The antidepressant phenelzine enhances memory in the double Y-maze and increases GABA levels in the hippocampus and frontal cortex of rats

Abstract

Subchronic treatment with a non-competitive glutamate NMDA-receptor antagonist (e.g., MK-801, phencyclidine) or social isolation (SI) from weaning (age 21 days) to adulthood (age 56 days) produces deficits similar to some positive and negative symptoms of schizophrenia. Down-regulation of GABA-ergic neurons has been demonstrated in people with schizophrenia and treatment with GABA-ergic compounds (including benzodiazepines, valproate) has shown some favorable outcomes. We hypothesized that subchronic MK-801 (0.5 mg/kg 2 times daily for 7 days), post-weaning SI or the two in combination will alter activity in a novel environment and memory in the double Y-maze (a test with a spatial discrimination and spatial alternation component) and that treatment with phenelzine (PLZ), a monoamine oxidase (MAO)-inhibiting antidepressant that also produces a rapid increase in brain levels of GABA, will improve memory. SI rats (n=18) showed increased locomotor activity when exposed to a novel environment but no deficits in the double Y-maze and the combination of SI plus subchronic MK-801 did not alter these effects. Delays did not affect performance in the spatial discrimination component of the Y-maze and decreased performance in the alternation component for saline rats but not MK-801 rats. Treatment with PLZ improved performance in both components of the Y-maze in a dose-dependent manner. Neurochemical analyses confirmed that PLZ increased GABA levels in the brain and changes in levels of dopamine, serotonin and their metabolites were consistent with inhibition of MAO. It was concluded that PLZ does not specifically augment memory in SI or subchronic MK-801-treated rats.