The International Journal of Neuropsychopharmacology

Letter to the Editor

Brain regional α-[11C]methyl-L-tryptophan trapping correlates with post-mortem tissue serotonin content and [11C]5-hydroxytryptophan accumulation

Marco Leyton Ph.D. a1a2c1, Mirko Diksic Ph.D. a2 and Chawki Benkelfat M.D., DERBH a1a2
a1 Department of Psychiatry, McGill University, Montréal, Québec, Canada
a2 Department of Neurology & Neurosurgery, McGill University, Montréal, Québec, Canada

Article author query
leyton m   [PubMed][Google Scholar] 
diksic m   [PubMed][Google Scholar] 
benkelfat c   [PubMed][Google Scholar] 

The labelled tryptophan analog, α~[11C]methyl-L-tryptophan (α[11C]MTrp), has been developed as a tracer to provide an in-vivo index of brain serotonin (5-HT) synthesis (Chugani and Muzik, 2000; Diksic and Young, 2001). Autoradiography studies in rodents indicate that the α[14C]MTrp trapping rate constant [K*=K1k3/(k2+k3)] correlates with the conversion of the tracer into 5-HT but not the uptake of endogenous tryptophan across the blood–brain barrier or the incorporation of tryptophan into protein (Diksic et al., 2000). To cross-validate the positron emission tomography (PET) method, we compared brain regional differences in the α[11C]MTrp trapping rate constant in subjects assessed at McGill University (27 healthy subjects: 18 men, 9 women) to (1) α[11C]MTrp trapping values reported by researchers at Wayne State University (Chugani et al., 1998), (2) the brain regional rate of accumulation of a second PET tracer also proposed to provide an index of 5-HT synthesis, [11C]5-hydroxytryptophan ([11C]5-HTP) (Hagberg et al., 2002), (3) tissue concentrations of 5-HT in post-mortem human brain (Bucht et al., 1981), and (4) rate of accumulation of 5-HTP following NSD-1015 inhibition in rhesus monkeys (Brown et al., 1979).

(Received October 13 2004)
(Reviewed December 7 2004)
(Revised January 5 2005)
(Accepted January 16 2005)

c1 Department of Psychiatry, McGill University, 1033 Pine Avenue West, Montreal, Quebec H3A 1A1, Canada. Tel.: 514-398-5804 Fax: 514-398-4866 E-mail: MARCO.LEYTON@MCGILL.CA