Total number and distribution of inhibitory and excitatory synapses on hippocampal CA1 pyramidal cells
Section snippets
Experimental procedures
Seven adult (300 g) male Wistar rats (Charles River, Budapest) were used in these experiments. The animals were anesthetized with Equithesin (chlornembutal, 0.3 ml per 100 g of body weight). Biotinylated dextran amine (BDA, Molecular Probes; 10% in phosphate buffer, PB) was injected into the CA1 region at the following coordinates: Bregma: −3.2 mm; lateral: 2 mm (left and right); −2.4 mm from pia mater; and Bregma: −4.3 mm; lateral: 3 mm (left and right); −2.4 from pia mater. The BDA was
Light microscopy
Biotinylated dextran amine (BDA) injected into the CA1 area labeled a dense group of cells in the center of the injection site, as well as cells several hundred micrometers away from the injection site, probably by retrograde transport. These solitary cells (Fig. 1D) showed very dense precipitation of DAB so that dendrites could be followed and morphological features described in detail (Fig. 1C). The labeling visualized the fine dendritic spines and the dendrites could be followed until their
Discussion
The main findings of the present study are: (1) Pyramidal cell dendrites are heterogeneous in diameter, spine density and in the number of asymmetrical and symmetrical synaptic inputs. Strata radiatum and oriens dendrites (SRO) are similar to each other both at the light and electron microscopic levels and are different from stratum lacunosum-moleculare dendrites (SLM) with respect to dendritic shaft diameter, branching pattern and spine density. (2) The ratio of symmetrical versus asymmetrical
Acknowledgements
We are grateful to Drs L. Acsády, K. Kaila and R. Miles for helpful discussions and comments on the manuscript, and to Mrs E. Borók, Mr G. Goda and Mrs E. Oswald for excellent technical assistance. This work was supported by the Howard Hughes Medical Institute; the McDonnell Foundation; NIH (MH 54671); FPI grants, Ministerio de Edución y Ciencia, Spain; and OTKA (Hungarian Scientific Research Found, T23261), Hungary.
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