Interaction of morphine and haloperidol on agonistic and motor behaviors of male mice

The role of mesocorticolimbic dopamine in regulating interactions between drugs of abuse and social behavior

The use of addictive drugs can have profound short- and long-term consequences on social behaviors. Similarly, social experiences and the presence or absence of social attachments during early development and throughout life can greatly influence drug intake and the susceptibility to drug abuse. The following review details this reciprocal interaction, focusing on common drugs of abuse (e.g., psychostimulants, opiates, alcohol and nicotine) and social behaviors (e.g., maternal, sexual, play, aggressive and bonding behaviors). The neural mechanisms underlying this interaction are discussed, with a particular emphasis on the involvement of the mesocorticolimbic dopamine system.

Prenatal cocaine alters later responses to morphine in adult male mice

Mice prenatally exposed to cocaine (25 mg/kg), physiological saline or non-treated during the last 6 days of pregnancy were evaluated as adults for the rewarding properties of 2 mg/kg of morphine, using the conditioned place preference (CPP) procedure. Likewise, isolated animals underwent a social interaction test with conspecifics after receiving the same morphine dose. Unlike control or animals pre-treated with saline, subjects prenatally treated with cocaine did not develop CPP with this dose of morphine. Only cocaine-exposed animals showed increased threat, avoidance and fleeing during the social encounter. No differences in motor effects of morphine were observed. Analysis of monoamines revealed effects of housing conditions, isolated animals having fewer DOPAC but higher levels of HVA than those grouped, but in both groups there was a decrease in DOPAC in cocaine- and saline-treated mice. Prenatal cocaine exposure decreases the response to the rewarding properties of drugs in mature offspring. They also implicate cocaine consumption during pregnancy could affect the response of offspring to take other drugs of abuse.

Development of tolerance to the antiaggressive effects of morphine

Many reports have demonstrated that there is a development of tolerance to many effects produced by morphine. This study was conducted with the aim of determining whether the antiaggressive actions of morphine develop tolerance after chronic administration. Acute morphine administration produced antiaggressive effects which disappeared after chronic (7 days) treatment in isolated mice. An increase in non-social exploration was observed, representing morphine-induced hyperactivity, after acute treatment, which was not present after chronic administration. In conclusion, there is a development of tolerance to the antiaggressive and motor effects of morphine.

Lack of specific effects of selective D(1) and D(2) dopamine antagonists vs. risperidone on morphine-induced hyperactivity

In the present study, three different dopamine antagonists were challenged in order to counteract hyperactivity induced by 50 mg/kg of morphine. A wide range of doses of morphine (50, 25, 12.5, 6.25, or 3.12 mg/kg) were evaluated on spontaneous locomotor activity. A significant increase was observed only with the two higher doses tested (25 and 50 mg/kg). No decrease was found with any of the doses used at any period of time. After analyzing doses of SCH 23390 (0.5, 0.1, and 0.05 mg/kg), raclopride (0.5, 0.25, and 0.125 mg/kg) and risperidone (0.1, 0.05, and 0.025 mg/kg) administered alone, only the 0.5 mg/kg dose of SCH 23390 decreased locomotor activity. The three compounds counteracted morphine-induced hyperactivity, but with SCH 23390 it was only achieved with the dose of 0.5 mg/kg, which also decreased spontaneous locomotor activity and induced catalepsy. On the other hand, raclopride and risperidone neutralized morphine-induced hyperactivity at doses that did not affect locomotor activity, although the former induced catalepsy when administered with morphine. It is concluded that although the blockade of D(1) and D(2) DA receptors decreases morphine-induced hyperactivity, this action is not specific, contrary to the action of risperidone, which counteracts this hyperactivity without any other motor effects.

Behavioural characterization of interleukin-6 overexpressing or deficient mice during agonistic encounters

Interleukin-6 (IL-6) is a cytokine released by activated immune cells which has been shown to affect brain function. In this experiment aggressive and affiliative behaviour exhibited during agonistic encounters by transgenic male mice either not expressing (IL-6 -/-) or overexpressing (NSE-hIL-6) IL-6 in the central nervous system was investigated. All subjects were isolated for 24 days before the aggressive encounter and were 52 days old at the time of testing. Subjects were placed for 5 consecutive days in a neutral cage for 15 min with an opponent of the Balb/c strain that had been previously isolated for the same amount of time. The first and the last test sessions were videotaped to evaluate the first approach and the establishment of the social role, respectively. A number of behavioural categories were later scored. When compared with wild-type controls, IL-6 -/- mice showed a higher degree of aggressive behaviour as indicated by a higher frequency of Offensive Upright Posture, an effect more pronounced on the fifth encounter. On the contrary, NSE-hIL-6 subjects showed a tendency to be more involved in affiliative-type social interactions, displaying a higher frequency and duration of behaviours such as Anogenital, Nose or Body Sniff. IL-6 -/- mice showed a clear tendency to exhibit less affiliative interactions compared with their controls while dopamine levels were found to be modified in a number of brain regions in these mice. Overall, these data suggest that IL-6 affects both aggressive and affiliative-type interactions, although the behaviour of the NSE-hIL-6 subjects was less affected than that of the IL-6 -/- group. The effects of the genetic background of the animal in screening the outcome of gene manipulations on behaviour are also discussed.

Effects of risperidone and SCH 23390 on isolation-induced aggression in male mice

In this study, the antiaggressive effects of risperidone and SCH 23390 have been explored. Using the paradigm of isolation-induced aggression, 150 albino male mice of the OF1 strain were allocated to control and experimental groups which received three doses of risperidone (0.01, 0.05 and 0.1 mg/kg) or two doses of SCH 23390 (0.05 and 0.1 mg/kg). Only the highest doses of risperidone decreased threat and attack behaviours but all doses significantly impaired motor behaviour. SCH 23390 decreased attack with the two doses used and also produced significant increases in immobility. Although both antipsychotics are antiaggressive, this action seems to be more specific in the case of risperidone. Finally, both drugs failed to affect animals with short attack latency, being antiaggressive only in subjects with long attack latency, which suggests that these two types of animals are different in their dopamine and serotonin neurotransmission.

Endogenous opiates: 1997

This paper is the twentieth installment of our annual review of research concerning the opiate system. It summarizes papers published during 1997 that studied the behavioral effects of the opiate peptides and antagonists, excluding the purely analgesic effects, although stress-induced analgesia is included. The specific topics covered this year include stress; tolerance and dependence; eating and drinking; alcohol; gastrointestinal, renal, and hepatic function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurologic disorders; electrical-related activity; general activity and locomotion; sex, pregnancy, and development; immunologic responses; and other behaviors.