Direct synaptic contacts of medial septal efferents with somatostatin immunoreactive neurons in the rat hippocampus.
Anterogradely labeled projections from the medial septum to hippocampal somatostatin immunoreactive (SOM-i) neurons were studied with double-label immunocytochemistry under light (LM) and electron microscopic (EM) conditions. Medial septal projections were identified after injecting the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) followed by immunohistochemical visualization of PHA-L presynaptic terminal labeling and concurrent immunocytochemical staining of SOM in hippocampal target cell bodies. This double-label procedure yielded blue-black nickel enhanced DAB stained, PHA-L-immunoreactive terminals on light brown SOM-i neurons that were investigated by correlative LM and EM observations. PHA-L-labeled terminal contacts with often basket-like appearance were localized with highest densities on soma and proximal dendrites of SOM-i neurons in stratum oriens of Ammon's horn and hilus of dentate gyrus, and some minor projections to stratum pyramidale and radiatum. Most double-labeled contacts could be identified as symmetric type synapses equally divided over soma and proximal dendrites of several forms of SOM-i neurons. These data indicate monosynaptic regulation of the hippocampal intrinsic SOM system by septal input, which probably represents a peptidergic subpopulation of the hippocampal GABAergic system.
Yamano
M
M
Department of Animal Physiology, University of Groningen, AA Haren, The Netherlands.
Luiten
P G
PG
D000818:Animals; D006624:Hippocampus / Q000378:metabolism / Q000648:ultrastructure*; D007150:Immunohistochemistry; D008297:Male; D008854:Microscopy, Electron; D010835:Phytohemagglutinins; D051381:Rats; D011919:Rats, Inbred Strains; D012686:Septal Nuclei / Q000648:ultrastructure*; D013004:Somatostatin / Q000378:metabolism*; D013569:Synapses / Q000378:metabolism / Q000648:ultrastructure*
D010835:Phytohemagglutinins; C100156:leukoagglutinins, plants; D013004:Somatostatin