Yoder RM, Pang KCH (2003) Medial septal and entorhinal cortical involvement in hippocampal theta rhythm. Neuroscience 2003 Abstracts 719.19. Society for Neuroscience, New Orleans, LA.
Summary: Hippocampal theta rhythm (HPCΘ) may be involved in various phenomena, including attention and the acquisition of sensory information. Two projections to HPC, the medial septum-diagonal band of Broca (MSDB) and entorhinal cortex (EC), are involved in the activation or synchronization of HPCΘ. MSDB contains excitatory (cholinergic) and inhibitory (GABAergic) hippocampal projections via the fimbria/fornix. EC contains excitatory (glutamatergic) hippocampal projections via the perforant path (PP). MSDB GABAergic, MSDB cholinergic, or bilateral PP lesions eliminate HPCΘ during urethane anesthesia (HPCΘ-II). In unanesthetized recordings, each of these lesions reduced but did not eliminate HPCΘ during locomotion (HPCΘ-I); MSDB cholinergic and EC lesions caused similar reductions in HPCΘ, and MSDB GABAergic lesions produced a greater amplitude reduction. In an attempt to determine whether interactions exist between MSDB projections and EC, we examined the effects of MSDB GABAergic or cholinergic lesions combined with PP lesions on HPCΘ-I. MSDB GABAergic and cholinergic lesions were produced by intraseptal injection of kainic acid and 192 IgG-saporin, respectively. Bilateral PP lesions were produced by passing cathodal current through an electrode located in the medial PP. HPCΘ amplitude was calculated as the square root of power at peak frequency (Fourier analysis) within the HPCΘ range. The combination of MSDB GABAergic and PP lesions eliminated HPCΘ-I. The combination of MSDB cholinergic and PP lesions did not reduce HPCΘ-I amplitude further than MSDB cholinergic or PP lesions alone. These results suggest the inhibitory (MSDB GABAergic) and excitatory (MSDB cholinergic or EC glutamatergic) projections interact to support HPCΘ-I. Furthermore, MSDB cholinergic and EC glutamatergic projections may be redundant for HPCΘ-I.
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