Effects of bacterial melanin on motor recovery and regeneration after unilateral destruction of Substantia Nigra pars compacta in rats.

We examined the potential neuroprotective action of bacterial melanin (BM) in rats after unilateral destruction of Substantia Nigra pars compacta (SNc) dopaminergic neurons. 24 rats were initially trained to an instrumental conditioned reflex (ICR) and then subjected to unilateral electrolytic destruction of SNc. Unilateral deficit in balancing hindlimb movements was observed in all rats after the destruction. On the next day after the destruction part of the animals (n=12) was intramuscularly injected with BM solution at the concentration 6 mg/ml (0.17 g/kg). The other 12 operated rats served as a control group. On the second day after the operation the testing of instrumental conditioned reflex was resumed in both groups. Comparison of recovery periods for the ICR in both groups showed that recovery of the reflex and balancing hindlimb movements in melanin treated rats took place in three postoperative testing days, whereas in control group the recovery was not complete after 23 testing days. Electrophysiological study was conducted in 12 intact rats to show the effects of BM on the activity of SNc neurons. The firing rate of neurons was significantly increased by the BM injection. Morpho-histochemical study of brain sections was conducted after the completion of behavioral experiments. In melanin injected rats the study revealed absence of destruction or electrode trace in Substantia Nigra pars compacta of melanin injected rats. BM stimulates regeneration and microcirculation in SNc. Increased electrical activity of SN neurons and regenerative efforts induced by BM accelerate motor recovery after unilateral SNc destruction.