A choice behavior for morphine reveals experience-dependent drug preference and underlying neural substrates in developing larval zebrafish.

Transparent larval zebrafish offer the opportunity to unravel genetic and neuronal networks underlying behavior in a developing system. In this study, we developed a choice chamber paradigm to measure reward-associated behavior in larval zebrafish. In the chamber where larval zebrafish have a choice of spending their time in either a water- or morphine-containing compartment, larvae that have previously experienced morphine spend significantly more time in the compartment containing morphine. This behavior can be attentuated by pre-treatment with antagonists of the opioid receptor or the dopamine receptor, and furthermore, is impaired in the too few mutant, which has a genetic deficiency in the production of specific groups of dopaminergic and serotonergic neurons in the ventral forebrain. These results uncover a choice behavior for an addictive substance in larval zebrafish that is mediated through central opioid and monoaminergic neurotransmitter systems.