JOURNAL OF NEUROCHEMISTRY
| 2016 | 136 | 217–219
doi: 10.1111/jnc.13236
A comment on “Positive allosteric modulation of alpha-7 nicotinic receptors promotes cell death by inducing Ca2+ release from the endoplasmic reticulum” by M. Cano-Abad et al. (2014) J Neurochem 133(3), 309–319 (DOI: 10.1111/jnc.13049).
Dear Editor, In a recent research article published in the May 2015 issue of this journal (Journal of Neurochemistry 2015, 133: 309– 319), Guerra-Alvarez et al. (2015) reported a cytotoxic potential of PNU120596, a Type-II positive allosteric modulator (PAMII) of a7 nicotinic acetylcholine receptors (a7 nAChRs). The authors used human SH-SY5Y neuroblastoma cells, rat organotypic hippocampal slice culture, electrophysiology and fluorescent Ca2+ imaging to evaluate cellular responsiveness and survival after various treatments with nicotinic agonists and PNU120596. The study concluded that treatments that combine a7 agonists with PNU120596 could result in cytotoxicity via a release of Ca2+ from intracellular stores and intracellular Ca2+ overloading. The results are interesting and may contribute to understanding the mechanisms of cytotoxicity as related to excessive activation of a7 nAChRs in the presence of PAMIIs. However, the impact could have been considerably greater if clinically- and physiologically relevant experimental conditions were used. The pharmacokinetics of PNU120596 and the common clinically relevant a7 agonists are available in scientific literature. Judging by the existing information, the study by Guerra-Alvarez et al. 2015 attempts to predict clinical limitations of PAMIIs from in vitro modeling of strictly overdose conditions. My skepticism about the value of this approach stems from the following illustrative comparisons of concentrations and exposure durations used in Guerra-Alvarez et al. 2015 versus previous in vivo studies: 3–10 lM PNU120596 versus estimated 0.5–1.5 lM found therapeutic in vivo (Hurst et al. 2005; McLean et al. 2012; Kalappa et al. 2013); 100 lM nicotine versus a maximum < 1 lM found in vivo (Russell et al. 1980; Gourlay and Benowitz 1997; Rose et al. 2010); and 10 lM PNU282987, a selective a7 agonist versus a realistic < 1 lM expected in vivo (Walker et al. 2006). The drug exposure duration was set to 24 h for a7 agonists and 48 h for PNU120596 versus ~ 8 h, the half-life time of PNU120596 in vivo (McLean et al. 2012) or ~ 2 h, the halflife time of nicotine in vivo (Russell et al. 1980; Gourlay and Benowitz 1997; Rose et al. 2010). One would understandably question the rationale for extreme drug concentrations and exposure durations employed by Guerra-Alvarez et al. 2015.
By purposely targeting only excessive levels of a7 nAChR activation, the study fuels the very ‘controversy’ it attempted to resolve: cytoprotection versus cytotoxicity in the presence of PAMIIs. This letter is written with the intention of facilitating discussion and efforts toward the resolution of an important question: are PAMIIs clinically safe? Clearly, the convincing answers to this question can only come from animal studies and clinical trials. Nevertheless, useful insights can be gained from the results of in vitro studies. The cytotoxic potential of PAMIIs has been recognized in the past as seen in at least two earlier in vitro studies (Ng et al. 2007; Williams et al. 2012) referenced by GuerraAlvarez et al. 2015 which have reported cytotoxicity by PNU120596 at concentrations above 3 lM. In contrast to Guerra-Alvarez et al. 2015; those previous studies used choline (a selective endogenous a7 nAChR agonist) and a broad range of drug concentrations. However these studies failed to detect cytotoxicity at a lower range of PNU120596 concentrations: i.e., 0.3–1 lM. In fact, in both studies a trend for increased cell viability was apparent for 0.3–1 lM PNU120596 [see Fig. 3 in (Ng et al. 2007) and Figs 4 and 6 in (Williams et al. 2012)]. This increase in cell viability is consistent with our own studies that demonstrated < 1 lM PNU120596 significantly reduced brain injury and neurological deficits after focal ischemia in a transient 90 min middle cerebral artery occlusion model of ischemic stroke in young adult rats (Kalappa et al. 2013; Sun et al. 2013), as well as significantly reduced brain cell damage and reactive gliosis after brain injury in a control cortical impact model of traumatic brain injury (Gatson et al. 2015). A concentration of < 1 lM PNU120596 can be achieved in rodents shortly after intravenous 1 mg/kg (Hurst et al. 2005) or subcutaneous 10–30 mg/kg (McLean et al. 2012; Kalappa et al. 2013) administration. In these in vivo studies, there was no
Received June 26, 2015; accepted July 2, 2015. Address correspondence and reprint requests to Victor Uteshev, Department of Pharmacology & Neuroscience, Institute of Aging and Alzheimer’s Disease Research, University of North Texas Health Science Center, Fort Worth, TX 76107, USA. E-mail: [email protected]
© 2015 International Society for Neurochemistry, J. Neurochem. (2016) 136, 217--219
217
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Letter to the Editor
indication of PNU120596 toxicity. On the contrary, PNU120596-treated animals seemed to exhibit an apparent lower rate of post-surgical mortality than vehicle-treated animals (Sun and Uteshev, unpublished). These previous in vitro studies by (Ng et al. 2007) and (Williams et al. 2012) have tested a broad range of experimental conditions including those likely present in vivo and have already created an informative picture of cytotoxic potential of excessive a7 activation in the presence of PNU120596 in vitro. Further extending these points to clinical settings is unnecessary, while exposing a7-expressing cells in a dish to mind-bogglingly high concentrations of nicotinic agents for extreme durations may only be relevant for modeling cases of medical malpractice. Therefore, the argument by Guerra-Alvarez et al. 2015 that ‘until now, no such modulators have succeeded in clinical trials, probably because of this cytotoxic effect’ has to be viewed with a healthy dose of skepticism. The solution to this type of cytotoxicity in a dish seems simple: reduce the drug concentrations and exposure durations (Ng et al. 2007; Williams et al. 2012). Another concern is Fig. 3 (Guerra-Alvarez et al. 2015). Although conceptually, Fig. 3 makes sense because it demonstrates that PNU120596 increases Ca2+ influx by reducing desensitization of a7 nAChRs, there is a clear problem with Fig. 3, as presented. For example, the second paragraph on page 314 of Guerra-Alvarez et al. 2015 states: ‘this pronounced elevation of [Ca2+]c in the presence of PNU/Nic was not observed in C-SH cells’. This statement seems to contradict with representative traces shown in Fig. 3b where the Area Under Curve (AUC) of the bottom trace (i.e., C-SH) seems to account for > 25% of the AUC of the top trace (i.e., a7-SH) (Fig. 3b). However, the corresponding summary graph in Fig. 3d shows virtually no AUC for C-SH traces (second column from right in Fig. 3d). Furthermore, the authors’ conclusion that ‘the PAMs of a7nAChRs caused marked Ca2+ overloading in the a7-SH cells’ seems biased as both top and bottom traces shown in Fig. 3b can be equally defined as an overload because the normal load is not defined. Moreover, ‘nicotine alone’ and ‘nicotine plus PNU’ responses as shown cannot be meaningfully compared because the durations of drug application as shown in Fig. 3a and Fig. 3b are very different: ~ 30 s as illustrated in Fig. 3a versus ~ 10 min as illustrated in Fig. 3b (durations are marked as horizontal bars below traces). Thus, as presented, Fig. 3 is overloaded with glitches. An additional concern is Fig. 6 (Supporting Information) which indicates that activation of voltage-dependent calcium channels is required for cytotoxicity by PNU120596. This conclusion assumes that nifedipine and x-conotoxin exhibit little to none inhibitory efficacy for a7 nAChRs. That may be true in the absence of PNU120596, but may not hold anymore in the presence of PNU120596 as we have discussed recently (Kalappa and Uteshev 2013). By stabilizing the open
state of a7 nAChRs, PNU120596 modifies the pharmacology of these receptors and makes them more susceptible to open channel block (Kalappa and Uteshev 2013). The lack of efficacy of nifedipine and x-conotoxin for a7 nAChRs in the presence of PNU120596 needs to be confirmed to avoid misinterpretation of data summarized in Fig. 6. If indeed nifedipine and x-conotoxin cause a7 open channel block in the presence of PNU120596 then, the contribution of voltage-dependent calcium channels to cytotoxicity elicited by excessive a7 activation may be overstated. In summary, while (Guerra-Alvarez et al. 2015) provide interesting insights into potential mechanisms of cytotoxicity as related to excessive activation of a7 nAChRs in the presence of PAMIIs, the study is not as informative as it could have been because it models pharmacological conditions not achievable in realistic clinical settings. In general, the use of clinically relevant drug concentrations and experimental conditions in in vitro studies of cytotoxicity should become obligatory because the continuing global burden of neurological disorders, cerebral stroke and traumatic brain injury demands immediate effective solutions. Victor Uteshev Department of Pharmacology & Neuroscience, Institute of Aging and Alzheimer’s Disease Research, University of North Texas Health Science Center, Fort Worth, Texas, USA The authors of the article were offered the opportunity to reply, but did not respond.
References Gatson J. W., Simpkins J. W. and Uteshev V. V. (2015) High therapeutic potential of positive allosteric modulation of alpha7 nAChRs in a rat model of traumatic brain injury: proof-of-concept. Brain Res. Bull. 112C, 35–41. Gourlay S. G. and Benowitz N. L. (1997) Arteriovenous differences in plasma concentration of nicotine and catecholamines and related cardiovascular effects after smoking, nicotine nasal spray, and intravenous nicotine. Clin. Pharmacol. Ther. 62, 453–463. Guerra-Alvarez M., Moreno-Ortega A. J., Navarro E., FernandezMorales J. C., Egea J., Lopez M. G. and Cano-Abad M. F. (2015) Positive allosteric modulation of alpha-7 nicotinic receptors promotes cell death by inducing Ca(2+) release from the endoplasmic reticulum. J. Neurochem. 133, 309–319. Hurst R. S., Hajos M., Raggenbass M. et al. (2005) A novel positive allosteric modulator of the alpha7 neuronal nicotinic acetylcholine receptor: in vitro and in vivo characterization. J. Neurosci. 25, 4396–4405. Kalappa B. I. and Uteshev V. V. (2013) The dual effect of PNU-120596 on alpha7 nicotinic acetylcholine receptor channels. Eur. J. Pharmacol. 718, 226–234. Kalappa B. I., Sun F., Johnson S. R., Jin K. and Uteshev V. V. (2013) A positive allosteric modulator of alpha7 nAChRs augments neuroprotective effects of endogenous nicotinic agonists in cerebral ischaemia. Br. J. Pharmacol. 169, 1862–1878.
© 2015 International Society for Neurochemistry, J. Neurochem. (2016) 136, 217--219
Letter to the Editor
McLean S. L., Idris N. F., Grayson B., Gendle D. F., Mackie C., Lesage A. S., Pemberton D. J. and Neill J. C. (2012) PNU-120596, a positive allosteric modulator of alpha7 nicotinic acetylcholine receptors, reverses a sub-chronic phencyclidine-induced cognitive deficit in the attentional set-shifting task in female rats. J. Psychopharmacol. 26, 1265–1270. Ng H. J., Whittemore E. R., Tran M. B., Hogenkamp D. J., Broide R. S., Johnstone T. B., Zheng L., Stevens K. E. and Gee K. W. (2007) Nootropic alpha7 nicotinic receptor allosteric modulator derived from GABAA receptor modulators. Proc. Natl Acad. Sci. USA 104, 8059–8064. Rose J. E., Mukhin A. G., Lokitz S. J., Turkington T. G., Herskovic J., Behm F. M., Garg S. and Garg P. K. (2010) Kinetics of brain nicotine accumulation in dependent and nondependent smokers assessed with PET and cigarettes containing 11C-nicotine. Proc. Natl Acad. Sci. USA 107, 5190–5195.
219
Russell M. A., Jarvis M., Iyer R. and Feyerabend C. (1980) Relation of nicotine yield of cigarettes to blood nicotine concentrations in smokers. Br. Med. J. 280, 972–976. Sun F., Jin K. and Uteshev V. V. (2013) A Type-II Positive Allosteric Modulator of alpha7 nAChRs Reduces Brain Injury and Improves Neurological Function after Focal Cerebral Ischemia in Rats. PLoS ONE 8, e73581. Walker D. P., Wishka D. G., Piotrowski D. W. et al. (2006) Design, synthesis, structure-activity relationship, and in vivo activity of azabicyclic aryl amides as alpha7 nicotinic acetylcholine receptor agonists. Bioorg. Med. Chem. 14, 8219–8248. Williams D. K., Peng C., Kimbrell M. R. and Papke R. L. (2012) Intrinsically low open probability of alpha7 nicotinic acetylcholine receptors can be overcome by positive allosteric modulation and serum factors leading to the generation of excitotoxic currents at physiological temperatures. Mol. Pharmacol. 82, 746–759.
© 2015 International Society for Neurochemistry, J. Neurochem. (2016) 136, 217--219
| 2016 | 136 | 217–219
doi: 10.1111/jnc.13236
A comment on “Positive allosteric modulation of alpha-7 nicotinic receptors promotes cell death by inducing Ca2+ release from the endoplasmic reticulum” by M. Cano-Abad et al. (2014) J Neurochem 133(3), 309–319 (DOI: 10.1111/jnc.13049).
Dear Editor, In a recent research article published in the May 2015 issue of this journal (Journal of Neurochemistry 2015, 133: 309– 319), Guerra-Alvarez et al. (2015) reported a cytotoxic potential of PNU120596, a Type-II positive allosteric modulator (PAMII) of a7 nicotinic acetylcholine receptors (a7 nAChRs). The authors used human SH-SY5Y neuroblastoma cells, rat organotypic hippocampal slice culture, electrophysiology and fluorescent Ca2+ imaging to evaluate cellular responsiveness and survival after various treatments with nicotinic agonists and PNU120596. The study concluded that treatments that combine a7 agonists with PNU120596 could result in cytotoxicity via a release of Ca2+ from intracellular stores and intracellular Ca2+ overloading. The results are interesting and may contribute to understanding the mechanisms of cytotoxicity as related to excessive activation of a7 nAChRs in the presence of PAMIIs. However, the impact could have been considerably greater if clinically- and physiologically relevant experimental conditions were used. The pharmacokinetics of PNU120596 and the common clinically relevant a7 agonists are available in scientific literature. Judging by the existing information, the study by Guerra-Alvarez et al. 2015 attempts to predict clinical limitations of PAMIIs from in vitro modeling of strictly overdose conditions. My skepticism about the value of this approach stems from the following illustrative comparisons of concentrations and exposure durations used in Guerra-Alvarez et al. 2015 versus previous in vivo studies: 3–10 lM PNU120596 versus estimated 0.5–1.5 lM found therapeutic in vivo (Hurst et al. 2005; McLean et al. 2012; Kalappa et al. 2013); 100 lM nicotine versus a maximum < 1 lM found in vivo (Russell et al. 1980; Gourlay and Benowitz 1997; Rose et al. 2010); and 10 lM PNU282987, a selective a7 agonist versus a realistic < 1 lM expected in vivo (Walker et al. 2006). The drug exposure duration was set to 24 h for a7 agonists and 48 h for PNU120596 versus ~ 8 h, the half-life time of PNU120596 in vivo (McLean et al. 2012) or ~ 2 h, the halflife time of nicotine in vivo (Russell et al. 1980; Gourlay and Benowitz 1997; Rose et al. 2010). One would understandably question the rationale for extreme drug concentrations and exposure durations employed by Guerra-Alvarez et al. 2015.
By purposely targeting only excessive levels of a7 nAChR activation, the study fuels the very ‘controversy’ it attempted to resolve: cytoprotection versus cytotoxicity in the presence of PAMIIs. This letter is written with the intention of facilitating discussion and efforts toward the resolution of an important question: are PAMIIs clinically safe? Clearly, the convincing answers to this question can only come from animal studies and clinical trials. Nevertheless, useful insights can be gained from the results of in vitro studies. The cytotoxic potential of PAMIIs has been recognized in the past as seen in at least two earlier in vitro studies (Ng et al. 2007; Williams et al. 2012) referenced by GuerraAlvarez et al. 2015 which have reported cytotoxicity by PNU120596 at concentrations above 3 lM. In contrast to Guerra-Alvarez et al. 2015; those previous studies used choline (a selective endogenous a7 nAChR agonist) and a broad range of drug concentrations. However these studies failed to detect cytotoxicity at a lower range of PNU120596 concentrations: i.e., 0.3–1 lM. In fact, in both studies a trend for increased cell viability was apparent for 0.3–1 lM PNU120596 [see Fig. 3 in (Ng et al. 2007) and Figs 4 and 6 in (Williams et al. 2012)]. This increase in cell viability is consistent with our own studies that demonstrated < 1 lM PNU120596 significantly reduced brain injury and neurological deficits after focal ischemia in a transient 90 min middle cerebral artery occlusion model of ischemic stroke in young adult rats (Kalappa et al. 2013; Sun et al. 2013), as well as significantly reduced brain cell damage and reactive gliosis after brain injury in a control cortical impact model of traumatic brain injury (Gatson et al. 2015). A concentration of < 1 lM PNU120596 can be achieved in rodents shortly after intravenous 1 mg/kg (Hurst et al. 2005) or subcutaneous 10–30 mg/kg (McLean et al. 2012; Kalappa et al. 2013) administration. In these in vivo studies, there was no
Received June 26, 2015; accepted July 2, 2015. Address correspondence and reprint requests to Victor Uteshev, Department of Pharmacology & Neuroscience, Institute of Aging and Alzheimer’s Disease Research, University of North Texas Health Science Center, Fort Worth, TX 76107, USA. E-mail: [email protected]
© 2015 International Society for Neurochemistry, J. Neurochem. (2016) 136, 217--219
217
218
Letter to the Editor
indication of PNU120596 toxicity. On the contrary, PNU120596-treated animals seemed to exhibit an apparent lower rate of post-surgical mortality than vehicle-treated animals (Sun and Uteshev, unpublished). These previous in vitro studies by (Ng et al. 2007) and (Williams et al. 2012) have tested a broad range of experimental conditions including those likely present in vivo and have already created an informative picture of cytotoxic potential of excessive a7 activation in the presence of PNU120596 in vitro. Further extending these points to clinical settings is unnecessary, while exposing a7-expressing cells in a dish to mind-bogglingly high concentrations of nicotinic agents for extreme durations may only be relevant for modeling cases of medical malpractice. Therefore, the argument by Guerra-Alvarez et al. 2015 that ‘until now, no such modulators have succeeded in clinical trials, probably because of this cytotoxic effect’ has to be viewed with a healthy dose of skepticism. The solution to this type of cytotoxicity in a dish seems simple: reduce the drug concentrations and exposure durations (Ng et al. 2007; Williams et al. 2012). Another concern is Fig. 3 (Guerra-Alvarez et al. 2015). Although conceptually, Fig. 3 makes sense because it demonstrates that PNU120596 increases Ca2+ influx by reducing desensitization of a7 nAChRs, there is a clear problem with Fig. 3, as presented. For example, the second paragraph on page 314 of Guerra-Alvarez et al. 2015 states: ‘this pronounced elevation of [Ca2+]c in the presence of PNU/Nic was not observed in C-SH cells’. This statement seems to contradict with representative traces shown in Fig. 3b where the Area Under Curve (AUC) of the bottom trace (i.e., C-SH) seems to account for > 25% of the AUC of the top trace (i.e., a7-SH) (Fig. 3b). However, the corresponding summary graph in Fig. 3d shows virtually no AUC for C-SH traces (second column from right in Fig. 3d). Furthermore, the authors’ conclusion that ‘the PAMs of a7nAChRs caused marked Ca2+ overloading in the a7-SH cells’ seems biased as both top and bottom traces shown in Fig. 3b can be equally defined as an overload because the normal load is not defined. Moreover, ‘nicotine alone’ and ‘nicotine plus PNU’ responses as shown cannot be meaningfully compared because the durations of drug application as shown in Fig. 3a and Fig. 3b are very different: ~ 30 s as illustrated in Fig. 3a versus ~ 10 min as illustrated in Fig. 3b (durations are marked as horizontal bars below traces). Thus, as presented, Fig. 3 is overloaded with glitches. An additional concern is Fig. 6 (Supporting Information) which indicates that activation of voltage-dependent calcium channels is required for cytotoxicity by PNU120596. This conclusion assumes that nifedipine and x-conotoxin exhibit little to none inhibitory efficacy for a7 nAChRs. That may be true in the absence of PNU120596, but may not hold anymore in the presence of PNU120596 as we have discussed recently (Kalappa and Uteshev 2013). By stabilizing the open
state of a7 nAChRs, PNU120596 modifies the pharmacology of these receptors and makes them more susceptible to open channel block (Kalappa and Uteshev 2013). The lack of efficacy of nifedipine and x-conotoxin for a7 nAChRs in the presence of PNU120596 needs to be confirmed to avoid misinterpretation of data summarized in Fig. 6. If indeed nifedipine and x-conotoxin cause a7 open channel block in the presence of PNU120596 then, the contribution of voltage-dependent calcium channels to cytotoxicity elicited by excessive a7 activation may be overstated. In summary, while (Guerra-Alvarez et al. 2015) provide interesting insights into potential mechanisms of cytotoxicity as related to excessive activation of a7 nAChRs in the presence of PAMIIs, the study is not as informative as it could have been because it models pharmacological conditions not achievable in realistic clinical settings. In general, the use of clinically relevant drug concentrations and experimental conditions in in vitro studies of cytotoxicity should become obligatory because the continuing global burden of neurological disorders, cerebral stroke and traumatic brain injury demands immediate effective solutions. Victor Uteshev Department of Pharmacology & Neuroscience, Institute of Aging and Alzheimer’s Disease Research, University of North Texas Health Science Center, Fort Worth, Texas, USA The authors of the article were offered the opportunity to reply, but did not respond.
References Gatson J. W., Simpkins J. W. and Uteshev V. V. (2015) High therapeutic potential of positive allosteric modulation of alpha7 nAChRs in a rat model of traumatic brain injury: proof-of-concept. Brain Res. Bull. 112C, 35–41. Gourlay S. G. and Benowitz N. L. (1997) Arteriovenous differences in plasma concentration of nicotine and catecholamines and related cardiovascular effects after smoking, nicotine nasal spray, and intravenous nicotine. Clin. Pharmacol. Ther. 62, 453–463. Guerra-Alvarez M., Moreno-Ortega A. J., Navarro E., FernandezMorales J. C., Egea J., Lopez M. G. and Cano-Abad M. F. (2015) Positive allosteric modulation of alpha-7 nicotinic receptors promotes cell death by inducing Ca(2+) release from the endoplasmic reticulum. J. Neurochem. 133, 309–319. Hurst R. S., Hajos M., Raggenbass M. et al. (2005) A novel positive allosteric modulator of the alpha7 neuronal nicotinic acetylcholine receptor: in vitro and in vivo characterization. J. Neurosci. 25, 4396–4405. Kalappa B. I. and Uteshev V. V. (2013) The dual effect of PNU-120596 on alpha7 nicotinic acetylcholine receptor channels. Eur. J. Pharmacol. 718, 226–234. Kalappa B. I., Sun F., Johnson S. R., Jin K. and Uteshev V. V. (2013) A positive allosteric modulator of alpha7 nAChRs augments neuroprotective effects of endogenous nicotinic agonists in cerebral ischaemia. Br. J. Pharmacol. 169, 1862–1878.
© 2015 International Society for Neurochemistry, J. Neurochem. (2016) 136, 217--219
Letter to the Editor
McLean S. L., Idris N. F., Grayson B., Gendle D. F., Mackie C., Lesage A. S., Pemberton D. J. and Neill J. C. (2012) PNU-120596, a positive allosteric modulator of alpha7 nicotinic acetylcholine receptors, reverses a sub-chronic phencyclidine-induced cognitive deficit in the attentional set-shifting task in female rats. J. Psychopharmacol. 26, 1265–1270. Ng H. J., Whittemore E. R., Tran M. B., Hogenkamp D. J., Broide R. S., Johnstone T. B., Zheng L., Stevens K. E. and Gee K. W. (2007) Nootropic alpha7 nicotinic receptor allosteric modulator derived from GABAA receptor modulators. Proc. Natl Acad. Sci. USA 104, 8059–8064. Rose J. E., Mukhin A. G., Lokitz S. J., Turkington T. G., Herskovic J., Behm F. M., Garg S. and Garg P. K. (2010) Kinetics of brain nicotine accumulation in dependent and nondependent smokers assessed with PET and cigarettes containing 11C-nicotine. Proc. Natl Acad. Sci. USA 107, 5190–5195.
219
Russell M. A., Jarvis M., Iyer R. and Feyerabend C. (1980) Relation of nicotine yield of cigarettes to blood nicotine concentrations in smokers. Br. Med. J. 280, 972–976. Sun F., Jin K. and Uteshev V. V. (2013) A Type-II Positive Allosteric Modulator of alpha7 nAChRs Reduces Brain Injury and Improves Neurological Function after Focal Cerebral Ischemia in Rats. PLoS ONE 8, e73581. Walker D. P., Wishka D. G., Piotrowski D. W. et al. (2006) Design, synthesis, structure-activity relationship, and in vivo activity of azabicyclic aryl amides as alpha7 nicotinic acetylcholine receptor agonists. Bioorg. Med. Chem. 14, 8219–8248. Williams D. K., Peng C., Kimbrell M. R. and Papke R. L. (2012) Intrinsically low open probability of alpha7 nicotinic acetylcholine receptors can be overcome by positive allosteric modulation and serum factors leading to the generation of excitotoxic currents at physiological temperatures. Mol. Pharmacol. 82, 746–759.
© 2015 International Society for Neurochemistry, J. Neurochem. (2016) 136, 217--219
