EFFECTS OF GLYCINE ON NEURONS IN THE RAT SUBSTANTIA NIGRA ZONA COMPACTA - INVITRO ELECTROPHYSIOLOGICAL STUDY

The effects of bath‐applied glycine to substantia nigra zona compacta neurons of rat were investigated byintracellular recording techniques in vitro. Superfusion of glycine (1 mM) in the medium hyperpolarized 53% of the neurons recorded with KCI electrodes, whereas 32% of the cells were depolarized. The remaining 15% of neurons was hyperpolarized and then depolarized by the amino acid. In spite of these membrane changes, the action potential firing was depressed. Both hyperpolarization and depolarization were correlated to an outward and an inward current, respectively, when recording in single‐electrode voltage‐clamp mode. In response to bath application of glycine, the neurons showed a concentration‐dependent conductance increase. Micromolar concentrations of glycine (100–300 m̈M) in the superfusion medium produced a membrane hyperpolarization (outward current) in most of the tested cells, whereas millimolar concentration of amino acid could cause depolarization (inward current) in the same neurons. When the recording electrodes contained K acetate, only hyperpolarizations (outward current) were produced. The potential and current changes and the increase in membrane conductance produced by glycine showed little desensitization when neurons were recorded with K acetate electrodes. The mean reversal potential for the membrane hypolarization was –80 mV with intracellular electrodes containing KCI and –84 mV with electrodes containing K acetate. The mean null potential for the depolarizing effect was –46 mV. The reversal potential for the glycinergic responses was shifted to less negative values upon lowering the extracellular concentration of chloride or increasing the extracellular concentration of potassium. Strychnine (1–10 m̈M) reversibly antagonized both the conductance increase and the membrane changes produced by glycine. Bath application of bicuculline (100 m̈M) and picrotxin (200 m̈M) did not affect glycine responses, while depressing the actions of GABA and muscimol. It is concluded the glycine exerts and inhibition on substantia nigra zona compacta neurons by acting on strychnine‐sensitive receptors. The membrane effects produced by glycine result from the activation of a cloride current. In addition, the simultaneous involvement of porassium ions may contribute to the overall effects of glycine. Copyright © 1990 Wiley‐Liss, Inc.