Induction of excessive grooming in the rat by fragments of lipotropin

Spreading depression induced by microinjection of enkephalins into the hippocampus and neocortex

The opioid peptides Leu-enkephalin, Met-enkephalin and D-Ala2-Met-enkephalinamide were injected at various concentrations into the neocortex and hippocampus of rats to examine their effects on EEG activity and DC potentials. All three compounds were found to elicit spreading depression (SD) in both structures. Higher doses of Met-enkephalin were required to elicit SD as well as seizure activity. In the hippocampus the wave of SD was frequently preceded by seizure activity which was antagonized by naloxone pretreatment (40 mg/kg i.p.). Naloxone also prevented Leu-enkephalin-induced SD in the neocortex (but not in the hippocampus) and Met-enkephalin-induced SD in the hippocampus (but not in the neocortex). It failed to block SD elicited by D-Ala2-Met-enkephalinamide in both structures. Some of the various reported behavioral effects of intracranial injections of enkephalins could be artefacts of hippocampal and/or cortical spreading depression.

Comparison of the effects of beta-endorphin and morphine on exploratory and socio-sexual behaviour in the male rat

The socio-sexual and exploratory behaviour profiles were studied in male rats after intracerebral administration of beta-endorphin and morphine. Two social test situations were used, one with a sexually receptive female and one with a castrated male as the stimulus subject. Time (10-60 min)-response and dose (0.25-5.0 millimicron)-response relationships were investigated. A dose of 5 millimicron of beta-endorphin or morphine decreased exploratory activity and socio-sexual approaches. At lower doses (0.5-1.0 millimicron) beta-endorphin produced a more selective inhibitory effect on copulatory behaviour than morphine, which still caused a general depression of both social and sexual behaviours. In contrast to morphine, beta-endorphin increased amicable social contacts at a dose (1 millimicron) which decrease sexual responses. The dissimilarities in morphine and beta-endorphin effects suggest involvement of different brain areas or opiate receptors. The particular behaviour profiles observed after treatment with beta-endorphin indicate the possibility that beta-endorphin influences mechanisms implicated in perception or interpretation of environmental stimuli.

Short-term modulation of domestic pigeon (Columbia livia L.) behaviour induced by intraventricular administration of ACTH

The behavioural responses induced in adult domestic pigeons by intraventricular injections of 0 to 6 IU of ACTH 1-39 are reported. The frequency of 10 different behaviour patterns was recorded for 90 min after administration of the peptide. The effect that was induced was complex, the frequency of some patterns increasing (yawning, headshaking, body shaking, wing-flapping), or some others decreasing (feeding, one-wing stretching, eye closing) or remaining unchanged (preening). The frequency of several patterns was maximal during the first 30 min following the injections but this was shown in some cases to be independent on the hormone administration.

Effects of naloxone on the self-stimulation behavior of the postero-lateral area of the hypothalamus in rats--influence of procedural conditions

Rats exhibiting self-stimulation behavior through chronic electrodes implanted in the posterolateral part of the hypothalamus were subcutaneously injected with low doses (0.003-0.3 mg/kg) of naloxone. The animals were allowed to self-regulate the duration of rewarding brain stimulation. It was found that naloxone increases the duration of self-stimulation in rats in which the brain stimulation has previously been associated with footshock. Vehicle injections or injections of naloxone in rats that had not received footshock prior to testing, did not modify self-stimulation behavior. It is suggested that naloxone may facilitate an aversive central component of the brain stimulation; the conditioned rats therefore increased the duration of brain stimulation to compensate for this negative process.

Blockade of endogenous opiates reduces activity in the rat

Naloxone (2 mg/kg, SC) was found to result in a substantial and significant reduction in general activity levels in the rat (90--120 days old). This effect was seen both under baseline conditions and after stress manipulations which would be expected to result in elevated levels of endogenous opiate peptides. Thus, under baseline conditions general activity was reduced to less than half of the saline control value thirty min after injection. Similarly, a reduction was seen after stress induced by a 30 min swim. While naloxone may have some non-opiate effects, these results support the view that endogenous opiate systems may play an important activational role in behavioral regulation, under baseline conditions and conditions of stress.

beta-Endorphin induces general anaesthesia by an interaction with opiate receptors

beta-endorphin, administered into the cerebral ventricles of rats, provokes a sequence of behavioural and electroencephalographic (EEG) responses similar to those observed with general anaesthetics used clinically. Initial behavioural and EEG excitation, motor incoordination and exaggerated responsiveness to sensory stimuli are followed by a stage of rigid immobility with maintenance of local reflexes (withdrawal, corneal) and EEG arousal in response to stimulation. Finally, there is immobility associated with both EEG and behavioural unresponsiveness to severely noxious stimuli. Such a state of unconsciousness with complete analgesia defines general anaesthesia. This state was completely and rapidly reversed by the specific opiate antagonist, naloxone. The induction of general anaesthesia by a water-soluble neurohormonal peptide acting at specific receptor sites has important implications for traditional theories of anaesthesia.

Opiate receptors may mediate the suppressive but not the excitatory action of ACTH on motor activity in rats

Subcutaneous injections of adrenocorticotropin (ACTH) or of the opiate antagonist naltrexone produced a one (2.0 mg/kg) dpressed, whereas smaller doses of ACTH (50 micrograms/kg) and of naltrexone (0.125 and 0.25 mg/kg) stimulated motor activity in the open field test. Furthermore, naltrexone at a dose level that had no effect on motor activity blocked the suppressive effect of the high doses of ACTH but had no effect on the stimulating effect of the intermediate dose of ACTH. Finally, chronic naltrexone administration resulted in enhanced sensitivity to the suppressive but not to the stimulating effect of ACTH on motor activity. It is argued that opiate receptors may play a selective role in the effect of ACTH on motor activity. Such receptors may mediate the supressive effect of high doses of ACTH whereas other, naltrexone insensitive receptor systems may mediate the stimulating effect of ACTH on activity functions.

The role of endorphins in stress: evidence and speculations

Several lines of evidence suggest that the endogenous opioid peptides endorphins may play a role in the defensive response of the organism to stress. The present paper summarizes these findings as well as evidence linking endorphins to the anterior pituitary polypeptide hormone adrenocorticotropin (ACTH). Evidence is presented that endorphins may function as trophic hormones in peripheral target organs such as the adrenal medulla and the pancreas. As such they may be part of the physiological mechanisms that mediate adrenaline and glucagon release in response to stress. Endorphins (enkephalins) are also suggested to play a role in the control of the pituitary gland during stress. In such capacity they may act as hormone-releasing or inhibiting factors. Finally, endorphins appear to play a role in the behavioral concomitants of stress. In such capacity endorphins are suggested to function as modulators of neural systems that mediate the elaboration and expression of the reactive/affective components of stress. Speculations on the mode of interaction between endorphins and ACTH in the global response to stress are discussed.

Behavioral effects of dynorphin 1-13 in the mouse and rat: initial observations

Dynorphin is a recently identified, pharmacologically potent endogenous opioid peptide. Heretofore it has not been characterized for its behavioral effects. The effects of centrally infused dynorphin upon a variety of behaviors were therefore examined in mice and rats. The present findings point to a specific profile of behavioral activity. The peptide was active in facilitating feeding and grooming, but was inactive in modifying pain sensitivity and rearing behavior. Naloxone was generally ineffective in reversing behavioral effects. Dynorphin thus appears to have some opiate-like effects upon exogenous administration but may be rapidly broken down into a behaviorally potent non-opiate peptide fragment.

Endogenous opiates: through 1978

The discovery of receptors in the brain for opiates and the structure of the endogenous peptides for these receptors has led to an explosion of interest in this field. The present review is the first of an annual series. It summarizes many of the highlights of research with opiate peptides published with a date of 1978 or earlier.

Specific nonopiate receptors for beta-endorphin

Iodinated beta H-[2-D-alanine]endorphin exhibits specific binding to cultured human lymphocytes. The binding is inhibited by low concentrations of beta-endorphin and its D-alanine derivative, but is not affected by opiate agonists and antagonists, or by enkephalin analogs, beta-lipotropin, adrenocorticotrophic hormone, or alpha-melanocyte-stimulating hormone; this suggests the existence of a specific, non-opiate binding site (receptor) for beta-endorphin. The carboxy-terminal region of beta-endorphin is essential for this binding activity, since alpha-endorphin is not active. beta-Endorphin may be a circulating hormone with peripheral physiological effects that are not primarily mediated through interactions with opiate or enkephalin receptors.

Do endorphin residues of beta lipotropin in hormone reinforce reproductive functions?

The beta-endorphin residue of pituitary beta-lipotropin hormone, which regulates utilization and storage of body fat, is several times more potent than morphine in raising pain tolerance. It also produces habituation and dependency behavior. Recently it was found to be present in amniotic fluid and to be a releaser of prolactin. It now appears that the placenta is a rich source of endorphins. These findings may open a new chapter in understanding molecular determinants of behavior patterns responsible for natural selection and survival of vertebrate species. Clinical application of basic information and new concepts relating endorphins to maternal behavior patterns and neonatal physiology is the purpose of this communication. A brief review of the literature, some data from [3H]opiate-binding assays, observation of maternal performance, and reports of maternity patients' feelings and motivations suggesting that these hormone molecules mediate formation of affectional attitude, appetitive systems, and maternal behavior will be presented.

Adrenocorticotrophic hormone fragments mimic the effect of morphine in vitro

1 Fragments of the N terminal part of adrenocorticotrophic hormone (ACTH) inhibited the electrically evoked contractions of the mouse vas deferens. This inhibition could be antagonized by naloxone. 2 The same fragments displaced radiolabelled morphine from morphine antiserum. 3 Structure-activity relationship studies showed that in both assay systems the active core is located within the sequence ACTH 7--10. 4 It is postulated that the Trp9 residue and the peptide bond between Trp9 and Gly10 are particularly important for interaction of ACTH fragments with morphine receptors.

Isolation of the C-fragment and C'-fragment of lipotropin from pig pituitary and C-fragment from brain

Three novel peptides derived from lipotropin, the C-Fragment (residues 61-91), C'-Fragment (61-87) and N-Fragment (1-38), were isolated from pig pituitary, and the C-Fragment was shown to be present in brain. The experimental procedures developed for their isolation are described. The formation of each of the fragments involves enzymic cleavage of lipotropin at consecutive basic residues, with specificity identical with that involved in the activation of known prohormones. In brain assays C-Fragment exhibits a range of biological activities related to its ability to act as an inhibitory neurotransmitter.

Lipotropin, melanotropin and endorphin: in vivo catabolism and entry into cerebrospinal fluid

Anesthetized rabbits were given intravenous injections of either beta-lipotropin (beta-LPH), beta-melanotropin (beta-MSH) or beta-endorphin. The postinjection concentrations of these peptides in plasma and cerebrospinal fluid (CSF) were measured by radioimmunoassay (RIA). The plasma disappearance half-times were 13.7 min for beta-LPH, 5.1 min for beta-MSH, and 4.8 min for beta-endorphin. Circulating beta-LPH is cleaved to peptides tentatively identified as gamma-LPH and beta-endorphin. Each of these peptides appeared in the CSF within 2 min postinjection. The maximum CSF to plasma ratios were 0.08 for beta-LPH, 1.48 for beta-MSH,and 0.23 for beta-endorphin.

Lysergic acid diethylamide antagonizes shaking induced in rats by five chemically different compounds

Thyrotropin-releasing hormone (TRH), sodium valproate, AF-3-5 (1-[2-hydroxyphenyl]-4-[3-nitrophenyl]-1,2,3,6-tetrahydropyrimidine-2-one), RX336-M (7,8-dihydro-5',6'-dimethylcyclohex-5'-eno-1',2',8',14 codeinone), and Sgd 8473 (alpha-[4-chlorobenzylideneamino)-oxy]-isobutyric acid) each induced repetitive shaking of the body of rats after intraperitoneal injection. This action of the five diverse chemicals appears to be subserved by a common pharmacological component, because pretreatment with d-lysergic acid diethylamide (0.03--1.0 mg kg-1, s.c.) attenuated the shaking behavior in a dose-related manner, and cross tolerance was found between RX336-M and TRH, sodium valproate, and AG-3-5.

Opiate peptide modulation of amino acid responses suggests novel form of neuronal communication

Mouse spinal neurons grown in tissue culture were used to study the electrophysiological pharmacology of the opiate peptide leucine-enkephalin. Enkephalin depressed glutamate-evoked responses in a noncompetitive manner independent of any other effects on membrane properties. The results demonstrate a neuromodulatory action of opiate peptide functionally distinct from the conventional neurotransmitter class of operation.

beta-Endorphin: endogenous opiate or neuroleptic?

The opiatelike neuropeptide beta-endorphin produces a spectrum of effects that contrasts with that induced by the neuroleptic haloperidol. Rats injected intraventricularly or directly into the periaqueductal gray with beta-endorphin (0.5 to 50 micrograms) exhibited rigid immobility accompanied by the loss of righting reflex; the period of rigidity was preceded or followed (depending upon dose) by a state of hyperactivity. In contrast, no dose of haloperidol tested (0.5 to 12 milligrams per kilogram) produced rigidity, loss of righting reflex, or behavioral excitation. Furthermore, whereas animals injected with haloperidol remained stationary on a vertical grid, rats injected with beta-endorphin typically slid off the grid. Moreover, combined beta-endorphin and haloperidol treatment produced flaccidity in most animals. These results do not support the contention that this opiatelike peptide may be a naturally occurring neuroleptic.