The effects of water deprivation on conditioned freezing to contextual cues and to a tone in rats

Abstract

In two experiments we used an automated system for quantifying freezing responses in rats to replicate and extend Maren et al. (Maren S, DeCola JP, Fanselow MS. Water deprivation enhances fear conditioning to contextual, but not discrete, conditional stimuli in rats. Behav Neurosci 1994;108:645–9; Maren S, DeCola JP, Swain RA, Fanselow MS, Thompson RF. Parallel augmentation of hippocampal long-term potentiation, theta rhythm and contextual fear conditioning in water deprived rats. Behav Neurosci 1994;108:44–57) who found that water deprivation in rats produced a selective enhancement in conditioning to context, as opposed to conditioning to a tone. In experiment 1 we gave water deprived and non-deprived rats either three or ten pairings of a tone and foot shock. During conditioning water deprivation decreased overall freezing only in rats that received ten pairings. On 2 subsequent days we assessed conditioned freezing (1) to the contextual cues of the conditioning chamber and (2) to the tone when presented in a distinctive, novel environment. We found, in direct contrast to Maren et al. (Maren S, DeCola JP, Fanselow MS. Water deprivation enhances fear conditioning to contextual, but not discrete, conditional stimuli in rats. Behav Neurosci 1994;108:645–9), that (a) water deprived rats did not differ from non-deprived rats in levels of conditioned contextual freezing and that (b) water deprived rats did show reduced levels of freezing to the tone stimulus. In the same experiment we found that the number of tone–shock pairings did not affect levels of conditioned contextual freezing but that rats that had received three pairings did show reduced levels of freezing to the tone stimulus compared with rats that had received ten pairings, thereby demonstrating that the behavioural procedure and analysis system that we used was appropriately sensitive to differences in conditioning. In experiment 2, therefore, we sought to replicate Maren et al. (Maren S, DeCola JP, Fanselow MS. Water deprivation enhances fear conditioning to contextual, but not discrete, conditional stimuli in rats. Behav Neurosci 1994;108:645–9) using, as far as possible, exactly the same procedural parameters. Here we found that water deprivation produced no effects on conditioned freezing to the contextual cues or to the tone. We conclude that there is sufficient reason to doubt the generality of the previously reported findings.