Does sensitization occur to prepulse inhibition of the startle reflex effects of repeated apomorphine treatments in rats?
There are conflicting reports as to whether or not the effects of dopamine agonist effects at reducing prepulse inhibition of the acoustic startle reflex develop sensitization with repeated treatments. In this experiment, rats (12 per each dose group) were treated for 10 days prior to startle-testing on each day with 0 (vehicle), 50, 200 or 800 microg/kg of apomorphine. Startle testing was conducted with each rat receiving no stimulus trials (null trials), startle pulse only trials (40 ms 105 dB white noise), prepulse only trials (20 ms 72 dB 5 kHz tone) and prepulse+pulse trials with a 100 ms stimulus onset asynchrony (SOA, i.e. the lead time from onset of prepulse to onset of pulse). The rats were then challenged after 5-7 days of withdrawal from the treatment regimen with a vehicle and apomorphine (200 microg/kg) injection with the order of injection counterbalanced. A range of SOAs and two different prepulse intensities (68 and 70 dB) were presented to every rat on the challenge te
