Behavioral effects of neuropeptides related to ACTH, MSH, and betaLPH

Optogenetically enhanced pituitary corticotroph cell activity post-stress onset causes rapid organizing effects on behaviour

The anterior pituitary is the major link between nervous and hormonal systems, which allow the brain to generate adequate and flexible behaviour. Here, we address its role in mediating behavioural adjustments that aid in coping with acutely threatening environments. For this we combine optogenetic manipulation of pituitary corticotroph cells in larval zebrafish with newly developed assays for measuring goal-directed actions in very short timescales. Our results reveal modulatory actions of corticotroph cell activity on locomotion, avoidance behaviours and stimulus responsiveness directly after the onset of stress. Altogether, the findings uncover the significance of endocrine pituitary cells for rapidly optimizing behaviour in local antagonistic environments.

Altered expression of adrenocorticotropic hormone in the epileptic gerbil hippocampus following spontaneous seizure

We investigated the temporal alterations of adrenocorticotropic hormone (ACTH) immunoreactivity in the hippocampus after seizure onset. Expression of ACTH was observed within interneurons in the pre-seizure group of seizure sensitive gerbils, whereas its immunoreactivities were rarely detected in seizure resistant gerbil. Three hr after the seizure, ACTH immunoreactivity was significantly increased in interneurons within all hippocampal regions. On the basis of their localization and morphology through immunofluorescence staining, these cells were identified as GABA_A α1-containing interneurons. At the 12 hr postictal period, ACTH expression in these regions was down-regulated, in a similar manner to the pre-seizure group of gerbils. These findings support the increase in ACTH synthesis that contributes to a reduction of corticotrophin-releasing factor via the negative feedback system which in turn provides an opportunity to enhance the excitability of GABAergic interneurons. Therefore, ACTH may play an important role in the reduction of excitotoxicity in all hippocampal regions. [BMB Reports 2013; 46(2): 80-85]

Tobacco addiction and the dysregulation of brain stress systems

Tobacco is a highly addictive drug and is one of the most widely abused drugs in the world. The first part of this review explores the role of stressors and stress-associated psychiatric disorders in the initiation of smoking, the maintenance of smoking, and relapse after a period of abstinence. The reviewed studies indicate that stressors facilitate the initiation of smoking, decrease the motivation to quit, and increase the risk for relapse. Furthermore, people with depression or an anxiety disorder are more likely to smoke than people without these disorders. The second part of this review describes animal studies that investigated the role of brain stress systems in nicotine addiction. These studies indicate that corticotropin-releasing factor, Neuropeptide Y, the hypocretins, and norepinephrine play a pivotal role in nicotine addiction. In conclusion, the reviewed studies indicate that smoking briefly decreases subjective stress levels but also leads to a further dysregulation of brain stress systems. Drugs that decrease the activity of brain stress systems may diminish nicotine withdrawal and improve smoking cessation rates.

Moderate level alcohol during pregnancy, prenatal stress, or both and limbic-hypothalamic-pituitary-adrenocortical axis response to stress in rhesus monkeys

This study examined the relationship between moderate-level prenatal alcohol exposure, prenatal stress, and postnatal response to a challenging event in 6-month-old rhesus monkeys. Forty-one rhesus monkey (Macaca mulatta) infants were exposed prenatally to moderate level alcohol, maternal stress, or both. Offspring plasma cortisol and adrenocorticotrophic hormone (ACTH) were determined from blood samples before maternal separation and after separation. Behavioral observations were made repeatedly across separation. Moderate-level prenatal alcohol exposure was associated with significantly higher plasma ACTH response to maternal separation. Offspring exposed to prenatal alcohol, prenatal stress, and prenatal alcohol and stress showed reduced behavioral adaptation to stress compared with controls. Baseline, 2-hr, and 26-hr plasma ACTH levels were intercorrelated and predicted behavior during separation.

ACTH treatment of infantile spasms: mechanisms of its effects in modulation of neuronal excitability

The efficacy of ACTH, particularly in high doses, for rapid and complete elimination of infantile spasms (IS) has been demonstrated in prospective controlled studies. However, the mechanisms for this efficacy remain unknown. ACTH promotes the release of adrenal steroids (glucocorticoids), and most ACTH effects on the central nervous system have been attributed to activation of glucocorticoid receptors. The manner in which activation of these receptors improves IS and the basis for the enhanced therapeutic effects of ACTH--compared with steroids--for this disorder are the focus of this chapter. First, a possible "common excitatory pathway," which is consistent with the many etiologies of IS and explains the confinement of this disorder to infancy, is proposed. This notion is based on the fact that all of the entities provoking IS activate the native "stress system" of the brain. This involves increased synthesis and release of the stress-activated neuropeptide, corticotropin-releasing hormone (CRH), in limbic, seizure-prone brain regions. CRH causes severe seizures in developing experimental animals, as well as limbic neuronal injury. Steroids, given as therapy or secreted from the adrenal gland upon treatment with ACTH, decrease the production and release of CRH in certain brain regions. Second, the hypothesis that ACTH directly influences limbic neurons via the recently characterized melanocortin receptors is considered, focusing on the effects of ACTH on the expression of CRH. Experimental data showing that ACTH potently reduces CRH expression in amygdala neurons is presented. This downregulation was not abolished by experimental elimination of steroids or by blocking their receptors and was reproduced by a centrally administered ACTH fragment that does not promote steroid release. Importantly, selective blocking of melanocortin receptors prevented ACTH-induced downregulation of CRH expression, providing direct evidence for the involvement of these receptors in the mechanisms by which ACTH exerts this effect. Thus, ACTH may reduce neuronal excitability in IS by two mechanisms of action: (1) by inducing steroid release and (2) by a direct, steroid-independent action on melanocortin receptors. These combined effects may explain the robust established clinical effects of ACTH in the therapy of IS.

How do the many etiologies of West syndrome lead to excitability and seizures? The corticotropin releasing hormone excess hypothesis

West syndrome (WS) is associated with diverse etiological factors. This fact has suggested that there must be a 'final common pathway' for these etiologies, which operates on the immature brain to result in WS only at the maturational state present during infancy. Any theory for the pathogenesis of WS has to account for the unique features of this disorder. For example, how can a single entity have so many etiologies? Why does WS arise only in infancy, even when a known insult had occurred prenatally, and why does it disappear? Why is WS associated with lasting cognitive dysfunction? And, importantly, why do these seizures--unlike most others--respond to treatment by a hormone, ACTH? The established hormonal role of ACTH in human physiology is to function in the neuroendocrine cascade of the responses to all stressful stimuli, including insults to the brain. As part of this function, ACTH is known to suppress the production of corticotropin releasing hormone (CRH), a peptide that is produced in response to diverse insults and stressors.The many etiologies of WS all lead to activation of the stress response, including increased production and secretion of the stress-neurohormone CRH. CRH has been shown, in infant animal models, to cause severe seizures and death of neurons in areas involved with learning and memory. These effects of CRH are restricted to the infancy period because the receptors for CRH, which mediate its action on neurons, are most abundant during this developmental period. ACTH administration is known to inhibit production and release of CRH via a negative feedback mechanism. Therefore, the efficacy of ACTH for WS may depend on its ability to decrease the levels of the seizure-promoting stress-neurohormone CRH.This CRH-excess theory for the pathophysiology of WS is consistent not only with the profile of ACTH effects, but also with the many different 'causes' of WS, with the abnormal ACTH levels in the cerebrospinal fluid of affected infants and with the spontaneous disappearance of the seizures. Furthermore, if CRH is responsible for the seizures, and CRH-mediated neuronal injury contributes to the worsened cognitive outcome of individuals with WS, then drugs which block the actions of CRH on its receptors may provide a better therapy for this disorder.

Comparative study of the roles of ACTH and beta-endorphin in regulating conditioned reflex activity in the hedgehog

Data on the relative effects of the neurohormone ACTH1-39 and the opioid peptide beta-endorphin on conditioned reflex activity in the hedgehog are presented. It was demonstrated that administration of ACTH (30-50 micrograms/kg s.c.) led to facilitation of learning and strengthening of memory processes (conditioned reflex traces). ACTH promoted strengthening of movement, orientational-investigative, and intersignal activities, produced hyperalgesia, and blocked the effects of naloxone. Administration of beta-endorphin (30-40 micrograms/kg s.c.) lengthened the latent periods of conditioned reflexes, produced a pronounced analgesic effect, and reduced movement and intersignal activities. The effects of beta-endorphin were eliminated by dosage with naloxone. Administration of beta-endorphin blocked the inhibitor effects of stimulation of the limbic cortex; doses of ACTH produced partial release of inhibitory effects. The differences between the effects of ACTH and beta-endorphin on higher nervous activity are discussed, as are the possible mechanisms of these effects.

Melanotropic peptides in the mammalian brain: the melanin-concentrating hormone

Melanin-concentrating hormone (MCH) has been identified in neurons of the mammalian brain. This review summarizes some current information regarding the cell biology of this neuropeptide and the topography of MCH-immunoreactive (-IR) neurons in several species including mouse, rat, hamster, guinea pig, rabbit, dog and monkey; and atlas of MCH-IR neurons in the hypothalamus and subthalamus of the brain of guinea pig is presented. Based upon the location of this MCH cell group, it is hypothesized that they may be functionally involved in circuits of extrapyramidal motor systems from striatal centers to the thalamus and cerebral cortex and to the midbrain and spinal cord.

Cognitive deficits induced in young rats by long-term corticosterone administration

Corticosterone slow-release pellets, implanted for 9 weeks in young Fischer 344 rats, resulted in continuous high plasma levels of the hormone which are comparable to those of rats under mild stress. One week following termination of the drug treatment, the rats were tested in an eight-arm radial maze. During the initial acquisition stages, corticosterone-treated rats exhibited cognitive impairments in contrast to placebo-treated rats. The deficits were observed in all three parameters which were monitored, the total number of errors, the number of correct entries out of the first eight, and the total time needed to complete the test. This study is the first to report specific behavioral decrements related to the previously observed morphological hippocampal changes induced by long-term corticosterone administration.

Isolation and structural characterization of peptides related to alpha- and gamma-melanocyte-stimulating hormone (MSH) from the frog brain

Peptides that are derived from the processing of proopiomelanocortin were isolated in pure form from the brain of the frog Rana ridibunda. The primary structure of the most abundant of those peptides was established as: Ser-Tyr-Ser-Met-Glu-His-Phe-Arg-Trp-Gly-Lys-Pro-Val. This amino acid sequence is identical to that of mammalian and frog pituitary alpha-melanocyte-stimulating hormone (MSH) and the peptide co-eluted with synthetic desacetyl alpha-MSH, indicating that it is COOH-terminally alpha-amidated. A second component, which exhibited a shorter retention time, co-eluted with the glycine-extended form of desacetyl alpha-MSH [ACTH(1-14)]. The primary structure of the third peptide isolated in pure form from the brain extract was established as: Lys-Tyr-Val-Met-Ser-His-Phe-Arg-Trp-Asn-Lys-Phe-NH2. This sequence corresponds to Lys-gamma 1-MSH as predicted from the nucleotide sequence of frog proopiomelanocortin. The presence of substantial amounts of desacetyl alpha-MSH and Lys-gamma 1-MSH in the frog brain supports the concept that, in amphibia, melanotropins may act as neurotransmitters and/or neuromodulators as well as hormonal peptides.

Characterization of pro-opiomelanocortin cDNA from the Old World monkey, Macaca nemestrina

An observation from high-pressure liquid chromatography (HPLC) suggesting that monkey beta-endorphin (BE) was chemically different from human or rat BE was investigated by determining the cDNA sequence for the monkey pro-opiomelanocortin (POMC) precursor. A full-length cDNA for POMC was isolated from a Macaca nemestrina whole pituitary cDNA library. The longest open reading frame predicts a 264-residue polypeptide exhibiting the basic structure of POMC that is closely homologous to the human counterpart. The monkey BE sequence apparently diverged from the human sequence after the latter had made the His-27 to Tyr-27 change but prior to the Gln-31 to Glu-31 transition, leaving it more hydrophobic than rat or human BE, consistent with its chromatography on reverse-phase HPLC. Comparison of the monkey POMC precursor with those of other species highlights conserved domains, presumably reflecting regions of physiological activity that await elucidation.

Effects of locally infused pharmacological agents on spontaneous and sensory-evoked activity of locus coeruleus neurons

Electrophysiological activity of individual locus coeruleus (LC) neurons was recorded in halothane-anesthetized rats before, during, and after the infusion of adrenergic, cholinergic, or peptidergic compounds about 400 micron lateral to LC. The alpha-adrenergic agonist clonidine (CLON), in concentrations ranging from 5-20 microM (67-270 pg/50 nl injection), reversibly suppressed activity with latencies to onset of 5-15 min and durations of 20-120 min. During the onset of suppressed firing, responses to sensory stimuli (footshock) were relatively preserved, but at later times the reliability of footshock responses was greatly reduced. The alpha-adrenergic antagonist piperoxane (PIP) rapidly reversed the inhibitory effects of CLON. Infusion of 0.1 microliter of 0.02 M acetylcholine (ACh) produced a 3-4 min period of increased LC firing, with a 1 min latency to onset. Larger volumes (0.15 microliter) produced greater increases in firing rate lasting 10-12 min. ACh effects were readily reversed with equimolar doses of scopolamine (SCOP). The effects of 0.02 M ACh were also rapidly reversed by equal volumes of 0.001 M CLON, SCOP and CLON reduced basal firing rates without blocking responses to sensory stimuli. Infusion of the cholinergic agonist carbamyl-beta-choline (carbachol) produced robust, reliable activation of LC neurons at doses of 25-1,000 ng per 100 nl injection. The electrophysiological effects of 3 adrenocorticotropin hormone (ACTH) fragments [1-24], [4-10], and [1-10] were also evaluated. ACTH[1-10] and ACTH[4-10] decreased LC activity for up to 2 hr. ACTH[1-24] exhibited more complex effects, with an increase in discharge rate being accompanied by a decrease in action potential amplitude.(ABSTRACT TRUNCATED AT 250 WORDS)

Psychoneurogenic stress influences upon retention of an inhibitory avoidance response in the rat

Hormones and peptides involved in the response of an organism to stress play a modulating role in learning and memory processes. We studied whether psychoneurogenic stressors such as sound stimulation or novelty influence retention of an inhibitory avoidance response. An impairing effect on retention was observed when these stressors were applied shortly after the acquisition trial, but not after a 3-h delay. However, sound stimulation and novelty applied shortly before the retention test may facilitate retention behavior. It is suggested that the effect of psychoneurogenic stressors on retention behavior may be linked to influences on consolidation and retrieval processes mediated through the neurohumoral response of the organism to stress.

alpha-Melanocyte-stimulating hormone (alpha-MSH) release from perifused rat hypothalamic slices

A perifusion system was developed to investigate the control of alpha-melanocyte-stimulating hormone (alpha-MSH) release from rat brain. Hypothalamic slices were perifused with Krebs-Ringer bicarbonate (KRB) medium supplemented with glucose, bacitracin and bovine serum albumin. Fractions were set apart every 3 min and alpha-MSH levels were measured by means of a specific and sensitive radioimmunoassay method. Hypothalamic tissue in normal KRB medium released alpha-MSH at a constant rate corresponding to 0.1% of the total hypothalamic content per 3 min. The basal release was not altered by Ca2+ omission in the medium or addition of the sodium channel blocker tetrodotoxin (TTX). Depolarizing agents such as potassium (50 mM) and veratridine (50 microM), which is known to increase Na+ conductance, significantly stimulated alpha-MSH release in a Ca2+-dependent manner. When Na+-channels were blocked by TTX (0.5 microM) the stimulatory effect of veratridine was completely abolished whereas the K+-evoked release was unaffected. These findings suggest that: voltage-dependent sodium channels are present on alpha-MSH hypothalamic neurons; depolarization by K+ induces a marked stimulation of alpha-MSH release; K+- and veratridine-evoke releases are calcium-dependent. Altogether, these data provide evidence for a neurotransmitter or neuromodulator role for alpha-MSH in rat hypothalamus.

Existence of different forms of adrenocorticotropin in rat hypothalamus

Adrenocorticotropin (ACTH)-like immunoreactivity and bioactivity were extracted from rat hypothalamus and fractionated by high pressure liquid chromatography. Analysis of the fractions either by radioimmunoassay or bioassay (corticosteroid production from rat adrenal cells) revealed several peaks of immunoreactivity and bioactivity. Only 20-25% of total ACTH-like immunoreactivity and bioactivity eluted with the same retention time as authentic ACTH 1-39. The results suggest that different forms of ACTH exist in rat hypothalamus.

The ACTH-(4-9) analog ORG 2766 and desglycinamide9-(Arg8)-vasopressin reverse the retrograde amnesia induced by disrupting circadian rhythms in rats

Disrupting circadian organization by exposing rats to a shifted illumination schedule after training for passive avoidance and shuttle box avoidance behavior resulted in retrograde amnesia as evidenced by impaired performance during retention and extinction testing respectively. A single treatment with either the ACTH-(4-9) analog ORG 2766 or desglycinamide9-(Arg8)-vasopressin (DGAVP) 1 hour prior to the retention of passive avoidance or extinction of shuttle box avoidance behavior restored the behavioral impairment. It is suggested that these peptides may be useful to relieve memory deficits induced by disturbances in circadian organization.

ACTH 4-9 analogue (Org 2766) in depressed elderly patients. I. Effect on depressed mood

Sixty-two moderately depressed elderly in- and out-patients were administered 80 mg ACTH 4-9 analogue (Org 2766) or placebo daily for 4 weeks in a double-blind interindividual comparison. Patients were rated on days 0, 15 and 29 with the Hamilton Psychiatric Depression Rating Scale (HPDRS), The Hamilton Anxiety Scale (HAS) and the Sandoz Clinical Assessment Geriatric Scale (SCAG). After 4 weeks 23 patients crossed over to the opposite treatment for a further 2 weeks. A statistically significant reduction in the severity of depression and anxiety was found in both treatment groups. No statistically significant differences were found between the treatment groups, when comparing scores for each item and total scores of HPDRS, HAS and SCAG on day 0, 15 or 29. Nor were there any statistically significant differences after the cross-over. Somatic examination and laboratory screenings before and at the end of the study did not reveal any pathological changes. No side effects were recorded.

ACTH 4-9 analogue (Org 2766) in depressed elderly patients. II. Effect on memory and vigilance

In a double-blind interindividual comparison 80 mg of an ACTH 4-9 analogue (Org 2766) or placebo was administered daily to 49 elderly depressed in- and out-patients for 4 weeks. 20 patients then changed to the opposite treatment in a cross-over study for a further 2 weeks. All patients were tested for memory on days 0 and 29 with a battery consisting of the 30 World-Pair Test, the 30 Figure-Test and the 30 Personal-Facta Test. Three scores were obtained from each test, immediate memory score (IMS), delayed memory score (DMS) and their difference, forgetting score (FS). Cross-over patients were tested for vigilance on days 0, 29 and 43 in an apparatus testing ability to rapidly detect and react to specific minor changes at random intervals. Org 2766 had no better effect than placebo on learning, consolidation, or retrieval of memorized material in elderly depressed patients. Statistically significant fewer target misses in the test of vigilance suggest a higher degree of sustained attention after treatment with Org 2766.

Behavioral support for an ACTH receptor in the CNS

In this report we present a series of experiments which have led us to support the notion of the presence of an ACTH receptor in the CNS. A short intense heat-stress (hot-plate) applied to the paws of rats will temporarily reduce activity. During the course of experimentation we were able to eliminate a number of logical mediators. Neither adrenalectomy, adrenal-medullectomy, naloxone administration, nor alpha-MSH-(1-12) were able to affect the observed akinesia. Hypophysectomy, however, was able to abolish or mask the behavior and the reduction in activity could be reinstated by the administration of ACTH-(4-10) to hypophysectomised rats. These data support the notion that a short intense stressor can release ACTH and that this ACTH can be responsible for mediating the short term reduction in activity. In addition, the fact that ACTH-(4-10) has only minimal steroidogenic properties and was able to reinstate the behavior led us to speculate that these effects were of central origin. Furthermore, since naloxone was not capable of altering the behavior, the suggestion is that ACTH in this paradigm acted at a receptor site apart from the naloxone sensitive receptor. This site may in fact be an ACTH specific receptor.

NH2-terminal specificity and axonal localization of adrenocorticotropin binding sites in rat median eminence

Adrenocorticotropin binding sites in the rat median eminence have been localized in vivo. These binding sites occur in the basalar zone, which is rich in axonal endings. Using competitive binding and quantitative light-microscope radioautography, we found that the median-eminence binding site, in contradistinction to the adrenal receptor, binds specifically the residue 4-10 region of the adrenocorticotropin molecule. Using quantitative electron-microscope radioautography and median-eminence deafferentation, we localized the binding sites to axon terminals in this region. In time-delayed uptake studies using light-microscope radioautography, we failed to observe concentration of radiolabel in neurons of the medial basal hypothalamus after the direct injection of radioiodinated adrenocorticotropin(1-24) into the median eminence.

Adrenocorticotropic hormone (ACTH)-lipid interactions. Implications for involvement of amphipathic helix formation

ACTH-lipid interactions were investigated by: (1) lipid-monolayer studies using several zwitterionic and anionic phospholipids and gangliosides, (2) permeability experiments by following the swelling rate of liposomes in isotonic glycerol solutions by light scattering, using liposomes of synthetic lipids and liposomes made of lipids extracted from light synaptic plasma membranes, and (3) by steady-state fluorescence anisotropy measurements on liposomes derived from light synaptic plasma membranes employing 1,6-diphenyl-1,3,5-hexatriene as fluorescent probe. (1) The monolayer experiments demonstrated an interaction with gangliosides GT1, GM1, dioleoylphosphatidic acid and phosphatidylserine, but little or no interaction with phosphatidylcholine or sphingomyelin. The interaction with monolayers of GT1 or phosphatidic acid decreased for ACTH1-13-NH2 and ACTH1-10. (2) The liposome experiments showed that 2 X 10(-5) M ACTH1-24 increased the glycerol permeability by 20% and decreased the activation energy only when liposomes derived from light synaptic plasma membranes were used. Treatment of the liposomes with neuraminidase abolished the ACTH-induced permeability increase. (3) Steady-state fluorescence depolarization measurements revealed that ACTH1-24, ACTH1-16-NH2 and ACTH1-10 did not change the fluidity of liposomes derived from light synaptic plasma membranes as sensed by diphenylhexatriene. It is concluded that ACTH1-24 can bind to negatively charged lipids and can form an amphipathic helix aligned parallel to the membrane surface involving the N-terminal residues 1 to 12, possibly to 16. Polysialogangliosides will favorably meet the condition of a high local surface charge density under physiological circumstances. It is suggested that ACTH-ganglioside interactions will participate in ACTH-receptor interactions.

Peptide hormone analogues and novel clinical applications

Clinical application of peptide hormone analogues is rapidly expanding. Peculiar aminoacid residues, conformational turns and the degree of molecular flexibility may represent critical keys for differential interaction with the receptor sites, hence for specific biological effects. Broadly different biological responses may be elicited as a function of dose and timing of administration. The clinical use of the heptadecapeptide analogue ACTH 1-17 (Synchrodyn 1-17) has provided new diagnostic information about subtle alterations of the adrenal function and has been valuable to presenting the rhythmic ordering of several functions, especially of those which are more dependent on the glucocorticoid modulation. In this sense, the use of a synthetic hormone analogue presenting a wide range of programmable effects appears essential for a better medicine. A large body of evidence indicates that the same concept applies to most actions of the gonadotropin-releasing hormone (LH-RH) related analogues. The availability of small computerized instruments for data collection and analysis of the endogenous rhythmicities, on the one hand, and for programmable administration of the analogues, on the other hand, is already providing new approaches to heretofore unsuccessful therapies.

Alpha-melanocyte stimulating hormone increases plasma levels of glucagon and insulin in rabbits

Intravenous injections of 25 and 2.5 micrograms alpha-melanocyte stimulating hormone (alpha-MSH) increased plasma levels of glucagon, insulin and free fatty acids in fasted and fed rabbits. 45 micrograms beta-melanocyte stimulating hormone (beta-MSH) had similar effects, whereas 22 micrograms gamma-2-melanocyte stimulating hormone (gamma-MSH) was inactive. The alpha-MSH-induced increases in the plasma levels of glucagon, insulin and free fatty acids were not inhibited by alpha- or beta-adrenergic blocking drugs. The alpha-MSH-induced increases in the plasma levels of insulin were, however, augmented by phentolamine (an alpha-adrenergic receptor blocking drug). The plasma levels of glucose were increased by 25 micrograms alpha-MSH in fed rabbits, only, and were decreased by alpha-MSH during alpha-receptor blockade. The acute in vivo effects of alpha-MSH and beta-MSH on the plasma levels of glucagon, insulin and free fatty acids were rather similar to those previously reported for corticotropin (ACTH). It is possible that the 4-10 ACTH sequence, present in alpha-MSH, beta-MSH and ACTH, but not in gamma-MSH, is a message sequence for the observed effects. However, ORG 2766, a 4-9 ACTH analogue, was inactive. The mechanism by which alpha-MSH increased the plasma levels of glucagon and insulin in rabbits remains to be determined. It is possible, that the effects were mediated by both a central nervous action and a direct action on the endocrine pancreas.

Stress, ACTH, salt intake and high blood pressure

Epidemiological evidence supports the thesis that high salt intake is involved in the aetiology of hypertension. If sodium intake is not causal, it appears other factors do not cause high blood pressure in unacculturated societies with low sodium intake. In this context, it is potentially important that stress causing ACTH release, as well as other neurohumoral effects, causes increased salt appetite and can impair renal sodium excretion.

Sites of behavioral and neurochemical action of ACTH-like peptides and neurohypophyseal hormones

In order to localize the site of action of neuropeptides in relation to their effects on behavior and memory various approaches have been used. As a result of studies using rats bearing lesions in different areas of the limbic system as well as of studies in which neuropeptides were locally applied into various areas of the brain it appeared that the limbic system (amygdala, hippocampus, septum and some thalamic areas) plays an essential role in the effect of vasopressin and ACTH and their derivatives on behavior and memory. Neurochemical studies generally indicate that changes occur in catecholamine utilization in these various limbic regions upon administration of these neuropeptides. It can be concluded that the effects of vasopressin in the terminal regions of the coeruleo-telencephalic noradrenalin system correlate with its effects on consolidation of memory. It is likely that the effects of vasopressin on other transmitter systems (e.g. dopamine in the amygdala and serotonin in the hippocampus) correspond with the effect of this neuropeptide on retrieval processes. In addition, regional differences in biotransformation of the neurohypophyseal hormones suggest that different patterns of behaviorally active fragments of these peptides may be present locally in the brain.

Biological and immunological characterization of alpha-melanocyte-stimulating hormone (alpha-MSH) in two neuronal systems of the rat brain

Recent immunocytochemical studies have demonstrated the existence of two different neuronal systems containing alpha-MSH-like material in the brain: one originating from the arcuate nucleus and the other one from the dorsolateral hypothalamus. The aim of the present study was to further characterize alpha-MSH in these two discrete regions of the rat diencephalon. Intracerebroventricular administration of colchicine resulted in a marked decrease in the number of ACTH and beta-endorphin nerve fibers and a significant reduction in ACTH and beta-endorphin content in the dorsolateral hypothalamus. Conversely, colchicine treatment did not alter alpha-MSH, ACTH or beta-endorphin content in the arcuate nucleus and did not significantly affect alpha-MSH concentration in the dorsal region. Reverse-phase high-performance liquid chromatography showed that the major alpha-MSH-like compound localized in the dorsal hypothalamus co-migrated exactly with synthetic alpha-MSH, whereas the arcuate nucleus contained 5 peptides cross-reacting with alpha-MSH antibodies, 4 of them being different from standard alpha-MSH. Significant amounts of biologically active melanotropin, which migrated on Sephadex G-25 columns like synthetic alpha-MSH, were also detected in both the arcuate nucleus and dorsolateral hypothalamus. Taken together, these data demonstrate that the alpha-MSH cell bodies located in the dorsolateral hypothalamus specifically produce authentic alpha-MSH, whereas the alpha-MSH cell bodies in the arcuate nucleus also contain ACTH, beta-endorphin and several peptides immunologically related but not identical to alpha-MSH.

Circumventricular organs: receptors and mediators of direct peptide hormone action on brain

The concept of the brain as an endocrine target organ is not new, nor is it novel to consider the circumventricular organs as receptive regions of the brain for circulating substances. However, in this review we have emphasized the relatively novel concept that CVOs mediate exclusively the direct feedback actions of circulating peptide hormones on brain function. In addition we have presented speculations concerning the neural mechanisms by which signals arising from peptide hormone-receptor interaction might be relayed into the CNS, and indicated the possible involvement of CVO receptors in endocrine disorders. We hope that this analysis provides a conceptual framework for evaluating the functional relationship of circulating peptides to brain and inspires interest in this fascinating area of neuroendocrinology.

Effect of ACTH, epinephrine, beta-endorphin, naloxone, and of the combination of naloxone or beta-endorphin with ACTH or epinephrine on memory consolidation

The effect on retention of the post-training intraperitoneal administration of ACTH1-24 (0.2 or 2.0 micrograms/kg), epinephrine HCl (5.0 or 50.0 micrograms/kg), human beta-endorphin (0.1 or 1.0 microgram/kg), naloxone (0.4 mg/kg), and of the combination of naloxone or beta-endorphin with ACTH or epinephrine was studied in two different but closely related step-down inhibitory avoidance tasks in rats: task 1 (5 cm high 25 X 25 cm platform; 0.5 mA continuous footshock) and task 2 (7 X 25 cm platform, 0.3 mA discontinuous footshock). In task 1, saline control animals showed good retention in a test session carried out 24 hr later; beta-endorphin, ACTH and epinephrine caused amnesia; beta-endorphin potentiated the amnesic effect of ACTH and epinephrine; and naloxone caused memory facilitation and reversed the amnesic effect of ACTH and epinephrine. In task 2, control animals showed poor retention; beta-endorphin caused amnesia at the dose of 0.1 but not 1.0 microgram/kg; the other three drugs caused memory facilitation; naloxone potentiated the facilitatory effect of ACTH and epinephrine; and beta-endorphin reversed it and transformed it into a deep amnesia. These findings suggest that an opioid-mediated amnesic mechanism modulates the effect of ACTH and epinephrine on memory consolidation, either by dampening that effect when training parameters tend to make it facilitatory, or by enhancing it when training conditions tend to make it amnesic. On the basis of these and previous data it seems likely that the amnesic effect of ACTH and epinephrine could be mediated by endogenous beta-endorphin release.

An analog of ACTH/MSH (4-9), ORG-2766, reduces cerebral uptake of morphine

The uptake of morphine was significantly reduced in most regions of the brains of conscious, unrestrained rats within 10 minutes after treatment with an analog of ACTH/MSH (4-9), ORG-2766. The effect was most obvious in regions with significant densities of enkephalin receptors, namely basal ganglia, hippocampus and cortex. The results explain, in part, how some fragments and analogs of ACTH/MSH may antagonize behavioral actions of morphine, even though some of these peptides lack significant opiate receptor binding properties. We believe that this effect of ORG-2766 is related to an action on the permeability characteristics of the brain microvasculature. The underlying mechanism is unknown.

Characterization of immunoreactive alpha-melanocyte stimulating hormone (alpha-MSHi) in human brain tissue

Adult human hypothalamic tissue was analyzed for the presence of products generated by post-cleavage processing of ACTH 1-13. The displacement curve generated by immunoreactive alpha-melanocyte stimulating hormone (alpha-MSHi) in extracts (5 M acetic acid or acidified ethanol) of adult human hypothalamic tissue was parallel to the alpha-MSH radioimmunoassay standard curve, and alpha-MSHi eluted as a single peak on Sephadex G-10, G-25, and G-50 columns in a manner identical to that of synthetic alpha-MSH. The alpha-MSHi was clearly distinguishable in its mobility on Sephadex G-50 columns from such peptides as beta-MSH, luteinizing hormone releasing hormone, and ACTH. After high performance liquid chromatography of extracts of hypothalamic tissue from young as well as aged men and women, we found that the major peak of alpha-MSHi (75-95% of total alpha-MSHi) coeluted with desacetyl alpha-MSH (ACTH 1-13 amide) rather than alpha-MSH. We suggest that desacetyl alpha-MSH, rather than alpha-MSH, is the predominant alpha-MSHi in adult human brain tissue.

ACTH LPH and related peptides in the ectopic ACTH syndrome

Adrenocorticotrophin, lipotrophin and the related peptides alpha-MSH, CLIP, beta-endorphin and met-enkephalin have been measured, and characterized chromatographically in tumour extracts from seven patients with the ectopic ACTH syndrome. Four of the seven tumours contained the complete family of peptides, although the proportion of one to another varied between tumours. In addition, large molecule weight forms of ACTH and met-enkephalin were seen. The potential clinical importance of these observations is discussed.

Purification and characterization of a gamma-melanotropin precursor from frozen human pituitary glands

A new melanocyte-stimulating peptide has been isolated from acid extracts of frozen human pituitary glands by salt/ethanol fractionation, Sephadex G-75 gel filtration and DEAE- and cM-cellulose ion-exchange chromatography. The peptide is glycosylated, has an N-terminal tryptophan residue and an apparent mol.wt. of 16000 as estimated by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. Its amino acid analysis closely resembles residues Trp-105 to Gln-29 predicted for the common precursor protein of bovine corticotropin and beta-lipotropin by Nakanishi, Inoue, Kita, Nakamura, Chang, Cohen & Numa [(1979) Nature (London) 278, 423-427]. This fragment is expected to have melanotropin activity due to the tetrapeptide -His-Phe-Arg-Trp- (residues -51 to -48) of the predicted sequence of the common precursor. It was found to have a molar potency of 1 X 10(-5) relative to alpha-melanotropin in the frog skin bioassay. These characteristics are consistent with the isolated melanotropin peptide being a non-corticotropin, non-lipotropin peptide of the human common precursor protein of corticotropin and lipotropin. The peptide neither potentiates the adrenal weight-maintenance activity of corticotropin-(1-24)-tetracosapeptide when administered to hypophysectomized rats, nor stimulates release of non-esterified fatty acids from isolated rat epididymal cells. A second N-terminal-tryptophan glycopeptide was also isolated, which had an amino-acid composition similar to that predicted for the bovine common precursor protein, residues Trp-105 to Gly-35.

Entry of opioid peptides into the central nervous system

Cerebrovascular permeability of four modified opioid peptides--[D-Ala2]methionine enkephalin amide, beta-[D-Ala62,14C-Homoarg69]lipotropin 61 -69, alpha-[D-Ala2,14C-Homoarg9]endorphin, and beta-[D-Ala2,14C-Homoarg]endorphin--ranged from 1.4 to 3.9 X 10(-6) centimeters per second in brain regions of the conscous rat. These significant permeabilities should allow the peptides to fill the extracellular brain space with a half time of 3 to 11 minutes, as a result of a step increase in plasma concentration of unbound peptide.

ACTH4-9 analog (ORG 2766) facilitates acquisition of an inhibitory avoidance response in rats

These experiments examined the effects of an ACTH4-9 analog (ORG 2766) on an inhibitory avoidance response in rats. Graded doses of ORG 2766 were administered either 1 hr prior to training, immediately after training, or 1 hr prior to the retention test. The animals were tested 24 hr after training. A 5.0 mg/kg dose was administered prior to training significantly facilitated acquisition of the response. ORG 2766 did not significantly affect retention when administered after training or prior to the retention test. Since ORG 2766 only affected acquisition of the response, it is suggested that the drug acts by influencing sensory, motivationl or attentional variables rather than directly affecting memory consolidation or retrieval processes.