Vasopressin in the septum: not important versus causally involved in learning and memory--two faces of the same coin?

Intraseptal arginine vasopressin (AVP) has been suggested to control in laboratory rodents not only emotionality but also learning and memory. However, depending upon the nature of the test procedure and, thus, the specific memory paradigm under study, administration of synthetic AVP into the lateral septum can have no effect, enhance or even impair learning and memory. Similar contradictory results were obtained after local administration of AVP V1 receptor antagonists in different learning and memory paradigms: blockade of AVP signalling in the lateral septum revealed either no essential function or a significant contribution of the endogenous neuropeptide. Based on the data available from studies investigating the impact of AVP in classical and operant conditioning, olfactory recognition and Morris water maze learning, it is proposed that endogenous AVP released within the lateral septum acts as neurotransmitter and neuromodulator to favour elemental (mono-modal) over complex (multi-modal) stimulus processing. Excessive availability of AVP, for example by intraseptal administration of the synthetic neuropeptide, interferes with memory performance in such tasks in which the integration of complex stimuli by the dorsal hippocampus is required, most likely by an inhibition of the septo-hippocampal pathway. In contrast, performance in tasks which focus on the processing of elemental stimuli such as olfactory recognition and classical and operant conditioning can be improved by intraseptal AVP administration, presumably due to an attenuation of complex stimulus processing.