Acute trytophan depletion decreases intensity dependence of auditory evoked magnetic N1/P2 dipole source activity

Abstract

ATD decreased the intensity dependence of N1m/P2m source dipole moments in the primary auditory cortex at the hemisphere contralateral to the ear stimulated. These results suggest that serotonin participates in the regulation of intensity of auditory stimulation.

Effects of selective and combined serotonin and dopamine depletion on the loudness dependence of the auditory evoked potential (LDAEP) in humans

“…However, despite such pronounced levels of tryptophan depletion in the current study, no significant effect was noted on the LDAEP. This result is consistent with the majority of previous studies using ATD which similarly found no effects on the LDAEP (Debener et al, 2002;Dierks et al, 1999;Massey et al, 2004), although a paradoxical decrease in the LDAEP has been noted following ATD in one study (Kähkönen et al, 2002). These variable results using ATD methodology are analogous to other investigations reporting inconsistent outcomes following acute serotonin augmentation using SSRIs.…”

“…This ratio of amino acid precursor to LNAA is thought to be a more accurate reflection of the amount of central depletion of the precursor (Fernstrom, 1979;Van der Does, 2001). This level of depletion is comparable to, if not exceeding that obtained in other studies involving the LDAEP (Debener et al, 2002;Dierks et al, 1999 andKähkönen et al, 2002). In addition, these levels of depletion have been shown to significantly affect measures of central serotonergic function such as brain serotonin synthesis (Moja et al, 1988;Nishizawa et al, 1997) and CSF concentrations of serotonin metabolites (Carpenter et al, 1998;Williams et al, 1999).…”

“…For example, the physiological effects of ATD may occur at later than 5 h post-administration. In previous investigations involving ATD and the LDAEP, a 5-h period has been applied (Dierks et al, 1999;Kähkönen et al, 2002) as plasma tryptophan concentrations reach their nadir after this time. However, apparently more specific measures of central serotonergic function (i.e.…”

“…This latency period for testing was chosen to coincide with the timing of maximal monoamine depletion determined in previous research detailing the time course of monoamine depletion in both animals and humans (for reviews see Moore et al, 2000;Reilly et al, 1997). In addition, this time period has frequently been employed in previous studies investigating the effects of ATD on the LDAEP (Debener et al, 2002;Kähkönen et al, 2002;Massey et al, 2004). Upon conclusion of the testing procedure, participants were provided with high protein snacks in order to replenish their amino acid levels.…”

“…In humans, ATD has been shown to acutely decrease serotonin and its metabolites (Carpenter et al, 1998;Moja et al, 1988;Nishizawa et al, 1997;Williams et al, 1999), and impair serotonin-dependant cognitive processes such as memory consolidation and learning Sambeth et al, 2007). Using this procedure, a number of studies have examined the effects of ATD on the LDAEP, showing no effect (Debener et al, 2002;Dierks et al, 1999;Massey et al, 2004) or a paradoxical decrease in the LDAEP (Kähkönen et al, 2002). Acute tyrosine/ phenylalanine depletion (ATPD) has been used as a method to reduce dopamine function.…”