2016
Volume 16, Number 3, pp. 137–141
Manganese loading induces mouse-killing behaviour in nonaggressive rats
I. Lazrishvili, T. Bikashvili, L. Gelazonia and N. Mitagvaria
I. Beritashvili Centre of Experimental Biomedicine, 14 Gotua St, 0160 Tbilisi, Georgia
It is generally accepted that aggression and violent behaviour may stem from certain toxic metals excessively accumulated in the body. Despite numerous studies on the problem of the neurotoxicity of manganese (Mn), issues concerning its rôle in manifestations of aggressive and violent behaviour are almost unknown. Published data impinging on this problem are indirect and often contradictory. The effect of 30 (group I)- and 75 (group II)-day exposure to different doses of manganese chloride (10 and 15 mg MnCl2·4H2O/mL of drinking water) on the mouse-killing behaviour (MKB) of initially nonaggressive rats was studied. Prior to the Mn loading, in order to eliminate any spontaneously aggressive animals from subsequent experiments the rats were tested for MKB (male interspecific predatory aggression): each nonaggressive rat was placed in an observation cage for 5 min before the MKB test for adaptation. Thereafter, a naïve mouse was placed in the cage with the rat and the following parameters of the rat’s behaviour recorded for 3 min: (1) nonaggressive attack; (2) MKB attempt (aggressive attack); (3) MKB. 30-day exposure to the lower dose did not stimulate aggressive behaviour of subgroup Ia rats, while after exposure to the higher dose 38% of rats (subgroup Ib) manifested MKB and 25% attempted MKB. After 75-day exposure to 10 mg/mL 38% of subgroup IIa rats manifested MKB and 37.5% attempted MKB. After exposure to the higher dose, 75% of rats (subgroup IIb) manifested attempted MKB and 25% nonaggressive behaviour. The data obtained supports the idea that excess Mn in the body might cause aggressive behaviour. 30-day exposure to manganese chloride (10 mg/mL) is not sufficient for achieving the cumulative dose needed for revealing aggressive behaviour. It is known that long-term, high-dose Mn-intoxication leads to an abrupt disruption of neurotransmitter systems, especially the nigrostriatal dopaminergic system. We propose that this violates motor activity and, hence, animals of subgroup IIb, despite repeated attempts, are not able to exhibit MKB.