Effectiveness of a paediatric weight management intervention for rural youth (iAmHealthy): Primary outcomes of a cluster randomised control trial

BACKGROUND

Youth in rural areas are disproportionally affected by obesity. Given the unique barriers rural populations face, tailoring and increasing access to obesity interventions is necessary.

OBJECTIVE

This paper evaluates the effectiveness of iAmHealthy, a family-based paediatric obesity intervention delivered to rural children, compared to a Newsletter Control.

METHODS

Participating schools (n = 18) were randomly assigned to iAmHealthy or Newsletter Control. iAmHealthy consists of individual health coaching and group sessions delivered via televideo to a participant's home. The child and parent's body mass index (BMI), child physical activity and child dietary intake were assessed at baseline, post-treatment (8 months) and follow-up (20 months). Multilevel modeling estimated the effect of treatment at both time points.

RESULTS

Parent and child dyads were recruited (n = 148) and randomised to iAmHealthy (n = 64) or the Control group (n = 84). The Control group had significant increases in child BMIz from baseline to follow-up. iAmHealthy youth had no significant changes in BMIz from baseline to post or follow-up. Child dietary intake, physical activity and parent BMI results are also discussed.

CONCLUSIONS

This trial extends previous paediatric obesity work by simultaneously increasing convenience and dose of treatment. Results suggest iAmHealthy resulted in a change in BMIz trajectories and long-term health behaviour for youth.

Validation of remote anthropometric measurements in a rural randomized pediatric clinical trial in primary care settings

Rural children are more at risk for childhood obesity but may have difficulty participating in pediatric weight management clinical trials if in-person visits are required. Remote assessment of height and weight observed via videoconferencing may provide a solution by improving the accuracy of self-reported data. This study aims to validate a low-cost, scalable video-assisted protocol for remote height and weight measurements in children and caregivers. Families were provided with low-cost digital scales and tape measures and a standardized protocol for remote measurements. Thirty-three caregiver and child (6-11 years old) dyads completed remote (at home) height and weight measurements while being observed by research staff via videoconferencing, as well as in-person measurements with research staff. We compared the overall and absolute mean differences in child and caregiver weight, height, body mass index (BMI), and child BMI adjusted Z-score (BMIaz) between remote and in-person measurements using paired samples t-tests and one sample t-tests, respectively. Bland-Altman plots were used to estimate the limits of agreement (LOA) and assess systematic bias. Simple regression models were used to examine associations between measurement discrepancies and sociodemographic factors and number of days between measurements. Overall mean differences in child and caregiver weight, height, BMI, and child BMIaz were not significantly different between remote and in-person measurements. LOAs were - 2.1 and 1.7 kg for child weight, - 5.2 and 4.0 cm for child height, - 1.5 and 1.7 kg/m2 for child BMI, - 0.4 and 0.5 SD for child BMIaz, - 3.0 and 2.8 kg for caregiver weight, - 2.9 and 3.9 cm for caregiver height, and - 2.1 and 1.6 kg/m2 for caregiver BMI. Absolute mean differences were significantly different between the two approaches for all measurements. Child and caregiver age were each significantly associated with differences between remote and in-person caregiver height measurements; there were no significant associations with other measurement discrepancies. Remotely observed weight and height measurements using non-research grade equipment may be a feasible and valid approach for pediatric clinical trials in rural communities. However, researchers should carefully evaluate their measurement precision requirements and intervention effect size to determine whether remote height and weight measurements suit their studies.Trial registration: ClinicalTrials.gov NCT04142034 (29/10/2019).

Recruitment and reach in a school-based pediatric obesity intervention trial in rural areas

Introduction

The purpose of this study is to evaluate two recruitment strategies on schools and participant participation rates and representativeness (reach) within a pediatric obesity treatment trial tailored for families who live in rural areas.

Methods

Recruitment of schools was evaluated based on their progress toward enrolling participants. Recruitment and reach of participants were evaluated using (1) participation rates and (2) representativeness of demographics and weight status of participants compared to eligible participants (who did not consent and enroll) and all students (regardless of eligibility). School recruitment, as well as participant recruitment and reach, were evaluated across recruitment methods comparing opt-in (i.e., caregivers agreed to allow their child to be screened for eligibility) vs. screen-first (i.e., all children screened for eligibility).

Results

Of the 395 schools contacted, 34 schools (8.6%) expressed initial interest; of these, 27 (79%) proceeded to recruit participants, and 18 (53%) ultimately participated in the program. Of schools who initiated recruitment, 75% of schools using the opt-in method and 60% of schools using the screen-first method continued participation and were able to recruit a sufficient number of participants. The average participation rate (number of enrolled individuals divided by those who were eligible) from all 18 schools was 21.6%. This percentage was higher in schools using the screen-first method (average of 29.7%) compared to schools using the opt-in method (13.5%). Study participants were representative of the student population based on sex (female), race (White), and eligibility for free and reduced-price lunch. Study participants had higher body mass index (BMI) metrics (BMI, BMIz, and BMI%) than eligible non-participants.

Conclusions

Schools using the opt-in recruitment were more likely to enroll at least 5 families and administer the intervention. However, the participation rate was higher in screen-first schools. The overall study sample was representative of the school demographics.

Riding into Health: A Case Study on an Equine-Assisted Childhood Obesity Intervention

In this article, we present an exploratory case study that describes the initial outcomes of the Equine-Assisted Positively Fit (EAPF) program. Children with obesity and their caregivers were recruited to participate in the eight-session program. Results indicated that treatment completers (n = 2) had a decrease in fat mass and fat mass percentage and an increase in fat-free mass and fat-free mass percentage. Moreover, results from accelerometer measurements of physical activity indicated that participants increased their moderate to vigorous physical activity, as well as reported increased self-efficacy for physical activity. Qualitative data from the post-intervention focus group suggested children perceived the treatment acceptable and enjoyable. Findings from this study provide support for future investigations on the feasibility and potential efficacy of pairing children and their caregivers with horses to accomplish health-related goals.

Interaction between synaptic excitation and slow afterhyperpolarization current in rat hippocampal pyramidal cells

1. Whole cell recordings from CA1 pyramidal cells were performed to investigate the interaction between excitatory postsynaptic potentials (EPSPs) or currents (EPSCs), and the slow Ca(2+)-dependent K(+) current, I(sAHP). Blockers of the slow afterhyperpolarization (sAHP) such as isoprenaline (ISO) or noradrenaline (NA) reduced the hyperpolarization that followed a short train of EPSPs, and slowed the decay of summated EPSPs or EPSCs. 2. ISO/NA action on synaptic responses was observed in the absence of action potentials, but was curtailed by Ca(2+) chelation (10 mM EGTA in the electrode) and was not observed with a caesium-based recording solution. This suggests the involvement of an ISO/NA-sensitive Ca(2+)-dependent K(+) current without a requirement for regenerative spiking. 3. An ISO/NA-sensitive sAHP was observed following both NMDA and non-NMDA receptor-mediated EPSP trains in nominally zero Mg(2+) medium. Isoprenaline sensitivity was blocked by hyperpolarization during EPSPs or by isradipine, suggesting a requirement for voltage-dependent Ca(2+) influx during EPSPs. The data indicate that bursts of EPSPs can activate voltage-gated Ca(2+) channels, which trigger I(sAHP) during synaptic responses. 4. A decrease in EPSP temporal summation occurred during both spike-evoked sAHPs and persistent activation of sAHP conductance following internal dialysis with diazo-2 (2 mM). At constant membrane potential, diazo-2 caused a decrease in membrane time constant and input resistance and accelerated the rate of EPSP decay. Photolysis of diazo-2 or application of NA reduced the resting sAHP conductance, causing an increased membrane time constant and input resistance in association with an increase in EPSP half-width. 5. These results indicate that short bursts of EPSPs can activate a Ca(2+)-dependent K(+) current resembling I(sAHP), and that activation of this current reduces the postsynaptic response to high-frequency synaptic input. The findings imply that modulation of I(sAHP) can regulate synaptic efficacy and may influence the threshold for tetanus-induced synaptic plasticity.

Health promotion in the city: a structured review of the literature on interventions to prevent heart disease, substance abuse, violence and HIV infection in US metropolitan areas, 1980-1995

To achieve its national public health goals, the US must improve the health of low-income urban populations. To contribute to this process, this study reviewed published reports of health promotion interventions designed to prevent heart disease, HIV infection, substance abuse, and violence in US cities. The study's objectives were to describe the target populations, settings, and program characteristics of these interventions and to assess the extent to which these programs followed accepted principles for health promotion. Investigators searched five computerized databases and references of selected articles for articles published in peer-reviewed journals between 1980 and 1995. Selected articles listed as a main goal primary prevention of one of four index conditions; were carried out within a US city; included sufficient information to characterize the intervention; and organized at least 25% of its activities within a community setting. In general, programs reached a diverse population of low-income city residents in a variety of settings, employed multiple strategies, and recognized at least some of the principles of effective health promotion. Most programs reported a systematic evaluation. However, many programs did not involve participants in planning, intervene to change underlying social causes, last more than a year, or tailor for the subpopulations they targeted, limiting their potential effectiveness. Few programs addressed the unique characteristics of urban communities.

Novel action of BAPTA series chelators on intrinsic K+ currents in rat hippocampal neurones

1. Whole-cell recordings were made from rat CA1 neurones in brain slices. When electrodes contained diazo-2 (2 mM) or dibromo BAPTA (1 mM) a large steady-state outward current (hundreds of picoamps) developed within 5 min of breakthrough at a VH of -60 mV. BAPTA itself (1 mM) caused qualitatively similar but smaller effects. 2. The outward current was accompanied by increased conductance with a null potential close to the calculated K+ equilibrium potential (EK) of -110 mV. Development of outward current occurred concurrently with progressive loss of slow AHP tail current (IsAHP) evoked by brief depolarizations. The peak latency of IsAHP increased during the onset of chelator action. 3. The persistent outward current was reversibly inhibited by noradrenaline (10 microM) or isoprenaline (2-5 microM), and completely prevented by 8-bromoadenosine 3',5' cyclic monophosphate (8-Br cAMP; 100 microM) or QX-314 (10 mM) in recording electrodes. After development of outward current, diazo-2 photolysis caused inward current and decreased conductance. Both flash- and noradrenergic-sensitive responses were inwardly rectifying outward currents with null potentials close to EK. 4. The outward current induced by dibromo BAPTA was not blocked by internal EGTA (10 mM). However, experiments incorporating Ca2+ influx or Ca2+ loading of the buffer indicate that Ca2+ facilitated the outward current. 5. The outward currents induced by dibromo BAPTA or diazo-2 were not associated with significant changes in resting [Ca2+]i. Regions of the cell contributing to the outward current were deduced from measurements of fura-2 diffusion. These were compared with regions of [Ca2+]i elevation during IsAHP. 6. These results are consistent with the hypothesis that the BAPTA series Ca2+ buffers can activate those Ca2+-activated K+ channels that underlie the slow AHP, without the predicted elevation of bulk [Ca2+]i. Therefore these results cannot be interpreted solely in terms of Ca2+ concentration changes, although the observations illustrate a novel, investigative role for these compounds in the study of Ca2+-dependent processes.

A peptide activator of endogenous tyrosine kinase enhances synaptic currents mediated by NMDA receptors

N-methyl-D-aspartic acid (NMDA) receptor currents in cultured cells or expression systems are increased by the addition of purified tyrosine kinases. However, there is no direct demonstration of this effect at NMDA receptors in intact synapses of rat brain slices. Transmitters which might be used to activate tyrosine kinases in situ are unlikely to have a sufficiently selective action to allow a clear interpretation of their effects. Therefore, we used a phosphotyrosine-containing decapeptide which can be included in recording electrodes to activate postsynaptic src-family tyrosine kinases. This peptide enhanced NMDA responses in dissociated hippocampal CA1 neurons. These effects were not reproduced by a non-phosphorylated peptide or a scrambled-sequence phosphopeptide. The enhancement of NMDA responses was blocked by a tyrosine kinase inhibitor. In brain slices the phosphopeptide, but not control peptide, increased NMDA receptor-mediated synaptic current indicating that endogenous tyrosine kinase can upregulate the response of NMDA receptors at glutamatergic synapses in the hippocampus.

Age, ethnicity, and comorbidity in a national sample of hospitalized alcohol-dependent women veterans

OBJECTIVE

Treatment patterns in a national sample of hospitalized women veterans diagnosed with alcohol dependence were identified with the goal of improving health services to women veterans with alcohol-related disorders.

METHODS

Information from VA's patient treatment file for fiscal year 1993 was used to identify 854 women veterans diagnosed with alcohol dependence. Of that group, 546 received a primary diagnosis of alcohol dependence, and 308 received a secondary diagnosis of alcohol dependence after they sought treatment for other health problems. Chi square tests and multivariate logistic regression analyses were used to examine relationships between the sociodemographic profiles of these women and the types of services they received.

RESULTS

The study population's largest age group (49 percent) was 30 to 39 years old. Fifty-two percent of the women were divorced or separated, and 62 percent were Caucasian. The overwhelming majority of comorbid diagnoses were of psychiatric disorders. Overall, only 47 percent of the 854 patients received formal treatment for their alcohol disorder, and only 34 percent completed alcohol treatment. Women over age 60 were significantly less likely than women in other age groups to enter or complete formal treatment. Native-American women were significantly more likely than Caucasians or African Americans to receive formal alcohol treatment services.

CONCLUSIONS

The results indicate a need for targeting interventions more effectively in certain groups of women veterans diagnosed with alcoholism. Low completion rates also suggest a need for greater incentives for patients to complete treatment programs.

Disease prevention and health promotion in urban areas: CDC's perspective

The mission of the Centers for Disease Control and Prevention (CDC) is to prevent disease, injury, and premature death and to promote quality of life. This mission applies to all Americans, especially to the poor and underserved. As so many people who are impoverished live in America's urban areas, the CDC has a unique and specific interest in the health problems of our urban population. The CDC has established five priorities: (1) strengthen essential public health services, (2) enrich capacity to respond to urgent threats to health, (3) develop a nationwide prevention network and program, (4) promote women's health, and (5) invest in our nation's youth. Each of these priorities will contribute to improving the health of people living in urban areas. The CDC has recently undertaken numerous initiatives to address health promotion and disease prevention issues in the urban setting. Future directions for the CDC lie in better understanding the role of socioeconomic and cultural factors in promoting health and how resources within urban areas can be used to promote health. The CDC needs to explore potential relationships with various types of partners. Solving urban health problems requires actions from many federal agencies as well as from state and local organizations.

Tyrosine kinase is required for long-term depression in the cerebellum

Long-term depression (LTD) at the parallel fiber-Purkinje cell synapse in the cerebellum is a well-known example of synaptic plasticity. Although LTD is thought to reflect an enduring loss of postsynaptic AMPA receptor sensitivity, the underlying mechanisms are unclear. Protein-tyrosine kinases (PTKs) are able to modulate ionotropic receptor function and are enriched in Purkinje cells. Using intracellular recording from Purkinje cells, it is shown that two structurally and mechanistically distinct PTK inhibitors, lavendustin A and herbimycin A, block LTD induced by pairing parallel fiber stimulation with postsynaptic Ca2+ spiking. Intracellular application of the protein kinase C (PKC) activator, (-)-indolactam V, consistently depressed parallel fiber-Purkinje cells EPSPs and occluded pairing-induced LTD. Herbimycin A nullified the run-down produced by (-)-indolactam V. These data suggest that PTKs are necessary for LTD at the parallel fiber-Purkinje cell synapse and that PKC-induced synaptic depression requires PTK activity.

Laparoscopic drainage of right subphrenic abscess: report of one case

Laparoscopic surgery has proven to be a very useful technique. Subphrenic abscess, although a rare entity, occurs in the majority of the cases in association with gastroduodenal and biliary disease, appendicitis, or following abdominal surgery. We present the case of a 45-year-old male with a right subphrenic abscess that was successfully treated by laparoscopy. Laparoscopic drainage of subphrenic abscess should be considered as an alternative modern option when dealing with this problem.

Interaction of the antiepileptic drug lamotrigine with recombinant rat brain type IIA Na+ channels and with native Na+ channels in rat hippocampal neurones

Actions of the new antiepileptic drug lamotrigine (LTG, Lamictal) were characterised using recombinant rat brain type IIA Na+ channels expressed in Chinese hamster ovary (CHO) cells and native Na+ channels in rat hippocampal pyramidal neurones, using whole-cell recording and intracellular recording techniques. In CHO cells, LTG caused a tonic inhibition of Na+ currents in a concentration-dependent and voltage-dependent manner. The half-maximal inhibitory concentration (IC50) of approximately 500 microM was obtained at a holding potential (Vh) of -90 mV compared with an IC50 of 100 microM at a Vh of -60 mV. LTG (50 microM) caused a 10-mV negative shift in the slow, steady-state inactivation curve and delayed considerably the recovery from inactivation, but had no significant effects on the voltage dependence of activation or fast inactivation, suggesting that LTG acts mainly on the slow inactivated state. The affinity for the inactivated channels was estimated at 12 microM. The tonic inhibition was augmented by a use-dependent action in which a further inhibition by the drug developed during rapid repetitive stimulation using a train of 20-ms duration pulses (11 Hz). These results were consistent with the drug action being on firing properties of pyramidal neurones. Only in those epilepti-form bursts which caused cumulative inactivation of Na+ spikes did LTG produce a potent inhibition. Our data suggest that the inactivated channel is a primary target for LTG action at therapeutic concentrations.

Drainage of hepatic amebic abscess successfully treated by laparoscopy

A case of hepatic amebic abscess is presented that was treated successfully by laparoscopy. The patient was fully worked up, including computed tomography (CT) scan, video-colonoscopy, and blood profiles. The laparoscopic surgical technique is fully discussed and proved to be a very useful tool in the management of this problem, obviating the need for a formal laparotomy and its potential complications.

Photolytic manipulation of Ca2+ and the time course of slow, Ca(2+)-activated K+ current in rat hippocampal neurones

1. Experiments were performed on hippocampal CA1 pyramidal cells to investigate the time course of a slow, Ca(2+)-activated K+ current that follows a burst of action potentials. At a temperature of 27-30 degrees C, this current rises to a peak 200-400 ms following the cessation of Ca2+ entry before decaying to baseline in 4-8s. 2. Intracellular recordings were made using electrodes containing the photolabile calcium buffers nitr-5 or DM-nitrophen loaded appropriately with Ca2+. Under these conditions, photolysis of the compound using an ultraviolet flashlamp caused an instantanous increase in cytoplasmic Ca2+ throughout the cell. The response to flash photolysis was a membrane hyperpolarization with an onset limited by the membrane time constant. Multiple (up to twenty) flash responses could be generated. 3. The postspike slow after-hyperpolarization (AHP) and flash-induced hyperpolarizations showed a common sensitivity to the beta-adrenergic receptor agonist isoprenaline. 4. Following a burst of spikes, the current underlying an AHP in progress could be terminated or reduced by photolysis-induced production of calcium buffer from diazo-4 within the cell. This action was rapid (within the setting time of the flash artifact, i.e. < 10 ms) despite the fact that the manipulation occurred 400-500 ms following the end of Ca2+ entry. 5. Partial block of the slow AHP by buffer production was accompanied by an increase in the time to peak of the event. 6. The time to peak of the slow AHP could also be manipulated by experiments which altered the spatial distribution of Ca2+ entry, such as production of calcium spikes or dendritic depolarization by glutamate in the presence of tetrodotoxin. 7. The Ca(2+)-dependent K+ current responsible for the slow AHP responds immediately to increase or decreases in cytoplasmic Ca2+. It seems likely, therefore, that the slow AHP is controlled solely by changes in free Ca2+ and that the time course is governed by the redistribution of cytoplasmic Ca2+ following activity-induced entry through voltage- or receptor-operated channels.

Temporal limits on the rise in postsynaptic calcium required for the induction of long-term potentiation

The induction of long-term potentiation (LTP) in hippocampal CA1 pyramidal cells requires a rise in postsynaptic intracellular Ca2+ concentration ([Ca2+]i). To determine the time for which Ca2+ must remain elevated to induce LTP, the photolabile Ca2+ buffer diazo-4 was used to limit the duration of the rise in postsynaptic [Ca2+]i following a tetanus. The affinity of diazo-4 for Ca2+ increases approximately 1600-fold upon flash photolysis, permitting almost instantaneous buffering of [Ca2+]i without disturbing resting [Ca2+]i prior to the flash. Photolysis of diazo-4 1 s following the start of the tetanus blocked LTP, while delaying photolysis for more than 2 s had no discernible effect on LTP. Photolyzing diazo-4 at intermediate delays (1.5-2 s) or reducing photolysis of diazo-4 often resulted in short-term potentiation (STP). These results indicate that a tetanus-induced rise in postsynaptic [Ca2+]i lasting at most 2-2.5 s is sufficient to generate LTP. Smaller increases or shorter duration rises in [Ca2+]i may result in STP.

Calcium activates two types of potassium channels in rat hippocampal neurons in culture

Several calcium-dependent potassium currents can contribute to the electrophysiological properties of neurons. In hippocampal pyramidal cells, 2 afterhyperpolarizations (AHPs) are mediated by different calcium-activated potassium currents. First, a rapidly activated current contributes to action-potential repolarization and the fast AHP following individual action potentials. In addition, a slowly developing current underlies the slow AHP, which occurs after a burst of action potentials and contributes substantially to the spike-frequency accommodation observed in these cells during a prolonged depolarizing current pulse. In order to investigate the single Ca2(+)-dependent channels that might underlie these currents, we performed patch-clamp experiments on hippocampal neurons in primary culture. When excised inside-out patches were exposed to 1 microM Ca2+, 2 types of channel activity were observed. In symmetrical bathing solutions containing 140 mM K+, the channels had conductances of 19 pS and 220 pS, and both were permeable mainly to potassium ions. The properties of these 2 channels differed in a number of ways. At negative membrane potentials, the small-conductance channels were more sensitive to Ca2+ than the large channels. At positive potentials, the small-conductance channels displayed a flickery block by Mg2+ ions on the cytoplasmic face of the membrane. Low concentrations of tetraethylammonium (TEA) on the extracellular face of the membrane specifically caused an apparent reduction of the large-channel conductance. The properties of the large- and small-conductance channels are in accord with those of the fast and slow AHP, respectively.

Properties of two calcium-activated hyperpolarizations in rat hippocampal neurones

1. Intracellular recording from hippocampal CA1 pyramidal cells in the slice preparation was used to analyse the pharmacological sensitivity of action potential repolarization and the hyperpolarizations that follow the action potential. The Ca2+-activated after-hyperpolarizations (a.h.p.s) could be divided into a fast a.h.p. with a time course of milliseconds, and a slow a.h.p. which lasted for a few seconds at a temperature of 30 degrees C. 2. The repolarization of the action potential is sensitive to the Ca2+ channel blocker Cd2+. This effect is simultaneous with a block of the fast a.h.p. which follows immediately upon the repolarization of the action potential. The slow a.h.p. was also blocked by Cd2+. 3. Low concentrations of the K+ channel blocker, tetraethylammonium (TEA; 200-500 microM), block the fast a.h.p. and slow down action potential repolarization. The slow a.h.p. was not affected by low concentrations of TEA. 4. The action potential repolarization and the fast a.h.p. are also reversibly sensitive to charybdotoxin. This agent had no effect on the slow a.h.p. 5. When EGTA or BAPTA were added to the normal recording electrolyte (KMeSO4), the generation of slow a.h.p.s was prevented. In addition, cells impaled with BAPTA-containing electrodes displayed broader action potentials and much reduced fast a.h.p.s compared to recordings made with electrodes containing KMeSO4 alone or with EGTA. 6. The slow a.h.p. can be eliminated by noradrenaline, 8-bromocyclic AMP or carbachol. Under these conditions there are no effects on the fast a.h.p. or on action potential duration. 7. Block of the fast a.h.p. with TEA or CTX (charybdotoxin) is associated with an increased frequency of the first few action potentials during a depolarization. This is a quite distinct effect from the greatly increased number of action potentials which results from block of the slow a.h.p. 8. The results support a conclusion that the fast a.h.p. is generated by the TEA- and voltage-sensitive Ca2+-activated K+ current, IC. This current is involved in spike repolarization and turns off upon the return to resting potential. Thus block of IC has no effect on the slow a.h.p. which is caused by a separate membrane current.

Potassium currents evoked by brief depolarizations in bull-frog sympathetic ganglion cells

1. Sympathetic neurones of the bull-frog Rana catesbeiana were subjected to a two-electrode voltage-clamp technique in order to investigate the K+ currents which can be elicited by action potentials or similar brief depolarizations. 2. Four separate K+ currents were observed (IC, IK, IAHP and IM). These could be separated on the basis of voltage sensitivity, Ca2+ dependence and deactivation kinetics. 3. Two of these currents, which were clearly activated by an action potential, were Ca2+ dependent. A voltage- and TEA (tetraethylammonium)-sensitive K+ current, IC, was activated within the first 1-2 ms of a depolarizing command. This current decayed on average with a time constant of 2.4 ms at -40 mV. The maximal conductance was outside the range which could be adequately voltage clamped but, as much as 2 muS could be activated by brief (2-3 ms) commands. Activation of IC during an action potential accounts for the Ca2+ dependence of the repolarization. IC did not exhibit a transient component. 4. A second Ca2+-dependent K+ current, IAHP, was also activated after as little as 1 ms depolarization but was not voltage sensitive and was much less sensitive to TEA. The current decayed with a time constant of around 150 ms at -40 mV. The maximal conductance was about 30 nS. 5. The voltage-sensitive delayed rectifying current, IK, made a contribution to the total K+ conductance of the cell similar to IC in magnitude; however, the current is not activated within the normal voltage range or time course of an action potential. The current decayed on average with a time constant of 21 ms at -40 mV. 6. IM, a muscarine- and voltage-sensitive current, is not activated to any significant degree by a single action potential. The data further imply that the rate of opening of the ion channels mediating IM is less voltage sensitive than the rate of closing. 7. Large changes in the K+ reversal potential occur following depolarizing commands which evoke large K+ currents. This is attributed to K+ accumulation within a restricted extracellular space. Extracellular K+ may double or even triple during a single action potential.

Voltage clamp analysis of cholinergic action in the hippocampus

A slow muscarinic EPSP, accompanied by an increase in membrane input resistance, can be elicited in hippocampal CA1 pyramidal cells in vitro by electrical stimulation of cholinergic afferents in the slice preparation. Associated with the slow EPSP is a blockade of calcium-activated potassium afterhyperpolarizations (AHPs) (Cole and Nicoll, 1984a). In this study a single-electrode voltage clamp was used to examine the currents affected by activation of muscarinic receptors, using either bath application of carbachol or electrical stimulation of the cholinergic afferents. The 3 main findings of this study are that (1) of the 2 calcium-activated potassium currents (termed IAHP and IC) in hippocampal pyramidal cells, only IAHP is sensitive to carbachol; (2) IAHP is approximately 10-fold more sensitive to carbachol than is another muscarine-sensitive current, IM; and (3) neither blockade of IAHP nor of IM can account for the production of the slow EPSP. Rather, the slow EPSP appears to be generated by the blockade of a nonvoltage-dependent, resting potassium current. We propose that the muscarinic blockade of IAHP, which largely accounts for spike frequency adaptation, is primarily involved in enhancing action potential discharge to depolarizing stimuli, while the slow EPSP acts directly to cause action potential discharge.

A method for the rapid exchange of solutions bathing excised membrane patches

In this communication we describe a technique for rapidly exchanging solutions bathing excised membrane patches, and present examples of its implementation using both outside-out and inside-out patches. The ability to make step changes in the concentration of channel-activating ligands (e.g., acetylcholine, calcium) offers a novel and direct means of measuring kinetic processes in the 10-100-ms range. The responses to step ligand concentration changes are well suited to ensemble variance analysis, yielding estimates of the number of channels in a patch, and testing assumptions of channel independence and homogeneity. Kinetic analysis of the pseudomacroscopic currents obtained by averaging large numbers of responses can be compared and correlated with analysis of the microscopic behavior of single channels, using the same membrane patch for both approaches. Practical and theoretical limitations associated with the method are briefly discussed.

Slow synaptic transmission in frog sympathetic ganglia

Bullfrog ganglia contain two classes of neurone, B and C cells, which receive different inputs and exhibit different slow synaptic potentials. B cells, to which most effort has been directed, possess slow and late slow EPSPs. The sEPSP reflects a muscarinic action of acetylcholine released from boutons on B cells, whereas the late sEPSP is caused by a peptide (similar to teleost LHRH) released from boutons on C cells. During either sEPSP there is a selective reduction in two slow potassium conductances, designated ‘M’ and ‘AHP’. The M conductance is voltage dependent and the AHP conductance is calcium dependent. Normally they act synergistically to prevent repetitive firing of action potentials during maintained stimuli. Computer stimulation of the interactions of these conductances with the other five voltage-dependent conductances present in the membrane allows a complete reconstruction of the effects of slow synaptic transmission on electrical behaviour.

Calcium-dependent current generating the afterhyperpolarization of hippocampal neurons

A single-electrode voltage-clamp technique was employed on in vitro hippocampal slices to examine the membrane current responsible for the slow afterhyperpolarization (AHP) in CA1 pyramidal cells. This was achieved by using conventional procedures to evoke an AHP in current clamp, followed rapidly by a switch into voltage clamp (hybrid clamp). The AHP current showed a dependence on extracellular K+, which was close to that predicted for a K+ current by the Nernst equation. The AHP current could be blocked by Cd2+ or norepinephrine. Although the AHP current showed a requirement for voltage-dependent Ca2+ entry, the current did not show any clear intrinsic voltage dependence. Once activated, AHP current is not turned off by hyperpolarizing the membrane potential. The effects of norepinephrine, Cd2+, and tetraethylammonium (TEA) were used to identify an AHP current component to the outward current evoked by depolarizing voltage commands from holding potentials that approximate to the resting potential for these cells. The AHP current can contribute significantly to the outward current during the depolarizing command. Upon repolarization it is evident as a slow outward tail current. This slow tail current had the same time constant as AHP currents evoked by hybrid clamp. Fast components to the tail currents were also observed. These were sensitive to Cd2+ and TEA. They probably represent a voltage-sensitive gKCa, sometimes termed C-current. The strong sensitivity to voltage and TEA displayed by the conventionally described gKCa (IC) are properties inconsistent with the AHP. It seems likely that the AHP current (IAHP) represents a Ca2+-activated K+ current separate from IC and that these two currents coexist in the same cell.

Intracellular electrophysiology of CA1 pyramidal neurones in slices of the kainic acid lesioned hippocampus of the rat

Intracellular recordings were made from hippocampal CA1 pyramidal cells in slices where the CA3/CA4 region had been lesioned using intracerebroventricular kainic acid. In 55% of the cells studied orthodromic excitation evoked bursts of action potentials. This bursting activity was associated with a decrease in or loss of the early phase to the hyperpolarisation which normally follows orthodromically evoked action potentials. The recurrent inhibitory post-synaptic potential produced by antidromic activation of pyramidal cells was also reduced or absent. A late phase to the orthodromic hyperpolarisation was reduced in cells from lesioned slices. However, in normal slices treated with bicuculline this potential showed an apparent increase. The afterhyperpolarisation which follows a short current evoked burst of action potentials was reduced in bursting cells from lesioned slices. In addition, a silent period in the firing pattern produced by long depolarising current pulses was reduced or absent in these cells. These results together with observations made with bicuculline suggest that the bursting activity in lesioned slices is largely due to a loss of inhibition mediated by gamma-aminobutyric acid. It is proposed that the kainic acid-lesioned in vitro hippocampus may be a suitable preparation for studying the electrophysiology of temporal lobe epilepsy.

Two distinct Ca-dependent K currents in bullfrog sympathetic ganglion cells

Healthy bullfrog sympathetic ganglion cells often show a two-component afterhyperpolarization (AHP). Both components can be reduced or abolished by adding Ca-channel blockers or by removing external Ca. Application of a single electrode "hybrid clamp"--i.e., switching from current- to voltage-clamp at the peak of the AHP, reveals that the slow AHP component is generated by a small, slow, monotonically decaying outward current, which we call IAHP. IAHP is blocked by Ca-removal or by apamin and is a pure K current. It is slightly sensitive to muscarine and to tetraethylammonium ion but is much less so than muscarine-sensitive (IM) and fast Ca-dependent (IC) K currents. It also can be recorded in dual-electrode voltage-clamp experiments, where it is seen as a slow, small component of the outward tail current that follows brief depolarizations to 0 mV or beyond. IC is seen as an early, fast, large component of the same tail current. Both components are blocked by Ca removal, but only the IC component is blocked by low doses of tetraethylammonium ion. Thus, bullfrog ganglion cells exhibit two quite distinct Ca-dependent K currents, which differ in size, voltage-sensitivity, kinetics, and pharmacology. These two currents also play quite separate roles in shaping the action potential.

The synaptically evoked late hyperpolarisation in hippocampal CA1 pyramidal cells is resistant to intracellular EGTA

It has been suggested that the late hyperpolarisation following synaptic activation of hippocampal CA1 pyramidal neurons is activated by calcium influx. This hypothesis was examined using microelectrodes containing EGTA. Intracellular injection of EGTA blocked the afterhyperpolarisation which normally followed cell firing produced by injection of a depolarising current or the ionophoresis of glutamate onto the apical dendrites. In contrast, the hyperpolarisation following synaptic activation was resistant to EGTA. The results suggest that this potential is not dependent on intracellular Ca2+. Other possible mechanisms are discussed.

Chronic failure of inhibition of the CA1 area of the hippocampus following kainic acid lesions of the CA3/4 area

The chronic effects of the lesioning agent, kainic acid, on paired pulse inhibition in the CA1 area were investigated in the hippocampus both in vivo and in vitro. Pretreatment of animals with a unilateral intracerebroventricular (i.c.v.) injection of kainic acid resulted in a lesion of the CA3/4 area of the hippocampus ipsilateral to the injection site. On activating the surviving Schaffer collateral afferents in the contralateral hippocampus, normal paired-pulse inhibition of the extracellularly recorded population spike in CA1 was observed. On activating the surviving commissural afferents to the CA1 area ipsilateral to the lesion, no such inhibition could be observed. However, paired-pulse inhibition was recorded in the dentate gyrus ipsilateral to the lesion in response to stimulation of the perforant path. The chronic failure of inhibition following the unilateral i.c.v. injection of kainic acid further supports the use of this method to provide a chronic model in the rat for the study of epileptogenesis in the hippocampus.

In vivo and in vitro studies on putative interneurones in the rat hippocampus: possible mediators of feed-forward inhibition

Extracellular and intracellular recordings have been made from non-pyramidal neurones in the rat hippocampus in vivo and in vitro. These cells were situated in the stratum pyramidale but were orthodromically activated with a lower threshold than pyramidal neurones in response to stimulation of the Schaffer collateral/commissural afferents. Cells fired earlier than pyramidal neurones in response to suprathreshold stimulation and, in contrast to pyramidal cells, often fired a burst of action potentials. The non-pyramidal neurones also appeared to be orthodromically activated on stimulating the alveus and fired later than antidromically activated pyramidal cells. A very short action potential duration and the ability to fire at high frequencies in response to long depolarizing current pulses also distinguished these neurons from pyramidal cells. It is suggested that these non-pyramidal cells are interneurones which could mediate an early feed-forward activity onto pyramidal cells such as feed-forward inhibition. They may also be recurrently activated and hence could conceivably mediate a recurrent inhibition.

Long-term potentiation in Schaffer collateral and commissural systems of the hippocampus: in vitro study in rats pretreated with kainic acid

Experiments were carried out on hippocampal slices from rats pretreated with a unilateral intraventricular injection of kainic acid. The kainic acid produced a lesion of the CA3 area in the hippocampus ipsilateral to the site of injection. The resulting neuroanatomically modified hippocampal slices allowed the independent study of the Schaffer collateral and commissural afferents that synapse onto CA1 pyramidal cells. The Schaffer collateral and commissural afferents were both found to independently support long-term potentiation (LTP), and the properties of the LTP were similar to those observed in slices cut from unlesioned hippocampi.

Long-term potentiation in commissural and Schaffer projections to hippocampal CA1 cells: an in vivo study in the rat

Rats were given unilateral injections of kainic acid into the lateral ventricle to produce a unilateral lesion of CA3 pyramidal cells in the hippocampus. This procedure allowed the commissural and associational Schaffer projections of the surviving contralateral CA3 field to be studied separately for their ability to sustain long-term potentiation (l.t.p.) of synaptic efficacy. Both Schaffer and commissural projections showed l.t.p. of the population excitatory post-synaptic potential (e.p.s.p.) and the population spike. No significant difference was seen in the degree or duration of l.t.p. sustained by the two projections.