FIGURE 5.

Autocrine modulation of vasopressin magnocellular neurosecretory cell (MNC) activity. Vasopressin (VP) MNCs secrete vasopressin, ATP and dynorphin (and other transmitters) from their somata and dendrites. Endogenous arginine vasopressin (AVP) (2) inhibits spike discharge throughout bursts via inhibition of the excitory post-synaptic current (EPSC) amplitude. Endogenous ATP is rapidly converted to adenosine (3), which enhances the medium afterhyperpolarisation (mAHP) amplitude over the first few seconds of bursts to contribute to spike frequency adaptation. Endogenous dynorphin (4) inhibition of the afterdepolarisation (ADP) increases progressively over the course of bursts, eventually resulting in burst termination. Combined, these autocrine feedback effects of somato-dendritic vasopressin and co-secreted transmitters shape phasic activity for efficient secretion vasopressin into the circulation from the posterior pituitary gland