1315-P: Optogenetic Activation of Vagal Motor Neurons in Mice Modulates Heart Rate but Not Blood Glucose Levels

Abstract

Parasympathetic neurons in the dorsal motor nucleus of the vagus (DMV) control glucose metabolism through the vagus nerve and so are potential targets for diabetes treatment. Yet, little is known about the molecular identity and organization of glucose-regulating DMV neurons. To identify these neurons for further investigation, we optogenetically activated them in mice while measuring blood glucose. We targeted a light-sensitive ion channel, CaTCh, selectively to DMV neurons based on their co-expression of Chat and Phox2b, which resulted in CaTCh expression in most or all DMV neurons but no surrounding neurons. To photostimulate CaTCh+ DMV neurons, we then implanted optical fibers over the DMV in 9 adult Chat::Phox2b::CaTCh mice (4 females, 5 males; mean age ± S.D., 24 ± 13 weeks) . After acclimation we fasted the mice overnight and then delivered pulses of blue laser light (20Hz, 10ms pulse, 3 sec off, 1 sec on) for 15 min to activate DMV neurons. We used a glucometer on tail blood samples drawn every 5 minutes for 1 hour, beginning 20 minutes before and ending 25 minutes after photostimulation. Before, during, and after photostimulation, blood glucose averaged 2± 35 mg/dL, 220 ± 36 mg/dL, and 215 ± 45 mg/dL and did not change significantly with photostimulation (p>0.05, ANOVA) . To rule out stress as a confound, we repeated these studies after anesthetizing 4-hour fasted mice with isoflurane but still did not detect a significant effect of photostimulation on blood glucose. Interestingly, however, heart rate decreased significantly with photostimulation (pre, 5± 23 bpm; during, 429 ± 32 bpm; post, 517 ± 24 bpm; p<0.001, ANOVA) , indicating that the photostimulation parameters were sufficient to activate vagal neurons. Further work is underway to address whether the lack of effect of DMV poststimulation on blood glucose is due to antagonistic signaling (e.g., coincident release of insulin and glucagon) or represents a limitation of the method. Disclosure J.Campbell: None. N.J.Conley: None. L.S.Kauffman: None. Funding American Diabetes Association (1-18-INI-14) ;