In normal rats treated with the inhibitor of cerebral
decarboxylase,
NSD-1015 (100 mg kg-1 i.p.),
umespirone (1.9-30.0 mumol kg-1 s.c.) produced an increase in neostriatal
DOPA (
dihydroxyphenylalanine) accumulation, whereas decreased
DOPA accumulation was obtained in
reserpine-pretreated (5 mg kg-1 s.c., -18 h) animals. The latter effect was statistically significant only in the ventral, limbic, portion of the neostriatum. Neostriatal
5-hydroxytryptophan (5-HTP) accumulation was decreased in the
reserpine-treated animals but not in normal controls.
DOPA accumulation in the neocortex was not affected by
umespirone treatment in either preparation, whereas
5-HTP accumulation was decreased in the
reserpine-treated animals. Spontaneous locomotor activity was suppressed by
umespirone at doses that did not affect treadmill locomotion (7.9-31.2 mumol kg-1 s.c., -30 min), and there were no signs of
catalepsy at doses ranging from 31.2-249.6 mumol kg-1 s.c. up to 2 h after injection. Thus,
umespirone behaves as a mixed
dopamine receptor agonist/antagonist and also displays
5-HT receptor agonist properties. This biochemical profile was associated with sedation, as observed in the open-field, at doses which did not affect treadmill locomotion or induced
catalepsy.