The Voice of Travel Nurses: Facilitating Effective Staffing During Pandemic and Expansion-Related Demands in a Children's Hospital

OBJECTIVE

The aim of this study was to explore the experience and perceived value of travel nurses in a children's hospital.

BACKGROUND

Children's hospitals face unique challenges related to highly specialized care requirements and workforce expansion limitations. Travel nurses can augment nurse staffing capacity during times of intense demand and may offer insights as organizations seek to strengthen work environments.

METHODS

Pediatric travel nurses currently contracted at the hospital were invited to participate in a focus group or interview. Content analysis was used to summarize information and identify themes.

RESULTS

From the 56 participants, 5 themes emerged. The themes were financial, flexibility, searching for healthy work environments, nursing care, and solutions.

CONCLUSIONS

Hearing the voices of travel nurses may offer valuable feedback to strengthen future professional practice environments.

Perceptions of Interprofessional Practitioners Regarding Pediatric Palliative Transports

BACKGROUND

Pediatric palliative transport (PPT) is the practice of offering critically and terminally ill children requiring life-sustaining measures the opportunity to be discharged from the hospital to home or a hospice facility for end-of-life care. Although studies have shown PPT to favorably affect both children and their families, limited research exists on the perspectives of health care practitioners.

OBJECTIVES

To understand the experience of interprofessional practitioners who have cared for a critically or terminally ill child during a PPT and their perception of PPT as a care option.

METHODS

This study is a qualitative descriptive inquiry conducted using 8 focus groups. Participants included interprofessional staff from 4 specialty intensive care units, the pediatric advanced care team, and the critical care transport team at a quaternary, freestanding children's hospital. Content analysis was used to summarize themes and recommendations.

RESULTS

Five overarching themes were identified: PPT as a care pathway, education, communication, support, and closure. Use of PPT was perceived as aligned with the hospital's mission of family-centered care and as providing a way for the health care team to support a family's choice. Participants recommended further development of information to guide communication and processes of care that would enhance the experience for families and staff and support PPT as a care pathway.

CONCLUSIONS

Pediatric palliative transport is considered a feasible, valuable, and critical end-of-life intervention. The value that PPT has brought to participating families warrants continued investment in the intervention's standardization and enhancement.

Measuring Acuity and Pediatric Critical Care Nursing Workload by Using ICU CAMEO III

BACKGROUND

The Intensive Care Unit Complexity Assessment and Monitoring to Ensure Optimal Outcomes (ICU CAMEO III) acuity tool measures patient acuity in terms of the complexity of nursing cognitive workload.

OBJECTIVE

To validate the ICU CAMEO III acuity tool in US children's hospitals.

METHODS

Using a convenience sample, 9 sites enrolled children admitted to pediatric intensive care units (ICUs). Descriptive statistics were used to summarize patient, nursing, and unit characteristics. Concurrent validity was evaluated by correlating the ICU CAMEO III with the Therapeutic Intervention Scoring System-Children (TISS-C) and the Pediatric Risk of Mortality III (PRISM III).

RESULTS

Patients (N = 840) were enrolled from 15 units (7 cardiac and 8 mixed pediatric ICUs). The mean number of ICU beds was 23 (range, 12-34). Among the patients, 512 (61%) were diagnosed with cardiac and 328 (39%) with noncardiac conditions; 463 patients (55.1%) were admitted for medical reasons, and 377 patients (44.9%) were surgical. The ICU CAMEO III median score was 99 (range, 59-163). The ICU CAMEO complexity classification was determined for all 840 patients: 60 (7.1%) with level I complexity; 183 (21.8%) with level II; 201 (23.9%), level III; 267 (31.8%), level IV; and 129 (15.4%), level V. Strong correlation was found between ICU CAMEO III and both TISS-C (ρ = .822, P < .001) and PRISM III (ρ = .607, P < .001) scores, and between the CAMEO complexity classifications and the PRISM III categories (ρ = .575, P = .001).

CONCLUSION

The ICU CAMEO III acuity tool and CAMEO complexity classifications are valid measures of patient acuity and nursing cognitive workload compared with PRISM III and TISS-C in academic children's hospitals.

Macronutrient Analysis of Modified-Fat Breast Milk Produced by 3 Methods of Fat Removal

BACKGROUND

Infants with chylothorax after congenital heart disease surgery are commonly treated using modified-fat breast milk. The effect of fat removal on breast milk macronutrients remains unclear. We compared macronutrient content of breast milk with breast milk skimmed using 3 methods, including a novel device, a cream separator.

METHODS

Thawed frozen breast milk samples from 30 women were defatted using refrigerated centrifuge, cream separator, and manual separation after refrigeration. We used standard assays to measure energy, protein, and fat content of breast milk samples.

RESULTS

All fat removal methods yielded skimmed breast milk with substantially lower fat and energy content. Mean energy content in breast milk skimmed by centrifuge (36.7 [SD 3.6] kcal/100 mL) was similar to that from cream separator (38.8 [3.5] kcal/100 mL). Both centrifuge and cream separator methods removed almost all fat and substantially more fat than the manual fat removal method. For unprocessed milk, energy and fat content estimated by creamatocrit was similar to reference method measurements; in skimmed milk, the creamatocrit significantly overestimated fat content. Mean protein content of skimmed breast milk was similar to unprocessed breast milk (mean 1.25 [0.31] g/100 mL).

CONCLUSION

Breast milk fat removal did not significantly alter protein levels. In skimmed breast milk, the overestimation of fat content using creamatocrit method suggests a need for more accurate bedside methods to assess macronutrient content. The similar macronutrient composition of breast milk skimmed by cream separator and centrifuge suggests the potential for cream separator use as a new, portable defatting method for hospitals and families.

Interprofessional Use and Validation of the AACN Healthy Work Environment Assessment Tool

BACKGROUND

Health care work environments affect patient outcomes, staff satisfaction and retention, and organizational financial viability. The American Association of Critical-Care Nurses (AACN) Healthy Work Environment Assessment Tool (HWEAT) is a resource for patient care units and organizations to assess the work environment and track progress on their journey to excellence.

OBJECTIVE

To validate interprofessional use of the AACN HWEAT across a large free-standing children's hospital.

METHODS

The AACN HWEAT was administered to staff members across professional categories. Responses were averaged to achieve an overall score and a score for each standard included in the instrument. Nurses' and physicians' scores were further stratified. Test-retest reliability and internal consistency were assessed. Construct validity was measured by correlating the AACN HWEAT and the Agency for Healthcare Research and Quality (AHRQ) Hospital Survey on Patient Safety Culture (H-SOPS).

RESULTS

Of 2621 AACN HWEAT surveys, 1030 (39.3%) were returned for review. The organization-wide HWEAT mean overall score was 3.58 (3.87 for physicians vs 3.54 for nurses, P= .02). Test-retest reliability was indicated by Spearman correlation coefficients of 0.50 to 0.68. Internal consistency was shown by a Cronbach α of 0.77 overall (range for standards, 0.77-0.81). Convergent validity between AACN HWEAT standards and AHRQ H-SOPS items was shown by correlation coefficients of 0.30 to 0.52.

CONCLUSION

The AACN HWEAT was both reliable and valid, supporting its interprofessional use as an organizational measure. Active evaluation of health care environments is critical to achieving optimal patient outcomes.

Measurement of Quality of Nursing Practice in Congenital Cardiac Care

BACKGROUND

The impact of nursing care on patients' outcomes has been demonstrated in adult and pediatric settings. However, limited attention has been given to standardized measurement of pediatric nursing care. A collaborative group, the Consortium for Congenital Cardiac Care Measurement of Nursing Practice, was formed to address this gap. The purpose of this study was to assess the current state of measurement of the quality of pediatric cardiovascular nursing in freestanding children's hospitals across the United States.

METHODS

A qualitative descriptive design was used to assess the state of measurement of nursing care from the perspective of experts in pediatric cardiovascular nursing. Nurse leaders from 20 sites participated in audiotaped phone interviews. The data were analyzed by using conventional content analysis.

RESULTS

Each level of data coding was increasingly comprehensive. Guided by Donabedian's quality framework of structure, process, and outcome, 2 encompassing patterns emerged: (1) structure and process of health care delivery and (2) structure and process of evaluation of care. Similarities in the structure of health care delivery included program expansion and subsequent hiring of nurses with a bachelor of science in nursing and experienced nurses to provide safety and optimal outcomes for patients. Programs varied in how they evaluated care in terms of structure, measurement, collection and dissemination of data.

CONCLUSION

External factors and response to internal processes of health care delivery were similar in different programs; evaluation was more varied. Seven opportunities for measurement that address both structure and process of nursing care were identified to be developed as benchmarks.

Complexity Assessment and Monitoring to Ensure Optimal Outcomes Tool for Measuring Pediatric Critical Care Nursing

BACKGROUND

Historically, nursing productivity has been measured in adult settings and based on time, intensity, and resource allocation.

OBJECTIVE

To develop a comprehensive measure of pediatric critical care nursing workload.

METHODS

An expert panel of pediatric critical care nurses used a modified Delphi method to identify 14 domains of nursing care with a number of corresponding care items in each domain. By consensus, they assigned each care item a cognitive complexity rating from 1 to 5. The panel next developed a classification system (classes I-V) to support interpretation of the patient's total score. The Complexity Assessment and Monitoring to Ensure Optimal Outcomes (CAMEO) tool was initiated with a cohort of 75 pediatric cardiac critical care patients to verify comprehensive capture of nursing care. Results of completed CAMEO tools were summarized by using descriptive statistics.

RESULTS

The cognitive workload across 14 domains of care was described, and each care item in the domain was scored. The range of CAMEO total scores was 25 to 230 (median, 124). For the initial cohort of patients, the cognitive complexity of care classifications were 13% as class I or II, 80% as class III or IV, and 7% as class V.

CONCLUSIONS

The CAMEO tool was comprehensive in describing and quantifying the cognitive workload of pediatric critical care nurses. The CAMEO classification process informs staffing needs that support synergy between the needs of patients and their families and nurses' knowledge and skill. Articulation of nursing care focused on informed clinical decision making is needed to justify the value of skilled nurses.

Heat retention head wrap for rewarming infants undergoing cardiopulmonary bypass surgery

BACKGROUND

A major postoperative problem for infants undergoing cardiopulmonary bypass surgery is hypothermia.

OBJECTIVE

To determine the safety and feasibility of a newly designed Heat Retention Head Wrap on infants during the rewarming period of cardiopulmonary bypass surgery.

METHODS

A sample of 10 infants was recruited into this descriptive pilot study. The health care providers completed ease-of-use questionnaires to describe the feasibility of the head wrap. Interval body temperatures were recorded to characterize temperature progression from onset of rewarming to arrival in the cardiac intensive care unit (ICU) and were compared with the temperature progression of a similar group of nonparticipants. Adverse events were recorded on the basis of perioperative body temperatures and skin assessments.

RESULTS

The head wrap was easily applied to the infant's head and was removed without difficulty. A steady increase in median body temperature from (1) the onset of rewarming (28°C), to (2) removal of bypass cannulas (28.9°C), to (3) removal of the rectal temperature probe before transfer from the operating room to the cardiac ICU (34.5°C), and (4) upon arrival in the cardiac ICU (36.0°C) was observed. No skin lesions or temperature-related adverse events were observed.

CONCLUSIONS

The newly designed Heat Retention Head Wrap was associated with a gradual normalization of temperature during rewarming and did not interfere with routine perioperative care of infants undergoing bypass surgery. This pilot study indicates that the head wrap is both safe and feasible for use in infants undergoing cardiopulmonary bypass surgery.

Management of peripherally inserted central catheters (PICC) in pediatric heart failure patients receiving continuous inotropic support

The study aim was to evaluate present practice of maintaining PICC line patency in pediatric heart failure patients receiving continuous inotropes by comparing one cohort receiving low dose continuous heparin with one receiving no heparin. A case control retrospective chart review compared the two cohorts on duration of patency (measured in days) and need for thrombolytic agents. Median duration of patency for the heparin group was 24 days versus 16 days for the no heparin group (p=0.07). Use of thrombolytic agents was 28% in the heparin group compared to 50% in the no heparin group (p=0.08). Although not statistically significant, findings were clinically significant and supportive of current practice.

Coping while caring for the dying child: nurses' experiences in an acute care setting

The aim of this study was to describe and understand behavior and coping strategies used by pediatric nurses caring for dying children on an inpatient acute care cardiology unit. Qualitative descriptive methods consisting of semistructured questions were presented to acute care nurses participating in focus groups. The nurses who participated in the focus groups had cared for an acutely ill child who died. Conventional content analysis was used to analyze data and organize results. The categories that emerged included the following: boundaries, memories, disconnecting, and labeling. Colleague support, institutional resources, and nurses' experience level were critical to the process of coping. Coping and grieving are facilitated by colleague and unit resources. Studies exploring job dissatisfaction, stress, and burnout from an inadequate grieving process are required.

Paediatric nurse practitioner managed cardiology clinics: patient satisfaction and appointment access

AIM

This article summarizes a comparative study of patient/family satisfaction and appointment wait times in physician managed vs. paediatric nurse practitioner managed cardiology clinics.

BACKGROUND

Appointment wait times exceeded 40 days in the outpatient cardiology department at a children's hospital. To address the gap in available appointments, paediatric nurse practitioner managed cardiology clinics were implemented.

METHODS

A sample of 128 patients who presented concurrently in physician or paediatric nurse practitioner managed cardiology clinics from December 2009 through February 2010 was recruited for participation. The hospital's ambulatory patient satisfaction survey was utilized to measure level of patient satisfaction with care. Survey responses were evaluated using Fisher's exact test. Appointment wait times were compared pre and post implementation of paediatric nurse practitioner managed clinics.

RESULTS

Sixty-five physician families and 63 paediatric nurse practitioner families completed the satisfaction survey. There was no statistically significant difference in patient satisfaction between clinic types. Appointment wait time decreased from 46 to 43 days, which was not statistically significant. Paediatric nurse practitioner clinics included a statistically higher percentage total of urgent appointments compared to that in physician clinics.

CONCLUSIONS

Paediatric nurse practitioner managed cardiology clinics are a strategic solution for improving patient access and facilitating high quality patient care while earning high levels of patient satisfaction. This healthcare delivery model illustrates the potential for expanded utilization of advanced practice nurses.

Transient transfection induces different intracellular calcium signaling in CHO K1 versus HEK 293 cells

For the controlled production of recombinant proteinsin mammalian cells by transient transfection, it maybe desirable not only to manipulate, but also todiagnose the expression success early. Here, weapplied laser scanning confocal microscopy to monitortransfection induced intracellular Ca(2+)responses. We compared Chinese hamster ovary (CHO K1)versus human embryo kidney (HEK) 293 cell lines, whichdiffer largely in their transfectability. An improvedcalcium phosphate transfection method was used for itssimplicity and its demonstrated upscale potential.Cytosolic Ca(2+) signaling appeared to inverselyreflect the cellular transfection fate. Virtually allCHO cells exhibited asynchronous, cytosolicCa(2+) oscillations, which peaked 4 h afteraddition of the transfecting solution. Yet, most ofthe HEK cells displayed a slow and continuousCa(2+) increase over the time of transfection. CHOcells, when exposed to a transfection-enhancingglycerol shock, strongly downregulated their Ca(2+)response, including its oscillations. When treatedwith thapsigargin, a Ca(2+) store depleting drug,the number of successfully transfected CHO cells was significantly reduced. Our result points tointracellular store release as a critical componentfor the transfection fate of CHO cells, and its early detection before product visualization.

The meaning of cost for families of children with congenital heart disease

INTRODUCTION

The purpose of this study was to describe the cost burden of congenital heart disease (CHD) and the associated social impact as experienced by families.

METHOD

Qualitative methods were used to collect and interpret data. Semi-structured interviews were conducted with parents of children with various degrees of CHD complexity and socioeconomic status currently admitted for congenital heart surgery at a large tertiary care regional center.

RESULTS

The meaning of cost burden as defined by participants resulted in the emergence of two major categories, lifestyle change and uncertainty. Cost was described beyond monetary terms and as a result, data in each category were further clustered into three underlying subcategories labeled financial, emotional, and family burden. The child's disease complexity and parent's socioeconomic status seem to be linked to higher levels of stress experienced in terms of finances, emotional drain, and family member burden. Prenatal diagnosis was noted to trigger early discussion of financial uncertainty, often resulting in altered personal spending prior to birth.

DISCUSSION

The cost experienced by parents of children with complex CHD was described as both life-changing and uncertain. Informing families of these types of additional stressors may allow issues of finances to be considered early in the overall preparation of caring for a child with complex CHD.

Intracellular Zn2+ increases contribute to the progression of excitotoxic Ca2+ increases in apical dendrites of CA1 pyramidal neurons

Sustained intracellular Ca(2+) elevation is a well-established contributor to neuronal injury following excessive activation of N-methyl-d-aspartic acid (NMDA)-type glutamate receptors. Zn(2+) can also be involved in excitotoxic degeneration, but the relative contributions of these two cations to the initiation and progression of excitotoxic injury is not yet known. We previously concluded that extended NMDA exposure led to sustained Ca(2+) increases that originated in apical dendrites of CA1 neurons and then propagated slowly throughout neurons and caused rapid necrotic injury. However the fluorescent indicator used in those studies (Fura-6F) may also respond to Zn(2+), and in the present work we examine possible contributions of Zn(2+) to indicator signals and to the progression of degenerative signaling along murine CA1 dendrites. Selective chelation of Zn(2+) with N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) significantly delayed, but did not prevent the development and progression of sustained high-level Fura-6F signals from dendrites to somata. Rapid indicator loss during the Ca(2+) overload response, which corresponds to rapid neuronal injury, was also not prevented by TPEN. The relationship between cytosolic Zn(2+) and Ca(2+) levels was assessed in single CA1 neurons co-loaded with Fura-6F and the Zn(2+)-selective indicator FluoZin-3. NMDA exposure resulted in significant initial increases in FluoZin-3 increases that were prevented by TPEN, but not by extracellular Zn(2+) chelation with Ca-EDTA. Consistent with this result, Ca-EDTA did not delay the progression of Fura-6F signals during NMDA. Removal of extracellular Ca(2+) reduced, but did not prevent FluoZin-3 increases. These results suggest that sustained Ca(2+) increases indeed underlie Fura-6F signals that slowly propagate throughout neurons, and that Ca(2+) (rather than Zn(2+)) increases are ultimately responsible for neuronal injury during NMDA. However, mobilization of Zn(2+) from endogenous sources leads to significant neuronal Zn(2+) increases, that in turn contribute to mechanisms of initiation and progression of progressive Ca(2+) deregulation.

Modulation of the amplitude of NAD(P)H fluorescence transients after synaptic stimulation

In brain slices, excitatory synaptic stimulation results typically in transient initial decreases in NAD(P)H fluorescence, followed by longer-lasting NAD(P)H increases that overshoot pre-stimulus NAD(P)H levels before returning slowly to baseline. We concluded recently that mitochondrial metabolism (rather than NADH generation by glycolysis) was responsible for the "overshoot" phase of responses evoked in murine hippocampal slices. The present study examined factors that may influence the amplitude of the overshoot phase, without necessarily directly influencing mitochondrial or glycolytic metabolism. The amplitudes of overshoots were influenced strongly by changes in pre-stimulus NAD(P)H fluorescence levels produced by a prior electrical stimulus. In contrast, these changes in pre-stimulus redox state had little effect on the amplitude of evoked initial NAD(P)H decreases. Resting NAD(P)H fluorescence levels differed significantly across sub-regions of each slice, however, this is not due to differences in resting redox state, and the relative amplitude of NAD(P)H overshoots were not different in different slice regions. Exposure to an A1 receptor agonist (CPA) reduced the amplitude of postsynaptic potentials, and preferentially reduced the amplitude of NAD(P)H overshoots, before initial oxidizing components of biphasic transients were reduced significantly. These results suggest that amplitudes of NAD(P)H overshoots may not be good quantitative measures of the intensity of a discrete stimulus, under some conditions where the stimulus is small relative to recent activity in the slice. Comparison of flavoprotein autofluorescence with NAD(P)H levels seems useful when making quantitative comparisons of responses from different regions of slices, where optical properties and ongoing activity may be substantially different.

Hypoplastic left heart syndrome

Hypoplastic left heart syndrome(HLHS) refers to the abnormal development of the left-sided cardiac structures, resulting in obstruction to blood flow from the left ventricular outflow tract. In addition, the syndrome includes underdevelopment of the left ventricle, aorta, and aortic arch, as well as mitral atresia or stenosis. HLHS has been reported to occur in approximately 0.016 to 0.036% of all live births. Newborn infants with the condition generally are born at full term and initially appear healthy. As the arterial duct closes, the systemic perfusion becomes decreased, resulting in hypoxemia, acidosis, and shock. Usually, no heart murmur, or a non-specific heart murmur, may be detected. The second heart sound is loud and single because of aortic atresia. Often the liver is enlarged secondary to congestive heart failure. The embryologic cause of the disease, as in the case of most congenital cardiac defects, is not fully known. The most useful diagnostic modality is the echocardiogram. The syndrome can be diagnosed by fetal echocardiography between 18 and 22 weeks of gestation. Differential diagnosis includes other left-sided obstructive lesions where the systemic circulation is dependent on ductal flow (critical aortic stenosis, coarctation of the aorta, interrupted aortic arch). Children with the syndrome require surgery as neonates, as they have duct-dependent systemic circulation. Currently, there are two major modalities, primary cardiac transplantation or a series of staged functionally univentricular palliations. The treatment chosen is dependent on the preference of the institution, its experience, and also preference. Although survival following initial surgical intervention has improved significantly over the last 20 years, significant mortality and morbidity are present for both surgical strategies. As a result pediatric cardiologists continue to be challenged by discussions with families regarding initial decision relative to treatment, and long-term prognosis as information on long-term survival and quality of life for those born with the syndrome is limited.

Otolaryngologists' responses to errors and adverse events

OBJECTIVES

The objectives of this study were to describe otolaryngologists' emotional reactions to errors and adverse events, their efforts to take responsibility, and their attempts to implement improvements.

STUDY DESIGN AND METHODS

A retrospective, anonymous survey of 2,500 U.S. otolaryngologists who were members of the American Academy of Otolaryngology-Head and Neck Surgery about errors in their practice was conducted. Respondents were asked whether an error had occurred in their practice in the past 6 months and, if so, to describe the error, its consequences, and any corrective actions taken. Two aspects of these reports stood out, which were beyond the scope of the original study: the respondents' emotional responses and their corrective actions.

RESULTS

The response rate was 18.6%. Two hundred ten (45%) respondents reported a total of 212 analyzable error reports and 230 corrective actions. Corrective actions included disclosure to the patient (20 [9%]), ameliorating the consequences of the event to the patient (107 [50%]), personal practice changes (14 [7%]), improvements in the respondent's practice or department (60 [28%]), and hospitalwide or broader corrective actions (19 [9%]). Emotional reactions to errors and adverse events were reported by 22 (10%) otolaryngologists, including regret, embarrassment, guilt, anxiety, loss of temper, and irritation. Legal action was mentioned by five physicians (2%).

CONCLUSIONS

Otolaryngologists took actions not only to treat their patients, but also to improve patient care in their practice, department, hospital, or community. Emotional reactions to errors and adverse events are common and need to be addressed in medical training and practice.

Factors associated with increased resource utilization for congenital heart disease

OBJECTIVE

To identify patient, institutional, and regional factors that are associated with high resource utilization for congenital heart surgery.

METHODS

We used hospital discharge data from the Healthcare Cost and Utilization Project (HCUP) Kids' Inpatient Database (KID) year 2000 (data from 27 states). Patients who had congenital heart surgery and were younger than 18 years were identified using International Classification of Diseases, Ninth Revision, Clinical Modification codes. High resource utilization admissions were defined as those in the highest decile for total hospital charges. Univariate and multivariate analyses with and without deaths were used to determine demographic and hospital predictors for cases of high resource use. Case-mix severity was approximated using Risk Adjustment for Congenital Heart Surgery risk groups. Regional and state differences were also examined.

RESULTS

Among 10,569 cases of congenital heart surgery identified, median total hospital charges were 53,828 dollars. Statewide differences in the number of high resource use admissions were present; California, Colorado, Florida, Hawaii, Pennsylvania, and Texas were more likely to have high resource use cases, and Maine and South Carolina were less likely. Subsequent analyses were performed adjusting for baseline state effects. Multivariate analyses using generalized estimating equations models revealed Risk Adjustment for Congenital Heart Surgery risk category (odds ratio [OR]: 1.66-14.1), age (OR: 3.81), prematurity (OR: 4.85), the presence of other major noncardiac structural anomalies (OR: 2.53), Medicaid insurance (OR: 1.48), and admission during a weekend (OR: 1.62) to be independent predictors of a higher odds of high cost cases. Although some institutional differences were noted in univariate analyses, gender, race, bed size, teaching and children's hospital status, hospital ownership, and hospital volume of cardiac cases were not independently associated with greater odds of high resource utilization.

CONCLUSIONS

States varied in the frequency of high resource utilization for congenital heart surgery. Patients who had greater disease complexity, younger age, prematurity, other anomalies, and Medicaid and were admitted during a weekend were more likely to result in high resource utilization. Institutions of various types did not differ in high cost admissions, regardless of children's hospital or teaching status.

GABA(B)-receptor modulation of short-term synaptic depression at an excitatory input to murine hippocampal CA3 pyramidal neurons

GABA(B) agonists inhibit excitatory transmission to hippocampal CA3 neurons during low frequency stimulation. We examined whether GABA(B) receptor activation can also enhance synaptic efficacy, when investigated at an input with high initial release probability. Short-term depression of field excitatory postsynaptic potential (EPSP) amplitude was observed during trains of stimuli applied to associational/commissural inputs (10-50 Hz; 22 degrees C). Baclofen (10 microM) reduced the amplitude of initial EPSPs in a train, and also reduced the degree of short-term depression. EPSPs recorded late in a train were significantly larger in baclofen than those recorded in control solution. These dual effects were mimicked by another selective GABA(B) agonist (SKF 97541, 10 microM), and abolished by a GABA(B)-selective antagonist (SCH 50911, 20 microM). The effects of baclofen were similar at a higher recording temperature (32 degrees C), where short-term depression was observed at higher stimulation frequencies. These results are consistent with the idea that a reduction of transmitter release probability could increase the fidelity of high-frequency transmission at this input, an effect that could help account for excitatory effects of GABA(B) agonists in some seizure models.

Clinical outcomes and secondary diagnoses for infants born with hypoplastic left heart syndrome

OBJECTIVE

To explore clinical outcomes and secondary diagnoses present at discharge for infants born with hypoplastic left heart syndrome (HLHS), from a national perspective.

METHODS

We examined hospitalizations for infants < or =30 days of age who were born with HLHS, using hospital discharge data from the 1997 Kids Inpatient Database. To explore treatment choices, clinical outcomes, and resource use, we used International Classification of Diseases, 9th Revision, Clinical Modification diagnostic and procedure codes to classify discharges according to type of surgical intervention versus no surgical intervention. To investigate outcomes in more detail, we identified secondary diagnoses noted at discharge, using International Classification of Diseases, 9th Revision, Clinical Modification codes, and stratified results according to type of surgical intervention.

RESULTS

Of a total of 550 patients with HLHS, 234 underwent the Norwood procedure, 17 underwent orthotopic heart transplantation, and 106 died in the hospital with no reported surgical intervention. Although we found no demographic variables to be significantly associated with the type of treatment received, discharged patients who died without surgical intervention were significantly more likely to have received care in hospitals identified as small (odds ratio [OR]: 1.5; 95% confidence interval [CI]: 1.03-3.1) or not children's hospitals (OR: 2.02; 95% CI: 1.13-3.6). Secondary diagnoses of cardiac arrest (OR: 2.0; 95% CI: 1.1-3.4) and seizures (OR: 2.6; 95% CI: 1.2-5.5) occurred more frequently in orthotopic heart transplantation cases than in Norwood procedure cases.

CONCLUSIONS

These data from a national perspective reflect outcomes of infants with HLHS during a time when rates of initial survival after surgical intervention were considered to be improved. These findings may be useful to clinicians when they are considering and recommending initial medical and surgical strategies currently being proposed for the treatment of HLHS.

Physiological and structural evidence for hippocampal involvement in persistent seizure susceptibility after traumatic brain injury

Epilepsy is a common outcome of traumatic brain injury (TBI), but the mechanisms of posttraumatic epileptogenesis are poorly understood. One clue is the occurrence of selective hippocampal cell death after fluid-percussion TBI in rats, consistent with the reported reduction of hippocampal volume bilaterally in humans after TBI and resembling hippocampal sclerosis, a hallmark of temporal-lobe epilepsy. Other features of temporal-lobe epilepsy, such as long-term seizure susceptibility, persistent hyperexcitability in the dentate gyrus (DG), and mossy fiber synaptic reorganization, however, have not been examined after TBI. To determine whether TBI induces these changes, we used a well studied model of TBI by weight drop on somatosensory cortex in adult rats. First, we confirmed an early and selective cell loss in the hilus of the DG and area CA3 of hippocampus, ipsilateral to the impact. Second, we found persistently enhanced susceptibility to pentylenetetrazole-induced convulsions 15 weeks after TBI. Third, by applying GABA(A) antagonists during field-potential and optical recordings in hippocampal slices 3 and 15 weeks after TBI, we unmasked a persistent, abnormal APV-sensitive hyperexcitability that was bilateral and localized to the granule cell and molecular layers of the DG. Finally, using Timm histochemistry, we detected progressive sprouting of mossy fibers into the inner molecular layers of the DG bilaterally 2-27 weeks after TBI. These findings are consistent with the development of posttraumatic epilepsy in an animal model of impact head injury, showing a striking similarity to the enduring behavioral, functional, and structural alterations associated with temporal-lobe epilepsy.

Neonatal exposure to a novel environment enhances the effects of corticosterone on neuronal excitability and plasticity in adult hippocampus

Electrophysiological studies have shown that activation of glucocorticoids receptors (GRs) influences neuronal excitability and activity dependent synaptic plasticity. In developmental studies, early life stimulation such as neonatal handling results in an up-regulation of glucocorticoid-receptor (GR) binding in the hippocampus that persists into adulthood. It is, therefore, hypothesized that early environment-induced changes in receptor sensitivity to corticosterone (CORT) might have functional effects on adult neuronal excitability and synaptic plasticity. To test this hypothesis, we exposed rats daily from post-natal days 1-21 to a non-home environment for 3 min. When the animals became adults, we studied the effects of glucocorticoid hormone corticosterone (CORT) on population spike (PS) amplitude and long-term potentiation of population spikes (PS-LTP) in vitro in the hippocampal CA1 region following activation of the Schaffer collateral fibers. Bath application of CORT reduced PS amplitude and subsequent induction of PS-LTP. This inhibitory effect of CORT was significantly greater in the slices from the novelty exposed rats (Novel) than the control rats that remained in their home cage (Home). Inhibition of population spike amplitude during CORT perfusion was 28.0+/-5.3% of baseline in Novel slices, and 9.1+/-4.4% in Home slices. CORT pre-exposure (20 min) also inhibited the subsequent induction of PS-LTP in Novel slices by 57.7+/-17.7% and by 7.5+/-12.1% in Home slices. These results provide electrophysiological evidence that neonatal novelty exposure results in functional increases in receptor sensitivity to CORT that enhances the inhibitory effects of CORT on field CA1 neuronal excitability and plasticity.

Strain-dependent differences in calcium signaling predict excitotoxicity in murine hippocampal neurons

Commonly used inbred murine strains differ substantially in their vulnerability to excitotoxic insults. We investigated whether differences in dendritic Ca(2+) signaling could underlie the differential vulnerability of C57BL/6 (resistant to kainate excitotoxicity) and C57BL/10 strains (vulnerable). A striking difference was found in fine dendrite Ca(2+) responses after kainate exposure. Ca(2+) signals in distal dendrites were large in C57BL/10 neurons, and, if a threshold concentration of approximately 1.5 microm was reached, a region of sustained high Ca(2+) was established in the distal dendritic tree. This region then served as an initiation site for a degenerative cascade, producing high Ca(2+) levels that slowly spread to involve the entire neuron and led to cell death. Dendritic Ca(2+) signals in C57BL/6 neurons were much smaller and did not trigger these propagating secondary responses. Strain differences in dendritic Ca(2+) signaling were also evident after tetanic stimulation of Schaffer collaterals. Ca(2+) responses were much larger and peaked earlier in distal dendrites of C57BL/10 compared with those in C57BL/6. Neurons from both strains had similar membrane properties and responded to kainate with intense action potential firing. Degenerative Ca(2+) responses were seen in both strains if soma Ca(2+) could be sustained above 1.5 microm. The early phases of secondary Ca(2+) responses were attributable to Ca(2+) influx and were abolished rapidly by buffered zero Ca(2+) saline. Taken together, these data indicate that the substantial difference in Ca(2+) signals in fine distal dendrites and in the initiation of spreading secondary responses may underlie the selective vulnerability of these neurons to excitotoxic insults.

Bidirectional synaptic plasticity correlated with the magnitude of dendritic calcium transients above a threshold

The magnitude of postsynaptic Ca(2+) transients is thought to affect activity-dependent synaptic plasticity associated with learning and memory. Large Ca(2+) transients have been implicated in the induction of long-term potentiation (LTP), while smaller Ca(2+) transients have been associated with long-term depression (LTD). However, a direct relationship has not been demonstrated between Ca(2+) measurements and direction of synaptic plasticity in the same cells, using one induction protocol. Here, we used glutamate iontophoresis to induce Ca(2+) transients in hippocampal CA1 neurons injected with the Ca(2+)-indicator fura-2. Test stimulation of one or two synaptic pathways before and after iontophoresis showed that the direction of synaptic plasticity correlated with glutamate-induced Ca(2+) levels above a threshold, below which no plasticity occurred (approximately 180 nM). Relatively low Ca(2+) levels (180-500 nM) typically led to LTD of synaptic transmission and higher levels (>500 nM) often led to LTP. Failure to show plasticity correlated with Ca(2+) levels in two distinct ranges: <180 nM and approximately 450-600 nM, while only LTD occurred between these ranges. Our data support a class of models in which failure of Ca(2+) transients to affect transmission may arise either from insufficient Ca(2+) to affect Ca(2+)-sensitive proteins regulating synaptic strength through opposing activities or from higher Ca(2+) levels that reset activities of such proteins without affecting the net balance of activities. Our estimates of the threshold Ca(2+) level for LTD (approximately 180 nM) and for the transition from LTD to LTP (approximately 540 nM) may assist in constraining the molecular details of such models.

Ca2+ signaling in gerbil CA3 hippocampal neurons following transient in vivo ischemia

Using the gerbil model of post-ischemic neuron death in the hippocampal CA1 region, it was recently shown that there is a strong down-regulation of voltage-gated Ca2+ influx in neurons examined at 2 days after the ischemic insult (Connor, J.A., Razani-Boroujerdi, S., Greenwood, A.C., Cormier, R.J., Petrozzino, J.J. and Lin, R.C., Reduced voltage-dependent Ca2+ signaling in CA1 neurons after brief ischemia in gerbils, J. Neurophysiol., 81 (1999) 299-306). The aim of the present study was to determine whether a similar change occurs in pyramidal neurons of the CA3 region that are relatively resistant to transient ischemia. In vitro intracellular recordings and fluorometric Ca2+ measurements were made from CA3 neurons in coronal slices prepared from controls and 1 or 2 days following in vivo ischemia. In slices from control and post-ischemic animals, the electrophysiological properties of CA3 neurons were consistent with significant voltage-gated Ca2+ influx, leading to spike frequency adaptation. Quantitative results indicated no significant difference in Ca2+ transients evoked by action potential trains. This Ca2+ signaling was compared with responses in CA1 neurons from the same preparations, which showed substantially diminished Ca2+ influx at 2 days post-ischemia. These findings suggest that diminished Ca2+-signaling is not a general feature of pyramidal neurons following ischemia, but is characteristic of neurons destined to die.

Microheterogeneity of calcium signalling in dendrites

Transient changes in the intracellular concentration of free Ca2+ ([Ca2+]i) originating from voltage- or ligand-gated influx and by ligand- or Ca2+-gated release from intracellular stores, trigger or modulate many fundamental neuronal processes, including neurotransmitter release and synaptic plasticity. Of the intracellular compartments involved in Ca2+ clearance, the endoplasmic reticulum (ER) has received the most attention because it expresses Ca2+ pumps and Ca2+ channels, thus endowing it with the potential to act as both an intracellular calcium sink and store. We review here our ongoing work on the role of calcium sequestration into, and release from, ER cisterns and the role that this plays in the generation and termination of free [Ca2+]i transients in dendrites of pyramidal neurons in hippocampal slices during and after synaptic activity. These studies have been approached by combining parallel microfluorometric measurements of free cytosolic [Ca2+]i transients with energy-dispersive X-ray microanalytical measurements of total Ca content within specific dendritic compartments at the electron microscopy level. Our observations support the emerging realization that specific subsets of dendritic ER cisterns provide spatial and temporal microheterogeneity of Ca2+ signalling, acting not only as a major intracellular Ca sink involved in active clearance mechanisms after voltage- and ligand-gated Ca2+ influx, but also as an intracellular Ca2+ source that can be mobilized by a signal cascade originating at activated synapses.

Cumulative effects of glutamate microstimulation on Ca(2+) responses of CA1 hippocampal pyramidal neurons in slice

Glutamate stimulation of hippocampal CA1 neurons in slice was delivered via iontophoresis from a microelectrode. Five pulses (approximately 5 muA, 10 s duration, repeated at 1 min intervals) were applied with the electrode tip positioned in the stratum radiatum near the dendrites of a neuron filled with the Ca(2+) indicator fura-2. A single stimulus set produced Ca(2+) elevations that ranged from several hundred nM to several microM and that, in all but a few neurons, recovered within 1 min of stimulus termination. Subsequent identical stimulation produced Ca(2+) elevations that outlasted the local glutamate elevations by several minutes as judged by response recoveries in neighboring cells or in other parts of the same neuron. These long responses ultimately recovered but persisted for up to 10 min and were most prominent in the mid and distal dendrites. Recovery was not observed for responses that spread to the soma. The elevated Ca(2+) levels were accompanied by membrane depolarization but did not appear to depend on the depolarization. High-resolution images demonstrated responsive areas that involved only a few mu(m) of dendrite. Our results confirm the previous general findings from isolated and cell culture neurons that glutamate stimulation, if carried beyond a certain range, results in long-lasting Ca(2+) elevation. The response characterized here in mature in situ neurons was significantly different in terms of time course and reversibility. We suggest that the extended Ca(2+) elevations might serve not only as a trigger for delayed neuron death but, where more spatially restricted, as a signal for local remodeling in dendrites.

Characterization of L-homocysteate-induced currents in Purkinje cells from wild-type and NMDA receptor knockout mice

L-Homocysteic acid (HCA), an endogenous excitatory amino acid in the mammalian CNS, potently activates N-methyl-D-aspartate (NMDA) receptors in hippocampal neurons. However, the responses to HCA in Purkinje cells, which lack functional NMDA receptors, have been largely unexplored: HCA may activate conventional non-NMDA receptors by its mixed agonistic action on both NMDA and non-NMDA receptors, or it may activate a novel non-NMDA receptor that has high affinity for HCA. To test these possibilities, we compared the responses to HCA in cultured Purkinje cells with those in hippocampal neurons by using the whole cell patch-clamp technique. To clearly isolate HCA responses mediated by non-NMDA receptors, we complemented pharmacological methods by using neurons from mutant mice (NR(-/-)) that lack functional NMDA receptors. A moderate dose of HCA (100 microM) induced substantial responses in Purkinje cells. These responses were blocked by non-NMDA receptor antagonists but were insensitive to NMDA receptor antagonists. HCA also activated responses mediated by non-NMDA receptors in both wild-type and NR1(-/-) hippocampal neurons. HCA responses in Purkinje cells had a pharmacological profile (EC(50) and Hill coefficient) very similar to that of non-NMDA receptor components of HCA responses in hippocampal neurons. Moreover, the amplitude of the non-NMDA receptor component of HCA responses was directly correlated with that of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)- and kainate-induced responses in both types of neurons. Finally, in both types of neurons, HCA currents mediated by non-NMDA receptors were potently blocked by the AMPA receptor antagonist GYKI52466. These findings indicate that HCA-activated AMPA receptors in Purkinje cells are similar to those in hippocampal neurons and that there is no distinct HCA-preferring receptor in Purkinje cells. We also found that in hippocampal neurons, the EC(50)s of HCA for non-NMDA receptors and for NMDA receptors were more similar than originally reported; this finding indicates that HCA is similar to other mixed agonists, such as glutamate. HCA responses may appear to be selective at NMDA receptors in cells that express these receptors, such as hippocampal neurons; in cells that express few functional NMDA receptors, such as Purkinje cells, HCA may appear to be selective at non-NMDA receptors.

Correlated measurements of free and total intracellular calcium concentration in central nervous system neurons

Transient changes in the intracellular concentration of free calcium ([Ca2+])i) act as a trigger or modulator for a large number of important neuronal processes. Such transients can originate from voltage- or ligand-gated fluxes of Ca2+ into the cytoplasm from the extracellular space, or by ligand- or Ca2+(-)gated release from intracellular stores. Characterizing the sources and spatio-temporal patterns of [Ca2+]i transients is critical for understanding the role of different neuronal compartments in dendritic integration and synaptic plasticity. Optical imaging of fluorescent indicators sensitive to free Ca2+ is especially suited to studying such phenomena because this approach offers simultaneous monitoring of large regions of the dendritic tree in individual living central nervous system neurons. In contrast, energy-dispersive X-ray (EDX) microanalysis provides quantitative information on the amount and location of intracellular total, i.e., free plus bound, calcium (Ca) within specific subcellular dendritic compartments as a function of the activity state of the neuron. When optical measurements of [Ca2+]i transients and parallel EDX measurements of Ca content are used in tandem, and correlated simultaneously with electrophysiological measurements of neuronal activity, the combined information provides a relatively general picture of spatio-temporal neuronal total Ca fluctuations. To illustrate the kinds of information available with this approach, we review here results from our ongoing work aimed at evaluating the role of various Ca uptake, release, sequestration, and extrusion mechanisms in the generation and termination of [Ca2+]i transients in dendrites of pyramidal neurons in hippocampal slices during and after synaptic activity. Our observations support the long-standing speculation that the dendritic endoplasmic reticulum acts not only as an intracellular Ca2+ source that can be mobilized by a signal cascade originating at activated synapses, but also as a major intracellular Ca sink involved in active clearance mechanisms after voltage- and ligand-gated Ca2+ influx.

Calcium signals in long-term potentiation and long-term depression

We describe postsynaptic Ca2+ signals that subserve induction of two forms of neuronal plasticity, long-term potentiation (LTP) and long-term depression (LTD), in rat hippocampal neurons. The common induction protocol for LTP, a 1-s, 50-Hz tetanus, generates Ca2+ increases of about 50-Hz in dendritic spines of CA1 neurons. These very large increases, measured using a low affinity indicator (Mg fura 5), were found only in the spines and tertiary dendrites, and were dependent upon influx through N-methyl-D-aspartate (NMDA) gated channels. High affinity Ca2+ indicators (e.g., fura 2) are unable to demonstrate these events. In acute slices, neighboring dendritic branches often showed very different responses to a tetanus, and in some instances, neighboring spines on the same dendrite responded differently. LTD in mature CA1 neurons was induced by a low frequency stimulus protocol (2 Hz, 900 pulses), in the presence of GABA- and NMDA-receptor blockers. This LTD protocol produced dendritic Ca2+ increases of <1 microM. Duration of the Ca2+ increase was approximately 30 s and was due to voltage-gated Ca2+ influx. Finally, the ability of synaptically addressed Ca2+ stores to release Ca2+ was studied in CA3 neurons and was found to require immediate preloading and high intensity presynaptic stimulation, conditions unlike normal LTP-LTD protocols.

Influence of Alkyl Chain Length and Structure on the Extraction of Copper(II) from Aqueous Acid by 5-Alkyl-2-hydroxybenzaldoximes in Hydrocarbon Solvents: Diffusion Coefficients of Extractants and Their Complexes

Measurement of the kinetics of extraction of copper(II) by 19 different 5-alkyl-2-hydroxybenzaldoximes (alkyl is C7H15 and C9H19) from acidic (hydrogen sulfate buffer) aqueous solution in the range pH 3.4-2.0, into 20% v/v toluene in n-hexane is reported. The lowering of the interfacial tension has been measured in some cases. The solubility of the extractants in water has been measured spectrophotometrically. A modified Taylor-Aris dispersion technique has been used to measure the diffusion coefficients in n-hexane and Orfom SX7 of some of the extractants and of the copper(II) complexes which they form. At low initial bulk concentrations (<10 mol m-3) of the extractants, the rate of extraction is controlled by the rate of diffusion of the extractant from the bulk to the organic-aqueous interface. The diffusion coefficient is related to the steric bulk of the alkyl substituent. At higher initial bulk concentrations (200 mol m-3) of the extractants, when the interface is saturated, the rate of extraction is inversely related to the apparent steric bulk of the alkyl substituent. Copyright 1999 Academic Press.

Reduced voltage-dependent Ca2+ signaling in CA1 neurons after brief ischemia in gerbils

An initial overload of intracellular Ca2+ plays a critical role in the delayed death of hippocampal CA1 neurons that die a few days after transient ischemia. Without direct evidence, the prevailing hypothesis has been that Ca2+ overload may recur until cell death. Here, we report the first measurements of intracellular Ca2+ in living CA1 neurons within brain slices prepared 1, 2, and 3 days after transient (5 min) ischemia. With no sign of ongoing Ca2+ overload, voltage-dependent Ca2+ transients were actually reduced after 2-3 days of reperfusion. Resting Ca2+ levels and recovery rate after loading were similar to neurons receiving no ischemic insult. The tetrodotoxin-insensitive Ca spike, normally generated by these neurons, was absent at 2 days postischemia, as was a large fraction of Ca2+-dependent spike train adaptation. These surprising findings may lead to a new perspective on delayed neuronal death and intervention.

Requirement of rapid Ca2+ entry and synaptic activation of metabotropic glutamate receptors for the induction of long-term depression in adult rat hippocampus

1. During block of gamma-aminobutyric acid-A-mediated inhibition, low-frequency stimulation (2 Hz, 900 pulses) to Schaffer collateral-CA1 neuron synapses of adult rat hippocampus induced an N-methyl-D-aspartate receptor-independent, postsynaptic Ca2+-dependent depression of synaptic strength (long-term depression; LTD). 2. Ratio imaging with fura-2 revealed moderate dendritic [Ca2+] increases (approximately 500 nM) during only the initial approximately 30 s of the 7.5 min stimulation period. Conditioning for 30 s was, however, insufficient to induce LTD. 3. The [Ca2+] changes were insensitive to the metabotropic glutamate receptor (mGluR) antagonist (+)-alpha-methyl-4-carboxyphenylglycine (MCPG). MCPG, however, completely blocked LTD when present during conditioning. 4. The [Ca2+] changes were abolished by postsynaptic hyperpolarization (-110 mV at the soma). Hyperpolarizing neurons to -110 mV during conditioning significantly attenuated LTD induction. 5. LTD induction was also blocked by the postsynaptic presence of the protein kinase C inhibitor peptide PKC(19-36). 6. These results suggest that LTD induction in adult hippocampus by prolonged low-frequency stimulation depends on both a rapid Ca2+ influx through voltage-sensitive channels and synaptic stimulation of mGluRs which may be coupled to phospholipase C.

Global ischemia induces downregulation of Glur2 mRNA and increases AMPA receptor-mediated Ca2+ influx in hippocampal CA1 neurons of gerbil

Transient, severe forebrain or global ischemia leads to delayed cell death of pyramidal neurons in the hippocampal CA1. The precise molecular mechanisms underlying neuronal cell death after global ischemia are as yet unknown. Glutamate receptor-mediated Ca2+ influx is thought to play a critical role in this cell death. In situ hybridization revealed that the expression of mRNA encoding GluR2 (the subunit that limits Ca2+ permeability of AMPA-type glutamate receptors) was markedly and specifically reduced in gerbil CA1 pyramidal neurons after global ischemia but before the onset of neurodegeneration. To determine whether the change in GluR2 expression is functionally significant, we examined the AMPA receptor-mediated rise in cytoplasmic free Ca2+ level ([Ca2+]i) in individual CA1 pyramidal neurons by optical imaging with the Ca2+ indicator dye fura-2 and by intracellular recording. Seventy-two hours after ischemia, CA1 neurons that retained the ability to fire action potentials exhibited a greatly enhanced AMPA-elicited rise in [Ca2+]i. Basal [Ca2+]i in these neurons was unchanged. These findings provide evidence for Ca2+ entry directly through AMPA receptors in pyramidal neurons destined to die. Downregulation of GluR2 gene expression and an increase in Ca2+ influx through AMPA receptors in response to endogenous glutamate are likely to contribute to the delayed neuronal death after global ischemia.

Regulation by insulin of a unique neuronal Ca2+ pool and of neuropeptide secretion

The insulin receptor is a tyrosine kinase receptor that is found in mammalian brain and at high concentrations in the bag cell neurons of Aplysia. We show here that insulin causes an acute rise in intracellular Ca2+ concentration ([Ca2+]i) in these neurons and triggers release of neuropeptide. The insulin-sensitive intracellular Ca2+ pool differs pharmacologically from previously described Ca2+ stores that are sensitive to inositol trisphosphate and from mitochondrial Ca2+ stores. Insulin, but not thapsigargin, stimulates Ca2+ release at the distal tips of neurites, the presumed site of neuropeptide secretion. The effects of insulin on intracellular Ca2+ release and neuropeptide secretion occur without triggering spontaneous action potentials. The insulin-sensitive rise in [Ca2+]i moves into the distal tips of neurites after exposure to a cyclic AMP analogue, a treatment that causes a similar translocation of neuronal vesicles. Our data indicate that Ca2+ release from a distinct intracellular pool associated with secretory vesicles may contribute to secretion of neuropeptide in the absence of neuronal discharge.

Rapid dendritic Ca2+ influx is associated with induction of homosynaptic long-term depression in adult rat hippocampus

Homosynaptic long-term depression was induced in area CA1 of adult hippocampus by prolonged low-frequency stimulation (900 pulses at 2 Hz) in the presence of the GABAA receptor antagonist picrotoxin. Using ratio imaging with fura-2, we demonstrate that the induction of this long-term depression is associated with a rapid and transient (approximately 30 s) dendritic Ca2+ increase (approximately 500 nM) dependent on the activation of voltage-gated Ca2+ channels. This transient increase, by itself, was insufficient for long-term depression induction.

Activation of a metabotropic excitatory amino acid receptor potentiates spike-driven calcium increases in neurons of the dorsolateral septum

(1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD), an agonist for metabotropic glutamate receptors (mGluRs), causes depolarization and burst firing in rat dorsolateral septal nucleus (DLSN) neurons and results in long-term potentiation (LTP) at DLSN synapses. In the present study, we investigated whether these actions of 1S,3R-ACPD are attributable to the release of calcium from an inositol triphosphate-sensitive store after activation of mGluRs coupled to phospholipase C. Our data demonstrated that the ACPD-induced depolarization was associated with a small but significant decrease, not an increase, in [Ca2+]i; however, changes of [Ca2+]i, during ACPD-induced bursting were up to seven times larger than those produced by regular firing. Depletion of internal calcium stores by thapsigargin or ryanodine had a small to insignificant effect on the maximum changes of [Ca2+]i, associated with ACPD-induced bursting. Thus, elevation of [Ca2+]i, during firing by 1S,3R-ACPD is likely attributable to enhancement of calcium influx through voltage-gated channels and not to calcium release from internal stores. ACPD-induced burst firing elevated somatic and dendritic calcium levels up to 3 and 6 microM, respectively. Such an increase may be the underlying mechanism for ACPD-induced LTP as well as ACPD-induced acute cell death in rat DLSN.

Selective activation of calcium permeability by aspartate in Purkinje cells

Glutamate and aspartate are endogenous excitatory amino acid neurotransmitters widely distributed in the mammalian central nervous system. Aspartate was shown to induce a large membrane current sensitive to N-methyl-D-aspartate (NMDA) and non-NMDA receptor antagonists in Purkinje cells from mice lacking functional NMDA receptors (NR1(-/-)). This response was accompanied by high permeability to calcium. In contrast, no current was induced by aspartate in hippocampal neurons and cerebellar granule cells from NR1(-/-) mice. Several other glutamate receptor agonists failed to evoke this response. Thus, in Purkinje cells, aspartate activates a distinct response capable of contributing to synaptic plasticity through calcium permeability.

The cytosolic subunit p67phox contains an NADPH-binding site that participates in catalysis by the leukocyte NADPH oxidase

The NADPH-dependent respiratory burst oxidase of human neutrophils catalyzes the reduction of oxygen to superoxide using NADPH as the electron donor and is essential for normal host defenses. To gain insight into the function of the various oxidase subunits that are required for the full expression of catalytic activity, we studied the interactions between the 2',3'-dialdehyde derivative of NADPH (NADPH dialdehyde) and neutrophil cytosol. NADPH dialdehyde treatment of cytosol resulted in the loss of the ability of the cytosol to participate in cell-free oxidase activation; this inactivation was blocked by NADPH but not by NAD, NADP, or GTP. Partial purification of neutrophil cytosol yielded a single peak which could restore the activity lost in cytosol treated with NADPH dialdehyde. This peak contained p67phox but not p47phox or Rac2. Purified recombinant p67phox was similarly able to restore the activity lost in NADPH dialdehyde-treated cytosol and bound [32P]NADPH dialdehyde in a specific fashion. The activity of recombinant p67phox in cell-free oxidase assays was lost on treatment with NADPH dialdehyde. Together, these data suggest p67phox contains the catalytic NADPH-binding site of the leukocyte NADPH oxidase.

Functional NMDA receptors are transiently active and support the survival of Purkinje cells in culture

Conflicting evidence exists concerning the activity of NMDA receptors (NMDARs) in cerebellar Purkinje cells and their possible functions. To investigate the activity of NMDARS, we used whole-cell recording on immunocytochemically identified Purkinje cells in primary culture. In addition, we used mice with a disrupted NMDAR1 gene that lack functional NMDARs (NR1-/-) to assess the physiological role of NMDARs. In cultures from normal mice, NMDA-medicated currents were detected in all identified Purkinje cells at 4 d in vitro (div). After 14 d, however, NMDA responses were reduced in amplitude, whereas the responses to kainate and glutamate increased steadily in amplitude. In addition, the NMDA-induced current displayed a pronounced desensitization at these later stages; peak current declined to zero during steady application of NMDA. At 7 div, the number of surviving Purkinje cells was less in cultures treated with NMDA antagonists, and their survival was dose-dependent. Purkinje cell survival was correspondingly poorer in cultures from the NR1-/- mice than in wild-type controls, suggesting that NMDAR activity enhances the survival of Purkinje cells in vitro. The addition of moderate doses of NMDA promoted the survival of wild-type Purkinje cells in the presence of tetrodotoxin. Feeder layers of cerebellar granule cells derived from wild-type or NR1-/- mice promoted survival of Purkinje cells to a similar degree, suggesting that the NMDAR in Purkinje cells, but not in other cells, is directly involved in Purkinje cell viability. The results demonstrate that NMDARs transiently produce membrane current in Purkinje cells and may serve as one of the epigenetic factors that support the survival of Purkinje cells in vitro.

Ca2+ influx and activation of a cation current are coupled to intracellular Ca2+ release in peptidergic neurons of Aplysia californica

1. Stimulation of inputs to bag cell neurons in the abdominal ganglion of Aplysia californica causes an increase in their intracellular Ca2+ concentration ([Ca2+]i). We have used thapsigargin, a specific inhibitor of the endoplasmic reticulum Ca2+ pump, to analyse the effects of Ca2+ released from intracellular stores on the electrophysiological responses of bag cell neurons. 2. Using digital imaging of fura-2-loaded isolated bag cell neurons we found that thapsigargin rapidly evoked an increase in [Ca2+]i in somata, with smaller increases in neurites. Thapsigargin-induced elevation of [Ca2+]i peaked at about 1 microM within 5-10 min and then decayed to basal levels by 30 min. 3. Placement of an extracellular vibrating Ca(2+)-selective microelectrode to within 1 micron of somata revealed a relatively large steady-state Ca2+ efflux. Thapsigargin produced a rapid increase in Ca2+ influx. Changes in Ca2+ flux were not detected at neurites. 4. Thapsigargin produced a small depolarization in isolated bag cell neurons in artificial sea water (ASW). Sometimes enhanced depolarizations were observed when extracellular Na+ was replaced by TEA or Tris, but not N-methyl-D-glucamine (NMDG). The depolarization was not blocked by 100 microM tetrodotoxin (TTX), removal of extracellular Ca2+ (0.5 mM EGTA) or addition of 10 mM Co2+ to the bath solution. 5. In voltage-clamp experiments, thapsigargin induced an inward current (ITg) that was recorded in Ca(2+)-free media containing TEA or Tris substituted for Na+. The apparent reversal potential of ITg was -16.8 +/- 1.2 mV in TEA-ASW. Induction of ITg was inhibited in neurons that were microinjected with the Ca2+ chelator BAPTA-Dextran70 or treated with the membrane-permeant analogue BAPTA AM. Activation of ITg was not observed when Na+ was replaced with NMDG. Manipulation of [Na+]o and [K+]o produced shifts in the reversal potential of ITg consistent with the underlying channels being permeable to both Na+ and K+. 6. Thapsigargin did not alter the amplitude or kinetics of voltage-activated Ba2+ currents, but in some experiments it did increase the amplitude of a component of outward K+ current. 7. Thapsigargin neither induced bag cell neurons within the intact ganglion to depolarize and fire spontaneously, nor did it alter the frequency or duration of firing of an electrically stimulated bag cell after-discharge. 8. We conclude that thapsigargin-sensitive Ca2+ pools are present predominantly in the somata of bag cell neurons. Ca2+ that is released from thapsigargin-sensitive Ca2+ stores activates a non-selective cation current that may help sustain depolarization of the somata, but does not by itself trigger an after-discharge.

Ca2+ release from intracellular stores induced by afferent stimulation of CA3 pyramidal neurons in hippocampal slices

1. Ca2+ imaging and simultaneous intracellular recording were performed on CA3 pyramidal neurons in hippocampal slice cultures and standard acute slices. Both fura-2 and a dextran conjugate of fura-2 (MW = 10,000) were used in the Ca2+ measurements to control for compartmentalization artifacts. Experiments were performed under conditions giving minimal ligand- and voltagegated Ca2+ influx, with the use of competitive and noncompetitive antagonists of ionotropic glutamate receptors and steady-state depolarization, respectively. 2. Tetanic stimulation of stratum lucidum evoked dendritic Ca2+ transients with rapid onset that were blocked by the noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist, MK-801 (2-5 microM), but not by the competitive alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) (10-50 microM). Zn(2+)-containing mossy fiber terminals (assessed by Timm's staining) and postsynaptic structures (thorny excrescences) are preserved in s. lucidum of hippocampal slice cultures. 3. A Ca2+ store loading protocol, consisting of brief repolarizations followed by steady depolarization, primed most of the neurons so that a subsequent tetanus gave a Ca2+ increase in the presence of MK-801 that was reported by both fura-2 and the dextran conjugate. The onset of the Ca2+ increase was significantly delayed (by 2-3 s) with respect to the MK-801-sensitive increase, and often had a different spatial pattern within the neuron. Response characteristics were similar in slice cultures and acute slices. 4. The delayed Ca2+ increase showed a steep rundown with subsequent stimuli, but was restored by further priming by the Ca2+ store loading paradigm. Postsynaptic currents evoked by the tetani under these conditions were not correlated with the magnitude of the delayed Ca2+ transients. 5. Delayed Ca2+ increases were observed in 44% of the neurons dialyzed with normal intracellular solution at room temperature. The success rate of observing delayed Ca2+ transients was increased to 86% in neurons maintained at 30 degrees C, and dialyzed with an inhibitor of the inositol-triphosphate-3-kinase. 6. The delayed Ca2+ transients could not be initiated after inhibition of endosomal Ca(2+)-ATPase-mediated uptake by thapsigargin. 7. Both fura-2 and the dextran conjugate reported increases in resting Ca2+ levels after the loading protocols, that were absent after priming in thapsigargin, and decreases in resting Ca2+ levels after successive tetani in MK-801, suggesting that the Ca2+ changes were largely cytosolic. 8. The present results support the hypothesis that these synaptically mediated, delayed Ca2+ transients represent release from intracellular Ca2+ stores that can be loaded and depleted repeatedly, and are evoked by presynaptic release of endogenous neurotransmitter.

A novel synaptic interaction underlying induction of long-term depression in the area CA1 of adult rat hippocampus

1. We describe a novel synaptic property that regulates induction of homosynaptic long-term depression (LTD), and slowly developing heterosynaptic LTD, of Schaffer collateral-pyramidal cell synapses in adult rat hippocampus. 2. Two independent pathways converging on the same neuron were alternately tested with 0.017 Hz single pulses, and LTD was induced by 900 conditioning stimuli delivered at 2 Hz. All experiments were performed in the presence of the GABA(A) antagonists picrotoxin or bicuculline. 3. After delivery of the 2 Hz stimulation to the homosynaptic pathway, the 0.017 Hz test pulses to the heterosynaptic pathway were interrupted for 25 min. When the test stimulations were resumed, heterosynaptic LTD could not be observed. Homosynaptic LTD also failed to be induced in this protocol. Interruption of test pulses did not itself cause a general increase of synaptic responses. 4. Doubling the frequency of homosynaptic test pulses (to 0.033 Hz) during a 25 min interruption of heterosynaptic stimulus did not preserve homosynaptic LTD. This suggests that the failure of homosynaptic LTD induction seen when the test pulses were interrupted was not caused by a decrease in the number of synaptic inputs at the postsynaptic neuron following conditioning. 5. When only the homosynaptic pathway was involved, with no heterosynaptic stimulation, as in conventional experiments, 2 Hz conditioning successfully induced homosynaptic LTD. 6. We propose that when a heterosynaptic pathway has been recently used, continuous input to that pathway following conditioning is necessary for induction of homosynaptic LTD on the same neuron.

Neuropeptide Y1 receptors inhibit N-type calcium currents and reduce transient calcium increases in rat dentate granule cells

Neuropeptide Y (NPY) is far more abundant in the dentate gyrus than elsewhere in the hippocampal formation, but it does not alter the synaptic excitation of dentate granule cells (DGCs) as it does for pyramidal cells in areas CA1 and CA3. NPY inhibited depolarization-induced increases in intracellular Ca2+ concentrations ([Ca2+]i) in DGCs in hippocampal slices, without altering the resting [Ca2+]i. NPY inhibited Ca2+ currents (ICa) via a Y1 receptor in 84% of acutely isolated DGCs and via a Y2 receptor in 31% of the NPY-responsive cells tested. ICa inhibition was completely occluded by omega-conotoxin-GVIA but not by nimodipine. The inhibition of ICa was accompanied by a change in the time course of ICa activation in only 27% of NPY-responsive cells. Only 23% of DGCs responded to NPY when Ba2+ was substituted for extracellular Ca2+ and when [Ca2+]i was strongly buffered. Therefore, NPY inhibits an N-type ICa in DGCs, mainly via Y1 receptors. Furthermore, it seems that more than one mechanism, one of which may be sensitive to [Ca2+]i, may couple NPY receptors to the Ca2+ channels in DGCs. Because the release of dynorphin from DGCs depends in part on N-type currents, NPY receptors are poised to regulate the release of opioid peptides from DGC somata and dendrites.