Avoidance expression in rats as a function of signal-shock interval: strain and sex differences

Abstract

Inbred Wistar Kyoto (WKY) rats express inhibited temperament, increased sensitivity to stress, and exaggerated expressions of avoidance. A long-standing observation for lever press escape/avoidance learning in rats is the duration of the warning signal (WS) determines whether avoidance is expressed over escape. Outbred female Sprague-Dawley (SD) rats trained with a 10-s WS efficiently escaped, but failed to exhibit avoidance; avoidance was exhibited to a high degree with WSs longer than 20-s. We examined this longstanding WS duration function and extended it to male SD and male and female WKY rats. A cross-over design with two WS durations (10 or 60 s) was employed. Rats were trained (20 trials/session) in four phases: acquisition (10 sessions), extinction (10 sessions), re-acquisition (8 sessions) and re-extinction (8 sessions). Consistent with the literature, female and male SD rats failed to express avoidance to an appreciable degree with a 10-s WS. When these rats were switched to a 60-s WS, performance levels in the initial session of training resembled the peak performance of rats trained with a 60-s WS. Therefore, the avoidance relationship was acquired, but not expressed at 10-s WS. Further, poor avoidance at 10-s does not adversely affect expression at 60-s. Failure to express avoidance with a 10-s WS likely reflects contrasting reinforcement value of avoidance, not a reduction in the amount of time available to respond or competing responses. In contrast, WKY rats exhibited robust avoidance with a 10-s WS, which was most apparent in female WKY rats. Exaggerated expression of avoidances by WKY rats, especially female rats, further confirms this inbred strain as a model of anxiety vulnerability.

Partial Predictability in Avoidance Acquisition and Expression of Wistar-Kyoto and Sprague-Dawley Rats: Implications for Anxiety Vulnerability in Uncertain Situations

“…Consistent with earlier studies (19,23,24), WKY rats expressed avoidance to a higher degree than SD rats. Avoidance expression was accompanied by increased nonreinforced responding, ITRs reduced over sessions in those trained with a full contingency.…”

“…These findings fit with long held theories that posit that both classical and operant conditioning are mechanisms through which the psychopathologies observed in PTSD are manifested [for review, see ( 22 )]. Specifically, WKY rats acquire active discrete-trial lever press avoidance with a tone conditioned stimulus (CS) and foot shock unconditional stimulus (US) more rapidly and express avoidance to a higher degree than outbred Sprague-Dawley (SD) rats ( 19 , 23 , 24 ) and are more resistant to extinction of avoidance ( 19 , 25 ). In addition, WKY rats acquired conditioned eyeblink responses faster and to a greater degree than uninhibited SD rats ( 26 – 28 ) and exhibited slower extinction on CS-alone trials as compared to SD controls ( 26 ).…”

“…When conditions are uncertain or suboptimal, learning biases may also be apparent for the acquisition or expression of avoidance ( 23 , 24 ). One relatively unexplored topic in the current avoidance literature with translational value to our understanding of anxiety disorders and PTSD is the relative contingency between the CS and US.…”

Inhibited Personality Temperaments Translated Through Enhanced Avoidance and Associative Learning Increase Vulnerability for PTSD

“…WKY rats are faster to acquire the lever-press avoidance response and exhibit higher levels of avoidance than SD rats (Servatius et al., 2008; Beck et al., 2010; Jiao et al., 2011b) as shown in Figure 1. In addition, WKY rats exhibit avoidance with non-optimal training situations in which SD rats fail to acquire avoidance (Servatius et al., 2015). For example, although both WKY and SD rats can acquire a lever-press avoidance response when the warning signal is 60 s in duration, WKY rats, but not SD controls, exhibited avoidance with a shorter (10 s) warning signal (Servatius et al., 2015).…”

“…In addition, WKY rats exhibit avoidance with non-optimal training situations in which SD rats fail to acquire avoidance (Servatius et al., 2015). For example, although both WKY and SD rats can acquire a lever-press avoidance response when the warning signal is 60 s in duration, WKY rats, but not SD controls, exhibited avoidance with a shorter (10 s) warning signal (Servatius et al., 2015). WKY rats are also more motivated to escape and avoid foot shock than SD rats, even though pain sensitivity to the shock is similar (Fragale et al., 2017; Spiegler et al., 2018).…”