Endogenous GABA mediates presynaptic inhibition of spontaneous and evoked excitatory synaptic potentials in the rat neostriatum.
The effect of the blockade of the gamma-aminobutyric acid (GABA) uptake system on the amplitude of glutamatergic synaptic potentials was studied by using a corticostriatal slice preparation. Nipecotic acid (0.1-1 mM), a GABA uptake blocker, produced a dose-dependent decrease of the amplitude of kynurenate-sensitive excitatory synaptic potentials recorded in the neostriatum following cortical stimulation. Nipecotic acid did not affect the postsynaptic responses to exogenously applied glutamate. The presynaptic effect of endogenous GABA was bicuculline-resistant and was mimicked by baclofen (0.3-3 microM). This effect was not blocked by phaclofen (0.5-1 mM). These findings show that phaclofen-insensitive GABAB receptors, activated by endogenous GABA, mediate presynaptic inhibition of cortical glutamatergic inputs in the neostriatum.
Calabresi
P
P
Clinica Neurologica, 2a Università di Roma, Italy.
Mercuri
N B
NB
De Murtas
M
M
Bernardi
G
G
D000818:Animals; D001418:Baclofen / Q000031:analogs & derivatives / Q000494:pharmacology; D003342:Corpus Striatum / Q000187:drug effects / Q000502:physiology*; D005071:Evoked Potentials / Q000187:drug effects / Q000502:physiology; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009557:Nipecotic Acids / Q000494:pharmacology; D011392:Proline / Q000031:analogs & derivatives*; D051381:Rats; D011919:Rats, Inbred Strains; D013569:Synapses / Q000187:drug effects / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000502:physiology*
D009557:Nipecotic Acids; C052329:phaclofen; C030278:nipecotic acid; D013779:Tetrodotoxin; D005680:gamma-Aminobutyric Acid; D011392:Proline; C010983:homoproline; D001418:Baclofen