Powerlab 4 20t

Electrophysiological recordings were performed by connecting the pin connectors of optrode devices to an extracellular amplifier (DAM50, World Precision Instruments). Endogenous electrophysiological activities were filtered within the frequency range of 300–3000 Hz and digitized at a sampling frequency of 40 kHz (PowerLab 4/20T, ADInstruments). Subsequent signal processing and analysis were conducted using ROSS Offline Spike Sorter^{68 (link)}. Optical illumination was carried out using a 473 nm laser connected to the implanted optrode devices via a ferrule-sleeve-ferrule connecting system. The laser (10 mW/mm²) was pulsed at a frequency of 0.5 Hz with a pulse width of 50 ms during optical stimulation. Signals were digitized at 10 kHz (DI-1100, DATAQ Instruments) and filtered between 1 and 1000 Hz. The amplitude and noise level of evoked potentials were assessed utilizing a MATLAB algorithm incorporating a bandpass filter ranging from 0.1 to 300 Hz.

Mice were anesthetized with isoflurane (3% for induction and 1.5% for maintenance) via inhalation using a laboratory animal anesthesia machine (Vet Equipment Inc., Pleasanton, CA, USA). Following anesthesia, electrodes were inserted subcutaneously in the left and right forelimbs and left hindlimb in all animals 7 weeks after the administration of the tamoxifen injections. ECG recordings were performed using a PowerLab 4/20T with an animal BioAmp (ADInstruments, Sydney, Australia).

Heart rates and hematocrit levels were recorded 14 days after fear conditioning. Rats were cradled and heart rates were measured using a PowerLab 4/20T with LabChart 5 data recording software (ADInstruments). Hematocrit levels were also assessed because there is a relationship between chronically elevated blood pressure and elevated hematocrit levels (Mandal et al., 1993 (link); Milanovic et al., 2012 (link)). Though indirect, this provides a physiological measure of blood pressure that is both easier to obtain and potentially more reliable than cumbersome blood pressure monitoring equipment typically designed to attach to an individual rat’s tail. Hematocrit levels were measured from blood samples obtained by pricking the tip of the rats’ tails and collecting blood in microcapillary tubes, which were subsequently centrifuged for 60 s (Mandal et al., 1993 (link); Abatan et al., 2008 (link); Milanovic et al., 2012 (link)).