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Int J Obes Relat Metab Disord. 1998 Apr;22(4):325-8.

Effects of phentermine on striatal dopamine and serotonin release in conscious rats: in vivo microdialysis study.

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Massachusetts Institute of Technology, Department of Brain and Cognitive Sciences, Cambridge 02139, USA.



To measure the effects of phentermine, an appetite supressant, on the release of brain dopamine (DA) and serotonin (5-HT) into striatal dialysates of freely moving rats.


Microdialysis and high performance liquid chromatography.


Unanesthetized rats.


Samples collected every 20 min were assayed for both neurotransmitters in a single run, using high performance liquid chromatography with electrochemical detection.


Baseline levels of DA and 5-HT in dialysates were 56+/-16 and 3+/-0.6 fmol/20 microl, respectively. Administration of phentermine (2 or 5 mg/kg) increased dialysate DA concentrations to 147+/-17% (P < 0.01) and 320+/-89% (P < 0.01) of baseline, respectively, without significantly affecting 5-HT concentrations. Pretreatment with tetrodotoxin (TTX, 60 min, 1 microM), which abolished the basal release of DA and 5-HT into striatal dialysates, diminished the increase in DA concentrations induced by phentermine, but did not completely block it. Phentermine (2 or 5 mg/kg, i.p.) still stimulated DA release to 27+/-13% and 85+/-15% of baseline, respectively, in the presence of TTX.


Phentermine increases brain DA but not 5-HT release in freely moving rats, and TTX reduces, but does not fully block this effect. This pattern is similar to that known to be produced by d-amphetamine.

[Indexed for MEDLINE]

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