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Article

Recovery from AMPA Receptor Potentiation by Ampakines

by
Daniel P. Radin
1,*,
Rok Cerne
1,2,
Jodi L. Smith
2,
Jeffrey M. Witkin
1,2 and
Arnold Lippa
1
1
RespireRx Pharmaceuticals Inc., 126 Valley Road, Glen Rock, NJ 07452, USA
2
Laboratory of Antiepileptic Drug Discovery, Ascension St. Vincent Hospital, Indianapolis, IN 46260, USA
*
Author to whom correspondence should be addressed.
Future Pharmacol. 2025, 5(2), 27; https://doi.org/10.3390/futurepharmacol5020027
Submission received: 9 April 2025 / Revised: 26 May 2025 / Accepted: 28 May 2025 / Published: 31 May 2025
Browse Figures
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Abstract

:
Background: Ampakines are a family of molecules that enhance the functioning of AMPA-glutamate receptors (AMPAR). High-impact ampakines completely offset receptor desensitization and enhance agonist binding affinity, while low-impact ampakines only modestly affect receptor desensitization and do not alter agonist binding affinity. Nonetheless, little is known about AMPAR recovery following ampakine treatment. Methods: Herein, we study the effects of ampakines on AMPAR recovery and the interaction between high- and low-impact ampakines. Results: The high-impact ampakine CX729 did not induce any current in the absence of glutamate, but it dramatically increased glutamate-induced steady-state inward currents. Recoveries from the enhancement were significantly slower than those for the low-impact ampakine CX516, as was also seen on miniature synaptic currents. Electrophysiological interaction studies suggest that high- and low-impact ampakines may have different binding sites. We further investigated the induction of the potentiated response by measuring glutamate-induced responses after transient applications of CX729 or CX729 plus glutamate. Under both circumstances, subsequent application of glutamate yielded comparably potentiated responses. Furthermore, the recovery time was not different if saline was substituted for glutamate during the recovery period. Conclusions: These observations show that AMPAR potentiation by CX729 does not require the simultaneous presence of glutamate, nor is the slow reversal of the effects of the ampakine altered by subsequent receptor activation. Hence, the slow recovery from the effects of these select ampakines on the AMPAR may be the result of slow dissociation kinetics. We posit that the slow recovery of AMPAR from high-impact ampakines may contribute to the seizurogenic effects of this drug class and that high-impact ampakines that allow for more rapid AMPAR recovery may be safer and more clinically viable candidates.

1. Introduction

Positive allosteric modulation of AMPA-glutamate receptors (AMPAR) by ampakines has emerged as a prospective therapeutic avenue for treating several neurological and neuropsychiatric disorders that are characterized by deficient glutamatergic signaling. It has been demonstrated that neurodegenerative disorders such as Parkinson’s [1,2,3], Huntington’s [4,5], Alzheimer’s [6] are amenable to ampakine treatment in preclinical studies. Ampakines have shown positive effects in ADHD [7] and depression [8,9] in addition to instances of neurological damage such as stroke [10,11] and bladder [12] and breathing dysfunction [13,14,15] following spinal cord injury.
Though ampakines serve as tools to study AMPAR function and potential therapeutics, certain ampakines have demonstrated excitotoxicity in doses near to those that produce profound therapeutic effects [16,17], effectively hampering their therapeutic development. These ampakines, termed high-impact ampakines, completely offset receptor desensitization [18], enhance agonist binding affinity [18], and induce calcium release from the endoplasmic reticulum [19]. On the other hand, low-impact ampakines only modestly offset receptor desensitization [18,20], do not alter agonist binding affinity [18], and do not trigger calcium release from the endoplasmic reticulum in cortical neurons [19]. Low-impact ampakines accordingly exhibit a 100–10,000-fold separation of their efficacious doses from doses that produce seizures or lethality [20,21,22], which could allow for the safe clinical translation of a candidate low-impact ampakine.
Multiple studies have been undertaken to understand the pharmacology of ampakines and the numerous distinctions between high- and low-impact ampakines. However, much less is known about how AMPAR recover from potentiation by ampakines and whether recovery is different between high- and low-impact ampakines. Herein, we evaluate the recovery from potentiation by high- and low-impact ampakines and assess whether glutamate is required for ampakine-mediated AMPAR potentiation. We also employ competitive electrophysiological experiments to infer whether low- and high-impact ampakines share a common binding site. We believe that recovery from AMPAR potentiation may dictate seizurogenicity and excitotoxicity of ampakines and that by delineating the recovery kinetics of high- and low-impact ampakines, we can further distinguish the pharmacological properties that have halted the development of the high-impact ampakines and permitted clinical translation of low-impact ampakines.

2. Material and Methods

All animal procedures were conducted in accordance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals and with protocols approved by the Institutional Animal Care and Use Committee of the University of California at Irvine (Irvine, CA, USA). Efforts were made to minimize animal suffering, and the number of animals used was reduced to the minimum required.

2.1. Cortical Neuron Cell Culture and Whole Cell Recording

Pregnant Sprague–Dawley rats were anesthetized by inhalation of CO2, and embryos (at day 18–19) were immediately removed by caesarean section. Brains from the embryos were rapidly removed under sterile conditions and digested at 36 °C for 10 min with 1 mg/mL papain (Roche, Indianapolis, IN, USA) in 5 mL Hanks’ balanced salt solution lacking calcium or magnesium (GIBCO, Grand Island, NE, USA). The supernatant was removed, and the enzymatic reaction was stopped by the addition of 2 mL plating medium (EMEM; Sigma, St. Louis, MO, USA) containing 2.5% fetal bovine serum (Hyclone, Logan, UT, USA), 2.5% equine serum (Hyclone), and 0.5 mM Glutamax (GIBCO). The mixture was triturated using a 5 mL pipette until the cells were dispersed into a cloudy solution. Approximately 60,000 cells were plated in an area 15 mm in diameter at the middle of a 35 mm plastic culture dish (Corning, Corning, NY, USA) that had been coated with poly-DL-lysine (Sigma). Cultures were maintained at 36 °C in a 5% CO2 incubator. Recordings were performed on DIV (days in vitro) 4 to 6 cells. For miniature synaptic currents (minis), the recordings were performed on neurons after 2 to 3 weeks in culture.
Prior to recording, a dish was removed from the incubator and the culture medium was replaced with recording saline containing the following (in mM): NaCl, 145; KCl, 5.4; CaCl2, 1.8; MgCl2, 0.8; Hepes, 10; D-glucose, 10; sucrose, 30, and tetrodotoxin, 40 nM, titrated to pH 7.4 with NaOH. The whole-cell current was measured with a patch-clamp amplifier (Axopatch 200B), filtered at 2 kHz, digitized at 5 kHz, and recorded on a computer with pClamp 8. The cells were voltage-clamped at −80 mV. Minis were recorded in the presence of 1 μM tetrodotoxin.
All compounds and saline were applied using a DAD-12 superfusion system (ALA Scientific Instruments Inc., New York, NY, USA). The 13-to-1 tip was placed approximately 100 to 150 μm from the cell. The mean value of plateau current between 600 ms and 900 ms after application of 500 μM glutamate or glutamate/ampakine was calculated and used as the parameter to measure the compound’s effect. Values reported in the text and figure legends are the mean ± SEM.

2.2. Data Analysis

The mean value of the steady-state current between 600 ms and 900 ms after application of glutamate or glutamate + ampakine was calculated and used as the parameter to quantify the efficacy of the ampakine. The minis were analyzed with Mini Analysis Program (Synaptosoft Inc., Leonia, NJ, USA). Statistical analysis was performed with Microsoft Excel and Graphpad Prism.

3. Results

This study utilized the well-characterized, low-impact ampakine CX516 and the high-impact ampakines CX614 and CX729 (Figure 1). As the modulatory effects of CX614 [23] and CX516 [18] have been previously described, we investigated the electrophysiological properties of CX729, an ampakine which has been found to have neurotrophic effects in previous investigations [24]. In cortical neurons, CX729 augments glutamate-induced currents, and dose-dependently increases steady-state currents elicited by glutamate, offsetting receptor desensitization (Figure 2A). Curve fitting reveals that CX729 positively modulates glutamate-induced currents with an EC50 of 7.4 μM and a hill slope of 1.027 (Figure 2B). These findings illustrate that like CX614 [23], CX729 possesses the electrophysiological properties of a high-impact ampakine.
To understand the kinetics of AMPAR recovery from potentiation by an ampakine, we assessed glutamate-induced currents before, during, and following co-treatment with 10 μM CX729 (which approximates EC50). Without CX729 co-treatment, glutamate application resulted in a quickly desensitizing current (Figure 3A). When glutamate was co-applied with CX729, there was a marked increase in peak and steady-state current that terminated after cessation of glutamate and ampakine treatment. As can be seen, 15 s following co-application, glutamate alone still induces a substantial peak and non-desensitizing current that is ~80% of the peak current observed upon co-application of glutamate and CX729 (Figure 3A). Subsequent applications of glutamate indicate that recovery from AMPAR potentiation by CX729 took place over several minutes. Three min following co-application of glutamate and CX729, the glutamate-induced current is still greater than the glutamate-induced current prior to CX729 application. Recovery from CX729 potentiation is plotted in Figure 3B. Additional studies examined whether the number of subsequent times AMPAR were activated affected recovery from potentiation by CX729. Figure 4 illustrates that after co-application of glutamate and CX729, subsequent application of glutamate every 30 s (Figure 4(A1,A2)), every 15 s (Figure 4(B1,B2)), or every 45 s (Figure 4(C1,C2)) did not change the kinetics of recovery from AMPAR potentiation by CX729.
Our findings thus far also beg the question as to whether the slow recovery requires the simultaneous presence of glutamate when CX729 is applied. To interrogate this question, we applied either CX729 or CX729 + glutamate and assessed recovery from potentiation at 30 s intervals. As expected, glutamate alone produced a rapidly desensitizing current and desensitization was offset by co-application with 10 μM CX729 (Figure 5A). CX729 application alone did not elicit an inward current (Figure 5B). However, in both conditions, subsequent application of glutamate 30, 60, and 90 s later produced comparatively potentiated responses (Figure 5C). Two-way ANOVA revealed a significant effect of time on the recovery from CX729 potentiation (p < 0.0001) but also revealed that there was no significant effect of treatment on recovery from ampakine potentiation (p = 0.8494). Post-hoc Bonferroni multiple comparison tests at 30, 60, and 90 s revealed no difference in the recovery from CX729 application, suggesting that glutamate is not necessary for ampakine modulation of AMPAR and to observe subsequent potentiated responses.
Following these studies, we sought to investigate the interaction between low- and high-impact ampakines. While the binding site for high-impact ampakines has been previously characterized [25], the site of action of low-impact ampakines has yet to be fully elucidated. To test whether they may be acting at the same or different sites, we recorded the potentiation of glutamate-induced currents alone or with co-application of CX516, CX729, or with both ampakines. Co-application of glutamate + 6 mM CX516 (a concentration that produces maximal potentiation [18,26,27]) increased steady-state currents by ~1000% (Figure 6A,B). Meanwhile, 3 μM CX729 potentiated glutamate-induced currents by ~3000%. Co-application of both ampakines with glutamate augmented steady-state currents by ~4000% (Figure 6A,B). This potentiation by both ampakines is similar to the summation of the potentiation produced by each ampakine individually, indicating that these ampakines may be acting at different sites.
In addition to investigating the kinetics of AMPAR recovery from potentiation by an ampakine, we also sought to interrogate the on rate of several ampakines in cortical neurons. When ampakines are co-applied with glutamate, CX729, CX614, and CX516 exhibit disparate on rates. CX516 reaches steady-state currents within one second of application (Figure 7A,B). For the high-impact ampakines, one-second co-application of each ampakine with glutamate was too short to measure their constants. However, the estimated decay times of on rates indicate that CX729 had a slower time constant than what was observed for CX614 (Figure 7A,B). Further, termination of CX516 application resulted in diminution back to baseline within 0.8 s (Figure 7A). In the case of CX614 and CX729, cessation of ampakine application resulted in a slower reduction of current. For CX729, it was only after stopping glutamate application that inward currents returned to baseline, correlating with slow recovery from potentiation. After stopping application of CX614, the current reached its peak when glutamate was applied alone, began to diminish during glutamate application, and returned to baseline upon application of saline.
We concluded our studies by assessing the effects of CX516 and CX729 on minis. We found that 6 mM CX516 increased the amplitude and half-width of minis (Figure 8A). Within 30 s of drug cessation, amplitude and half-width returned to baseline (Figure 8A,B). This is in contrast to the effects seen with treatment with CX729. Ee also found that 10 μM CX729 significantly increased the amplitude of minis as well as half-width. Notably, five minutes after drug termination, amplitude as well as half-width remained elevated (Figure 8A). The kinetics of amplitude and half-width diminution to baseline are shown in Figure 8C, demonstrating a much slower recovery than what is observed with CX516.

4. Discussion

In this study, we explored how AMPAR recover from potentiation by ampakines with distinct pharmacological properties. Potentiation of AMPAR by CX729 does not require the simultaneous presence of glutamate (Figure 5), nor is recovery from potentiation affected by subsequent receptor activation (Figure 4 and Figure 5). Additional experiments indicate that the effects of high-impact ampakines may wash out more quickly than those of low-impact ampakines (Figure 7 and Figure 8). Additionally, the results of competitive electrophysiological experiments imply that high- and low-impact ampakines may indeed have different binding sites (Figure 6).
Though high-impact ampakines have demonstrated extraordinary therapeutic effects in numerous preclinical studies [3,4,5,11,28,29,30], their seizurogenic potential has severely limited their capacity as clinically meaningful therapeutics. Delineating pharmacological differences between the ampakine subclasses can enhance our understanding of AMPAR positive modulators in general and enhance our understanding of why high-impact ampakines are endowed with their excitotoxic properties. A further understanding of the pharmacological detriments of high-impact ampakines can also open up avenues, for example, to screen for ampakines that effectively enhance AMPAR-mediated currents but also do not take several minutes to wash out nor cause the release of calcium from the endoplasmic reticulum [19]. Whether the detrimental effects of high-impact ampakines can be truly separated from their therapeutic effects remains to be seen.
Additional work by other groups seems to have identified high-impact ampakines that exhibit excellent therapeutic ratios. Eloquent studies by Kunugi and colleagues indicate that high-impact molecules such as Lilly AMPAR potentiators LY451646 and LY451395 exhibit epileptogenic effects in part due to their intrinsic agonistic properties at high concentrations, while TAK-137 and TAK-653 do not possess agonistic properties [17,31,32,33]. In the presence of agonist, however, TAK-137 and TAK-653 produce a full offset of AMPAR desensitization [17,32,33] and acutely stimulates BDNF synthesis [17,34]. TAK-653 (osavampator, NBI-1065845) also met its primary endpoint in a Phase 2 study of adults with major depressive disorder, demonstrating the clinical potential of the AMPAR potentiators [35]. These drug candidates, deemed strictly potentiators, are devoid of the epileptogenic effects observed with other high-impact ampakines [17]. Compared to CX729, AMPAR recover more quickly from potentiation by TAK-137 [17], which may also potentially explain why TAK-137 does not exhibit seizurogenic effects at therapeutic doses. Whether Takeda AMPAR potentiators such as TAK-137 or TAK-653 possess other characteristics of high-impact ampakines, such as the capacity to induce calcium release from the endoplasmic reticulum is currently unknown, though a potential avenue for future research.
Our findings underpin the idea that high- and low-impact ampakines possess different binding sites on the AMPAR. Competitive binding experiments by Arai et al. [18] indicate that the high-impact ampakines CX546 and CX516 may bind the AMPAR at different sites. In an elegant series of biochemical studies, Arai et al. found that CX546, but not CX516, enhances AMPAR agonist binding affinity. Further, saturating concentrations of CX516 does not alter the ability of CX516 to enhance agonist binding affinity, suggesting that low- and high-impact ampakines bind to a different site on the receptor [18]. It is possible that low-impact ampakines bind to the piracetam allosteric site on AMPAR [36], though future structural studies would be needed to confirm this possibility. We have found that CX614 and CX729, but not the low-impact ampakine CX1739, displace a tritiated high-impact ampakine (unpublished observations). These observations are bolstered by the observation that the effects of CX516 and CX729 are additive in electrophysiological studies (Figure 6). Though it is not known where newer-generation, low-impact ampakines such as CX717, CX1739, and CX1763 bind on the AMPAR, it is possible that newer-generation low-impact ampakines also bind the piracetam binding site [36] that is distinct from where CX614 interacts with the receptor [25]. It is possible that low-impact ampakines such as CX717, CX1739, and CX1763 bind to the receptor in a distinct fashion, which may result in modest receptor modulation that produces augmented AMPAergic activity but is insufficient to hyperactivate AMPAR throughout the brain. Structural studies are still needed to determine the mechanism of AMPAR modulation by newer-generation, low-impact ampakines.
Our study, while further delineating the pharmacological differences between low- and high-impact ampakines, does have several limitations that could guide future research endeavors. Since rat cortical neurons are were, the extent to which these findings exist in human AMPAR remains to be determined. Future studies may seek to replicate these findings in a model that examines human AMPAR, such as transfecting HEK293 cells with human AMPAR subunits and human auxiliary proteins, in a manner similar to our group’s prior work [37,38]. It should be noted, however, that since ampakines have shown activity in the clinical setting [39,40,41], we believe that ampakines should be able to sufficiently modulate human AMPAR. Additionally, crystallography data with the ampakines used in this study or ampakines that have shown increased translational potential (high-impact ampakines such as CX1837 [10,11,42] and low-impact ampakines such as CX1739, CX717, and CX1942/CX1763 [19,20,21,22,43,44,45,46]) may be worthwhile to gain more structural insight into how these modulators are able to safely potentiate AMPAR conductance to exert a wide range of therapeutic effects.
Safe high-impact ampakines could revolutionize how neurological and neuropsychiatric disorders are treated [47,48,49,50,51,52,53]. However, the characteristics that impart them with their previously described toxicities must be fully understood in order to be able to identify other drug candidates that are safe for clinical translation. In this respect, low-impact ampakines can serve as comparator ligands for certain pharmacological screens to identify high-impact ampakines that enhance AMPAergic currents but do not overstimulate receptors. It is conceivable that one of the properties of a safe high-impact ampakine is swift washout upon cessation of drug application. Drug candidates with slow dissociation kinetics may be more epileptogenic and hamper the development of high-impact ampakines. Nonetheless, our findings systematically examine the kinetics of AMPAR recovery from positive allosteric modulation by high-impact and low-impact ampakines. These results add to our existing knowledge of ampakines and open up avenues for future research that may inform as to why high-impact ampakines, but not low-impact ampakines, exhibit increased potential for excitotoxicity, a pharmacological property that has greatly hampered their clinical development over the past three decades.

Author Contributions

Conceptualization, D.P.R., R.C., J.M.W. and A.L.; Methodology, A.L.; Software, D.P.R.; Validation, D.P.R. and A.L.; Formal analysis, D.P.R.; Investigation, D.P.R.; Resources, A.L.; Data curation, D.P.R. and A.L.; Writing—original draft preparation, D.P.R., R.C., J.L.S., J.M.W. and A.L.; Writing—review and editing, D.P.R., R.C., J.L.S., J.M.W. and A.L.; Visualization, D.P.R., J.M.W. and A.L.; Supervision, R.C., J.M.W. and A.L.; Project administration, J.M.W. and A.L.; Funding acquisition, A.L. All authors have read and agreed to the published version of the manuscript.

Funding

Funding was provided by RespireRx Pharmaceuticals Inc.

Institutional Review Board Statement

This study was conducted according to the guidelines of the Declaration of Helsinki and was approved by UC Irvine IACUC (protocol #61-05-05B, first approved May 2005).

Informed Consent Statement

Not applicable.

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors on request.

Conflicts of Interest

With respect to the manuscript, Daniel Radin, Arnold Lippa, Jeffrey Witkin, and Rok Cerne all are associated with RespireRx, where A.L. is acting CEO, and D.P.R., R.C., and J.M.W. are non-paid researchers who occasionally conduct studies on these compounds. The company had no role in this study’s design, data gathering, interpretation of the results, or writing of the manuscript. All authors of this study consented to publication. None of the ampakines used in the study are currently under clinical development. The company, RespireRx Pharmaceuticals, funded the studies. However, the authors decided to publish the results.

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Figure 1. Ampakines used in this study. CX516 is a low-impact ampakine, while CX614 and CX729 are high-impact ampakines.
Figure 1. Ampakines used in this study. CX516 is a low-impact ampakine, while CX614 and CX729 are high-impact ampakines.
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Figure 2. CX729, a high-impact ampakine, did not induce any whole-cell current in the absence of applied glutamate, but it dramatically increased steady-state inward currents induced by 1 s applications of 500 μM glutamate. (A) Experimental traces show the effects of CX729 at different concentrations; (B) fold increase in steady-state current. The EC50 value is 7.4 µM, and the Hill coefficient is 1.027. Values are the mean ± SEM of 7 replicates.
Figure 2. CX729, a high-impact ampakine, did not induce any whole-cell current in the absence of applied glutamate, but it dramatically increased steady-state inward currents induced by 1 s applications of 500 μM glutamate. (A) Experimental traces show the effects of CX729 at different concentrations; (B) fold increase in steady-state current. The EC50 value is 7.4 µM, and the Hill coefficient is 1.027. Values are the mean ± SEM of 7 replicates.
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Figure 3. Recoveries from the enhancement by CX729 were slow. (A) Glutamate was applied every 15 s after co-application of CX729 and glutamate. After 3 min, the glutamate-induced current was still greater than that induced before CX729 exposure; (B) time-dependent recovery from the potentiation. The time constant was 0.73 min. Values are the mean ± SEM of 6 replicates.
Figure 3. Recoveries from the enhancement by CX729 were slow. (A) Glutamate was applied every 15 s after co-application of CX729 and glutamate. After 3 min, the glutamate-induced current was still greater than that induced before CX729 exposure; (B) time-dependent recovery from the potentiation. The time constant was 0.73 min. Values are the mean ± SEM of 6 replicates.
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Figure 4. The recovery time was not different if saline was substituted for glutamate during the recovery period. (A1,A2) Glutamate was applied every 30 s; (B1,B2) glutamate was applied every 15 s; (C1,C2) glutamate was applied every 45 s. Saline was substituted/applied between the applications of glutamate. Values are the mean ± SEM of 4–5 replicates.
Figure 4. The recovery time was not different if saline was substituted for glutamate during the recovery period. (A1,A2) Glutamate was applied every 30 s; (B1,B2) glutamate was applied every 15 s; (C1,C2) glutamate was applied every 45 s. Saline was substituted/applied between the applications of glutamate. Values are the mean ± SEM of 4–5 replicates.
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Figure 5. The slow recovery does not require the simultaneous presence of glutamate and CX729. There was no difference between glutamate-induced responses after transient applications of CX729 or CX729 plus glutamate. (A) Glutamate was applied simultaneously with CX729; (B) CX729 application alone did not induce inward currents. For (A,B), subsequent test currents were evoked by the application of glutamate 30, 60, or 90 s after CX729 or CX729 plus glutamate application. (C). Recovery of steady-state current. Average data from 5 cells. Two-way ANOVA, effect of time F (2, 12) = 232.1, p < 0.0001. Effect of time F (1, 6) = 0.03932, p = 0.8494. effect of time × treatment F (2, 12) = 0.1225, p = 0.8858. NS, not significant, p > 0.9, Bonferroni’s multiple comparison test. Bars are the mean ± SEM of 4 replicates.
Figure 5. The slow recovery does not require the simultaneous presence of glutamate and CX729. There was no difference between glutamate-induced responses after transient applications of CX729 or CX729 plus glutamate. (A) Glutamate was applied simultaneously with CX729; (B) CX729 application alone did not induce inward currents. For (A,B), subsequent test currents were evoked by the application of glutamate 30, 60, or 90 s after CX729 or CX729 plus glutamate application. (C). Recovery of steady-state current. Average data from 5 cells. Two-way ANOVA, effect of time F (2, 12) = 232.1, p < 0.0001. Effect of time F (1, 6) = 0.03932, p = 0.8494. effect of time × treatment F (2, 12) = 0.1225, p = 0.8858. NS, not significant, p > 0.9, Bonferroni’s multiple comparison test. Bars are the mean ± SEM of 4 replicates.
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Figure 6. (A) Effects of 6 mM CX516 on AMPA receptor responses (blue), 3 μM CX729 (green), and finally CX729 plus CX516 (red) were measured. The purple line shows the summary of blue and green lines; (B) mean values from 7 individual cells. ANOVA F (3, 18) = 60.76, NS, not significant, p < 0.0001. ** p < 0.01, **** p < 0.0001, Bonferroni’s multiple comparison test. Values are the mean ± SEM of 7 replicates.
Figure 6. (A) Effects of 6 mM CX516 on AMPA receptor responses (blue), 3 μM CX729 (green), and finally CX729 plus CX516 (red) were measured. The purple line shows the summary of blue and green lines; (B) mean values from 7 individual cells. ANOVA F (3, 18) = 60.76, NS, not significant, p < 0.0001. ** p < 0.01, **** p < 0.0001, Bonferroni’s multiple comparison test. Values are the mean ± SEM of 7 replicates.
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Figure 7. CX729 not only shows slow wash back activity but also a slow on rate. Without pre-treatment, ampakines take time to reach steady-state responses when applied with glutamate. However, as shown in (A), 1 s is long enough for CX516 to reach its maximal responses, but this was not the case for CX614 and CX729. Although a 1 s application of CX614 or CX729 was not sufficient to measure their constants, the estimated decay times (τ) indicated that CX729 had a slower time constant than that of CX614 (B). Brown–Forsythe ANOVA F (2.000, 5.423) = 16.80, p = 0.0024. * p < 0.05, ** p < 0.01, Dunnett’s T3 multiple comparison test. Values are the mean ± SEM of 4–6 replicates.
Figure 7. CX729 not only shows slow wash back activity but also a slow on rate. Without pre-treatment, ampakines take time to reach steady-state responses when applied with glutamate. However, as shown in (A), 1 s is long enough for CX516 to reach its maximal responses, but this was not the case for CX614 and CX729. Although a 1 s application of CX614 or CX729 was not sufficient to measure their constants, the estimated decay times (τ) indicated that CX729 had a slower time constant than that of CX614 (B). Brown–Forsythe ANOVA F (2.000, 5.423) = 16.80, p = 0.0024. * p < 0.05, ** p < 0.01, Dunnett’s T3 multiple comparison test. Values are the mean ± SEM of 4–6 replicates.
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Figure 8. The effects of CX729 on minis were slow to recover. (A) Both of 10 μM CX729 and 6 mM CX516 increased the amplitude and half-width (HW) of minis. It took seconds for the effects of CX516 to diminish back to baseline (B). Meanwhile, it took more than 8 min to appreciate diminution of CX729’s effects (C).
Figure 8. The effects of CX729 on minis were slow to recover. (A) Both of 10 μM CX729 and 6 mM CX516 increased the amplitude and half-width (HW) of minis. It took seconds for the effects of CX516 to diminish back to baseline (B). Meanwhile, it took more than 8 min to appreciate diminution of CX729’s effects (C).
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Radin, D.P.; Cerne, R.; Smith, J.L.; Witkin, J.M.; Lippa, A. Recovery from AMPA Receptor Potentiation by Ampakines. Future Pharmacol. 2025, 5, 27. https://doi.org/10.3390/futurepharmacol5020027

AMA Style

Radin DP, Cerne R, Smith JL, Witkin JM, Lippa A. Recovery from AMPA Receptor Potentiation by Ampakines. Future Pharmacology. 2025; 5(2):27. https://doi.org/10.3390/futurepharmacol5020027

Chicago/Turabian Style

Radin, Daniel P., Rok Cerne, Jodi L. Smith, Jeffrey M. Witkin, and Arnold Lippa. 2025. "Recovery from AMPA Receptor Potentiation by Ampakines" Future Pharmacology 5, no. 2: 27. https://doi.org/10.3390/futurepharmacol5020027

APA Style

Radin, D. P., Cerne, R., Smith, J. L., Witkin, J. M., & Lippa, A. (2025). Recovery from AMPA Receptor Potentiation by Ampakines. Future Pharmacology, 5(2), 27. https://doi.org/10.3390/futurepharmacol5020027

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