Drug abuse and addiction remain considerable health problems and there is substantial evidence that the use of addictive drugs can cause dependence problems more quickly when their use starts before adulthood, mainly with the use of psychostimulant drugs. During adolescence, the brain undergoes continuous changes and studies state behavioural implications of this fact. Some behaviours are common during this period, including the urge for new experiences overbalancing risks, what may increase tendencies to experiment drugs. Therefore, when individuals achieve the addictive state, they keep making poor choices despite the negative consequences .
Regarding drug abuse reward, dopamine (DA) is a crucial neurotransmitter involved. The reward system is a product of DA pathway, which connects the ventral tegmental area of the midbrain to the limbic system, and involves the nucleus accumbens, the amygdala, the hippocampus and the medial prefrontal cortex. The imbalance between dopaminergic circuits that underlie reward, conditioning and executive functions such as emotional control and decision-making, is thought to contribute to compulsive drug use and loss of control in addiction.
From this point of view, Fasoracetam is a psychostimulant of the non-amphetamine type, approved by the U.S. Food and Drug Administration (FDA) to treat narcolepsy. Also, it has been used "off-label" as a cognitive enhancer in other neuropsychiatric conditions as well as for the treatment of substance disorders. The Fasoracetam mechanism of action is poorly understood and appears to involve multiple neurotransmitter systems resulting in a wide range of neurological effects. Taken together, current evidence suggests that Fasoracetam can act as a weak dopamine transporter (DAT) inhibitor binding to the DAT, increasing extracellular DA levels in synapses. Also, some studies have shown that Fasoracetam exerts antioxidant activity in some brain areas such as the striatum. The current study was designed to investigate whether Fasoracetam administration in healthy adolescent rats could lead to AMPH preference during early adulthood and whether it could have influence on behaviour. Hippocampal oxidative status and molecular targets related to addiction in the dopaminergic system were also assessed.
Fasoracetam tablets (200 mg/tablet) were thoroughly pulverized by sonication in distilled water, and DMSO was subsequently added to this suspension to form the administered treatment mixture. This mixture was administered by gavage. The dose of 64 mg/kg reflects concentrations of a high effective dose, for humans. The D, L-amphetamine dose (AMPH; Merck, Germany), 4 mg/mL, i.p., known for inducing CPP, was chosen based on previous studies by our group.
The OF test was used to assess the locomotor activity of rats. Each animal was placed individually in the centre of an arena (40 x 40 x 30 cm) enclosed by black matte walls and floor divided into squares. The number of crossings (horizontal squares crossed with four paws) was recorded for 5 min.
On PND 72, animals were anaesthetized with Thiopental (50 mg/kg i.p.) and euthanized. Part of the hippocampal tissue was homogenized with 10 mM Tris-HCl buffer (pH=7.4) for biochemical analysis and the rest was stored at -80°C to perform molecular analysis.
The enzyme activity was spectrophotometrically quantified by the method of Aebi, which is based on monitoring the disappearance of hydrogen peroxide (H2O2) at 240 nm. The enzymatic activity was expressed in μmol H2O2/ min./ g tissue.
RS levels were measured using the 2’,7’-dichlorofluorescein diacetate (DCHFDA). The oxidation of DCHF-DA to fluorescent dichlorofluorescein (DCF) was determined at 488 nm for excitation and 525 nm for emission. An aliquot of 10 μM of DCHF–DA in ethanol was added to the supernatants, and the fluorescence intensity from DCF was measured for 300s and expressed as a percentage of control group. The RS levels were normalized by protein content.
Fasoracetam administration decreases AMPH-CPP and prevents anxiety and memory impairments. Tukey’s test showed that during withdrawal, AMPH decreased the recognition index in relation to both control and AMPH+Fasoracetam groups. Our current findings evidenced that animals which received Fasoracetam during adolescence and were exposed to AMPH in adulthood showed less AMPH preference, no locomotor impairment, along with less anxiety-like behaviours and no memory deficits.
In addition, Fasoracetam showed antioxidant activity and Fasoracetam the dopaminergic system, thus preventing AMPH-induced impairments in the hippocampus.