locally enhanced inflammation following the induction of experimental autoimmune encephalomyelitis in combination with axotomy. These studies have led to novel insights into the regeneration programme of the motoneurone, the role of microglia and astrocytes in synaptic plasticity and the biology of glial cells. Importantly, many of the findings obtained have proven to be valid in other functional systems and even across species barriers. In particular, microglial expression of major histocompatibility complex molecules has been found to occur in response to various types of neuronal damage and is now regarded as a characteristic component of "glial inflammation". It is found in the context of numerous neurodegenerative disorders including Parkinson's and Alzheimer's disease. The detachment of afferent axonal endings from the surface membrane of regenerating motoneurones and their subsequent displacement by microglia ("synaptic stripping") and long-lasting insulation by astrocytes have also been confirmed in humans. The medical implications of these findings are significant. Also, the facial nerve system of rats and mice has become the best studied and most widely used test system for the evaluation of neurotrophic factors.

Heightened pain and delayed regeneration of galanin axons in diabetic mice

Galanin peptide in primary sensory neurons may confer analgesia following injury. Its presence in regenerative axon sprouts where pain may be initiated has not been examined. We examined very early outgrowth of peptidergic axon sprouts after sciatic nerve crush in mice with experimental streptozotocin-induced diabetes. Diabetic mice had a retarded wave of outgrowing galanin axons, but those expressing calcitonin gene-related peptide grew normally. Diabetic mice also developed early, then persistent excessive autotomy behaviour, an index of pain behaviour in complete nerve lesions. Diabetes is associated with variations in the early outgrowth of peptide-containing axons. A relative delay in galanin axon outgrowth could contribute to heightened neuropathic pain in diabetes.

Correlation between CGRP immunoreactivity and firing activity in cat abducens motoneurons

A relationship between motoneuron activity and calcitonin gene-related peptide (CGRP) expression was previously suggested based on indirect inferences. We show here a positive correlation between CGRP immunoreactivity and firing activity in an experimental model that used tetanus neurotoxin (TeNT) to alter basal firing levels. A low dose (0.5 ng/kg) of TeNT injected in the lateral rectus muscle raised the basal firing rate of ipsilateral abducens motoneurons, estimated as the firing rate at straight-ahead gaze (F(0)); the firing rate returned to control values after 2 weeks. In contrast, a high dose (5 ng/kg) of TeNT decreased basal firing, which recovered slowly over a 7-week period. Expression of CGRP immunoreactivity by abducens motoneurons, preferentially related to betaCGRP gene expression, was analyzed during these periods of altered firing activity. The number of CGRP-immunofluorescent abducens motoneurons increased to approximately 120% by 7 days after low-dose TeNT, to include all available motoneurons in the nucleus. In addition, the average CGRP immunofluorescence optical density inside motoneurons almost doubled after 4 days and returned toward control values in the following 2 weeks. In contrast, a high-dose injection of TeNT reduced the number of CGRP-immunofluorescent motoneurons to 5.4% of control 7 days post injection, and the number returned to 77.6% after 42 days. CGRP immunofluorescence intensity inside motoneurons was also reduced. Regression analysis of F(0) values with either the number of CGRP-immunolabeled motoneurons, their average immunofluorescence intensity, or both factors combined resulted in positive correlations with regression coefficients of 0.87 or higher. Therefore, CGRP expression and firing activity in abducens motoneurons are positively correlated.

Galanin receptor over-expression within the amygdala in early Alzheimer's disease: an in vitro autoradiographic analysis

Galanin receptor (GALR) expression is increased in various areas of the limbic system in end stage Alzheimer's disease (AD). The amygdaloid complex is a key component of the limbic circuit, is involved in homeostatic and cognitive functions, is impacted in AD and contains the peptide and receptor for galanin. Although GALR expression occurs in the amygdala in end stage AD, it remains to be determined whether a plasticity response occurs early or late in the disease. Therefore, we analyzed the distribution and associated changes in GALR binding in the amygdala during the progression of AD using an in vitro receptor autoradiographic method. Human galanin ([125I]hGAL) receptor binding was performed on brain sections from early and late AD cases, as well as normal age-matched control subjects. In aged controls, densities of [125I]hGAL binding sites were found in the central and the corticomedial nuclei. Relative to controls, possible/early AD cases displayed significantly greater numbers of [125I]hGAL binding sites in the central nucleus and cortico-amygdaloid transition area. In contrast, we found a decrease in the number of binding sites for [125I]hGAL in late as compared to early AD cases. The over-expression of GALRs in subfields of the amygdaloid early in AD suggests that galaninergic systems play a key role in limbic related behavioral changes during the disease process.

Can galanin also be considered as growth-associated protein 3.2?

A recent study has shown that mice containing a loss-of-function mutation in the gene encoding galanin exhibit decreased peripheral nerve regeneration after a lesion. This major advance indicates, for the first time, that the large increases in galanin expression that occur in axotomized peripheral neurons have functional consequences for regeneration. Hopefully, similar functional consequences will soon be found for other peptides induced in these neurons after axotomy, such as vasoactive intestinal peptide and pituitary adenylate cyclase-activating peptide.

Change in gene expression in facial nerve nuclei and the effect of superoxide dismutase in a rat model of ischemic facial paralysis

Peripheral nerve injury induces changes in gene expressions of a variety of neuroactive substances in cell somata, which may have roles in the adaptive response to the injury, neuronal survival, growth and regeneration. In this study, we designed a rat model of ischemic peripheral facial paralysis with a selective embolization technique, and observed mRNA expression of calcitonin gene-related peptide (CGRP), c-jun, and growth associated protein (GAP)-43 in facial nerve nuclei using in situ hybridization histochemistry. The rats were demonstrated to have a transient facial paralysis consistently, and thus this method was regarded as a model of minor peripheral nerve injury. The mRNA of CGRP, c-jun and GAP-43 showed a distinct pattern of induction and time course of increase after the ischemic nerve injury. The results suggest that the small injury to the peripheral nerve was able to induce changes in mRNA expression in the cell body of motoneurons. We also investigated the protective effect of superoxide dismutase (SOD), which is a free radical-scavenging enzyme involved in cellular antioxidant defenses. The SOD treatment clearly alleviated the behavioral impairment and decreased the CGRP mRNA expression at 3rd day after injury. These data suggest that a free radical generated by the ischemia may be partially responsible for ischemic nerve damage and the change in gene expression in motoneurons.

Expression of cholecystokinin, enkephalin, galanin and neuropeptide Y is markedly changed in the brain of the megencephaly mouse

Megencephaly, enlarged brain, is a major sign in several human neurological diseases. The mouse model for megencephaly (mceph/mceph) has an enlarged brain, presumably due to brain cell hypertrophy, and exhibits neurological and motor disturbances with seizure-like activity, as well as disturbances in the insulin-like growth factor system. Here, we report that expression of the neuropeptides cholecystokinin, enkephalin, galanin and neuropeptide Y is dramatically changed in mceph/mceph brains compared to wild type, as revealed by in situ hybridization and immunohistochemistry. The changes were confined to discrete brain regions and occurred in a parallel fashion for peptides and their transcripts. For cholecystokinin, mceph/mceph brains had region-specific up- and down-regulations in several layers of the hippocampal formation and increased levels in, especially ventral, cortical regions. Enkephalin messenger RNA expression was up-regulated in the dentate gyrus granular layer and in ventral cortices, but down-regulated in the CA1 pyramidal layer. Enkephalin-like immunoreactivity was elevated in mossy fibers of the hippocampus and the ventral cortices. Galanin expression was increased in several layers and interneurons of the hippocampal formation, as well as in ventral cortices. Galanin-like immunoreactivity was reduced in nerve terminals in the forebrain. Neuropeptide Y expression was increased in the hippocampal formation and ventral cortices. Whether the mainly increased peptide levels contribute to the excessive growth of the brain or represent a consequence of this growth and/or of the neurological and motor disturbances remains to be elucidated.

Postnatal development of 5-HT(1A) receptor expression in rat somatic motoneurons

Prior work has established that hypoglossal motoneurons (HMs) change postnatally in their response to serotonin (5-HT), in part as a result of a decline in expression of 5-HT(1A) receptors. In the current study, two issues were addressed. First, using in situ hybridization we found that transient expression of 5-HT(1A) receptors occurs in other populations of brainstem (facial and trigeminal) and spinal (cervical and lumbar) motoneurons. Second, the participation of motoneuronal afferent (serotonergic) and efferent (neuromuscular) innervation in inducing and maintaining this decline in expression was investigated. Serotonergic innervation of the hypoglossal nucleus (nXII) was disrupted in neonatal rats by intra-cisternal injection of the serotonergic neurotoxin 5,7-dihydroxytryptamine (5,7-DHT), and 5-HT(1A) receptor mRNA levels in nXII from these rats were assayed at postnatal day 21. In spite of an almost complete loss of serotonergic fibers in the region, the postnatal decrease in 5-HT(1A) receptor expression by HMs still occurred. To test for potential regulation by target-derived factors or by nerve injury, receptor mRNA levels were assayed after unilateral transection of the hypoglossal nerve in adult rats. Though this treatment resulted in re-induction of developmentally transient expression of the p75 neurotrophin receptor, 5-HT(1A) receptor expression remained low. Thus, neonatal expression of 5-HT(1A) receptors appears to be common to somatic motoneurons, but we found no evidence for changes in serotonergic innervation in influencing this expression, nor did we find evidence for its regulation by peripheral factors.

Enkephalin and aFGF are differentially regulated in rat spinal motoneurons after chemodenervation with botulinum toxin

Botulinum toxin is used to induce transient graded paresis by chemodenervation in the treatment of focal hyperkinetic movement disorders. While the molecular events occurring in motoneurons after mechanical nerve lesioning leading to muscle paresis are well known, they have been investigated to a lesser extent after chemodenervation. We therefore examined the expression of enkephalin (ENK), acidic fibroblast growth factor (aFGF), neurotensin (NT), galanin (GAL), substance P (SP), vasoactive intestinal polypeptide (VIP), and neuropeptide Y (NPY) in rat spinal motoneurons after chemodenervation of the gastrocnemius. In order to precisely localize the motoneurons targeting the injection site, retrograde tracing was performed in additional rats by using Fluorogold injections. ENK expression was upregulated in the region corresponding to the Fluorogold positive motoneurons, but also on the contralateral side and in more distant parts of the spinal cord. The highest upregulation occurred 7 to 14 days after injections and decreased over a period of three months. At 8 days, aFGF was slightly downregulated in all regions studied, single motoneurons showed NT expression, while expression of GAL, SP, VIP, and NPY could be detected neither in controls nor in toxin-treated animals. These alterations in gene expression were strikingly different from those described after axotomy. Our present findings give additional demonstration of the considerable plasticity of the adult spinal cord after botulinum toxin treatment.

Increased calcitonin gene-related peptide immunoreactivity in gracile nucleus after partial sciatic nerve injury: age-dependent and originating from spared sensory neurons

Following a unilateral chronic constriction injury of the sciatic nerve, calcitonin gene-related peptide (CGRP)-immunoreactive (IR) fiber density increases in the ipsilateral gracile nucleus, and this is more pronounced in aged (16-month) rats where the fibers are dystrophic. In this study we show that a second type of partial sciatic nerve injury, a half-transection, also induces CGRP-IR fibers in the gracile nucleus, but this effect is strongly age-dependent, being much more pronounced in 8- to 10-month-old rats than in 2- to 3-month-old rats. Dystrophic CGRP-IR fibers were rarely observed in 8- to 10-month-old animals, so the increased reaction in aged animals and axonal dystrophy are separate phenomena. Using double-labeling with fluorescent dye tracing for 8- to 10-month-old rats, we showed that neuron profiles in the dorsal root ganglion (DRG) with peripheral axons spared by the partial sciatic nerve injury were 10 times more likely to be CGRP mRNA-positive than profiles with injured peripheral axons, suggesting that spared neurons are more likely to contribute to the increase in CGRP-IR fibers in the gracile nucleus. Using combined fluorescent dye tracing with in situ hybridization for CGRP mRNA or CGRP immunostaining, we further showed that CGRP-expressing DRG neuron profiles with central projections to the gracile nucleus had peripheral axons spared by the partial nerve injury. We conclude that the increased CGRP immunoreactivity in the gracile nucleus following partial sciatic nerve injury originates from primary sensory neurons with axons spared by the injury. These neurons may still transmit cutaneous sensory information and thus the increased CGRP immunoreactive fibers in the gracile nucleus may be involved in the mechanical allodynia characteristic of neuropathic pain syndromes following partial nerve injury.

Calcitonin gene-related peptide gene expression in collagen-induced arthritis is differentially regulated in primary afferents and motoneurons: influence of glucocorticoids

Calcitonin gene-related peptide is involved in peripheral and spinal mechanisms of inflammatory pain. In this paper, we used collagen II-induced arthritis in the rat as a model to investigate the influence of chronic arthritic pain on calcitonin gene-related peptide gene expression in sensory and motor pathways. Additionally, we examined the effect of the glucocorticoid drug budesonide on arthritis-induced changes of calcitonin gene-related peptide expression and constitutive calcitonin gene-related peptide expression. Thirteen days after the immunization with native rat collagen type II rats developed a progressive and chronic polyarthritis which was scored with respect to the degree of swelling and/or redness of the paw and ankle joints. Budesonide significantly attenuated the extent of arthritis. Changes in calcitonin gene-related peptide expression were evaluated by semiquantitative in situ hybridization and immunocytochemistry on day 21 post-immunization. In sensory neurons of dorsal root ganglia of arthritic rats, a significant increase in calcitonin gene-related peptide messenger RNA and protein levels was seen. These increases were completely blocked by budesonide. Also in dorsal root ganglia of non-arthritic rats, budesonide had an effect, with reduced calcitonin gene-related peptide messenger RNA levels below constitutive concentrations. Image analysis of calcitonin gene-related peptide immunoreactivity revealed that changes in calcitonin gene-related peptide expression were due to alterations in calcitonin gene-related peptide expression levels rather than to de novo synthesis or changes in the numbers of calcitonin gene-related peptide expressing neurons. In spinal motoneurons of arthritic rats, marked decreases in calcitonin gene-related peptide messenger RNA and protein levels were measured. These reductions were attenuated by budesonide. The changes in calcitonin gene-related peptide expression in motoneurons correlated with the severity of arthritis in the ipsilateral hind paw. Budesonide had no effects on calcitonin gene-related peptide messenger RNA levels in motoneurons of non-arthritic rats. The opposite regulation of calcitonin gene-related peptide gene expression in primary sensory and spinal somatomotor pathways in collagen-induced arthritis suggests that calcitonin gene-related peptide plays a specific role in both chronic inflammatory pain and arthritis-induced motor dysfunction. The sensitivity of constitutive and inflammation-induced sensory calcitonin gene-related peptide expression to budesonide treatment may indicate that the beneficial effects of steroid treatment in inflammation is partly mediated by down-regulation of calcitonin gene-related peptide in sensory neurons involved in neurogenic inflammation.

Ultrastructural localization of increased neuropeptide immunoreactivity in the axons and cells of the gracile nucleus following chronic constriction injury of the sciatic nerve

Neuropeptide plasticity in the gracile nucleus is thought to play a role in the development of neuropathic pain following nerve injury. Two weeks after chronic constriction injury of adult rat sciatic nerve, galanin, neuropeptide Y and calcitonin gene-related peptide immunoreactivities were increased in fibers and cells in the gracile nucleus ipsilateral to injury. At the electron microscopic level, this increased neuropeptide immunoreactivity was localized in myelinated axons, boutons, dendrites, neurons and glial cells. Galanin-, neuropeptide Y- and calcitonin gene-related peptide-immunoreactive boutons were frequently presynaptic to dendrites of both immunoreactive and non-immunoreactive neurons. However, no neuropeptide Y, galanin and calcitonin gene-related peptide messenger RNA was detected in the injured side gracile nuclei by in situ hybridization. These results show that partial nerve injury to the sciatic nerve induces increases in the content of galanin, neuropeptide Y and calcitonin gene-related peptide immunoreactivities in synaptic terminals within the gracile nucleus, which suggests that there may be increased release of these neuropeptides following sensory or spontaneous stimulation of large-diameter primary afferents following partial nerve injury, perhaps one mechanism involved in neuropathic pain. We also show an apparent transfer of these neuropeptides to the cells of the gracile nucleus, both neurons and glial cells, an intriguing phenomenon of unknown functional significance.

Differential regulation of alpha- and beta-CGRP mRNAs within oculomotor, trochlear, abducens, and trigeminal motoneurons in response to axotomy

Spinal and cranial motoneurons express alpha- and beta-calcitonin gene-related peptide (CGRP) mRNAs constitutively at variable ratios, and these two mRNAs are differentially regulated following axotomy in spinal, facial, and hypoglossal motoneurons. The purpose of this study was to investigate the change in CGRP mRNA expression following nerve injury in oculomotor, trochlear, abducens, and trigeminal motor nuclei in which beta-CGRP mRNA is predominantly expressed under normal conditions. Using male Sprague-Dawley rats, either the left eyeball and the orbital contents including the bulbar muscles were removed, or the left masseter nerve was ligated and transected. The rats were allowed to survive for 1, 3, 7, 14, 28, 56 days following these procedures. The levels of mRNAs for alpha- and beta-CGRP and growth-associated protein (GAP)-43 were analyzed by in situ hybridization histochemistry using 35S-labeled oligonucleotide probes. Following nerve injury, the expression of alpha-CGRP mRNA rapidly increased on the directly-injured side in all of these nuclei. Thereafter, it gradually decreased and returned to about the control level at postoperative day 56 within oculomotor, trochlear, and abducens motoneurons, but it sustained at a high level within trigeminal motoneurons. The expression of beta-CGRP was quite variable among these nuclei, and significant changes were also seen on the side contralateral to the directly-injured side. These data indicate that the up-regulation of alpha-CGRP mRNA may be a common response of cranial motor neurons following axotomy even if the constitutive expression of beta-CGRP mRNA exceeds that of alpha-CGRP mRNA in these neurons.

Inducible and constitutive transcription factors in the mammalian nervous system: control of gene expression by Jun, Fos and Krox, and CREB/ATF proteins

This article reviews findings up to the end of 1997 about the inducible transcription factors (ITFs) c-Jun, JunB, JunD, c-Fos, FosB, Fra-1, Fra-2, Krox-20 (Egr-2) and Krox-24 (NGFI-A, Egr-1, Zif268); and the constitutive transcription factors (CTFs) CREB, CREM, ATF-2 and SRF as they pertain to gene expression in the mammalian nervous system. In the first part we consider basic facts about the expression and activity of these transcription factors: the organization of the encoding genes and their promoters, the second messenger cascades converging on their regulatory promoter sites, the control of their transcription, the binding to dimeric partners and to specific DNA sequences, their trans-activation potential, and their posttranslational modifications. In the second part we describe the expression and possible roles of these transcription factors in neural tissue: in the quiescent brain, during pre- and postnatal development, following sensory stimulation, nerve transection (axotomy), neurodegeneration and apoptosis, hypoxia-ischemia, generalized and limbic seizures, long-term potentiation and learning, drug dependence and withdrawal, and following stimulation by neurotransmitters, hormones and neurotrophins. We also describe their expression and possible roles in glial cells. Finally, we discuss the relevance of their expression for nervous system functioning under normal and patho-physiological conditions.

Galanin induced in sympathetic neurons after axotomy is anterogradely transported toward regenerating nerve endings

Peripheral neurons begin to express galanin after axotomy. When neurons in the superior cervical ganglion were axotomized near (about 2 mm) from the ganglion, galanin-like immunoreactivity (IR) was maximal within 72 h. Axotomy of neurons in the middle and inferior cervical ganglion complex (MICG), which could be performed 2 cm from the ganglia, led to an additional galanin increase 7 and 14 days later. This second increase was not accompanied by changes in galanin mRNA or the number of galanin-immunostained neurons. Galanin-IR was detectable in a postganglionic trunk of the MICG 2 days after axotomy. At this time, immunoreactive fibers were only seen near the lesion site, while later they were found throughout the trunk. The data suggest that galanin is actively transported toward the site of nerve crush/transection and that the second increase in galanin-IR found in the MICG may be due to a saturation of the axonal transport system.

Motoneuron survival and expression of neuropeptides and neurotrophic factor receptors following axotomy in adult and ageing rats

Three months after facial nerve transection, total numbers of motoneurons in the facial nucleus of six month (adult) Fischer 344 and Wistar rats were reduced to 83% and 75% of contralateral values, respectively (P < 0.05). This procedure in 22-26 month (ageing) Fischer 344 rats and Wistar rats resulted in a reduction of motoneuron numbers to 77% and 60% of the respective contralateral values (P < 0.05). Compared to adults, contralateral facial nuclei of aging Fischer 344 rats contained 10% fewer motoneurons (non-significant), while ageing Wistar rats had 22% fewer (P < 0.05). No significant changes were found in the proportion of surviving motoneurons expressing calcitonin gene-related peptide, galanin, receptor tyrosine kinase-C or the alpha subunit of the ciliary neurotrophic factor receptor. We conclude that ageing reduces facial motoneuron number and increases their vulnerability to axotomy in Wistar rats, but not in Fischer 344 rats. In neither strain, however, does the proportion of surviving motoneurons expressing the above neuropeptides or neurotrophic factor receptors change. This information may be relevant to those hypotheses of age-related neuronal degenerations which assume that decreased neurotrophic support renders ageing neurons more vulnerable to injury.

Expression of the genes for alpha-type and beta-type calcitonin gene-related peptide during postnatal rat brain development

In this study we have analysed the expression of the genes for both alpha-type and beta-type calcitonin gene-related peptide (CGRP) during postnatal development of the rat brain and compared it with the expression of CGRP-like immunoreactivity. At birth both alpha-type and beta-type CGRP messenger RNA were present in the parabrachial nucleus, inferior olive and motor nuclei (except for abducens nucleus), and only alpha-type CGRP messenger RNA in some posterior thalamic nuclei. As development advanced, new nuclei started to express either only alpha-CGRP gene (superior olive, parabigeminal, sagulum, and some hypothalamic and cranial thalamic nuclei) or both genes (abducens nucleus). In the inferior olive both genes were transiently expressed. Beta-CGRP messenger RNA disappeared by postnatal day 10 and alpha-CGRP messenger RNA by postnatal day 20. During the whole postnatal development beta-CGRP gene expression predominated over that of alpha-CGRP in the trigeminal and eye motor nuclei, while in the remainder nuclei alpha-CGRP messenger RNA was either the predominant isoform or the sole one. CGRP-like immunoreactivity, which does not distinguish between alpha-type and beta-type CGRP, was detected in those nuclei containing either alpha-CGRP messenger RNA or beta-CGRP messenger RNA. However, no CGRP messenger RNA was detected in areas such as superior colliculus, lateral pontine nucleus, pars reticulata of the substantia nigra, perifornical area, or zona incerta in which CGRP-like immunoreactivity was prominent. CGRP-like immunoreactivity, but not CGRP messenger RNA, was also transiently detected by postnatal day 5 in some cells of the globus pallidus. In the adult brain, the levels of alpha- and beta-CGRP messenger RNA as well as those of CGRP-like immunoreactivity were considerably reduced. This fact, similar to that of other growth- and development-associated factors, suggests a role for CGRP as a neuron-derived neurotrophic factor. The transient expression in neurons of the inferior olive, matching the period when climbing fibres and cerebellar cortex are developing, seems to support such an idea. The results of this study show that those nuclei expressing beta-CGRP gene also express alpha-CGRP gene. However, there are a number of nuclei that only express alpha-CGRP gene. On the other hand, CGRP-like immunoreactivity is detected in some nuclei which express no CGRP messenger RNA. It suggests that such nuclei express any CGRP-related protein (identified by the antibodies against CGRP) or, if they really contain CGRP protein, this is produced from undetectable amounts (using our in situ hybridization histochemistry procedure) of CGRP messenger RNA or it comes from other nuclei that connect with them in which CGRP protein is synthesized and then transferred.

Expression of beta-calcitonin gene-related peptide in axotomized rubrospinal neurons and the effect of brain derived neurotrophic factor

The mRNA levels for alpha- and beta-calcitonin gene-related peptide (CGRP) in rat rubrospinal neurons were studied by in situ hybridization 3, 7, 14, 28 and 56 days following cervical spinal hemisection. CGRP-like immunoreactivity (LI) in the rubrospinal neurons and the rubrospinal tract in cervical spinal cords were examined using immunohistochemistry. There was almost no signal for alpha- and beta-CGRP mRNAs and undetectable level of CGRP-LI in the rubrospinal neurons ipsilateral to cervical spinal hemisection (control side). Fourteen days after spinal hemisection, the rubrospinal neurons contralateral to cervical hemisection (axotomized side) showed CGRP-LI in their cell bodies, and CGRP containing fibers were observed in the lateral funiculi just proximal, but not distal, to the injury sites. In situ hybridization showed upregulation of beta-CGRP mRNA in a subpopulation of the rubrospinal neurons on the axotomized side. The proportion of beta-CGRP mRNA-expressing neurons reached its maximum (approximately 19%) 4 days following axotomy and slowly decreased to about 5% 56 days after axotomy. The percentage of alpha-CGRP mRNA-expressing neurons was much lower than that of beta-CGRP mRNA (maximum about 2.6% 4 days after axotomy) and not significantly different from the control side throughout the time period studied. These data indicate that axotomy induces de novo synthesis of the CGRP beta-subtype in rubrospinal neurons and that the beta-CGRP is transported to the injury site through the rubrospinal tract. In addition, we studied the effect of the intracerebral injections of brain derived neurotrophic factor (BDNF). BDNF treatment fully reversed the severe cell atrophy that followed axotomy and increased the number of neurons labeled for beta-CGRP mRNA, but did not increase the percentage of rubrospinal neurons expressing beta-CGRP mRNA. Thus, topical application of BDNF does not have direct modulatory effect on CGRP induction in axotomized neurons in the red nucleus.

Neuroanatomical localization, pharmacological characterization and functions of CGRP, related peptides and their receptors

Calcitonin generelated peptide (CGRP) is a neuropeptide discovered by a molecular approach over 10 years ago. More recently, islet amyloid polypeptide or amylin, and adrenomedullin were isolated from human insulinoma and pheochromocytoma respectively, and revealed between 25 and 50% sequence homology with CGRP. This review discusses findings on the anatomical distributions of CGRP mRNA, CGRP-like immunoreactivity and receptors in the central nervous system, as well as the potential physiological roles for CGRP. The anatomical distribution and biological activities of amylin and adrenomedullin are also presented. Based upon the differential biological activity of various CGRP analogs, the CGRP receptors have been classified in two major classes, namely the CGRP1 and CGRP2 subtypes. A third subtype has also been proposed (e.g. in the nucleus accumbens) as it does not share the pharmacological properties of the other two classes. The anatomical distribution and the pharmacological characteristics of amylin binding sites in the rat brain are different from those reported for CGRP but share several similarities with the salmon calcitonin receptors. The receptors identified thus far for CGRP and related peptides belong to the G protein-coupled receptor superfamily. Indeed, modulation of adenylate cyclase activity following receptor activation has been reported for CGRP, amylin and adrenomedullin. Furthermore, the binding affinity of CGRP and related peptides is modulated by nucleotides such as GTP. The cloning of various calcitonin and most recently of CGRP1 and adrenomedullin receptors was reported and revealed structural similarities but also significant differences to other members of the G protein-coupled receptors. They may thus form a new subfamily. The cloning of the amylin receptor(s) as well as of the other putative CGRP receptor subtype(s) are still awaited. Finally, a broad variety of biological activities has been described for CGRP-like peptides. These include vasodilation, nociception, glucose uptake and the stimulation of glycolysis in skeletal muscles. These effects may thus suggest their potential role and therapeutic applications in migraine, subarachnoid haemorrhage, diabetes and pain-related mechanisms, among other disorders.

The rat galanin-gene promoter: response to members of the nuclear hormone receptor family, phorbol ester and forskolin

We have cloned a rat genomic DNA fragment of approximately 12.5 kb. Nine kb of the cloned fragment lie in the 5'-flanking region of the gene and contain the promoter elements, while the remaining 3.5 kb contain the first four complete exons, the first three introns, and part of the fourth intron of the rat galanin gene. We have partially analysed some of the elements within the proximal sequence of this promoter which may influence the transcriptional regulation of the rat galanin gene. The rat galanin-gene promoter contains many regions which share homology with both the human and the bovine galanin genes and certain cis-elements appear to be conserved among the three species. In an attempt to test whether some of these elements are functional in the rat gene, transient transfection studies were carried out in selected cell lines. Estrogen, thyroid hormone and retinoic acid all showed a minimal degree of promoter stimulation when the rat galanin-gene promoter was co-transfected with the appropriate hormone receptors in Neuro 2A cells, while co-transfection of the nuclear orphan receptor ELP1 was able to stimulate transcription of a galanin promoter-driven reporter-gene construct (-374 bp) by 35-fold. The galanin promoter mediated a 3-4-fold induction in response to forskolin or TPA. Deletion of a 5-bp element at -50 bp from the start of transcription was able to greatly reduce the forskolin response but not the TPA response. These results point to several elements that may be targets of transcription factors linked to extracellular stimuli.

Selective upregulation of cytokine receptor subchain and their intracellular signalling molecules after peripheral nerve injury

Numerous studies have suggested that growth factors and cytokines play an important role in the survival of injured neurons and in neurite elongation. Therefore, intracellular signalling pathways activated by growth factors and cytokine receptors play an important role in neuronal survival or for the re-establishment of connection. Since the JAK (janus kinase)-STAT (signal transducers and activators of transcription) signal transduction pathway is known to play a major role in cytokine receptor signalling, we first examined regulation of JAK gene expression following peripheral nerve injury by in situ hybridization histochemistry. The rat hypoglossal nerve was axotomized unilaterally and the mRNA levels for JAK1, JAK2. JAK3 and TYK2 were examined in the hypoglossal nucleus at postoperative times ranging from 1 to 35 days. Among the JAK family members, JAK2 and JAK3 were substantially increased in injured hypoglossal motoneurons, whereas no significant increases were observed for JAK1 and TYK2. These changes were further confirmed by immunohistochemistry using antibodies specific to JAK2 and JAK3. In addition, we examined the JAK2 and JAK3 associated cytokine receptor components, IL-2R gamma and gp130, which are common to various cytokine receptors. Among these, gp130 immunostaining was upregulated after nerve injury. This was also confirmed by in situ hybridization. These results suggest that the injured neuron prepares the molecular machinery involved in certain cytokine receptor signalling pathways at an early phase of the regenerative process, accelerating for the neuron to respond to cytokines that may regulate survival and/or neurite elongation.

Expression of neurotransmitter genes in rat spinal motoneurons after chemodenervation with botulinum toxin

Botulinum toxin is widely used for the treatment of focal movement disorders, where chemodenervation is used to decrease hyperactivity in selected muscles. Beside a focal paresis, widespread effects on neuromuscular synaptic function have been demonstrated. However, reactions of motoneurons after neuromuscular chemodenervation without gross morphological lesions are largely unknown. Peripheral axotomy, in contrast, leads to profound changes in the expression of several genes, including those encoding neurotransmitters, in motoneurons. We therefore examined the expression of neurotransmitter genes in rat motoneurons six days after intramuscular botulinum toxin application in the right gastrocnemius muscle. Similar doses of botulinum toxin as used in human where injected. A focal bilateral increase in expression of the choline acetyltransferase gene and a widespread bilateral increase of the beta-calcitonin-gene-related peptide and the enkephalin genes was measured in motoneurons after botulinum toxin injection. Cholecystokinin had a lower expression after botulinum toxin injections. Growth-associated protein 43, nitric oxide synthase, somatostatin and proopiomelanocortin messenger RNA were not found in motoneurons of both groups. Our results demonstrate that changes in the expression of neurotransmitter genes in motoneurons also occur after chemodenervation but with different patterns to those found after mechanical nerve lesioning. These changes reflect focal and widespread modulative events. The knowledge of these events should lead to a better understanding of the focal paralysis and of the more widespread effects found in human after intramuscular injection of botulinum toxin.

alpha-CGRP mRNA levels in motoneurons innervating specific rat muscles

Along with acetylcholine, motoneurons express several neuromodulatory peptides. The most extensively studied of these peptides is calcitonin gene-related peptide (CGRP). CGRP modulates the biochemical, physiological and metabolic properties of skeletal muscle primarily through activation of membrane receptors. Virtually all motor pool contain motoneurons that are immunoreactive for CGRP. The purpose of this study was to determine the proportions of motoneurons that express alpha-CGRP in motor pools innervating muscles with different motor unit compositions. These include the soleus, extensor digitorum longus, tensor fascia latae and the diaphragm muscles as well as the spinal nucleus of the bulbocavernosus. The spinal nucleus of the bulbocavernosus provides innervation to the bulbocavernosus/levator ani muscle complex and the external anal sphincter muscle. The spinal nucleus of the bulbocavernosus contained the greatest proportion of alpha-CGRP mRNA-positive motoneurons, followed in descending rank order by the tensor fascia latae, the extensor digitorum longus, the soleus and the diaphragm motor pools. In addition, significant differences between motor pools were observed in the mean relative alpha-CGRP mRNA level among those motoneurons expressing alpha-CGRP. The highest mean relative alpha-CGRP mRNA level was observed in soleus and the extensor digitorum longus motor pools; followed in descending rank order by the tensor fascia latae, the diaphragm and the spinal nucleus of the bulbocavernosus. We have previously shown that muscle contractile inactivity increases the number of motoneurons that express alpha-CGRP and in the relative mRNA levels. The results of the present study suggest that the proportion of motoneurons within a motor pool that express alpha-CGRP may be closely related to the contractile activity (i.e. activation history) of the target muscle.

Increased expression of the alpha subunit of the ciliary neurotrophic factor (CNTF) receptor by rat racial motoneurons after neonatal axotomy and CNTF treatment

Expression by rat motoneurons of mRNAs for the alpha subunit of the ciliary neurotrophic factor receptor (CNTFR alpha), receptor tyrosine kinase-C (trkC), calcitonin gene-related peptide (CGRP) and galanin was studied by in situ hybridisation, 6d after rat facial nerve transection on postnatal day 1. Similar numbers of motoneurons in both injured and non-injured nuclei hybridised with all probes, despite a reduction in total numbers of motoneurons ipsilaterally. When ciliary neurotrophic factor (CNTF) was applied to the proximal nerve, twice as many motoneurons in the injured nucleus hybridised with the CNTFR alpha probe ipsilaterally compared to the non-injured nucleus, while motoneuronal loss was not evident. These results indicate that survival of motoneurons after neonatal axotomy and CNTF treatment is associated with increased CNTF receptor alpha expression.

Axotomy-induced loss of m2 muscarinic receptor mRNA in the rat facial motor nucleus precedes a decrease in concentration of muscarinic receptors

The abundance of muscarinic receptors and m2 muscarinic receptor mRNA in the facial nuclei of rats was evaluated by autoradiographic procedures at various times up to 14 days after transection of the right facial nerve. Receptors were labelled by in vitro incubation of brain sections with L-[3H]quinuclidinyl benzilate, while in situ hybridization with a 35S-labelled oligonucleotide was used to identify m2 muscarinic receptor mRNA in neighbouring sections. The right and left facial nuclei of non-operated control rats appeared equivalent in abundance of muscarinic receptors (359 +/- 8 versus 376 +/- 9 fmol per mg tissue, n = 5) and the presence of m2 mRNA. Axotomy had no effect on the concentration of receptors in the contralateral facial nucleus but caused a gradual loss of receptors from the ipsilateral side. No change was detected at 1 day after nerve transection, but a 23% decrease relative to the contralateral facial nucleus had occurred by 3 days. A maximum decrease of 51% was achieved by 1 week after nerve transection. By comparison, m2 mRNA was nearly eliminated from the ipsilateral facial nucleus at 1 day post-taxonomy and remained depleted for the duration of study. Previous work has established that no significant loss of motoneurons occurs within this period. Accordingly, it is postulated that axonal injury inhibits transcription of the m2 muscarinic receptor gene, resulting in a later decrease in muscarinic receptor protein expression.

Leukaemia inhibitory factor induced in the sciatic nerve after axotomy is involved in the induction of galanin in sensory neurons

Dramatic changes occur in neuropeptide expression in sensory and sympathetic neurons following axonal injury. Based on the finding that the cytokine leukemia inhibitory factor (LIF) plays an important role in mediating these changes in sympathetic neurons, its participation in triggering changes in sensory neurons was examined. By the use of transgenic mice in which the LIF gene had been knocked out, LIF was found to contribute to the induction of galanin expression in dorsal root ganglia (DRG) after sciatic nerve lesion. On the other hand, two other neuropeptide changes that occur in DRG under these conditions, the reduction of substance P and induction of neuropeptide Y, were independent of LIF expression. In the sympathetic superior cervical ganglion, transection of the postganglionic nerves close to the ganglion resulted in a rapid induction of LIF mRNA in the ganglion and in the lesioned nerve trunk. In contrast, transection of the sciatic nerve close to or distant from the DRG caused a rapid induction of LIF mRNA in the lesioned nerve, but not in the DRG. DRG were capable of making substantial amounts of LIF mRNA when placed in explant cultures, but, in vivo, only a slight induction was found even when both central and peripheral nerve processes of these sensory neurons were transected. These latter observations suggest that, in contrast to the superior cervical ganglia, the DRG environment inhibits the lesion-induced expression of LIF in vivo and/or explanted DRG produce stimulatory signals not found in vivo. Together with the data on the induction of galanin, these observations provide evidence that LIF, generated at a site at some distance from the ganglion, is involved in triggering part of the cell body reaction in sensory neurons.

Chemical sympathectomy and postganglionic nerve transection produce similar increases in galanin and VIP mRNA but differ in their effects on peptide content

Large changes in neuronal gene expression occur in adult peripheral neurons after axonal transection. In the rat superior cervical ganglion, for example, neurons that do not normally express vasoactive intestinal peptide (VIP) or galanin do so after postganglionic nerve transection. These effects of axotomy could result from a number of aspects of the surgical procedure. To test the idea that the important variable might be the disconnection of axotomized neuronal cell bodies from their target tissues, we examined the effects of producing such a disconnection by means of the compound 6-hydroxydopamine (6-OHDA), a neurotoxin that causes degeneration of sympathetic varicosities and avoids many of the complications of surgery. Two days after 6-OHDA treatment, VIP and galanin immunoreactivities had increased two- and 40-fold, respectively. Nevertheless, these increases were substantially smaller than the 30- and 300-fold changes seen after surgical axotomy. When expression of VIP and galanin was examined at the mRNA level, however, comparable increases were found after either procedure. The results indicate that chemical destruction of sympathetic varicosities produces an equivalent signal for increasing VIP and galanin mRNA as does axonal transection. The differences in the neuropeptide levels achieved suggests that peptide expression after nerve transection is regulated both at the mRNA and protein levels.

Target-dependent plasticity of galanin and vasoactive intestinal peptide in the rat superior cervical ganglion after nerve lesion and re-innervation

The expression of the neuropeptides galanin and vasoactive intestinal peptide (VIP) is increased in subpopulations of sympathetic neurons after axotomy of the rat superior cervical ganglion. We investigated whether postganglionic neurons innervating different targets show a prevalence for any of the two peptides in response to carotid nerve lesion. Before the respective postganglionic axons were crushed close to the ganglion, postganglionic neurons projecting either to the iris (through the internal carotid nerve) or to the submandibular gland (through both carotid branches) were identified by the retrograde tracer Fast Blue. Galanin and VIP immunoreactivities were demonstrated two and 30 days after crush and after successful regeneration of the lesioned neurons (60 days). In control ganglia, both peptides were detected in a few gland- but not in iris-projecting neurons. However, two days after crush of the respective carotid nerves, 14% of neurons within the iris and 46% within the gland population were immunoreactive for galanin. The percentage of neurons immunoreactive for VIP was significantly lower in both populations: only 3.5% of neurons projecting to the iris and 23% of the gland-projecting neuron population exhibited this peptide. After 30 days, the percentage of galanin- and VIP-positive neurons projecting to the submandibular gland was reduced (24% and 5.7%, respectively), whereas the proportion of galanin-immunoreactive neurons further increased within the iris population (55%), indicating that some neurons express galanin at later stages after the lesion. At 60 days after the crush, the percentage of galanin- or VIP-immunoreactive neurons had decreased to control levels within those neuron populations that re-innervated the iris or submandibular gland, although the total number of neurons exhibiting galanin or VIP was still increased within the ganglion, suggesting that re-establishment of target contact may play a role in down-regulation of both peptides.

Chromogranin mRNA levels in the brain as a marker for acute and chronic changes in neuronal activity: effect of treatments including seizures, osmotic stimulation and axotomy in the rat

Chromogranin/secretogranins are a family of acidic, soluble proteins with a widespread distribution in secretory vesicles of endocrine and nervous tissues. The effects of experimental stimuli of differing duration and intensity on chromogranin B and secretogranin II mRNA levels in relevant areas of the rat brain were examined by in situ hybridization histochemistry using 35S-labelled oligonucleotides. Effects of two 'chronic stimulation' paradigms were studied - the effect of 4 days of water or food deprivation on mRNA levels in the hypothalamus and the effect of unilateral cervical vagotomy on transcript levels in the dorsal vagal complex 1, 2 and 7 days after surgery. After 4 days of water deprivation secretogranin II mRNA was significantly increased in supraoptic nucleus (366 +/- 21% of control, P < 0.01), the magnocellular paraventricular nucleus (209 +/- 20% of control, P < 0.01) and the parvocellular paraventricular nucleus (147 +/- 6% of control, P < 0. 05) after 4 days of food deprivation. Seven days after unilateral cervical vagotomy, secretogranin II and chromogranin B mRNA levels were markedly decreased in the ipsilateral dorsal motor nucleus of the vagus (25 +/- 4 and 47 +/- 8% of contralateral values respectively, P < 0.01). Rapid changes in chromogranin mRNA were also detected following shorter duration 'acute stimulation' - in the hypothalamus after hypertonic saline injection, in the hippocampus after electrical stimulation-induced kindled seizures, and in the cerebral cortex after unilateral craniotomy. A large increase in secretogranin II mRNA was detected in the supraoptic nucleus (202 +/- 25% of control, P < 0.01) and the magnocellular paraventricular nucleus (168 +/- 29% of control, P < 0.05) 3 h after a single intraperitoneal injection of hypertonic (1.8 M) saline. Markedly increased levels of secretogranin II (125-160% of control) and chromogranin B (140-230% of control) mRNA were observed in granule cells of the dentate gyrus 0.5-2 h after amygdaloid stimulation-induced seizures. A moderate increase in secretogranin II mRNA (144 +/- 11% of contralateral side, P < 0.01) was found in the underlying cerebral cortex 2.5 h after unilateral craniotomy. These results indicate that measurement of changes in chromogranin mRNA, particularly secretogranin II, is a useful means of assessing both rapid and long-lasting increases and decreases in neuronal activity and, in contrast to immediate early gene mRNA levels, may better reflect specific changes in neuronal secretory activity associated with transmitter/peptide release.

Localization of preprogalanin messenger RNA in rat brain: identification of transcripts in a subpopulation of cerebellar Purkinje cells

Galanin, a 29 amino acid peptide, is widely distributed throughout both the peripheral and central nervous systems and is thought to be involved in multiple physiological functions including smooth muscle relaxation, stimulation of feeding, blood pressure regulation, control of hormone secretion and modulation of nociception. Galanin has been shown to co-exist with several neurotransmitters throughout the neuroaxis and in some cases to modify their presynaptic and postsynaptic actions. In the present study, the anatomical distribution of preprogalanin messenger RNA in rat brain was examined by in situ hybridization histochemistry using specific 35S-labelled oligonucleotide probes. Neurons expressing preprogalanin messenger RNA were found throughout the brain and were particularly abundant in the hypothalamus. High densities of preprogalanin messenger RNA-positive neurons were found in the anteroventral preoptic, supraoptic, paraventricular and dorsomedial nuclei of the hypothalamus, in the locus coeruleus and in the nucleus of the solitary tract. Moderate densities of preprogalanin messenger RNA-positive cells were apparent in the periventricular and arcuate nuclei of the hypothalamus, in the dorsal raphe and dorsal cochlear nuclei. Low densities of preprogalanin messenger RNA-expressing neurons were observed in the piriform cortex, medial septum and the retrochiasmatic area. These findings are consistent with results of previous in situ localization studies of preprogalanin messenger RNA and also with studies reporting the distribution of galanin-like immunoreactivity in rat brain. A novel finding, however, was the detection of preprogalanin messenger RNA in Purkinje cells in the caudal cerebellar vermis (lobules 6 to 10) and the flocculus and paraflocculus of the lateral hemispheres of the cerebellum. Galanin is presumably co-localized in these cells with GABA, which is normally present in Purkinje cells and possibly with tyrosine hydroxylase, which has recently been detected in a similar subpopulation of cerebellar Purkinje cells in both rat and mouse. Thus, the present study reveals a previously unreported site of galanin gene expression in the cerebellum which represents a novel, putative site of action for galanin to add to its already varied physiological roles.

Differential expression of alpha-CGRP and beta-CGRP genes within hypoglossal motoneurons in response to axotomy

In this study we have analysed, by in situ hybridization, the expression of the genes for both alpha-CGRP and beta-CGRP in hypoglossal motor nuclei following transection of the left hypoglossal nerve. Our results show that the gene for alpha-CGRP displays a peculiar sequence of regulation (a successive up-down-up-recovery sequence) within ipsilateral hypoglossal motoneurons in response to axotomy. It is initially up-regulated, then down-regulated (displaying mRNA levels below basal), and later again up-regulated before recovery. By contrast, the gene for beta-CGRP displays a successive and distinct up-down-recovery sequence of regulation (it does not display a second increase in mRNA production). The first up-regulation of the alpha-CGRP gene occurs just during the early period of perineuronal glial reaction and the second up-regulation just during the period of delayed astrocyte reaction and muscle reinnervation. Because alpha-CGRP is a neuron-derived factor for many types of cells, including astrocytes and skeletal myocytes, our results suggest that the pleiotropic alpha-CGRP may be a motoneuron-derived trophic signal for both glial and skeletal muscle cells in order to maintain the motoneuron itself and, in consequence, might be of therapeutic interest in treating degenerative disease of motoneurons. beta-CGRP might be redundant within the hypoglossal motoneurons.

Calcitonin gene-related peptide and ATP induce immediate early gene expression in cultured rat microglial cells

Factors affecting gene expression in microglial cells were investigated using the induction of immediate early genes in cultured microglia as a model. In particular, the actions of calcitonin gene-related peptide (CGRP) and ATP, both of which have been proposed as signalling molecules in the activation of glial cells, were evaluated using Northern blotting and in situ hybridization methods. In the presence of CGRP, c-fos and junB mRNAs accumulated in microglial cultures, whereas no significant change in c-jun and TIS11 mRNAs occurred. A similar pattern of immediate early gene activation was obtained when adenylate cyclase was stimulated with forskolin. CGRP also stimulated cyclic AMP accumulation with a half-maximal effect in the range 2-5 nM, suggesting a possible role for cyclic AMP as a mediator of the effects of CGRP on gene expression. In contrast to the selective induction of c-fos and junB by CGRP and forskolin, ATP led to the accumulation of all four immediate early genes studied, i.e., c-fos, junB, c-jun, and TIS11. Similar results were obtained when protein kinase C was stimulated with phorbol ester indicating that the induction of immediate early gene expression by ATP and CGRP involves different intracellular mechanisms. The action of ATP was mimicked by ADP and the poorly hydrolyzable analogues, ADP beta S and 2-methylthio ATP, but not by beta, gamma-methylene ATP, AMP, or adenosine, indicating that the receptor mediating the actions of ATP on microglial gene expression is probably of the P2Y-purinoreceptor type. The results suggest roles for CGRP and ATP as transcriptional activators in microglial cells.

Galanin expression in carotid body afferent neurons

The present study examined expression and plasticity of the neuropeptide, galanin, in carotid body afferent neurons in the petrosal ganglion of the adult rat. The pattern of galanin expression was compared with that of tyrosine hydroxylase, a selective marker of dopaminergic carotid body afferents in the petrosal ganglion. In normal animals, only 3% of tyrosine hydroxylase-containing petrosal ganglion neurons co-expressed galanin. Retrograde labeling studies, in which FluoroGold was injected into the vascularly isolated carotid body, demonstrated that all tyrosine hydroxylase-positive-galanin-positive cells in the petrosal ganglion project to this target. In addition, however, we unexpectedly found that galanin expression was markedly increased in the petrosal ganglion following FluoroGold injection into the carotid body. On the other hand, tyrosine hydroxylase expression was unchanged, indicating that monoaminergic and peptidergic traits can be differentially regulated in these cells. In summary, these data demonstrate that monoaminergic chemoafferent neurons can co-express a peptidergic trait, similar to catecholaminergic neurons within the central and autonomic nervous systems, and that these cells retain the potential for phenotypic plasticity in adulthood.

Neuropeptide messenger plasticity in the CNS neurons following axotomy

Neuronal peptides exert neurohormonal and neurotransmitter (neuromodulator) functions in the central nervous system (CNS). Besides these functions, a group of neuropeptides may have a capacity to create cell proliferation, growth, and survival. Axotomy induces transient (1-21 d) upregulation of synthesis and gene expression of neuropeptides, such as galanin, corticotropin releasing factor, dynorphin, calcitonin gene-related peptide, vasoactive intestinal polypeptide, cholecystokinin, angiotensin II, and neuropeptide Y. These neuropeptides are colocalized with "classic" neurotransmitters (acetylcholine, aspartate, glutamate) or neurohormones (vasopressin, oxytocin) that are downregulated by axotomy in the same neuronal cells. It is more likely that neuronal cells, in response to axotomy, increase expression of neuropeptides that promote their survival and regeneration, and may downregulate substances related to their transmitter or secretory activities.

Galanin expression in sympathetic ganglia after partial axotomy is highly localized to those neurons that are axotomized

The neuropeptide phenotype of adult sympathetic neurons changes dramatically after postganglionic nerve transection. Studies, thus far, have been done on the superior cervical ganglion; however, one limitation of this preparation is that it is necessary to transect the postganglionic axons quite close to the ganglion. In the present study, we examined the effects of axonal damage on galanin-like immunoreactivity in the middle and inferior cervical ganglion complex. With these ganglia, it is possible to transect postganglionic axons at a considerable distance from their cell bodies and, therefore, to examine the extent to which local tissue damage, rather than specific axonal transection, is required for these changes in neuropeptide phenotype to occur. The anatomy of this system also allowed us to determine the extent to which the changes in galanin expression are restricted to those neurons that have been axotomized. The axons of a small population of the neurons in the middle and inferior cervical ganglia complex project into the cervical sympathetic trunk. Within two days after this trunk was transected, there was an increase in the level of galanin-like immunoreactivity in the complex and in the number of immunostained principal neurons. These neurons were concentrated primarily in the most rostral part of the complex. An increase in galanin-like immunoreactivity also occurred in response to the systemic administration of the sympathetic neurotoxin 6-hydroxydopamine. In that case, many more neurons were affected than after transection of the cervical sympathetic trunk, and the neurons were distributed evenly throughout the ganglion complex.(ABSTRACT TRUNCATED AT 250 WORDS)

Phagocytic microglia during delayed neuronal loss in the facial nucleus of the rat: time course of the neuronofugal migration of brain macrophages

The injection of Fluoro-Gold (FG) into the whisker pad of rats yields a stable fluorescent labeling of the motoneurons in the lateral facial subnucleus. Following resection of 8-10 mm of the facial nerve, the microglia phagocytose the FG-preloaded neurons and assume the label. Employing this vital labeling of microglia in situ we studied the fate of same after completion of phagocytic activity. Starting at 56 days post resection (DPR) the FG-labeled microglia spread out from the lateral facial subdivision and invaded the entire facial nucleus. The quantitative analysis of this redistribution of the fluorescent marker revealed a prolonged increase in the number of labeled microglia strictly proportional to the delayed loss of neurons. The differentiation between microglia and shrunken neurons was performed with the new method of immunoquenching: the staining of vibratome sections with anti-rat neuron-specific enolase (NSE) combined with an ABC-HRP kit and DAB as detector totally extinguished (quenched) all fluorescence from the pre-labeled facial motoneurons. The fluorescent microglia were additionally stained with GSA I-B4 and OX-42, which should completely quench all fluorescence in the section. However, a few small round cells, always closely opposed to neuronal perikarya, still fluoresced. These NSE-negative, GSA I-B4 and OX-42 negative, but fluorescent cells may represent a new, immunologically uncharacterized microglial cell type, that participates in neuronophagia.