title: Unusual target selectivity of perisomatic inhibitory cells in the hilar region of the rat hippocampus.
abstract: Perisomatic inhibitory innervation of all neuron types profoundly affects their firing characteristics and vulnerability. In this study we examined the postsynaptic targets of perisomatic inhibitory cells in the hilar region of the dentate gyrus where the proportion of potential target cells (excitatory mossy cells and inhibitory interneurons) is approximately equal. Both cholecystokinin (CCK)- and parvalbumin-immunoreactive basket cells formed multiple contacts on the somata and proximal dendrites of mossy cells. Unexpectedly, however, perisomatic inhibitory terminals arriving from these cell types largely ignored hilar GABAergic cell populations. Eighty-ninety percent of various GABAergic neurons including other CCK-containing basket cells received no input from CCK-positive terminals. Parvalbumin-containing cells sometimes innervated each other but avoided 75% of other GABAergic cells. Overall, a single mossy cell received 40 times more CCK-immunoreactive terminals and 15 times more parvalbumin-positive terminals onto its soma than the cell body of an average hilar GABAergic cell. In contrast to the pronounced target selectivity in the hilar region, CCK- and parvalbumin-positive neurons innervated each other via collaterals in stratum granulosum and moleculare. Our observations indicate that the inhibitory control in the hilar region is qualitatively different from other cortical areas at both the network level and the level of single neurons. The paucity of perisomatic innervation of hilar interneurons should have profound consequences on their action potential generation and on their ensemble behavior. These findings may help explain the unique physiological patterns observed in the hilus and the selective vulnerability of the hilar cell population in various pathophysiological conditions.
authors.affiliation: Institute of Experimental Medicine, Hungarian Academy of Sciences, H-1450 Budapest, Hungary.
authors.forename: L
authors.initials: L
authors.lastname: Acsády
authors.forename: I
authors.initials: I
authors.lastname: Katona
authors.forename: F J
authors.initials: FJ
authors.lastname: Martínez-Guijarro
authors.forename: G
authors.initials: G
authors.lastname: Buzsáki
authors.forename: T F
authors.initials: TF
authors.lastname: Freund
mesh_terms: D000818:Animals; D001369:Axons / Q000378:metabolism / Q000648:ultrastructure; D015740:Calcitonin Gene-Related Peptide / Q000378:metabolism; D002766:Cholecystokinin / Q000378:metabolism; D003712:Dendrites / Q000648:ultrastructure; D018891:Dentate Gyrus / Q000166:cytology / Q000378:metabolism; D006624:Hippocampus / Q000166:cytology* / Q000378:metabolism / Q000648:ultrastructure; D007395:Interneurons / Q000378:metabolism / Q000648:ultrastructure*; D008297:Male; D019599:Mossy Fibers, Hippocampal / Q000378:metabolism / Q000648:ultrastructure; D009433:Neural Inhibition / Q000502:physiology*; D010320:Parvalbumins / Q000378:metabolism; D017729:Presynaptic Terminals / Q000378:metabolism / Q000648:ultrastructure; D051381:Rats; D017208:Rats, Wistar; D018091:Receptors, AMPA / Q000378:metabolism
chemical_list: D010320:Parvalbumins; D018091:Receptors, AMPA; C104723:glutamate receptor ionotropic, AMPA 3; D002766:Cholecystokinin; D015740:Calcitonin Gene-Related Peptide; C104722:glutamate receptor ionotropic, AMPA 2