Cocaine and amphetamine depress striatal GABAergic synaptic transmission through D2 dopamine receptors

The striation is a brain area implicated in the pharmacological action of drugs of abuse. To test the possible involv,ement of both cocaine and amphetamine in the modulation of synaptic transmission in this nucleus, we coupled whole-cell patch clamp recordings from striatal spiny neurons to the focal stimulation of glutamatergic or GABAergic nerve terminals. We found that neither cocaine (1-600 AM) nor amphetamine (0.3-300 AM) significantly affected the glutamate-mediated EPSCs recorded from these cells. Conversely, both pharmacological agents depressed GABA-mediated IPSCs in a dose-dependent manner. This effect was mediated by the stimulation of dopamine (DA) D2 receptors since it was prevented by 3 AM L-sulpiride (a DA D2-like receptor antagonist), mimicked by the DA D2-like receptor agonist quinpirole (0.3-30 AM), and absent in mice lacking DA D2 receptors. A presynaptic mechanism Ems likely involved in this action since both cocaine and amphetamine depress GABAergic transmission by increasing paired-pulse facilitation. Cocaine and amphetamine failed to affect GABAergic IPSCs after 6-OHDA-induced nigral lesion, indicating that both drugs cause their effects through the release of endogenous DA. The modulation of GABAergic synaptic transmission in the striatum might underlie some motor and cognitive effects of psychostimulants in mammalians.