Presynaptic GABA autoreceptors on GABAergic nerve endings of the rat substantia nigra.
The release of 3H-GABA evoked by exposure to 30 mM potassium during 1 min was found to calcium independent in the rat occipital cortex and calcium dependent in the substantia nigra. Exposure to either muscimol 1 microM or GABA 1 microM inhibited the potassium-evoked release of 3H-GABA from the substantia nigra but not from the occipital cortex. The inhibitory effect of muscimol 1 microM on the potassium-evoked release of 3H-GABA from the substantia nigra was significantly antagonized by picrotoxin 10 microM. Exposure to either 10 or 100 microM pricrotoxin alone did not affect the potassium-evoked release of 3H-GABA. These results are compatible with the presence of a negative feedback mechanism in bagaergic nerve terminals of the rat substantia nigra which is mediated by presynaptic GABA autoreceptors. In addition, these results emphasize the importance of the calcium-dependent nature of the release of the neurotransmitter for demonstrating the modulation of transmitter release through presynaptic receptors.
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002540:Cerebral Cortex / Q000378:metabolism; D066298:In Vitro Techniques; D008297:Male; D009118:Muscimol / Q000494:pharmacology; D009411:Nerve Endings / Q000502:physiology*; D010852:Picrotoxin / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D011956:Receptors, Cell Surface / Q000502:physiology*; D013378:Substantia Nigra / Q000378:metabolism / Q000502:physiology*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism / Q000502:physiology*
D002118:Calcium; D009118:Muscimol; D010852:Picrotoxin; D011188:Potassium; D011956:Receptors, Cell Surface; D005680:gamma-Aminobutyric Acid