Basolateral amygdala dopamine receptor antagonism modulates initial reactivity to but not habituation of the acoustic startle response.
Although the basolateral amygdala (BLA) plays a role in the habituation to sensory stimuli, the receptor mechanisms mediating this process remain unclear. In the present study, we investigated the role of BLA dopamine (DA) in the habituation of the acoustic startle response (ASR) with intra-BLA infusions of DA receptor antagonists. Male Long Evans rats were subjected to startle pulses over two consecutive once-daily sessions. Prior to testing on Day 1, separate groups of animals received bilateral intra-BLA infusions of a D1 (SCH 23390: 0, 3.2, 6.4 microg per side) or a D2/D3 (raclopride: 0, 2.5, 5.0 microg per side) receptor antagonist. Animals were retested 24h later (Day 2) without prior drug infusion in order to assess possible treatment effects on within- and between-session habituation of the ASR. As expected, within- and between-session habituation was observed in vehicle-treated controls. Within-session habituation was also seen in SCH 23390- and raclopride-treated animals both on Day 1 as well as 24h later (Day 2). Evidence of between-session habituation was observed in SCH 23390-treated animals. However, compared to vehicle, intra-BLA SCH 23390 or raclopride attenuated the initial startle response on Day 1, but not Day 2. No evidence of between-session habituation was found in raclopride-treated animals, although this probably reflected the attenuated initial response to the startling stimulus on Day 1 rather than a reduced rate of habituation on Day 2. The present study suggests that while BLA DA is not involved in habituation of the ASR, it may mediate the perceived aversive nature of the initially startling stimuli.
Stevenson
C W
CW
Douglas Hospital Research Centre, McGill University, 6875 Boul. LaSalle, Montréal, Que., H4H 1R3, Canada.
Gratton
A
A
D000161:Acoustic Stimulation; D000679:Amygdala / Q000187:drug effects*; D000818:Animals; D001143:Arousal / Q000187:drug effects*; D001307:Auditory Perception / Q000187:drug effects*; D001552:Benzazepines / Q000494:pharmacology*; D001931:Brain Mapping; D065127:Dopamine D2 Receptor Antagonists; D004305:Dose-Response Relationship, Drug; D006185:Habituation, Psychophysiologic / Q000187:drug effects*; D007267:Injections; D008297:Male; D020891:Raclopride / Q000494:pharmacology*; D051381:Rats; D020318:Rats, Long-Evans; D017447:Receptors, Dopamine D1 / Q000037:antagonists & inhibitors*; D050637:Receptors, Dopamine D3; D013216:Reflex, Startle / Q000187:drug effects*
D001552:Benzazepines; D065127:Dopamine D2 Receptor Antagonists; C493595:Drd3 protein, rat; D017447:Receptors, Dopamine D1; D050637:Receptors, Dopamine D3; D020891:Raclopride