Research in experimental animals suggests that type 1 diabetes could diminish the functional activity of the serotonergic system, the authors explain.

Dr. Gabriel Manjarrez from National Medical Center, Mexico City, Mexico and colleagues measured plasma free fraction of L-tryptophan (FFT) and intensity-dependent auditory-evoked potentials (IDAEPs) as indicators of brain serotonergic neurotransmission in 11 children with type 1 diabetes and in 12 normal children.

Children with diabetes had significantly lower FFT than did normal children, the researchers report, and there was a decrease in the FFT-to-neutral amino acids ratio in the children with type 1 diabetes.

"The decrease of FFT in plasma with a concomitant decrease of the FFT-to-neutral amino acids ratio suggests a decrease in the transport of the precursor amino acids of the brain related to a decrease in its availability at the blood brain barrier level that in turn may induce a decrease in the serotonin synthesis rate, similar to that observed in the brain of diabetic rats," the investigators explain.

The latencies of the N1 and P2 components of the IDAEP increased at all intensities, the report indicates, and the slope of the amplitude/stimulus intensity function (ASF slope) of the N1/P2 component increased significantly.

"The increase of the ASF slope in children with type 1 diabetes suggests that the response of the auditory cortex to sound intensity stimulus may be regulated by the serotonergic tone and that decreased serotonergic neurotransmission may provoke a different behavior of sensory cortices," Dr. Manjarrez and colleagues write.

They say their findings may have clinical relevance, "because brain serotonin is known to play an important role in the pathophysiology of various neuropsychiatric disorders that are commonly present in patients with type 1 diabetes like anxiety and depression."

"Therefore," the investigators say, "we propose the use of the IDAEP (N1/P2 component) as a noninvasive electrophysiological indicator of changes in brain serotonin synthesis and activity in patients with type 1 diabetes."

Source: Diabetes In Control: Diabetes Care 2006;29:73-77.