Anatomical properties of fast spiking cells that initiate synchronized population discharges in immature hippocampus.
Minislices of the CA3 hippocampal subfield were prepared from 10- to 15-day-old rats and exposed to penicillin, a GABAA receptor antagonist. Synchronized population discharges occurred spontaneously but could also be entrained by action potentials in single, fast spiking cells. This was unexpected, since fast spiking cells in the hippocampus are normally thought to be inhibitory interneurons. Experiments were thus undertaken to determine the anatomical identity of these cells. Biocytin injections showed that these cells had the anatomical feature of inhibitory interneurons. Two classes of cells were identified: basket cells (including cells with pyramidal or multipolar dendritic arbors) and bistratified cells. Basket cells had characteristic dense axonal arbors in the stratum pyramidale. They also possessed wide ranging axons in strata radiatum and oriens. The axons of bistratified cells avoided the cell body layer and produced a web-like plexus of axons in strata radiatum and oriens. In the majority of minislices, dye coupling was also observed. Interneurons were preferentially dye-coupled to other interneurons. We speculate that, in early life, hippocampal interneurons may have dualistic synaptic properties. Normally, they inhibit nearby pyramidal cells; however, when GABAA receptors are suppressed a secondary excitatory property of these cells is uncovered.
Cesare
C M
CM
Department of Anatomy, Cell Biology and Neurobiology, Albany Medical College, NY 12208, USA.
Smith
K L
KL
Rice
F L
FL
Swann
J W
JW
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D000833:Animals, Suckling; D002450:Cell Communication; D004396:Coloring Agents; D004058:Diffusion; D018756:GABA Antagonists / Q000494:pharmacology; D058787:GABA-A Receptor Antagonists; D006624:Hippocampus / Q000166:cytology* / Q000187:drug effects / Q000254:growth & development / Q000502:physiology; D007395:Interneurons / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D008239:Lysine / Q000031:analogs & derivatives; D009474:Neurons / Q000145:classification / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure*; D010406:Penicillins / Q000494:pharmacology; D017966:Pyramidal Cells / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D051381:Rats; D017208:Rats, Wistar
D004396:Coloring Agents; D018756:GABA Antagonists; D058787:GABA-A Receptor Antagonists; D010406:Penicillins; C013411:biocytin; D008239:Lysine