Structure activity relationship studies with C-terminal fragments of vasopressin and oxytocin on avoidance behaviors of rats.

The potency of various C-terminal fragments of the neurohypophyseal hormone [Arg8]vasopressin [AVP-(1-9)] was determined using different avoidance behavioral test procedures in rats. Passive avoidance behavior was facilitated by these peptides. The fragments [Cyt6]AVP-(5-8) and [Cyt6]AVP-(5-9) were the most potent peptides tested after postlearning injection (consolidation) and preretention treatment (retrieval), respectively, after s.c. treatment. Comparable results were found when the peptides were injected into the lateral brain ventricle, but after this route of administration the peptides were about 3 to 4 order of magnitude more potent as compared to the s.c. route. Pentylenetetrazol-induced retrograde amnesia was reversed by AVP-(1-9) and various C-terminal fragments. In this respect [Cyt6] AVP-(5-9) and [pGlu4,Cyt6]-AVP-(4-9) appeared to be the most potent peptides. Injection of AVP-(1-9) and various C-terminal fragments after the acquisition of pole-jumping avoidance behavior induced resistance to extinction of the behavior. The fragment [pGlu4,Cyt6]AVP-(4-8) was the most potent peptide for this effect. Passive avoidance behavior was attenuated by s.c. administered oxytocin [OXT-(1-9)] and various C-terminal fragments. [pGlu4,Cyt6]-OXT-(4-9), [pGlu4,Cyt6]OXT-(4-8) and [Cyt6]OXT-(5-8) were the most potent of the peptides tested after postlearning administration, whereas [Cyt6]OXT-(5-9) was the most potent sequence after preretention injection. In all experiments the effects of the peptides were dose-dependent and of a long term nature. The results show that C-terminal fragments of the neurohypophyseal hormones potently modulate various aspects of memory processes, as assessed with different avoidance behaviors.(ABSTRACT TRUNCATED AT 250 WORDS)