EFFECTS OF D-2 DOPAMINE-RECEPTOR AGONIST AND ANTAGONIST ON BRAIN ACTIVITY IN THE RAT ASSESSED BY FUNCTIONAL MAGNETIC-RESONANCE-IMAGING

The effects of D-2 dopamine receptor agonist, bromocriptine (BROMO), a nd antagonist, haloperidol (HPD), on brain activity were investigated in rats by functional magnetic resonance imaging. T2-weighted signal intensity was increased in the hypothalamus at 120 min after acute adm inistration of BROMO, and in the ventral posterior and dorsomedial nuc lei of the thalamus from 30 to 120 min. In contrast, the signal intens ity was decreased in the caudate-putamen at 30 min after acute adminis tration of HPD, in the hypothalamus from 30 to 60 min, and in the peri rhinal cortex at 30 min. After chronic (2 weeks) HPD treatment, acute administration of HPD decreased signal intensity in the caudate-putame n at 60 min, in the hypothalamus at 30 min, the perirhinal cortex from 2 to 120 min, the dorsomedial and ventral posterior nuclei of the tha lamus fi-om 2 to 120 min, and the medial nucleus of the amygdala from 60 to 120 min. These results suggest that (1) the D-2 receptor agonist increased the activity of the thalamic nuclei and the hypothalamus, w hile the D-2 receptor antagonist suppressed brain activity in the regi ons where D-2 receptors were present, (2) the suppression of brain act ivity in the thalamic nuclei and the perirhinal cortex by acute HPD ad ministration was enhanced by chronic HPD treatment, and (3) the effect s of antipsychotic drugs on the thalamus, amygdala, and perirhinal cor tex may be related to their therapeutic efficacy, since clinical impro vement in schizophrenic patients appears several days after the start of HPD treatment. (C) 1998 Elsevier Science B.V. All rights reserved.