Environment associated with morphine and experience of aggression modulate behaviors of postdependent mice.

Contexts associated with drug use can acquire secondary reinforcing properties. Furthermore, context-specific withdrawal has been observed to reflect a relatively long-lasting learned response. The aim of this study was to evaluate the effect of the environment paired with morphine after 15 days of abstinence. In the first experiment, isolated male mice received saline or morphine either in their home cage or in the distinctive environment, performing two agonistic encounters in the distinctive environment during spontaneous withdrawal. Similar groups were assigned but without aggression encounters during withdrawal. In the second experiment, animals received saline or morphine as previously described but suffered two naloxone-induced withdrawals during agonistic encounters. In all cases, after the second withdrawal, animals were drug-free during 15 days and then an aggression test took place in the distinctive environment. Results show that experience of aggression during this spontaneous withdrawal causes an increase in the level of aggression exhibited when animals are drug free, in comparison with others in which this experience does not exist. Environment associated with morphine administration decreases conditioned physical signs of withdrawal and to a smaller extent aggression. It could be suggested that environment associated with morphine administration decreases the abnormal behaviors exhibited in postdependent mice.

Naloxone-induced opiate withdrawal produces long-lasting and context-independent changes in aggressive and social behaviors of postdependent male mice.

The purpose of this study was to determine whether an environment associated with naloxone-induced morphine withdrawal affects aggressive or social behaviors in postdependent mice. Morphine-dependent or saline-treated mice received 3 naloxone injections in 1 of 2 different environments (A or B); 15 days afterward, when the mice were completely drug free, an aggression test was carried out in Environment A. All the mice suffering morphine withdrawal showed a significant increase in aggression, irrespective of the environment in which the withdrawal took place. In these conditions, the impact of morphine dependence and the 3 induced withdrawals was so profound that the environment could not be discriminative. In addition, modifications in the behavioral profile of postdependent mice that suffered only spontaneous withdrawal were long-lasting, with the mice carrying out more attacks during social investigation without presenting threat postures.

The dopamine D3 antagonist U-99194A maleate increases social behaviors of isolation-induced aggressive male mice.

RATIONALE: Blockade of D1/D2 dopamine receptors produce an antiaggressive action commonly associated with an impairment of other motor behaviors. The D3 receptor seems to present opposite actions to the D1 and D2, since the blockade of this receptor produces stimulation of motor activity which has been associated with an increase in dopamine neurotransmission. OBJECTIVE: In this work, the action of the dopamine D3 antagonist U-99194a maleate on locomotor activity and in a social interaction test in male mice was evaluated. METHODS: Animals isolated during 30 days were treated with U-99194a maleate (20-40 mg/kg) or saline and locomotor activity was measured 20 min after drug administration. The behavioral interaction test was performed afterwards, between the experimental isolated animal and a standard opponent. RESULTS: The higher dose used produces a significant decrease in spontaneous motor activity and presents an antiaggressive action without impairment of other behaviors, such as nonsocial exploration or immobility. At all doses tested, U-99194a maleate significantly increases social investigation. CONCLUSIONS: Our results give support to the hypothesis that the D3 receptor could play a role in emotional behaviors.