Locomotion and self-administration induced by cocaine in 129/OlaHsd mice lacking galanin

Previous studies have demonstrated that the galanin system modulates responses to drugs of abuse such as morphine. The current study examined whether genetic deletion of galanin could affect the locomotor and reinforcing effects of cocaine in mice. We analyzed spontaneous motor activity and cocaine-induced hyperactivity in wild-type (GAL-WT) and knockout mice lacking galanin (GAL-KO) maintained on the 129/OlaHsd background. Our results indicate that cocaine enhanced locomotion (defined as moving more than 5 cm) dose-dependently in GAL-WT and GAL-KO mice. However, general activity (total beam breaks) was increased by cocaine only in GAL-WT mice. An additional experiment indicated that galnon, a nonselective galanin receptor agonist, did not affect cocaine-induced hyperactivity. In a second set of experiments, mice of both genotypes were trained to self-administer cocaine under a fixed ratio schedule, tested with various doses of cocaine and under different schedules of reinforcement. This set of experiments showed that cocaine self-administration did not differ markedly between genotypes. However, while GAL-WT mice acquired cocaine self-administration, a median split analysis showed that mice could be divided into large and small drug takers, whereas all GAL-KO mice behaved as small drug takers. Our results indicate that wild-type and galanin knockout mice on a congenic 129/OlaHsd background are responsive to the locomotor effects of cocaine and can acquire intravenous cocaine self-administration. However, the phenotype observed in GAL-KO mice does not support a major role for galanin in cocaine-induced hyperlocomotion and self-administration.