The orexinergic neurons receive synaptic input from C1 cells in rats.

Bochorishvili G, Nguyen T, Coates MB, Viar KE, Stornetta RL, Guyenet PG. J Comp Neurol. 2014 Jul 1 In this paper, they wanted to see if there was a C1-mediated activation of hypothalamic orexinergic cells. The idea was that even though C1s can directly activate the sympathetic system, they are also suspected to be able to activate the hypothalamic-pituitary axis to reinforce their effects. To test for C1 hypothalamic connections, they used a prsx8-chr2-mcherry vector (to cause mcherry expression preferentially in C1 neurons) to see innervation of C1 in to orexinergic cells of the hypothalamus. They also confirmed the prsx8 vector by using TH-cre rats and injecting them with a virus carrying a cre-dependent reporter and saw the same thing. They found many unmyelinated PNMT axons in the region throughout the hypothalamus including in the region of the PVN. They found that, of the synaptic terminals they could identify, 77% of them had terminals that synapsed mostly on to dendrites of orexinergic cells. All of these terminals had dense core vesicles AND small clear vesicles. The clear vesicles are evidence that they release glutamate to activate the orexinergic neurons, but dense core vesicles usually contain polypeptides. They didn't discuss what that would mean in this instance… maybe norepinephrine or epinephrine? -DH