The modulation of memory processes by vasotocin, the evolutionarily oldest neurosecretory principle.

Publisher Summary This chapter presents the experiments to show that effects on consolidation, retrieval, and amnesia (repression) are present in various parts of the oldest neurohypophysial principle, vasotocin. The different behavioral effects of the neurohypophysial hormones and their fragments suggest that they act as precursor molecules for neuropeptides that modulate memory processes. If this were true, one would expect that specific enzymes that generate the linear and the ring portion of these molecules would be present in the brain. It has been found that a membrane-bound hypothalamic exopeptidase is able to generate MIF—prolyl-leucyl-glycinamide (PLG)—from oxytocin that inhibits the release of melanocyte-stimulating hormone (MSH). Such enzymes have not been detected for vasopressin. There are enzymes in the brain that inactivate vasopressin by hydrolysis of peptide bonds in the acyclic position of the molecule, but no enzymes have been identified so far that remove the proline residue to yield pressinamide. The ancestral molecule of the neurohypophysial hormones vasopressin and oxytocin, which generated these hormones during evolution, is arginine 8 -vasotocin (AVT). This peptide is found in the neurohypophysis of all non-mammalian vertebrates and in the pineal gland of mammals.