Growing evidence implicates neurons that project from the lateral parabrachial nucleus (
LPBN) to the hypothalamic ventromedial nucleus (VMN) in a neurocircuit that drives counterregulatory responses to
hypoglycemia, including increased
glucagon secretion. Among
LPBN neurons in this circuit is a subset that expresses
cholecystokinin (LPBNCCK neurons) and is tonically inhibited by
leptin. Because uncontrolled diabetes is associated with both
leptin deficiency and hyperglucagonemia, and because intracerebroventricular (ICV)
leptin administration reverses both
hyperglycemia and hyperglucagonemia in this setting, we hypothesized that deficient
leptin inhibition of LPBNCCK neurons drives activation of this LPBN→VMN circuit and thereby results in hyperglucagonemia. Here, we report that although bilateral microinjection of
leptin into the
LPBN does not ameliorate
hyperglycemia in rats with
streptozotocin-induced
diabetes mellitus (STZ-DM), it does attenuate the associated hyperglucagonemia and
ketosis. To determine if
LPBN leptin signaling is required for the
antidiabetic effect of ICV
leptin in STZ-DM, we studied mice in which the
leptin receptor was selectively deleted from LPBNCCK neurons. Our findings show that although
leptin signaling in these neurons is not required for the potent
antidiabetic effect of ICV
leptin, it is required for
leptin-mediated suppression of diabetic hyperglucagonemia. Taken together, these findings suggest that
leptin-mediated effects in animals with uncontrolled diabetes occur through actions involving multiple brain areas, including the
LPBN, where
leptin acts specifically to inhibit
glucagon secretion and associated
ketosis.