Septal innervation regulates the function of alpha7 nicotinic receptors in CA1 hippocampal interneurons.
The hippocampus receives substantial input from the medial septum/diagonal band of broca (MS/DB) via the fibria-fornix (FF). Projections from the MS/DB innervate hippocampal interneurons that express alpha7 nicotinic receptors and regulate excitation in principal cell populations. In the present report we used stereotaxic surgery, whole-cell patch clamping, and immunohistochemical techniques to evaluate the effects of FF and MS/DB lesions on alpha7 nicotinic receptors in stratum radiatum interneurons. Focal somatic application of ACh (1 mM) evoked methyllycaconitine (MLA)-sensitive currents that were markedly reduced following aspirative lesions of the FF. Reductions in current amplitudes were prevented or restored to levels not significantly different from controls following in vivo treatment with the alpha7-selective agonist GTS-21, and GTS-21 treatment did not change current amplitudes measured in tissue from unlesioned animals. MS/DB injections of the selective cholinergic neurotoxin 192 IgG-saporin did not affect alpha7 receptor currents, although MS/DB ChAT and hippocampal AChE immunolabeling were significantly reduced. In contrast, kainic acid lesions of the MS/DB, potentially more selective for GABAergic projection neurons, produced significant reductions in current amplitudes. These findings are the first to show functional changes in alpha7 receptors following hippocampal denervation and suggest that MS/DB hippocampal innervation regulates functional aspects of hippocampal alpha7 receptors. The results confirm hippocampal alpha7 nicotinic receptors as viable therapeutic targets in diseases that involve degradation of the septohippocampal pathway and may indicate that GABAergic MS/DB hippocampal input plays a more substantial role in the regulation of alpha7 nicotinic receptor function than MS/DB hippocampal cholinergic input.
Evelyn F. McKnight Brain Institute, Department of Neuroscience, University of Florida, Gainesville, FL 32610, USA.
Jeffrey S
JS
Thinschmidt
Charles J
CJ
Frazier
Michael A
MA
King
Edwin M
EM
Meyer
Roger L
RL
Papke
D000101:Acetyl-CoA C-Acetyltransferase / Q000378:metabolism; D000109:Acetylcholine / Q000494:pharmacology; D000157:Aconitine / Q000031:analogs & derivatives / Q000493:pharmacokinetics; D000818:Animals; D000831:Animals, Newborn; D001597:Benzylidene Compounds / Q000494:pharmacology; D002795:Choline O-Acetyltransferase / Q000378:metabolism; D004558:Electric Stimulation / Q000379:methods; D018690:Excitatory Amino Acid Agonists / Q000633:toxicity; D007839:Functional Laterality / Q000502:physiology; D006624:Hippocampus / Q000166:cytology*; D007150:Immunohistochemistry / Q000379:methods; D066298:In Vitro Techniques; D007395:Interneurons / Q000187:drug effects / Q000502:physiology*; D007608:Kainic Acid / Q000633:toxicity; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D018722:Nicotinic Agonists / Q000494:pharmacology; D018733:Nicotinic Antagonists / Q000493:pharmacokinetics; D018408:Patch-Clamp Techniques / Q000379:methods; D011725:Pyridines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011978:Receptors, Nicotinic / Q000502:physiology*; D012685:Sepharose / Q000031:analogs & derivatives / Q000633:toxicity; D020665:Septum of Brain / Q000293:injuries / Q000378:metabolism / Q000473:pathology / Q000502:physiology*; D014316:Tritium / Q000493:pharmacokinetics; D064569:alpha7 Nicotinic Acetylcholine Receptor
D001597:Benzylidene Compounds; C579165:Chrna7 protein, rat; D018690:Excitatory Amino Acid Agonists; D018722:Nicotinic Agonists; D018733:Nicotinic Antagonists; D011725:Pyridines; D011978:Receptors, Nicotinic; D064569:alpha7 Nicotinic Acetylcholine Receptor; C036210:immunoglobulin G-sepharose; D014316:Tritium; C054634:methyllycaconitine; C088936:3-(2,4-dimethoxybenzylidene)anabaseine; D012685:Sepharose; D002795:Choline O-Acetyltransferase; D000101:Acetyl-CoA C-Acetyltransferase; D000109:Acetylcholine; D007608:Kainic Acid; D000157:Aconitine