Journal of Neurophysiology, Vol 72, Issue 6 2903-2910, Copyright © 1994 by APS

ARTICLES

Inhibitory postsynaptic currents and the effects of GABA on visually identified sacral parasympathetic preganglionic neurons in neonatal rats

I. Araki
Department of Physiology, Kyoto University Faculty of Medicine, Japan.

1. The actions of gamma-aminobutyric acid (GABA) on sacral parasympathetic preganglionic (SPP) neurons were examined in slice preparations using the whole cell patch-clamp technique. 2. Inhibitory postsynaptic currents (IPSCs), which were evoked by focal electrical stimulation, were recorded from SPP neurons in the presence of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a glutamate receptor antagonist. The IPSCs were substantially reduced by strychnine (1 microM), a glycine receptor antagonist. The remaining IPSCs were completely blocked by bicuculline (20 microM), a GABAA receptor antagonist. The mean peak amplitude of bicuculline-sensitive, GABAergic currents recorded at -60 mV was 53.6 +/- 10.9%, mean +/- SD (n = 8), of that of the total IPSCs. The GABAergic currents were reversed in polarity at about -30 mV, near the Cl- equilibrium potential. 3. GABA (5-50 microM) induced inward currents in SPP neurons with symmetrical internal and external Cl- concentrations. This response was completely blocked by 100 microM bicuculline. Muscimol (2-8 microM), a GABAA agonist, mimicked the GABA-induced responses, whereas a GABAB receptor agonist, baclofen (20-200 microM), produced responses in only a few cells. The GABA-induced currents reversed their polarity at approximately 0 mV, near the Cl- equilibrium potential. When the internal Cl- concentration was reduced, the reversal potential was shifted according to the Nernst equation for Cl-. 4. GABA-induced currents exhibited an outward "hump" between -35 and 15 mV. This voltage range coincided with that at which a depolarization-induced inward whole cell current was elicited.(ABSTRACT TRUNCATED AT 250 WORDS)

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