Ž . European Journal of Pharmacology 393 2000 179–195 www.elsevier.nlrlocaterejphar a 7 Receptor-selective agonists and modes of a 7 receptor activation Roger L. Papke a, ) , Edwin Meyer a , Tom Nutter a , Vladimir V. Uteshev b,1 a Department of Pharmacology and Therapeutics, Box 100267 JHMHSC, Medical College, UniÕersity of Florida, GainesÕille, FL 32610-0267, USA b Department of Molecular Physiology and Biophysics, UniÕersity of Vermont, GiÕen Building, Burlington, VT 05405, USA Accepted 21 January 2000 Abstract Ž . Ž . Ž The a7-selective agonists 3- 2,4-dimethoxybenzylidene -anabaseine GTS-21 , also known as DMXB, and 3- 4-hydroxy,2-methoxy- . Ž . benzylidene anabaseine 4OH-GTS-21 produce a variety of behavioral and cytoprotective effects that may be related to the activation of either large transient currents at high concentrations or small sustained currents at lower agonist concentrations. We are using acutely Ž . dissociated hypothalamic neurons, which express a central nervous system CNS a7-type receptor, to test a model for the concentration- dependent desensitization of a7-mediated responses. Our results confirm that 4OH-GTS-21 is a potent activator of neuronal a7 nicotinic-acetylcholine receptor. The rapid application of agonist leads to a brief period of maximal receptor-activation followed by desensitization. Rise rates, decay rates, and the degree to which current was desensitized were all concentration-dependent. Following the initial peak response to a 300-mM 4OH-GTS-21 application, current is reduced to baseline values within about 100 ms. Application of 30 mM 4OH-GTS-21 produced both a transient peak current and a sustained current that decayed only slowly after the removal of agonist. In the case of a 300-mM 4OH-GTS-21 application, after agonist was removed, we saw a rebound response up to the level of the 30-mM sustained current. The data, therefore, suggest that a sufficient level of agonist occupation can be retained on the receptor to promote activation for up to several hundred milliseconds. q 2000 Elsevier Science B.V. All rights reserved. Keywords: GTS-21; 4OH-GTS-21; a7 Receptor-selective agonist 1. Introduction Alzheimer’s disease is a progressive neurodegenerative disorder that causes significant memory-related dysfunc- tions. Therapeutic approaches for this disorder generally fall into either of the two categories: short-term enhance- ment of memory-function or longer-term protection of vulnerable neuronal populations. Examples of the former class of drug include the cholinesterase inhibitors Tacrine and Aricept, which are clinically accepted. Efforts to de- velop neuroprotective agents remain largely preclinical in Ž . nature and focus on nerve growth factor NGF or com- pounds with NGF-like properties. Recent evidence de- scribed below suggests that nicotine receptor agonists may provide both types of therapeutic improvement: behavioral ) Corresponding author. Tel.: q 1-352-392-4712; fax: q 1-352-392- 9696. Ž . E-mail address: rpapke@college.medical.ufl.edu R.L. Papke . 1 Present address: Department of Pharmacology and Therapeutics, Box 100267 JHMHSC, University of Florida, Gainesville, FL 32610-0267, USA. and neuroprotective. The identification of new nicotinic agents with potential therapeutic efficacy has drawn atten- tion to the a7, a-bungarotoxin-sensitive, neuronal nico- Ž tinic acetylcholine receptor subtype De Fiebre et al., . 1995 . High affinity a-bungarotoxin binding sites in mam- malian brain are associated with the a7 nicotinic acetyl- choline receptor subunit and are of roughly equal abun- dance to the high affinity nicotine binding sites which are believed to be primarily composed of a 4 and b 2 subunits. Despite well-documented effects of nicotine on a wide variety of memory-related behaviors, the effects of this drug in Alzheimer’s disease are not clear. In one study, nicotine improved word recall in a manner that approached Ž . significance P - 0.06 in Alzheimer’s patients at one dose, but the next higher dose caused too many side effects Ž . to continue the study Newhouse et al., 1988 . These results suggested that a more selective nicotinic agonist, acting on memory-related pathways without peripheral, Ž . and unwanted central nervous system CNS actions might elicit more significant memory-related improvement. Along Ž this line, a new experimental agent 3- 2,4-dimethoxyben- . Ž . zylidene -anabaseine GTS-21 , also known as DMXB, 0014-2999r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž . PII: S0014-2999 00 00009-1