INHIBITORY CONNECTIONS OF FAST-SPIKING GABAERGIC INTERNEURONS ARE ALTERED IN CHRONICALLY EPILEPTOGENIC RAT NEOCORTEX
Abstract number :
2.097
Submission category :
Year :
2005
Submission ID :
5401
Source :
www.aesnet.org
Presentation date :
12/3/2005 12:00:00 AM
Published date :
Dec 2, 2005, 06:00 AM
Authors :
Fran Shen, Katrina M. Fu, Judith J. Li, Isabel Parada, Alberto Bacci, and David A. Prince
To assess structural abnormalities in GABAergic interneurons that might contribute to decreases in the frequency of spontaneous and miniature GABAergic currents in layer V pyramidal cells of epileptogenic chronic cortical isolations ([quot]undercut[quot], [quot]UC[quot]) we labeled fast-spiking (FS) interneurons in layer V of UC and control cortex and analyzed properties of axonal boutons and sites of presumed inhibitory synaptic contacts, using immunocytochemical techniques. Sensorimotor cortical isolations were made in P21 rats. 3 weeks later, layer V FS interneurons from UC (n = 7) and control cortex (n = 9) were intracellularly labeled with biocytin using patch clamp techniques. Sections containing labeled cells were processed for biocytin, vesicular GABA transporter (VGAT) and gephyrin, using standard immunocytochemical techniques. Confocal z-stack images of labeled cells and axonal and dendritic processes were analyzed using, Neurolucida and Volocity software to assess bouton diameters, density and co-localization with VGAT and/or gephyrin. (see Table below)
1. Axons of control versus UC FS neurons tended to have a greater proportion of boutons with a diameter [ge]1.0 [mu]m (big boutons).
2. A significantly larger % of total boutons colocalized with VGAT/gephyrin in control versus UC cells.
3. The % of small boutons ([lt] 1.0 [mu]m) was 2x greater in UC compared to control axons, however, a significantly smaller % of UC small boutons colocalized with VGAT or VGAT/gephyrin.
4. There were large reductions in the density of VGAT-containing structures in close apposition to dendrites of UC FS interneurons. 1. Structural remodeling occurs in axons of FS interneurons from partially isolated cortex.
2. Boutons containing VGAT closely applied to postsynaptic gephyrin, or to FS cell dendrites, are likely sites of inhibitory synapses and are decreased in UC axons.
3. Small boutons in UC axons may represent degenerating boutons, attempts by the injured interneuron to reestablish presynaptic structures, or boutons with altered and undetected pre- and postsynaptic markers.
4. These results are consistent with reductions in inhibitory currents found in previous experiments.[table1] (Supported by NIH grant NS 12151 from the NINDS and the Pimley Research Fund.)