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Intrabulbar associational system in the rat olfactory bulb comprises cholecystokinin‐containing tufted cells that synapse onto the dendrites of GABAergic granule cells
Author(s) -
Liu WeiLin,
Shipley Michael T.
Publication year - 1994
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.903460407
Subject(s) - biocytin , biology , olfactory bulb , neuroscience , anterograde tracing , gabaergic , postsynaptic potential , granule cell , inhibitory postsynaptic potential , interneuron , excitatory postsynaptic potential , anatomy , central nervous system , dentate gyrus , biochemistry , receptor
The intrabulbar associational system (UAS) originates from tufted cells whose axons terminate in the internal plexiform layer (IPL) on the opposite side of the same olfactory bulb. The postsynaptic targets of the IAS are unknown. Subpopulations of tufted cells contain different neuropeptides and transmitters but it is not known if tufted cells forming the IAS are homogeneous with respect to neurotransmitters. Therefore, the goals of the present study were to identify thepostsynaptic targets of the IAS and to determine the major transmitter in this intrabulbar circuit. Biocytin anterograde tracing revealed that the axons of superficially situated tufted cells coursed directly to the IPL where they turned abruptly to run ventrally and dorsally to terminate in the IPL on the opposite side of the olfactory bulb. WGAapoHRP‐Au retrograde tracing combined with immunohistochernistry for CCK revealed that all tufted cells retrogradely labeled by WGAapoHRP‐Au injection in the IPL were immunoreactive for CCK Anterograde transport of biocytin combined with postembedding immunocytochemical goldlabeling for GABA demonstrated that labeled IAS axons terminate predominantly, if not exclusively, on GABAergic granule cell dendrites in the IPL. These results confirm that the IAS arises from tufted cells and is topographically organized. We further demonstrate that tufted cells forming the IAS use the neuropeptide CCK as a transmitter. In addition, we show that the postsynaptic targets of the CCKergic IAS are the dendrites of GABAergic granule cells coursing through the IPL toward the EPL. As CCK is generally an excitatory neuropeptide, we suggest that the IAS functions to excite topographically discrete populations of granule cells. This action may lead to inhibition of equally discrete populations of mitral/tufted cells. Thus, the IAS may be an intrabulbar inhibitory circuit that coordinates topographically organized neural networks in the olfactory bulb. © 1994 Wiley‐Liss, Inc.