Stress cause the significant alterations of neurotransmitters metabolism. Stress states are accompanied by processes of adaptation or pathology. It was shown that peculiarities of brain metabolism are connected to individual and typological characteristics of central nervous system and they are the basis of brain stress answer.
The purpose of our work was to study the effects of long treatment L-DOPA and its withdrawal on some cytochemical indices of monoaminergic and acetylcholinergic metabolism in brain of Wistar rats with different motor activities in "open field" test.
Quantitative cytochemical methods were used for measurement of monoamine oxidase (MAO - substrate triptamine) and acetylcholine esterase (AChE) activities in sensorimotor cortex (layers III and V), nucleus caudatus, nucleus accumbens and hippocampus (CA3 field) - the structures responsible for formation and realization of the purposive behavior. The study groups comprised control animals and those receiving intraperitoneal injections of L-DOPA (50 mg/kg body mass per day during 2 weeks) inducing hyperfunction of dopaminergic system, and its withdrawal.
It was shown that L-DOPA administration resulted in the decrease of MAO activity in layer V sensorimotor cortex, nucleus accumbens and nucleus caudatus of rats with high levels of motor activities. MAO activity remained unaffected in brain hippocampus of these rats. In response to L-DOPA the activity of AChE increased in hippocampus and remained unaffected in other brain structures of these rats. When comparing MAO activities in control and experimental rats after L-DOPA withdrawal we have revealed the increase MAO activity in cortex and caudate nucleus and its normalization in nucleus accumbens and hippocampus. AChE activity increased in nucleus accumbens significantly and no changes were noticed in AChE activity in cortex, caudate nucleus and hippocampus in comparison with the control.
In response to L-DOPA on rats with low levels of motor activities the activity of MAO decreased in caudate nucleus and remained unaffected in cortex, nucleus accumbens and hippocampus of rat brain. AChE activity increased significantly in layer V sensorimotor cortex and hippocampus and did not change in layer III sensorimotor cortex, nucleus accumbens and nucleus caudatus of rat brain in comparison with the control. When comparing MAO activities in control and experimental rats after L-DOPA withdrawal we have revealed the decrease MAO activity in layer V sensorimotor cortex and the lower level of its activity in nucleus accumbens in comparison with the control. We have revealed also that layer V sensorimotor cortex had higher AChE activity in comparison with the control.
Our results shown that activity of MAO or AChE in some rat brain structures change differently after administration of L-DOPA and its withdrawal and the effects depended on motor activities of rats.
The expression plasticity was observed in the dynamics of changes of MAO activity in brain of rats with high level of locomotion after DOPA administration, and its withdrawal. The changes of AChE activity in brain of rats with high level of locomotion were non significant. The MAO activity in brain of rats with low level of locomotion mainly changed after L-DOPA withdrawal and degree alterations of AChE activity were similar to the alterations of MAO activity.
Thus, it is shown that the response of brain neurotransmitters metabolism to activation of dopaminergic system depended on individual animal features, that manifested in their behaviour, and in particular, in their motor activities.