Postsynaptic targets of somatostatin-immunoreactive interneurons in the rat hippocampus
Section snippets
Perfusion and preparation of tissue sections
Eight male Wistar rats (300–350 g, two-months-old; Charles River, Budapest, Hungary) were deeply anaesthetized by Equithesin (chlornembutal, 0.3 ml/100 g), and perfused through the heart first with saline followed by a phosphate-buffered (PB, 0.1 M) fixative containing 4% paraformaldehyde, 0.15% picric acid and 0.05% glutaraldehyde in the case of series A (n=5) for single somatostatin-immunostaining and for somatostatin–parvalbumin, somatostatin–CCK, somatostatin–calretinin, somatostatin–VIP,
General pattern of somatostatin-immunostaining in the hippocampus
Somatostatin-immunoreactive neurons showed the same basic morphological features as observed in several previous studies in the rat21, 34, 36, 38, 50, 64with some additional morphological details due to the enhanced sensitivity of the present antiserum. Briefly, cell bodies were located in stratum oriens of the CA1, stratum oriens and stratum lucidum of the CA3 regions and in the hilus of the dentate gyrus (Fig. 1A). Occasionally, some cells were also found in stratum radiatum of the CA1 and
Discussion
On the basis of morphological characteristics, somatostatin-immunoreactive interneurons could be separated into three distinct subtypes, (i) HIPP cells of the dentate gyrus, (ii) conventional O-LM cells in stratum oriens of the CA1 and CA3 regions and (iii) neurons with dendrites similar to O-LM cells, but with a characteristically different axon. The first two subtypes have dense axonal projections to stratum lacunosum-moleculare (O-LM) or stratum moleculare (HIPP), where entorhinal afferents
Conclusion
The present data demonstrate that somatostatin-containing GABAergic interneurons driven in a feedback manner terminate predominantly on the most distal dendritic segments of pyramidal cells in conjunction with entorhinal afferents (i.e. they are O-LM and HIPP cells). We propose that, if the role of theta oscillation is to separate signal transmission from background firing in time,[19]then these feedback dendritic inhibitory cells may help confine time periods when entorhinal synapses on
Acknowledgements
We are grateful to Dr T. J. Görcs for antisera against somatostatin, vasoactive intestinal polypeptide and cholecystokinin, to Dr K. G. Baimbridge and to Dr J. H. Rogers for antisera against parvalbumin and calretinin, respectively, and to Dr P. Somogyi for antisera against GABA. The valuable discussions with Drs A. M. Thomson, Gy. Buzsáki, H. Markram and R. Miles concerning the activation of O-LM cells, and the time-course of back-propagating action potentials and disynaptic IPSPs are highly
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