Opposing effects of dopamine on agonistic behaviour in crayfish

The effects of dopamine on the agonistic behaviour of crayfish were analysed. When dopamine concentrations of 1 µM were injected into large crayfish, individuals were beaten by smaller opponents, despite their physical advantage. Injection of 10 µM dopamine into small animals increased their winning rate against larger opponents. The inhibitory effect of dopamine on larger animals would be mediated by D1 receptors, and the injection of D1 receptor antagonist prohibited the onset of a loser effect in subordinate animals. The facilitating effect of dopamine on small animals would be mediated by D2 receptors, and the injection of D2 receptor antagonist prohibited the onset of a winner effect in dominant animals. Since the inhibitory effect of 1 µM dopamine was similar to 1 µM octopamine and the facilitating effect of 10 µM dopamine was similar to 1 µM serotonin, functional interactions among dopamine, octopamine, and serotonin were analyzed by co-injection of amines with their receptor antagonists in various combinations. The inhibitory effect of 1 µM dopamine disappeared when administered with D1 receptor antagonist, but remained when combined with octopamine receptor antagonist. Octopamine effects disappeared when administered with either D1 receptor antagonist or octopamine receptor antagonist, suggesting the dopamine system was downstream of octopamine. The facilitating effect of 10 µM dopamine disappeared when combined with serotonin 5HT1 receptor antagonist, as well as D2 receptor antagonist. Serotonin effects also disappeared when combined with D2 receptor antagonist, suggesting that dopamine and serotonin activated each other through mutual parallel pathways.

Quetiapine-Induced Place Preference in Mice: Possible Dopaminergic Pathway

Quetiapine, an atypical antipsychotic, is effective in the management of schizophrenia, depression, and anxiety. Although quetiapine overdosage and misuse have been reported, its abuse potential has not been investigated in animals. In this study, the abuse potential of quetiapine was assessed based on the conditioned place preference (CPP) paradigm of drug addiction in a mouse model. First, mice received intraperitoneal injections of quetiapine (40, 80, or 120 mg/kg) every other day during the conditioning phase. In the second experiment, mice were pretreated with 0.03 mg/kg SKF-35866, a D1 receptor antagonist, before receiving saline or quetiapine (120 mg/kg) during the conditioning phase. No significant changes in time spent in the quetiapine-paired chamber were observed compared with time spent in the saline-paired chamber in mice treated with 40 or 80 mg/kg. In contrast, the preference to the quetiapine-paired chamber was significantly increased in mice treated with 120 mg/kg quetiapine, and this effect was blocked by SKF-35866 pretreatment. These results demonstrated, for the first time, the abuse potential of quetiapine in an animal model of drug addiction. Interestingly, this CPP-inducing effect was likely mediated by activating D1 receptors.

Shoaling behaviour is differentially altered by ethanol and dopamine D1 receptor modulators in tropical marine forage fish

Anchovies are filter-feeding fish that inhabit nearshore environments worldwide. With increasing human pharmaceutical use, drugs that alter neurological functioning are becoming more prevalent in aquatic ecosystems via wastewater effluent, creating the need for tests that can reliably determine sublethal effects of these drugs on coastal fish populations. In this study, we used Caribbean anchovies (Anchoa spp.) as a tropical marine fish model to test drug-induced alterations of locomotion and shoaling behaviour with a video-based analysis system. Consistent with its anxiolytic effects in zebrafish (Danio rerio), ethanol decreased shoal cohesion in anchovies. We also characterized the effects of drugs known to modulate the dopaminergic system in zebrafish and rodents. A D1 receptor agonist (SKF 38393) and a D1 receptor antagonist (SCH 23390) increased the time anchovy spent in the center of the arena, but neither drug had an impact on shoal cohesion. Finally, the D1 receptor agonist caused significantly lower meandering compared with fish treated with the D1 receptor antagonist and ethanol. This study suggests that anchovy is a suitable Caribbean marine model for toxicology studies.