Cocaine self-administration improves performance in a highly demanding water maze task.
BACKGROUND
Long-term potentiation (LTP) is considered to be a cellular substrate of learning and memory. Indeed, the involvement of LTP-like mechanisms in spatial learning has consistently been demonstrated in the Morris water maze test. We have previously shown that hippocampal LTP in Lewis rats was modulated by cocaine self-administration, although the performance of cocaine-self-administered rats in the Morris water maze was not altered.


OBJECTIVE
Given that the ease of the task previously used could have masked any possible effects of the cocaine-induced LTP enhancement on spatial learning, a new and more difficult water maze task was devised to address this issue.


METHODS
Animals self-administered cocaine (1 mg/kg) or saline under a fixed ratio 1 schedule of reinforcement for 22 days. Spatial learning was assessed in a difficult water maze task (four sessions, two trials per session with a 90-min intertrial interval), and spatial memory was also evaluated 48 h after training (a 90-s test). Additionally, reversal learning and perseverance were also studied.


RESULTS
There was a reduced latency in finding the hidden platform during training, as well as improved memory of the platform location in cocaine-self-administered rats with respect to animals that self-administered saline. No differences were observed in reversal learning or perseverance between groups.


CONCLUSIONS
Our data suggest that cocaine self-administration facilitates learning and memory in the water maze test only when animals are submitted to highly demanding tasks, involving working memory or consolidation-like processes during the intertrial interval.
Del Olmo
N
N
Departamento Psicobiología, Facultad de Psicología, UNED, C/ Juan del Rosal no 10, 28040, Madrid, Spain.
Higuera-Matas
A
A
Miguéns
M
M
García-Lecumberri
C
C
Ambrosio
E
E
D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D003042:Cocaine / Q000008:administration & dosage / Q000494:pharmacology*; D007275:Injections, Intravenous; D008297:Male; D018782:Maze Learning / Q000187:drug effects*; D011939:Mental Recall / Q000187:drug effects; D051381:Rats; D011917:Rats, Inbred Lew; D012055:Reinforcement Schedule; D012646:Self Administration / Q000379:methods; D013037:Spatial Behavior / Q000187:drug effects; D013550:Swimming; D013647:Task Performance and Analysis; D013997:Time Factors; D014662:Vasoconstrictor Agents / Q000008:administration & dosage / Q000494:pharmacology
D014662:Vasoconstrictor Agents; D003042:Cocaine