Evidence for pretreatment LICI deficits among depressed children and adolescents with nonresponse to fluoxetine.

BACKGROUND: Research suggests that alterations in gamma-aminobutyric acid receptor functioning have a role in depression. Paired-pulse transcranial magnetic stimulation (TMS) paradigms are noninvasive measures of cortical inhibitory and excitatory circuits.

OBJECTIVE/HYPOTHESIS: The present study examined pretreatment short-interval intracortical inhibition (SICI), long-interval cortical inhibition (LICI), and intracortical facilitation (ICF) in children and adolescents with major depressive disorder who were initiating fluoxetine treatment. The primary objective was to examine the relationship of these measures with subsequent treatment response. It was hypothesized that alterations in pretreatment GABA and glutamate mediated neurotransmission, would be associated with fluoxetine nonresponse.

METHODS: Sixteen children and adolescents with major depressive disorder underwent paired-pulse TMS testing before beginning fluoxetine treatment. Response was prospectively characterized by scores of 1 or 2 on the Clinical Global Impression Scale and less than 40 on the Children's Depression Rating Scale-Revised after 6 weeks of fluoxetine treatment (20-40 mg/day).

RESULTS: Eight patients responded to treatment. Least-squares mean LICI values were consistently higher bilaterally for treatment nonresponders. Higher LICI values indicate less inhibition and impaired GABAB functioning. There was no significant effect of treatment response on the measures of SICI and ICF.

CONCLUSIONS: Our findings suggest that deficits in pretreatment GABAB may be related to fluoxetine nonresponse in depressed youth. This is congruent with prior work demonstrating that GABAB interneurons have serotonergic input and antidepressants modulate GABAB receptors. These findings also show that TMS paradigms have utility in studying the neurophysiology and treatment of childhood mood disorders.

REGISTRATIONS: Cortical Excitability and Inhibition in Children and Adolescents With Major Depressive Disorder, https://www.clinicaltrials.gov/ct2/show/NCT00896090?term=cortical+excitability+and+inhibition&rank=2, NCT00896090; Sequential Treatment of Pediatric MDD to Increase Remission and Prevent Relapse, https://www.clinicaltrials.gov/ct2/show/NCT00612313?term=Sequential+Treatment+and+MDD&rank=1, NCT00612313.