Memory effects of arginine vasopressin (AVP) and [7-9] fragment of its peptide chain in rats.

The effect of arginine vasopressin (AVP) and [7-9]-vasopressin on different memory types was examined in tests of active avoidance, passive avoidance and water maze after both intraventricular and subcutaneous injections. Results were compared with AVP and [7-9]AVP effects in open field and holeboard tests. Significant latency time elongation was observed after both icv and s.c. injections of AVP but not [7-9]AVP in the passive avoidance test. This effect was blocked by [beta-Mercapto-beta, beta-cyclopentanometyleno1-propionylo1-O-Et-Tyr2,Val4,Arg8]-vasopressin, an antagonist of V1 receptors. Injections of both peptides did not improve the performance in other performed tests including the open field test and the holeboard test. Therefore the results confirmed that AVP improves memory only in the passive avoidance test. This effect is probably mediated by central V1 receptors and is not induced by exploratory and locomotor activity impairment. Considering the above results together with the literature data, it seems that the most important fragment of AVP is [4-6] AVP.