DENDRITICALLY RELEASED PEPTIDES ACT AS RETROGRADE MODULATORS OF AFFERENT EXCITATION IN THE SUPRAOPTIC NUCLEUS IN-VITRO

Oxytocin (OXT) and vasopressin (VP) are known to be released from dend rites of magnocellular neurons. Here, we show that these peptides redu ced evoked EPSCs by a presynaptic mechanism, an effect blocked by pept ide antagonists and mimicked by inhibition of endogenous peptidases. D endritic release of peptides, elicited with depolarization achieved by high frequency stimulation of afferents or with current injection int o an individual neuron, induced short-term synaptic depression similar to that seen following exogenous peptide application and was prevente d by peptide antagonists. Thus, dendritically released peptides depres s evoked EPSCs in magnocellular neurons by activating presynaptic OXT and/or VP receptors. Such a retrograde modulatory action on afferent e xcitation may serve as a feedback mechanism to permit peptidergic neur osecretory neurons to autoregulate their own activity.