Influence of conspecific stress odors and shock controllability on conditioned defensive burying

Abstract

In Experiment 1, rats received a session of 80 inescapable tail shocks or no shocks while restrained in a tube. During tests of conditioned defensive burying 24 h later, the bedding of the chamber contained odors from either stressed or nonstressed conspecific donor rats. Following a single prod shock, subjects that had had prior shocks or that were tested with the stress odors spent significantly less time burying the prod, made smaller piles of bedding, and displayed more freezing behavior. The combination of prior shock and stress odors during later testing enhanced these effects. In Experiment 2, a yoked group of rats that was given inescapable shocks, in contrast to a group that had wheel-turn escape training and one that was restrained but not shocked, later showed significantly less burying and more freezing when tested for defensive burying with stress odors present. In both experiments the duration of burying and the heights of piles were positively correlated, and both of these measures were negatively correlated with freezing. The demonstrated capacity of unconditioned stress odors to mediate different degrees offear, depending upon the controllability of prior shock, is related to other studies of learned helplessness, and the predominance offreezing over burying is discussed in terms of various types of defensive strategies, stimulus-control processes, and the author's stress-coping-fear-defense (SCFD) theory.

Effects of a Synthetic Predator Odor (TMT) on Freezing, Analgesia, Stereotypy, and Spatial Memory

“…Furthermore, it was found that this analgesia was controlled by an endogenous opioid system because it was blocked when rats were given an injection of an opiate antagonist prior to the formalin test (Fanselow & Baackes, 1982). The stress-induced, opioid analgesia that we observed with TMT has also been reported in studies using the following stressors: conditioned stimuli paired with foot shock (Fanselow, 1984;Fanselow & Baackes, 1982;Helmstetter & Fanselow, 1987), unconditioned odors of previously shocked con specifics (Williams, 1987), conditioned odors of intruder rats that were attacked and defeated during a single resident-intruder session (Williams & Scott, 1989;Williams, Worland, et aI., 1990), and exposure to the unconditioned fear of cat odor (Lester & Fanselow, 1985). Finally, the present results of TMT-elicited analgesia support our previous study which revealed that TMT was not only an effective conditioned stimulus, when paired with an injection of an anxiogenic, but it also elicited a moderate level of freezing and analgesia in the control condition in which the anxiogenic was not given as an unconditioned stimulus (Hotsenpiller & Williams, 1997).…”

“…Similarly, repeated presentations of inescapable shock increased the frequency of specific reactions, such as response stereotypy, following an injection of a small dosage of d-amphetamine (Anisman, Hahn, Hoffman, & Zacharko, 1985). Prior exposure to shock interfered with the following: one-trial classical conditioning of rats learning to bury a prod that was the source of a single electric shock (Williams, 1987), escape learning by double crossing in a shuttlebox (Maier, 1984), operant learning for a positive reinforcer (Rosellini, 1978), and choice or position learning in a Y maze (Jackson, Alexander, & Maier, 1980). Furthermore, much research has been devoted to the neurophysiological mechanisms that underlie, or are at least correlated with, these shock-induced disruptions in behavior.…”

Conditioned fear and neophobia following inescapable shock

“…Previous studies of associative transfer in the helplessness paradigm strongly suggest that similar odors must be present in the pretreatment and test apparatus for impaired test performance to occur (Coen, 1985;Minor & LoLordo, 1984;Williams, 1987). When odors are mismatched across experimental phases, inescapably shocked rats perform as well as restrained controls.…”

“…If so, a 72-h test would be functionally equivalent to a 24-h test in which the pretreatment odor was physically absent. As several recent studies indicate, performance deficits are attenuated or eliminated under the latter conditions (Coen, 1985;Minor & LoLordo, 1984;Williams, 1987).…”

“…As a result, odor becomes a critical retrieval cue in later tests of aversive learning. In a helplessness experiment, similar odors must be present in both experimental phases for impaired escape latencies (Minor & LoLordo, 1984), defensive behavior (Williams, 1987), and long-term hypoalgesia to occur 24 h after pretreatment (Coen, 1985). When odors are mismatched, inescapably shocked rats perform as well as restrained controls.…”