Inhibitory postsynaptic currents and the effects of GABA on visually identified sacral parasympathetic preganglionic neurons in neonatal rats.
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)
Araki
I
I
Department of Physiology, Kyoto University Faculty of Medicine, Japan.
D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D004594:Electrophysiology; D005071:Evoked Potentials / Q000187:drug effects; D058787:GABA-A Receptor Antagonists; D058788:GABA-B Receptor Antagonists; D005726:Ganglia, Parasympathetic / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D018009:Receptors, Glycine / Q000187:drug effects; D013116:Spinal Cord / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D013569:Synapses / Q000502:physiology*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
D015220:Calcium Channels; D058787:GABA-A Receptor Antagonists; D058788:GABA-B Receptor Antagonists; D018009:Receptors, Glycine; D005680:gamma-Aminobutyric Acid