Normalizing effect of an adrenocorticotropic hormone (4-9) analog ORG 2766 on disturbed social behavior in rats

Bridging the species gap in translational research for neurodevelopmental disorders

The prevalence and societal impact of neurodevelopmental disorders (NDDs) continue to increase despite years of research in both patient populations and animal models. There remains an urgent need for translational efforts between clinical and preclinical research to (i) identify and evaluate putative causes of NDD, (ii) determine their underlying neurobiological mechanisms, (iii) develop and test novel therapeutic approaches, and (iv) translate basic research into safe and effective clinical practices. Given the complexity behind potential causes and behaviors affected by NDDs, modeling these uniquely human brain disorders in animals will require that we capitalize on unique advantages of a diverse array of species. While much NDD research has been conducted in more traditional animal models such as the mouse, ultimately, we may benefit from creating animal models with species that have a more sophisticated social behavior repertoire such as the rat (Rattus norvegicus) or species that more closely related to humans, such as the rhesus macaque (Macaca mulatta). Here, we highlight the rat and rhesus macaque models for their role in previous psychological research discoveries, current efforts to understand the neurobiology of NDDs, and focus on the convergence of behavior outcome measures that parallel features of human NDDs.

Neural mechanisms of social homeostasis

Social connections are vital to survival throughout the animal kingdom and are dynamic across the life span. There are debilitating consequences of social isolation and loneliness, and social support is increasingly a primary consideration in health care, disease prevention, and recovery. Considering social connection as an "innate need," it is hypothesized that evolutionarily conserved neural systems underlie the maintenance of social connections: alerting the individual to their absence and coordinating effector mechanisms to restore social contact. This is reminiscent of a homeostatic system designed to maintain social connection. Here, we explore the identity of neural systems regulating "social homeostasis." We review findings from rodent studies evaluating the rapid response to social deficit (in the form of acute social isolation) and propose that parallel, overlapping circuits are engaged to adapt to the vulnerabilities of isolation and restore social connection. By considering the neural systems regulating other homeostatic needs, such as energy and fluid balance, we discuss the potential attributes of social homeostatic circuitry. We reason that uncovering the identity of these circuits/mechanisms will facilitate our understanding of how loneliness perpetuates long-term disease states, which we speculate may result from sustained recruitment of social homeostatic circuits.

Physical but not emotional stress induces a delay in behavioural coping responses in rats

Physical stress (PS) and emotional stress (ES) have opposite long-term effects on open field behaviour. PS consisted of a repeated mild foot shock treatment, which the ES animals witnessed. PS caused a long-term decrease in locomotor activity and exploration behaviours and increased immobility. ES induced an increase in locomotor activity. These changes in open field behaviour could be the result of several factors such as increased anxiety, a shift in coping strategy or simply a change in locomotor activity. To investigate the effect of the PS and ES treatment on these separate factors, the following behavioural tests were performed: defensive withdrawal, shock prod bury, large open field and social interaction. PS animals initially showed immobility in the shock prod bury test and the large open field, while the differences measured over the entire test period were small or not present. PS did not induce differences in the defensive withdrawal and the social interaction tests. ES and control animals did not differ significantly in any of the tests. The effects of PS in the shock prod bury test in particular can be interpreted as an indication of a passive coping style. However, PS animals showed the same behaviour as controls, but started displaying the behaviour after the initial immobility response. It is concluded that neither PS nor ES affects the coping style and anxiety level of the rats. PS induces a delay in behavioural responding and ES induces locomotor activation per se. It seems that the shock prod bury test is most suitable to distinguish between exploration and coping style.

Effects of juvenile isolation and morphine treatment on social interactions and opioid receptors in adult rats: behavioural and autoradiographic studies

The consequences of juvenile isolation and morphine treatment during the isolation period on (social) behaviour and mu-, delta- and kappa-opioid receptors in adulthood were investigated by using a social interaction test and in vitro autoradiography in rats. Juvenile isolation reduced social exploration in adults. Morphine treatment counteracted this reduction in isolated rats, but decreased social exploration in nonisolated rats. Self-grooming and nonsocial exploration were enhanced after juvenile isolation. Morphine treatment had no effect on self-grooming, but suppressed nonsocial exploration in isolated rats. With respect to the opioid receptors, juvenile isolation resulted in regiospecific increases in mu-binding sites with a 58% increase in the basolateral amygdala and a 33% increase in the bed nucleus of stria terminalis. Morphine treatment in isolated rats reversed this upregulation in both areas. The number of delta-binding sites did not differ between the experimental groups. A general upregulation of kappa-binding sites was observed after juvenile isolation, predominantly in the cortical regions, the hippocampus and the substantia nigra. Morphine treatment did not affect the upregulation of kappa-receptors. The results show that juvenile isolation during the play period causes long-term effects on social and nonsocial behaviours and on the number of mu- and kappa- but not delta-opioid receptors in distinct brain areas. The number of mu-receptors in the basolateral amygdala appears to be negatively correlated with the amount of social exploration in adult rats.

Inhibition of neuronal nitric oxide synthase (n-cNOS) reverses the corticotrophin-induced behavioral effects in rats

The nitric oxide (NO) synthase inhibitor NG-monomethyl-L-arginine (N-NMMA) and the competitive substrate for NO synthase L-arginine were used to determine the role of endogenous NO on the behavioral and neuroendocrine responsiveness following systemic corticotrophin in dexamethasone-suppressed rats. Corticotrophin (50-200 mU/kg, s.c.) dose-dependently decreased behavioral activity in the actimeter and produced significant anxiolytic and anti-risk activity in the plus-maze behavior test, without affecting systolic blood pressure. Rats given corticotrophin showed significant increased plasma corticosterone and reduced adrenal ascorbic acid level. These behavioral and adrenal responses of corticotrophin were dose dependently blocked by metyrapone (20 and 50 mg/kg, i.p.), an inhibitor of steroid 11beta-hydroxylase in adrenal and neural tissues that block steroidogenesis. Intracerebroventricular administration of L-NMMA (20 microg/rat in 10 microl) significantly prevented the behavioral hypoactivity and anxiolytic-like responses of corticotrophin without influencing the adrenal responsiveness. The effect of L-NMMA was completely reversed by preadministration of L-arginine (300 mg/kg, i.p.). These results suggest that neuronal nitric oxide pathway plays an important modulating role in the behavioral effects of corticotrophin by mechanisms other than those involving cardiovascular effects.

Chronic administration of Org2766 and morphine counteracts isolation-induced increase in social interest: implication of endogenous opioid systems

In complex behaviors, like social behavior, the MSH/ACTH (4-9) analog Org2766 is found to counteract changes in social interest caused by preceding housing or test conditions. Previous studies have indicated an involvement of endogenous opioid systems in these outcomes. In the present study we have counteracted isolation-induced enhanced social interest by chronic treatment (7 x every 48 h) with Org2766 or with the opiate morphine. These effects were blocked by previous administration of naloxone. However, in group-housed animals, both Org2766 and morphine treatment did not result in changes in social activity as compared to saline-treated group-housed controls. Chronic administration of naloxone in group-housed rats resulted in an increase in social interest. These results are discussed in relation to possible function of Org2766 and morphine as a substitute for the release of endogenous opioids caused by social contact.

A controlled trial with ORG 2766, an ACTH-(4-9) analog, in 50 relatively able children with autism

The aim of the present study was to replicate earlier findings of beneficial effects of ORG 2766, an ACTH-(4-9) analog, in autistic children. Fifty children with autism, 7-15 years old and with a Performance IQ of more than 60, participated in a double-blind placebo controlled parallel trial. Active treatment was 40 mg ORG 2766 for 6 weeks. The outcome was assessed on the basis of the Aberrant Behavior Checklist completed by parents and teachers, and by means of a detailed behavioral observation (30 subjects). ORG 2766 failed to improve social and communicative behavior at a group level. The rate of individual response, defined as a reliable change in social withdrawal at home and at school, to ORG 2766 (10 out of 30) and placebo (4 out of 20) was not significant either. The children who responded to ORG 2766, but not those who responded to placebo, manifested significant improvements outside the changes in the defining variables, including a decrease in hyperactivity at school. The responders to ORG 2766 were characterized mainly by a relatively lower PIQ; further by more initial hyperactivity, stereotypies and abnormal speech, and less initial eye contact. The responders to placebo could not be differentiated from the non-responders to placebo. Future studies should examine whether ORG 2766 differentially affects various subtypes of autism.

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

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

Effects of morphine on different aspects of social play in juvenile rats

To clarify the influence of opioids on social play, the effects of morphine on playful and non-playful social behavior in juvenile rats was investigated under different conditions. Environmental variables employed were different (dim and intense) levels of illumination during testing, familiarity to the test cage, and different periods of social isolation prior to testing. Under dim light conditions, morphine markedly increased playful social behavior, such as pinning, boxing/wrestling and following/chasing, whereas non-playful social behavior such as social exploration and contact behavior was hardly affected. This effect of morphine was independent of duration of previous isolation and dose-dependent, with a maximal effect at 1.0 mg/kg. The mechanism of this effect is interpreted as an action on the rewarding aspects of play. A dose of 0.1 mg/kg of morphine abolished the initial suppression of play induced by unfamiliarity to the test cage, without influencing total levels of play. This may be an effect of morphine on the integration of sensory stimuli. Under intense light conditions, whereas playful behavior was completely suppressed, morphine itself hardly affected such behavior, but decreased some aspects of non-playful social behavior. These results suggest that in juvenile rats playful and non-playful forms of social behavior are differentially regulated. In addition, opioid systems may be involved at different levels in the regulation of social play.

The adrenocorticotrophic hormone (4-9) analog ORG 2766 benefits autistic children: report on a second controlled clinical trial

In a second controlled crossover trial, 20 autistic children received 40 mg/day of the neuropeptide ORG 2766, a synthetic analog of ACTH (4-9), for 8 weeks. Parents' checklist ratings (ABC) as well as clinicians' ratings (CGI) pointed to significant improvements after the course of treatment; improvements were clearest on the ABC social withdrawal subscale. The analysis of individual target symptoms and the parents' treatment preferences substantiated the beneficial effects of ORG 2766. In an ethologically analyzed playroom session, ORG 2766 treatment was associated with an improvement in the children's play behavior and a significant increase in the social interaction between child and experimenter. Gaze coordination between child and experimenter also was improved.

Effects of the ACTH4-9 analog Org2766 on brain plasticity: modulation of excitatory neurotransmission?

ACTH-like neuropeptides have been investigated in various paradigms such as cognition, neuronal damage and neuronal excitation. All their effects may be collectively described as modulation of neural plasticity. However, the mechanism of action accounting for these effects remains to be demonstrated. This report is an overview of the data and has incorporated some additional findings of the influence of the ACTH4-9 analog, Org2766, on neuronal excitation, especially in the hippocampus. An interaction with NMDA receptors may account for the various aspects of plasticity. Based on recent findings demonstrating that the ACTH4-9 analog counteracts both the NMDA antagonist, AP5, and NMDA-induced explosive running behavior, the hypothesis is put forward that glutamatergic neurotransmission is involved in behavioral changes induced by the ACTH4-9 analog.

The use of adrenocorticotrophic hormone (4-9) analog ORG 2766 in autistic children: effects on the organization of behavior

In a double-blind placebo-controlled crossover trial, 14 autistic children were treated with the neuropeptide ORG 2766, a synthetic analog of adrenocorticotrophic hormone (ACTH) (4-9). ORG 2766 treatment (20 mg per day during 4 weeks) was associated with an increased amount and an improved quality of the social interaction of the autistic children with a familiar experimenter. These changes in interaction were clinically relevant. Following treatment with ORG 2766 gaze and smile behaviors of child and experimenter showed stronger temporal contingencies. Further, after ORG 2766, stereotypies were temporally disconnected from verbal initiatives. The data supported the notion of a stimulating effect of ORG 2766 on social interaction. The implications of these findings for the endogenous opioid theory of autism are discussed.

The MSH/ACTH(4-9) analog Org2766 counteracts isolation-induced enhanced social behavior via the amygdala

MSH/ACTH-like peptides influence social behavior induced by isolation It has been previously demonstrated that changes in locomotor activity as a result of isolation can be counteracted by Org2766 via the amygdala. The present study investigates whether isolation-induced changes in social behavior can also be affected by this peptide via the amygdala. A fully automated observation system was applied for detailed registration and analysis of movements of group-housed and 7-day isolated rats in a social interaction test. Administration of the MSH/ACTH(4-9) analog into the central nucleus of the amygdala elicited decreased locomotion, approach, and avoidance behaviors after isolation as compared to placebo-treated controls. However, general activity and social interest of group-housed rats were not affected by the MSH/ACTH(4-9) fragment. It is hypothesized that the amygdala is a site of action for neuropeptides in modulating social behavior.

Deficits in social behavior in autism and their modification by a synthetic adrenocorticotrophic hormone (4-9) analog

When charting the structure of the social behavior of autistic children by means of an ethologically analyzed playroom session, deficits appeared in the reciprocity of eye-contact and in the location of verbal initiatives. These deficits in social behavior were beneficially influenced by treatment with the adrenocorticotrophic hormone (4-9) analog ORG 2766.

Stimulation of glycolysis by corticotropin and phorbol ester in cultured neurons

Incubation of cultured neurons from chick embryo forebrain with corticotropin (ACTH) or the phorbol ester TPA (12-O-tetradecanoylphorbol 13-acetate) stimulates the production of lactate. The stimulation is seen after 2 h of treatment and is maximal after 12 h. Both ACTH (1-24) and TPA increase the concentration of fructose 2,6-bisphosphate (Fru-2,6-P2), a metabolic activator of 6-phosphofructo-1-kinase (PFK-1). This effect is concentration-dependent and is maximal after 4 h of treatment. PFK-1 activity is increased in a dose-dependent manner by ACTH (1-24) or TPA. This increase is not visible during the first 6 h and reaches its maximum after 18 h of treatment. The stimulation of PFK-1 activity is not due the increase of Fru-2,6-P2 by ACTH (1-24) or TPA, since saturating concentrations of Fru-2,6-P2 are present in the PFK-1 assay medium. Thus, it appears that ACTH (1-24) and TPA regulate glycolysis through two modes with different time responses: increase in Fru-2,6-P2 is the main mechanism operating during the first 6 h following the treatments and increase in the amount, or stable increase in activity of PFK-1, takes place during the later phase. It is suggested that the action of corticotropin on glycolysis is part of the mechanism of the neurotrophic activity of this hormone.

Brain transfer of a new neuromodulating ACTH analog, ebiratide, in rats

The transfer of ebiratide into the brain was examined in rats. Its brain levels after intravenous administration (2-20 mg/kg), determined by radioimmunoassay, peaked at 5 min and declined almost in parallel with the plasma levels. Brain/plasma ratios (B/P) were constantly about 0.05 ml/g at all doses. Brain distribution study at 5 min after 125I-ebiratide at an effective dose (0.4 microgram/kg) revealed that unchanged ebiratide had larger B/P than the metabolites and region selectivity. The combined use with unlabeled ebiratide resulted in marked decreases in B/P, particularly in the hippocampus, suggesting a specific uptake of this peptide.

Behavioral effects of Org 2766, a synthetic analog of the adrenocorticotrophic hormone (4-9), in 14 outpatient autistic children

Fourteen children (12 infantile autism full syndrome present, 2 atypical pervasive developmental disorder) between 5 and 13 years of age participated in a double-blind placebo-controlled cross-over trial. Each child received 20 mg Org 2766 (synthetic analog of ACTH 4-9)/day during 4 weeks, or placebo in a randomly assigned sequence. Drug effects were monitored by ethological playroom observation and by Aberrant Behavior Checklist ratings by parents and teachers. Data of the playroom observation pointed to an activating influence of Org 2766, as revealed by a significant decrease of stereotypic behavior and significant increases in "change toys," "locomote," and "talk." Checklist ratings did not show significant changes. The clinical implications of these findings are discussed.

Corticotropin-like immunoreactivity in the brain and pituitary of three teleost species (goldfish, trout and eel)

Immunostaining of brain and pituitary sections of three teleost species (goldfish, trout and eel) with antisera to porcine and human ACTH 1-39 revealed the presence of an ACTH (adrenocorticotropic hormone)-like peptide in the ventral hypothalamus. Perikarya were localized in the rostral, median and posterior portions of the nucleus lateralis tuberis (NLT); some were in contact with the cerebrospinal fluid. A dense network of immunoreactive (ir) fibers occurred in the peri-infundibular region and extended into the periventicular tissue, around the lateral and posterior recesses. Rostrally directed ir-fibers reached the telencephalon either ventrally or mediodorsally; some were observed in the olfactory lobe. In the mesencephalon, ir-fibers penetrated into the optic tectum of the goldfish. In the pituitary, both antisera intensely labeled rostral ACTH cells. Small groups of labeled cells were scattered in the rostral pars distalis and the proximal pars distalis. A gradient of activity was evident among ACTH cells: those located along the rostral neurohypophysis containing corticotropin-releasing factor nerve terminals were larger and often more marked than those farther away from the neural tissue. ACTH-like peptide in the brain may act as a neuromodulator, mainly in the NLT and the preoptic nucleus, and around the nuclei of the ventricular recesses containing serotonin and catecholamines.

Opioid systems in the amygdala can serve as substrate for the behavioral effects of the ACTH-(4-9) analog ORG 2766

Rats housed individually for 7 days showed a marked decrease in motor activity when tested under intense light conditions in a novel environment as compared to group-housed rats tested under low light conditions. The ACTH analogue ORG 2766 administered into the amygdala decreased the motor activity of group-housed rats tested under low light conditions and increased the motor activity of 7-days isolated rats tested under intense light conditions (ED50: 1-10 pg). Injection of the peptide into the nucleus accumbens was not effective, suggesting that ORG 2766 affects the integration of sensoric stimuli rather than the specific motor output systems. Pretreatment of the rats with the opiate antagonist naltrexone in the amygdala completely blocked the effect of ORG 2766. A similar blockade of the ORG 2766-induced effect could be induced by pretreatment with endorphin antibody suggesting that the "normalizing" activity of ORG 2766 on environmentally induced behavioral changes is mediated by the release of endogenous opioid peptides.

Neuropeptides: animal behaviour and human psychopathology

Animal studies have demonstrated that neuropeptides modulate nervous system functions. It has been postulated that disturbances in neuropeptide systems may be aetiological factors in psychiatric and neurological disorders. Neuropeptides related to ACTH/MSH, including ORG 2766, increase motivation and attention and facilitate recovery processes after nerve damage. These peptides may be effective during the early stage of dementia. Vasopressin and related peptides improve memory processes in animals and humans. In addition, these peptides influence social behaviour, mood and addictive behaviour. The non-opioid gamma-type endorphins have neuroleptic-like activities in animals and antipsychotic effects in a category of schizophrenic patients. Peptides related to CCK have also been found to be effective in these patients. Some neuropeptides, e.g. TRH and PLG, have been reported to exert antidepressant effects. Further research may eventually produce neuropeptides with therapeutic action in psychiatric and neurological diseases.

Involvement of opioid and dopaminergic systems in isolation-induced pinning and social grooming of young rats

Pinning, as a measure for play, and social grooming were simultaneously studied in juvenile rats. Short-term social isolation increased both behavioural responses. This increase was attenuated by the opioid antagonist naltrexone, whilst the opiate, morphine, and the opioid peptide beta-endorphin, increased the responses. Pinning was more sensitive to the effects of naltrexone, whilst beta-endorphin stimulated particularly social grooming. Small doses of the dopaminergic drug, apomorphine, decreased both pinning and grooming behaviour of the short-term isolated rats. Some of the effects were partially antagonized by the dopamine antagonist haloperidol, and the neurolepticum-like peptide, desenkephalin-gamma-endorphin (DE-gamma-E). A small dose of haloperidol and DE-gamma-E stimulated social grooming in particular, whilst a larger dose of haloperidol decreased pinning and social grooming. It is concluded that both opioid and dopaminergic systems are implicated in the increase of pinning and social grooming induced by short-term social isolation. The differences in sensitivity of pinning and social grooming for opioid and dopaminergic drugs and peptides are discussed in relation to possible differences in the neural systems underlying both social activities.

Stress-induced hypokinesia is facilitated by ACTH-(7-10)

Subcutaneous treatment with the neuropeptide ACTH-(4-10) induced hypokinesia in rats subjected to a mild stress induced by placing the animals on a non-functional "hot" plate (21 degrees C) for 30 sec, but not in control animals not exposed to this stress-inducing environment. The lowest effective dose of ACTH-(4-10) was 5 micrograms/kg, administered 50 min before testing. The combination of peptide treatment and the mild stress-inducing procedure mimicked the effect of a short intense stress induced by placing the rats on a hot plate (57 degrees C) for 30 sec, suggesting that this stress-induced hypokinesia is mediated by ACTH neuropeptides. Structure-activity relationship studies revealed that the active core for the ACTH-(4-10)-induced hypokinesia is located in the C-terminal tetrapeptide Phe-Arg-Try-Gly (ACTH-(7-10)). Pretreatment with the opioid antagonist naltrexone did not influence the effect of ACTH-(4-10) indicating that activation of opioid systems is not implicated in this behavioral effect of the peptide.

The ACTH4-9 analog ORG 2766 'normalizes' the changes in motor activities of rats elicited by housing and test conditions

Motor activities of rats were decreased by short-term (7 days) social isolation as well as by intense light test conditions. The ACTH4-9 analog ORG 2766, s.c. administered 50 min before testing, dose-dependently decreased the high motor activities of group-housed rats tested under low light conditions and increased the low motor activities of short-term isolated rats tested under intense light conditions (ED50: 0.01-0.03 microgram/kg). Structure-activity studies suggest that the essential structure for these effects may be located in the C-terminal tripeptide Phe-D-Lys-Phe. Treatment with ACTH4-10 (100 micrograms/kg) tended to enhance some of the effects of the environmental conditions. Pretreatment of rats with the opioid antagonist naltrexone (450 micrograms/kg, s.c.) completely blocked the 'normalizing' effects of ORG 2766, implicating endogenous opioids in this action of ORG 2766. Since social behaviors of rats are similarly affected by ORG 2766 as motor activities, it is suggested that this peptide affects the integration of sensoric stimuli rather than the specific motor output systems of these behaviors.

Behavior and brain neurotransmitters: correlations in different strains of mice

Correlations of behavioral patterns in a social setting with catecholamines, serotonin, and several metabolites and precursors in three brain regions were examined in the DeFries H2, C1, and L1 strains of mice. In Experiment I, behavioral observations were recorded for two 15-min sessions in same-sex, same-strain pairs at about 65 days of age. In Experiment II, sex and strain groups were subdivided into 4% and 24% protein diet groups about 1 week before a second set of behavioral observations at about 120 days of age. Brain tissue content of neurotransmitters, precursors, and metabolites was determined by high-performance liquid chromatography after the second set of observations. Significant multivariate strain differences were shown for behavioral variables (both experiments) as well as concentrations of various neurochemicals. Strain H2 showed relatively high levels of locomotion, while rearing and social investigation were high in strain C1 and self-grooming in strain L1. Significant neurochemical differences were found in the following sets of variables: dopamine variables in the cortex, norepinephrine variables and serotonin variables in the combined diencephalon and midbrain, and norepinephrine and serotonin variables in the hindbrain. Effects of diet were found only on serotonin and tryptophan in the subcortical regions. Significant multivariate correlation with the behavioral variables was demonstrated for the catecholamines but not for serotonin. The results suggest that these strain differences in behavior may be mediated by catecholamine systems.

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.

Corticotropin-peptide regulation of intracellular cyclic AMP production in cortical neurons in primary culture

Previous studies have provided evidence for adrenocorticotropic hormone (ACTH) effects on a wide variety of behaviors. However, the precise sites of action and the mechanisms by which these effects may be mediated have yet to be clearly elucidated. Although ACTH was shown to augment cyclic AMP levels in glial cells isolated from whole brain, other studies found little or no effect of ACTH peptides on cyclic nucleotide metabolism in slices of cerebral cortex or homogenates of whole brain. In the present study, our objective was to determine whether ACTH peptides regulate intracellular cyclic AMP levels in neurons of the cerebral cortex in primary culture. ACTH peptides stimulated cyclic AMP synthesis up to threefold in a dose-dependent manner; stimulation was complete within 5-10 min of exposure to agonists. Neurohormone efficacy was augmented by 0.1 microM forskolin (which was virtually ineffective alone); potency was unaffected. The order of potency (EC50) for increasing intracellular cyclic AMP levels was as follows: ACTH (1-24), ACTH (1-17) (10 nM) greater than alpha-melanocyte stimulating hormone, beta-melanocyte stimulating hormone (alpha-MSH, beta-MSH) (100 nM) greater than ACTH (1-10) (1 microM) greater than ACTH (4-10) (5 microM). The hexapeptide ACTH (4-9) as well as ACTH (11-24) were inactive at concentrations as high as 10 microM. Other neuropeptides derived from proopiocortin, such as beta-endorphin and Met- and Leu-enkephalin were without effect on basal or hormonally stimulated cyclic AMP synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Disrupting circadian rhythms in rats induces retrograde amnesia

Disrupting circadian organization in rats by phase-shifting the illumination cycle or by exposure to a reversed day/night cycle or to continuous light, resulted in retrograde amnesia for passive avoidance behavior. This retrograde amnesia induced by phase-shifting lasted at least 2 days, and gradually diminished the longer the rats were exposed to the new illumination cycle. Retention performance was not impaired when rats were exposed to phase-shifting for 3-5 days before the learning trial. The retrograde amnesia due to changing the illumination cycle is probably due to retrieval disturbances. Extinction of active avoidance behavior was facilitated in rats exposed to a phase-shifted illumination cycle, but social and explorative behavior of rats tested in dyadic encounters were not affected by changing the normal illumination cycle. It is concluded that phase-shifting may result in amnesia for newly learned behavioral responses, but not for more innate behavioral patterns.

Neuropeptides and social behavior of rats tested in dyadic encounters

The effects of various neuropeptides on social behavior was studied in a test procedure in which 7-day isolated animals were tested together with non-isolated partners in dyadic encounters. The short-term isolation procedure increased the frequency and duration of social activities of the rats, but hardly affected non-social explorative behaviors of the animals. Systemic injection of certain neuropeptides, i.c. prolyl-leucyl-glycinamide (PLG), thyrotropin releasing hormone (TRH) and the ACTH 4-9 analog ORG 2766, reversed the isolation-induced increase in social activity, similarly as previously observed with antidepressant drugs. Subcutaneous treatment with beta-endorphin, alpha-endorphin and des-Tyr-gamma-endorphin increased social interactions in 7-day isolated animals. beta-Endorphin enhanced social behavior of non-isolated rats as well, whereas gamma-MSH decreased the social interactions of these animals. Both peptides affected especially social contact behavior. The potent action of beta-endorphin suggests that this peptide and opioid systems may play a physiological role in social behavior. It is proposed that a possible functional antagonism between ACTH-like peptides, especially gamma-MSH, and beta-endorphin may operate in social behavior. The action of the peptides may be rather specific for social behavior, since none of the neuropeptides affected non-social explorative behaviors of the rats during the social interaction test.

Cerebral 2-deoxyglucose accumulation in mice following chronic treatment with an ACTH4-9 analog, ORG 2766

Mice were treated with [MET(O2)4, D-Lys8,Phe9]ACTH4-9 (ORG 2766, 100 micrograms/kg per day SC) for 10 days. On the tenth day mice were injected with [3H]2-deoxyglucose and its cerebral accumulation determined in 17 brain areas. The combined results of four experiments indicated a significant decrease of the 2-deoxyglucose accumulation in the septum. Changes observed in other brain areas were not statistically significant in the combined analysis of all four experiments. This selective change in the septum is consistent with selective uptake of ORG 2766 in this region, and with the lack of behavioral activity of ACTH in septal lesioned animals. It also suggests that the behavioral activity of this peptide, generally considered to be on arousal, vigilance, and/or selective attention, may be mediated through the septum, a limbic system structure.