PET studies with low and high affinity dopamine D2 receptor radioligands: Effects of 4-hydroxybutyrate (4HB)
- Brookhaven National Lab., Upton, NY (United States); and others
D2 radioligands of varying affinities have been developed as PET and SPECT radiotracers, but no consensus has been reached on the abilities of these tracers to quantify D2 receptor concentrations in vivo. Amongst other differences, competition of the radioligand with endogenous DA is expected to depend on affinity for the D2 receptor, so that changes in DA might confound estimates of Bmax. We examined the uptake and kinetics if C-11 raclopride (RAC; Kd = 1.2 nM) and C-11 N-methylspiperone (NMS); Kd = 75 pM in baboon striatum after pretreatment with 4HB (200 mg/Kg, i/v) which inhibits DA release by nigrostriatal nerve terminals. While 4HB diminished uptake (%ID/g) of NMS, it prolonged tissue retention of RAC, confirming previous observations in rodent models. Logan (for RAC) and Patlak (for NMS) plots gave changes of +24% and -20%, respectively, between control and 4HB treated animals. Since decreased competition with DA should increase uptake of NMS as well as RAC the paradoxical decrease in NMS uptake could be due to a second synaptic effect of DA, such as a decrease in agonist mediated internalization of NMS. Alternatively, it could result from an independent effect of 4HB, perhaps related to this drug`s ability to induce anesthesia and to depress cerebral glucose utilization. Although previous work in the rat suggests that 4HB does not alter brain blood flow, we found O-15 water that baboon striatal blood flow was decreased 22% and 42% at 30 and 60 minutes, respectively, after 4HB. Smaller changes were seen in cerebellar blood flow. Though a 4HB induced decrease in blood flow does not rule out a DA mediated alteration in D2 receptor Bmax or Kd for NMS, or other factor, it is unnecessary to invoke this to account for our results.
- OSTI ID:
- 198005
- Report Number(s):
- CONF-940605--
- Journal Information:
- Journal of Nuclear Medicine, Journal Name: Journal of Nuclear Medicine Journal Issue: Suppl.5 Vol. 35; ISSN 0161-5505; ISSN JNMEAQ
- Country of Publication:
- United States
- Language:
- English
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