Melanotropins as growth factors

Melanotan-II reverses memory impairment induced by a short-term HF diet

A high-fat (HF) diet has been shown to increase the risk of neurological impairments and neurodegenerative disorders. The melanotropins used in this study have been associated with diet-related disorders; however, there is an absence of studies on their effect on diet-induced neurobehavioral conditions. Here, we investigated the possible relationship among diet, Melanotan-II (MT-II) targeting melanotropin receptors, and the behavior of zebrafish (Danio rerio). Surprisingly, even a short-term HF diet lasting for ∼ 1 % of the zebrafish's life had a strong developmental effect. Zebrafish fed the HF diet showed an impairment in recognition memory, elevated anxiety levels, and reduced exploratory propensity after just three weeks compared to zebrafish fed the control diet. These HF diet-induced abnormalities were reversed by MT-II. Animals fed a HF diet and treated with MT-II demonstrated recognition memory, anxiety, and exploratory behavior similar to the control group. This study provides evidence that even a short-term HF diet has an impact on memory and emotions and is the first study to show that MT-II reverses these changes.

Ghrelin: a novel neuromuscular recovery promoting factor?

Promoting neuromuscular recovery after neural injury is a major clinical issue. While techniques for nerve reconstruction are continuously improving and most peripheral nerve lesions can be repaired today, recovery of the lost function is usually unsatisfactory. This evidence claims for innovative nonsurgical therapeutic strategies that can implement the outcome after neural repair. Although no pharmacological approach for improving posttraumatic neuromuscular recovery has still entered clinical practice, various molecules are explored in experimental models of neural repair. One of such molecules is the circulating peptide hormone ghrelin. This hormone has proved to have a positive effect on neural repair after central nervous system lesion, and very recently its effectiveness has also been demonstrated in preventing posttraumatic skeletal muscle atrophy. By contrast, no information is still available about its effectiveness on peripheral nerve regeneration although preliminary data from our laboratory suggest that this molecule can have an effect also in promoting axonal regeneration after nerve injury and repair. Should this be confirmed, ghrelin might represent an ideal candidate as a therapeutic agent for improving posttraumatic neuromuscular recovery because of its putative effects at all the various structural levels involved in this regeneration process, namely, the central nervous system, the peripheral nerve, and the target skeletal muscle.

Alpha-melanocyte-stimulating hormone and related tripeptides: biochemistry, antiinflammatory and protective effects in vitro and in vivo, and future perspectives for the treatment of immune-mediated inflammatory diseases

Alpha-MSH is a tridecapeptide derived from proopiomelanocortin. Many studies over the last few years have provided evidence that alpha-MSH has potent protective and antiinflammatory effects. These effects can be elicited via centrally expressed melanocortin receptors that orchestrate descending neurogenic antiinflammatory pathways. alpha-MSH can also exert antiinflammatory and protective effects on cells of the immune system and on peripheral nonimmune cell types expressing melanocortin receptors. At the molecular level, alpha-MSH affects various pathways implicated in regulation of inflammation and protection, i.e., nuclear factor-kappaB activation, expression of adhesion molecules and chemokine receptors, production of proinflammatory cytokines and mediators, IL-10 synthesis, T cell proliferation and activity, inflammatory cell migration, expression of antioxidative enzymes, and apoptosis. The antiinflammatory effects of alpha-MSH have been validated in animal models of experimentally induced fever; irritant and allergic contact dermatitis, vasculitis, and fibrosis; ocular, gastrointestinal, brain, and allergic airway inflammation; and arthritis, but also in models of organ injury. One obstacle limiting the use of alpha-MSH in inflammatory disorders is its pigmentary effect. Due to its preserved antiinflammatory effect but lack of pigmentary action, the C-terminal tripeptide of alpha-MSH, KPV, has been delineated as an alternative for antiinflammatory therapy. KdPT, a derivative of KPV corresponding to amino acids 193-195 of IL-1beta, is also emerging as a tripeptide with antiinflammatory effects. The physiochemical properties and expected low costs of production render both agents suitable for the future treatment of immune-mediated inflammatory skin and bowel disease, fibrosis, allergic and inflammatory lung disease, ocular inflammation, and arthritis.

Stress as a modulator of motor system function and pathology

Stress is one of the most significant influences on behaviour and performance. The classical account is that stress mainly affects functions of the limbic system, such as learning, memory and emotion. Recent evidence, however, suggests that stress also modulates motor system function and influences the pathology of movement disorders. Most parts of the motor system show the presence of glucocorticoid receptors that render their circuits susceptible to the influence of stress hormones. Stress and glucocorticoids have been shown to modulate temporal and spatial aspects of motor performance. Skilled movements seem to be most prone to stress-induced disturbances, but locomotion and posture can also be affected. Stress can modulate movement through activation of the hypothalamic-pituitary-adrenal axis and via stress-associated emotional changes. The dopaminergic system seems to play a central role in mediating the effects of stress on motor function. This route might also account for the finding that stress influences the pathology of dopamine-related diseases of the motor system, such as Parkinson's disease. Clinical observations have indicated that stress might lead to the onset of Parkinsonian symptoms or accelerate their progression. Glucocorticoids are modulators of neuronal plasticity, thus determining the degree of structural and functional compensation of the damaged motor system. This may particularly affect slowly progressive neurodegenerative diseases, such as Parkinson's disease. That stress represents a significant modulator of motor system function in both the healthy and the damaged brain should be recognized when developing future therapies for neurodegenerative diseases.

Semax, an analog of ACTH(4–10) with cognitive effects, regulates BDNF and trkB expression in the rat hippocampus

The heptapeptide Semax (Met-Glu-His-Phe-Pro-Gly-Pro) is an analog of the adrenocorticotropin fragment (4-10) which after intranasal application has profound effects on learning and exerts marked neuroprotective activities. Here, we found that a single application of Semax (50 microg/kg body weight) results in a maximal 1.4-fold increase of BDNF protein levels accompanying with 1.6-fold increase of trkB tyrosine phosporylation levels, and a 3-fold and a 2-fold increase of exon III BDNF and trkB mRNA levels, respectively, in the rat hippocampus. Semax-treated animals showed a distinct increase in the number of conditioned avoidance reactions. We suggest that Semax affects cognitive brain functions by modulating the expression and the activation of the hippocampal BDNF/trkB system.

Neuroprotective effects of melanocortins in experimental spinal cord injury. An experimental study in the rat using topical application of compounds with varying affinity to melanocortin receptors

The possibility that local administration of low molecular weight non-peptide compounds with varying affinities at melanocortin receptors in the spinal cord will influence pathophysiological outcome of spinal cord injury (SCI) was examined in a rat model. Five new Melacure compounds ME10092, ME10354, ME10393, ME10431 and ME10501 were used in this investigation. Each compound was dissolved in saline and tested at 3 different doses, i.e. 1 microg, 5 microg and 10 microg total dose in 10 microl applied topically 5 min after SCI. The animals were allowed to survive 5 h and trauma induced edema formation, breakdown of the blood-spinal cord barrier (BSCB) and cell injuries were examined and compared with untreated injured rats. A focal SCI inflicted by an incision into the right dorsal horn of the T10-11 segments resulted in marked edema formation, breakdown of the BSCB to Evans blue albumin and caused profound nerve cell injury in the T9 and the T12 segments. Topical application of ME10501 (a compound with high affinity at melanocortin, MC-4 receptors) in high doses (10 microg) resulted in most marked neuroprotection in the perifocal spinal cord (T9 and T12) segments. On the other hand, only a mild or no effect on spinal cord pathology was observed in the traumatized animals that received ME10092, ME10354, ME10393 and ME10431 at 3 different doses. These observations suggest that non-peptide compounds with varying affinity to melanocortin receptors are able to influence the pathophysiology of SCI. Furthermore, compounds acting at melanocortin, MCR4 receptors are capable to induce neuroprotection in spinal cord following trauma.

Effects of the COOH-terminal tripeptide alpha-MSH(11-13) on corneal epithelial wound healing: role of nitric oxide

It is known that alpha-melanocyte stimulating hormone (alpha-MSH) may exert anti-inflammatory effects and facilitate reparative processes in different tissues. The effective message sequence of alpha-MSH resides in the COOH-terminal tripeptide alpha-MSH(11-13). This study was undertaken to investigate the effects of topical administration of the COOH-terminal tripeptide sequence of alpha-MSH (alpha-MSH(11-13), KPV) on corneal epithelial wound healing in rabbits and the possible role of nitric oxide (NO) in these effects. The whole corneal epithelium was denuded in both eyes by mechanical abrasion. The area of the corneal epithelial defect was stained with fluorescein, photographed, and then measured before the treatment and every 12 h by a computerized software. The mean epithelial wound area and the mean percent of epithelial defect remaining at each follow-up control were compared between experimental groups. Rabbits were topically treated with KPV 1, 5 or 10 mg/ml (30 microl), two drops four times in a day, for 4 days, starting immediately after corneal abrasion, while control animals received topical phosphate-buffered saline as vehicle. In order to study the role of NO in corneal repair processes, the NO donor, sodium nitroprusside (SP, 10 mg/ml, 30 microl) was administered in both eyes, two drops four times in a day, for 4 days. The effects of KPV or SP were challenged by pre-treatment with the nitric oxide synthase inhibitor, N omega-nitro-L-arginine methyl ester (L-NAME, 10 mg/ml, 30 microl) 30 min prior to KPV or SP instillation. The mean percent epithelial defect remaining each time was significantly smaller in animals treated with KPV or SP in comparison to controls. Sixty hours later, eight out of eight (100%) corneas treated with KPV or SP were completely re-epithelized (P<0.05) while none of the corneas treated with placebo were re-epithelized. Pre-treatment with L-NAME inhibited the facilitating effect of KPV on corneal epithelial wound healing process and totally prevented the effect of SP. Rabbit corneal epithelial cells (RCE) in culture were exposed for 1, 6 and 24 h to different KPV concentrations (0.1, 1 and 10 microM) in medium containing 15% foetal bovine serum (FBS). Cell viability was stimulated by 1 and 10 microM concentrations of the substance. Thus, KPV may facilitate corneal epithelial wound healing in rabbits with a mechanism that may involve NO disposition in corneal tissue. However, it is not known whether this mechanism is likely to depend on a direct stimulating repairing activity shared by the entire molecule of alpha-MSH.

Semax, an analogue of adrenocorticotropin (4-10), binds specifically and increases levels of brain-derived neurotrophic factor protein in rat basal forebrain

The heptapeptide Semax (Met-Glu-His-Phe-Pro-Gly-Pro) is an analogue of the N-terminal fragment (4-10) of adrenocorticotropic hormone which, after intranasal application, has profound effects on learning and memory formation in rodents and humans, and also exerts marked neuroprotective effects. A clue to the molecular mechanism underlying this neurotropic action was recently given by the observation that Semax stimulates the synthesis of brain-derived neurotrophic factor (BDNF), a potent modulator of synaptic plasticity, in astrocytes cultured from rat basal forebrain. In the present study, we investigated whether Semax affects BDNF levels in rat basal forebrain upon intranasal application of the peptide. In addition, we examined whether cell membranes isolated from this brain region contained binding sites for Semax. The binding of tritium-labelled Semax was found to be time dependent, specific and reversible. Specific Semax binding required calcium ions and was characterized by a mean+/-SEM dissociation constant (KD) of 2.4+/-1.0 nm and a BMAX value of 33.5+/-7.9 fmol/mg protein. Sandwich immunoenzymatic analysis revealed that Semax applied intranasally at 50 and 250 microg/kg bodyweight resulted in a rapid increase in BDNF levels after 3 h in the basal forebrain, but not in the cerebellum. These results point to the presence of specific binding sites for Semax in the rat basal forebrain. In addition, these findings indicate that the cognitive effects exerted by Semax might be associated, at least in part, with increased BDNF protein levels in this brain region.

Effects of semax against the background of dopaminergic receptor blockade with haloperidol

We studied the neurotropic effects of ACTH(4-10) analog semax against the background of dopaminergic receptors blockade with haloperidol. Intranasal administration of semax (0.05, 0.2, and 0.6 mg/kg) produced virtually no effect on disturbances of orientation and exploratory reactions and motor activity caused by intraperitoneal injection of 0.2 mg/kg haloperidol. By contrast, preliminary administration of 0.05 mg/kg semax prevented haloperidol-induced disturbances in active avoidance conditioning.

Accelerating sensory recovery after sciatic nerve crush: non-selective versus melanocortin MC4 receptor-selective peptides

Melanocortin receptor ligands accelerate functional recovery after peripheral nerve crush. It is not known which mechanism is involved or via which melanocortin receptor this effect occurs, albeit indirect evidence favours the melanocortin MC4 receptor. To test whether the melanocortin MC4 receptor is involved in the effects of melanocortins on functional recovery, we used melanocortin compounds that distinguish the melanocortin MC4 receptor from the melanocortin MC1, MC3 and MC5 receptors on basis of selectivity and agonist/antagonist profile. Activation and binding studies indicated that the previously described peptides JK1 (Ac-Nle-Gly-Lys-D-Phe-Arg-Trp-Gly-NH2) and [D-Tyr4]melanotan-II ([D-Tyr4]MTII. Ac-Nle-c[Asp-His-D-Tyr-Arg-Trp-Lys]NH2) are selective for the rat melanocortin MC4 receptor as compared to the rat melanocortin MC3 and MC5 receptors, but are also potent on the melanocortin MC1 receptor. Both peptides did not accelerate sensory recovery in rats with a sciatic nerve crush, whereas the non-selective melanocortin agonist melanotan-II (MTII, Ac-Nle-c[Asp-His-D-Phe-Arg-Trp-Lys]NH2) was effective. The melanocortin MC3/MC4 receptor antagonist SHU9119 (Ac-Nle-c[Asp-His-D-Nal(2)-Arg-Trp-Lys]NH2) also enhanced sensory recovery. This effect was probably not due to interaction with the melanocortin MC4 receptor, since JK46 (Ac-Gly-Lys-His-D-Nal(2)-Arg-Trp-Gly-NH2), a selective melanocortin MC4 receptor antagonist, was ineffective. Taken together, these data suggest that melanocortins do not accelerate sensory recovery via interaction with the melanocortin MC4 receptor. From the known melanocortin receptors, only the involvement of the melanocortin MC5 receptor in acceleration of recovery could not be excluded.

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.

The potent melanocortin receptor agonist melanotan-II promotes peripheral nerve regeneration and has neuroprotective properties in the rat

The neurotrophic and neuroprotective potential of the alpha-melanocyte-stimulating hormone (alpha-MSH) analog cyclo-[Ac-Nle(4),Asp(5),D-Phe(7),Lys(10)]alpha-MSH-(4-10) amide (melanotan-II), a potent melanocortin receptor agonist, was investigated. The sciatic nerve crush model was used as a paradigm to investigate the neurotrophic properties of melanotan-II. Melanotan-II significantly enhanced the recovery of sensory function following a crush lesion of the sciatic nerve in the rat at a dose of 20 microg kg(-1) per 48 h, s.c., but not at a dose of 2 or 50 microg kg(-1). In addition, we observed that melanotan-II also possesses neuroprotective properties, as it partially protected the nerve from a toxic neuropathy induced by cisplatin. Thus, the present data for the first time demonstrate the effectiveness of the potent alpha-MSH analog melanotan-II in nerve regeneration and neuroprotection.

Menkes protein contributes to the function of peptidylglycine alpha-amidating monooxygenase

Menkes protein (ATP7A) is a P-type ATPase involved in copper uptake and homeostasis. Disturbed copper homeostasis occurs in patients with Menkes disease, an X-linked disorder characterized by mental retardation, neurodegeneration, connective tissue disorders, and early childhood death. Mutations in ATP7A result in malfunction of copper-requiring enzymes, such as tyrosinase and copper/zinc superoxide dismutase. The first step of the two-step amidation reaction carried out by peptidylglycine alpha-amidating monooxygenase (PAM) also requires copper. We used tissue from wild-type rats and mice and an ATP7A-specific antibody to determine that ATP7A is expressed at high levels in tissues expressing high levels of PAM. ATP7A is largely localized to the trans Golgi network in pituitary endocrine cells. The Atp7a mouse, bearing a mutation in the Atp7a gene, is an excellent model system for examining the consequences of ATP7A malfunction. Despite normal levels of PAM protein, levels of several amidated peptides were reduced in pituitary and brain extracts of Atp7a mice, demonstrating that PAM function is compromised when ATP7A is inactive. Based on these results, we conclude that a reduction in the ability of PAM to produce bioactive end-products involved in neuronal growth and development could contribute to many of the biological effects associated with Menkes disease.

Topiramate promotes neurite outgrowth and recovery of function after nerve injury

Topiramate is a structurally novel neurotherapeutic agent with a unique combination of pharmacological properties and currently is available in most world markets for treating several seizure disorders. Because its pharmacological profile was suggestive of possible activity as a neuroprotectant, topiramate was evaluated and found to be active in several animal models of stroke or neuropathic pain. This prompted an evaluation of topiramate as a possible neurotrophic agent. In this study, topiramate enhanced the recovery of facial nerve function after injury when administered orally at therapeutically relevant doses, and significantly increased neurite outgrowth in cell cultures derived from fetal rat cortical and hippocampal tissues.

David and Goliath - the slingshot that started the neuropeptide revolution

This review in honor of David de Wied summarizes the work done in my laboratory that first indicated that adrenocorticotropic hormone (ACTH) has a direct effect on the neuromuscular system. Cold stress or ACTH and its related peptides alpha-melanocyte-stimulating hormone (alpha-MSH ) and beta-lipotropin improve the electromechanical characteristics of adrenalectomized and hypophysectomized rats. ACTH-(1-39) accelerates the return of motor and sensory function and improves the morphological characteristics of the motor endplate after peripheral nerve crush. The non-corticotropic fragments ACTH-(4-10), alpha-MSH, the ACTH-(4-9) analogue Organon 2766 (Org 2766) or the ACTH-(4-10) analogue Biomeasure 22015 (BIM 22015) improve electrophysiological and morphological parameters of the regenerating neuromuscular system. ACTH-(4-10) immunoreactivity, present in ventral horn motor neurons in low levels, is decreased ipsilaterally following ipsilateral nerve crush but increases both ipsilaterally and contralaterally if injured animals are treated with ACTH-(4-10) indicating a neuroprotective action. Similarly, Org 2766 appears to have a protective action in the brain following nigrostriatal lesions. In developmental studies, perinatal exposure to ACTH peptides improves the structure of the neuromuscular junction, accelerates the maturation of electromechanical properties and enhances nerve-muscle integration and nerve regeneration. Perinatal exposure to these peptides decreases adult male sexual behavior, a change correlated with increased serotinergic input within the medial preoptic area. Similar changes occur in female rats and appear to be long-lasting. In tissue culture studies, both Org 2766 and BIM 22015 promote neurite outgrowth in the absence of nerve growth factor, indicating a neurotrophic role for these peptides.

Regulation of ischemic cell death by glucocorticoids and adrenocorticotropic hormone

Transient global ischemia results in delayed selective neuronal death of hippocampal CA1 pyramidal cells. Glucocorticoids increase and adrenalectomy decreases the rate of neuronal death; however, they also produce changes in brain temperature, serum glucose and adrenocorticotropic hormone levels. In order to understand the role of glucocorticoids in regulating ischemic cell death, we studied RU 38486, a glucocorticoid receptor blocker, and Org 2766, a non-steroidogenic adrenocorticotropic hormone 4-9 analog. Male Mongolian gerbils were subjected to 5 min of bilateral carotid artery occlusion under a controlled temperature environment (37.0-38.0 degrees C). Animals were injected with either physiological saline, Org 2766 (10 microg/kg/24 h) or RU 38486 (50 mg/kg/8 h), beginning just prior to the occlusion until killing at either day 4 or 7. Blood was collected for serum glucose and cortisol analysis. Damage was evaluated by blinded counts of CAI neurons. Both RU 38486 and Org 2766 treatment significantly (P<0.004) reduced hippocampal CA1 damage at day 4, but not on day 7. While RU 38486 raised serum cortisol and adrenocorticotropic hormone levels, neither treatment affected temperature or serum glucose. The fact that RU 38486 mimicked adrenalectomy without changing temperature suggests that the decreased rate of cell death resulted from either removal of glucocorticoids or increases in adrenocorticotropic hormone. The ability of Org 2766 to affect this rate strongly suggests that adrenocorticotropic hormone is the active regulatory hormone rather than glucocorticoids. While both RU 38486 and Org 2766 prolong the survival of CA1 neurons after transient global ischemia, only RU 38486, which is available and tested in both animals and humans, can block the detrimental effects of post-ischemia glucocorticoid elevations. Thus, the administration of RU 38486 may be a practical adjunct to other neuroprotective agents for victims of cardiac arrest, anesthetic accidents or drowning.

Autoradiographic discrimination of melanocortin receptors indicates that the MC3 subtype dominates in the medial rat brain

In the present study, we developed an autoradiographic method to visualize the distribution of melanocortin (MC) receptors 3 and 4 in sagittal sections of the rat brain. The method takes advantage of the MC3 and MC4 receptor selective compounds, gamma1-MSH and HS014. First, we characterized the binding of gamma1-MSH, HS014 and the radioligand [125I]NDP-MSH to the rat MC3 and MC4 receptors expressed in COS cells. [125I]NDP-MSH was found to be non-selective, whereas gamma1-MSH showed a 40-fold preference for the rat MC3 receptor, and HS014 an over 300-fold preference to the rat MC4 receptor. Second, to discriminate between the MC3 and MC4 receptors in rat brain sections, the sections were incubated with [125I]NDP-MSH in the presence of graded concentrations of the MC3 selective ligand, gamma1-MSH, or the MC4 selective ligand, HS014. From the autoradiograms thus made, competition curves of gamma1-MSH and HS014 could be constructed for different regions of the rat brain. Our results indicate that in the nucleus accumbens shell, the medial preoptic area, and the ventromedial nucleus of the hypothalamus, there is a clear dominance of the MC3 receptor, whereas in the lateral septum and the olfactory tubercle, there seem to be present both MC3 and MC4 receptors, although the MC3 receptor may still be the dominating subtype. In the optic layer of the superior colliculus, our data indicate a more abundant expression of the MC4 receptor. In the ventral tegmental area, there might be an additional MSH-peptide binding site of unknown origin.

Differentiation of rat hypothalamic dopaminergic neurons is stimulated in vitro by target cells: the melanotrophs

We have investigated in vitro the influence of pituitary intermediate lobe melanotrophs on the differentiation of their afferent hypothalamic dopaminergic neurons. The presence of melanotrophs in primary cultures of foetal hypothalamic neurons induces an increase of the number of dopaminergic neurons (while the total neuronal population remains unchanged) and induces a stimulation of their neuritic outgrowth. These effects are mediated by diffusible factors since they are reproduced by application of conditioned medium issued from co-cultures with intermediate lobe cells from newborn rats. Moreover, by immunoneutralization of alpha-melanocyte-stimulating hormone (alphaMSH) in the co-culture or conditioned medium, or by application of the peptide itself, we demonstrate that the neuritotrophic effect on dopaminergic neurons is mediated by alphaMSH, the main secretory product of melanotrophs, whereas the inductive effect on the number of dopaminergic neurons is attributable to another diffusible neurotrophic factor(s) present in foetal, but not adult, adenohypophysis. Similar effects are observed on cultures of newborn hypothalamic neurons. However, at this stage of neuronal development, alphaMSH also increases the number of dopaminergic neurons, which could be due to a change of neuronal receptivity. We show that the neuritotrophic influence of alphaMSH is restricted to the dopaminergic neurons connected to the melanotrophs, and that in addition, these neurons systematically co-express the tyrosine hydroxylase and glutamate decarboxylase as the neurons innervating the melanotrophs in situ. These findings indicate that the differentiation of dopaminergic hypothalamic neurons is influenced by the target cells, melanotrophs, and that this trophic influence implicates alphaMSH.

Target-dependent synaptogenesis: inductive effect of pituitary melanotrophs on their central innervation

The glandular activity of the vertebrate pituitary intermediate lobe (IL) is regulated by direct cellular innervation, in contrast with the purely humoral regulation of adjacent pituitary anterior lobe (AL). Thus in the rat IL, melanotrophs receive a dopaminergic and GABAergic innervation from the basal hypothalamus, which tonically inhibit their glandular activity. We studied this model of neuron-target interactions in cocultures in defined medium of fetal hypothalamic neurons with neonate pituitary glandular cells. In the cocultures with IL cells, neuroglandular contacts occurred after 4 days in vitro (DIV) but required another 8 DIV to exhibit ultrastructural and immunocytochemical features of fully differentiated functional synapses; by contrast, neuroneuronal synapses developed much faster and could already be detected after 4 DIV. In the cocultures with AL cells, neuroglandular contacts never mature in differentiated synapses. Confocal microscope observation revealed that dopaminergic neurons, which represented less than 1% of total neurons in the cocultures, established 50% of the synapses detected on the melanotrophs. These cells are thus able, contrary to the AL cells, to promote the establishment of functional synapses and, to some extent, to select their specific innervation.

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.

Structure-based search for peptide ligands that cross-react with melanocortin receptors

PURPOSE

To define sequence motifs that can be used to identify peptide ligands of the melanocortin receptor (MCR).

METHODS

Screening of combinatorial libraries has led to identification of D-Trp-Nle-NH2 (Nle, norleucine) and D-Trp-Arg-NH2 as the smallest structures known to antagonize the amphibian MCR (1). As the basis of a search paradigm, peptide-ligands containing these or similar motifs within their larger primary structure were examined for ability to antagonize amphibian and recombinant human MCRs. Compounds examined include analogs of substance P, leutinizing-hormone releasing-hormone, endothelin, neurotensin, and opioid-somatostatin.

RESULTS

Of seven compounds tested containing the predetermined search motif D-Trp-AAx (where AAx is Arg, Leu, Nle, or Ile), six were found to have previously unrecognized antagonist activity at the amphibian MCR (Kd 30 to 5000 nM). In contrast, of 14 similar control peptides lacking the D-Trp-AAx search motif, only somatostatin displayed measurable antagonist potency. The anticancer peptide, [Arg8, D-Trp7.9, N-methyl-Phe8]-substance P, was the most potent of the motif-containing peptides with a Kd of 31 nM. The mu-opioid antagonist D-Phe-cyclic[Cys-Tyr-D-Trp-Arg-Thr-Pen]-Thr-NH2 (CTAP) also blocked the amphibian MCR (Kd 1 microM), but the related mu-antagonist CTOP, different only by only by substitution of Arg with ornithine within the search motif, was found to agonize the amphibian MCR (EC50 67 nM). CTAP and the anticancer peptide were also tested on human MCRs (hMCRs); while CTAP competed with alpha-MSH at the hMC1 receptor, the anticancer peptide had no effect or was slightly stimulatory.

CONCLUSIONS

We have identified dipeptide motifs that help distinguish antagonist ligands of the amphibian MCR from ligands known to interact with other G-protein coupled receptors. This approach might be generally applicable if motifs can identified for other receptors and their subtypes. In studies employing CTAP and CTOP, analogs previously considered highly selective for the mu-opioid receptor, cross-reaction with MCRs must be considered.

Early loss of the retinoblastoma gene is associated with impaired growth inhibitory innervation during melanotroph carcinogenesis in Rb+/- mice

To better understand the cell lineage-specific character of retinoblastoma (Rb) gene inactivation during tumor formation, the earliest stages of spontaneous melanotroph carcinogenesis in Rb+/- heterozygous mice have been subjected to sequential analyses. The first atypical cells are detected in the pituitary intermediate lobe during a period corresponding to the cessation of melanotroph proliferation between 35 and 60 days after birth. Atypical cells contain no wild-type copy of the Rb gene and synchronously form early atypical proliferates (EAP) in the subsequent 30-60 day period. In contrast to surrounding mature melanotrophs with the wild-type Rb gene, Rb-negative cells in EAP continue to proliferate well past postnatal day 60, and fail to be innervated by growth inhibitory dopaminergic nerve terminals. Atypical melanotrophs remain competent for dopamine D2 receptor stimulation and undergo S-phase apoptosis in close proximity to nerve terminals. These results indicate a key role for the Rb protein in the onset of neuron-neuroendocrine cell interactions. This role may explain cell-type-specific neuroendocrine carcinogenesis associated with inactivation of the ubiquitously expressed Rb gene.

Priming events and retrograde injury signals. A new perspective on the cellular and molecular biology of nerve regeneration

Successful axon regeneration requires that signals from the site of injury reach the nucleus to elicit changes in transcription. In spite of their obvious importance, relatively few of these signals have been identified. Recent work on regeneration in the marine mollusk Aplysia californica has provided several insights into the molecular events that occur in neurons after axon injury. Based on these findings, we propose a model in which axon regeneration is viewed as the culmination of a series of temporally distinct but overlapping phases. Within each phase, specific signals enter the nucleus to prime the cell for the arrival of subsequent signals. The first phase begins with the arrival of injury-induced action potentials, which act via calcium and cAMP to turn on genes used in the early stages of repair. In the next phase, MAP-kinases and other intrinsic constituents activated at the injury site are retrogradely transported through the axon to the nucleus, informing the nucleus of the severity of the axonal injury, reinforcing the earlier events, and triggering additional changes. The third phase is characterized by the arrival of signals that originate from extrinsic growth factors and cytokines released by cells at the site of injury. In the last phase, signals from target-derived growth factors arrive in the cell soma to stop growth. Because many of these events appear to be universal, this framework may be useful in studies of nerve repair in both invertebrates and vertebrates.

Region- and stage-specific patterns of melanocortin receptor ontogeny in rat central nervous system, cranial nerve ganglia and sympathetic ganglia

Observations on developmental actions of melanotropic peptides in nervous system have been difficult to interpret in the absence of data on receptor ontogeny. We investigated binding of [125I]Nle4,D-Phe7-alpha-MSH ([125I]NDP) in developing Long Evans rats from gestational day (E) 13 by quantitative autoradiography. Regional [125I]NDP binding characteristics were assessed by competition experiments in early postnatal brain. The study revealed region- and stage-specific, often transient ontogenetic patterns. Sympathetic ganglia exhibit high [125I]NDP binding from E13, with a peak in superior cervical ganglion at E16-E18. The first central [125I]NDP binding sites transiently appear in parts of thalamus between E13 and E15. The early fetal period is characterized by prominent peaks of receptor density in somatosensory and viscerosensory nuclei (trigeminal sensory nuclei, solitary tract nucleus), paralleled by receptor expression in 5th, 7th, 9th and 10th cranial nerve ganglia. During late fetal life, receptor density peaks in dorsal motor nucleus of vagus and inferior olive; binding sites transiently appear in cerebellum. Caudate-putamen, nucleus accumbens, olfactory tubercle and septohippocampal nucleus show a high perinatal maximum. Starting with late fetal piriform cortex, [125I]NDP binding peaks sequentially in cerebral cortical areas, with highest levels in entorhinal cortex. Preoptic, septal, hypothalamic and amygdaloid areas known for elevated receptor densities in adulthood, exhibit a slow, peri- and postnatal receptor ontogeny. Temporal relations to regional developmental processes support the idea of a role of melanocortins during ontogeny.

Immunohistochemical evidence of alpha-, beta- and gamma 3-melanocyte stimulating hormone expression in cutaneous malignant melanoma of nodular type

Opiomelanocortins are formed after cleavage of the larger precursor molecule, proopiomelanocortin (POMC), which contains several peptide residues, sharing certain amino acid homology, including adrenocorticotrophic hormone (ACTH) and alpha-, beta- and gamma-melanocyte stimulating hormone (MSH). The expressions of alpha-, beta- and gamma 3-MSH in human cutaneous malignant melanoma of nodular type are demonstrated. For the MSHs, the immunolabelling was concentrated mostly in the tumour cellular cytoplasm, with occasional cells displaying a nuclear staining. Labelled tumour cells were dispersed throughout the epidermis and dermis as individual cells or in so-called 'pearl-like nests', most of which consisted mainly of round or oval shaped cells as well as a few pleomorphic or spindle-shaped cells. The fluorescence intensity seemed to increase in accordance with the development of the tumours. All cases examined were clearly stained with protein S-100, which provided us with a definite diagnosis. Considering the overall MSHs-related staining intensity of each section, the general perception we got was that the closer to the centre of the tumour parenchyma, the stronger was the staining and, furthermore the larger/more poorly differentiated the cells, the stronger was the staining. We also found the MSHs expressions to appear in the peripheral part of the tumour and the perilesional tissues including epidermis, sweat glands, sebaceous glands as well as hair follicles. Neurohypertrophic features were encountered including increases in both the number of nerve fibres and their diameter. Our results presented here strongly support the viewpoint earlier proposed that MSH peptides, by an autocrine and/or paracrine production from melanoma cells, are engaged in the regulation of melanogenesis, growth and proliferation of the tumour cells. We also conclude that, although alpha-, beta- and gamma 3-MSH peptides do not provide as high a sensitivity for diagnosis as protein S-100, they appear as useful markers for supportive diagnosis and assessment of malignant melanoma.

Combinatorial diffusion assay used to identify topically active melanocyte-stimulating hormone receptor antagonists

alpha-Melanocyte-stimulating hormone (alpha-MSH) is implicated in pigmentation, central nervous system and immune system functions, growth, mitogenesis, and melanoma. Evaluation of these roles has been hindered by the lack of alpha-MSH antagonists. A combinatorial chemistry-based diffusion assay is used to find random tripeptides that antagonize normal frog and human melanoma MSH receptors and to identify pharmacological groups responsible for receptor interaction. The alpha-MSH antagonist D-Trp-Arg-Leu-NH2 is used to demonstrate directly the contribution of MSH to normal skin tone in frogs following injection or topical application.

The role of trophic factors and autocrine/paracrine growth factors in brain metastasis

The brain is a unique microenvironment enclosed by the skull, lacking lymphatic drainage and maintaining a highly regulated vascular transport barrier. To metastasize to the brain malignant tumor cells must attach to microvessel endothelial cells, respond to brain-derived invasion factors, invade the blood-brain barrier and respond to survival and growth factors. Trophic factors are important in brain invasion because they can act to stimulate this process. In responsive malignant cells trophic factors such as neurotrophins can promote invasion by enhancing the production of basement membrane-degradative enzymes (such as type IV collagenase/gelatinase and heparanase) capable of locally destroying the basement membrane and the blood-brain barrier. We examined human melanoma cell lines that exhibit varying abilities to form brain metastases. These melanoma lines express low-affinity neurotrophin receptor p75NTR in relation to their brain-metastatic potentials but the variants do not express trkA, the gene encoding a high affinity nerve growth factor (NGF) tyrosine kinase receptor p140trkA. Melanoma cells metastatic to brain also respond to paracrine factors made by brain cells. We have found that a paracrine form of transferrin is important in brain metastasis, and brain-metastatic cells respond to low levels of transferrin and express high levels of transferrin receptors. Brain-metastatic tumor cells can also produce autocrine factors and inhibitors that influence their growth, invasion and survival in the brain. We found that brain-metastatic melanoma cells synthesize transcripts for the following autocrine growth factors: TGF beta, bFGF, TGF alpha and IL-1 beta. Synthesis of these factors may influence the production of neurotrophins by adjacent brain cells, such as oligodendrocytes and astrocytes. Increased amounts of NGF were found in tumor-adjacent tissues at the invasion front of human melanoma tumors in brain biopsies. Trophic factors, autocrine growth factors, paracrine growth factors and other factors may determine whether metastatic cells can successfully invade, colonize and grow in the central nervous system.