An electrophoretic method for the determination of the proportion of gamma-aminobutyric acid in a mixture of labeled neurotransmitter and its catabolites

Evaluation of the mechanisms by which gamma-amino-butyric acid in association with phosphatidylserine exerts an antiepileptic effect in the rat

The i.p. injection in rats of GABA (740 mg/Kg) after sonication with an equal amount of phosphatidylserine (PS) has an antiepileptic effect. The injection of plain GABA has no such an effect. Blood, brain and synaptosomal accumulation of exogenous labeled GABA under the two circumstances are evaluated. In the case of GABA/PS injection there is a higher passage of the exogenous labeled neurotransmitter into the blood and brain nerve endings (synaptosomes). A higher synaptosomal accumulation of the exogenous labeled neurotransmitter is found even when GABA and PS are injected separately. Since these accumulation increases occur at a time when there is the antiepileptic effect, they seem relevant to it. Our interpretation of the chain of the events resulting in the antiepileptic action is that the phospholipid facilitates from the beginning the first passage of the exogenous neurotransmitter form the peritoneum to the blood. Then a higher passage to the brain tissue and eventually to the GABA-ergic nerve endings ensues. The brisker accumulation of the exogenous neurotransmitter in the nerve endings could be at the basis of a more efficient GABA-ergic inhibitory control in the brain.

Accumulation of labeled gamma-aminobutyric acid into rat brain and brain synaptosomes after i.p. injection

The accumulation of labeled GABA into brain and brain nerve endings was studied in the adult rat after i.p. injection of large doses of neurotransmitter (740 mg/Kg). In the first 5-30 minutes after the injection the exogenous neurotransmitter reaches a stable plasma level of around 5 mM. The accumulation of radioactive GABA into the brain presents a latency of a few minutes from the time of the injection. Thereafter, the accumulation of the neurotransmitter is almost linear with time. Once in the brain tissue labeled GABA is in part broken down. The exogenous neurotransmitter is taken up in GABA-ergic nerve endings with a steep increase between 20 and 30 minutes after the injection. From a quantitative point of view, the data show that the brain accumulation of labeled GABA at 30 minutes post injection is minimal in the respect of the steady state average concentration of the endogenous neurotransmitter (0.014%). However, the amount of radioactive GABA which accumulates in the nerve endings, at the same post injection time, is around 7% of the endogenous neurotransmitter in that compartment. The data thus show a selective enrichment of exogenous systemic GABA in a physiologically important compartment of the brain.

A microelectrophoretic method for the evaluation of GABA transaminase activity

The reduction to the micro-scale of a recently described electrophoretic method for the evaluation of GABA catabolism by GABA-T is presented. The micromethod involves the electrophoresis, in 1 mm diam. capillaries, of small samples of mixtures of [14C]GABA and its metabolites. By coupling this procedure to previously devised micromethods, it was possible to evaluate GABA-T attack to 14C labeled GABA diffusing across a single microdissected neuronal membrane.

Phosphatidylserine increases in vivo the synaptosomal uptake of exogenous GABA in rats

A sonicated liposome suspension of gamma-aminobutyric acid (GABA) and phosphatidylserine (liposome-entrapped GABA), intraperitoneally administered in rats, inhibited EEG epileptic activity induced by penicillin, whereas GABA did not. A significant increase (20.4%) in brain radioactivity accumulation occurred at 5 min after i.p. administration of [14C]GABA associated with phosphatidylserine in comparison with the administration of [14C]GABA; such an increase persisted after 20 min. However, the accumulation of radioactivity into brain synaptosomes demonstrated a 24.1% increase at 5 min and subsequently showed a 43.3% increase at 20 min after injection of liposome-entrapped GABA. The above findings suggest that phosphatidylserine stimulates exogenous GABA uptake into brain GABAergic nerve terminals.