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Updated: Aug 13, 2026
Whole-cell Patch-clamp Recordings from Morphologically- and Neurochemically-identified Hippocampal Interneurons
Published on: September 30, 2014
Cat intraamygdaloid inhibitory network: ultrastructural organization of parvalbumin-immunoreactive elements
Insights
Parvalbumin-positive (PV+) interneurons in the amygdala receive significant excitatory input. These PV+ interneurons strategically control amygdala neuron activity through inhibitory synapses.
Area of Science:
- Neuroscience
- Cell Biology
Background:
- The basolateral (BL) amygdaloid complex's projection neurons are regulated by intrinsic inhibitory networks.
- Parvalbumin-immunopositive (PV+) cells, a subpopulation of GABAergic interneurons, are key components of this inhibitory circuit.
Purpose of the Study:
- To elucidate the synaptic connections of PV+ elements within the BL amygdala.
- To understand the specific roles of different interneuron populations in regulating amygdala circuitry.
Main Methods:
- Utilized electron microscopy to analyze the synaptology of PV+ cells in the lateral and BL nuclei.
- Classified synaptic contacts based on bouton morphology and synapse type (symmetric/asymmetric).
- Differentiated PV+ cell populations (Type A and Type B) based on soma shape.
Main Results:
- Identified two PV+ cell populations (Type A and Type B), with Type B neurons receiving denser innervation.
- Observed that PV+ cells receive predominantly asymmetric (excitatory) synaptic inputs (94%).
- Found that PV+ boutons form symmetric (inhibitory) synapses, primarily on proximal dendrites and somata of PV+ neurons.
Conclusions:
- PV+ interneurons in the amygdala receive substantial excitatory input, suggesting complex regulatory mechanisms.
- PV+ interneurons are strategically positioned to exert significant inhibitory control over amygdala output neurons.
Abstract:
Projection neurons of the basolateral (BL) amygdaloid complex are regulated by an intrinsic inhibitory network. To improve our understanding of this inhibitory circuit, we studied the synaptology of parvalbumin-immunopositive (PV+) elements as this calcium-binding protein is localized in a subpopulation of gamma-aminobutyric acid (GABA)-ergic interneurons. Two populations of PV+ cells were identified on the basis of soma shape (ovoid, type A vs. polygonal, type B). In the lateral and BL nuclei, the majority of boutons in contact with PV+ cells formed asymmetric synapses (types 1-3; 94%), whereas a minority (type 4, 6%) established symmetric synaptic contacts and resembled GABAergic terminals. In both nuclei, type B PV+ perikarya were more densely innervated than were type A neurons. However, the pattern of synaptic innervation of type B PV+ neurons differed in the two nuclei: in the lateral nucleus, they were almost exclusively innervated by a population of small, presumed excitatory terminals (type 1), whereas the four categories of terminals contributed more equally to their innervation in the BL nucleus. PV+ boutons belonged to a single category of terminals that was enriched with GABA and formed symmetric synapses mostly with the proximal part of PV neurons. The proportion of axosomatic synapses was significantly higher in the lateral nucleus than in the BL nucleus (33% vs. 18%). The reverse was true for the contacts with proximal dendrites (33% in the lateral nucleus vs. 46% in the BL nucleus). The remaining terminals formed synapses with distal dendrites (23-28%) and spines (8-12%). These results indicate that PV+ interneurons receive massive excitatory inputs and that PV+ terminals are strategically located to exert a powerful inhibitory control of amygdala neurons.
