A novel subpopulation of 5-HT type 3A receptor subunit immunoreactive interneurons in the rat basolateral amygdala

Neuroscience. 2007 Feb 9;144(3):1015-24. doi: 10.1016/j.neuroscience.2006.10.044. Epub 2006 Dec 5.


The amygdalar basolateral nuclear complex (BLC) has very high levels of the 5-HT type 3 receptor (5-HT(3)R). Previous studies have reported that 5-HT(3)R protein in the BLC is expressed in interneurons and that 5-HT(3)R mRNA is coexpressed with GABA and certain neuropeptides or calcium-binding proteins in these cells. However, there have been no detailed descriptions of the distribution of 5-HT(3)R+ neurons in the rat amygdala, and no quantitative studies of overlap of neurons expressing 5-HT(3)R protein with distinct interneuronal subpopulations in the BLC. The present investigation employed dual-labeling immunohistochemistry using antibodies to the 5-HT-3A receptor subunit (5-HT(3A)R) and specific interneuronal markers to address these questions. These studies revealed that there was a moderate density of nonpyramidal 5-HT(3A)R+ neurons in the BLC at all levels of the amygdala. In addition, immunostained cells were also seen in anterior portions of the cortical and medial nuclei. Although virtually all 5-HT(3A)R+ neurons in the BLC were GABA+, very few expressed neuropeptide or calcium-binding protein markers for individual subpopulations. The main interneuronal marker expressed by 5-HT(3A)R+ neurons was cholecystokinin (CCK), but only 8-16% of 5-HT(3)R+ neurons in the BLC, depending on the nucleus, were CCK+. Most of these CCK+/5-HT(3A)R+ double-labeled neurons appeared to belong to the subpopulation of large type L CCK+ interneurons. Very few 5-HT(3A)R+ neurons expressed calretinin, vasoactive intestinal peptide, or parvalbumin, and none expressed somatostatin or calbindin. Thus, the great majority of neurons expressing 5-HT(3A)R protein appear to constitute a previously unrecognized subpopulation of GABAergic interneurons in the BLC.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amygdala / cytology
  • Amygdala / metabolism*
  • Animals
  • Biomarkers / metabolism
  • Calcium-Binding Proteins / metabolism
  • Cholecystokinin / metabolism
  • Immunohistochemistry
  • Interneurons / cytology
  • Interneurons / metabolism*
  • Male
  • Neural Inhibition / physiology
  • Protein Subunits / metabolism
  • Rats
  • Rats, Sprague-Dawley
  • Receptors, Serotonin, 5-HT3 / metabolism*
  • Serotonin / metabolism*
  • Synaptic Transmission / physiology
  • gamma-Aminobutyric Acid / metabolism*


  • Biomarkers
  • Calcium-Binding Proteins
  • Protein Subunits
  • Receptors, Serotonin, 5-HT3
  • Serotonin
  • gamma-Aminobutyric Acid
  • Cholecystokinin