Powerlab 4 30

Following the HR and BP assessments, we assessed the HRV for 10 min. The HRV data were achieved by lead II electrocardiography (PowerLab 4/30, AD Instruments) and analyzed by the HRV module (LabChart® Pro, AD Instruments). HRV variables included the time and frequency domains. The time‐domain consisted of the values of SDNN and the root mean square of successive R‐R interval differences (RMSSD). The frequency‐domain was analyzed using the values of total power, very‐low‐frequency power (direct current potential: −0.04 Hz), low‐frequency power (direct current potential: 0.04–0.15 Hz), high‐frequency power (direct current potential: 0.15–0.4 Hz), and low‐frequency to high‐frequency ratio. Sympathetic and parasympathetic activities, as well as baroreceptor activity, are all described by HRV data. Low‐frequency power, for example, reflects sympathetic activity most of the time, whereas high‐frequency power reflects parasympathetic activity, and the low‐frequency to high‐frequency ratio reflects a balance of sympatho‐vagal activity (Shaffer and Ginsberg, 2017 (link)).

For subsurface ECG recordings, anesthesia was provided by isoflurane in oxygen at a flow rate of 1.0 liter/min. Mice were placed in a prone position on a heated pad to maintain body temperature, and subcutaneous electrodes were placed under the skin (lead II configuration). ECGs were recorded for 5 min on a PowerLab 4/30 (AD Instruments). Anesthesia was maintained for the duration of the reading. Manual visual inspection of ECG tracings for artifacts or abnormalities was performed before data analysis. ECG traces were then analyzed using LabChart 8 Pro software (AD Instruments) wherein the analysis software performed automatic detection of P, Q, R, S, and T wave onsets, amplitudes, and intervals following data recording. The selections generated by the software were then manually optimized, and individual values and averages of 10-s intervals were recorded.

Sensory stimulation (0.5 Hz) was given to the center of the whisker pad of awake mice by means of air puffs given from approximately 5 mm at an angle of 30 degrees with the whisker pad. Each puff was around 2 bar and had a duration of 30 ms. Videos of the movements of the untrimmed large facial whiskers were made from above using a bright LED panel as back-light (λ = 640 nm) at a frame rate of 1,000 Hz (480 × 500 pixels using an A504k camera from Basler Vision Technologies, Ahrensburg, Germany). Respiration was recorded using a PowerLab 4/30 analog-to-digital converter (AD Instruments, Oxford, United Kingdom) in combination with a pressure sensor that was placed at the abdomen of the mice.

At day 35 post‐M. avium infection, subsurface electrocardiogram (ECG) was recorded. Young and old M. avium infected mice and aged matched control (sham) mice were anesthetized using 2% isoflurane in oxygen (flow rate 1.0 L/min), which was subsequently lowered to 1% (1.0 L/min) for the duration of the ECG recordings. Mice were placed in the prone position and kept on a heated pad to maintain body temperature. The subcutaneous electrodes for ECG were placed in the lead II configuration and ECGs were recorded for 10 min on a PowerLab 4/30 (AD Instruments, Houston, TX; Makara et al., 2016). ECG traces were analyzed using LabChart 8 Pro (AD Instruments).

We recorded from 13 male Eristalis tenax (Linnaeus 1758) hoverflies, 0.5–10 months old, reared and housed as described earlier (Nicholas et al., 2018 (link)). At the start of the experiment, the animal was immobilized ventral side up with a beeswax and resin mixture, and a small hole cut at the anterior end of the thorax. A sharp polyimide-insulated tungsten electrode (2 MΩ, Microprobes, Gaithersburg, MD, USA) was inserted into the cervical connective, with mechanical support given by a small wire hook. The animal was grounded via a silver wire inserted into the ventral cavity, which also served as the recording reference.
We recorded from type 2 optic flow-sensitive descending neurons, which were identified by their receptive field and physiological response properties (Nicholas et al., 2020 (link)). Extracellular signals were amplified at 1000× gain and filtered through a 10–3000 Hz bandwidth filter on a DAM50 differential amplifier (World Precision Instruments), with 50 Hz noise removed with a HumBug (Quest Scientific, North Vancouver, BC, Canada). The data were digitized via a Powerlab 4/30 (ADInstruments, Sydney, NSW, Australia) and acquired at 40 kHz with LabChart 7 Pro software (ADInstruments).