Naloxone reduces social locomotor activity in rats

Establishment of a preference by the newborn lamb for its mother: the role of opioids

Mother-young relationships in sheep are characterized by individual recognition and a rapidly developing exclusive bond. The authors examined the role of opioids in establishment of the lamb's preference for its mother. Newborn lambs received the opioid receptor antagonist naltrexone (0.0, 1.5, or 3.0 mg/kg i.p.), and lambs were tested at 24 hr and 48 hr of age. At 24 hr, controls spent significantly more time near the mother than near an alien ewe; no significant difference was obtained for the naltrexone-treated groups. The effect of naltrexone persisted at 48 hr. No other significant behavioral difference was observed. Results support the hypothesis that opioids mediate the establishment of mother preference and the view that positive affect associated with social attachment and maternal care may be modulated by opioids.

Morphine treatment during juvenile isolation increases social activity and opioid peptides release in the adult rat

The consequences of juvenile isolation and morphine treatment on general activity, social activity and endogenous opioid release during a social interaction test were investigated in the adult rat. Rats were either isolated or socially housed during weeks 4 and 5 of age and treated daily during this isolation period subcutaneously with either saline or morphine. Directly after a social interaction test at 10 weeks of age, rats were injected with [3H]-diprenorphine and subsequently prepared for in vivo autoradiography. The autoradiographic technique was used to visualise neuroanatomical changes in opioid receptor occupancy, probably reflecting changes in opioid peptide release, as a result of social activity. Juvenile isolation increased general activity during the social interaction test, an effect which was accompanied by a reduction of opioid receptor occupancy in many brain areas, suggesting an increased opioid peptide release as a consequence of socially-induced general activity. Morphine treatment in isolated rats caused an increase in adult social activity and enhanced opioid peptide release in some cortical regions and the ventral tegmental area as compared to saline treated rats. Both social activity and opioid receptor occupancy were unaffected by morphine treatment in non-isolated rats. The present study underscores the role of opioid systems in adult social behaviors as a consequence of juvenile isolation. The results suggest a relationship between social activity and opioid peptide release during social contact. Increased social activity seems to be accompanied by elevated opioid peptide release in distinct brain areas after morphine treatment during juvenile isolation.

The effect of naloxone on spontaneous and evoked dopamine release in the central and peripheral nervous systems

A number of studies have reported that the opiate antagonist naloxone (NX) inhibits behaviors dependent upon central dopamine (DA) release. However, equally compelling evidence from other studies suggests that NX excites a facilitatory effect. The present review was undertaken to resolve the issue by critically evaluating the effects of NX on DA release; the substrate subserving these behaviors. Included are studies reporting an effect of NX on spontaneous as well as drug altered DA release in various central regions. In the preponderant majority of these studies, NX was found to significantly enhance DA release in the virtually every major DA pathway, irrespective of whether DA release was initially stimulated or inhibited by various agents. It is concluded that NX most probably enhances behaviors induced by DA release, especially when administered in low, specific doses. Studies finding an inhibitory effect of NX on such behaviors may inadvertently produce conditions which mask the stimulatory effects of NX on DA release-dependent behaviors.

Appetitive sexual behavior in male rats: 1. The role of olfaction in level-changing behavior

Level-changing behavior is a form of anticipatory behavior of a male rat, when tested in a bilevel testbox. The male explores the testcage prior to introduction of a female. The female is introduced after 5 min. The number of level changes displayed by the male in this period reflects appetitive aspects of sexual behavior and it was suggested that analysis of this level-changing behavior may function as assessment of sexual motivation. In this study the increase of anticipatory level changes over repeated weekly tests was dependent upon (sexual) olfactory stimulation. The number of anticipatory level changes was reliably reduced by administration of the opioid antagonist naloxone, suggesting that endogenous opioids facilitate this behavior. These results suggest that the increase of anticipatory level changes over repeated tests is a response to olfactory stimuli and reflects appetitive aspects of sexual behavior, which are stimulated by endogenous opioids. These results are in accordance with the concept that analysis of anticipatory level-changing behavior can be used to assess sexual motivation.

The effects of chronic naltrexone treatment in young autistic children: a double-blind placebo-controlled crossover study

In a double-blind placebo-controlled crossover trial 23 autistic children, aged 3-7 years, were treated with a mean daily dosage of 1 mg/kg naltrexone for 4 weeks. Drug effects were monitored with behavior checklists rated by parents and teachers, and ethological playroom observations. On average, parents' checklists and playroom data could not differentiate between naltrexone treatment and placebo treatment; however, teachers significantly favored naltrexone treatment. They reported a decrease in hyperactivity and irritability. No effects of naltrexone on social and stereotypic behavior could be demonstrated.

Social isolation and social interaction alter regional brain opioid receptor binding in rats

Endogenous opioid systems have been implicated in the consequences of social isolation and in the regulation of social behavior, although their precise role is not clear. There is not much information on a possible locus in the brain at which opioids exert their effects on social behavior. In an effort to address this issue we analyzed regional opioidergic activity upon social isolation-induced social interaction using in vivo autoradiography. Animals were either socially isolated for 7 days or group housed, and tested singly or in a dyadic encounter. Subsequently, a tracer dose of [3H]diprenorphine was administered and in vivo autoradiographic analysis was performed. Seven days of social isolation caused changes in both social behavior (dyadic encounters) and non-social behavior (singly tested animals). Opioid receptor binding was increased in the medial prefrontal cortex and the parafascicular area in isolates, suggesting that social isolation may evoke an upregulation of opioid receptors in these areas. Social interaction increased opioid binding in the parafascicular area of non-isolated rats. In substantia nigra para compacta and ventral tegmental area binding was increased upon social isolation, and social interaction decreased opioid binding in isolates, but these changes failed to reach significance. These observed local changes in opioid receptor binding suggest a role for opioid systems in discrete areas in the consequences of social isolation and the regulation of social behavior in rats.

Effects of opioid receptor blockade on the social behavior of rhesus monkeys living in large family groups

Rhesus monkeys of 9 weeks, 48 weeks, 100 weeks, 150 weeks of age (young subjects), or mature parous females that were not lactating were given acute single doses of the opioid antagonist naloxone (0.5 mg/kg) and vehicle on different days and observed in their familial social groups. Naloxone increased the occurrence of affiliative behaviours. Young subjects spent more time in contact with their mothers but showed no changes in social grooming. Maternal contact was actively sought through contact vocalizations, decreasing proximity, and, for the youngest infants, increased attempts to suckle. Mature females made more solicitations for grooming and received more grooming from their companions. These results are interpreted in terms of naloxone blocking the positive effect arising from social contact and thus causing subjects to seek further affiliative comfort.

Effects of chronic naloxone administration on vacuous chewing movements and catalepsy in rats treated with long-term haloperidol decanoate

Most antipsychotic medications produce motoric side effects, including parkinsonism and tardive dyskinesia (TD). Correlates of these behaviors in rats (catalepsy and vacuous chewing movements, respectively) were used as a model to assess the usefulness of chronic naloxone administration in symptom reduction. Previous studies have suggested that increased neurotransmission in the endogenous opioid system modulates neuroleptic-induced motoric side effects. Rats were treated with haloperidol decanoate or vehicle for 27 weeks, and withdrawn for 30 weeks. Subsequently, naloxone (0.5 to 2.0 mg/kg SC twice daily) was given for 5 weeks. Long-term haloperidol treatment produced a syndrome of vacuous chewing movements (VCMs) that persisted during the drug withdrawal period. Catalepsy developed rapidly and also persisted. Naloxone treatment had little effect on VCMs but increased catalepsy scores in both haloperidol and vehicle treated groups. Naloxone reduced rearing and grooming in haloperidol rats while increasing these measures in vehicle treated rats. The results indicate that neuroleptic-induced motoric side effects are not reversed by naloxone in rats. Furthermore, they suggest that increased opioid neurotransmission may not underlie the expression of VCMs. This does not rule out the possibility that endogenous opioid system may be involved in the development of VCMs. To the extent that this animal model is valid, naloxone may not be effective in treating TD and neuroleptic-induced parkinsonism in humans.

Endogenous opiates: 1992

This paper is the fifteenth installment of our annual review of research concerning the opiate system. It includes papers published during 1992 involving the behavioral, non-analgesic, effects of the endogenous opiate peptides. The specific topics this year include stress; tolerance and dependence; eating; drinking; gastrointestinal and renal function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical-related activity; general activity and locomotion; sex, pregnancy, and development; immunological responses; and other behaviors.