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1 Pharmacology and Therapeutics, University of Florida, Gainseville, FL, USA
2 Neuroscience, Case Western Reserve University, Cleveland, OH, USA
3 Pharmacology and Therapeutics, University of Florida, Gainseville, FL, USA; Neuroscience, University of Florida, Gainseville, FL, USA
* To whom correspondence should be addressed. E-mail: cjfraz{at}ufl.edu.
Although the dentate gyrus is one of the primary targets of septo-hippocampal cholinergic afferents, relatively little is known about the cholinergic physiology of neurons in the area. By combining whole-cell-patch-clamp recording with brief local application of exogenous agonists in horizontal slices, we found that there is robust expression of functional somatic
7-containing nAChRs on molecular layer interneurons, hilar interneurons, and the glutamatergic mossy cells of the dentate hilus. In contrast, the principle output neurons of the dentate gyrus, the granule cells, are generally unresponsive to focal somatic or dendritic application of acetylcholine (ACh) in the presence of atropine. We also demonstrate that cholinergic activation of
7-containing nAChRs on the subgranular interneurons of the hilus can produce methyllycaconitine (MLA) sensitive GABAergic inhibitory postsynaptic currents (IPSCs) in nearby granule cells and enhance the amplitude of an electrically evoked monosynaptic IPSC. Further, activation of
7-containing nAChRs on subgranular interneurons that is timed to coincide with synaptic release of glutamate onto these cells will enhance the functional inhibition of granule cells. These findings suggest that a complex interplay between glutamatergic afferents from the entorhinal cortex and cholinergic afferents from the medial septum could be involved in the normal regulation of granule cell function. Such a relationship between these two afferent pathways could be highly relevant to the study of both age-related memory dysfunction, and disorders involving regulation of excitability, such as temporal lobe epilepsy.
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