Effects of acute manganese neurotoxicity in young chicks

Manganese (Mn) is an industrial neurotoxicant in humans and animal models limited to rodent species. The present study analyses the potential neurotoxicity of acute Mn administration in young chicks. The acute (24 h) LD50 values of Mn following intraperitoneal, intramuscular, subcutaneous and oral administrations of MnCl2 in seven-day-old chicks were 21.3 mg kg-1, 28.1 mg kg-1, 28.1 mg kg-1 and 469.5 mg kg-1 body weight of Mn, respectively. Signs of Mn poisoning appeared in the chicks within 2 min and 13 min after parenteral administration and within 20 min and 32 min after oral administration. The signs demonstrated the depressant action of Mn in the chicks. The behavioural effects of Mn given at 5 mg kg-1, 10 mg kg-1 and 20 mg kg-1 intramuscularly were examined in 7 to 12 day old chicks using the three-minute open-field and tonic immobility tests. Manganese decreased the overall locomotor activity of the chicks in the open-field arena as manifested by a significant increase in the latency to move from the central square and decreases in line crossing, frequency of defecation and vocalization score when compared to control values. It also increased the duration of the chicks' tonic immobility response. Pharmacological challenges of Mn-treated chicks with general anaesthetics xylazine-ketamine and thiopental caused the loss of right reflex at a faster rate in comparison with control values. Thiopental increased the duration of loss of righting reflex in Mn-treated chicks when compared with that of the control group. Chlorpromazine challenge of Mn-treated chicks significantly increased the depressant action of Mn in the open-field arena and increased the duration of tonic immobility response produced by the metal. The injections of Mn at 10 mg kg-1, 20 mg kg-1, 50 mg kg-1 and 100 mg kg-1 intramuscularly significantly increased the Mn levels in the plasma, liver, kidneys and entire brain of the chicks. The data suggests acute neurotoxicity of Mn chloride in the young chicks as a form of depressant action that could be determined by open-field and tonic immobility tests with further support from pharmacological challenges.