Neurons Expressing Parvalbumin and Calretinin in the Human Amygdaloid Complex: A Quantitative and Qualitative Analysis in Every Nucleus and Nuclear Subdivision

Abstract

The primate amygdaloid complex (AC) contains projection neurons as well as subsets of interneurons (IN), many of which express calcium-binding proteins, that through their local circuits control the activity of the projection neurons. The inhibitory parvalbumin (PV) and calretinin (CR)-positive (+) AC IN have a crucial role in the appearance of synchronized oscillations in local ensembles of projection neurons that mediate the consolidation and recall of fear memories. The GABAergic transmission of these subsets of IN is modulated by dopamine. To expand the knowledge regarding the cellular composition and distribution of IN in the human AC, we focused on two non-overlapping populations: the PV+ and CR+. We have analyzed the distribution of these IN throughout the AC from subjects without any neurological or psychiatric disorders and estimated their absolute number and density using stereological methods. We have also provided percentages of the IN with respect to the total AC neurons. The CR + IN were distributed throughout the AC, whereas the PV+ were only present in the basolateral nuclear group. The quantity of CR + IN was four times higher than that of PV+ and the percentages varied from less than 1% for PV + IN to 6–20% for CR+. The differences in quantity and distribution of CR+ and PV + IN could be related to their differential inhibitory properties and to the intrinsic and extrinsic connections of every amygdaloid region.