Effect of metergoline on delayed response in cats and its relation to the metabolism of dopamine and serotonin in neostriatal and mesolimbic neurons.

In cats the effect of Metergoline (Liserdol, Farmitalia) was investigated on the performance of a delayed response task and was related to the associated changes in the concentrations of dopamine, nonadrenaline and serotonin in the brain. Metergoline (14 microgram/kg/day, i.m.) administered during the first 10 days of the training significantly decreased response latencies at delay periods of 0, 3, 9 and 27 sec without significantly affecting the number of errors. Biochemical assays showed that the improved performance correlated with the increased dopamine content of limbic structures and the decreased serotonin content in all brain structures. The concentrations of dopamine in the neostriatum remain unchanged. Response latencies and the number of errors in cats treated with Metergoline were significantly different from those in animals treated with L-DOPA (30 mg/kg/day) probably relfecting the specific biochemical disturbance induced by the two drugs. These results suggest an inhibitory influence of serotoninergic pathways on areas like the meso-limbic system retaining high concentrations of dopamine.