L Sivilotti — Page 2 | PubMed Health

PubMed1985

An unusual effect of gamma-aminobutyric acid on synaptic transmission of frog tectal neurones in vitro.

Bath-applied gamma-aminobutyric acid (GABA) enhanced, in a dose-dependent fashion, the amplitude of optic nerve-evoked monosynaptic excitatory responses of the frog optic tectum superfused in vitro at 7 degrees C. Muscimol was more potent than GABA in eliciting similar effects. GABA-induced responses were antagonized by picrotoxin and were insensitive to bicuculline or strychnine. Raising the bath temperature to 20 degrees C reduced the potency of GABA on these preparations. No significant effect of GABA on the compound action potential of the whole optic nerve was found. These data indicate that GABA can amplify visual inputs to the tectum through bicuculline-insensitive mechanisms.

Action Potentials↗

PubMed1984

Different approaches to study acetylcholine release: endogenous ACh versus tritium efflux.

Superfused slices of guinea-pig cerebral cortex (CC), caudate nucleus (CN) and thalamus (Th) were used to compare i) the resting and electrically-evoked release of endogenous acetylcholine (ACh) in the presence of physostigmine (Phys) and ii) the resting and electrically-evoked tritium efflux (after preloading with 3H choline) in the absence or in the presence of Phys and hemicholinium (HC-3). In addition, the effect of GABA, morphine and their antagonists on both effluxes was investigated. By matching the ACh and tritium outflow on a molar basis, an average ratio of 100: 2-4 was found. When expressed as a percentage of tissue content, the ACh release at 2 Hz (2 min) was 4.1 in CN, 0.92 in CC and 0.44 in Th. Lower percent values in the same rank order, were found for tritium outflow with Phys. Thus, CN has the highest secretory activity. Tritium evoked outflow in the presence of Phys was nearly halved in comparison with the normal values (without Phys). Therefore, the autoreceptor-mediated negative feed-back seems to be similar in the three areas. Tritium evoked outflow in the presence of HC-3 was more than doubled in Th (less so in CC and CN) in comparison with the normal values. A second stimulation at 2 Hz (2 min) gave rise to the same outflow in Th while an evident fall in radiolabel efflux was found in CN. Therefore the blockade of high affinity choline uptake plays a different role in Th and CN.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗