Effect of neonatally injected ACTH and ACTH analogues on eye-opening of the rat

Functions of alpha-melanotropin and other opiomelanocortin peptides in labour, intrauterine growth and brain development

In a number of animals and in humans, factors from the fetal hypothalamus function in intrauterine growth, in labour and in brain development. Peptides of the opiomelanocortin family are produced by the pituitary, brain and placenta and are probably involved in these developmental processes. In the rat, alpha-MSH stimulates fetal growth, protein synthesis, wound healing and liver regeneration and it reduces periosteal bone resorption. In chick embryos, alpha-MSH restores the corticosteroid-induced growth retardation. Thus alpha-MSH seems to possess general trophic properties. The fetal brain in humans is involved in timing the moment of birth. This process is probably mediated by peptides of the opiomelanocortin family as suggested from observations in anencephaly and other congenital brain anomalies and from the influence of corticosteroids or ACTH on labour. The high percentage of premature deliveries in heroin addicts is worth examining endocrinologically, in this respect. The exact nature of the peptides and mechanisms involved in labour is not yet known. Some peptides of the opiomelanocortin family induce an acceleration of brain development. Neonatal treatment of rats with alpha-MSH alters their later behaviour while ACTH fragments accelerate the onset of eye-opening. Opiates and methadone inhibit brain development, and neonatal administration of beta-endorphin or naloxone causes permanent insensibility to temperature stimuli. The interrelated nature of the fetal pituitary, brain and placenta does not, at present, allow us to pin down which of these structures is primarily involved in the regulation of intrauterine growth, labour and brain development.

New vistas for melanocortins. Finally, an explanation for their pleiotropic functions

This paper presents a historical overview of melanocortin (MC) research from the early investigations of the many noncorticotropic effects of peptide fragments of adrenocorticotropic hormone to the present focus on the discovery and cloning of the MC receptors (MCRs). Final acceptance of the passage of neuropeptides through the blood-brain barrier provided the scientific basis for the neuropeptide concept, formulated previously by both De Weid and Kastin, that peripherally administered neuropeptides affect neural processes. The discussion includes melanocortin effects on behavior, the cardiovascular system, central and peripheral electrophysiological parameters, food intake, inflammation and analgesia, nerve regeneration and neuroprotection, and development. The localization of specific MCRs in both neural and nonneural tissues is correlated with the pleiotropic effects discussed.

Melanocortins and the treatment of nervous system disease. Potential relevance to the skin?

For several decades melanocortins have been implicated in the modulation of brain function. More recently, this idea has been supported by the identification and cloning of melanocortin (MC) receptors in the nervous system. MCs stimulate axonal growth in fetal neural tissue or in neural cell lines in culture. This feature was utilized in screening their neurotrophic or neuroprotection potential in animal studies of nervous system disease (peripheral nerve and spinal cord trauma, toxic and metabolic neuropathies, EAN, EAE, etc.). Some of these effects may be mediated by MC4 receptor activation, although as yet unknown receptors may also be involved (for instance, protection by Org 2766). To what extent MC-nervous system effects are related to known effects of MCs in skin- and neuro-immune systems, remains to be discovered. Nevertheless, it is of interest to note that activation of brain MC4 receptors profoundly affects care behavior for the body surface (skin and fur). The excessive grooming response in rodents exhibits a remarkable functional correlation with MSH activity in a brain-skin axis.

Old rats are unresponsive to the behavioral effects of adrenocorticotropin

In 28 month-old male rats, the i.c.v. injection of adrenocorticotropin [ACTH-(1-24)] (4 micrograms/rat) did not induce the typical behavioral syndrome (excessive grooming, stretching, yawning, penile erections). This indicates that the behavioral effects of melanocortins are age-dependent, suggesting either an aging-linked impairment of the nervous circuitries involved or a reduction of the number (or affinity, or both) of the brain melanocortin receptors in the elderly.

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)

Neonatal administration of oxytocin increases novelty-induced grooming in the adult rat

Three-day-old Sprague-Dawley rat pups were intracisternally infused with a single dose of oxytocin (1 microgram/2 microliters) or saline, or were untreated. As adults, these animals were observed for novelty-induced grooming, analgesia measured by the hot-plate test, and behavior in the open field. Oxytocin treatment during infancy resulted in an elevation of novelty-induced grooming when compared to saline and untreated animals. There were no significant oxytocin treatment effects on analgesia response or open-field behaviors. Oxytocin given early in life may have permanent effects on certain behavioral responses to stress.

Prenatal ontogenesis of pro-opiomelanocortin in the mouse central nervous system and pituitary gland: an in situ hybridization and immunocytochemical study

Pro-opiomelanocortin (POMC) mRNA detected by in situ hybridization and POMC/ACTH (adrenocorticotropin)-containing neurons detected by immunocytochemistry were first observed in the presumptive arcuate nucleus of embryonic mouse brain on gestational day 10.5 (E10.5). Immunostained fibers were also evident on E10.5 in the lateral and dorsal diencephalon. In these areas, a dense network of processes developed by E11.5 and extended into the mesencephalon. Fibers were detected in the myelencephalon at this stage and a day later (E12.5) in the spinal cord. Adult-like patterns of POMC/ACTH fibers were established in the diencephalon, mesencephalon, metencephalon and the myelencephalon between E13.5 and E15.5. POMC-expressing cells in the anterior and intermediate lobes of the pituitary gland appeared on E12.5 and E14.5, respectively. The early expression of POMC and the rapid establishment of dense fiber tracts in the brain is consistent with a role for POMC-derived peptides in the development of the central nervous system.

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)

Pre- and postnatally administered ACTH, Organon 2766 and CRF facilitate or inhibit active avoidance task performance in young adult mice

This study investigated the effect of learning/memory-related neuropeptides on behavioral task performance in later life. A 1 mg/kg dosage of adrenocorticotropic hormone 4-9, Organon 2766, ACTH/MSH 4-10, ACTH 1-24, CRF, or diluent was subcutaneously injected into either pregnant females or into newborn pups during specific neural developmental windows. Each of the progeny was trained in an active-avoidance task and tested for acquisition on postpartum days 35-37. The mice were then tested for memory task performance and reacquisition on days 42-44 postpartum using the identical experimental paradigm as that used in the training sessions. Prenatal treatment with these memory-related neuropeptides resulted in significant facilitation of learning/memory task performance in male and female mice treated with Organon 2766 (p less than 0.001), and a significant inhibition of learning/memory task performance in males and females treated with ACTH 1-24 (p less than 0.01). Additional sex-specific performance facilitations and inhibitions resulted from the pre- or postnatal administration of the various neuropeptides used in this study. These results suggest that neuropeptides, when available in increased amounts during specific neural developmental windows, can significantly improve or suppress related behavioral performance capability in later life.

alpha-MSH and Org.2766 in peripheral nerve regeneration: different routes of delivery

The efficacy of melanocortins (alpha-MSH and an ACTH-(4-9) analog, Org.2766) in accelerating functional recovery from sciatic nerve damage following various types of subcutaneous and oral administration was assessed in the rat. Furthermore, the effectiveness of the local delivery of melanocortins to the site of injury was examined. An accelerated recovery was evident following subcutaneous constant delivery of Org.2766 from an osmotic mini-pump and from biodegradable polymere microspheres, and was as effective as repeated subcutaneous injections of alpha-MSH or Org.2766. Oral administration of Org.2766 was ineffective. Local application of Org.2766, achieved by wrapping a peptide-impregnated biodegradable gelatine foam matrix around the site of injury, facilitated recovery as well. The biodegradable microspheres and gelatine foam matrix may be of importance in eventual clinical use as effective vehicles for administration of melanocortins in the treatment of peripheral nerve damage.

The effects of maternal isolation and light and feeding cycles on the growth of rat pups

Rat pups were implanted with intragastric catheters and reared in isolation from their dams and siblings from 3 to 18 days postnatally. They were kept in 12:12 LD or DL, constant light, or constant darkness and were fed with one of three feeding schedules: equal amounts of food delivered during the light and dark periods, 65.3% of the food delivered during the light period, or 65.3% of the food delivered during the dark period. At 18 days postnatally the body, spleen, and kidney weights of all isolated pups did not differ from those of their mother-reared littermates. The isolated pups had smaller cerebellums and forebrains and heavier livers than mother-reared pups. Heavier body and spleen weights and smaller livers were observed in pups with cyclic feeding. Heavier body and forebrain weights were associated with a predominantly diurnal feeding schedule--the schedule which most closely approximated the natural nursing rhythm. Isolated pups opened their eyes sooner than mother-reared littermates. These results suggest that interactions between feeding and light cycles may influence growth and development.

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.

Alpha-melanocyte-stimulating hormone infusions during pregnancy in the rat: effects on offspring weight, pain reactivity and sexual behavior

Pregnant rats treated during the last third of pregnancy with a continuous infusion of alpha-melanocyte-stimulating hormone (alpha-MSH) produced offspring that weighed less at birth and in adulthood. These offspring of the alpha-MSH treated mothers were less sensitive to pain and as adults showed a reduced analgesic response to morphine. Male offspring of alpha-MSH treated mothers and of control animals responded similarly in sexual performance tests, except that the treated animals significantly shifted their pattern of responding when they encountered a new testing arena or experienced defeat. The offspring of alpha-MSH treated mothers were influenced more by changes in their environment than were control offspring. These effects are similar to those reported following perinatal treatment with opiate drugs or peptides.

Neonatal peptides affect developing rats: beta-endorphin alters nociception and opiate receptors, corticotropin-releasing factor alters corticosterone

The dose-response relationship of neonatal (days 1-7) administration of beta-endorphin (BE) and corticotropin-releasing factor (CRF) on body weight, eye opening, response to thermal pain, and concentrations of plasma and adrenal corticosterone were measured in developing rat pups. At the highest dose (50 micrograms/pup), neonatal CRF reduced body weight, while 10 and 50 micrograms/pup accelerated eye opening. In addition, a reduction in concentration of plasma and adrenal corticosterone was correlated with the dose of neonatal CRF, whereas adrenal weights were not altered. BE produced none of these effects, but 1, 10 and 50 micrograms/pup on days 1-7 significantly reduced baseline latencies in a novel water-bath tail-flick test on day 9. These same animals showed reduced numbers of brain opiate receptors on day 14. The results indicate that peptide administration during the sensitive neonatal period can alter the development of physiological processes that will later be influenced by the peptide.

Melanocortins, neural plasticity and aging

Peptides derived from ACHT and alpha-MSH are known to exert trophic influences on peripheral and central nervous structures. Age-related brain diseases may in part be related to loss of neural plasticity. Melanocortins improve adaptional abilities of the nervous system. Chronic treatment with melanocortins may counteract age-related brain pathology.

Developmental, behavioral, and opiate receptor changes after prenatal or postnatal beta-endorphin, CRF, or Tyr-MIF-1

Developmental and long-term behavioral effects of perinatal injection of beta-endorphin (BE), CRF and Tyr-Pro-Leu-Gly-NH2 (Tyr-MIF-1) in male rats were investigated along with the possibility that opiate receptors may be altered by the injection of BE during this critical time. Daily injections of peptide were given to pregnant females (100 micrograms/rat) in the week before birth or to the offspring (50 micrograms/rat) of untreated mothers during the first week of life. Prenatal BE and CRF reduced body weight on day 1, in contrast to Tyr-MIF-1 which produced a significant increase over controls by day 7 as well as a slight but significant acceleration of eye opening. Among the postnatal treatments, CRF-treated animals showed the most dramatic changes. These included decreased body weight, accelerated eye opening, and, in adulthood, increased open field rearing behavior and a tendency for a monotonic body temperature response to low doses of morphine, in contrast to the biphasic response shown by controls. BE, when given to pregnant mothers, increased the number (Bmax) of [3H]naloxone-labeled (mu) receptors in whole brains of offspring assayed on day 14, but it did not significantly alter [3H]D-Ala-D-Leu-enkephalin-labeled (delta) receptors. In contrast, a significant decrease in both mu and delta receptors was observed on day 14 in rats given BE postnatally. These differences in receptors were no longer apparent in adulthood, and no significant differences in tail-flick response were detectable at this time. Nevertheless, some of the effects of these three peptides endured well beyond their presence, and for BE included changes in the number of opiate receptors.

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.

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.

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).

Neonatal administration of Met-enkephalin facilitates maze performance of adult rats

Newborn rats were injected SC during the first week of life with 80 microgram/kg Met-enkephalin, DSIP, MIF-I, or diluent. When tested 3 months later in a 12-choice maze for a reward of food, hungry rats injected neonatally with Met-enkephalin were found to run the maze faster and with fewer errors than the controls. DSIP and MIF-I did not improve performance in the maze, indicating some specificity to the findings. Tyrosine hydroxylase and choline acetyltransferase activity in several parts of the brain were not significantly different among the groups. Radioimmunoassay of brain parts from a small number of adult rats indicated slightly more DSIP-like material in the thalamus and striatum of females injected neonatally with DSIP as compared with those injected with diluent. The results extend our previous observations of the persistence of central effects of peripherally injected Met-enkephalin from several minutes to three months when administration occurs early in life. The findings further suggest an effect of peptides on the organization of the developing brain.