INTRODUCTION
It has been established recently restricted movement activity or hypokinesia (HK) is a peculiar chronic stress and it is the most significant risk factor in the development of cardio- and cerebrovascular, metabolic diseases, neurological and behavioral disorders etc. During last years a considerable attention has been given to the metabolism of neuroactive amino acids (GABA, Glutamate and Glycine) with the connection of their adaptive role in stress situations. The specific aim of this study is determination of the influence of hypokinesia (15, 30 and 45 days) on GABA, Glutamate and Glycine levels in the rats' brain cortex.
Design and Methods
White male rats (n=36) were killed by decapitation after anesthetizing with Nembutal 40 mg/kg IP. HK was achieved by placing rats in the individual narrow Plexiglas cages during 15, 30 and 45 days. Isocratic separation of GABA, Glutamate and Glycine derivates (derivatized by O-phthalaldehyde) obtained using a reverse-phase HPLC-system with electrochemical detection, which comprised 150×4.6 mm “Nucleosil” 100–5 C18 column. The mobile phase comprised phosphate buffer at pH5.6 containing 5% methanol. Statistical data manipulation was performed by software SPSS11.0. Statistical significance of the data was computed by two-way analysis of variance followed by Student's t test.
Results
The analysis of GABA and Glutamate contents in the brain cortex has shown decrease in the all studied periods which is more expressed on the 45th day of HK. So, the content of GABA on the 45th day of HK valid decreased by 49,28%(p=0.0005) compared to the control (258.3±52.8 mcg/g – in control group and 131±21.2mcg/g – after 45-day HK). The decrease in Glutamate level was statistically valid compared to the control during the all studied periods (2.9±0.58 mg/g – in control group; 2.07±0.29 mg/g – after 15-day HK (p=0.02); 2.04±0.15 mg/g – after 30-day HK (p=0.001); 1.5±0.1 mg/g – after 45-day HK (p=0.005)). The analysis of Glycine level has shown statistically valid increased by 74% (p=0.03) on the 30th day of HK compared to the control (72.1±17.2 mcg/g – in control group and 125.6±40.3 mcg/g – after 30-day HK). The changes in Glycine level on the 45th-day of HK were analogous to GABA and Glutamate, but decrease comparison with control was statistically invalid.
Conclusion
Earlier, we showed decrease of brain's energetic metabolism under the conditions of HK. By comparison of energy metabolism changes with GABA and Glutamate contents we can suppose the participation of these neuroactive amino acids in Robertson's GABA-shunt. Taking into consideration the reducing of Glycine's level on the 45th-day of HK we attempt to explain by means of Glycine deamination into pyruvate and its subsequent oxidation into TCA-cycle. Thus, we can conclude that neuroactive amino acids forme their adaptative ability not only by neurotransmission but also by participation in energy metabolism.