Effect of the dopamine receptor agonist apomorphine on sensory input

The study examines the hypothesis that changes in behavioural responsiveness induced by apomorphine reflect an effect of the drug on visual, tactile, vestibular, or proprioceptive sensory input. Rats were injected with apomorphine (1.25 mg/kg) and administered a neurological examination in which stimuli from the different sensory modalities were tested for their ability to elicit a limb placing response. Results indicate that these sensory stimuli were equally effective in eliciting reflex placing reactions in saline- and apomorphine-treated rats. Thus, contrary to the hypothesis, apomorphine does not appear to affect the reception of visual, tactile, vestibular, or proprioceptive sensory input. Tests of equilibration (righting) induced by static tilt revealed a fractionated response under apomorphine (0.6-5 mg/kg). Since the response to tilt probably involves striatal integration of vestibular and proprioceptive input, it is suggested that apomorphine disrupts sensory or sensorimotor integration.