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Updated: Aug 19, 2026
Habituation and Prepulse Inhibition of Acoustic Startle in Rodents
Published on: September 1, 2011
Apomorphine effects on emotional modulation of the startle reflex in rats
Mathew T Martin-Iverson1, Kirsten N Stevenson
1School of Medicine and Pharmacology, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia. matt@ccrn.uwa.edu.au
Rationale:
Emotional modulation of the startle reflex in the rat may be used to assess whether activation of dopamine receptors specifically increases hedonia, incentive, fear or arousal.
Objectives:
The objective of the study is to determine the effects of apomorphine (0.8 mg/kg s.c.) on the startle reflex of rats (72 male Sprague-Dawley rats) exposed to one of three affective conditions. These conditions were negative affective stimulus (exposure to cat smell), positive affective stimulus (availability of a 20% sucrose solution), neutral stimulus (no additional affective stimulus) and one of two appetitive "drive" states (food deprived or non-food deprived).
Methods:
The startle response (whole-body flinch response) was measured after presentation of a range of intensities of acoustic stimuli (65-120 dB, 40-ms duration white noise). The resulting sigmoidal stimulus intensity-response magnitude (SIRM) curves were fitted using a logistic regression procedure, and features of these functions were abstracted for analysis.
Results:
Maximal startle amplitudes were increased by the negative affect (fear) stimulus in non-food-deprived rats and decreased by the positive affect stimulus in food-deprived rats. Apomorphine mimicked the effects of food deprivation under both affect conditions, but also produced an effect in food-deprived rats similar to that of the positive affect condition.
Conclusions:
The results are consistent with both a positive incentive effect and a direct hedonic action of apomorphine, but inconsistent with a role in general arousal. In addition, a method of analysing SIRM functions with logistic regressions is introduced as a useful means of standardising startle reflex measurements.
