5-HT modulation of pain in SI and SII revealed by fMRI.
OBJECTIVE
To observe the different cerebral activations between pre-administration and post-administration of tryptophan-depleted amino acid mixture (TRP-)/balanced amino acid mixture (BAL) in healthy volunteers through functional magnetic resonance imaging (fMRI) when they received electrical stimulation at the same time. Furthermore, the effects of 5-hydroxytryptamine (5-HT) were explored in pain modulation network.


METHODS
Two-phase crossover design was adopted. Six right-handed healthy volunteers participated in the experiment. TRP- and BAL were administered to each participant according to the Young's method. Volunteers were scanned under fMRI with or without administration of TRP- or BAL when receiving electrical stimulation simultaneously. Analysis of functional neuroimages (AFNI) software was used to show the different activations in the human brain between pre- and post-administration of TRP-/BAL. Then all the results were analyzed by SPSS 14.0.


RESULTS
(1) Bilateral primary somatosensory cortex (SI) and secondary somatosensory cortex (SII) were activated during pre-administration and post-administration of TRP-, but the activated volumes of bilateral SI and SII during post-administration of TRP- were found significantly larger than that during pre-administration of TRP (P<0.05). (2) All the activated regions showed no difference between pre- and post-administration of BAL. (3) There were significant differences of pain threshold between pre- and post-administration of TRP- (P<0.01), which meant that pain threshold reduced remarkably after TRP- administration, while it showed no difference between pre- and post-administration of BAL (P>0.05).


CONCLUSIONS
5-HT plays an important role in pain modulation in the central nervous system, TRP- causes acute tryptophan depletion (ATD) through reducing the level of 5-HT in the human brain, which can induce the decrease of volunteers' pain threshold. The activated volumes of bilateral SI and SII display significant difference between pre- and post-administration of TRP-, suggesting these brain areas may not only involve in the 5-HT related activities but in pain modulation network as well.
Wang
Weiwei
W
Imaging Center, The First Hospital of Xi'an Jiaotong University, Xi'an 710061, China.
Zhang
Ming
M
Wang
Yuan
Y
Jin
Chenwang
C
Yan
Bin
B
Ma
Shaohui
S
D000293:Adolescent; D000328:Adult; D000596:Amino Acids / Q000008:administration & dosage / Q000494:pharmacology; D001921:Brain / Q000378:metabolism / Q000502:physiology; D018592:Cross-Over Studies; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D017288:Pain Threshold / Q000187:drug effects / Q000502:physiology*; D012701:Serotonin / Q000378:metabolism*; D013003:Somatosensory Cortex / Q000378:metabolism / Q000502:physiology*; D014364:Tryptophan / Q000008:administration & dosage / Q000494:pharmacology*; D055815:Young Adult
D000596:Amino Acids; D012701:Serotonin; D014364:Tryptophan