Effects of glycine and GABA on bulbar respiratory neurons of cat

Abstract

1. Bulbar respiratory neurons of unanesthetized, decerebrate cats were impaled with the center pipette of a compound, coaxial microelectrode. This electrode allowed intracellular recording of membrane potential (MP) through the central pipette and extracellular iontophoresis of glycine or gamma-aminobutyric acid (GABA) from micropipettes encircling the center pipette with their tips recessed 20-40 microns from the tip of the center pipette. 2. Seventy-seven studies were carried out on 32 inspiratory and 28 postinspiratory neurons with the use of brief pulses (0.3-0.5 s) or long pulses (3-10 s) spanning one or more respiratory cycles. In both neuronal types, GABA and glycine decreased spike frequency, synaptic "noise," respiratory fluctuations of MP, and "input" resistance in a dose-related fashion. 3. In most cases, the membrane was hyperpolarized by the amino acid. The reverse response (depolarization) was observed when the membrane had been hyperpolarized by current clamp. This reversal from hyperpolarization to depolarization occurred at a MP of -81 +/- 2.3 mV (mean +/- SE, n = 7) for glycine and -81 +/- 1.6 (n = 6) for GABA. 4. After intracellular iontophoresis of chloride ions, application of GABA and glycine depolarized the membrane. 5. During relatively long (3-10 s) periods of iontophoresis of glycine or GABA, the effects on MP and input resistance waned. In some cases (23%), the amino acid depolarized the membrane at the most hyperpolarizated portion of the MP trajectory. This was never observed with brief iontophoretic pulses. Such effects of long duration iontophoresis may reflect changes in membrane properties secondary to the primary action of the amino acid on the membrane of the impaled neuron or indirect synaptic actions via changes in discharge of neighboring neurons. 6. Extracellular iontophoresis of a GABA uptake inhibitor, nipecotic acid, potentiated the effects of GABA. 7. Extracellular application of tetrodotoxin appeared to act pre- and postsynaptically to reduce respiratory fluctuations in membrane potential and to increase input resistance without altering the effects of iontophoresed glycine and GABA, suggesting that the amino acids act on postsynaptic membrane receptors not linked to fast sodium channels.(ABSTRACT TRUNCATED AT 400 WORDS)

A Simple Method for Measurement of Ureteric Peristaltic Function In Vivo and the Effects of Drugs Acting on Ion Channels Applied from the Ureter Lumen in Anesthetized Rats

“…Tetrodotoxin (TTX) was dissolved at 0.5 mM in 165 mM NaCI solution (pH 6.5), contained in a peripheral drug pipette of the coaxial multibarrelled electrode (8), and ejected by positive pulses of between 25 and 50 nA. A retaining current of -3 nA was applied between test periods.…”

“…In addition, a coaxial multibarrelled microelectrode (8) was used in some experiments, which allowed an intracellular recording combined with an ex tracellular iontophoresis of drugs. This technique would discriminate possible pre and postsynaptic effects of isoflurane by selectively eliminating action potentials and postsynaptic potentials in the recorded neuron (8)(9)(10).…”

Effect of Amino Acid Infusion on the Ventilatory Response to Hypoxia in Protein-Deprived Neonatal Piglets

“…The AA solution used in this study contained proportionally more excitatory AA such as glutamate and aspartate than inhibitory AA such as glycine. which may also have an influence on the ventilatory response to hypoxia (5,30,31). Furthermore, the fact that this AA solution docs not contain GABA, an important inhibitory ncurotransmitter, may facilitate the effects of excitatory AA on the central respiratory system.…”

A Modified Coaxial Compound Micropipette for Extracellular Iontophoresis and Intracellular Recording: Fabrication, Performance and Theory.

“…The iontophoretically induced flux of glycine from the tips of pipettes constructed from 16-mm glass exceeded that from pipettes derived from 10-mm glass when low currents (50 nA) were used. Similarly, the transport num ber was greater for pipettes derived from 16-mm than 10 mm glass when the electrode resistance was low (< 10 MQ (12,13). We postulated that the high dynamic responsiveness of respiratory neurons to brief pulse iontophoresis derives principally from the close approximation of the tips of the recording and iontophoresis electrodes.…”

“…Steady iontophore sis with currents ranging from 25 -100 nA of inhibitory amino acids routinely decreased input resistance and syn aptic noise and generally hyperpolarized the membrane (see refs. [12][13][14]. A typical example of effects of glycine (100 nA) on an inspiratory neuron is shown in Fig.…”