EFFECTS OF TRYPTOPHAN DEPLETION ON ANXIETY AND ON PANIC PROVOKED BY CARBON-DIOXIDE CHALLENGE

Results of several studies suggest that anxiety is under serotonergic control. We studied the influence of tryptophan depletion on generaliz ed anxiety and on the response to a 35% carbon dioxide (CO2) challenge . Fifteen healthy male volunteers received both a mixture of amino aci ds without tryptophan and a placebo mixture under double-blind conditi ons. The tryptophan-free mixture led to an 80% decrease in blood trypt ophan levels compared to the placebo. There was a significant increase in anxiety on the Spielberger Anxiety Inventory and a trend towards m ore tension on the Profile of Mood States-'tension' items, both of whi ch were interpreted as increased nervousness. Furthermore, a significa nt increase in neurovegetative panic symptoms occurred after the CO2 c hallenge. We conclude that the serotonergic system is causally involve d in anxiety-related mechanisms and that it may be worth pursuing the role of tryptophan depletion on CO2-induced panic in patients with anx iety disorders. (C) 1998 Elsevier Science Ireland Ltd.