Regulation of the activity of hippocampal stratum oriens interneurons by α7 nicotinic acetylcholine receptors

• Published in: Neuroscience Vol. 106; no. 1; pp. 55 - 67
• Main Authors: Buhler, A.V, Dunwiddie, T.V
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01-09-2001; Elsevier
• Subjects: acetylcholinesterase; Biological and medical sciences; Central nervous system; desensitization; Electrophysiology; Fundamental and applied biological sciences. Psychology; GABA; synaptic; theta rhythm; Vertebrates: nervous system and sense organs; α-bungarotoxin; APV, DL-(−)-2-amino-5-phosphonovaleric acid; BTX, α-bungarotoxin; VTA, ventral tegmental area; MEC, mecamylamine; DIC, differential interference contrast; nAChR, nicotinic acetylcholine receptor; acetylcholinesterase; DHβE, dihydro-β-erythroidine; MDL 72222, 1αH, 3α, 5αH-tropan-3-yl-3,5-dichlorobenzoate; HEPES, N-(2-hydroxyethyl)piperazine- N′-(2-ethanesulfonic acid); desensitization; synaptic; theta rhythm; DNQX, 6,7-dinitroquinoxaline-2,3(1 H,4 H)-dione; ACh, acetylcholine; MLA, methyllycaconitine; α-bungarotoxin; GABA; ANOVA, analysis of variance; EGTA, ethyleneglycol-bis(2-aminoethyl-ether)- N, N, N′, N′-tetraacetic acid; BMI, bicuculline methiodide; IPSP, inhibitory post-synaptic potential; Rat; Rodentia; Central nervous system; Electrophysiology; Gabaergic neurone; Interneuron; Cholinergic receptor; Vertebrata; Mammalia; Theta rhythm; Nicotinic receptor; Hippocampus; Brain (vertebrata)
• ISSN: 0306-4522; 1873-7544
• DOI: 10.1016/S0306-4522(01)00257-3

GABAergic interneurons have been shown to be a major target of cholinergic inputs to the hippocampus. Because these interneurons project to pyramidal neurons as well as other interneurons, activation of the cholinergic system is likely to produce a complex modulation of local inhibitory activity. To better understand the role of post-synaptic α7 nicotinic acetylcholine receptors in the hippocampus, we have characterized the effects of nicotinic agents on local interneurons of the rat CA1 stratum oriens in terms of activation, desensitization, and region of axonal termination. Fast application of acetylcholine onto stratum oriens interneurons during whole-cell recordings from hippocampal slices activated the majority of cells tested, and these responses were mediated almost entirely by α7 nicotinic acetylcholine receptors. Anatomical reconstructions showed no clear relationship between the acetylcholine responsivity of interneurons and the regions to which their axons project. Currents mediated by α7 receptors declined markedly during repetitive activation in the theta rhythm range (4–12 Hz) when activated by either pressure application or synaptic release of acetylcholine. However, the decay of α7 receptor-mediated currents was unaffected by treatment with the cholinesterase inhibitor neostigmine (10 nM–10 μM), suggesting that hydrolysis of acetylcholine is not a rate-limiting step in the termination of these responses.
From these findings we suggest that nicotinic receptor activity in this region has an extensive and complex impact on local inhibitory circuits that is mediated by activation of several classes of intrinsic GABAergic cells. In addition, desensitization of the α7 nicotinic acetylcholine receptor is likely to contribute to the decay of individual responses to pressure application of agonist, and may also act in a cumulative fashion to impair the ability of these receptors to support repetitive activity during trains of activation. If applicable to α7 receptor responses
in vivo, we suggest it may be difficult to enhance these responses for therapeutic purposes with cholinesterase inhibitors.