Dose-dependent behavioural effects of two protein-free peptide derivatives on the passive avoidance reaction of rats

Cerebrolysin is an aqueous protein-free solution produced by biotechnological methods, using a standardised enzymatic breakdown of lipid-free pig brain proteins. The present study investigated the behavioural effects of various doses (0.01; 0.1; 1; 10 and 100 mg/kg b.wt.) of this peptide derivative PD, and the related experimental peptide derivative PD-exp on passive avoidance reaction (PAR) of 2-month-old rats. PD consists of 15% small peptides (< 10 kD) and 85% free amino acids. The peptide composition of PD-exp is identical to that of PD but the overall peptide concentration is five times greater than that of PD. In the presented experiments, rats were treated with only one single injection of PD, PD-exp or saline as a control. Passive avoidance procedure started 24 h after the subcutaneous injection with a single PAR-acquisition training. Animals were trained in a step-through avoidance task using an unavoidable footshock of 0.75 mA (2 s). PAR extinction testing started 24 h later and was recorded on five consecutive days. The results of our experiments demonstrate that already a single injection of PD (100 mg/kg b.wt.), but to a higher extent of PD-exp (1 mg/kg b.wt.) induce an improvement on PA reaction of 2-month-old healthy rats.