support-information-section).

Isoflurane (ISO) is a commonly used anesthetic that offers rapid recovery for laboratory animal research. Initial studies indicated no difference in arterial Pco2 (normalPaCO2) or pH between conscious (NO ISO) and 1% ISO-exposed CD-1 mice. Our laboratory investigated whether arterial blood sampling with 1% ISO is a suitable alternative to NO ISO sampling for monitoring ventilation in a commonly studied mouse strain. We hypothesized similar blood chemistry, breathing patterns, and cardiovascular responses with NO ISO and 1% ISO. C57BL/6J mice underwent unrestrained barometric plethysmography to quantify the pattern of breathing. Mice exposed to hypoxic and hypercapnic gas under 1% ISO displayed blunted responses; with air, there were no breathing differences. Blood pressure and heart rate were not different between NO ISO and 1% ISO-exposed mice breathing air. Oxygen saturation was not different between groups receiving 2% ISO, 1% ISO, or air. Breathing frequency stabilized at ~11 min of 1% ISO following 2% ISO exposure, suggesting that 11 min is the optimal time for a sample in C57BL/6J mice. Blood samples at 1% ISO and NO ISO revealed no differences in blood pH and normalPaCO2 in C57BL/6J mice. Overall, this method reveals similar arterial blood sampling values in awake and 1% ISO CD-1 and C57BL/6J mice exposed to air. Although this protocol may be appropriate in other mouse strains when a conscious sample is not feasible, caution is warranted first to identify breathing frequency responses at 1% ISO to tailor the protocol.NEW & NOTEWORTHY Conscious arterial blood sampling is influenced by extraneous factors and is a challenging method due to the small size of mice. Through a series of experiments, we show that arterial blood sampling with 1% isoflurane (ISO) is an alternative to awake sampling in C57BL/6J and CD-1 male mice breathing air. Monitoring breathing frequency during 1% ISO is important to the protocol and should be closely followed to confirm adequate recovery after the catheter implantation.

Metabolic state can alter olfactory sensitivity, but it is unknown whether the activity of the olfactory bulb (OB) may fine tune metabolic homeostasis. Our objective was to use CRISPR gene editing in male and female mice to enhance the excitability of mitral/tufted projection neurons (M/TCs) of the OB to test for improved metabolic health. Ex vivo slice recordings of MCs in CRISPR mice confirmed increased excitability due the targeted loss of Kv1.3 channels, which resulted in a less negative resting membrane potential (RMP), enhanced action potential (AP) firing, and insensitivity to the selective channel blocker margatoxin (MgTx). CRISPR mice exhibited enhanced odor discrimination using a habituation/dishabituation paradigm. CRISPR mice were challenged for 25 weeks with a moderately high-fat (MHF) diet, and compared with littermate controls, male mice were resistance to diet-induced obesity (DIO). Female mice did not exhibit DIO. CRISPR male mice gained less body weight, accumulated less white adipose tissue, cleared a glucose challenge more quickly, and had less serum leptin and liver triglycerides. CRISPR male mice consumed equivalent calories as control littermates, and had unaltered energy expenditure (EE) and locomotor activity, but used more fats for metabolic substrate over that of carbohydrates. Counter to CRISPR-engineered mice, by using chemogenetics to decrease M/TC excitability in male mice, activation of inhibitory designer receptors exclusively activated by designer drugs (DREADDs) caused a decrease in odor discrimination, and resulted in a metabolic profile that was obesogenic, mice had reduced EE and oxygen consumption (VO 2 ). We conclude that the activity of M/TC projection neurons canonically carries olfactory information and simultaneously can regulate whole-body metabolism.

Neuromodulation influences neuronal processing, conferring neuronal circuits the flexibility to integrate sensory inputs with behavioral states and the ability to adapt to a continuously changing environment. In this original research report, we broadly discuss the basis of neuromodulation that is known to regulate intrinsic firing activity, synaptic communication, and voltage-dependent channels in the olfactory bulb. Because the olfactory system is positioned to integrate sensory inputs with information regarding the internal chemical and behavioral state of an animal, how olfactory information is modulated provides flexibility in coding and behavioral output. Herein we discuss how neuronal microcircuits control complex dynamics of the olfactory networks by homing in on a special class of local interneurons as an example. While receptors for neuromodulation and metabolic peptides are widely expressed in the olfactory circuitry, centrifugal serotonergic and cholinergic inputs modulate glomerular activity and are involved in odor investigation and odor-dependent learning. Little is known about how metabolic peptides and neuromodulators control specific neuronal subpopulations. There is a microcircuit between mitral cells and interneurons that is comprised of deep-short-axon cells in the granule cell layer. These local interneurons express pre-pro-glucagon (PPG) and regulate mitral cell activity, but it is unknown what initiates this type of regulation. Our study investigates the means by which PPG neurons could be recruited by classical neuromodulators and hormonal peptides. We found that two gut hormones, leptin and cholecystokinin, differentially modulate PPG neurons. Cholecystokinin reduces or increases spike frequency, suggesting a heterogeneous signaling pathway in different PPG neurons, while leptin does not affect PPG neuronal firing. Acetylcholine modulates PPG neurons by increasing the spike frequency and eliciting bursts of action potentials, while serotonin does not affect PPG neuron excitability. The mechanisms behind this diverse modulation are not known, however, these results clearly indicate a complex interplay of metabolic signaling molecules and neuromodulators that may fine-tune neuronal microcircuits.

Isoflurane is a commonly used inhaled anesthetic that can be adjusted for level of anesthetic depth and offers a rapid recovery for both clinical settings and laboratory animal research. Initial studies in our laboratory indicated no difference in PaCO2 (36.7±2.4 vs. 34.8±2.6 mmHg) or pH (7.43±0.02 vs. 7.43±0.02) between conscious (NO ISO) and 1% isoflurane (ISO) exposed CD‐1 mice. Our purpose was to investigate if arterial blood sampling with 1% ISO is a suitable alternative to conscious sampling for monitoring ventilation in a commonly studied mouse strain. This study aimed to test the hypothesis that breathing patterns and blood pressure in conscious and lightly isoflurane anesthetized B6/C57 mice are similar. At 3 months of age, 8 male B6/C57 mice (27.5±1.9 g body weight; MEAN±SD) underwent whole body unrestrained barometric plethysmography to quantify the pattern of breathing. Mice were tested during the light cycle with an isoflurane vaporizer preceding the animal chamber and a vacuum following the chamber (100 mL/min) to prevent accumulation of ISO. After a 30 min acclimation period with air (20.93% O2, balanced N2), mice were exposed to 5 minutes of the following: 2% ISO/air, 1% ISO/air, 1% ISO/10% O2 (hypoxia),1% ISO/air, 1% ISO/5% CO2 (hypercapnia); the last minute of each gas exposure was analyzed with Ponemah™ software. The same mice were administered these gas exposures without ISO (NO ISO) a week later; quiet baseline breathing was considered during this exposure as the 5 minutes when mice were not moving or sniffing in the cage. Breathing frequency (F; breaths/min), tidal volume (TV; mL/breath), and minute ventilation (MV; mL/min) were quantified; NO ISO vs. 1% ISO (MEAN±SD; *=p<0.05) shown in the following text. Quiet breathing compared to 1%ISO/air was not different for F: 185±30 vs. 168±31, TV: 0.29±0.04 vs. 0.31±0.16, or MV: 57.5±10.6 vs. 52.6±26.4. A blunted hypoxic response resulted with ISO; this was due to a lower F and MV (F: 265±31 vs. *176±22, TV: 0.41±0.07 vs. 0.39±0.14, MV: 123.8±27.1 vs. *72.3±29.9). Hypercapnia also resulted in a reduced response to ISO with F, TV and MV differences (F: 352±28 vs. *157±23, TV: 0.63±0.07 vs. *0.43±0.21, MV: 237.1±53.7 vs. *72.6±45.3). Conscious and 1% ISO arterial blood sampling in B6/C57 mice showed no difference in PaCO2 (38.8±1.9 vs. 35.2±2.3 mmHg), but differences did emerge with pH (7.43±0.02 vs. *7.38±0.03). Additional experiments were conducted to measure blood pressure with the volume‐pressure recording tail cuff method to determine other possible systemic changes with ISO, but no differences were uncovered (96±8 vs. 85±11 mmHg) although the data did approach significance. These experiments demonstrate the pattern of quiet breathing, ventilation and blood pressure are similar in conscious and 1% ISO exposed mice. However, the capacity to respond to respiratory stressors is attenuated with 1% ISO. Overall due to the near significant p‐values, along with clear differences from hypoxia/hypercapnia, we do not recommend blood sampling with 1% ISO as an alternative to monitoring conscious ventilation.Support or Funding InformationFunded by 1 R15 HD076379‐01A1, AML supported by McDevitt Fellowship, CNR supported by 1 R15 HD076379‐01A1S1.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.