Synaptic Connectivity of Distinct Hilar Interneuron Subpopulations

• Published in: Journal of neurophysiology 1998-06, Vol.79 (6), p.3229-3237
• Main Authors: Forti, Matteo, Michelson, Hillary B
• Format: Article
• Language: English
• Subjects: 4-Aminopyridine - pharmacology; Animals; Bicuculline - pharmacology; Cell Communication; GABA Antagonists - pharmacology; GABA-A Receptor Antagonists; GABA-B Receptor Antagonists; Guinea Pigs; In Vitro Techniques; Interneurons - physiology; Interneurons - ultrastructure; Membrane Potentials - physiology; Pyramidal Cells - physiology; Pyramidal Cells - ultrastructure; Receptors, GABA-A - physiology; Receptors, GABA-B - physiology; Synapses - physiology; Synapses - ultrastructure
• ISSN: 0022-3077; 1522-1598
• DOI: 10.1152/jn.1998.79.6.3229

Matteo Forti and Hillary B. Michelson Department of Pharmacology, State University of New York Health Science Center at Brooklyn, Brooklyn, New York 11203 Forti, Matteo and Hillary B. Michelson. Synaptic connectivity of distinct hilar interneuron subpopulations. J. Neurophysiol. 79: 3229-3237, 1998. Dual intracellular recordings of hilar interneurons and CA3 pyramidal cells were performed in transverse slices of guinea pig hippocampus in the presence of the convulsant compound 4-aminopyridine (4-AP) and ionotropic glutamate receptor antagonists. Under these conditions, interneurons burst fire synchronously, producing synchronized inhibitory postsynaptic potentials (sIPSPs) in pyramidal cells. Three different hilar interneuron subpopulations that contributed to the sIPSP were identified based on their projection properties and morphology. These three types were pyramidal-like stellate interneurons, spheroid interneurons, and oviform interneurons. Physiologically, pyramidal-like stellate interneurons could be differentiated from the other interneuron subpopulations because they generated short synchronized bursts of action potentials coincident with the hyperpolarizing and depolarizing -aminobutyric acid-A (GABA A )-mediated inhibitory postsynaptic potentials (IPSPs) recorded in pyramidal cells. The bursts in pyramidal-like stellate cells were abolished by theGABA A -receptor blocker, bicuculline. In contrast, spheroid interneurons of the dentate-hilus (D-H) border and oviform hilar interneurons exhibited prolonged bicuculline-resistant bursts that occurred coincident with the GABA B pyramidal cell sIPSPs. Pyramidal-like stellate interneurons likely did not contribute to the generation of synchronized GABA B responses in hippocampal pyramidal cells. Spheroid interneurons were unique among these subpopulations of interneurons in that the bicuculline-resistant bursts in spheroid interneurons were sustained by a synaptic depolarization that persisted in the presence of antagonists of ionotropic glutamate, GABA A and GABA B receptors [6-cyano-7-nitroquinoxaline-2,3-dione, 20 µM; 3-3(2-carboxipiperazine-4-yl)propyl-1-phosphonate, 20 µM; bicuculline, 10-15 µM; CGP 55845A, 20 µM]. This novel depolarizing potential reversed between 30 and 0 mV. No noticeable synaptic depolarization sustaining burst firing could be isolated in oviform interneurons, suggesting that firing in this interneuron subpopulation was synchronized by nonsynaptic mechanisms. The results of the