Pyramidal cells of the rat basolateral amygdala: Synaptology and innervation by parvalbumin-immunoreactive interneurons

• Published in: Journal of comparative neurology (1911) Vol. 494; no. 4; pp. 635 - 650
• Main Authors: Muller, Jay F., Mascagni, Franco, McDonald, Alexander J.
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 01-02-2006
• Subjects: Amygdala - metabolism; Amygdala - ultrastructure; Animals; Calcium-Calmodulin-Dependent Protein Kinases - metabolism; calcium/calmodulin-dependent protein kinase II; Dendritic Spines - metabolism; Dendritic Spines - ultrastructure; electron microscopy; gamma-Aminobutyric Acid - metabolism; immunocytochemistry; Immunohistochemistry; inhibition; inhibition, calcium/calmodulin‐dependent protein kinase II; Interneurons - metabolism; Interneurons - ultrastructure; Male; Neural Pathways - metabolism; Neural Pathways - ultrastructure; Parvalbumins - metabolism; Pyramidal Cells - metabolism; Pyramidal Cells - ultrastructure; Rats; Rats, Sprague-Dawley; Synapses - ultrastructure
• ISSN: 0021-9967; 1096-9861
• DOI: 10.1002/cne.20832

The generation of emotional responses by the basolateral amygdala is determined largely by the balance of excitatory and inhibitory inputs to its principal neurons, the pyramidal cells. The activity of these neurons is tightly controlled by γ‐aminobutyric acid (GABA)‐ergic interneurons, especially a parvalbumin‐positive (PV+) subpopulation that constitutes almost half of all interneurons in the basolateral amygdala. In the present semiquantitative investigation, we studied the incidence of synaptic inputs of PV+ axon terminals onto pyramidal neurons in the rat basolateral nucleus (BLa). Pyramidal cells were identified by using calcium/calmodulin‐dependent protein kinase II (CaMK) immunoreactivity as a marker. To appreciate the relative abundance of PV+ inputs compared with excitatory inputs and other non‐PV+ inhibitory inputs, we also analyzed the proportions of asymmetrical (presumed excitatory) synapses and symmetrical (presumed inhibitory) synapses formed by unlabeled axon terminals targeting pyramidal neurons. The results indicate that the perisomatic region of pyramidal cells is innervated almost entirely by symmetrical synapses, whereas the density of asymmetrical synapses increases as one proceeds from thicker proximal dendritic shafts to thinner distal dendritic shafts. The great majority of synapses with dendritic spines are asymmetrical. PV+ axon terminals form mainly symmetrical synapses. These PV+ synapses constitute slightly more than half of the symmetrical synapses formed with each postsynaptic compartment of BLa pyramidal cells. These data indicate that the synaptology of basolateral amygdalar pyramidal cells is remarkably similar to that of cortical pyramidal cells and that PV+ interneurons provide a robust inhibition of both the perisomatic and the distal dendritic domains of these principal neurons. J. Comp. Neurol. 494:635–650, 2006. © 2005 Wiley‐Liss, Inc.