heh. I gave out some very similar info a few minutes ago, and the thread got deleted. I think they might be milking me. I believe info should be passed along, so here ya go.

D2 interacts with the opioid receptors to induce "satisfaction". Mu is 'forward', delta is 'good, keep on the same' and kappa is 'stop, go back!/pain/noxious stimulus'. All three enhance the production of prolactin and endorphin/endomorphins.

Without prolactin, the D2 network continues to self-activate; it will activate the adrenergic/mu opioid pathways to induce motivation. This, when lined up with the opioid system, predicts motivation; forward, stay, or backwards.