Effects of opiate agonists and antagonists on aggressive encounters and subsequent opioid-induced analgesia, activity and feeding responses in male mice

μ-Opioid Receptor Stimulation in the Nucleus Accumbens Increases Vocal-Social Interactions in Flocking European Starlings, Sturnus Vulgaris

Social connections in gregarious species are vital for safety and survival. For these reasons, many bird species form large flocks outside the breeding season. It has been proposed that such large social groups may be maintained via reward induced by positive interactions with conspecifics and via the reduction of a negative affective state caused by social separation. Moreover, within a flock optimal social spacing between conspecifics is important, indicating that individuals may optimize spacing to be close but not too close to conspecifics. The μ-opioid receptors (MORs) in the nucleus accumbens (NAc) are well known for their role in both reward and the reduction of negative affective states, suggesting that MOR stimulation in NAc may play a critical role in flock cohesion. To begin to test this hypothesis, social and nonsocial behaviors were examined in male and female European starlings (Sturnus vulgaris) in nonbreeding flocks after intra-NAc infusion of saline and three doses of the selective MOR agonist d-Ala²-N-Me-Phe⁴-Glycol⁵-enkephalin (DAMGO). DAMGO in NAc dose-dependently increased singing behavior and facilitated social approaches while at the same time promoting displacements potentially used to maintain social spacing. These findings support the hypothesis that MORs in NAc promote social interactions important for group cohesion in nonsexual contexts and suggest the possibility that MORs in the NAc play a role in optimizing the pull of joining a flock with the push of potential agonistic encounters.

Molecular, spatial, and functional single-cell profiling of the hypothalamic preoptic region

The hypothalamus controls essential social behaviors and homeostatic functions. However, the cellular architecture of hypothalamic nuclei-including the molecular identity, spatial organization, and function of distinct cell types-is poorly understood. Here, we developed an imaging-based in situ cell-type identification and mapping method and combined it with single-cell RNA-sequencing to create a molecularly annotated and spatially resolved cell atlas of the mouse hypothalamic preoptic region. We profiled ~1 million cells, identified ~70 neuronal populations characterized by distinct neuromodulatory signatures and spatial organizations, and defined specific neuronal populations activated during social behaviors in male and female mice, providing a high-resolution framework for mechanistic investigation of behavior circuits. The approach described opens a new avenue for the construction of cell atlases in diverse tissues and organisms.

κ-Opioid receptors within the nucleus accumbens shell mediate pair bond maintenance

The prairie vole is a socially monogamous species in which breeder pairs typically show strong and selective pair bonds. The establishment of a pair bond is associated with a behavioral transition from general affiliation to aggressive rejection of novel conspecifics. This "selective aggression" is indicative of mate guarding that is necessary to maintain the initial pair bond. In the laboratory, the neurobiology of this behavior is studied using resident-intruder testing. Although it is well established that social behaviors in other species are mediated by endogenous opioid systems, opiate regulation of pair bond maintenance has never been studied. Here, we used resident-intruder testing to determine whether endogenous opioids within brain motivational circuitry mediate selective aggression in prairie voles. We first show that peripheral blockade of κ-opioid receptors with the antagonist norbinaltorphimine (nor-BNI; 100 mg/kg), but not with the preferential μ-opioid receptor antagonist naloxone (1, 10, or 30 mg/kg), decreased selective aggression in males. We then provide the first comprehensive characterization of κ- and μ-opioid receptors in the prairie vole brain. Finally, we demonstrate that blockade of κ-opioid receptors (500 ng nor-BNI) within the nucleus accumbens (NAc) shell abolishes selective aggression in both sexes, but blockade of these receptors within the NAc core enhances this behavior specifically in females. Blockade of κ-opioid receptors within the ventral pallidum or μ-opioid receptors with the specific μ-opioid receptor antagonist H-D-Phe-Cys-Tyr-D-Trp-Arg-Thr-PenThr-NH2 (1 ng CTAP) within the NAc shell had no effect in either sex. Thus, κ-opioid receptors within the NAc shell mediate aversive social motivation that is critical for pair bond maintenance.

Experimentally induced aggressiveness in heroin-dependent patients treated with buprenorphine: comparison of patients receiving methadone and healthy subjects

Objective measures of experimentally induced aggressiveness were evaluated in heroin-dependent patients (HDP), 15 receiving buprenorphine (BUP) and 15 receiving methadone (METH) treatment. HDP were randomly assigned to BUP and METH groups. Fifteen healthy subjects (CONT) were included in the study as controls. During a laboratory task, the Point Subtraction Aggression Paradigm, subjects earned monetary reinforcement and could respond by ostensibly subtracting money from a fictitious subject (the aggressive response). Money-earning (points maintained) responses did not differ in BUP patients and in controls. In contrast, point-maintained responses were significantly lower in the group of HDP treated with METH than in both the BUP and CONT groups. Aggressive responses were significantly higher in the HDP group than in the CONT group. No significant differences in aggressive responses were found between the BUP and METH groups. Baseline concentrations of plasma adrenocorticotropic hormone (ACTH) and cortisol (CORT) were higher in HDP than in CONT. During the experimental task, ACTH and CORT increased significantly less in METH patients than in BUP patients and CONT. Norepinephrine (NE) and epinephrine (EPI) levels increased significantly more in HDP than in CONT, without any difference between the METH and BUP patients. PSAP aggressive responses positively correlated with NE and EPI changes, as well as with Buss-Durkee Hostility Inventory (BDHI) scores in both METH and BUP patients and also in CONT subjects. No correlation was found between the extent of heroin exposure, drug doses and aggressiveness levels. BUP, similarly to METH, does not seem to affect outward-directed aggressiveness, as aggressive responses related more to monoamine levels and personality traits than to the action of opioid agonists. Money-earning responses seemed to be unimpaired in BUP patients.

Novel object test: examining nociception and fear in the rainbow trout

This study aimed to assess fear responses to a novel object while experiencing a noxious event to determine whether nociception or fear will dominate attention in a fish in novel object testing paradigm. This experimentally tractable animal model was used to investigate (1) the degree of neophobia to a novel object while experiencing noxious stimulation, (2) the response of the fish after removing the fear-causing event by using a familiar object, and (3) the effects of removing the nociceptive response by morphine administration and examining the response to a novel object. Control animals displayed a classic fear response to the novel objects and spent most of their time moving away from this stimulus, as well as showing an increase in respiration rate when the novel object was presented. In contrast, noxiously stimulated animals spent most of their time in close proximity to the novel object and showed no additional increase in respiration rate to novel object presentation. There was evidence of a slight hypoalgesia in noxiously stimulated animals. The responses to familiar objects demonstrated that by familiarizing the animal with the object, fear was removed from the experiment. Both control and noxiously treated animals responded in similar ways to a novel object by spending the majority of their time in close proximity. Treatment with morphine reduced effects of noxious stimulation and appears to be an effective analgesic. After morphine administration, the acid-injected animals showed a neophobic response to a novel object and this was similar to the response of the control fish, with a similar amount of time spent moving away from the object and an increase in ventilation in response to the novel object. Morphine affected the fear response because both groups approached the novel object more quickly than the non-morphine controls. These results suggest that nociception captures the animal's attention with only a relatively small amount of attention directed at responding to the fear of the novel object.

Far-upstream elements are dispensable for tissue-specific proenkephalin expression using a Cre-mediated knock-in strategy

Several cis-regulatory DNA elements are present in the 5' upstream regulatory region of the enkephalin gene (ENK) promoter. To determine their role in conferring organ-specificity of ENK expression in mice and to circumvent the position effects from random gene insertion that are known to often frustrate such analysis in transgenic mice, we used a Cre-mediated gene knock-in strategy to target reporter constructs to a "safe haven" loxP-tagged locus in the hypoxanthine phosphoribosyltransferase (HPRT) gene. Here we report reliable and reproducible reporter gene expression under the control of the 5' upstream regulatory region of the mouse ENK gene in gene-modified mice using this Cre-mediated knock-in strategy. Comparison of two 5'ENK regulatory regions (one with and the other without known cis-regulatory DNA elements) in the resulting adult mice showed that conserved far-upstream cis-regulatory DNA elements are dispensable for correct organ-specific gene expression. Thus the proximal 1.4 kb of the murine ENK promoter region is sufficient for organ-specificity of ENK gene expression when targeted to a safe-haven genomic locus. These results suggest that conservation of the far-upstream DNA elements serves more subtle roles, such as the developmental or cell-specific expression of the ENK gene.

Effects of opiate ligands on intraspecific aggression in crickets

In the cricket Gryllus bimaculatus, the opiate antagonist naloxone, 30 microg in 50 microl into hemolymph per animal, caused a release of intraspecific aggression in male-losers and in females. Naloxone had no significant effect on the aggression of winners and isolated males. The agonist of mu-opiate receptors DAGO, 45 microg, suppressed aggression in male winners and decreased the percentage and duration of contact fights between previously isolated males. The results suggest that, during social contacts, the activity of the endogenous opioid system may contribute to suppressing aggression in subordinate males, as well as in females.

Snake odor alters behavior, but not pain sensitivity in mice

It is known that predator cues (both mammalian odor or avian vocalization) elicit marked analgesia in rodents. The present experiment used olfactory cues produced by an opportunistic rodent predator snake species (100 cc of sawdust scented by Elaphe quatuorlineata). Upon exposure to snake odor (for 30 s, 20 min, or 40 min), adult mice of both the CD-1 and DBA2 strains were assessed for tail-flick or hot-plate analgesia at different times after exposure (from 0 to 40 or 45 min, respectively). In both strains, snake odor exposure induced significant alteration in the frequencies of sniffing, self-grooming, and digging, while it inhibited habituation of locomotor activity in DBA/2 mice. No analgesia emerged with both tests as a consequence of exposure to snake odor. Results suggest that although endogenous analgesia has been demonstrated by other authors to be elicited in response to cues emanating from common and widely distributed mouse predators (such as carnivores or owls), predators such as reptiles, which under natural conditions exert a limited predatory pressure on the house mouse gene pool, may only induce fear-associated behavioral responses but cannot provide ethologically relevant stimuli triggering mouse analgesia.

Physiological bases for parasite-induced alterations of host behaviour

Parasitism is defined in various ways as an intimate relationship in which one partner, the parasite, lives on or in another, the host, generally at the expense of the latter. Parasitism commonly results in a unique array of host physiological responses and adaptations. Most studies of the physiological effects of parasitism have focused on the pathological consequence of infection and disease. While many physiological changes contribute to pathogenesis, it is now recognized that parasitic infections at sub-clinical levels also produce physiological effects that either ameliorate or may not contribute to the disease process. Moreover, these physiological changes are often manifested by altered host behaviour. Behavioural studies have enabled an ecological- and evolutionary-oriented evaluation of host responses. In this fashion, physiological effects may be assessed as to whether they affect fitness and confer benefit or harm to one or both of the symbionts involved. We briefly examine how these physiological responses, specifically neural, endocrine, neuromodulatory, and immunomodulatory components, may interact to modify host behaviors. We consider the adaptiveness of these responses and how the behavioural patterns elicited may simultaneously appear adaptive for the parasite as well as the host. In addition, we address how parasite-host physiological and behavioural interactions may be altered during the course of parasitism.

Opioid receptors and their pharmacological profiles

Opioid receptors can be divided into three major classes, which are called mu, delta and kappa-receptors. The molecular basis of the receptors is discussed and a hypothesis of the binding of bivalent ligands to the receptor is presented. Furthermore the mechanism of action, the distribution and the probable function of these classes is overviewed. Increasing evidence is accumulating that the classical binding model cannot explain completely the interaction of opioids with their receptors. In addition to the mu-receptors, high affinity mu 1 binding sites have been demonstrated. Similarly, the delta receptors may be divided in delta 1 and delta 2. The significance of these subclasses is not yet fully understood. The high affinity mu 1-binding sites, however, represent probably an activated receptor complex, e.g. the complex between the receptor and the guanine-nucleotide-binding protein.

Sex differences in opioid and non-opioid mediated predator-induced analgesia in mice

The present study compared the nociceptive responses of male and female mice exposed to a predator, an ecologically relevant threatening stimulus. After 15 min of exposure to the presence of an experienced predatory cat, mice displayed a naloxone (1.0 mg/kg)-sensitive opioid mediated analgesic response, while after a brief 30-s exposure to the cat mice displayed a lower amplitude, relatively brief, non-opioid analgesia that was insensitive to naloxone and blocked by the serotonin-1A (5-HT1A) agonist, 8-hydroxy-2-(di-n-propylamino)tetralin. Male mice displayed a significantly greater opioid mediated predator-induced analgesia than females, whereas female mice showed a significantly greater non-opioid, 5-HT1A sensitive, analgesia than males. These results indicate that there are significant sex differences in both the opioid and non-opioid analgesic responses arising from exposure to a natural aversive stimulus.

Effects of mammalian FMRF-NH2-related peptides and IgG from antiserum against them on aggression and defeat-induced analgesia in mice

The effects of two endogenous mammalian FMRFamide (Phe-Met-Arg-Phe-NH2)-related peptides, an octapeptide F8Fa (Phe-Leu-Phe-Gln-Pro-Gln-Arg-Phe-NH2) and an octadecapeptide A18Fa (Ala-Gly-Glu-Gly-Leu-Ser-Ser-Pro-Phe-Trp-Ser-Leu-Ala-Pro-Gln-Arg-Phe-NH2 ), and IgG from serum against them on the responses to aggression and defeat-induced analgesia were examined in subordinate mice in "resident-intruder" pairings. Intracerebroventricular (ICV) administrations of F8Fa and A18Fa (0.10-10 micrograms) reduced, in a dose-dependent manner, the number of bites to obtain defeat in the subordinate mice during the agonistic encounters, as well as attenuating defeat-induced analgesia, with F8Fa having a greater inhibitory effect than A18Fa. Peripheral administration of naloxone (1.0 mg/kg) had a similar inhibitory effect on the number of bites to defeat and the level of defeat-induced analgesia. In contrast, ICV administrations of F8Fa-IgG and A18Fa-IgG antisera increased the number of bites to defeat and augmented the levels of defeat-induced analgesia, with F8Fa-IgG having a greater effect than A18Fa-IgG. These results provide further evidence that the peptides, F8Fa and A18Fa, are involved in the modulation of opioid-mediated analgesia accompanying biological stressors and suggest that these endogenous FMRF-NH2-related peptides may also be associated with the expression of opioid-sensitive components of aggressive behavior.

Modifications of social conflict-induced analgesic and activity responses in male mice receiving chronic opioid agonist and antagonist treatments

This study examined the effects of chronic (7 day) administrations of opioid agonists, via osmotic minipumps (20 micrograms/microliters/h, or 2 mg/kg/h for each agent) on: 1) nociception and activity, and 2) the analgesic and locomotor responses of subordinate male mice experiencing social conflict (aggression without defeat) and defeat in a "resident-intruder" paradigm. Chronic infusion of the mu opioid antagonist, naltrexone, resulted in a hypoanalgesic response and a decrease in basal locomotor activity on days 3-7 postimplantation which returned to the basal levels of saline-implanted control mice after termination of the infusions on day 9. Naltrexone reduced defeat-induced analgesia on the second day after implantation, but had no consistent effects on analgesia on test days 6 and 9 or on the aggression-induced (nondefeat) analgesia and increases in activity. The delta opioid antagonist ICI-154, 129, while having no significant effects on basal nociception or locomotor activity, augmented nondefeat-induced analgesia (day 2) and reduced the defeat-induced increases in activity (days 2 and 6). The mu agonist, levorphanol, resulted in a significant analgesia on the first two days after infusion, followed by the development of tolerance to the analgesic effects over days 3-7. On day 9, a hypoanalgesic response indicative of withdrawal was evident. Levorphanol also induced a marked decrease in locomotor activity over days 3-7 postimplantation, with no evidence of the development of tolerance or withdrawal following termination of infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

An ethological model for the study of activation and interaction of pain, memory and defensive systems in the attacked mouse. Role of endogenous opioids

The present work reviews neurochemical, physiological and behavioral data recorded from the attacked mouse and integrates them into a model of coping mechanisms during social conflict. More specifically, the possible relationships between systems of pain, memory and defense are presented, with special emphasis on the role of endogenous opioid peptides (EOPs). In recipients of attack, decreased beta-endorphin-like immunoreactivity and changes in opiate and benzodiazepine binding characteristics are found in structures of the brain defensive system. EOPs mediate the social conflict-induced increase of dopamine synthesis in the periaqueductal grey and frontal cortex. Social conflict analgesia in attacked mice is under the control of central opioid and nonopioid (e.g., benzodiazepine, glutamate) mechanisms, and is modified by experience (e.g., long-term analgesic reaction; tolerance). EOPs and pain-inhibitory mechanisms participate in the organization of behavioral defense, recuperative behavior and the memory of attack experience. The data are considered in relation to the perceptual-defensive-recuperative model of fear and pain, forwarded by Bolles and Fanselow.

The influence of stress on convulsive parameters in the mouse

Mice exposed to the stress of conspecific aggression for 10 min showed shorter latencies to convulsions induced by pentylenetetrazol but not by pilocarpine. This effect was short lived and was not influenced by pretreatment with naltrexone (5 mg/kg, SC). The onset of pilocarpine-induced convulsions in stressed mice was reduced by the opioid antagonist. Aggression stress did not change the incidence, duration or severity of convulsions triggered by the chemoconvulsants or electroshock. The results differ widely from those obtained using other stressogenic models such as cold-restraint or swim stress. This suggests that alterations of convulsive parameters and the involvement of opioid mechanisms in their mediation are critically dependent on the characteristics of the stressogenic procedure employed.

Endogenous opiates: 1988

This paper is the eleventh installment in our annual review of the research during the past year involving the endogenous opiate system. It is concerned with nonanalgesic and behavioral studies of the opiate peptides that were published during 1988. The specific topics this year include stress; tolerance and dependence; eating; drinking; gastrointestinal, renal, and hepatic functions; mental illness; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical activity; locomotor activity; sex, pregnancy, and development; immunology and cancer; and other behavior.

The effects of naloxone on body rotation-induced analgesia and anorexia in male mice

The effects of body rotation in a horizontal plane and the opiate antagonist, naloxone, on the nociceptive responses and the feeding behavior of male mice were examined. In the first experiment the mice were rotated (70 rpm, schedule of 15 sec on; 5 sec off) for 60 minutes or exposed to sham rotation for the same duration. Midway through the rotation or sham procedure the mice were either injected with naloxone (1 mg/kg) or isotonic saline. At the end of the 60-minute treatment period the animals were placed on a warm surface (47.5 degrees C) and their latency to show a foot-licking response was measured. The rotation procedure produced a significant (p less than 0.01) increase in response latency in the saline-injected mice and the naloxone injections blocked this analgesic effect. This finding provides evidence for opioid involvement in the rotation-induced analgesia. In Experiment 2 mice on a food restriction schedule were rotated (70 rpm, 15 sec on; 5 sec off) or sham exposed for 60 minutes. Midway through this treatment period the mice were either injected with naloxone (1 mg/kg) or isotonic saline. Following the treatment period the mice were given access to food for 2 hours. The rotation procedure produced a significant (p less than 0.01) reduction in feeding (anorexia) in the first 30 minutes of food access for the saline-injected mice. Injections of naloxone significantly (p less than 0.05) enhanced the rotation-induced anorexia. These experiments demonstrate that rotation-induced analgesia in mice is blocked by the opiate antagonist, naloxone, whereas rotation-induced anorexia is not.(ABSTRACT TRUNCATED AT 250 WORDS)

Day-night rhythms of shoaling behavior in goldfish: opioid and pineal involvement

Intracerebroventricular (ICV) administration of the opioid peptide, beta-endorphin (5.0 pg/g) to goldfish, Carassius auratus, significantly increased the cohesiveness and duration of shoaling ('bout' length) in shoals of five fish, as well as decreasing the latency of shoal formation in response to an external disturbance, while a higher dose of beta-endorphin (15 pg/g) decreased shoaling. There were day-night rhythms in shoaling and in the extent of the facilitatory effects of beta-endorphin (5.0 pg/g) on shoaling behavior, the fish displaying significantly greater shoaling responses in the day than during the night. The facilitatory effects of the low dose of beta-endorphin were blocked by systemic administration of naloxone (1.0 mg/kg), while ICV administrations of naloxone (1.0 pg/g) decreased daytime shoaling behavior. Removal of the pineal gland disrupted the day-night rhythm of shoaling, reducing daytime levels of shoaling. In addition, pinealectomy reduced the stimulatory effects of beta-endorphin (5.0 pg/g) on shoaling, and attenuated the day-night rhythms in the effects on beta-endorphin on shoaling. These results suggest that both opioid systems and the pineal gland influence shoaling behavior and the expression of its day-night rhythm in goldfish.

Inhibitory influences of the adrenal steroid, 3 alpha, 5 alpha-tetrahydrodeoxycorticosterone [correction of tetrahydroxycorticosterone] on aggression and defeat-induced analgesia in mice

The effects of intraperitoneal administrations of the deoxycorticosterone metabolite, 5 alpha-pregnane-, 21 diol-20-one (3 alpha, 5 alpha-tetrahydrodeoxycorticosterone; alpha-THDOC) on the responses to aggression and defeat-induced analgesia were examined in subordinate intruder male mice in "resident-intruder" pairings. alpha-THDOC reduced in a dose-dependent mannter (1-20 mg/kg) the number of bites and time to obtain defeat in subordinate mice during the agonistic encounters, as well as attenuating defeat-induced analgesia. These inhibitory effects of alpha-THDOC were separate from its sedative actions at 20-30 mg/kg. In addition, the stereo-isomer, 3 beta-pregnane-3 alpha, 21 diol-20-one (20 mg/kg) had no significant effects on the agonistic encounters and defeat, indicating that the inhibitory effects of alpha-THDOC on agonistic interactions are stereospecific. Pretreatment with the benzodiazepine antagonist Ro 15-1788 (5 and 10 mg/kg) attenuated the inhibitory effects of alpha-THDOC on defeat-induced analgesia. Ro 15-1788 (5, 10 mg/kg) by itself, however, had minimal effects on these agonistic interactions and subsequent defeat-induced analgesia. These results indicate that the naturally occurring steroid, alpha-THDOC, has significant effects on responses to aggression and defeat-induced analgesia.