Ethological and 6-[18F]fluoro-L-DOPA-PET profiles of long-term vulnerability to chronic amphetamine

A chronic 10-day amphetamine (Amp) protocol was used to induce significant long-term decrements of the striatal [18F]fluoro-L-DOPA influx rate constant (FDOPA Ki) in the vervet monkey. Longitudinal FDOPA-positron emission tomography (PET) assessment in Amp-treated subjects subsequently revealed a gradual recovery of striatal dopamine function: FDOPA Ki values were decreased by approximately 70% at 1 month, approximately 45% at 6 months, approximately 20% at 12 months and were similar to pre-Amp values at 24 months. Motoric and social behavioral measures were obtained on all subjects within a species-typical group setting. Behavioral observations were conducted during both basal and stressor-challenge conditions, the latter being created by placing a potential intruder-animal in an individual cage adjacent to the subject's group enclosure. During basal conditions, post-Amp stereotypies were present at 2 weeks and locomotor behaviors were increased throughout 1 month; both alterations occurred while FDOPA Ki values were significantly decreased. Social behaviors were also significantly affected; affiliative behavior was decreased up to 6 months while aggressive behavior was increased for 12 months. However, a different pattern of behavioral changes emerged under stressor-challenge conditions. Motoric and social changes were of greater magnitude and persisted longer than in basal settings while aggressive behavior remained elevated at 24 months. These results indicate that chronic Amp-induced decreases in FDOPA Ki values and behavioral alterations are reversible. Changes in striatal dopamine function as indexed with FDOPA-PET are not correlated with post-Amp alterations in behaviors and moreover, expression of those behaviors is context-dependent.