GABA and lioresal actions on the identified Onchidium neuron.

Abstract

Responses of identified single neurons in the isolated right cerebral ganglion of Onchidium to bath applied -aminobutyric acid (GABA) and lioresal (LRS) were measured using conventional intracellular microelectrode techniques under current and voltage clamp conditions. In normal medium the neurons responded to both GABA and LRS. GABA induced two successive hyperpolarizations (phase I and II). Phase I was a short-lasting Cl-permeability increase while phase II was a long-lasting K+ permeability increase. LRS evoked only a long-lasting K+ permeability increase. In Ca2+-free high Mg2+ medium GABA produced only short-lasting hyperpolarization while LRS had no effect. GABA-induced phase I responses behaved as a simple C1 electrode following changes of external Cl-concentrations. The Hill coefficient obtained from the relation between the relative change in the GABA current and the GABA concentration was almost one during the current increase phase in Ca2+-free high Mg2+ medium. These results indicate that GABA has a direct Cl-permeability increase action on the postsynaptic cell membrane of the identified Onchidium neuron while LRS has no such direct action.

Kinetic and pharmacological properties of the GABA‐induced chloride current in Aplysia neurones: a ‘concentration clamp’ study

“…In invertebrates, the Hill coefficient varied from 1 to 4 (Takeuchi & Takeuchi, 1969;Feltz, 1971;Brookes & Werman, 1973;Constanti, 1977;Matsumoto, 1982;Shimizu et al, 1983). Studies on molluscan neurones gave the coefficient of unity (Matsumoto, 1982;Shimizu et al, 1983) in agreement with the present study. The discrepancy may be due to differences in species and technique of application of the agonist.…”

“…In Aplysia neurones, the main contributing population may be single, since the activation phase was single exponential and activation of a single class of the receptor-channel complex was suggested in Figure 6 1986; Randle & Renaud, 1987). In invertebrates, the Hill coefficient varied from 1 to 4 (Takeuchi & Takeuchi, 1969;Feltz, 1971;Brookes & Werman, 1973;Constanti, 1977;Matsumoto, 1982;Shimizu et al, 1983). Studies on molluscan neurones gave the coefficient of unity (Matsumoto, 1982;Shimizu et al, 1983) in agreement with the present study.…”

Evolution and overview of classical transmitter molecules and their receptors

“…Evidence suggests this action of GABA is linked to a G protein-coupled mechanism. There is additional evidence that central neurones in both Achatina and Onchidium are sensitive to baclofen and GABA but not to muscimol (Takeuchi, 1992;Shimizu et al 1983). These studies using the molluscan nervous system clearly demonstrate that GABA-B-like receptors occur in invertebrates and are likely to be as widespread as GABA-A receptors though possibly less common.…”

GABAB-receptor-activated K+ current in voltage-clamped CA3 pyramidal cells in hippocampal cultures.

“…The inward rectification would explain why this hyperpolarization appeared to diminish when the cells were depolarized (22). A comparable current probably underlies the hyperpolarizing effect of baclofen on Onchidium neurones (38).…”