Pharmacological aspects of the influence of melanocortins on the formation of regenerative peripheral nerve sprouts

The role of melanocortins and their receptors in inflammatory processes, nerve regeneration and nociception

The melanocortins are a family of bioactive peptides derived from proopiomelanocortin. Those peptides, included among hormones and comprising ACTH, alpha-MSH, beta-MSH and gamma-MSH, are best known mainly for their physiological effects, such as the control of skin pigmentation by alpha-MSH, and ACTH effects on pigmentation and steroidogenesis. Melanocortins are released in various sites in the central nervous system and in peripheral tissues, and participate in the regulation of multiple physiological functions. They are involved in grooming behavior, food intake and thermoregulation processes, and can also modulate the response of the immune system in inflammatory states. Research of the past decade provided evidence that melanocortins could elicit their diverse biological effects by binding to a distinct family of G protein-coupled receptors with seven transmembrane domains. To date, five melanocortin receptor genes have been cloned and characterized. Those receptors differ in their tissue distribution and in their ability to recognize various melanocortins. These advances have opened up new horizons for exploring the significance of melanocortins, their ligands and their receptors for a variety of important physiological functions. We reviewed the origin of MSH peptides, the function and distribution of melanocortin receptors and their endogenous and exogenous ligands and the role of melanocortins and their receptors in inflammatory processes, nerve regeneration and nociception. Moreover, we analyzed their interaction with opioid peptides and finally, we discussed the postulated role of the melanocortin system in pain transmission at the spinal cord level.

Mast cell subsets and neuropeptides in leprosy reactions

The immunohistochemical identification of neuropeptides (calcitonin gene-related peptide, vasoactive intestinal polypeptide, substance P, alpha-melanocyte stimulating hormone and gamma-melanocyte stimulating hormone) quantification of mast cells and their subsets (tryptase/chymase-immunoreactive mast cells = TCMC and tryptase-immunoreactive mast cells = TMC) were determined in biopsies of six patients with leprosy reactions (three patients with type I reaction and three with type II). Biopsies were compared with those taken from the same body site in the remission stage of the same patient. We found a relative increase of TMC in the inflammatory infiltrate of the reactional biopsies compared to the post-reactional biopsy. Also, the total number of mast cells and the TMC/TCMC ratio in the inflammatory infiltrate was significantly higher than in the intervening dermis of the biopsies of both periods. No significant difference was found regarding neuroptide expression in the reactional and post-reactional biopsies. The relative increase of TMC in the reactional infiltrates could implicate this mast cell subset in the reported increase of the immune response in leprosy reactions.

Expression of melanocortin receptors and pro-opiomelanocortin in the rat spinal cord in relation to neurotrophic effects of melanocortins

Although neurotrophic effects of alpha-melanocyte-stimulating hormone (alpha-MSH) are well established, the mechanism underlying these effects is unknown. To identify candidate components of the signaling system that may mediate these effects, in the present study rat spinal cord, dorsal root ganglia, sciatic nerve and soleus muscle were analysed for the expression of the neural MC3, MC4 and MC5 receptors and for the expression of the melanocortin precursor pro-opiomelanocortin (POMC). In rat lumbar spinal cord, the MC4 receptor was the only MC receptor subtype for which mRNA was detectable using RNAse protection assays. In situ binding studies using 125I-NDP-MSH, a synthetic alpha-MSH analogue, demonstrated MC receptor protein in the rat spinal cord, predominantly localised in substantia gelatinosa and area X, surrounding the central canal. Furthermore, POMC mRNA was demonstrated in rat spinal cord and dorsal root ganglia. These findings suggest a functional melanocortin system in the rat spinal cord, that might be involved in peripheral nerve repair. Regulation of POMC or MC receptor transcripts does not appear to be involved in the response to peripheral nerve crush in rats, since no change in mRNA expression patterns was detected after sciatic nerve crush, using quantitative RNAse protection assays. Nevertheless, subtle changes in melanocortin receptor binding did occur postsurgically in several regions of the spinal cord in both sham-operated and sciatic nerve-lesioned rats. The robust expression of MC receptor protein in spinal cord regions that are generally associated with nociception suggests a potentially broader involvement of endogenous melanocortins in spinal pathways which mediate the responses to peripheral injury, in addition to any direct melanocortin effects on sprouting and neurite outgrowth.

GAP-43 mRNA and calcitonin gene-related peptide mRNA expression in sensory neurons are increased following sympathectomy

Sympathectomy has been shown to result in an increased density of fibers immunoreactive for sensory peptides in peripheral targets innervated by both sensory and sympathetic neurons, providing evidence for functional interactions between sympathetic and sensory systems. These findings provided the background for examining the hypothesis that axonal outgrowth is induced from sensory neurons following sympathectomy. We examined the expression of GAP-43 mRNA, a specific marker for axonal outgrowth, in cervical (C3, C7, C8) and thoracic (T1, T2) dorsal root ganglia (DRG) of the rat following bilateral removal of the superior cervical ganglion, to assess whether the described increases in peptidergic afferent fibers reflected axonal outgrowth. In situ hybridization was used with 35S labeled riboprobes complementary to GAP-43 mRNA, and to calcitonin gene-related peptide (CGRP) mRNA, a marker for a major subset of thin-fiber sensory neurons. The density of GAP-43 mRNA nearly doubled by 18 h following sympathectomy and reached a threefold increase by 3 days. By 45 days following surgery, the GAP-43 mRNA level was still nearly twice that of normal animals, CGRP immunoreactivity was also examined: the density of fibers in the iris and cornea of sympathectomized animals was considerably greater from two weeks to 45 days following surgery, than in sham-operated controls. Concomitantly, there was a slight but significant increase in CGRP mRNA expression in T1 and C3 DRG 14 days postsympathectomy. Quantitative computerized image analysis demonstrated that GAP 43 mRNA expression in sympathectomized animals was 1.5 times greater in medium-sized DRG neurons and almost fourfold greater in small DRG neurons than in control rats. These results indicate that sympathetic denervation elicits axonal outgrowth in the population of sensory neurons that give rise to the small unmyelinated and thinly myelinated axons of peripheral nerves.

Beneficial effects of the melanocortin alpha-melanocyte-stimulating hormone on clinical and neurophysiological recovery after experimental spinal cord injury

OBJECTIVE

Melanocortins, peptides related to melanocyte-stimulating hormone (MSH) and corticotropin (ACTH), exhibit neurotrophic and neuroprotective activity in several established models of peripheral and central nervous system damage. The beneficial effects of melanocortins on functional recovery after experimental brain damage and central demyelinating diseases have prompted us to investigate alpha MSH treatment in a weight drop model of traumatic spinal cord injury in rats.

METHODS

In two independent randomized blinded experiments, treatment with either alpha MSH (75 micrograms/kg of body weight administered subcutaneously every 48 h for 3 weeks after trauma) or single high-dose (30 mg/kg, 30 min after injury) methylprednisolone was compared with saline treatment in rats subjected to a moderately severe 20-gcm weight drop injury. Spinal cord function was monitored using behavioral, electrophysiological, and histological parameters.

RESULTS

In both experiments, alpha MSH significantly improved recovery, as illustrated by Tarlov scores, thoracolumbar height, and amplitude of rubrospinal motor evoked potentials. The magnitude of the alpha MSH effect on motor performance was comparable with the one observed after treatment with methylprednisolone.

CONCLUSION

The reproducible neurological and electrophysiological improvement in spinal cord function of animals treated with alpha MSH suggests a new lead in the treatment of traumatic spinal cord injury.

Alpha-MSH stimulates neurite outgrowth of neonatal rat corticospinal neurons in vitro

Peptides related to melanocortin (alpha MSH) and corticotropin (ACTH), collectively termed melanocortins, exert trophic effects on the outgrowth of neurites from peripheral and central nervous system in vitro. Here we study the neurite outgrowth promoting effect of alpha-MSH on corticospinal (CS) neurons in vitro. Corticospinal neurons were identified in cell culture of neonatal rat cortex by immunostaining of cholera toxin subunit B (CTB), retrogradely transported from the cervical parts of the spinal cord. The CTB-immunoreactive neurons represent a small percentage (3-5%) of the total cell population after 72 h in vitro. The axons or dendrites of cortical and CTB-labelled layer V neurons were visualized using antibodies against axon- or dendrite-specific markers and measured using a semi-automatic quantification device. Here we report that alpha-MSH stimulates axonal as well as dendrite outgrowth from both total and CTB-labelled neurons with a bell-shape response curve. Axonal outgrowth of CTB-labelled neurons was dose-dependently stimulated with a maximal effect of 50% at 10(-10) M alpha-MSH. The maximal effect for stimulation of axon outgrowth for the total cortex population was observed at 10(-8) M alpha-MSH. In addition dendrite outgrowth of both total and CTB-labelled neurons is stimulated in a dose-dependent manner with maximal effects (varying between 46 and 48%) at 10(-8) M alpha-MSH. Explanations in the shift for the optimal alpha-MSH concentration for stimulation of axonal outgrowth of CTB-labelled layer V neurons as compared to total cortex neurons are discussed.

The ACTH(4-9) analog ORG 2766 and recovery after brain damage in animal models--a review

Treatment with adrenocorticotrophic hormone (ACTH), as well as with ACTH fragments and analogues, can influence behaviour of animals and humans. Furthermore it facilitates recovery of damaged peripheral nervous tissue. The question whether ACTH/MSH peptides affect recovery processes after injury to the central nervous system as well is addressed in the present review. The effects of administration of the ACTH(4-9) analog ORG 2766 after brain lesions has been studied frequently. However, the interpretation of the available data is confused by the variability of the results. Several factors can be identified which influence the efficacy of the peptide: (i) not all behavioural tests are equally suitable to reveal a peptide effect on behavioural recovery; (ii) the affected brain area; (iii) whether cell bodies or terminals are affected; (iv) the post-operative housing conditions; and (v) the onset and duration of peptide administration. Two possible explanations of peptide efficacy on functional recovery are considered: first, the peptide may accelerate spontaneously occurring recovery processes and second, the peptide may induce compensatory mechanisms underlying functional recovery without recuperation of the damaged neurons. These compensatory mechanisms seem to rely mainly on enhanced non-selective attention by activation of limbic structures. It is as yet unknown to which receptor system ORG 2766 binds; the analog lacks affinity for the known melanocortin (MC) receptors in brain, yet ORG 2766 is able to modulate the activity of endogenous opioids and the NMDA-receptor. A modulating influence of the peptide on NMDA-receptor activity might indirectly account for both enhanced attention--with ensuing behavioural recovery--and the acceleration of spontaneous recovery.

Melanocortins and opioids modulate early postnatal growth in rats

This study was undertaken to investigate the effects of melanocortins and opioids on rat early postnatal body and organ growth. Among melanocortins tested desacetyl-alpha-melanocyte-stimulating hormone (alpha-MSH) at dosages of 0.3 and 3 micrograms/g/day was effective in stimulating neonatal growth with a weight gain of 7 and 5.6%, respectively, after 2 weeks of treatment. Likewise, a weight rise of 4.2 and 3% was obtained with 3 micrograms/g/day of both alpha-MSH and Nle4-D-Phe7 alpha-MSH. As far as opioids were concerned, while N-acetyl-beta-endorphin (beta-End) was ineffective, the activity of beta-End was dependent on dosage. Indeed, newborns treated with 0.03 microgram/g/day showed a slight, but significant, increase in weight, whereas a marked decrease in growth followed treatment with 0.3 and, mainly, 3 micrograms/g/day, with a final weight loss of 3.4 and 5.5%, respectively. All melanocortins exerted a positive action on muscular and brain trophism and, in addition, desacetyl-alpha-MSH also induced a rise of fat deposits. On the contrary, while the 0.03 microgram/g/day beta-End dose caused an increase in muscular and brain weight, the higher dosages of the opioid were detrimental, not only for muscle and brain, but also for both liver and spleen weight. A slight, although significant (P < 0.05), enhancement of serum dehydroepiandrosterone sulfate (DHEAS) level was found after the injection of 0.3 microgram/g desacetyl-alpha-MSH, whereas both the 0.3 and 3 micrograms/g doses of desacetyl-alpha-MSH and the 3 micrograms/g dose of alpha-MSH determined the rise of plasma androstenedione (P < 0.05). All tested melanocortins and opioids failed to modify the concentrations of corticosterone. Our results suggest that melanocortins and opioids can modulate early postnatal growth in rats either by direct or indirect mechanisms.

Effect of cisplatin and ACTH4-9 on neural transport in cisplatin induced neurotoxicity

Cisplatin causes a dose limiting peripheral neuropathy, however, the biological mechanism by which this occurs is unknown. Murine N1E.115 neuroblastoma cells and neural crest derived pigment cells have similar transport mechanisms to human neural cells and were used to study the effect of cisplatin on cellular transport. Cisplatin reduced both the number and velocity of organelles moving in the anterograde and retrograde direction, compared to control cells. Cisplatin induced inhibition of transport was prevented by the simultaneous administration of ACTH4-9. This analog alone had no effect on N1E.115 organelle, or erythrophore granule, movement. In both N1E.115 and pigment cells cisplatin inhibited transport within 1 h of exposure to the drug. The degree of inhibition did not increase insignificantly if pigment cells were incubated in cisplatin for 48 h compared to acute exposure. Microtubules in both pigment cells and N1E.115 neurites retained their structural integrity suggesting that factors other than changes in gross microtubule morphology are responsible for cisplatin neurotoxicity. Cisplatin reduces N1E.115 neurite growth after 48 h incubation but this can be prevented by simultaneous use of ACTH4-9. This study demonstrates for the first time that cisplatin and ACTH4-9 affect fast axonal transport by specific mechanisms which appear related to their observed neurotoxic and neuroprotective roles, respectively.

Melanocortin analogue Org2766 binds to rat Schwann cells, upregulates NGF low-affinity receptor p75, and releases neurotrophic activity

Binding of the stable melanocortin(4-9) analogue, Org2766 [Met(O2)-Glu-His-Phe-D-Lys-Phe] to cultured rat sciatic nerve Schwann cells was demonstrated using a biotinylated derivative in semiquantitative histochemical and CELISA assays. Org2766 bound to Schwann cells, but not to fibroblasts, and was displaced maximally by unlabeled Org2766, alpha-MSH and ACTH(1-24). Displacement of Org2766 from the binding sites was considerably reduced by N- and C-truncation of the peptide. Specific binding of Org2766 was also demonstrated in the immortal rat Schwann cell line SCL4.1/F7 and was more pronounced in cells displaying a differentiated morphology. Org2766 and alpha-MSH increased cyclic AMP content of Schwann cells but neither stimulated DNA synthesis when applied alone. However, in the presence of a priming (subthreshold) concentration of the mitogen, cholera toxin, Org2766 and alpha-MSH caused a delayed increase in DNA synthesis. Org2766 did not modulate the expression of several differentiation-related Schwann cell markers. However, Org2766 increased immunoreactivity for p75 low-affinity NGF receptor on Schwann cells and evoked the release of neurotrophic factor(s) that synergized with NGF in stimulating neurite outgrowth in rat DRG neurons. The results indicate that Schwann cells are a primary target for the action of Org2766 and provide evidence for an indirect mechanism by which melanocortins might stimulate neurite sprouting in regenerating peripheral nerve axons.

ACTH-related peptides: receptors and signal transduction systems involved in their neurotrophic and neuroprotective actions

ACTH-related peptides are promising neurotrophic and neuroprotective agents, as demonstrated in many in vivo and in vitro studies. They accelerate nerve repair after injury, improving both sensor and motor function. Furthermore, ACTH-related peptides have neuroprotective properties against cisplatin- and taxol-induced neurotoxicity, they improve neuronal function in animals with neuropathy due to experimental diabetes, and they prevent degeneration of myelinated axons in rats suffering from experimental allergic neuritis, a model of peripheral demyelinating neuropathy. Studies in neuronal cultures have corroborated these clinical observations and serve to investigate the mechanism of action of the ACTH-related peptide effects. This paper reviews both in vitro and in vivo effects and emphasizes the mechanism of action. Recent data on melanotrophic receptors and signal transduction systems will be discussed in this context.

Pharmacological evidence for the involvement of endogenous alpha-MSH-like peptides in peripheral nerve regeneration

The possible involvement of alpha-MSH-like peptides in the regenerative response of peripheral nerves was investigated with a competitive antagonist of alpha-MSH, the synthetic hexapeptide [D-Trp7,Ala8,D-Phe10)alpha-MSH(6-11)-amide. Subcutaneous administration of the alpha-MSH antagonist during the first 10 days following sciatic nerve crush significantly decreased functional recovery as measured by the foot flick withdrawal test and the walking pattern analysis. Hypophysectomy delayed both the initial sprouting response and the outgrowth rate after major caudal nerve crush. When hypophysectomized rats were treated with the alpha-MSH antagonist, a further delay in initial sprouting was observed, whereas the outgrowth rate of nerve fibers was not affected. These results suggest that 1) endogenous alpha-MSH-like peptides stimulate nerve outgrowth following peripheral nerve injury and 2) alpha-MSH-like peptides derived from a source other than the pituitary may contribute to the physiological stimulus leading to sprouting.

The neurotrophic peptide Org 2766 does not influence the expression of the immediate early gene c-fos following sciatic nerve crush in the rat

The neurotrophic peptide Org 2766 accelerates the regeneration of peripheral nerves. Although the mechanism of action of this neuropeptide is not yet understood, functional, pharmacological, and morphological evidence has demonstrated that Org 2766 exerts its beneficial effect during the early stages of nerve regeneration. The induction of some members of the Immediate Early Gene (IEG) family such as c-jun and c-fos is one of the first molecular events following peripheral nerve damage. The Fos and Jun proteins act as a transcription factor and may stimulate the expression of a number of genes implicated in nerve regeneration. We examined whether Org 2766 stimulates nerve regeneration by enhancing or prolonging the expression of c-fos mRNA. Following a crush lesion of the sciatic nerve, the expression of c-fos mRNA was induced in the spinal cord and in the damaged nerve at 30 min following injury in untreated animals as demonstrated with Northern blot. No effect of the crush lesion was observed in dorsal root ganglia (DRG). The induction of c-fos mRNA in the damaged nerve was more robust as compared to the relatively small induction observed in the spinal cord. With in situ hybridization an increase in c-fos mRNA expression both in the dorsal and in the ventral horn of the spinal cord was demonstrated at 30 min post-lesion. In the distal sciatic nerve portion the expression of c-fos mRNA was predominantly localized around Schwann cell nuclei at 30 min after nerve crush. The effect of Org 2766 treatment on the expression of c-fos mRNA was investigated using semiquantitative dot blots.(ABSTRACT TRUNCATED AT 250 WORDS)

CNS effects of peptides: a cross-listing of peptides and their central actions published in the journal Peptides, 1986-1993

The centrally mediated effects of peptides as published in the journal Peptides from 1986 to 1993 are tabulated in two ways. In one table, the peptides are listed alphabetically. In another table, the effects are arranged alphabetically. Most of the effects observed after administration of peptides are grouped, wherever possible, into categories such as cardiovascular and gastrointestinal. The species used in most cases has been rats; where other animals were used, the species is noted. The route of administration of peptides and source of information also are included in the tables, with a complete listing provided at the end. Many peptides have been shown to exert a large number of centrally mediated effects.

Maintenance of glial plasticity with aging in C-6 glial cells and normal astrocytes in culture: responsiveness to opioid peptides

In this study we used as glial cell models, early and late passage C-6 glial cells, 2B clone, and advanced passages of glial cells derived from aged mouse cerebral hemispheres (MACH) to examine responsiveness to opioids. We have previously reported that early passage C-6 glial cells, 2B clone, are bipotential and can be geared toward oligodendrocyte or astrocytic expression, whereas late passage C-6 glial cells are astrocytic. In addition, MACH cultures have been previously characterized and consist of astrocytes type 1 and 2, some oligodendrocytes, and few glial precursors. In this study, early passage (17-20) and late passage (106-108) C-6 glial cells or MACH cells of passages 16-19 were grown from plating time until harvesting, day 7 or 8, in DMEM + 10% FBS in the presence or absence of opioid peptides, Leu-enkephalin (10(-8) to 10(-10) M) or its synthetic analog, dalargin (Tyr-D-Ala-Gly-Phe-Leu-Arg; 10(-8) to 10(-10) M). We examined for the activities of glutamine synthetase (GS) and cyclic nucleotide phosphohydrolase (CNP), enzyme markers for astrocytes and oligodendrocytes, respectively. We found that CNP activity was markedly increased in the early passage following opioid treatment, indicative of a shift to oligodendrocytic expression. In the late passage cells, already committed to astrocytic expression, opioid treatment enhanced GS activity suggesting that astrocytes respond to opioids. GS activity was markedly increased in MACH cultures grown in the presence of opioids with no changes in CNP. Thus, type 1 astrocytes, the predominant glial type in MACH cultures, responded to opioids.(ABSTRACT TRUNCATED AT 250 WORDS)

The neurotrophic analogue of ACTH(4-9) reduces the perineuronal microglial reaction after rat facial nerve crush

Following peripheral nerve crush, microglial cells proliferate and migrate to motoneuron cell bodies of the injured nerves. Newly formed glial processes displace nerve terminals from the cell bodies. This process is known as synaptic stripping. In animal models of peripheral nerve diseases, the ACTH(4-9) analogue, ORG2766, was shown to facilitate axonal regeneration and to protect against experimental neuropathy. In the present study we examined the effect of ORG2766 on the microglial reaction. After facial nerve crush, rats were treated with either ORG2766 (75 micrograms/kg/48 h) or saline and were killed on day 2-6 after operation. Blind counting of the number of perineuronal glial cells in the facial nucleus was used to assess the effect of ORG2766 treatment on the microglial reaction. In the saline-treated animals the number of perineuronal glial cells per motoneuron cell body on the crushed side increased significantly. This number increased up to day 5 after operation and decreased significantly from day 5 to 6. After an initial increase in the peptide-treated animals, however, the number of perineuronal glial cells remained constant from day 3 onwards. Hence, on post-operation days 4 and 5, this number was significantly less than that seen in saline-treated animals. Microglial cells proliferate, presumably through signalling by injured motoneurons. It is suggested that the decrease in the number of perineuronal glial cells in the ORG2766-treated animals is the result of a peptide-induced reduction in the release of mediating signals/cytokines or, alternatively, increased protection of motoneurons by stress proteins. Further research should address the mechanism of action of ORG2766 in animal models of motoneuron disease.

Peripheral nerve lesions: the neuropharmacological outlook

A review is presented of compounds with trophic effects on the peripheral nervous system. A distinction should be made between three types of effect: enhancement of neurone survival, stimulation of regeneration and induction or stimulation of collateral sprouting. On the basis of data currently available, laminin and insulin-like growth factor I are the most promising substances for regeneration of peripheral nerve lesions. Future investigations of laminin should provide an answer to the query whether local administration facilitates sprouts to cross the gap between proximal and distal nerve stumps. Further experiments are required on effects of systemic administration of IGF-I in animal models of peripheral nerve lesions before investigations can be initiated in man.

Expression of the pro-opiomelanocortin gene in dorsal root ganglia, spinal cord and sciatic nerve after sciatic nerve crush in the rat

Neuropeptides related to alpha-melanocyte-stimulating hormone (alpha-MSH) stimulate nerve outgrowth following peripheral nerve injury and may play an important physiological role in peripheral nerve regeneration. The mechanism of action underlying the neurotrophic effect of pharmacologically administered alpha-MSH is unknown. Here we investigate the hypothesis that reexpression of the proopiomelanocortin (POMC) gene, the prohormone of alpha-MSH/adrenocorticotropic hormone (ACTH)-like peptides, is part of the endogenous repertoire of peripheral nerve responses following injury. The effect of sciatic nerve crush on the expression of POMC mRNA between 0.5 h and 14 days after crush was investigated using polymerase chain reaction (PCR) and Northern blot analysis. The presence of a POMC transcript in dorsal root ganglia (DRG), spinal cord and in the sciatic nerve at the crush site could be demonstrated in both control and lesioned animals by PCR using primers located in exon 1 and 3 of the POMC gene. Minute quantities of two POMC transcripts (1200 nt and 800 nt) could be detected by Northern blot analysis of total RNA prepared from DRG, spinal cord and the sciatic nerve of control animals and of animals subjected to nerve crush. POMC mRNA expression was, however, not increased following nerve crush. Probes specific for exons 1 and 2 or specific for exon 3 of the POMC gene were employed to demonstrate that the 800 nt transcript represents the truncated POMC mRNA previously shown to be present in extra-pituitary tissue. The larger 1200 nt transcript comigrates with the full length POMC mRNA expressed in the pituitary gland. The present results demonstrate the expression of small amounts of POMC mRNA in all compartments of the sciatic nerve. The absence of an induction of POMC expression in response to nerve crush suggests that the stimulating effect of exogenously applied alpha-MSH does not mimic a POMC derived neurotrophic peptide induced in the nerve following nerve injury.

Serum from patients with amyotrophic lateral sclerosis induces the expression of B-50/GAP-43 and neurofilament in cultured rat fetal spinal neurons

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease affecting motor neurons in the spinal cord, brain stem, and cortex. Cultures of fetal rat spinal cord cells were used to test sera from ALS patients (ALS sera) on their ability to influence the expression of the neuron-specific phosphoprotein B-50/GAP-43. Neurons were treated with ALS sera, sera of age-matched controls (CON sera), or sera of patients with autonomic neuropathy (AUTO sera) and fixed after 24 or 96 h. The levels of B-50 and neurofilament (NF) protein were assayed with an enzyme-linked immunoadsorbent assay (ELISA). No toxic effects of the ALS sera were observed. It appeared that after 24 h, both B-50 and NF levels were elevated in the ALS sera-treated cells by 12 and 11%, respectively. After 96 h, the B-50 level was 19% higher than in CON sera-treated neurons, and the NF level was 29% higher. AUTO sera did not differ from CON sera. The stimulating effect of ALS sera was absent if the sera were heated at 56 degrees C for 30 min. We conclude that ALS serum induces the expression of B-50 and the subsequent axonal outgrowth and maturation in vitro. This induction might be a reflection in vitro of the processes underlying the collateral sprouting responses observed in ALS patients.

Putative neurotrophic factors and functional recovery from peripheral nerve damage in the rat

1. In rats, recovery of sensory-motor function following a crush lesion of the sciatic or tibial nerve was monitored by measuring foot reflex withdrawal from a local noxious stimulation of the foot sole. 2. Putative neurotrophic compounds were tested on this functional recovery model: melanocortins (peptides derived from ACTH (corticotropin) and alpha-MSH (melanotropin], gangliosides and nimodipine were effective whereas isaxonine and TRH (thyrotropin releasing hormone) were not. 3. Structure-activity studies with melanocortins revealed a similar effectiveness of alpha-MSH, [N-Leu4, D-Phe7]-alpha-MSH, desacetyl-alpha-MSH and the ACTH analogue ORG 2766, questioning the validity of the previously suggested notion that the melanotrophic properties of these peptides are responsible for their neurotrophic effect. 4. As recovery of function after peripheral nerve damage follows a similar time course in hypophysectomized (five days post operation) and sham-operated rats, effective melanocortin therapy does not mimic an endogenous peptide signal in the repair process from pituitary origin. 5. Subcutaneous treatment with ORG 2766 (7.5 micrograms kg-1 48 h-1) facilitates recovery of function following peripheral nerve damage in young (6-7 weeks old), mature (5 month old) and old (20 month old) rats. 6. In view of the diversity in structure of the effective neurotrophic factors and the complexity of nerve repair, the present data support the notion that peripheral nerve repair may be facilitated by different humoral factors likely to be active on different aspects of the recovery process.

Neurotoxic acrylamide and neurotrophic melanocortin peptides--can contrasting actions provide clues about modes of action?

Experimental acrylamide neuropathy has been studied as a model of degenerative neurological disorders of the 'dying-back' type for over 30 years. Functional, histological, ultrastructural, electrophysiological and biochemical aspects of acrylamide neuropathy have been described and several hypotheses concerning the mode of action proposed. However, the mechanism whereby acrylamide causes axonal degeneration and inhibits nerve sprouting remains unknown. By analogy with agonist/antagonist comparisons used by the pharmacologist, we have reconsidered the acrylamide problem in the light of the opposite effects summarized in Table 1, of neurotrophic peptides related to ACTH/MSH (collectively termed melanocortins). The contrasting effects on sprouting and the eventual quality of repair of mechanically lesioned nerves have suggested a mechanism whereby sprouting may regulate perikaryal adjustments to injury. We have also posed the question as to whether a common biochemical mechanism, namely selective proteolysis of neurofilament protein may underlie the opposing effects of acrylamide and melanocortins on nerve sprouting. This possibility implies a hitherto unknown role for neurofilament protein turnover in neuronal maintenance and repair, a suggestion that may provoke further research and discussion.

Characterization of MSH/ACTH-like immunoreactivity in sciatic nerves of Xenopus laevis by immunocytochemistry, western blotting and radioimmunoassay

Previous studies have indicated that rat neurofilament protein may contain an endogenous MSH-like epitope with neuroregenerative properties. The presence of such an epitope has now been studied in nerve tissue from Xenopus laevis. Western blot analyses of sciatic nerve tissue using an assortment of sequence-specific MSH/ACTH antisera revealed the presence of two major immunoreactive protein bands of 52 and 50 kDa, which contained a mid-region MSH-like epitope. Weaker staining occurred in another protein band at 135 kDa. Immunocytochemistry revealed the immunoreactivity to reside in the axis cylinders of the nerve fibers. Other antisera, recognizing other regions of MSH/ACTH produced strong staining of Xenopus intermediate lobes, but failed to stain sciatic nerves. Thus, the proteins detected have no clear relation to either Xenopus neurofilament proteins or proopiomelanocortin.

Functional recovery after destruction of dopamine systems in the nucleus accumbens of rats. III. Further analysis of the facilitating effect of the ACTH-(4-9) analog ORG 2766

The functional recovery from impaired motor activity caused by 6-OHDA lesions in the nucleus accumbens is accelerated by the ACTH-related peptides ACTH-(4-10), alpha-MSH (ac-Ser1-ACTH-(1-13)NH2), ACTH-(7-10) and the ACTH-(4-9) analog ORG 2766. The peptides ACTH-(4-7) and Phe-D-Lys-Phe were not effective in this respect. This indicates that this effect of ACTH-derived peptides is located in the 7-10 part of the molecule whereas for the effect of ORG 2766 a bigger part of the molecule may be required. ORG 2766 was effective after intra-accumbal, subcutaneous and oral administration. The differences in potencies between the 3 routes of administration (ED50 0.76 ng/kg, 28.5 ng/kg and 80.6 micrograms/kg, respectively) suggest that the peptide exerts its effect by facilitating recovery processes at the lesion site. Studies with ORG 2766 showed that treatment during the first days following the induction of the lesion is essential for the facilitating action of the peptide on spontaneous recovery from brain damage.

Neuropeptides induce directional asymmetry in brain and spinal cord: facts and hypotheses

Directional behavioral and functional asymmetries (i.e., left-biased or right-biased in all or most animals of the population) induced by certain chemical substances are new types of brain and spinal cord asymmetry. The revealed asymmetry comprises: (1) left- or right-biased circle rotation in rat, (2) hind limb postural asymmetry resulting from alteration of the left or right flexion reflex in rat and cat, and (3) asymmetric alterations of the evoked potentials (EP) in the turtle visual cortex. Circle rotation of animals is induced by hypothalamic neurohormones (somatostatin, LH-RH, substance P, and TRH). Postural asymmetry develops under the effect produced by enkephalins and opioid kappa- and delta-agonists, sigma-agonist SKF 10.047, Arg-vasopressin. Endogenous peptide factors, the activity (or content) of which increased under brain and spinal cord unilateral injury, as well as the ones localized in the left or right hemisphere, also induced postural asymmetry. EP of the left and right turtle visual cortex were inhibited by enkephalins and opioid kappa-, and delta- and mu-agonists, and factors predominantly localized in the left or right turtle visual cortex in a different manner. The data reported here suggest the existence of a side-specific mechanism for a selective neurohormonal regulation of the neuronal activity and other processes in the left and right halves of brain and spinal cord which involves lateralized neuropeptides and their receptors. This mechanism might serve to maintain a certain balance between the activity of the left and right-side neurons, and other contralateral processes in the paired and bilateral structures in brain and spinal cord. Significant deviations from the balance occur most likely due to powerful unilateral stimuli, e.g., unilateral trauma. Many neuropeptides (opioid ones, somatostatin, MSH, ACTH) are, presumably, involved in the regeneration processes in the central and peripheral nervous system. In the case of brain lesions, some lateralized endogenous peptides may participate in the regulation of regeneration process on the left, whereas the other ones, on the right side of the midline, which depends on the side of the lesion. Some lateralized receptors and ligands may serve as positional markers of the left, whereas the other ones may serve as those of the right brain hemisphere. In ontogenesis, these markers are probably necessary to perform the function of the mechanism responsible for symmetrical brain formation.

Presence of alpha-melanocyte-stimulating hormone-like immunoreactivity in the innervation of amphibian skeletal muscle

Amphibian motor nerve terminals are sensitive to a wide variety of peptides, including alpha-melanocyte-stimulating hormone (alpha-MSH). We determined the presence and distribution of alpha-MSH-like immunoreactivity (alpha-MSHLI) in the innervation of the cutaneous pectoris muscle from bullfrog (Rana catesbeiana) tadpoles and postmetamorphic froglets, and adult frogs (R. catesbeiana and R. pipiens). alpha-MSHLI was found in unmyelinated, noncholinergic axons, in motor axons, and in motor nerve terminals. In motor axons, alpha-MSHLI was predominantly associated with neurofilaments. The distribution of this form of alpha-MSHLI changed during development and seasonally in adult frogs. The possible functional roles of this alpha-MSHLI are discussed.

The trophic responses of avian sensory ganglia in vitro to N-acetylated and des-acetyl forms of alpha-melanocyte stimulating hormone (alpha-MSH) are qualitatively distinct

alpha-Melanocyte-stimulating hormone (alpha-MSH) accelerates the regrowth of peripheral nerve axons in the rat following their transection (Verhaagen et al., Expl Neurol. 92, 451-454, 1986). The cellular mechanisms of this trophic response were investigated for several naturally occurring derivatives of alpha-MSH using Nerve Growth Factor (NGF)-stimulated quail sensory ganglion explants in vitro in which both neurite outgrowth and non-neuronal cell behaviour could be more reliably observed and quantified. Neurite outgrowth was determined with a semi-quantitative scoring assay. Glial migration into the outgrowth was quantified using a monoclonal antibody, GTE-52, which labels the nuclei of Schwann cells. Des-acetyl alpha-MSH caused a marginal increase in the neurite outgrowth density which was significant at concentrations of 0.04 and 0.1 microgram/ml. The response to acetylated (N-acetyl, N,O-diacetyl) forms of alpha-MSH was characterized by fascicle formation by neurites which resulted in an apparent decrease in the neurite score, and by the outgrowth of non-neuronal cells. Using monoclonal antibody GTE-52, which recognizes a glial nuclear antigen, these cells were identified as Schwann cells. N-Acetyl, but not des-acetyl alpha-MSH increased the number of GTE-52-labelled cells in the NGF-stimulated neurite outgrowth and stimulated their migration in the absence of neurites when NGF was omitted from the culture medium. Exposure of growing explants to two polyclonal antibodies against alpha-MSH resulted in an increased neurite outgrowth density. The results support the hypothesis that alpha-MSH peptides stimulate peripheral nerve growth by modulating the neurite sprouting response, and demonstrate that the nature of the neurotrophic response to naturally occurring melanotropins depends on the existence of acyl substitution at the N-terminal amino acid residue. A possible role of endogenous melanotropin peptides in the regulation of sensory nerve growth is discussed.

ACTH modulation of nerve development and regeneration

(1) The availability of short amino acid sequences of the naturally occurring ACTH 1-39 molecule has made it possible to separate the corticotropic characteristics of the parent molecule from its neurotrophic effects. Potent neurotrophic fragments are ACTH 4-10, an analog of ACTH 4-9 (Org 2766), and alpha-MSH (ACTH 1-13), peptide fragments that do not evoke corticosteroid secretion, yet clearly affect both the development and regeneration of peripheral nerve. (2) Early postnatal administration of either ACTH 4-10 or Org 2766 accelerates the neuromuscular development of the immature rat, increasing the contractile strength of the EDL muscle and inducing more rapid muscle contractions. Grasping strength and motor activity are increased; these are all changes indicative of more rapid neuromuscular maturation. Prenatal peptide treatment elicits a more complex pattern of response since administration early in gestation (GD 3-12) accelerates neuromuscular development whereas later administration (GD 13-21) decelerates maturation. (3) ACTH peptides have a similar accelerating effect on the morphology of the developing neuromuscular junction. At two weeks of age, nerve arborization is conspicuously increased by postnatal administration of either ACTH 4-10 or Org 2766, as is nerve terminal branching within the endplate itself. However, this is preceded by an initial depression of nerve branching in the 7-day-old rat pup. We conclude that while the developing neuromuscular system is sensitive to ACTH peptides, this susceptibility is age-related. The crucial role of these peptides may be limited to very brief, defined periods during which the peptides may interact with trophic or growth-associated substances, each of which may have its own decisive, circumscribed time frame of influence. (4) Perinatal administration of ACTH peptides affects CNS development. One measurable indication of this is an acceleration of eye opening. Early exposure to ACTH peptides has long-lasting effects on behavior, apparent when these animals are tested as adults. Increased spontaneous motor activity, heightened states of arousal and agitation, and changes in social behavior have been reported. Certain avoidance responses and tests of visual discrimination in male rats are improved by neonatal treatment with alpha-MSH. Overall motor activity is increased and the normal period of hyperactivity is initiated earlier. Male sexual behavior is decreased and sexually dimorphic behaviors in males are eliminated. alpha-MSH may alter the development of its own dopaminergic feedback circuitry while ACTH affects serotonin levels in the preoptic nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)

Trophic influences of alpha-MSH and ACTH4-10 on neuronal outgrowth in vitro

Slices of foetal spinal cords in culture were used to establish possible trophic effects of alpha-melanocyte stimulating hormone (alpha-MSH) and a fragment of the adrenocorticotropic hormone (ACTH4-10) on the outgrowth of neurites from spinal neurons. The spinal cord slices were treated with peptides over a wide concentration range. Using monoclonal antibodies against (subunits of) neurofilament followed by immunofluorescence, we could show that the extension consisted mainly of axons. After 5 and 7 days, outgrowth was quantified with 2 different techniques, namely by visual scoring under phase contrast and by means of an ELISA for neurofilament protein. Both methods yielded the same dose-response profile. Both alpha-MSH and ACTH4-10 stimulated the formation of neurites in a dose-dependent manner, with a maximal stimulatory effect at 0.001-0.01 nM (ACTH4-10) or 0.1-1.0 nM (alpha-MSH). The maximal effect of the peptides was 30-40% compared to controls. We conclude that alpha-MSH and ACTH4-10 stimulate axonal outgrowth from foetal spinal cord slices in vitro in a dose-dependent way.

Transient neurotensin in the human inferior olive during development

A large number of transient neurotensin-immunoreactive nerve terminals are found in the human principal inferior olive of the medulla oblongata during the first year of age and almost completely disappear in the adult. Their neurotensin content is further characterized as neurotensin(1-13) using radioimmunoassay and gel filtration and reaches 582 pmol per gram wet weight at 6 months. Neurotensin nerve terminals are exclusively located in the principal olive and a dense bundle of neurotensin nerve fibers is also present in the central tegmental tract. Thus, these olivary neurotensin nerve terminals probably originate in mesencephalic neurons. In addition to its recognized role in neurotransmission or neuromodulation, neurotensin may thus also be implicated in the postnatal development of the human principal olive and indirectly in that of the neocerebellum.

Damaged rat peripheral nerves do not contain detectable amounts of alpha-MSH

Peptides related to alpha-MSH (collectively termed melanocortins) stimulate nerve growth following injury and may play a physiological role in the repair process. Melanocortins are not normally present in mature peripheral nerves but MSH-like bioactivity has been observed in extracts of injured nerves. alpha-MSH could derive from reexpression of the POMC prohormone in injured nerves or from proteolysis of the intermediate-size neurofilament protein that bears antigenic similarities to melanocortins. Using a radioimmunoassay that will distinguish between alpha-MSH and neurofilament-derived fragments, we have shown that alpha-MSH is not present (detection limit 74 pg alpha-MSH/mg protein) in damaged rat sciatic nerves.

Acceleration of recovery from sciatic nerve damage by the ACTH (4-9) analog Org 2766: different routes of administration

Functional recovery following a sciatic nerve crush in rats was investigated by measuring the reflex withdrawal of the hindpaw to a hot air stream. The ACTH(4-9) analog Org 2766 accelerated recovery when administered subcutaneously (two-daily injections: 10 micrograms/animal; minipumps: 20-40 micrograms/animal per 24 hr: biodegradable microspheres: 40 micrograms/animal per 24 hr), but oral administration (1.5-20 mg/animal daily, in the drinking water; 1.5-15 mg/animal daily, by gavage) was not effective.