N1/P2 component of auditory evoked potential reflect changes of the brain serotonin biosynthesis in rats

It is known that L-tryptophan stimulates serotonin synthesis in the brain and serotonergic neuronal activity. Also, the N1/P2 component of auditory evoked potential (AEP) is a good indicator of this activity in the auditory cortex. In the present work, we examined the effect of the L-tryptophan administration on electric activity of the auditory cortex recorded as the N1/P2 component of the AEP in adult male rats. The effect of serotonergic agonists or antagonists was also tested. The results showed that indeed L-tryptophan was able to induce a drastic change in auditory cortex electric activity, reducing very significantly the amplitude of the N1/P2 component of the AEP. Quipazine maleate had a similar effect as L-tryptophan and the serotonergic antagonist spiperone induced an increase in the N1/P2 amplitude. These results show how an isolated nutrient is able to induce significant changes in brain auditory cortical function, through stimulation of serotonin synthesis. Besides, they add evidence about the important role of serotonergic neurotransmission modulating sensory cortical activity and that the N1/P2 component of AEPs represent a useful noninvasive indicator of brain serotonin tone.