Demonstration of disturbed activity of the lateral amygdaloid nucleus projection neurons in depressed patients by the AgNOR staining method

Background: The aim to find a morphological biomarker of disturbed activity of the lateral amygdaloid nucleus in depression was approached by a karyometric analysis of projection neurons.

Methods: The study was performed on paraffin-embedded brains from 19 depressed patients from both the major depressive disorder (MDD) and the bipolar disorder (BD) diagnostic groups, including 10 suicides, and 24 matched controls. The karyometric parameters of the lateral amygdaloid nucleus (La) projection neurons bilaterally were evaluated by the argyrophilic nucleolar organiser region (AgNOR) silver staining method.

Results: An increased AgNOR number was found in the right La in suicides compared to controls. The intra-group comparisons between the hemispheres suggest a disturbed amygdaloid lateralisation in depressed patients. The effects were independent from psychotropic medication. There was a strong positive correlation between the nuclear area in La projection neurons and prefrontal limbic areas pyramidal neurons in the right hemisphere specific for suicide and MDD.

Limitations: A major limitation of this study is the relatively small number of cases. A further limitation is given by the lack of data on drug exposure across the entire lifespan.

Conclusion: The results suggest that depressed patients from both the MDD and BD diagnostic groups exhibit an increased activity of the La output neurons specific for suicidal patients. The distinctness of the diagnostic groups of mood disorders was accentuated in the correlation analysis. This putative hyperactivity was specific for the right hemisphere and psychotropic medication most likely did not counteract it.