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Involvement of GABAergic and cholinergic medial septal neurons in hippocampal theta rhythm
Author(s) -
Yoder Ryan M.,
Pang Kevin C.H.
Publication year - 2005
Publication title -
hippocampus
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.767
H-Index - 155
eISSN - 1098-1063
pISSN - 1050-9631
DOI - 10.1002/hipo.20062
Subject(s) - neuroscience , diagonal band of broca , hippocampal formation , gabaergic , kainic acid , cholinergic , hippocampus , muscimol , chemistry , cholinergic neuron , inhibitory postsynaptic potential , medicine , psychology , gabaa receptor , glutamate receptor , receptor
Hippocampal theta rhythm (HPCθ) may be important for various phenomena, including attention and acquisition of sensory information. Two types of HPCθ (types I and II) exist based on pharmacological, behavioral, and electrophysiological characteristics. Both types occur during locomotion, whereas only type II (atropine‐sensitive) is present under urethane anesthesia. The circuit of HPCθ synchronization includes the medial septum‐diagonal band of Broca (MSDB), with cholinergic and γ‐aminobutyric acid (GABA)ergic neurons comprising the two main projections from MSDB to HPC. The primary aim of the present study was to assess the effects of GABAergic MSDB lesions on urethane‐ and locomotion‐related HPCθ, and compare these effects to those of cholinergic MSDB lesions. Saline, kainic acid (KA), or 192 IgG‐saporin (SAP) was injected into MSDB before recording. KA preferentially destroys GABAergic MSDB neurons, whereas SAP selectively eliminates cholinergic MSDB neurons. A fixed recording electrode was placed in the dentate mid‐molecular layer, and stimulating electrodes were placed in the posterior hypothalamus (PH), and medial perforant path (PP). Under urethane anesthesia, HPCθ was induced by tail pinch, PH stimulation, and systemic physostigmine; none of the rats with KA or SAP showed HPCθ in any of these conditions. During locomotion, HPCθ was attenuated, but not eliminated, in rats with KA or SAP lesions. Intraseptal KA in combination with either intraseptal SAP or PP lesions reduced locomotion‐related HPCθ beyond that observed with each lesion alone, virtually eliminating HPCθ. In contrast, intraseptal SAP combined with PP lesions did not reduce HPCθ beyond the effect of each lesion alone. We conclude that both GABAergic and cholinergic MSDB neurons are necessary for HPCθ under urethane, and that each of these septohippocampal projections contributes to HPCθ during locomotion. © 2005 Wiley‐Liss, Inc.