Pathophysiology 19 (2012) 71–80 Neuroprotective action of bacterial melanin in rats after corticospinal tract lesions Tigran R. Petrosyan a,∗ , Olga V. Gevorkyan b,1 , Irina B. Meliksetyan b,2 , Anna S. Hovsepyan c,3 , Levon R. Manvelyan b,4 a Department of Kinesiology, Armenian State Institute of Physical Culture, Alex Manukyan 11, Yerevan, Armenia b Institute of Physiology, NAS Armenia, Orbeli Str. 22, Yerevan, Armenia c Institute of Biotechnology, NAS Armenia, Gyurdjian Str. 14, Yerevan, Armenia Received 23 September 2011; received in revised form 21 November 2011; accepted 6 December 2011 Abstract Experiments were performed on 48 albino rats. Part of the experimental animals were initially trained to a balancing instrumental conditioned reflex (ICR). Unilateral bulbar pyramidotomy performed in all rats caused contralateral hemiparesis. On the next day following the operation 24 rats were injected intramuscularly with bacterial melanin solution. 12 of these rats were initially trained to ICR. Recovery periods of ICR and paralyzed hindlimb movements were registered for melanin injected rats (n = 24) and for operated rats, not treated with melanin (n = 24). In rats injected with bacterial melanin the posttraumatic recovery is shorter than in animals not treated with melanin. The fastest and complete recovery was registered in rats initially trained to ICR and injected after the operation with bacterial melanin. Electrophysiological experiments were performed in transected animals treated with melanin, transected animals without melanin treatment and intact animals. Spiking activity of motoneurons was registered in lumbar motoneurons of rats in response to high frequency stimulation above the corticospinal tract transection. Spiking activity was very similar in motoneurons of melanin injected and intact or non operated animals. In animals, not dosed with bacterial melanin after the operation, areactivity or no change in firing rate was registered in response to stimulus. Stimulation of the corticospinal tract of melanin injected rats produced potentiation of the motoneuronal firing rate and is an evidence of regeneration in corticospinal tract. Similarity in spiking activity of intact and melanin injected rats shows the recovery of conductance in pyramidal tract. Morphohistochemical examination was carried out to confirm the results of behavioral and electrophysiological experiments. Medulla slices were prepared to trace the regeneration of nerve fibers. Examination of transection area revealed that bacterial melanin increases vascularization, dilates the capillaries in nervous tissue and stimulates the process of sprouting. © 2012 Elsevier Ireland Ltd. All rights reserved. Keywords: Instrumental conditioned reflex; Recovery; Melanin; High frequency stimulation 1. Introduction One of the central problems of present-day medical biotechnology is production of physiologically active ∗ Corresponding author. Tel.: +374 093734579. E-mail addresses: tigpetrosyan@yahoo.com (T.R. Petrosyan), ogevorkyan@yahoo.com (O.V. Gevorkyan), iram@neuroscience.am (I.B. Meliksetyan), anichka h@mail.ru (A.S. Hovsepyan), lmanvel@neuroscience.am (L.R. Manvelyan). 1 Tel.: +374 093536796. 2 Tel.: +374 094240749. 3 Tel.: +374 091946199. 4 Tel.: +374 10272247. preparations for their application in medicine, biology and other fields. Testing of these preparations on models of various diseases can result in creation of new efficient drugs. Currently melanins of various origins are being actively studied and applied as medicinal and cosmetic preparations. Melanins are multicolored pigments of polymer structure. They are unique transmitters of energy with the properties of amorphous semiconductor. They can absorb the energy and convert it into various types of energy [1–3]. Melanins break free radical chain reactions and accomplish antioxidant protection. These unique abilities of melanin explain its presence in tissues and organs connected with energy transmission, such as skin, retina, inner ear and nervous 0928-4680/$ – see front matter © 2012 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.pathophys.2011.12.003