Effects of phentermine and fenfluramine on extracellular dopamine and serotonin in rat nucleus accumbens: therapeutic implications

Synapse. 2000 May;36(2):102-13. doi: 10.1002/(SICI)1098-2396(200005)36:2<102::AID-SYN3>3.0.CO;2-#.


Combined administration of the amphetamine analogs phentermine and fenfluramine (PHEN/FEN) has been used in the treatment of obesity. While these medications are thought to modulate monoamine transmission, the precise neurochemical effects of the PHEN/FEN mixture have not been extensively studied. To assess the mechanism of PHEN/FEN action, in vivo microdialysis studies were performed in the nucleus accumbens of conscious freely moving rats. A series of amphetamine derivatives including phentermine, chlorphentermine, fenfluramine, and PHEN/FEN (1:1 ratio), were infused locally into the accumbens via reverse-dialysis (1, 10, 100 microM) or injected systemically (1 mg/kg, ip). Dialysate samples were assayed for dopamine (DA) and serotonin (5-HT) by high-performance liquid chromatography with electrochemical detection. When infused locally, phentermine preferentially increased extracellular DA, whereas fenfluramine selectively increased extracellular 5-HT. Local administration of chlorphentermine or the PHEN/FEN mixture caused parallel elevations of both transmitters. Analogous results were obtained when the drugs were injected systemically. Phentermine stimulated robust locomotor activity in mice, whereas chlorphentermine and fenfluramine did not. PHEN/FEN caused modest locomotor stimulation after a low dose, but had no effect at the highest dose. Accumulating evidence suggests that chronic drug and alcohol abuse is associated with deficits in both DA and 5-HT neuronal function. Thus, dual activation of DA and 5-HT neurotransmission with monoamine releasing agents may be an effective treatment strategy for substance use disorders, as well as for obesity. Synapse 36:102-113, 2000. Published 2000 Wiley-Liss, Inc.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amphetamine / pharmacology
  • Animals
  • Chlorphentermine / pharmacology
  • Cocaine / analogs & derivatives
  • Cocaine / pharmacology
  • Dopamine / metabolism*
  • Extracellular Space / drug effects*
  • Extracellular Space / metabolism*
  • Fenfluramine / pharmacology*
  • In Vitro Techniques
  • Iodine Radioisotopes
  • Male
  • Microdialysis
  • Motor Activity / drug effects
  • Motor Activity / physiology
  • Nucleus Accumbens / cytology
  • Nucleus Accumbens / drug effects*
  • Nucleus Accumbens / metabolism*
  • Phentermine / pharmacology*
  • Radioligand Assay
  • Rats
  • Rats, Sprague-Dawley
  • Selective Serotonin Reuptake Inhibitors / pharmacology*
  • Serotonin / metabolism*
  • Sympathomimetics / pharmacology*


  • Iodine Radioisotopes
  • Serotonin Uptake Inhibitors
  • Sympathomimetics
  • Fenfluramine
  • Serotonin
  • 2beta-carbomethoxy-3beta-(4-iodophenyl)tropane
  • Phentermine
  • Amphetamine
  • Cocaine
  • Chlorphentermine
  • Dopamine