Assessing Astrocyte G-DREADD Impact on Fear

To examine the effect of astrocyte G_i-DREADD stimulation on fear learning (Experiment 3), the HW-EFL paradigm was conducted. This procedure has been previously described at length (Parekh et al. 2020 ). Briefly, animals were randomly assigned to drug (heroin or saline) treatment. Animals undergo chronic escalating heroin administration and withdrawal in their home cage. Seven days after the start of withdrawal, animals were placed into a novel context for 15 min of habituation. On Day 8, animals were placed into the same context for a single scrambled foot shock (1 mA, 1s) at 3 min, 12 s. On days 9, 10, 15, 22 (Test Days 1, 2, 7, and 14) animals were placed into the same context for 8 min, 32 s and behavior was recorded to measure freezing behavior, a measure of learned fear. Ethovision XT video tracking software (Noldus Information Technology Inc.) was used to analyze freezing behavior. The activity analysis feature (Activity Threshold = 10) was used and described previously (Jones et al. 2018a (link), b (link)). This feature detects the entire arena and asks what percentage of pixels in the entire arena are changing or the same. To calculate the percent of time each animal was inactive during each contextual fear test and at baseline we used the % of pixels that were inactive through the activity analysis feature in Ethovision XT.