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Vol. 287, Issue 1, 261-265, October 1998
Departments of
Physiology and Pharmacology (T.E.M., S.W.J.) and
Neurology (S.W.J.), Oregon Health Sciences University, Portland, Oregon
-Hydroxybutyric acid (GHB) is an abused substance that occurs
naturally in the basal ganglia. Electrophysiological recordings of
membrane voltage and current were made to characterize the effects of
GHB on dopamine neurons in the ventral tegmental area of the rat
midbrain slice. Perfusate containing GHB caused a
concentration-dependent membrane hyperpolarization (EC50 = 0.88 ± 0.21 mM) and a reduction in input resistance
(EC50 = 0.74 ± 0.21 mM). The highest concentration of
GHB studied (10 mM) hyperpolarized neurons by 20 ± 3 mV and reduced input resistance by 58% ± 9%. Changes in membrane potential and input resistance were blocked by the
-aminobutyric acid
antagonist CGP-35348 (300 µM), but neither bicuculline (30 µM) nor
strychnine (10 µM) was an effective antagonist. Voltage-clamp
recordings demonstrated that GHB (1 mM) evoked 80 ± 6 pA of
outward current (at
60 mV) that reversed at
110 mV (in 2.5 mM
K+). Increasing concentrations of extracellular
K+ progressively shifted the reversal to more depolarized
potentials. In tetrodotoxin (0.3 µM) and tetraethylammonium (10 mM),
depolarizing voltage steps (to
30 mV) evoked calcium-dependent
current spikes that were completely blocked by GHB (1 mM). These data
suggest that GHB is an agonist at
-aminobutyric acid receptors and
would be expected to inhibit DA release by causing
K+-dependent membrane hyperpolarization.
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