Neuromuscular response of the immature rat of ACTH/MSH 4--10

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.

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.

Effect of beta-endorphin on the contractile responses in mouse skeletal muscle

Tension development in response to direct and indirect electrical stimulation was studied in an isolated phrenic nerve hemidiaphragm preparation of the mouse. beta-Endorphin (beta-EP) caused an increase in the amplitude and a decrease in the time to peak of muscle contractions in response to low frequency stimulation of the nerve. Upon direct stimulation of the muscle the peptide had no effect. The actions of beta-EP were abolished in the presence of the opioid antagonist naloxone and mimicked by delta opioid agonists. Upon high frequency stimulation of the nerve, beta-EP caused an increase in the initial, maximum, and mean tension. It also prevented the fall in the final tension seen in the control preparations with repeated periods of stimulation. The findings are consistent with beta-EP having a role to improve neuromuscular function and delay fatigue, and indicate the possible therapeutic potential of opioid substances in conditions where muscle weakness is present.

Effect of beta-endorphin and alpha-melanotropin on muscle wasting in mice

The pro-opiomelanocortin-derived peptides beta-endorphin (beta-EP) and alpha-melanocortin (alpha-MSH) were administered to normal and dystrophic C57BL6J mice. All groups of normal and dystrophic mice which had been treated with the two peptides gained significant body weight, as did the normal and dystrophic saline-treated male controls, but the normal and dystrophic female controls did not. The plasma activity of creatine phosphokinase (CPK) was lower in normal mice and dystrophic males which had been treated with the two peptides compared to the corresponding controls. There was no significant difference between the plasma LDH activity in any of the peptide-treated and the corresponding control groups. The activity of CPK was significantly higher in the extensor digitorum longus (EDL) muscles, but not the soleus muscles, of the peptide-treated dystrophic mice compared to the corresponding controls. Administration of alpha-MSH alone or beta-EP alone had no significant effect on the body weight or plasma CPK activity of dystrophic mice compared to the controls. However the activity of CPK was significantly higher in the EDL muscles of the alpha-MSH-treated mice than in the corresponding controls. It is possible that beta-EP and alpha-MSH act synergistically on the neuromuscular system to protect the muscles from damage.

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.

Cloning, expression, and tissue distribution of a fifth melanocortin receptor subtype

The melanocortin (MC) peptides mediate a diverse spectrum of biological activities in both the central nervous system and peripheral tissues by interacting with specific guanine nucleotide binding (G protein)-coupled receptors. Previously, four human melanocortin receptor subtypes have been cloned and characterized. In this study, we have isolated mouse complementary DNA (cDNA) and human genomic clones encoding a fifth melanocortin receptor subtype, MC5. Melanocortin peptide stimulation of human MC5, transiently expressed in COS1 cells, results in activation of adenylate cyclase with the following rank order of potency: [Nle4, D-Phe7]-alpha-MSH (melanocyte stimulating hormone) > ACTH (1-24) (adrenocorticotropic hormone) > alpha-MSH > beta-MSH > gamma-MSH. Northern blot hybridization, ribonuclease protection, and reverse transcription/polymerase chain reaction assays indicate that mouse MC5 mRNA is most abundant in skeletal muscle and brain. Lower but detectable levels of MC5 mRNA are also found in RT2-2 retinal neuronal cells, lung, testis, spleen, heart, kidney, and liver.

Upregulation of the pro-opiomelanocortin gene in motoneurons after nerve section in mice

In the normal adult mouse a few of the ventral horn motoneurones were slightly immunoreactive for the pro-opiomelanocortin (POMC)-derived peptides beta-endorphin (beta-EP) and alpha-melanotropin (alpha-MSH). After unilateral section of the sciatic nerve the incidence of immunoreactive cells and the intensity of staining increased in both the ipsilateral and the contralateral ventral horns. The proportion of cells which expressed the peptides reached a maximum at approximately 24 h after nerve section, and thereafter declined, but the proportion was still higher than normal at 7 days after the section. Using histochemical in situ hybridization with cDNA oligonucleotide probes for POMC transcript regions which encode for adrenocorticotropin (ACTH) 4-11 and beta-endorphin 1-8, POMC mRNA was detected in very few motoneurones in unoperated or sham operated mice. After unilateral sciatic nerve section increases in the proportion of cells which expressed the POMC mRNA were seen in both the ipsilateral and contralateral ventral horns. The increase, like that seen for peptide immunoreactivity, was maximum at around 24 h and thereafter declined but at 7 days after the section the proportion of POMC mRNA-positive cells had returned to normal. Thus injury to the motoneurones is accompanied by synthesis of POMC-derived peptides via upregulation of the POMC gene in the motoneurone.

Melanocortins as factors in somatic neuromuscular growth and regrowth

Melanocortins, non-corticotropic fragments of adrenocorticotropic hormone, accelerate growth of the developing neuromuscular system and regrowth of damaged neurons, both in the adult and neonatal rat. Morphological, electrophysiological and behavioral characteristics are all improved by melanocortins, which, however, vary in potency, with alpha-MSH being the most effective. Tissue substrate, dosage, critical time periods and pattern of neuropeptide administration are all important variables. Melanocortins protect central neurons affecting motor behavior during development or following neuronal damage in the adult brain. Possible mechanisms of melanocortin action are discussed.

ACTH (4-10) increases quantal content at the mouse neuromuscular junction

Adrenocorticotropic hormone 4-10 (ACTH 4-10), in concentrations of 50 nM and 1 microM, increased both the frequency of miniature endplate potentials and the amplitude of the endplate potentials in addition to decreasing the number of failures following stimulation of the phrenic nerve in the mouse in vitro. There was no effect of the peptide on either the amplitude of the miniature endplate potentials or the resting membrane potential of the muscle fibres. These results indicate that the action of ACTH 4-10 was to increase the quantal content of the endplate potential via a presynaptic action.

Upregulation of the pro-opiomelanocortin gene in spinal motoneurones in muscular dystrophy in mice

Pro-opiomelanocortin (POMC) mRNA was detected in motoneurones of mice using histochemical in situ hybridization and cDNA oligonucleotide probes for the adrenocorticotropin (ACTH) 4-11 and beta-endorphin 1-8 regions of POMC. Staining for POMC mRNA was negligible in motoneurones in normal adult mice but in dystrophic mice the mRNA was present in > 60% of the ventral horn cells. It is concluded that neuropathic change in motoneurones is accompanied by upregulation of the POMC gene and synthesis of POMC-derived peptides.

Pro-opiomelanocortin neuropeptide receptors on developing and dystrophic muscle fibers

Autoradiography was used to investigate the presence of corticotropin and beta-endorphin receptors on soleus, extensor digitorum longus, and diaphragm muscles of normal and dystrophic adult mice and developing mice. In both adult and developing mice, specific binding sites for both [125I]ACTH and [125I]beta-endorphin were present in some fibers in all of the muscles examined. The specific binding sites appeared to be distributed over the length of the surface membrane in the fibers that expressed them. There were significantly higher proportions of fibers exhibiting the specific beta-endorphin and the specific ACTH binding sites in the three muscle types in mice of 5 d of age compared to the muscles of the normal adult. There was also a higher proportion of fibers with the putative ACTH and beta-endorphin receptors in the three muscle types in dystrophic mice.

Postnatal administration of two peptide solutions affects passive avoidance behaviour of young rats

The effects of two subcutaneously injected peptide solutions CERE (100 mg/kg b. wt.) and E021 (1 mg/kg b. wt.) and of 0.9% saline on passive avoidance reaction (PAR) of young rats were examined. Animals were trained and tested in a step-through avoidance task using a footshock of 0.5 mA or 1 mA. Step-through latencies were observed up to 200 s and from these data the percentage of good learners (latency = 200 s) and bad learners (latency < 200 s) was calculated. Two experimental schedules were performed (n > 6). In Expt. 1 rat pups were chronically treated with the substances within the first 7 days after birth. In Expt. 2 the 7 days of treatment started in the 4th postnatal week. In both experiments PAR acquisition was trained on the 28th day after birth (learning trial), PAR extinction testing started on the 29th day (retention trials). After applying a 0.5-mA footshock, rat pups treated with E021 within the first 7 days of life (Expt. 1) displayed significantly slower PAR extinction when compared to saline- and CERE-treated rats. In the 1 mA groups, significant differences in step-through latencies were measured between 0.9% saline- and E021-pretreated animals on retention day 11 and between saline and CERE on retention days 9 and 13. E021-treated rats of Expt. 2, receiving a footshock intensity of 0.5 mA, showed significant lower step-through latencies when compared to E021-treated rats of Expt. 1. In Expt. 2 no significant differences between treatment groups were observed.(ABSTRACT TRUNCATED AT 250 WORDS)

POMC-derived peptides in the neuromuscular system of streptozotocin-diabetic mice

Immunoreactivity for beta-endorphin and alpha-MSH/ACTH was demonstrated in intramuscular nerves in soleus, extensor digitorum longus, and diaphragm muscles of normal and streptozotocin-diabetic mice. There was a higher incidence of immunoreactive nerves in the muscles of the diabetic mice. Specific binding for [125I]ACTH was detected in a proportion of the muscle fibers, using autoradiography. There were significantly more fibers with specific [125I]beta-endorphin sites and specific [125]ACTH sites in some muscles in the diabetic mice. The increased expression of POMC-derived peptides and their receptors in the neuromuscular system of streptozotocin-diabetic mice may indicate early neuropathic change.

Effect of IDPN on the expression of POMC-derived peptides in rat motoneurones

Immunocytochemistry was used to detect beta-endorphin and alpha-melanotropin (alpha-MSH) in lumbar spinal motoneurones in rats treated with beta,beta'-iminodiproprionitrile (IDPN), a neurotoxicant that targets motoneurones or corn oil, which has no known neurotoxicity. After IDPN treatment most of the motoneurones were immunoreactive for both peptides but after corn oil treatment immunostaining was negligible. It is suggested that increased expression of the POMC-derived peptides may be part of the regenerative repertoire of the damaged motoneurone regardless of the cause of the lesion. Alternatively the peptides may simply accumulate in the motoneurones as a result of impaired axoplasmic transport.

Beta-endorphin and corticotropin immunoreactivity and specific binding in the neuromuscular system of obese-diabetic mice

Immunoreactivity for two derivatives of pro-opiomelanocortin, beta-endorphin and alpha-melanocortin (or corticotropin), was demonstrated, using a conventional immunoperoxidase method, in some of the intramuscular nerves in muscle sections from obese diabetic (ob/ob) mice and homozygous lean (+/+) mice. The endplate regions were visualized in the sections by staining for acetylcholinesterase reaction product. The proportion of muscle endplates with beta-endorphin-immunoreactive motor nerves was approximately 2.5-fold higher in soleus and extensor digitorum longus muscles and approximately 1.5-fold higher in the diaphragm of the obese (ob/ob) mice compared to the normal lean mice. The proportion of muscle endplates with alpha-melanotropin-immunoreactive motor nerves was between 30 and 53% lower, depending on the muscle type, in the ob/ob mice compared to the lean mice. The muscles of ob/ob and lean mice were investigated for the presence of specific binding sites for [125I]beta-endorphin and for [125I]corticotropin, using autoradiography. Some muscle fibres in soleus, extensor digitorum longus and diaphragm in both the ob/ob and the lean mice exhibited specific binding sites for the radioactive ligands. The binding sites were distributed over the entire surface in these muscle fibres. In the ob/ob mice the number of muscle fibres with specific [125I]beta-endorphin binding sites was six-fold higher in soleus and approximately 10-fold higher in extensor digitorum longus and diaphragm, than in the corresponding muscles of the lean mice. In contrast, the number of muscle fibres with specific [125I]corticotropin binding sites was similar in obese (ob/ob) and lean mice.(ABSTRACT TRUNCATED AT 250 WORDS)

Proopiomelanocortin-derived peptides in mice with motoneurone disease

beta-Endorphin and alpha-melanotropin immunoreactivity was detected in motor nerves in histological sections of murine skeletal muscle, using the peroxidase-antiperoxidase technique. In mice of the wobbler strain, which can inherit motoneurone disease, a significantly higher proportion of the intramuscular nerves in soleus, extensor digitorum longus and diaphragm muscles of the diseased mice were immunoreactive than in the corresponding muscles of their healthy littermates.

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)

Effect of nerve section on beta-endorphin and alpha-melanotropin immunoreactivity in motor nerves of normal and dystrophic mice

beta-Endorphin and alpha-melanotropin immunoreactivity was demonstrated in some motor nerves in histological sections of soleus and extensor digitorum longus muscles of the mouse. In two strains (C57BL/6J and 129/ReJ) which can inherit muscular dystrophy, the proportion of immunoreactive nerves was greater in the dystrophic individuals than in their healthy littermates. At 24 h after section of the sciatic nerve in the normal mice the proportion of immunoreactive nerve profiles had increased significantly in the denervated muscles even though most of the nerve axons had degenerated. Similar increases were also seen in nerves in the unoperated contralateral muscles.

ACTH peptides stimulate motor nerve sprouting in development

Maturational changes at the neuromuscular junction (nmj) of rat neonates were studied using scanning electron microscopy and light microscopy that permitted quantification of muscle fiber diameter, length of nerve terminal branching, end-plate area, and perimeter. Administration of ACTH 4-10 (10 micrograms/kg s.c. daily from day of birth) stimulated nerve terminal branching, an effect most evident in 14-day-old pups. The trisubstituted derivative of ACTH 4-9 (Org 2766) when administered at 0.01 microgram/kg/daily, had a more potent effect, increasing end-plate perimeter and nerve terminal branching on the first postnatal week and markedly increasing only nerve terminal branching at 14 days of age. This is a dose-responsive action since 10 micrograms/kg/daily severely inhibits nerve sprouting. By 21 days, there were no differences between peptide- and saline-treated neonates. Peptide-induced sprouting was elicited only in the first 2 weeks of postnatal life. This time course corresponds with the critical period for nmj maturation and ceases when polyneuronal innervation of muscle fibers also terminates. It is suggested that ACTH peptides may exert a physiological role on nerve sprouting during development.

Axonal transport of 16S acetylcholinesterase is increased in regenerating peripheral nerve in guinea-pig, but not in rat

The axonal transport of the molecular forms of acetylcholinesterase was investigated in regenerating facial nerves of guinea-pig and rat. Four forms were separated by velocity sedimentation corresponding to 16S (A12), 10S (G4), 6S (G2) and 4S (G1) acetylcholinesterase. They displayed species-specific changes, which are in good accordance with those previously found in the neuronal perikarya. In the rat, axonal transport decreased for all forms. In the guinea-pig, however, the molecular forms showed differential changes. Whereas after transection, the nerve content of 10S acetylcholinesterase decreased, 16S activity was considerably increased. Anterograde transport of 16S acetylcholinesterase was found to be enhanced, whilst transport of the 10S from decreased. The two lighter forms showed only minor changes. Similar results were obtained for the guinea-pig sciatic nerve. Changes in the localization of acetylcholinesterase activity were investigated by electron microscopical cytochemistry. In the normal facial nerve of both species, activity was located intra-axonally in tubular membraneous structures and on the outer surface of the axonal membrane. In the regenerating facial nerve of the rat, intra-axonal as well as axolemmal activity decreased. Axonal sprouts at the end of the proximal nerve stump showed no activity. In the guinea-pig, however, activity of the axonal membrane increased. This was especially prominent on the surface of axonal sprouts. Strong activity was found also in the extracellular space between the sprouting axons and in the endoneurial space filled by collagen fibres. Biochemical analysis of this region revealed that the histochemical activity was mainly due to the A12 form. Thus it was concluded that, in the guinea-pig, axonal sprouts represent a target for axonally transported A12 acetylcholinesterase, which may also be secreted to extracellular sites.

Is nicotine depression of neonatal motor behavior exerted through ACTH release?

Prenatal exposure to nicotine tartrate (0.25 mg/kg/pregnant female, gestation days 3 through 21.2x daily IP) markedly decreases ambulatory activity and the number of stop and go movements in 15 day old neonatal rats. Postnatal nicotine tartrate administration alone (0.05 mg/kg SC daily from birth) does not affect these movements nor does it further the motor depression induced by prenatal nicotine treatment. Thus the critical period of neural susceptibility to nicotine appears to be during prenatal life. However, when nicotine is given both pre- and postnatally, horizontal movements are increased in the 15 day old animals, an increase that may be due to inhibition of other types of movement. These alterations in motor behavior are correlated with sharp increases in plasma ACTH levels. As our previous studies [1,25] have shown ACTH to affect neonatal motor behavior, it is suggested that nicotine-evoked ACTH release may mediate some of the motor responses attributed to the drug.

Neonatal neuromuscular parameters vary in susceptibility to postnatal ACTH/MSH 4-10 administration

Neonatal Sprague-Dawley rats administered the fragment of adrenocorticotropic hormone ACTH/MSH 4-10 (10 micrograms/kg/daily, SC) postnatally, show marked differences in the plasticity of the functional and morphological parameters of their neuromuscular system. Initial contraction durations of the immature fast muscle, extensor digitorum longus (EDL), are shorter than saline-treated controls indicating accelerated development. Qualitative studies of the developing EDL neuromuscular junctions as viewed by the scanning electron microscope and quantitative analysis permitted by light microscopy confirms that ACTH/MSH 4-10 affects the maturation of the endplate region. Motor behavior of rat pups demonstrates an age-related difference in the susceptibility to this peptide fragment; one week old neonates showing no response to ACTH/MSH 4-10, two week old pups showing an increase in motor activity. The results indicate that while the developing neuromuscular system is sensitive to the input of ACTH/MSH peptide treatment, this susceptibility is age-related.

Mammalian neuromuscular development accelerated with early but slowed with late gestational administration of ACTH peptide

The neuropeptide ACTH 4-10, a nonsteroidogenic fragment of adrenocorticotropic hormone, has two distinct and opposite effects on developing nerve and muscle. Muscle is positively influenced by ACTH during the first part of gestation (G days 3-12) before innervation occurs. Subsequent effects on innervation are largely depressive and exerted only during G13-21. Treatment during G3-12 increases twitch amplitude, rise time and speed of contraction of directly and indirectly stimulated extensor digitorum longus (EDL) muscle of two wk old rats. Treatment during G13-21 slows contractions of indirectly stimulated EDL, whereas treatment throughout gestation (G3-G21) shows little effect. Thus, ACTH first accelerates muscle development then modulates this development through neuronal depression.

Neonatal exposure to a high level of ACTH4-10 impairs adult learning performance

Male offspring of Sprague-Dawley dams were injected with 25 micrograms of ACTH4-10 or the vehicle on days 2 through 7 postpartum. Peptide treated animals exhibited a marked motor response to the peptide injection. Adrenal weights of these animals were consistently heavier than littermate controls in both the developing and adult animals. ACTH4-10 treated neonates exhibited significantly poorer learning performance in the shuttle box and were slower to acquire the reversal learning problem of a visual discrimination task under light shock levels. In addition, these animals also exhibited an exaggerated startle response and a stronger thigmotaxis response in the open field than controls. These results indicate that exposing the developing nervous system to relatively high levels of ACTH4-10 can produce marked long-term effects on behavior.

Org.2766 improves functional and electrophysiological aspects of regenerating sciatic nerve in the rat

The beneficial effect of short-term (8 days) melanocortin therapy on regenerating peripheral nerves is demonstrated using functional and electrophysiological tests. Following a crush lesion of the rat sciatic nerve, recovery of sensory function is monitored by assessing the responsiveness of the rat to a small electric current applied to the footsole. Recovery of motor function is assessed by means of an analysis of walking patterns. Normalization of the walking pattern reflects reinnervation of different muscle groups. The motor and H-reflex related sensory nerve conduction velocity of the regenerated nerves are longitudinally investigated in the same rats in which the recovery of motor and sensory function had been assessed previously. Functional tests show an enhanced recovery under melanocortin therapy, but in the end both saline- and melanocortin-treated rats show 100% recovery. However, when compared to the contralateral sciatic nerve, in the peptide-treated animals motor nerve conduction in the regenerated nerves has fully recovered after about 90 days following the crush lesion and the sensory conduction after about 120 days, whereas in the saline-treated rats a deficit of 20-40% in both motor and sensory conduction remains. This difference is observed even 214 days following crush.

ACTH peptides as organizers of neuronal patterns in development: maturation of the rat neuromuscular junction as seen by scanning electron microscopy

SEM was used to visualize the normal postnatal development of the neonatal rat neuromuscular junction (nmj). Maturational changes evoked by ACTH/MSH 4-10 (10 micrograms/kg/day IP) or ACTH/MSH 4-9 (Org 2766) (0.01 microgram/kg/day IP) were compared to controls and to pups treated with nicotine during prenatal and postnatal life, or only during the gestation period. Pregnant females received 0.25 mg/kg 2X daily IP; neonates 0.05 mg/kg/day SC. The Desaki and Uehara and Fahim et al. methods revealed the nmj on the extensor digitorum muscle to be covered by a delicate drapery of postjunctional folds that surround the immature endplate region. By the second week of postnatal life, these folds become more complex and cover a larger area. Upon maturation the folds descend and invaginate into the muscle fiber. Peptide treatment with either ACTH/MSH 4-10 or ACTH/MSH 4-9 accelerates maturation of the endplate as demonstrated by the increased convolutions of the folds. Similar effects follow nicotine administration. The observed changes in morphology of the developing nmj subjected to nicotine may be mediated through nicotine-evoked ACTH release.

Vasopressin and brain development: studies using the Brattleboro rat

Anomalies in hormonal and neurotransmitter status during early stages of brain development, can lead to lifespan alterations in the functioning of central systems. The neuropeptide vasopressin is nowadays recognized as a putative neurotransmitter, after years of study on its neurosecretory hormonal aspect in water metabolism. Since vasopressin is moreover present early in the brain, and has various mitogenic, metabolic and physiological actions, one might expect vasopressin to be of importance for normal brain development as well. Indeed, the absence of brain vasopressin in the Brattleboro mutant rat coincides with impaired brain development, and some physiological and behavioral defects of these rats are not adjusted by treatment with vasopressin. Regionally the cerebellum seems to be the most affected brain area, both morphologically and biochemically. Only when vasopressin supplementation was done prenatally, this disturbed growth could be restored, which suggests an early role for vasopressin in neurogenesis. Enhanced levels of vasopressin during the perinatal period on the other hand, have been shown to affect permanently the 'setting' of peripheral vasopressin functions in cardiovascular and renal regulatory systems. It is not excluded as yet that after such treatments central organization of vasopressin systems is not impaired as well.

Development and regeneration of motor systems under the influence of ACTH peptides

ACTH peptides exert quantitative and qualitative influences on the formation and maturation of motor units in developing and regenerating neuromuscular systems. ACTH 4-10, administered daily (10 micrograms/kg. s.c.) from the day of birth, accelerated the rate at which muscle strength developed in the immature rat, the effect of this peptide being most marked in animals 11-15 days old. A similar increase in grasping time occurred in ACTH 4-10 treated animals, indicating that the peptide affects neuronal maturation at a time in development when organization and maturation of the neuromuscular system is most active. The synthetic analogue of ACTH 4-9 (Org 2766), administered in the same dosage, had little effect on these parameters, indicating a differential sensitivity to these similar peptides. Elevated circulating titers of ACTH, whether exogenous (0.2 U ACTH 1-39 IP daily), or endogenous (adrenalectomy), stimulated the formation of more functional motor units, as indicated by increased amplitude of muscle action potentials and tetanic tension following nerve stimulation. ACTH appears to favor the recovery of high threshold, small-size motor units. Fine control of muscle function in peptide-treated animals is partially restored, as indicated by the return of stepwise recruitment to an extent not seen in the reinnervated, saline-treated controls.

Neuropeptide effects on brain development to be expected from behavioral teratology

A wealth of literature has become available about lasting functional consequences of perinatal psychotropic drug exposure, having affected brain development in a subtle rather than gross structural way (behavioral teratology or functional neuroteratology). The underlying mechanism is thought to result from changing levels of neurotransmitters during neurogenesis induced by these neuroactive drugs, which as a consequence appears to lead to impaired cell acquisition and receptor setting i.e., to irreversible changes in particular neuronal circuitries. Neuropeptides are true candidates for a neurotransmission function as well, and are also present early in brain development. As for the classical neurotransmitters, a role for neuropeptides in the growth and functional organization of the nervous system, might therefore be expected. Anomalies in neuropeptide levels also would lead to functional neuroteratology. Although not overwhelming, several studies support this view, and the current state is summarized in this paper: a trophic role for some neuropeptides as well as neuroteratological effects upon perinatal manipulation for others were revealed. However, more detailed studies are necessary, certainly also because of the crying need for exposing possible adverse effects at a time when clinical applications of neuropeptides and their analogues are becoming a mode.

ACTH neuromodulation of the developing motor system and neonatal learning in the rat

ACTH peptides influence the developing nervous system during the first three weeks of life in the rat. ACTH 4-10 and Org 2766 (10.0 micrograms/kg) accelerate the expression of motor hyperactivity usually exhibited in 15-day old normal animals, with ACTH 4-10 increasing the force of extensor digitorum longus muscle contraction amplitude. Following cold stress and peptide treatment, rate changes in motor activity from one age to the next are dramatically enhanced, with vertical activity being exhibited at an earlier age than controls. Grasping ability is similarly enhanced in 13-day old ACTH 4-10-treated animals. The retention of a T-maze learning paradigm is significantly enhanced in 16-day old ACTH 4-10 (10.0 micrograms/kg)-treated and Org 2766 (0.01 micrograms/kg)-treated animals, with these animals running the maze significantly faster than controls. Peptide treatment appears to reverse the apparent turning preference in the maze during extinction. It is suggested that ACTH peptides modulate the organization of the nervous system and facilitate neurotransmission, and may act on dopaminergic and cholinergic neurotransmitter systems. Motor behavior seems to reflect underlying neural substrates that are integrated to produce the overt behavior of the organism.

Natriuretic and hypertensive activities reside in a fragment of ACTH

The hypertensive and natriuretic effects of chronic administration of adrenocorticotrophic hormone (ACTH) cannot be duplicated by the administration of glucocorticoids and/or mineralocorticoids. We investigated the effects of a fragment of this hormone (ACTH4-10) and an analog of the fragment (D-Phe7) ACTH4-10 and found them to have pressor and cardioaccelerator actions in rats as determined by bolus intravenous (i.v.) injections of 30 to 1000 nmol/kg. The pressor and cardioaccelerator effects of (D-Phe7) ACTH4-10 were attenuated by alpha-receptor (phentolamine) and beta-receptor (metoprolol) antagonists. The cardiovascular actions of ACTH4-10 were produced in adrenalectomized or ganglionic-blocked (with mecamylamine) rats. At a lower dose (7 nmol/kg i.v.), ACTH4-10 was natriuretic and had a pattern of activity similar to that of a larger ACTH fragment, alpha-melanocyte-stimulating hormone. Extraadrenal effects of the intact ACTH molecule or the in vivo production of an ACTH4-10-like fragment from ACTH may contribute to the hypertensive and natriuretic actions associated with this hormone.

Central nervous system and peripheral effects of ACTH, MSH, and related neuropeptides

Adrenocorticotropic Hormone (ACTH), Melanocyte-Stimulating Hormone (MSH), and related peptides have been shown to have several neurogenic effects: alteration of cerebral protein synthesis, RNA synthesis, protein phosphorylation, and neurotransmitter turnover. Furthermore, there appears to be an ACTH containing circuit in the CNS which originates in the arcuate nucleus. Changes in concentration of the peptides in this family have been shown to alter electrophysiology, neuromuscular function, and behavior (e.g., grooming, learning) in infrahuman subjects. These findings suggest that the neuropeptides MSH and ACTH influence the capacity of an organism to efficiently evaluate information and influence the affective functioning of humans.

Peptide influences on the development and regeneration of motor performance

ACTH 1-39 (0.2 U IP daily for up to 18 days) has a beneficial effect on the functional reorganization of regenerating motor units of the extensor digitorum longus (EDL) in the adrenalectomized adult rat following crushing of the peroneal nerve. Motor unit activity (maximum twitch tension amplitude/mean increment in twitch tension as voltage is increased by 0.1 V gradations) and nerve-muscle efficiency (tetanic tension from indirect stimulation/tetanic tension from direct stimulation of EDL) were enhanced by ACTH 1-39. Other electrophysiological and contractile parameters were unaffected by the peptide. Spontaneous motor activity in cold stressed 13 day old rats was prolonged by Org 2766, a substituted analogue of ACTH/MSH 4-9, (0.1 microgram/kg daily) but unaffected by the same dosage of ACTH/MSH 4-10. The responsiveness of developing and regenerating motor systems to neuropeptides indicates a plasticity of neuronal connections, which depends on peptide sequence, dosage and the physiological state of the animal (normal, depressed, regenerating or developing, at rest or stressed).