Behavioral and brain mechanisms mediating conditioned flight behavior in rats

ABSTRACTEnvironmental contexts and associative learning can inform animals of potential threats, though it is currently unknown how contexts bias defensive transitions. Here we investigated context-dependent flight responses in the Pavlovian serial-compound stimulus (SCS) paradigm. We show here that SCS-evoked flight behavior in male and female rats is dependent on contextual fear. Flight was reduced in the conditioning context after context extinction and could be evoked in a different shock-associated context. Although flight was exclusive to white noise stimuli, it was nonetheless associative insofar as rats that received an equal number of unpaired USs did not show flight-like behavior. Finally, we found that inactivation of either the central nucleus of the amygdala (CeA) or bed nucleus of the stria terminalis (BNST) attenuated both contextual fear and flight responses. This work demonstrates that contextual fear summates with cued and innate fear to drive a high fear state and freeze-to-flight transitions.

Limited replicability of drug-induced amnesia after contextual fear memory retrieval in rats

With the ultimate goal of investigating boundary conditions for post-reactivation amnesia, we set out to replicate studies in which systemic, post-reactivation administration of midazolam, propranolol, or cycloheximide resulted in amnesia for contextual fear memories. Our experiments involved conceptual as well as exact replications of previously published studies. In most of our experiments, we adopted a procedure that conformed to the standard 3-day protocol typically used in the literature, with contextual fear conditioning on day 1, unreinforced re-exposure to the conditioning context followed by systemic injection of the amnestic drug on day 2, and a memory retention test on day 3. Given the plethora of successful studies with large effects sizes and the absence of any failed replications in the literature, we were surprised to find that we were generally unable to replicate those findings. Our results suggest that post-reactivation amnesia by systemic drug administration in rats is more difficult to obtain than what would be expected based on published empirical reports. At present, it remains unclear which conditions determine the success of this procedure.

Effects of Scopolamine on Conditioning of Lever Pressing

The aim of this work was to determine the effects of scopolamine, a cholinergic antagonist, on the conditioning of an instrumental response and the contextual conditioning of this response. Five groups of rats were trained to lever-press on a Variable Interval 30 s schedule in context A. Scopolamine was administered 15 min before each conditioning session to AB 0.01 mg/kg, AB 0.10 mg/kg and AB 1.00 mg/kg groups. The AA Saline and AB Saline groups received saline injections.Contextual conditioning of the lever-pressing response was assessed in one extinction session. The AA group received this extinction session in the conditioning context (A), while the AB groups received this session in a different context (B). Results showed that scopolamine impaired the conditioning of the lever-pressing response but no effects on contextual conditioning were found.

Hunger as a Context: Food Seeking That Is Inhibited During Hunger Can Renew in the Context of Satiety

At the end of a diet, even a successful one, people often return to overeating. One potential reason is that the behavioral inhibition that people learn while dieting might not readily transfer outside the context in which it is learned: Basic research indicates that after a behavior is inhibited, a return to the conditioning context or simple removal from the treatment context can cause the behavior to return (i.e., to renew). Can states of hunger and satiety play the role of context? In two experiments, rats learned a food-seeking response that earned sucrose or sweet, fatty food pellets while they were satiated. Responding was then inhibited (i.e., extinguished) while the rats were hungry. On the rats’ return to the satiated state, their food seeking was renewed. Additional results suggest that associations with hunger or satiety stimuli were learned more readily than associations with other potentially useful exteroceptive stimuli. The findings have implications for understanding the role of interoceptive contexts in controlling the inhibition of motivated behavior.

Context Familiarity and Delayed Conditioned Taste Aversion in Young-Adult and Old-Age Rats

Familiarity with a conditioning context different from the home-cage environment was examined in immediate and delayed (3-hr.) conditioned taste aversion (CTA) learning for young-adult (90—120 days) and old-age (680—750 days) female Wistar albino rats. Context familiarity increased CTA for young adults at the 3-hr. delay. Old-age rats showed no aversion at 3-hr. delays. Results suggest that home-cage cues may be used in mediating long-delay CTA and that the role of these cues may differ with age.