Postsynaptic targets of somatostatin-immunoreactive interneurons in the rat hippocampus.
Two characteristic interneuron types in the hippocampus, the so-called hilar perforant path-associated cells in the dentate gyrus and stratum oriens/lacunosum-moleculare neurons in the CA3 and CA1 regions, were suggested to be involved in feedback circuits. In the present study, interneurons identical to these cell populations were visualized by somatostatin-immunostaining, then reconstructed, and processed for double-immunostaining and electron microscopy to establish their postsynaptic target selectivity. A combination of somatostatin-immunostaining with immunostaining for GABA or other interneuron markers revealed a quasi-random termination pattern. The vast majority of postsynaptic targets were GABA-negative dendritic shafts and spines of principal cells (76%), whereas other target elements contained GABA (8%). All of the examined neurochemically defined interneuron types (parvalbumin-, calretinin-, vasoactive intestinal polypeptide-, cholecystokinin-, substance P receptor-immunoreactive neurons) received innervation from somatostatin-positive boutons. Recent anatomical and electrophysiological data showed that the main excitatory inputs of somatostatin-positive interneurons originate from local principal cells. The present data revealed a massive GABAergic innervation of distal dendrites of local principal cells by these feedback driven neurons, which are proposed to control the efficacy and plasticity of entorhinal synaptic input as a function of local principal cell activity and synchrony.
Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest.
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Katona
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Acsády
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Freund
D000818:Animals; D018891:Dentate Gyrus / Q000166:cytology / Q000502:physiology; D006624:Hippocampus / Q000166:cytology / Q000502:physiology*; D007150:Immunohistochemistry; D007395:Interneurons / Q000166:cytology / Q000502:physiology*; D008297:Male; D016253:Microscopy, Immunoelectron; D008959:Models, Neurological; D009473:Neuronal Plasticity; D017966:Pyramidal Cells / Q000166:cytology / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D013004:Somatostatin / Q000032:analysis*; D013569:Synapses / Q000502:physiology* / Q000648:ultrastructure; D005680:gamma-Aminobutyric Acid / Q000032:analysis
D013004:Somatostatin; D005680:gamma-Aminobutyric Acid