The Changes Of Dopamine Transporter Function In Striatum During Acute Morphine Injection And Its Abstinence In Rhesus Monkey: A SPECT Study

The functional changes of dopamine transporter in striatum during acute morphine injection and its abstinence in rhesus monkey are unclear. So,we used SPECT to investigate this problem. Four rhesus monkeys, 6 to 9 years old, were examined. The whole study lasted for 12 DAys.Baseline SPECT DAta was gathered one DAy before morphine treatment with physiological salt solution injection/Then the morphine addiction and abstinence processes lasted for 11 DAys. Morphine was injected twice a DAy (at 12 and 24 O'clock) for 6 DAys with a dose of 0.5,1.6, 5, 8, 8, and 8mg/kg for each DAy respectively. SPECT DAta were gathered at the 1st, 4th, 7th, 9th, and 11th DAy within 14-16 O'clock. ⁹⁹Tc^m -TRODAT-1 was injected before the morphine injection at noon with about 100 MBq/kg (2.7 mCi). After 2 hours, the animals were then anaesthetized with Amobarbital Sodium. The ratios of SPECT signal between striatum and cerebellum (ST/CB) in different stages were calculated.The ST/CB ratio declined significantly at the first DAy of morphine injection, and continued declining with more morphine injection. After abstinence, the ratio increased with time, but was still lower than the normal level on the 5th DAy of abstinence significantly.From this study, we can get the conclusion that in rhesus monkey, acute morphine injection has both rapid and lasting effects on DAT by down-regulating its function. The declining can be reversible, at least partially, following morphine abstinence. Striatum is one effective target of morphine, and the DAT function in striatum is one index for morphine addiction.