Incubation of conditioned fear in the conditioned suppression model in rats: role of food-restriction conditions, length of conditioned stimulus, and generality to conditioned freezing

Abstract

We recently adapted the conditioned suppression of operant responding method to study fear incubation. We found that food-restricted rats show low fear 2 days after extended (10 d; 100 30-sec tone-shock pairings) fear training and high fear after 1-2 months. Here, we studied a potential mechanism of fear incubation: extended food-restriction stress. We also studied whether fear incubation is observed after fear training with a prolonged-duration (6-min) tone conditioned stimulus (CS), and whether conditioned freezing incubates after extended training in rats with or without a concurrent operant task. Conditioned fear was assessed 2 days and 1 month after training.In the conditioned suppression method, fear incubation was reliably observed in rats under moderate food-restriction conditions (18-20 g food/day) that allowed for weight gain, and after extended (10 d), but not limited (1 d), fear training with the 6-min CS. Incubation of conditioned freezing was observed after extended fear training in rats lever-pressing for food and, to a lesser degree, in rats not performing an operant task.Results indicate that prolonged hunger-related stress does not account for fear incubation in the conditioned suppression method, and that fear incubation occurs to a longer-duration (6-min) fear CS. Extended training also leads to robust fear incubation of conditioned freezing in rats performing an operant task and weaker fear incubation in rats not performing an operant task.

Conditioning- and time-dependent increases in context fear and generalization

“…2, 4) that remained stable, while repeatedly shocked rats displayed an increase in fear across the extended memory retention interval. This pattern in multitrial conditioned animals is consistent with evidence of incubation using overtraining with an auditory CS (8-100 trials), spaced over multiple days (2 or 10 d) and/or under food deprivation (Houston et al 1999;Pickens et al 2010). Here, we demonstrate using a more reduced conditioning preparation that a single trial does not yield fear incubation, but two conditioning trials within a single session were sufficient to generate a time dependent increase in context fear expression.…”

Incubation of Fear

“…This is the standard protocol that has been used repeatedly for pharmacological testing and investigations into the time-course and mechanisms underlying fear incubation (Pickens et al, 2009a; Pickens et al, 2009b; Pickens et al, 2010). It has reliably produced fear incubation under a wide variety of feeding conditions and after other manipulations were given (e.g.…”

“…However, it is also possible to cause incubation of a more diffuse emotional state by pairing longer cues (minutes long) with unpredictable shocks (proposed to model “conditioned anxiety”) (Pickens et al, 2010). The procedure is very similar to those used in the basic protocol (see Figure 1), with differences in the length of the tone cue and the timing of the shocks.…”

Neurocognitive and Biomarker Evaluation of Combination mTBI from Blast Overpressure and Traumatic Stress

“…A second difference is that we used a conditioned suppression procedure to evaluate conditioned fear whereas the former studies used a conditioned freezing procedure. Freezing, by definition, prevents lever pressing and previous studies have shown that conditioned freezing and conditioned suppression are correlated (e.g., Pickens, et al, 2010). Additional studies using lesioning have shown that the dependencies of these two behaviors on the basolateral and central nuclei of the amygdala, and the ventral periaqueductal grey differs (Amorapanth et al, 1999;Lee, et al, 2005;McDannald, 2010;;McDannald and Galarce, 2011).…”

“…It is notable that the conditioned suppression model is in contrast to conditioned freezing methods. While freezing would necessarily constitute response suppression, studies have shown that the suppression model involves additional conditioned fear processes (Amorapanth et al, 1999;Lee, et al, 2005;McDannald, 2010;Pickens, et al, 2010;McDannald and Galarce, 2011). 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 8 Clinically, the defining characteristics for the classification of mTBI are almost entirely based on signs or symptoms and include a relatively broad range of severity (Defense and Veterans Brain Injury Center, 2006).…”