Short toxic methamphetamine schedule impairs object recognition task in male rats

Performance on object recognition and object placement memory tasks was evaluated after a short-dosing model of methamphetamine (MA) regime and monoamines and metabolites were measured post-testing. Adult male rats received three injections of 10 mg/kg at 2-h intervals. In striatum DA and 5-HT were depleted by 65% and 79%, respectively, no significant changes were found in pre-frontal cortex, hippocampus, ventral tegmental area (VTA) or substantia nigra. The experimental group also showed less exploratory activity in the open field and the sample trials of both object recognition and object placement tasks. MA groups also showed decreased performance in the object recognition trial (1-h and 2-h inter-trial delays). Less exploration of the objects in the sample trial by the MA group might indicate deficits in general exploratory drive and/or to initiate actions. Nevertheless, in the spatial version of the recognition test (object placement task) the experimental group performed as well as the control group in two of the three delays (2 h and 4 h) even with significantly lower total exploration times in the sample trial. Our results demonstrate that a short toxic schedule induced profound changes in neurochemistry (comparable to classic acute toxic models of MA: four injections of 10 mg/kg) but selective declines in behavioral tasks.