Olfactory bulbectomy does not affect conditioned inhibition of fear as measured with fear-potentiated startle
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The present study examined the effects of olfactory bulbectomy, an animal model of depression, on conditioned inhibition as measured with fear-potentiated startle, an animal model of anxiety. The study was based on cognitive research suggesting that individuals diagnosed with either depression or anxiety share an attentional bias to negative or threatening stimuli. Animal studies suggest that bulbectomized animals demonstrate an increased vulnerability to stress as measured by fear-potentiated startle and shock sensitization. Based on these findings, it was hypothesized that olfactory bulbectomy would result in a biased attention, similar to that noted in depressed individuals, to a cue signaling danger (conditioned excitor) at the expense of a cue signaling safety (conditioned inhibitor). Specifically, bulbectomized animals were expected to be less able to inhibit their fear (conditioned inhibition) to a light previously paired with a shock when the light was accompanied by a noise safety signal not paired with shock relative to sham-operated and unoperated animals. The results of the study indicated that bulbectomized animals were able to inhibit their fear when presented with the conditioned inhibitor. Bulbectomized animals did not differ from sham-operated or unoperated animals in their ability to acquire conditioned inhibition of fear-potentiated startle. Further, bulbectomized animals did not differ from the control animals on baseline startle amplitudes or the acquisition of fear-potentiated startle. As such, the hypothesis was not supported. However, several possible empirical and theoretical explanations were identified and suggestions for future research on the relationship between depression and anxiety were explored.