Imaging oxytocin and oxytocin receptor activation.

<p>(<b>A</b>) Co-localization of ChR2-EYFP and oxytocin in brainstem fibers within the DMNV is shown (scale bar represents 28 microns). 55.7+3.7% of ChR2-EYFP PVN fibers in the DMNV are positive for oxytocin. (<b>B</b>) Both the oxytocin and vasopressin dose-response relationships of sniffer CHO cells expressing an oxytocin receptor and a R-GECO Ca²⁺ indicator were characterized. These oxytocin receptor expressing CHO cells are considerably more sensitive and responsive to oxytocin than vasopressin with a half maximal response (EC-50) for oxytocin of 1.5 nM, and an EC-50 for vasopressin of 12.1 nM. Responses to oxytocin were considerably more robust than that for vasopressin; at the concentration (1 µM) at which oxytocin maximally activates these cells, vasopressin evoked a blunted response of only 24+5% of the oxytocin response. Sniffer CHO cells deposited on slices with ChR2 PVN fibers (green) in dorsal motor nucleus of the vagus (DMNV) (<b>C</b>) detect optogenetic oxytocin receptor activation in brainstem DMNV tissue in close apposition to PVN fibers, (3-D reconstruction top down view (left) and side view (right)). <b>D</b>, Repeated stimulations (5 min apart) of ChR2 axons in DMNV increased Ca²⁺. Representative traces of one sniffer CHO cell, top, and averages of repeated stimulations in 9 CHO cells, * p<0.0001, bottom. <b>E</b>, Oxytocin antagonist OTA blocks Ca²⁺ response, representative trace of one cell, top, and average control increase in 7 cells (; * p<0.0001), bottom.