Effect of g-ethyl-g-phenyl-butyrolactone (EFBL), anticonvulsant and hypnotic drug, on mouse brain catecholamine levels g-Ethyl-g-phenyl-butyrolactone (EFBL) is a structural combination of the anticonvulsant g-hydroxy-g-ethyl-g-phenylbutyramide (HEPB) and the hypnotic g-butyrolactone (GBL), which inherits both properties. To clarify its mechanism of action, the effects of EFBL, GBL and HEPB on dopamine (DA) and noradrenaline (NA) brain levels were investigated. Influences of chlorpromazine, phenelzine and aminooxyacetic acid were also studied. EFBL increased DA in a dose-dependent manner, remaining enhanced by 80 % over a period of 24 h and augmented NA by 54 % one hour after treatment. HEPB increased DA and NA approximately 2-fold after the first hour. GBL raised DA and NA after three and 24 h, resp. EFBL reversed chlorpromazine effects but potentiated those of phenelzine on DA. Amino-oxyacetic modified neither DA nor NA brain levels, not even in the presence of EFBL. The anticonvulsant and hypnotic properties of EFBL are attributed to its effect on presynaptic dopaminergic receptors and its lasting effect on ethyl and phenyl radicals that hinder its degradation. The results support the role of DA and NA in regulating seizure activity in the brain and indicate that EFBL offers a potential treatment for refractory epilepsy without complementary drugs and Parkinson's disease, without the drawbacks of oral therapies. : g-ethyl-g-phenyl-butyrolactone (EFBL), anticonvulsant, hypnotic, mouse brain, catecholamine It is known that g-butyrolactone (GBL) has depressant effects on the central nervous system (CNS), causing sleepiness and anesthesia (1), whereas ethyl-phenyl-pyrrolidinone (EPP), the cyclic form of g-aminobutyric acid (GABA), is an anticonvulsant whose structure is known as g-hydroxy-g-ethyl-g-phenylbutyramide (HEPB). As a result of the structural combination of HEPB and GBL, g-ethyl-g-phenyl-butyrolactone (EFBL) was synthesized (2), showing both anticonvulsant (2, 3) and hypnotic (4) properties. Because of the abovementioned pharmacological properties, the mechanism of action of EFBL was investigated. It is fundamental to understand the role of GABA, a major inhibitory neurotransmitter in the CNS of mammals, in neuronal excitability, to fully comprehend its mechanism of action and rational design of anticonvulsant agents (5). Since an association between the activity of the GABA-synthesizing enzyme L-glutamate decarboxylase (DAG) and seizure generation was established, increasing the brain GABA levels has become a common strategy utilized in the rational design of anticonvulsants. One approach to accomplishing this goal has been the inhibition of the GABA-degrading enzyme GABA-transaminase (T-GABA). T-GABA inhibitors, such as hydroxylamine and amino-oxyacetic acid (AAOA), have been shown to protect against seizures induced by different chemoconvulsants (6). In any case, most anticonvulsants used in epilepsy treatment are related to GABA-ergic transmission. Therefore, we aimed to clarify the mechanism o...