Identification of Hypothalamic Glucoregulatory Neurons That Sense and Respond to Changes in Glycemia

To investigate whether glucoregulatory neurons in the hypothalamus can sense and respond to physiological variation in the blood glucose (BG) level, we combined continuous arterial glucose monitoring with continuous measures of the activity of a specific subset of neurons located in the hypothalamic ventromedial nucleus that express pituitary adenylate cyclase activating peptide (VMN(PACAP) neurons) obtained using fiber photometry. Data were collected in conscious, free-living mice during a 1-h baseline monitoring period and a subsequent 2-h intervention period during which the BG level was raised either by consuming a chow or a high-sucrose meal or by intraperitoneal glucose injection. Cross-correlation analysis revealed that, following a 60- to 90-s delay, interventions that raise the BG level reliably associate with reduced VMN(PACAP) neuron activity (P < 0.01). In addition, a strong positive correlation between BG and spontaneous VMN(PACAP) neuron activity was observed under basal conditions but with a much longer (∼25 min) temporal offset, consistent with published evidence that VMN(PACAP) neuron activation raises the BG level. Together, these findings are suggestive of a closed-loop system whereby VMN(PACAP) neuron activation increases the BG level; detection of a rising BG level, in turn, feeds back to inhibit these neurons. To our knowledge, these findings constitute the first evidence of a role in glucose homeostasis for glucoregulatory neurocircuits that, like pancreatic β-cells, sense and respond to physiological variation in glycemia. ARTICLE HIGHLIGHTS: By combining continuous arterial glucose monitoring with fiber photometry, studies investigated whether neurons in the murine ventromedial nucleus that express pituitary adenylate cyclase activating peptide (VMN(PACAP) neurons) detect and respond to changes in glycemia in vivo. VMN(PACAP) neuron activity rapidly decreases (within <2 min) when the blood glucose level is raised by either food consumption or glucose administration. Spontaneous VMN(PACAP) neuron activity also correlates positively with glycemia, but with a longer temporal offset, consistent with reports that hyperglycemia is induced by experimental activation of these neurons. Like pancreatic β-cells, neurons in the hypothalamic ventromedial nucleus appear to sense and respond to physiological variation in glycemia.