Elsevier

Neuroscience Letters

Volume 231, Issue 1, 1 August 1997, Pages 13-16
Neuroscience Letters

Bicuculline methiodide potentiates NMDA-dependent burst firing in rat dopamine neurons by blocking apamin-sensitive Ca2+-activated K+ currents

https://doi.org/10.1016/S0304-3940(97)00508-9Get rights and content

Abstract

Apamin, a bee venom toxin which blocks a Ca2+-dependent K+ current, potentiates N-methyl-d-aspartate (NMDA)-induced burst firing in dopamine neurons. We now report that burst firing is also potentiated by an apamin-like effect of bicuculline methiodide (BMI) at the same concentration (30 μM) which blocks GABAA receptors in vitro. Using microelectrodes to record intracellularly from rat dopamine neurons in the midbrain slice, BMI reduced the apamin-sensitive afterhyperpolarization in all cells tested. BMI also mimicked apamin (100 nM) by potentiating burst firing produced by a concentration of NMDA (10 μM) which is too low to evoke burst firing when perfused alone. When recording under voltage-clamp, both BMI and apamin reduced a depolarization-activated outward current which was also sensitive to perfusate containing no-added Ca2+. Although picrotoxin (100 μM) and bicuculline free base (30 μM) blocked the inhibition of firing produced by the GABAA agonist isoguvacine (100 μM), neither had apamin-like effects. We conclude that BMI potentiates burst firing by blocking an apamin-sensitive Ca2+-activated K+ current.

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Acknowledgements

This study was funded by PHS grant MH40416. We wish to thank B. Anna McCoy for her helpful comments.

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