Effects of corticotropin-releasing factor (CRF), tuftsin and dermorphin on behavior of squirrel monkeys maintained by different events

Appetite and reward

The tendency to engage in or maintain feeding behaviour is potently influenced by the rewarding properties of food. Affective and goal-directed behavioural responses for food have been assessed in response to various physiological, pharmacological and genetic manipulations to provide much insight into the neural mechanisms regulating motivation for food. In addition, several lines of evidence tie the actions of metabolic signals, neuropeptides and neurotransmitters to the modulation of the reward-relevant circuitry including midbrain dopamine neurons and corticolimbic nuclei that encode emotional and cognitive aspects of feeding. Along these lines, this review pulls together research describing the peripheral and central signalling molecules that modulate the rewarding effects of food and the underlying neural pathways.

Self-administration of fentanyl, cocaine and ketamine: effects on the pituitary-adrenal axis in rhesus monkeys

RATIONALE

Drugs of abuse can affect the functioning of the hypothalamic-pituitary-adrenal (HPA) axis. Acute administration of drugs that serve as reinforcers have been observed to stimulate the rat HPA axis, leading to the suggestion that these stimulatory effects may contribute to the development of drug-maintained behaviors.

OBJECTIVES

To determine whether reinforcing drugs that are dissimilar with respect to their mechanisms of action have similar effects on HPA axis activity at doses that are self-administered. Rhesus monkeys were randomly assigned to self-administer the mu-opioid agonist fentanyl, the psychomotor stimulant cocaine, or the NMDA antagonist ketamine.

METHODS

Each monkey was trained to press a lever in order to receive an intravenous injection of drug or saline. Blood samples were obtained before, during, and after the self-administration sessions and assayed for ACTH and cortisol by radioimmunoassay.

RESULTS

Fentanyl, cocaine, and ketamine were each self-administered across a range of doses. However, the three drugs differed in their effects on ACTH and cortisol. Cocaine stimulated ACTH and cortisol secretion, a finding that is consistent with previous rat and primate studies. Self-administration of both fentanyl and ketamine inhibited HPA axis activity. HPA inhibition by fentanyl is consistent with other monkey and human studies, and contrasts with the stimulatory effects of mu-opioids in rodents. The inhibitory effect of ketamine on ACTH and cortisol secretion contrasts with findings in the few primate studies that have evaluated NMDA antagonists. Neither fentanyl nor cocaine, at doses that maintained maximum rates of responding, produced significant changes in ACTH and cortisol levels.

CONCLUSIONS

There appears to be little commonality between different classes of abused drugs and their effects on the HPA axis, which calls into question the necessity for HPA axis stimulation in the reinforcement of drug-maintained behavior.

The Mouse Defense Test Battery: pharmacological and behavioral assays for anxiety and panic

The Mouse Defense Test Battery was developed from tests of defensive behaviors in rats, reflecting earlier studies of both acute and chronic responses of laboratory and wild rodents to threatening stimuli and situations. It measures flight, freezing, defensive threat and attack, and risk assessment in response to an unconditioned predator stimulus, as well as pretest activity and postthreat (conditioned) defensiveness to the test context. Factor analyses of these indicate four factors relating to cognitive and emotional aspects of defense, flight, and defensiveness to the test context. In the Mouse Defense Test Battery, GABA(A)-benzodiazepine anxiolytics produce consistent reductions in defensive threat/attack and risk assessment, while panicolytic and panicogenic drugs selectively reduce and enhance, respectively, flight. Effects of GABA(A)-benzodiazepine, serotonin, and neuropeptide ligands in the Mouse Defense Test Battery are reviewed. This review suggests that the Mouse Defense Test Battery is a sensitive and appropriate tool for preclinical evaluation of drugs potentially effective against defense-related disorders such as anxiety and panic.

Effects of peptides on animal and human behavior: a review of studies published in the first twenty years of the journal Peptides

This review catalogs effects of peptides on various aspects of animal and human behavior as published in the journal Peptides in its first twenty years. Topics covered include: activity levels, addiction behavior, ingestive behaviors, learning and memory-based behaviors, nociceptive behaviors, social and sexual behavior, and stereotyped and other behaviors. There are separate tables for these behaviors and a short introduction for each section.

Tuftsin: on the 30-year anniversary of Victor Najjar's discovery

After a short description of the results of Victor Najjar's research on tuftsin and of the discoveries done by other authors in the early stage of tuftsin investigation, the current state of work on tuftsin is presented, based mainly on the literature published in the years 1984-1997. The presentation follows this order: the occurrence of tuftsin and retro-tuftsin sequences in proteins, their synthesis and biology, the antigenic properties of tuftsin, its influence on phagocytic cells, and other biologic activities of tuftsin, including antimicrobial, antiviral, antitumor and central effects, and the search for tuftsin superactive analogs.

The dermorphin peptide family

1. In 1980, the skin of certain frogs belonging to the genus Phyllomedusinae was found to contain two new peptides that proved to be selective mu-opioid agonists. Given the name dermorphins, these were the first members of a peptide family that in the past 15 years has grown to reach a total of seven naturally occurring peptides and nearly 30 synthetic analogs. 2. Dermorphin peptides are potent analgesics in rodents and primates, including man. Some dermorphins can enter the blood-brain barrier and produce central antinociception after peripheral administration. 3. The dermorphin family also includes mu 1-opioid receptor selective agonists that produce intense opioid analgesia, but stimulate pulmonary ventilation. 4. Experiments in rats and mice chronically exposed to dermorphins have shown that not only do they have higher antinociceptive efficacy and potency than morphine, but they are also less likely than morphine to produce tolerance, dependence and opiate side effects.

The biobehavioral consequences of psychogenic stress in a small, social primate (Callithrix jacchus jacchus)

The biobehavioral consequences of psychogenic stress were examined using neuroendocrine and ethological methods in a captive colony of common marmosets (Callithrix jacchus jacchus). Specifically, hypothalamic-pituitary-adrenal (HPA) axis reactivity was evaluated as a function of gender and social status in four consecutive social environments [(1) stable heterosexual pairs; (2) isolation; (3) unstable peer groups; and (4) stable peer groups], by measuring both basal plasma cortisol, adrenocorticotropic hormone (ACTH) and beta-endorphin concentrations and responsiveness of these hormones to dexamethasone, ovine corticotropin-releasing hormone (oCRH), and ACTH1-24. Socially stressful conditions, such as isolation and peer group formation, were associated with increased HPA axis function and behavioral arousal, and individual profiles were related to gender and social status. Hormonal levels prior to group formation predicted subsequent status in peer groups. Basal morning concentrations of plasma cortisol, as well as cortisol responsiveness to dexamethasone suppression, were sensitive indices of HPA axis arousal during periods of social stress. The context-dependent development of hormonal and behavioral profiles, reminiscent of depression and/or anorexia nervosa, suggests that the common marmoset may be a useful model of psychiatric hypercortisolism.

CNS effects of peptides: a cross-listing of peptides and their central actions published in the journal Peptides, 1986-1993

The centrally mediated effects of peptides as published in the journal Peptides from 1986 to 1993 are tabulated in two ways. In one table, the peptides are listed alphabetically. In another table, the effects are arranged alphabetically. Most of the effects observed after administration of peptides are grouped, wherever possible, into categories such as cardiovascular and gastrointestinal. The species used in most cases has been rats; where other animals were used, the species is noted. The route of administration of peptides and source of information also are included in the tables, with a complete listing provided at the end. Many peptides have been shown to exert a large number of centrally mediated effects.

Effects of corticotropin releasing hormone on appetitive behaviors

Corticotropin releasing hormone (CRH) is a 41-residue hypothalamic neuropeptide that has been shown to have potent behavioral effects in animals and has been implicated in clinical disorders in man. This review focuses on those aspects of the behavioral effects of CRH related to food-associated behaviors. The effects of CRH on food intake are compared with its effects on performances maintained by food presentation, and contrasted with the effects of CRH on performances maintained by other events. The effects of CRH antagonists and drugs that interact with the behavioral effects of CRH are also reviewed, particularly with respect to their direct effects on food intake. Lastly, data assessing the effects of CRH administration on central neurotransmitter levels are presented and compared with levels seen in clinical populations. The effect of CRH on food intake seen in animals is consistent with a putative role for CRH in clinical syndromes where appetite suppression is apparent. Since some of the effects of CRH on food intake are subject to pharmacological intervention, strategies directed at peptidergic mechanisms of psychiatric disorders should be explored.

Selective anorexigenic effects of corticotropin releasing hormone in the rhesus monkey

1. Rhesus monkeys were equipped with a novel intracerebroventricular (i.c.v.) cannula system and trained to respond under operant schedules of food presentation or termination of stimuli associated with the delivery of shock (escape). 2. CRH decreased food-maintained behavior in a dose-related manner over the range of (0.3-10 micrograms/kg) but did not affect escape responding, demonstrating a selective effect on food-maintained responding. 3. This selective effect was related to the tendency for responding to stop after delivery of a food pellet when higher doses of CRH were given, consistent with the notion that a conditioned aversion to food was established in the presence of CRH. 4. This may suggest that in hyperaroused clinical states such as depression and anorexia nervosa, focus is shifted away from appetitive tasks as a result of increased levels of CRH.

Endogenous opiates: 1989

This paper is the twelfth installment of our annual review of the research published during 1989 involving the behavioral, nonanalgesic, effects of the endogenous opiate peptides. The specific topics this year include stress; tolerance and dependence; eating; drinking; gastrointestinal and renal functions; mental illness; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical-related activity; locomotor activity; sex, development, pregnancy, and aging; immunological responses; and other behavior.