Rationale: 2 beta -propanoyl-3 beta-(4-tolyl)-tropane (PTT) is a cocaine an
alog with high affinity at and selectivity for the dopamine transporter (DA
T). 2 beta -propanoyl-3 beta-(2-naphthyl)-tropane (HD-23), like cocaine, bi
nds with approximately equal affinity to the DAT, the serotonin transporter
, and the norepinephrine transporter but has over a 100-fold higher affinit
y for these monoamine transporters than cocaine. The reinforcing effects of
these drugs have not been evaluated in cocaine-na nonhuman primates. Objec
tive: The primary goal of the present study was to examine the reinforcing
effects of PTT and HD-23 in rhesus monkeys before and after a history of in
travenous cocaine self-administration. Methods: Monkeys (n=4) were initiall
y trained to respond under a fixed-ratio 30 schedule of food presentation.
When responding was stable, saline, PTT (0.001-0.03 mg/kg per injection), a
nd HD-23 (0.0003-0.0056 mg/kg per injection) were made available fur self-a
dministration fur least five sessions per dose. Next, a cocaine dose-effect
function (0.0003-0.3 mg/kg per injection) was determined and then PTT and
HD-23 dose-effect curves were redetermined. Results: When substituted for f
ood, neither drug maintained responding significantly higher than saline du
ring 3-h (PTT and HD-23) or 22-h (PTT) sessions. After determining the coca
ine dose-effect function, PTT and HD-23 functioned as reinforcers in one of
four monkeys, when substituted for food during daily 3-h sessions. However
, when PTT was made available during 22-h sessions, it had reinforcing effe
cts in three of the four monkeys tested. Conclusions: These results indicat
e that the reinforcing effects: of PTT were slightly modified by a brief hi
story of cocaine reinforcement, and that the weak reinforcing effects were
most apparent when the drug was available under unlimited-access conditions
.