Engaging Multistakeholder Perspectives to Identify Patient-Centered Research Priorities Regarding Vaccine Uptake Among Adults With Autoimmune Conditions

OBJECTIVE

The study objective was to prioritize topics for future patient-centered research to increase uptake of common vaccines, such as for pneumococcal pneumonia, influenza, herpes zoster, human papillomavirus, and severe acute respiratory syndrome coronavirus 2, among adults living with autoimmune conditions.

METHODS

A steering committee (SC) was formed that included clinicians, patients, patient advocates, and researchers associated with rheumatic diseases (psoriatic arthritis, rheumatoid arthritis, vasculitis), inflammatory bowel disease, and multiple sclerosis. Through a scoping review and discussions, SC members identified research topics regarding vaccine uptake and/or hesitancy for prioritization. A larger multistakeholder alliance that included patients and patient advocates, clinicians, researchers, policy makers, regulators, and vaccine manufacturers conducted a modified Delphi exercise online with three rating rounds and one ranking round. Frequency analysis and comparisons across stakeholder groups were conducted. A weighted ranking score was generated for each item in the ranking round for final prioritization.

RESULTS

Through the Delphi process, 33 research topics were identified, of which 13 topics were rated as critical by more than 70% of all stakeholders (n = 31). The two highest ranked critical topics per the full stakeholder group were "How well a vaccine works for adults with autoimmune conditions" and "How beliefs about vaccine safety affect vaccine uptake."

CONCLUSION

A multistakeholder group identified key topics as critically important priorities for future research to decrease vaccine hesitancy and improve uptake of vaccines for adults with autoimmune conditions.

Online Mindfulness-Based Interventions for Well-Being: Randomized Comparative Effectiveness Trial (Preprint)

Background

Mindfulness can improve overall well-being by training individuals to focus on the present moment without judging their thoughts. However, it is unknown how much mindfulness practice and training are necessary to improve well-being.

Objective

The primary aim of this study was to determine whether a standard 8-session web-based mindfulness-based cognitive therapy (MBCT) program, compared with a brief 3-session mindfulness intervention, improved overall participant well-being. In addition, we sought to explore whether the treatment effects differed based on the baseline characteristics of the participants (ie, moderators).

Methods

Participants were recruited from 17 patient-powered research networks, web-based communities of stakeholders interested in a common research area. Participants were randomized to either a standard 8-session MBCT or a brief 3-session mindfulness training intervention accessed on the web. The participants were followed for 12 weeks. The primary outcome of the study was well-being, as measured by the World Health Organization—Five Well-Being Index. We hypothesized that MBCT would be superior to a brief mindfulness training.

Results

We randomized 4411 participants, 3873 (87.80%) of whom were White and 3547 (80.41%) of female sex assigned at birth. The mean baseline World Health Organization—Five Well-Being Index score was 50.3 (SD 20.7). The average self-reported well-being in each group increased over the intervention period (baseline to 8 weeks; model-based slope for the MBCT group: 0.78, 95% CI 0.63-0.93, and brief mindfulness group: 0.76, 95% CI 0.60-0.91) as well as the full study period (ie, intervention plus follow-up; baseline to 20 weeks; model-based slope for MBCT group: 0.41, 95% CI 0.34-0.48; and brief mindfulness group: 0.33, 95% CI 0.26-0.40). Changes in self-reported well-being were not significantly different between MBCT and brief mindfulness during the intervention period (model-based difference in slopes: −0.02, 95% CI −0.24 to 0.19; P=.80) or during the intervention period plus 12-week follow-up (−0.08, 95% CI −0.18 to 0.02; P=.10). During the intervention period, younger participants (P=.05) and participants who completed a higher percentage of intervention sessions (P=.005) experienced greater improvements in well-being across both interventions, with effects that were stronger for participants in the MBCT condition. Attrition was high (ie, 2142/4411, 48.56%), which is an important limitation of this study.

Conclusions

Standard MBCT improved well-being but was not superior to a brief mindfulness intervention. This finding suggests that shorter mindfulness programs could yield important benefits across the general population of individuals with various medical conditions. Younger people and participants who completed more intervention sessions reported greater improvements in well-being, an effect that was more pronounced for participants in the MBCT condition. This finding suggests that standard MBCT may be a better choice for younger people as well as treatment-adherent individuals.

Trial Registration

ClinicalTrials.gov NCT03844321; https://clinicaltrials.gov/ct2/show/NCT03844321

Patient-Powered Research Networks of the Autoimmune Research Collaborative: Rationale, Capacity, and Future Directions

Patient-Powered Research Networks (PPRNs) are US-based registry infrastructures co-created by advocacy groups, patient research partners, academic investigators, and other healthcare stakeholders. Patient-Powered Research Networks collect information directly from patients to conduct and disseminate the results of patient-centered/powered research that helps patients make more informed decisions about their healthcare. Patient-Powered Research Networks gather and utilize real-world data and patient-reported outcomes to conduct comparative effectiveness, safety, and other research, and leverage the Internet to accomplish this effectively and efficiently. Four PPRNs focused on autoimmune and immune-mediated conditions formed the Autoimmune Research Collaborative: ArthritisPower (rheumatoid arthritis, spondyloarthritis, and other rheumatic and musculoskeletal diseases), IBD Partners (inflammatory bowel disease), iConquerMS (multiple sclerosis), and the Vasculitis PPRN (vasculitis). The Autoimmune Research Collaborative aims to inform the healthcare decision making of patients, care partners, and other stakeholders, such as clinicians, regulators, and payers. Illustrated by practical applications from the Autoimmune Research Collaborative and its constituent PPRNs, this article discusses the shared capacities and challenges of the PPRN model, and the opportunities presented by collaborating across autoimmune conditions to design, conduct, and disseminate patient-centered outcomes research.

The liver toxicity biomarker study phase I: markers for the effects of tolcapone or entacapone

The Liver Toxicity Biomarker Study is a systems toxicology approach to discover biomarkers that are indicative of a drug's potential to cause human idiosyncratic drug-induced liver injury. In phase I, the molecular effects in rat liver and blood plasma induced by tolcapone (a "toxic" drug) were compared with the molecular effects in the same tissues by dosing with entacapone (a "clean" drug, similar to tolcapone in chemical structure and primary pharmacological mechanism). Two durations of drug exposure, 3 and 28 days, were employed. Comprehensive molecular analysis of rat liver and plasma samples yielded marker analytes for various drug-vehicle or drug-drug comparisons. An important finding was that the marker analytes associated with tolcapone only partially overlapped with marker analytes associated with entacapone, despite the fact that both drugs have similar chemical structures and the same primary pharmacological mechanism of action. This result indicates that the molecular analyses employed in the study are detecting substantial "off-target" markers for the two drugs. An additional interesting finding was the modest overlap of the marker data sets for 3-day exposure and 28-day exposure, indicating that the molecular changes in liver and plasma caused by short- and long-term drug treatments do not share common characteristics.

Sample size and statistical power considerations in high-dimensionality data settings: a comparative study of classification algorithms

BACKGROUND

data generated using 'omics' technologies are characterized by high dimensionality, where the number of features measured per subject vastly exceeds the number of subjects in the study. In this paper, we consider issues relevant in the design of biomedical studies in which the goal is the discovery of a subset of features and an associated algorithm that can predict a binary outcome, such as disease status. We compare the performance of four commonly used classifiers (K-Nearest Neighbors, Prediction Analysis for Microarrays, Random Forests and Support Vector Machines) in high-dimensionality data settings. We evaluate the effects of varying levels of signal-to-noise ratio in the dataset, imbalance in class distribution and choice of metric for quantifying performance of the classifier. To guide study design, we present a summary of the key characteristics of 'omics' data profiled in several human or animal model experiments utilizing high-content mass spectrometry and multiplexed immunoassay based techniques.

RESULTS

the analysis of data from seven 'omics' studies revealed that the average magnitude of effect size observed in human studies was markedly lower when compared to that in animal studies. The data measured in human studies were characterized by higher biological variation and the presence of outliers. The results from simulation studies indicated that the classifier Prediction Analysis for Microarrays (PAM) had the highest power when the class conditional feature distributions were Gaussian and outcome distributions were balanced. Random Forests was optimal when feature distributions were skewed and when class distributions were unbalanced. We provide a free open-source R statistical software library (MVpower) that implements the simulation strategy proposed in this paper.

CONCLUSION

no single classifier had optimal performance under all settings. Simulation studies provide useful guidance for the design of biomedical studies involving high-dimensionality data.

The art and practice of systems biology in medicine: mapping patterns of relationships

Systems biology has developed in recent years from a technology-driven enterprise to a new strategic tool in Life Sciences, particularly for innovative drug discovery and drug development. Combining the ultimate in systems phenotyping with in-depth investigations of biomolecular mechanisms will enable a revolution in our understanding of disease pathology and will advance translational medicine, combination therapies, integrative medicine, and personalized medicine. A prerequisite for deriving the benefits of such a systems approach is a reliable and well-validated bioanalytical platform across complementary measurement modalities, especially transcriptomics, proteomics, and metabolomics, that operates in concert with a megavariate integrative biostatistical/bioinformatics platform. The applicable bioanalytical methodologies must undergo an intense development trajectory to reach an optimal level of reliable performance and quantitative reproducibility in daily practice. Moreover, to generate such enabling systems information, it is essential to design experiments based on an understanding of the complexity and statistical characteristics of the large data sets created. Novel insights into biology and system science can be obtained by evaluating the molecular connectivity within a system through correlation networks, by monitoring the dynamics of a system, or by measuring the system responses to perturbations such as drug administration or challenge tests. In addition, cross-compartment communication and control/feed-back mechanisms can be studied via correlation network analyses. All these data analyses depend critically upon the generation of high-quality bioanalytical platform data sets. The emphasis of this paper is on the characteristics of a bioanalytical platform that we have developed to generate such data sets. The broad applicability of Systems Biology in pharmaceutical research and development is discussed with examples in disease biomarker research, in pharmacology using system response monitoring, and in cross-compartment system toxicology assessment.

Metabolomics-based systems biology and personalized medicine: moving towards n = 1 clinical trials?

Personalized medicine – defined as customized medical care for each patient’s unique condition – in the broader context of personalized health, will make significant strides forward when a systems approach is implemented to achieve the ultimate in disease phenotyping and to create novel therapeutics that address system-wide molecular perturbations caused by disease processes. Combination drug therapies with individualized optimization are likely to become a major focus. Metabolomics incorporates the most advanced approaches to molecular phenotype system readout and provides the ideal theranostic technology platform for the discovery of biomarker patterns associated with healthy and diseased states, for use in personalized health monitoring programs and for the design of individualized interventions.

Lost in translation? Role of metabolomics in solving translational problems in drug discovery and development

Too few drug discovery projects generate a marketed drug product, often because preclinical studies fail to predict the clinical experience with a drug candidate. Improving the success of preclinical-to-clinical translation is of paramount importance in optimizing the pharmaceutical value chain. Here, we advance the case for a molecular systems approach to crossing the preclinical-to-clinical translational chasm and for metabolomic analysis of readily accessible bodyfluids as a key technology in translational activities.:

Rescuing drug discovery: in vivo systems pathology and systems pharmacology

The pharmaceutical industry is currently beleaguered by close scrutiny from the financial community, regulators and the general public. Productivity, in terms of new drug approvals, has generally been falling for almost a decade and the safety of a number of highly successful drugs has recently been brought into question. Here, we discuss whether taking an in vivo systems approach to drug discovery and development could be the paradigm shift that rescues the industry.

Solution-phase, parallel synthesis and pharmacological evaluation of acylguanidine derivatives as potential sodium channel blockers

Solution-phase synthesis of various acylguanidine derivatives and the evaluation of a small library of compounds as potential sodium channel blockers are described.

Identification and characterization of a potential ischemia-selective N-methyl-D-aspartate (NMDA) receptor ion-channel blocker, CNS 5788

The identification and characterization of a potentially ischemia-selective and orally-active sulfoxide based NMDA ion-channel blocker showing good neuroprotective activity, (R)-(+)-N-(2-chloro-5-methylthiophenyl)-N'-(3-methylsulfinylphenyl)-N'-methylguanidine (CNS 5788), is described.

Design, synthesis, and pharmacological evaluation of conformationally constrained analogues of N,N'-diaryl- and N-aryl-N-aralkylguanidines as potent inhibitors of neuronal Na+ channels

In the present investigation, the rationale for the design, synthesis, and biological evaluation of potent inhibitors of neuronal Na+ channels is described. N,N'-diaryl- and N-aryl-N-aralkylguanidine templates were locked in conformations mimicking the permissible conformations of the flexible diarylguanidinium ion (AS+, AA+, SS+). The resulting set of constrained guanidines termed "lockamers" (cyclophane, quinazoline, aminopyrimidazolines, aminoimidazolines, azocino- and tetrahydroquinolinocarboximidamides) was examined for neuronal Na+ channel blockade properties. Inhibition of [14C]guanidinium ion influx in CHO cells expressing type IIA Na+ channels showed that the aminopyrimidazoline 9b and aminoimidazoline 9d, compounds proposed to lock the N,N'-diarylguanidinium in an SS+ conformation, were the most potent Na+ channel blockers with IC50's of 0.06 microM, a value 17 times lower than that of the parent flexible compound 18d. The rest of the restricted analogues with 4-p-alkyl substituents retained potency with IC50 values ranging between 0.46 and 2.9 microM. Evaluation in a synaptosomal 45Ca2+ influx assay showed that 9b did not exhibit high selectivity for neuronal Na+ vs Ca2+ channels. The retention of significant neuronal Na+ blockade in all types of semirigid conformers gives evidence for a multiple mode of binding in this class of compounds and can possibly be attributed to a poor structural specificity of the site(s) of action. Compound 9b was also found to be the most active compound in vivo based on the high level of inhibition of seizures exhibited in the DBA/2 mouse model. The pKa value of 9b indicates that 9b binds to the channel in its protonated form, and log D vs pH measurements suggest that ion-pair partitioning contributes to membrane transport. This compound stands out as an interesting lead for further development of neurotherapeutic agents.

In vitro neuroprotection by substituted guanidines with varying affinities for the N-methyl-D-aspartate receptor ionophore and for sigma sites

Radioligand binding techniques were used to determine the affinity of a series of substituted guanidine derivatives for 1) the binding site within the ion channel of the N-methyl-D-aspartate (NMDA) receptor, as defined by displacement of MK-801 ([3H]dizocilpine) and 2) sigma sites as defined by displacement of [3H]N,N'-di-(o-tolyl)guanidine. The goal was to find ligands with high affinity and selectivity for the NMDA receptor ion-channel site. The neuroprotective activity of these compounds was assessed by their ability to protect cortical neurons from injury caused by a 5-min exposure to 500 microM glutamate in vitro. Release of lactate dehydrogenase into the culture medium by damaged neurons was used as an index of neuronal injury. The 14 compounds tested had IC50 values ranging from 37.3 nM to 12.7 microM for the NMDA receptor ion-channel site and from 8.3 nM to 7.25 microM for sigma sites. Affinity for the ion-channel site was improved by unsymmetrical substitutions on the guanidine moiety. All compounds in the series protected cortical neurons against glutamate toxicity, with EC50 values (concentration affording 50% protection) ranging from 0.38 to 28.25 microM. The neuroprotective effect of each compound was positively correlated with its ion-channel site affinity (r = 0.94); no correlation between neuroprotective efficacy and sigma site binding affinity was found (r V -0.13) establishing clearly that neuroprotection in this assay was linked to NMDA antagonist properties.

Synthesis and structure-activity studies of N,N'-diarylguanidine derivatives. N-(1-naphthyl)-N'-(3-ethylphenyl)-N'-methylguanidine: a new, selective noncompetitive NMDA receptor antagonist

Diarylguanidines, acting as NMDA receptor ion channel site ligands, represent a new class of potential neuroprotective drugs. Several diarylguanidines structurally related to N,N'-di-o-tolylguanidine (DTG), a known selective sigma receptor ligand, were synthesized and evaluated in in vitro radioligand displacement assays, with rat or guinea pig brain membrane homogenates, using the NMDA receptor ion channel site specific radioligand [3H]-(+)-5(S)-methyl-10(R),11-dihydro-5H-dibenzo[a,d]cyclohepten-5 ,10- imine (MK-801, 3), and the sigma receptor-specific radioligand [3H]-di-o-tolylguanidine (DTG, 5). This paper presents the structure-activity relationships leading to novel tri- and tetrasubstituted guanidines, which exhibit high selectivity for NMDA receptor ion channel sites and weak or negligible affinity for sigma receptors. The in vitro binding results from symmetrically substituted diphenylguanidines indicated that compounds having ortho or meta substituents (with respect to the position of the guanidine nitrogen) on the phenyl rings showed greater affinity for the NMDA receptor ion channel site compared with para-substituted derivatives. Among the group of ring substituents studied for symmetrical diarylguanidines, an isopropyl group was preferred at the ortho position and an ethyl group was preferred at the meta position. Several unsymmetrical guanidines containing a naphthalene ring on one nitrogen atom and an ortho- or a meta-substituted phenyl ring on the second nitrogen atom, e.g., N-1-naphthyl-N'-(3-ethylphenyl)guanidine (36), showed a 3-5-fold increase in affinity for the NMDA receptor ion channel site and no change in sigma receptor affinity compared to the respective symmetrical counterparts. Additional small substituents on the guanidine nitrogen atoms bearing the aryl rings resulted in tri- and tetrasubstituted guanidine derivatives which retained affinity for NMDA receptor ion channel sites but exhibited a significant reduction in their affinities for sigma receptors. For example, N-1-naphthyl-N'-(3-ethylphenyl)-N'-methylguanidine (40) showed high affinity for the NMDA receptor ion channel site (IC50 = 36 nM vs [3H]-3) and low affinity for sigma receptors (IC50 = 2540 nM vs [3H]-5). Selectivity for the NMDA receptor ion channel sites over sigma receptors appears to be dependent upon the structure of the additional substituents on the guanidine nitrogen atoms bearing the aryl groups. Methyl and ethyl substituents are most preferred in the tri- and tetrasubstituted diarylguanidines. The trisubstituted guanidine, N-1-naphthyl-N'-(3-ethylphenyl)-N'-methylguanidine (40) and its close analogues showed good in vivo neuroprotection and are potential neuroprotective drug candidates for the treatment of stroke and other neurodegenerative disorders.

10,5-(Iminomethano)-10,11-dihydro-5H-dibenzo[a,d]cycloheptene and derivatives. Potent PCP receptor ligands

IDDC (3, 10,5-(iminomethano)-10,11-dihydro-5H-dibenzo[a,d]cycloheptene++ +) and a series of substituted derivatives were synthesized and evaluated in vitro for their ability to displace tritiated MK-801 ([3H]-2) from its specific binding site in guinea pig brain homogenate. Substitution at the 3-position of 3 with bromine, chlorine, and fluorine led to increased binding affinity. In contrast, substitution of donor groups at the 3-position gave decreased binding affinities, as did all substitutions at the 7-position and on nitrogen. Where racemic mixtures were resolved, the (+)-optical antipodes were more active than their enantiomers or racemates. The most active ligand found in this study was (+)-13e (IC50 = 15.5 +/- 4.5 nM). The affinity of (+)-13e for the PCP receptor makes it among the most potent ligands known. In vitro neuroprotection was demonstrated by 3, (+)-3, and (+)-6 (N-Me-IDDC) against glutamate-induced cell death in rat hippocampal cells.

Effects of a novel NMDA antagonist on experimental stroke rapidly and quantitatively assessed by diffusion-weighted MRI

We employed diffusion-weighted MRI (DWI) to identify regions of focal brain ischemia during the first 3 hours after permanent occlusion of the middle cerebral artery in rats. Using DWI as early as 30 minutes after the onset of ischemia, it was possible to identify the areas of brain destined to progress to infarction over the next 24 hours in untreated animals, as demonstrated by postmortem evaluation. DWI studies revealed the cerebroprotective effects of a noncompetitive N-methyl-D-aspartate receptor antagonist, CNS 1102, administered 15 minutes postocclusion, both on the cortical and caudoputaminal regions during the initial 3 hours of ischemia. Although the treatment effect lessened over the next 21 hours in a few animals with lower plasma drug levels at 3 hours, postmortem studies demonstrated a 66% reduction in the total volume of infarcted tissue with the treatment and confirmed the DWI results. T2-weighted MRI obtained at similar times revealed little or no abnormality. These results suggest that DWI provides a sensitive in vivo measure of focal cerebral ischemic injury and can assess the beneficial effects of cytoprotective therapy. DWI may be useful in the early evaluation of human stroke patients and in monitoring the effects of cerebroprotective therapies in the clinical setting.

New CNS-specific calcium antagonists

Ischemic insults to the brain in stroke or traumatic brain injury produce excessive release of glutamate from depolarized nerve terminals. This excessive glutamate release in turn stimulates massive calcium entry into nerve cells, activating a biochemical cascade that results in cell death. A major pathway of calcium entry into depolarized nerve cells is through voltage-sensitive, high threshold calcium channels. A large fraction of this calcium entry is mediated through "R-type" calcium channels, channels resistant to blockage by dihydropyridine calcium antagonists such as nimodipine. A newly discovered compound derived from spider venom, CNS 2103, antagonizes both R-type channels and dihydropyridine-sensitive ("L-type") calcium channels. This broad spectrum of action, coupled with selectivity for calcium channels over other classes of voltage-sensitive and ligand-gated ion channels, makes CNS 2103 an interesting lead for development of drugs to treat ischemic brain injury. Activation of presynaptic ("N-type") calcium channels in nerve terminals is a primary cause of excessive neurotransmitter release in brain ischemia. Prevention of glutamate release by blockade of N-type channels in glutamatergic nerve terminals may, at an early stage in the pathophysiological cascade, abort the process leading to nerve cell death. Cambridge NeuroScience has developed a novel rapid kinetic approach for monitoring glutamate release from brain nerve terminals in vitro, and this has led to CNS 1145, a substituted guanidine that selectively blocks a kinetic component of calcium-dependent glutamate release mediated by persistent depolarization. Additional evidence suggests that CNS 1145 antagonizes presynaptic N-type calcium channels, and this may account at least in part for its ability to block glutamate release.

Synthesis and characterization of a series of diarylguanidines that are noncompetitive N-methyl-D-aspartate receptor antagonists with neuroprotective properties

Four diarylguanidine derivatives were synthesized. These compounds were found to displace, at submicromolar concentrations, 3H-labeled 1-[1-(2-thienyl)cyclohexyl]piperidine and (+)-[3H]MK-801 from phencyclidine receptors in brain membrane preparations. In electrophysiological experiments the diarylguanidines blocked N-methyl-D-aspartate (NMDA)-activated ion channels. These diarylguanidines also protected rat hippocampal neurons in vitro from glutamate-induced cell death. Our results show that some diarylguanidines are noncompetitive antagonists of NMDA receptor-mediated responses and have the neuroprotective property that is commonly associated with blockers of the NMDA receptor-gated cation channel. Diarylguanidines are structurally unrelated to known blockers of NMDA channels and, therefore, represent a new compound series for the development of neuroprotective agents with therapeutic value in patients suffering from stroke, from brain or spinal cord trauma, from hypoglycemia, and possibly from brain ischemia due to heart attack.

Conductance states activated by glycine and GABA in rat cultured spinal neurones

The conductance properties of single Cl- channels activated by glycine and gamma-aminobutyric acid (GABA) were examined in rat spinal cord neurones grown in cell culture. The majority (85%) of spinal neurones were sensitive to both glycine and GABA as were most (83%) outside-out patches tested. Glycine and GABA activated multiple conductance state Cl- channels with linear current-voltage properties when the chloride activities of the solutions bathing both sides of the membrane were similar. Glycine activated six distinct conductance states with conductances of 14, 20, 30, 43, 64 and 93 pS, whereas GABA activated five states with conductances of 13, 20, 29, 39 and 71 pS. The 30 and 43 pS states and the 20 and 29 pS states were observed most frequently with glycine and GABA, respectively. As the values of the glycine- and GABA-activated conductance states form a geometric progression when arranged in ascending order, we concluded that the channels do not consist of a cluster of identical pores. Additional conductance states (50 and 100 pS) were activated by glycine occasionally. The similarity between the conductances of the states activated by the two transmitters is consistent with the proposal that they both activate the same type of Cl- channel.

Caesium ions: a glycine-activated channel agonist in rat spinal cord neurones grown in cell culture

1. The chloride (Cl-) currents activated by caesium ions (Cs+), glycine and gamma-aminobutyric acid (GABA) were compared following their application to rat neurones that had been grown in cell culture. Recordings were made using the whole-cell patch clamp technique under voltage clamp conditions. 2. In spinal cord neurones, bicuculline methiodide antagonized GABA-activated currents more effectively than Cs+ - or glycine-activated currents. However, strychnine was more effective at blocking the currents activated by Cs+ or glycine than those activated by GABA. 3. Of the 3 agonists, only GABA activated currents in cells from the intermediate lobe of the rat pituitary. 4. In spinal neurones the size of the currents activated by 70 mM Cs+ was correlated to the size of the currents activated by 15 microM glycine (P less than 0.005; n = 10, Spearman's rank correlation), but there, was no significant correlation between the size of the currents activated by these agents and 10 microM GABA. 5. The joint application of glycine and Cs+ activated currents that were approximately twice as big as the sums of the currents activated by separate applications of the same doses. This synergism was consistent with Cs+ acting at the same receptor as glycine (7 microM glycine being equivalent to 31 +/- 7 mM Cs+). 6. It was concluded that Cs+ activates the same Cl- channel as the inhibitory neurotransmitter glycine.

The firing patterns of rat melanotrophs recorded using the patch clamp technique

Cell-attached and whole-cell recordings were made from adult rat melanotrophs maintained in vitro by standard cell culture techniques. In cell-attached recordings the cells showed small biphasic currents which reflected spontaneous cell firing. Single channel currents often had distinct relaxations and depolarizing currents through single channels could trigger the discharge of an action potential in the cell; both observations are consistent with the high input resistance (1-10 G omega) measured in the whole-cell configuration. The discharge of action potentials occurring either spontaneously or by current injection was eliminated by tetrodotoxin or by removing Na from the external medium. A Na-dependent plateau depolarization which activated near the spike threshold was also seen. In cells exposed to tetrodotoxin and K-channel blocking agents it was possible to evoke a long-lasting (up to 20 s) action potential which was enhanced and reduced, respectively, by Ba and Cd and thus appeared to reflect currents through voltage-activated Ca channels. Small amplitude Ca-dependent depolarizations could also be evoked at membrane potentials as low as -40 mV. In cell-attached and whole-cell recordings 10 mM Ba caused the discharge of tetrodotoxin-insensitive action potentials prior to a maintained depolarization of the membrane. The low threshold for Ca-dependent depolarizations suggest that Ca influx might occur in these cells even at the resting potential. Additionally, both a Ca current and the current underlying the Na-dependent plateau depolarization may influence the rate of cell firing and in doing so further increase Ca influx through voltage-activated channels.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrophysiology of neurosecretory cells from the pituitary intermediate lobe

One of the goals in studying the electrical properties of neurosecretory cells is to relate their electrical activity to the process of secretion. A central question in these studies concerns the role of transmembrane calcium ion flux in the initiation of the secretory event. With regard to the secretory process in pituitary cells, several research groups have addressed this question in vitro using mixed primary anterior pituitary cell cultures or clonal cell lines derived from pituitary tumours. Other workers, including ourselves, have used homogeneous cell cultures derived from the pituitary intermediate lobes of rats to examine the characteristics of voltage-dependent conductances, the contribution of these conductances to action potentials and their role in stimulus-secretion coupling. Pars intermedia (PI) cells often fire spontaneous action potentials whose frequency can be modified by the injection of sustained currents through the recording electrode. In quiescent cells action potentials can also be evoked by the injection of depolarizing current stimuli. At around 20 degrees C these action potentials have a duration of about 5 ms. Although most of the inward current during action potentials is carried by sodium ions, a calcium ion component can be demonstrated under abnormal conditions. Voltage-clamp experiments have revealed that the membrane of these cells contains high-threshold, L-type, Ca2+ channels and low-threshold Ca2+ channels. Since hormone release from PI cells appears not to be dependent on action potential activity but does depend on external calcium ions, it is not clear what role these Ca2+ channels play in stimulus-secretion coupling in cells of the pituitary pars intermedia. One possibility is that the low-threshold Ca2+ channels are more important to the secretory process than the high-threshold channels.

A patch clamp study of gamma-aminobutyric acid (GABA)-induced macroscopic currents in rat melanotrophs in cell culture

1. The macroscopic currents induced in cultured rat melanotrophs by exogenous gamma-aminobutyric acid (GABA) were analysed using the patch clamp recording technique. 2. Using various concentrations of intra- and extracellular chloride it was demonstrated that the conductance activated by GABA was chloride selective. Since these currents were blocked with bicuculline and enhanced with chlordiazepoxide the involvement of GABAA receptors similar to those in the CNS is indicated. 3. When chloride was symmetrically distributed across the membrane the voltage/current relationship was linear; pronounced rectification of GABA mediated currents was evident when there was an asymmetrical distribution of chloride. 4. With concentrations of GABA greater than 10 microM a fading of the current was seen during prolonged (5-10 s) applications. This effect appeared to be due to a decline of conductance rather than a shift of the chloride equilibrium potential. 5. Values for the Hill coefficient derived from dose-response curves suggested that the binding of 2 molecules of GABA to the receptor is required for the activation of the chloride channel. 6. There was no indication of a direct, GABAB receptor-mediated change of conductance.

Caesium ions activate chloride channels in rat cultured spinal cord neurones

1. Caesium ions (Cs+), applied extracellularly, caused a decrease in the input resistance of cultured spinal cord (s.c.) neurones and depolarized the neurones when they contained 140 mM-CsCl. 2. The reversal potential for Cs+-activated currents shifted 56 mV on average for a 10-fold reduction in the intracellular chloride ion (Cl-) activity, indicating that the Cs+-activated currents were specific to Cl-. 3. The activation of Cl- currents by Cs+ was not due to the depolarization-evoked release of neurotransmitter from presynaptic terminals. We therefore suggest that Cs+ were acting directly on the extracellular surface of the s.c. neurones to activate Cl- currents. 4. Cs+-activated currents showed desensitization in the presence of 140 mM-Cs+. 5. The log-log plot of the dose-response data could be fitted with a straight line with a slope of 1.7 +/- 0.4 (n = 6), indicating that at least 2 Cs+ were needed to activate a single Cl- channel. The KD of the Cs+-induced response was greater than 69 mM. 6. In outside-out patches Cs+ activated single Cl- channels. These channels were not activated by sodium or potassium ions. 7. The Cs+-activated channels displayed a total of five distinct conductance states which had mean conductances of 20, 30, 43, 66 and 92 pS. The 30 and 43 pS states were the most frequently occurring states. 8. The conductance states of the Cs+-activated channel have the same conductances as those reported for gamma-aminobutyric acid (GABA)- and glycine-activated channels in rat s.c. neurones. We therefore conclude that Cs+ activate the same type of Cl- channel as GABA and glycine through an unidentified receptor.

The measurement of changes in intracellular free calcium during action potentials in mammalian neurones

This report describes the techniques we have developed to record changes in intracellular calcium concentration which take place during action potentials in the cell body of rat dorsal root ganglion neurones in vitro. The photoprotein, aequorin, was microinjected into the cell body of individual sensory neurones and light output from Ca2+-activated aequorin molecules was recorded with a photomultiplier tube attached to a modified inverted microscope. Aspects of the technology outlined here include: cell culture methods; a flow chamber for electrophysiological experiments on cell culture preparations; modifications to our inverted microscope; use of 150 mM KCl-filled microelectrodes; and an electronic device for processing the photomultiplier output. Some preliminary results are presented.

Role for microsomal Ca storage in mammalian neurones?

Alterations in the intracellular concentration of calcium ions [( Ca2+]i) are increasingly being found to be associated with regulatory functions in cells of all kinds. In muscle, an elevation of [Ca2+]i is the final link in excitation-contraction coupling while at nerve endings and in secretory cells, similar rises in [Ca2+]i are thought to mediate exocytosis. The discovery of calcium-activated ion channels indicated a role for intracellular calcium in the regulation of membrane excitability. Calcium transients associated with either intracellular release or the inward movement of Ca2+ across the membrane have been recorded in molluscan neurons and more recently in neurones of bullfrog sympathetic ganglia. Here, we report the first recordings of calcium transients in single mammalian neurones. In these experiments we have found that the methylxanthine, caffeine, causes the release of calcium from a labile intracellular store which can be refilled by Ca2+ entering the cell during action potentials.

Convulsant-induced depression of amino acid responses in cultured mouse spinal neurones studied under voltage clamp

A two-microelectrode voltage-clamp technique was used to record membrane current responses induced by the application of the neutral amino acids, gamma-aminobutyric acid (GABA) and glycine, to mouse spinal neurones maintained in cell culture. Membrane current responses to GABA were depressed by the convulsant agents, bicuculline, picrotoxin and pentylenetetrazole. Membrane current responses to glycine were depressed by the convulsant compound, strychnine. Analysis of the fluctuations in membrane current about the mean response during prolonged applications of GABA revealed that neither the conductance nor the average open-time of GABA-activated ion-channels was altered in the presence of picrotoxin or bicuculline. Pentylenetetrazole caused a reduction in the open-time of GABA-activated ion-channels but this effect alone was too small to account for the depression of the current response. A similar analysis of glycine-induced responses in the presence of strychnine revealed that the depression of glycine responses by strychnine was not associated with any changes in the conductance or average open-time of glycine-activated ion-channels. We therefore conclude that the convulsant compounds act by reducing the rate of activation of ion-channels by the neutral amino acids either through a reduction in the number of free receptors or by a change in the kinetics of channel activation.

Fluctuation analysis of neutral amino acid responses in cultured mouse spinal neurones

1. Intracellular recordings using the voltage-clamp technique were made at room temperature (24 +/- 1.5 degrees C) from mouse spinal and sensory neurones growing in dissociated cell culture. 2. Membrane current responses could be elicited by ionophoresis of the neutral amino acids, gamma-aminobutyric acid (GABA), beta-alanine (BALA) and glycine to the cell body and processes of these neurones. 3. All membrane current responses were associated with increases in current fluctuations. Most of the analysis presented here was applied to responses generated at the cell body. 4. Many of the fluctuations in membrane current occurring during the responses could be interpreted as reflecting the kinetic behaviour of a single population of two-state Cl- ion-channels. 5. The properties of channels estimated during the desensitized phase of an amino acid-induced current response were not significantly different from those estimated during the peak of the response. 6. The properties of the amino acid-activated channels were relatively constant over the -40 to -90 mV range of membrane potential. 7. There was considerable variation in the estimated average conductance, gamma, and duration, tau, of the elementary events evoked by the neutral amino acids on spinal cord neurones. The properties of the elementary channel events activated by one of the amino acids were significantly different from those activated on the same neurones by either of the other amino acids. 8. In sensory neurones the average gamma and tau values for GABA-activated ion-channels were also determined and these values fell within the range of those for channels activated by GABA in spinal neurones. 9. The results indicate that different naturally occurring neutral amino acids activate channels with unique properties in cultured mouse spinal neurones. The relative charge transfer associated with these channels averages 1.00:0.74:0.32; GABA:glycine:beta-alanine.

Light-induced changes in membrane current in cone outer segments of tiger salamander and turtle

The peak change in membrane conductance of vertebrate photoreceptors in response to the isomerization of a single photopigment has been estimated from recordings of membrane potential to be about 8 pS in rods and 6 pS in cones. For rods the estimate has been largely confirmed by Yau et al. by directly recording membrane current responses of rod outer segments to single photoisomerizations. However, no similar measurements have been reported for cone outer segments. Here, we report on direct recordings of membrane currents of single cone outer segments using an extracellular patch electrode. The technique was similar to that described by Yau et al. for toad rods. We have measured dark currents of up to 40 pA, and calculate that the conductance change resulting from a single photoisomerization is less than 1 pS.

Phenobarbitone modulation of postsynaptic GABA receptor function on cultured mammalian neurons

The anticonvulsant barbiturate phenobarbitone increases membrane current and conductance responses to gamma-aminobutyric acid (GABA) in cultured mouse spinal neurons. Analyses of GABA current fluctuations under control conditions and in the presence of phenobarbitone show that the principle action is to increase the average time during which GABA-activated channels remain open. The duration of minature synaptic currents with a time constant of decay similar to the mean open-time of GABA-activated channels is prolonged by the drug. The results suggest that (1) the synaptic events are GABA-mediated and (2) the enhancement of these events by barbiturate is due to the postsynaptic action of the drug.

Octanol reduces end-plate channel lifetime

1. Post-synaptic effects of n-octanol at concentrations of 0.1-1 mM were examined in toad sartorius muscles by use of extracellular and voltage-clamp techniques.2. Octanol depressed the amplitude and duration of miniature end-plate currents and hence depressed neuromuscular transmission.3. The decay of miniature end-plate currents remained exponential in octanol solutions even when the time constant of decay (tau(D)) was decreased by 80-90%.4. The lifetime of end-plate channels, obtained by analysis of acetylcholine noise, was also decreased by octanol. The average lifetime measured from noise spectra agreed reasonably well with the time constant of decay of miniature end-plate currents, both in control solution and in octanol solutions.5. Octanol caused a reduction in the conductance of end-plate channels. Single channel conductance was on average about 25 pS in control solution and 20 pS in octanol.6. In most cells the normal voltage sensitivity of the decay of miniature end-plate currents was retained in octanol solutions. The lifetime of end-plate channels measured from acetylcholine noise also remained voltage-sensitive in octanol solutions. In some experiments in which channel lifetime was exceptionally reduced the voltage sensitivity was less than normal.7. In octanol solutions, tau(D) was still very sensitive to temperature changes in most cells although in some the temperature sensitivity of tau(D) was clearly reduced. Changes in tau(D) with temperature could generally be fitted by the Arrhenius equation suggesting that a single step reaction controlled the decay of currents both in control and in octanol solutions. In some cells in which tau(D) became less than 0.3 ms, the relationship between tau(D) and temperature became inconsistent with the Arrhenius equation.8. As the decay of end-plate currents in octanol solutions remains exponential, and the voltage and temperature sensitivity can be unchanged even when tau(D) is significantly reduced, it seems likely that octanol decreases tau(D) by increasing the rate of the reaction which normally controls the lifetime of end-plate channels.

The synergistic action of L-glutamate and L-aspartate at crustacean excitatory neuromuscular junctions

1. When L-glutamate and L-aspartate are simultaneously applied to the excitatory neuromuscular junctions of Maia squinado, they produce an increase in the conductance of the post-synaptic membrane much larger than the sum of conductance effects produced by the individual amino acids alone. 2. An examination of the synaptic noise occurring during this synergistic action reveals that the elementary conductnace events produced by aspartate are suppressed and that normal elementary conductance events produced by glutamate are occurring at an enormously increased rate. 3. It is suggested that aspartate causes this potentiation by inhibiting a system for transmitter inactivation in the region of the post-synaptic receptors and that this system, under normal conditions, prevents the access of externally applied glutamate to the synaptic receptors.

The termination of transmitter action at the crustacean excitatory neuromuscular junction

1. Excitatory junctional currents (e.j.c.s) and miniature excitatory junctional currents (mine.e.j.c.s) have been followed by recording the focal extracellular potential at excitatory neuromuscular junctions of Maia squinado, the Spider Crab. 2. If L-aspartate (concentrations less than or equal to 1 mM) is present in the saline, the average e.j.c. is prolonged by an increase in the duration of its falling phase. 3. No change occurs in the time course of the probablility of release of quanta in the e.j.c. as determined from the histogram of first quantal latencies. 4. The min.e.j.c. is also prolonged by L-aspartate (concentrations less than or equal to 0-5 mM). The rise time increases slightly, the pre-exponential period of the decay phase almost doubles, and the time constant of the final exponential decay increases to a value larger than the average lifetime of the elementary conductance event produced by L-glutamate. 5. Changes in e.j.c.s and min.e.j.c.s produced by aspartate show a striking similarity to the action of neostigmine on the time course of the vertebrate end-plate current. It is proposed that aspartate exerts its action by blocking a process normally reponsible for clearing the synaptic cleft of transmitter.

On the elementary conductance event produced by L-glutamate and quanta of the natural transmitter at the neuromuscular junctions of Maia squinado

1. The membrane potential of giant muscle fibres of Maia squinado was measured with an intracellular wire electrode. On applying L-glutamate to the fibre the cell deplorized and fluctuations of the membrane potential around its mean level--glutamate noise--were seen. 2. The variance of the glutamate voltage noise is proportional to the mean level of depolarization. The noise can be regarded as being caused by numerous exponentially decaying elementary voltage events about 5 X 10(-10) V in amplitude. The miniature excitatory junctional potential (min.e.j.p.) is approximately 6000 times the amplitude of the elementary voltage event produced by L-glutamate. 3. The power spectrum of glutamate voltage noise is a Lorentzian with a half-power frequency of approximately 20 Hz. 4. Min. e.j.p.s. decay exponentially with a time constant that coincides with the average lifetime of the elementary glutamate voltage event. 5. When glutamate is applied locally to a spot where extracellular min. e.j.p.s. can be recorded with a focal glass pipette, extracellular glutamate noise is seen. Glutamate noise could not be detected from elsewhere on the fibre. 6. The variance of the extracellular noise is proportional to the mean extracellular potential, and its power spectrum is a Lorentzian with a half-power frequency of about 110 Hz. 7. The extracellular min. e.j.p.s decay exponentially with a time constant that coincides with average lifetime of the elementary glutamate current event. 8. It is suggested that the decay of the quantal currents flowing at the excitatory junction is limited by the closure of the conductance channels in the post-synaptic membrane and not by the relaxation of the transmitter concentration in the synaptic cleft.

The post-synaptic action of some putative excitatory transmitter substances

L-Glutamate, L-aspartate and L-cysteate all produce current fluctuations when applied to the excitatory junctional membrane of Maia squinado . This post-synaptic ‘noise’ indicates that all three substances cause an elementary conductance event of approximately the same amplitude but with different average lifetimes. The mean lifetime of the ‘molecular shot effect’ produced by L-aspartate and L-cysteate is only about half that of L-glutamate.

Effects of membrane potential, temperature and neostigmine on the conductance change caused by a quantum or acetylcholine at the toad neuromuscular junction

1. Miniature end-plate currents were recorded at neuromuscular junctions of toads, either in voltage-clamped fibres or with extracellular electrodes. The two methods gave similar results. 2. Two types of m.e.p.c.s, differing in their growth times (50-300 musec and 0-5-5 msec) were found. The more frequent had the shorter growth times. 3. The decay of m.e.p.c.s was exponential with a single time constant. The time constant was an exponential function of membrane potential, becoming less as the membrane was depolarized. In contrast, there was little change, or in some cases an increase, in growth times of m.e.p.c.s when the membrane was depolarized. 4. The decay time constant had a Q-10 of 3-13 plus or minus 0-22 (mean plus or minus S.E. of mean) whereas the growth time had a significantly lower Q-10 of about 1-2. The change of decay time constant with temperature followed the Arrhenius equation giving an activation energy of 18 plus or minus 1-0 kcal (mean plus or minus S.E. of mean). The amplitude of m.e.p.c.s increased with temperature and had a Q-10 of 1-5 plus or minus 0-14 (mean plus or minus S.E. of mean) in voltage-clamped fibres. 5. Neostigmine prolonged the decay phase and increased the amplitude of m.e.p.c.s but had little effect on the growth phase. The changes in m.e.p.c.s caused by membrane potential and temperature were not affected by neostigmine. 6. The results show that the growth phase and decay phase of m.e.p.c.s are governed by processes with quite different characteristics. The reaction which limits the decay phase appears first-order, is voltage sensitive and has a Q-10 of about 3, whereas the reaction underlying the growth phase does not appear first-order, is less voltage-sensitive and has a Q-10 of about 1-2. It is suggested that diffusion of transmitter across the synaptic cleft may be the rate-limiting step during the growth phase.

Effects of some aliphatic alcohols on the conductance change caused by a quantum of acetylcholine at the toad end-plate

1. The post-synaptic effects of the aliphatic alcohols, ethanol to hexanol, were investigated at the neuromuscular junctions of toads, with particular emphasis on the effects of ethanol. 2. The alcohols increased the amplitude and duration of miniature end-plate potentials. It is shown that this effect was due to the prolongation of the decay phase of miniature end-plate currents (m.e.p.c.s). There was no effect of alcohols on the growth phase of m.e.p.c.s. 3. The prolonged decay of m.e.p.c.s in ethanol remained exponential and was normally sensitive to membrane potential. Prolonged m.e.p.c.s were associated with an equivalent prolongation of the mean duration of elementary events, as determined from power spectra of acetylcholine noise in 0-5 M ethanol. 4. The relationship betweeen the time constant of decay of m.e.p.c.s (tau) and the concentration of an alcohol of carbon chain length N (C-N) was exponential, conforming to the equation tau equals tau-s exp (B-N-C-N), in which tau-s is the decay time constant in standard solution and B-N is a constant, different for each alcohol. 5. There was also an exponential relationship between B-N and N, which closely followed the relationship between membrane-buffer partition coefficient and carbon chain length for the different alcohols, indicating that the alcohols are active in the lipid phase of the post-synaptic membrane. 6. It is suggested that the alcohols act by causing a change in the dielectric constant of the post-synaptic membrane which forms the environment of the rate-limiting reaction responsible for the decay of the end-plate conductance. On the assumption that this reaction involves dipoles, it is shown that the small changes in dielectric constant, calculated from the partition coefficients of the alcohols and by assuming an initial lipid dielectric constant of 3, would give an exponential relationship between the time constant of decay of m.e.p.c.s and alcohol concentration. 7. The results support the hypothesis that the decay (but not the onset) of acetylcholine-induced conductance changes is rate-limited by a first-order reaction which involves dipoles and occurs in the lipid environment of the post-synaptic membrane.

Miniature end-plate currents and potentials generated by quanta of acetylcholine in glycerol-treated toad sartorius fibres

1. Part of the end-plate region of glycerol-treated toad sartorius muscle fibres in a hypertonic solution was voltage-clamped using two microelectrodes. The control was adequate for recording miniature end-plate currents (m.e.p.c.s) in the vicinity of the electrodes only, at clamp potentials from - 20 to - 100 mV. At any potential, the peak amplitude of m.e.p.c.s varied widely but their mean amplitude was linearly related to clamp potential. The equilibrium potential, obtained by extrapolation, was more positive than in normal fibres.2. The growth phase of m.e.p.c.s was linear and rapid (< 0.7 msec). The decay phase was exponential. The time constant of decay of m.e.p.c.s was affected by temperature, and increased as the membrane potential was increased. At 20 degrees C, the time constant of decay ranged from 0.8 to 3.8 msec at membrane potentials from - 20 to - 100 mV.3. The mean conductance change caused by a quantum of acetylcholine was 5.5 x 10(-8) mho.4. Voltage responses to rectangular current injections through one electrode were recorded with three other electrodes in the end-plate region of glycerol-treated fibres. Miniature end-plate potentials (m.e.p.p.s) were also recorded with the same four electrodes.5. The decrement of both DC voltage responses and m.e.p.p.s along a fibre was exponential but the m.e.p.p. ;space constant' was significantly shorter than the DC space constant.