Increased stroop facilitation effects in schizophrenia are not due to increased automatic spreading activation

Studies using the single trial Stroop task consistently reveal increased reaction time (RT) facilitation effects among schizophrenia patients. One possible mechanism underlying this effect is increased automatic spreading activation in semantic networks. The current study was designed to test this hypothesis. We administered the Stroop task and two semantic priming tasks to the same subjects. Patients showed greater Stroop RT facilitation than controls, no evidence of increased semantic priming at short stimulus onset asynchronies (SOAs), and reduced semantic priming at long SOAs. In addition, abnormal Stroop performance was related to the severity of Disorganization symptoms. These results are inconsistent with the spreading activation hypothesis. Alternative hypotheses regarding the source of Stroop task performance deficits in schizophrenia are discussed.

The contribution of the anterior cingulate cortex to executive processes in cognition

The anterior cingulate cortex (ACC), on the medial surface of the frontal lobes, has frequently been hypothesized to make critical contributions to the function of neural systems involved in the executive control of cognition. Three principal theories have been developed to account for this role. The first, 'motivated attention', emphasizes the limbic identity of the ACC and the effects of lesions to this area of the brain. The second, 'attention allocation', emphasizes the fact that during functional neuroimaging studies activation of the ACC is seen during tasks that elicit incompatible response tendencies that must be resolved for correct performance. The third theory, 'error detection', reflects the observation of a negative scalp potential occurring during incorrect responses which appears to have a medial frontal generator. The first and last theories suggest evaluative functions by the ACC in the service of control, while attention allocation suggests a strategic function. We have proposed that the data supporting all three theories can be reconciled if the ACC were detecting conflicting processes during task performance that might be associated with errors. In support of this hypothesis we describe results using event-related fMRI which confirm that the ACC does show error related activity but that the same region of the brain also shows increased response related activity during correct responses associated with response competition. This suggests a re-conceptualization of the contribution of the ACC to executive processes that support an evaluative role, specifically the on-line detection of processing conflicts that may be associated with deteriorating performance. Unresolved questions related to the contribution of this region to executive processes and potential future directions for research on the function of this region of the brain are discussed.

A study of injected dose for brain mapping on the ECAT HR+: activation maps for a parametric verbal working memory task

The success of the 15O-water PET technique to localize statistically significant changes in regional cerebral blood flow is dependent on factors such as the activity level injected and the magnitude of the flow change. Undetectable changes may occur if insufficient activity is injected leading to high levels of statistical noise or the task performed results in only small changes in blood flow. To explore the relationship between injected activity and statistical significance, we performed a series of studies with the ECAT EXACT HR+, a high resolution PET tomograph. A parametric verbal working memory task (the N-back task) was selected to examine the relationship between regional cerebral blood flow and working memory load across a range of injected doses of 15O-water. At each activity level the volunteers were required to perform four different levels of the N-back task, a task in which a letter displayed on a monitor is matched with the letter displayed N letters previously. With increasing N, this task places increased load on working memory. For this study, 5, 10, and 15 mCi of 15O-water were injected into nine normal volunteers. The complete sequence of four tasks (N = 0, 1, 2, and 3) at three activity levels was repeated twice, for a total of 24 injections of 15O-water. We show that the peak count rate performance for the HR+ is approached at injected activity levels of 15O-water around 15 mCi. For this particular choice of N-back task, robust activation maps can nevertheless be obtained with as little as 5 mCi injected dose.

Neuroendocrine perspectives on social attachment and love

The purpose of this paper is to review existing behavioral and neuroendocrine perspectives on social attachment and love. Both love and social attachments function to facilitate reproduction, provide a sense of safety, and reduce anxiety or stress. Because social attachment is an essential component of love, understanding attachment formation is an important step toward identifying the neurobiological substrates of love. Studies of pair bonding in monogamous rodents, such as prairie voles, and maternal attachment in precocial ungulates offer the most accessible animal models for the study of mechanisms underlying selective social attachments and the propensity to develop social bonds. Parental behavior and sexual behavior, even in the absence of selective social behaviors, are associated with the concept of love; the analysis of reproductive behaviors, which is far more extensive than our understanding of social attachment, also suggests neuroendocrine substrates for love. A review of these literatures reveals a recurrent association between high levels of activity in the hypothalamic pituitary adrenal (HPA) axis and the subsequent expression of social behaviors and attachments. Positive social behaviors, including social bonds, may reduce HPA axis activity, while in some cases negative social interactions can have the opposite effect. Central neuropeptides, and especially oxytocin and vasopressin have been implicated both in social bonding and in the central control of the HPA axis. In prairie voles, which show clear evidence of pair bonds, oxytocin is capable of increasing positive social behaviors and both oxytocin and social interactions reduce activity in the HPA axis. Social interactions and attachment involve endocrine systems capable of decreasing HPA reactivity and modulating the autonomic nervous system, perhaps accounting for health benefits that are attributed to loving relationships.

Development of cholinergic neurons in rat brain regions: dose-dependent effects of propylthiouracil-induced hypothyroidism

The effects of hypothyroidism on development of cholinergic system in brain regions (prefrontal cortex and hippocampus) were evaluated by measuring choline acetyltransferase (ChAT) activity and hemicholinium-3 binding to the high-affinity choline transporter. Various degrees of thyroid deficiency were produced by perinatal exposure to propylthiouracil (PTU) in drinking water ranging from 5 ppm (mg/l) to 25 ppm beginning at gestational day 18 until postnatal day 21. ChAT, a marker for cholinergic nerve terminals, was reduced by PTU in a dose-dependent manner. Concomitant with the enzyme deficits, hemicholinium-3 binding was elevated, suggesting an increase in neuronal impulse activity. Although similar changes were seen in both brain regions examined, the magnitude and duration of these changes were more definitive in the prefrontal cortex. Nonetheless, these neurochemical alterations appeared to be recoverable when the rats returned to a euthyroid state, and no further changes were observed as the animals reached adulthood. In comparison, data reported in a succeeding article indicate that deficits in cognitive function were first seen in weanling hypothyroid rats, but that the behavioral impairments lasted well into adulthood when thyroid status and cholinergic parameters in the brain appeared to have recovered to normal. These results suggest that alterations of cholinergic system caused by perinatal hypothyroidism are associated with neurobehavioral deficits at weaning, and these developmental deviations may cause permanent impairment of cognitive function despite recovery from the hormonal imbalance at adult ages.

The Stroop task and attention deficits in schizophrenia: a critical evaluation of card and single-trial Stroop methodologies

The Stroop task, considered by many to be a paradigmatic measure of selective attention, has often been employed to investigate attention deficits in schizophrenia. Card and single-trial versions of this task have yielded different results. In this study both card and single-trial versions were administered to healthy controls (n = 24) and patients with schizophrenia (n = 55). No differences in reaction time (RT) interference were found on either version. On the single-trial version, patients showed greater RT facilitation and error rate interference, evidence for a deficit in selective attention. Methodologic and analytic issues that account for the mixed results from earlier card Stroop studies are addressed. It is concluded that single-trial versions provide greater sensitivity to selective attention pathology in schizophrenia.

Selective attention in schizophrenia: relationship to verbal working memory

In previous work using the Stroop task to examine cognitive function in schizophrenia, we have suggested that reaction time (RT) facilitation and error interference should be more sensitive measures of cognitive function than RT interference. We examined this hypothesis in 36 DSM-IV schizophrenia and schizoaffective patients, who performed both the Stroop and the Speaking Span, a measure of verbal working memory. The results supported our hypotheses, demonstrating that RT facilitation and error interference were associated more strongly with working memory performance than RT interference. The robust correlations between these measures of selective attention and Speaking Span performance has implications for understanding the nature and selectivity of cognitive dysfunction in schizophrenia. We present several different hypotheses that may explain this relationship, including: (1) a generalized deficit; (2) a common cognitive disturbance; and (3) a common neurobiological dysfunction.

Functional hypofrontality and working memory dysfunction in schizophrenia

OBJECTIVE

Hypofrontality is a common but not invariable finding in schizophrenia. Inconsistencies in the literature may reflect, in part, the fact that abnormal physiological responses in the prefrontal cortex are best identified under conditions that place well-specified functional demands on this region.

METHOD

The authors studied eight patients with schizophrenia and eight matched comparison subjects using [(15)O]H2O positron emission tomography and the "N-back" task, which activates the prefrontal cortex as a function of working memory load in normal subjects.

RESULTS

Under low-working-memory-load conditions, the accuracy of both groups in the N-back task was equal, but when the memory load increased, the patients' performance deteriorated more than did that of the comparison subjects. The regional cerebral blood flow response to increased working memory load was significantly reduced in the patients' right dorsolateral prefrontal cortex.

CONCLUSIONS

These results confirm the importance of using tasks that tap specific cognitive functions, linked to specific neural systems, in studies of brain-behavior relationships in schizophrenia. Hypofrontality is reliably demonstrated in schizophrenia during tasks that engage working memory functions of the prefrontal cortex.

Peripheral expansion of pre-existing mature T cells is an important means of CD4+ T-cell regeneration HIV-infected adults

The CD4+ T-cell pool in HIV-infected patients is in a constant state of flux as CD4+ T cells are infected and destroyed by HIV and new cells take their place. To study T-cell survival, we adoptively transferred peripheral blood lymphocytes transduced with the neomycin phosphotransferase gene between syngeneic twin pairs discordant for HIV infection. A stable fraction of marked CD4+ T cells persisted in the circulation for four to eighteen weeks after transfer in all patients. After this time there was a precipitous decline in marked cells in three of the patients. At approximately six months, marked cells were in lymphoid tissues in proportions comparable to those found in peripheral blood. In two patients, the proportion of total signal for the transgene (found by PCR analysis) in the CD4/CD45RA+ T-cell population relative to the CD4/CD45RO+ population increased in the weeks after cell infusion. These findings indicate that genetically-marked CD4+ T cells persist in vivo for weeks to months and that the CD4+ T-cell pool in adults is maintained mostly by the division of mature T cells rather than by differentiation of prethymic stem cells. Thus, after elements of the T-cell repertoire are lost through HIV infection, they may be difficult to replace.

The Stroop task and attention deficits in schizophrenia: a critical evaluation of card and single-trial Stroop methodologies

The Stroop task, considered by many to be a paradigmatic measure of selective attention, has often been employed to investigate attention deficits in schizophrenia. Card and single-trial versions of this task have yielded different results. In this study both card and single-trial versions were administered to healthy controls (n = 24) and patients with schizophrenia (n = 55). No differences in reaction time (RT) interference were found on either version. On the single-trial version, patients showed greater RT facilitation and error rate interference, evidence for a deficit in selective attention. Methodologic and analytic issues that account for the mixed results from earlier card Stroop studies are addressed. It is concluded that single-trial versions provide greater sensitivity to selective attention pathology in schizophrenia.

Dopamine and the mechanisms of cognition: Part I. A neural network model predicting dopamine effects on selective attention

BACKGROUND

Dopamine affects neural information processing, cognition, and behavior; however, the mechanisms through which these three levels of function are affected have remained unspecified. We present a parallel-distributed processing model of dopamine effects on neural ensembles that accounts for effects on human performance in a selective attention task.

METHODS

Task performance is stimulated using principles and mechanisms that capture salient aspects of information processing in neural ensembles. Dopamine effects are simulated as a change in gain of neural assemblies in the area of release.

RESULTS

The model leads to different predictions as a function of the hypothesized location of dopamine effects. Motor system effects are simulated as a change in gain over the response layer of the model. This induces speeding of reaction times but an impairment of accuracy. Cognitive attentional effects are simulated as a change in gain over the attention layer. This induces a speeding of reaction times and an improvement of accuracy, especially at very fast reaction times and when processing of the stimulus requires selective attention.

CONCLUSIONS

A computer simulation using widely accepted principles of processing in neural ensembles can account for reaction time distributions and time-accuracy curves in a selective attention task. The simulation can be used to generate predictions about the effects of dopamine agonists on performance. An empirical study evaluating these predictions is described in a companion paper.

Dopamine and the mechanisms of cognition: Part II. D-amphetamine effects in human subjects performing a selective attention task

BACKGROUND

A neural network computer model described in a companion paper predicted the effects of increased dopamine transmission on selective attention under two different hypotheses.

METHODS

To evaluate these predictions we conducted an empirical study in human subjects of D-amphetamine effects on performance of the Eriksen response competition task. Ten healthy volunteers were tested before and after placebo or D-amphetamine in a double-blind cross-over design.

RESULTS

D-amphetamine induced a speeding of reaction time overall and an improvement of accuracy at fast reaction times but only in the task condition requiring selective attention.

CONCLUSIONS

This pattern of results conforms to the prediction of the model under the hypothesis that D-amphetamine primarily affects dopamine transmission in cognitive rather than motor networks. This suggests that the principles embodied in parallel distributed processing models of task performance may be sufficient to predict and explain specific behavioral effects of some drug actions in the central nervous system.

Anterior cingulate cortex, error detection, and the online monitoring of performance

An unresolved question in neuroscience and psychology is how the brain monitors performance to regulate behavior. It has been proposed that the anterior cingulate cortex (ACC), on the medial surface of the frontal lobe, contributes to performance monitoring by detecting errors. In this study, event-related functional magnetic resonance imaging was used to examine ACC function. Results confirm that this region shows activity during erroneous responses. However, activity was also observed in the same region during correct responses under conditions of increased response competition. This suggests that the ACC detects conditions under which errors are likely to occur rather than errors themselves.

Cooperative breeding and monogamy in prairie voles: influence of the sire and geographical variation

Mammalian monogamy is characterized by pair bonding and a relative absence of sexual dimorphism in body size. Alloparental behaviour is a characteristic of mammalian cooperative breeding systems. Studies of prairie voles, Microtus ochrogaster, from stock captured in a resource-abundant habitat in Illinois have supported the assumption that this species is a monogamous, cooperative breeder, while other studies of prairie voles from a more arid habitat in Kansas have called this assumption into question. We hypothesized that reported differences between these populations represented true intraspecific variation. Patterns of sexual dimorphism in body size, partner preferences and parental contact behaviour were compared in prairie voles from stocks originating in Illinois or Kansas. Both Illinois and Kansas voles showed a strong preference for a familiar partner, which is suggestive of monogamy. Sexual dimorphism in body size was observed in Kansas, but not Illinois voles. Illinois voles displayed significantly higher levels of parental contact behaviour than did voles from Kansas. When animals from Illinois and Kansas were crossed, the expression of parental contact behaviour of the 'hybrid' offspring followed the pattern seen in the population of origin of the sire. Removal of the sire prior to the birth of the litter increased alloparenting in Kansas voles, but removal of the sire was associated with lower levels of alloparenting in Illinois voles. Thus, some traits associated with the social system may show intraspecific variation and can be influenced by the presence or absence of the sire during rearing. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

Intraspecific variation in the induction of female sexual receptivity in prairie voles

Prairie voles (Microtus ochrogaster) are monogamous New World rodents which show geographic variation in social behavior. In this study, parameters of female reproduction which might be related to mating system were compared in prairie voles from eastern Kansas (KAN) versus central Illinois (ILL). KAN females showed a more rapid onset of natural estrus following exposure to a male and were more likely to respond to injections of a low dose (0.5 microg) of exogenous estradiol benzoate than ILL females. Neither mating duration nor pregnancy success after mate removal differed in KAN versus ILL females. These results suggest that ILL voles are less sensitive than KAN voles to the estrus-inducing effects of either endogenous or exogenous estrogen, supporting the hypothesis that variations in reproductive strategy occur among geographically discrete populations of prairie voles.

Ontogeny of the conditioned eyeblink response in rats: acquisition or expression?

Eyeblink conditioning depends critically on an identified brainstem-cerebellar circuit and is modulated under some circumstances by the hippocampus, amygdala, and other forebrain regions. Developmental studies of eyeblink conditioning could help elucidate questions concerning the behavioral expression of plasticity within these brain circuits and regions, and of their functional interactions, as they unfold during ontogeny. Recently, this laboratory has shown that conditioning of the eyeblink reflex develops dramatically between Postnatal Days (PND) 17 and PND 24 in the rat. The present study asked whether the developmental emergence of the eyeblink conditioned response (CR) occurs gradually or abruptly over this age range, and whether it reflects developmental changes in acquisition or expression of the learned eyeblink reflex. In Experiment 1, rat pups received two consecutive days of training beginning on PND 17, 20, or 24. Conditioned responses occurred at low levels on PND 17-18, intermediate levels on PND 20-21, and high levels on PND 24-25. In Experiment 2, 17-day-old rats received 2 days of training, 72 h apart, so that effects of training on PND 17 could be examined at an age, PND 20, when expression of the eyeblink CR was clearly possible. On PND 20, rat pups that had received paired training on PND 17 showed significantly faster conditioning than controls that had received unpaired training or no training on PND 17. These findings suggest that neural plasticity underlying associative learning developmentally precedes its overt expression in behavior. Hypotheses concerning the nature and locus of this learning are discussed.

T cell-depleted granulocyte colony-stimulating factor (G-CSF) modified allogenic bone marrow transplantation for hematological malignancy improves graft CD34+ cell content but is associated with delayed pancytopenia

To increase the stem cell content of T cell-depleted bone marrow transplants (BMT), we treated 12 patients with hematological malignancies with BMT from HLA-identical sibling donors given G-CSF 10 microg/kg/day for 5 days before marrow harvest. After CD34+ cell selection, patients received a median of 1.7 (range, 0.82-3.1) x 10(6) CD34+ cells/kg and 2.3 (range, 0.25-4.0) x 10(5) CD3+ cells/kg. All patients had initial engraftment but four developed pancytopenia between days 55-130 post-BMT. In two patients, this required a second infusion of G-CSF-mobilized donor peripheral blood progenitor cells. We observed no delayed pancytopenia in a matched historical group of 24 patients receiving T cell-depleted BMT without prior G-CSF stimulation. Compared to this control group, G-CSF-stimulated marrow recipients showed a significant decline in neutrophil and monocyte counts after 8 weeks. However, outcome after BMT was otherwise comparable, with a similar incidence of acute graft-versus-host disease and transplant-related mortality. Disease-free survival was 63 vs 67% for controls matched for CD34+ cell dose (P = NS). These results indicate that G-CSF stimulation can increase the CD34+ cell content of T cell-depleted marrow but carries a risk of late graft failure.

Attentional effects of single dose triazolam

1. While the effects of benzodiazepines on human memory have been extensively studied little is known about the effects of these agents on attentional processes. The authors studied the effects of a single dose of triazolam on selective visual-spatial attention using a double blind, placebo controlled design. 2. In each of 2 sessions 12 normal volunteers ingested either 0.25 mg of triazolam or placebo. Attentional performance was evaluated using two versions of the covert orienting paradigm which measured automatic (exogenous) and controlled (endogenous) aspects of attentional orienting, respectively. 3. Triazolam selectively modified performance on automatic orienting to exogenous cues. Specifically, triazolam increased the facilitation of target detection seen at shorter (150 msec) SOA's. This may indicate an increase in facilitation and a reduction in inhibition or a slowing of the time course of the biphasic attentional effect normally resulting from exogenous cuing. 4. These results indicate the importance of using experimental paradigms which effectively dissociate endogenous and exogenous mechanisms of spatial orienting in studies evaluating the effects of pharmacological agents on visual-spatial attention.

Hypocapnia associated with cardiac stress scintigraphy in chest pain patients with panic disorder

OBJECTIVE

Patients with recurrent chest pain but no evidence of coronary artery disease often meet diagnostic criteria for panic disorder (PD). However, it can be argued that the phenomenological diagnosis of PD may not be valid in these normal coronary chest pain (NCCP) patients. The purpose of this study is to additionally validate the diagnosis of PD in chest pain patients by comparing PCO2 levels before and during myocardial stress scintigraphy in those with and without PD.

METHOD

End-tidal PCO2 was measured before and during myocardial stress scintigraphy in 22 patients being evaluated for chest pain. Psychiatric diagnoses were assessed by structured interview.

RESULTS

Eleven of the 19 patients (58%) with negative scintigrams met DSM-III-R diagnostic criteria for current panic disorder. Prestress PCO2 levels were significantly lower in these patients. Eight of the nine NCCP patients with prestress PCO2 < 34 mm Hg had PD.

CONCLUSIONS

The finding of stress-related hypocapnia associated with PD in NCCP patients provides additional support for the validity of the diagnosis of PD in this population. The potential value of PCO2 measurements in screening for PD in patients with chest pain merits additional study.

Anterior cingulate gyrus dysfunction and selective attention deficits in schizophrenia: [15O]H2O PET study during single-trial Stroop task performance

OBJECTIVE

Attentional deficits are a prominent aspect of cognitive dysfunction in schizophrenia. The anterior cingulate gyrus is proposed to be an important component of frontal attentional control systems. Structural and functional abnormalities have been reported in this region in schizophrenia, but their relationship to attentional deficits is unknown. The authors investigated the function of the anterior cingulate gyrus and the related neural systems that are associated with selective attention in patients with schizophrenia.

METHOD

While subjects performed multiple blocks of a single-trial Stroop task, [15O]H2O positron emission tomography scans were obtained. Fourteen patients with schizophrenia were compared with 15 normal subjects matched for age, gender, and parental education.

RESULTS

The patients with schizophrenia responded at the same rate but made more errors in color naming during the color-incongruent condition. Consistent with the authors' hypothesis, patients with schizophrenia showed significantly less anterior cingulate gyrus activation while naming the color of color-incongruent stimuli.

CONCLUSIONS

Patients with schizophrenia fail to activate the anterior cingulate gyrus during selective attention performance. This finding adds to the understanding of the functional significance of the structural and metabolic abnormalities in schizophrenia that have been previously reported in this region of the brain.

Sexual differentiation in prairie voles: the effects of corticosterone and testosterone

Prairie voles (Microtus ochrogaster) exhibit low levels of physical sexual dimorphism and have endogenous basal corticosterone levels that are 5-10 times higher than those measured in rats; prairie voles also do not show a postnatal period of adrenal hyporesponsivity. On the basis of studies in rats suggesting that adrenal hyperactivity during the perinatal period could reduce masculinization or feminize sexual behavior, we hypothesized that adrenal hormones might influence sexual differentiation in prairie voles. We also examined the hypothesis that the effects of testosterone in prairie voles might differ from those reported in other rodents. Treatments with either corticosterone or testosterone propionate (TP) were given prenatally (gestational Days 12-20), via maternal injection, or postnatally (Days 1-6), by directly injecting the pups. Additional groups of males were castrated or sham-operated on postnatal Day 1, and a subgroup of castrated males received postnatal TP. Male and female sexual behavior was observed in adulthood following gonadectomy and hormone treatments. Corticosterone treatment was associated with high levels of mounting in both sexes and did not inhibit lordosis behavior in females. Postnatal TP treatment inhibited lordosis in females but did not facilitate mounting in either sex. Males that were castrated at birth showed unexpectedly high levels of mounting in response to adult androgens. The results of this study suggest that in prairie voles corticosterone is capable of masculinizing without defeminizing sexual behavior, whereas postnatal testicular secretions are not essential for, and may actually inhibit, masculinization in this species.

Prolonged production of NADPH oxidase-corrected granulocytes after gene therapy of chronic granulomatous disease

Little is known about the potential for engraftment of autologous hematopoietic stem cells in human adults not subjected to myeloablative conditioning regimens. Five adult patients with the p47(phox) deficiency form of chronic granulomatous disease received intravenous infusions of autologous CD34(+) peripheral blood stem cells (PBSCs) that had been transduced ex vivo with a recombinant retrovirus encoding normal p47(phox). Although marrow conditioning was not given, functionally corrected granulocytes were detectable in peripheral blood of all five patients. Peak correction occurred 3-6 weeks after infusion and ranged from 0.004 to 0.05% of total peripheral blood granulocytes. Corrected cells were detectable for as long as 6 months after infusion in some individuals. Thus, prolonged engraftment of autologous PBSCs and continued expression of the transduced gene can occur in adults without conditioning. This trial also piloted the use of animal protein-free medium and a blood-bank-compatible closed system of gas-permeable plastic containers for culture and transduction of the PBSCs. These features enhance the safety of PBSCs directed gene therapy.

Enumeration of CD34+ hematopoietic progenitor cells in peripheral blood and leukapheresis products by microvolume fluorimetry: a comparison with flow cytometry

There is increasing interest in both standardization and simplification of methods for enumeration of CD34+ hematopoietic progenitor cells (HPC) to facilitate cellular therapies and to improve interinstitutional comparison of clinical and laboratory results. We evaluated a novel method for CD34+ cell enumeration based on microvolume fluorimetry (MVF) compared with our laboratory's routine flow cytometric method on samples of peripheral blood and leukapheresis products. The MVF method is semiautomated and uses a 633-nm light from a helium-neon laser to scan fluorochrome-labeled cells held in stasis in a capillary known volume. The performance of the MVF assay for enumeration of CD34+ cells was found to be comparable to our routine flow cytometric assay in linearity and accuracy in the range of 5-1500 cells per microliter. Precision of MVF for replicate assays on the same instrument was demonstrated by coefficient of variation (CV) values of 8.4% at a CD34+ cell concentration of 284/microliters for a sample volume of 0.8 microliters, and 15.7% at 12/microliters for a sample volume of 3.2 microliter. Precision among three different instruments was demonstrated, using sample volumes of 1.6 microliters, by CV values of 44% at 6 cells/microliters and 4.6% at 733 cells/microliters. In a field sample evaluation, precision of the entire assay system for paired measurements on 0.8-microliter sample volumes was demonstrated by CV values of 50%, 31%, and 15% for peripheral blood samples with concentrations of 0-10, 10-20, and 20-100 CD34+ cells/microliters, respectively, and 6.3%, 8.1% and 6.5% for leukapheresis samples with concentrations of 0-100, 100-1,000, and 1,000-2,500 CD34+ cells/microliters, respectively. The MVF assay was easy to perform, required minimal technical training time, and had a turnaround time of 40 min, of which less than 10 min was actual technical time. These observations suggest that the MVF method for CD34+ cell enumeration may prove useful to clinical laboratories providing support for HPC collection, processing, and transplantation services that require relatively simple, rapid assays for product quality control or to guide real-time clinical decisions.

Retroviral gene transduction of adult peripheral blood or marrow-derived CD34+ cells for six hours without growth factors or on autologous stroma does not improve marking efficiency assessed in vivo

Our previous work in patients undergoing autologous transplant for multiple myeloma (MM) or breast cancer (BC) has shown that retroviral transduction of adult CD34+ cells for 72 hours in the presence of interleukin-3 (IL-3), IL-6, and stem cell factor (SCF) resulted in .01% to 1% long-term marking of peripheral blood and marrow cells (Blood 85:3948, 1995). In this study we compare these previous studies to transduction with no added growth factors, previously shown to result in higher levels of marking in children (Lancet 342:1134, 1993) or transduction in the presence of an autologous stromal layer. Peripheral blood (PB) mononuclear cells were collected via apheresis after high-dose cyclophosphamide and granulocyte colony-stimulating factor. Bone marrow (BM) was also harvested in all patients. One third of both BM and PB collections were enriched for CD34+ cells and transduced with one of two marking vectors containing the neomycin-resistance gene to distinguish cells originating from BM and PB posttransplantation. Cells from 3 MM and 2 BC patients were transduced without growth factors for 6 hours and cells from 2 MM and 2 BC patients were transduced in the presence of autologous marrow stroma. Immediately posttransduction, the percentage of Neo-resistant PB and BM progenitors (colony-forming units) were: 0% to 19% in the 6-hour no growth factor group and 0% to 36% in the autologous stroma group. After conditioning therapy, both transduced and untransduced PB and BM fractions were infused into the patients. Semi-quantitative nested DNA polymerase chain reaction was performed on total, mononuclear, and granulocyte fractions of PB and BM at 1, 3, 6, 9, 12, and 18 months. Poor marking has been observed in both groups, with no consistently positive patients. These results compare unfavorably with our prior experience using growth factors during transduction. Further optimization of transduction conditions and vectors needs to be developed to improve transduction efficiency of adult human repopulating hematopoietic cells.

The hypothalamic-pituitary-adrenal axis of prairie voles (Microtus ochrogaster): evidence for target tissue glucocorticoid resistance

Basal plasma corticosterone levels in prairie voles (Microtus ochrogaster) are extremely high, in the absence of any apparent negative consequences of glucocorticoid excess. We tested the hypothesis that prairie voles are a novel rodent model of target tissue resistance to glucocorticoids. Prairie voles had a significantly higher adrenal-to-body weight ratio, 5- to 10-fold greater basal plasma corticosterone, and 2- to 3-fold greater basal plasma ACTH concentrations than montane voles (Microtus montanus) and rats. While plasma corticosterone binding globulin (CBG) was 2-fold higher in prairie voles than in rats, both estimated and directly measured plasma free corticosterone were significantly higher in prairie voles than in rats. Plasma corticosterone levels in prairie voles were responsive to both circadian cues and a stressor, but were resistant to suppression by the synthetic glucocorticoid, dexamethasone (DEX). Western blots of brain and liver protein extracts, using a glucocorticoid receptor (GR) antibody, revealed the presence of a approximately 97 kDa immunoreactive band, the expected size for GR. Binding assays revealed significantly lower DEX affinity of corticosteroid receptors (CR) in cytosol of prairie vole brain and liver than that in the same tissues in rats. We conclude that prairie voles are a novel rodent model of glucocorticoid resistance, and that decreased affinity of CR for ligand might be partially responsible for this phenomenon.