Multimodal mechanisms of attention related to rates of spatial shifting in vision and touch

Covert attention can be directed spatially in several different sensory modalities (e.g. vision and touch). Recent psychological experiments indicate the existence of crossmodal links in spatial attention, but their neural basis in humans remains underspecified. We used positron emission tomography (PET) to assess the role of stimulus modality in the activity of brain regions involved in different rates of spatial attention shifting. A 2×2 factorial design manipulated the rate (high versus low) of spatial attention shifts between left and right hemifields, plus the sensory modality (vision versus touch) of stimulation. Two brain regions showed activations related to attentional shift-rate, independent of the stimulated modality: these were the right frontopolar gyrus, and the right posterior superior temporal sulcus (STS). The anterior area showed higher blood flow with the high rate of shifts in spatial attention, while the posterior area showed higher flow during the low rate conditions, where attention was sustained for longer on one side. No area showed a significant rate effect in one modality without an effect in the second modality. These results demonstrate multimodal roles for the activated brain regions in relation to the rate of spatial attention shifting, plus right-hemisphere dominance for this. They also suggest that anterior and posterior regions of the spatial-attention network play different roles in attention shifting. Electronic Publication     

Startle eyeblink modulation: detecting changes in directed attentional allocation during early preattentive processing.

Startle eyeblink modification was examined as a measure of allocation of attentional resources during active attention tasks in the early stage of information processing. Fifty-five participants were presented with a series of 250- and 40-ms tones of either high or low pitch which were followed by startle-eliciting stimuli at a lead interval of 120 ms. Attentional allocation was manipulated by instructing one group (Passive) to simply listen to the tones; the second group (Active 1) to count the number of low tones and the third group (Active 2) to count the long high-pitched tones and the short low-pitched tones. Startle eyeblink was significantly more inhibited for the Active 1 group than the Passive group (control) with no significant difference between the two directed attentional conditions (Active 1 and Active 2 groups). However, across the three attentional groups, the degree of startle eyeblink modulation appeared to reflect the degree of attention allocated to the task. The results support the utility of the startle probe in evaluating controlled attentional allocation during the early stages of information processing.     

The effects of smoking on selective attention as measured by startle reflex, skin conductance, and heart rate responses to auditory startle stimuli

The present study examined the effects of cigarette smoking on attentional processing by measuring nondeprived smokers' ( n =39), minimally deprived smokers' ( n =36), and nonsmokers' ( n =34) startle eyeblink reflex, heart rate, and skin conductance responses (SCR) to acoustic startle stimuli (105 dB) during directed attention tasks. Whereas smokers demonstrated smaller startle responses than nonsmokers during a directed attention visual task, no difference in startle response magnitude emerged between the two smoking groups, nor did we observe an effect of smoking on SCR or heart rate response to the startle stimuli. Our findings suggest that smokers differ from nonsmokers in their selective attention abilities and that smoking does not enhance minimally deprived smokers' selective attention.     

Response of Isolated Muscle Spindles to Single Transient Stretches*

Jahn , Samia Al Azharia . Response of isolated muscle spindles to single transient stretches. Acta physiol. scand. 1968. 72. 441–455. The smallest stretch of isolated frog muscle spindles which regularly evoked an afferent discharge was 8 ± 2 μ measured as the displacement of a graphite granule placed above the equatorial region 5–8 mm from the distal tendon of the muscle. The threshold deformation (T) was independent of an increase in the rate of deformation from 0.016 × T/msec to 1.0 × T/msec and of an increase in the initial elongation from 10 to 25 per cent above equilibrium length. The rate below which the spindle did not respond to stretch was 0.01 × T/msec. With low rates of stretch (0.016–0.03 × T/msec) the afferent response occurred before the deformation was completed and with higher rates (0.1–1.0 × T/msec) after it was completed. A second afferent response was elicited when the deformation exceeded 2 times threshold (rate of stretch: 0.1–0.3 × T/msec) or 3–4 times threshold (rate of stretch: 0.6–2.7 × T/msec). The shortest interval between two afferent responses was 2 msec. Depending on the timing of the spontaneous afferent activity and the spontaneous intrafusal contractions the afferent response evoked by a stretch was abolished or its latency was shortened or increased.     

Comparison of three segmental multifrequency bioelectrical impedance techniques in healthy adults

Background: The analysis of segmental or limb bioimpedance has gained importance in human population biology. However, standardized measurement techniques are needed.

Aim: This study compared three techniques for segmental analysis (T1, conventional electrode measurement; T2, use of a novel additional switching unit; T3, equipotentials instead of switching unit) which are often used in population biology.

Subjects and methods: The techniques were compared in 124 healthy adults (19–83 years) using a tetrapolar bioimpedance analyser (Nutriguard-M) at multiple frequencies (5, 50, 100 kHz) to gain whole-body and segmental resistances, reactances and phase angles.

Results: Repeated measures ANOVA yielded a significant technique effect for most variables (26/27), a significant interaction technique × sex for half (13/27), and a significant interaction technique × age for a quarter (7/27) of variables.

Conclusions: Differences exist between the three techniques which are primarily caused by inconsistent current pathways. A comparison with literature data showed that, in addition, subject's posture during measurement, electrode contact and electrode site may lead to inconsistent resistance and reactance values. This makes comparisons between different populations difficult. Therefore, this study recommends generally using the T2 technique which is standardized, easy to use and, thereby, well suited for field studies in large population groups.     

Paradox lost? Exploring the role of alpha oscillations during externally vs. internally directed attention and the implications for idling and inhibition hypotheses.

Although slow waves of the electroencephalogram (EEG) have been associated with attentional processes, the functional significance of the alpha component in the EEG (8.1-12 Hz) remains uncertain. Conventionally, synchronisation in the alpha frequency range is taken to be a marker of cognitive inactivity, i.e. 'cortical idling'. However, it has been suggested that alpha may index the active inhibition of sensory information during internally directed attentional tasks such as mental imagery. More recently, this idea has been amended to encompass the notion of alpha synchronisation as a means of inhibition of non-task relevant cortical areas irrespective of the direction of attention. Here we test the adequacy of the one idling and two inhibition hypotheses about alpha. In two experiments we investigated the relation between alpha and internally vs. externally directed attention using mental imagery vs. sensory-intake paradigms. Results from both experiments showed a clear relationship between alpha and both attentional factors and increased task demands. At various scalp sites alpha amplitudes were greater during internally directed attention and during increased load, results incompatible with alpha reflecting cortical idling and more in keeping with suggestions of active inhibition necessary for internally driven mental operations.     

Effect of Substance P on Various Vascular Beds in the Dog

Using the electromagnetic flowmeter technique, the blood flow in the aorta, carotid, hepatic, superior mesenteric, renal and femoral arteries and portal vein was recorded during continuous i.v. infusion of synthetic Substance P (SP) in 8 dogs. Systemic and portal blood pressures were recorded. A significant decrease in mean arterial blood pressure was recorded at infusion of SP in the femoral vein at a rate of 2.5 ng × min^-1× kg b.w.^-1 or higher. Portal venous blood pressure increased. A rapid increase in the carotid, hepatic, mesenteric and portal blood flow was obtained at infusion rates of 1.2 ng × min^-1× kg b.w.^-1 or higher. The femoral artery responded with a late, transient increase in flow, with a return to the base level while the infusion was still in progress. The renal artery blood flow decreased slightly at low infusion rates and increased at higher. At SP infusions in the portal vein the infusion rate had to be increased to 20 ng × min^-1× kg b.w.^-1 or higher before any general vascular reactions were recorded, indicating that the liver has a high capacity for inactivating SP.     

Associative and non-associative blinking in classically conditioned adult rats

Over the last several years, a growing number of investigators have begun using the rat in classical eyeblink conditioning experiments, yet relatively few parametric studies have been done to examine the nature of conditioning in this species. We report here a parametric analysis of classical eyeblink conditioning in the adult rat using two conditioned stimulus (CS) modalities (light or tone) and three interstimulus intervals (ISI; 280, 580, or 880 ms). Rats trained at the shortest ISI generated the highest percentage of conditioned eyeblink responses (CRs) by the end of training. At the two longer ISIs, rats trained with the tone CS produced unusually high CR percentages over the first few acquisition sessions, relative to rats trained with the light CS. Experiment 2 assessed non-associative blink rates in response to presentations of the light or tone, in the absence of the US, at the same ISI durations used in paired conditioning. Significantly more blinks occurred with longer than shorter duration lights or tones. A higher blink rate was also recorded at all three durations during the early tone-alone sessions. The results suggest that early in classical eyeblink conditioning, rats trained with a tone CS may emit a high number of non-associative blinks, thereby inflating the CR frequency reported at this stage of training.     

Ontogeny of eyeblink conditioning in the rat: Auditory frequency and discrimination learning effects

The present study sought to determine whether acoustic properties of the auditory conditioned stimulus (CS) or the use of a discrimination learning procedure would alter the emergence of eyeblink conditioning between postnatal Days 17 and 24 (Days 17–24) in the rat. In Experiment 1, we employed a 3 × 2 × 2 factorial design, involving pitch of the auditory CS (2.8, 5.0, and 9.0 kHz), training condition (paired vs. unpaired), and age (Days 17 or 24). Associative learning was evident at all tone frequencies on Day 24, but increased across frequencies on Day 17, although large age differences in conditioning remained at all tone frequencies. In Experiment 2, rat pups were trained to discriminate 2.8 versus 9.0-kHz tones on Day 17 or Day 24. Eyeblink conditioning increased with tone frequency on Day 24 but discriminative conditioning failed to appear on Day 17. These findings are discussed in relation to the role of auditory system maturation in the ontogeny of eyeblink conditioning. © 1995 Johnv Wiley & Sons, Inc.     

New alleles at microsatellite loci in CEPH families mainly arise from somatic mutations in the lymphoblastoid cell lines

In the analysis of 40 CEPH families, under the EUROGEM project, with a total of 29 microsatellites (26 CA-repeats, a TCTA-repeat within the vWFII-3 gene, a TTA-repeat within the PLA-2 gene, and an AAAT-repeat intragenic to the NF1 gene) from human chromosomes 12, 17, and 21, we have detected 21 cases of abnormal segregation of alleles in 16 pedigrees for a total of 14 markers (48%). In 11 cases, the abnormal transmissions were of somatic origin, 10 of which (91%) occurred in the lymphoblastoid cell lines. In 9 other cases, it was not possible to determine if the origin of the new alleles was somatic or germline, and in one case hemizygosity in several family members was observed, so its origin was germline. The 20 new mutations detected in the 22,852 meioses analysed represent a mutation frequency of 8.7 × 10^?4 per locus per allele. The germline mutation rate could be as high as 3.9 × 10^?4 per locus per gamete (from 0 to 3.9 × 10^?4), but the rate of somatic mutations detected in the study was much higher (4.8 × 10^?4 to 8.7 × 10^?4 per locus per allele). Individual mutation rates ranged from 0 to 3.8 × 10^?3. Among the markers analysed, all three that were tri- or tetranucleotide repeats showed one or two new alleles, compared to only 10 of the 26 (38%) CA-repeats showing mutations. Three CEPH families (102, 45 and 1333) each had several mutational events, and one individual (10210) had somatic mutations for two microsatellites from different chromosomes. The mutation rate at microsatellite loci within families, using DNA directly obtained from cells from the individual, is less than 1 × 10^?4 (true germline mutation rate), which should not affect the use of these markers in diagnosis and linkage. However, these results and previous data suggest that for DNA obtained from cell lines, mutations are much more frequent (1 × 10^?2?1 × 10^?3). © 1994 Wiley-Liss, Inc.     

The effects of level of difficulty of mental arithmetic challenge on heart rate and oxygen consumption

Heart rate plus various metabolic and ventilatory indices were monitored while 18 young males engaged in a mental arithmetic task, structured to include 3 levels of difficulty; easy, difficult and impossible. Measurements were also taken while subjects undertook graded isotonic exercise on a bicycle ergometer; for each subject heart rate was plotted against oxygen consumption over the various exercise loads. Knowing oxygen consumption during the psychological tasks, these regression equations permitted the calculation of expected heart rates during each task condition and thus the computation of 'additional heart rate' as the difference between actual and predicted heart rate values. Additional heart rate was sensitive to variations in difficulty level; the difficult condition elicited reliably more additional heart rate than the easy and impossible conditions. Subjects' performance as well as their perceptions closely reflected the a priori classification of difficulty. Although subjects rated the easy condition as particularly unengaging, the impossible condition attracted relatively high rates of task involvement. It was argued that self-reports of this sort are probably more susceptible than cardiac activity to social demand characteristics.     

Age,Environment, and Lymphocyte Immunization Influence the Spontaneous Resorption Rate in the CBA/J × DBA/2J Mouse Model

PROBLEM: This study was designed to examine the influence of age, environment, and lymphocyte immunotherapy on fetal resorption rates in the CBA/J × DJA/2J mouse model. METHODS: After weaning, CBA/J female mice were randomly allocated to two different environments: room A was a conventional housing facility, and room B was a specific pathogen-free room. They were further divided into two groups in each room according to age (> three months and ≤ three months), and mated with CBA/J, DBA/2J, or BALB/c males. The fetal resorption rates were observed. The immunization study was conducted using CBA/J females greater than three months old in room B. Preimmunization with various preparations and dosages of lymphoctyes was performed 1 wk before mating with DBA/2J males, and fetal resorption rates were measured to investigate the effect of immunotherapy. RESULTS: In room A, the fetal resorption rates (9.4 to 11.8%) were not significantly different among the various mating combinations using CBA/J females greater or less than three months of age. In room B, CBA/J females older than three months and mated with DBA/2J males had a higher rate of fetal resorption than those younger than three months (28.9 versus 14.2%) and had higher rate of fetal resorption than those housed and mated in room A (28.9 versus 10.9%). This fetal resorption rate was also higher than those seen with other mating combinations. Preimmunization with male BALB/c splenic lymphocytes (optimal dose 1 × 10⁷ cells) was effective in decreasing fetal resorption rate (7.9%), whereas administration of normal saline, or immunization with male CBA/J or DBA/2J lymphocytes was not (20.7 to 27.0%). CONCLUSION: Age and environment influence the spontaneous resorption rate in the CBA/J × DBA/2J mouse model. The high fetal resorption rate of older CBA/J females mated with DBA/2J males in a pathogen-free environment can be reduced by immunization with BALB/c splenic lymphocytes. These results suggested that a variety of mechanisms might initiate early pregnancy failure and that immunological modulation during implantation might be a nonspecific factor.     

High dose concentration administration of ascorbic acid inhibits tumor growth in BALB/C mice implanted with sarcoma 180 cancer cells via the restriction of angiogenesis

To test the carcinostatic effects of ascorbic acid, we challenged the mice of seven experimental groups with 1.7 × 10^-4 mol high dose concentration ascorbic acid after intraperitoneal administrating them with sarcoma S-180 cells. The survival rate was increased by 20% in the group that received high dose concentration ascorbic acid, compared to the control. The highest survival rate was observed in the group in which 1.7 × 10^-4 mol ascorbic acid had been continuously injected before and after the induction of cancer cells, rather than just after the induction of cancer cells. The expression of three angiogenesis-related genes was inhibited by 0.3 times in bFGF, 7 times in VEGF and 4 times in MMP2 of the groups with higher survival rates. Biopsy Results, gene expression studies, and wound healing analysis in vivo and in vitro suggested that the carcinostatic effect induced by high dose concentration ascorbic acid occurred through inhibition of angiogenesis.     

Central command increases cardiac output during static exercise in humans

Neural control of the circulation during static two-leg exercise was evaluated in 10 subjects. External compression of the legs was employed to assess muscle mechano-receptor influence by achieving the same intramuscular pressure (80 mmHg) as developed during exercise. The muscle metabo-reflex contribution was assessed by post-exercise muscle ischaemia, and the influence from higher centres in the central nervous system (‘central command’) was taken as the part of the response that could not be accounted for by the two reflex contributions. During static exercise, mean arterial pressure was higher (26±3 mmHg; P<0.01) as compared with leg compression (10±2 mmHg) and with post-exercise muscle ischaemia (11±2 mmHg). Heart rate (25±4 b.p.m.) and cardiac output (0.8±0.3 L min^-1) were increased only during static exercise (P<0.05). Increase in total peripheral resistance were similar during static exercise, post-exercise muscle ischaemia and leg compression. The pressor response to static exercise with a large muscle group was equally attributable to mechanical and metabolic stimulation of afferent nerves; and the two influences were redundant in their effect on total peripheral resistance. In contrast, the influence from central command was directed to the heart with elevation of its rate and minute volume.     

Electromyography as a new means of navigation during endotracheal intubation

Abstract

This study tested a method of using rapid analysis of electromyographic response patterns to electrical stimulation to enable real-time navigation during endotracheal intubation. An electromyographic response detection device was constructed and integrated into a standard endotracheal tube. The rebound rates of the response voltages were measured in the trachea and oesophagus after stimulation in an acute study performed in three freshly euthanized male Suffolk sheep. In a blind study, a physician attempted to identify the tissue type solely from the electrical response signals. In the acute study, the observed rebound rate was found to be significantly faster in tracheal tissue (2.21?×?10^?3 V s^?1) than in oesophageal tissue (3.45?×?10^?2 V s^?1; p?=?0.000 05). In the blind study, the physician correctly determined the oesophagus response rate seven out of eight times and the tracheal rate eight out of nine times. These results suggest that electromyographic responses can be used to accurately differentiate tracheal from oesophageal tissue during ETT insertion, thus offering a valuable new means of enhancing patient safety.     

Significance of HPV 16 and 18 viral load quantitation in women referred for colposcopy

The clinical utility of HPV 16 and 18 viral loads remains debated. The aim of this study was to assess the clinical significance of HPV 16 and 18 viral load and to determine a cut‐off for optimal prediction of grade 2 or higher cervical intraepithelial neoplasia among patients referred to colposcopy. A total of 186 cervico‐vaginal specimens harboring HPV 16 and/or 18 obtained at the time of colposcopy from patients without previous cervical neoplasia were tested for HPV 16 and 18 detection and quantitation using quantitative duplex real‐time PCR method. Grade 2 or higher cervical intraepithelial neoplasia was diagnosed in 87 (46.8%) cases. Only HPV 16 median viral load increased significantly with the lesion grade: 9.1 × 10⁴ in normal cervix or grade 1 cervical intraepithelial lesion versus 4.0 × 10⁶ copies per million cells in grade 2 or higher cervical intraepithelial lesion (P < 0.001). The highest predictive value for grade 2 or higher cervical intraepithelial lesion was observed with a HPV 16 viral load cut‐off of 3.0 × 10⁶ copies per million cells (91% specificity, 58.2% sensitivity). Using this cut‐off, the highest predictive value of HPV 16 viral load was observed among those referred for previous low‐grade abnormal cervical cytology (96.4% specificity, 88% sensitivity). HPV 18 quantitation showed very poor predictive value. Specific attention should be given when performing colposcopic examination of women with an HPV 16 viral load higher than 3.0 × 10⁶ copies per million cells, especially among those referred after a low‐grade abnormal cytology. J. Med. Virol. 84:306–313, 2012. © 2011 Wiley Periodicals, Inc.     

Epidemiology of Injuries in National Collegiate Athletic Association Women's Track and Field: 2014–2015 Through 2018–2019

ContextWomen''s track and field events at the National Collegiate Athletic Association level have grown in popularity in recent years, and track and field athletes are vulnerable to a broad range of potential injuries.BackgroundRoutine examination of track and field injuries is important for identifying emerging patterns in injury incidence.MethodsExposure and injury data collected in the National Collegiate Athletic Association Injury Surveillance Program during the 2014–2015 to 2018–2019 academic years were analyzed. Injury counts, rates, and proportions were used to describe injury characteristics, and injury rate ratios were used to examine differential injury rates.ResultsThe overall injury rate was 2.20 per 1000 athlete exposures; the competition injury rate was higher than the practice injury rate (injury rate ratio = 1.73; 95% confidence interval = 1.51, 1.97). Hamstring tears (8.9%), medial tibial stress syndrome (5.4%), and lateral ligament complex tears (4.2%) were the most reported injuries.ConclusionsGiven the results of this study, further attention may be directed toward factors associated with noncontact injury risk in the competitions. The changing injury rates of most reported injuries also warrant monitoring post 2018–2019.     

Capillary transport of H2 gas generated locally in renal tissue

Previous measurements by microspheres have shown a higher blood flow in outer cortex and a lower blood flow in inner cortex than found by diffusible tracers. During vasodilation microspheres have indicated a disproportionate increase in deep cortical blood flow, whereas diffusible tracer distributions remained unchanged. These discrepancies could possibly be explained by a variable net inward transport of diffusible tracers in postglomerular vessels, the transport existing in control, but disappearing during vasodilation. To test this hypothesis H₂ gas was produced electrolytically for 1 s at a platinum electrode in midcortex and the resulting gas concentration curve measured polarographically at two electrodes placed above and below the source. Analysis of a mathematical model showed that the ratio of the curve maxima at the two electrodes (Cm_o/Cm_i) would best reveal a radial net transport. Average Cm_o/Cm_i at 25 positions in 7 clamped dog kidneys was close to unity, but rose to 1.24 at control flow. During acetylcholine infusion Cm_o/Cm_i rose to 1.68. Local washout rates at the two electrodes increased equally. Calculations indicated a small outwardly directed net transport in control (3×10^-4cm/s), becoming slightly reinforced during vasodilation (5×10^-4 cm/s). Thus the control transport direction is opposite to the hypothesis, and the change during vasodilation was estimated to be too small to explain the disparity between diffusible tracer uptake and microsphere distribution in control. H₂ concentration maximum was obtained earlier under control flow than in the clamped kidney, indicating an increase in apparent D of the gas in tissue from 3×10^-5 cm²/s to 5×10^-5 cm²/s, probably due to mixing of H₂ gas in the capillary net work.     

Spontaneous Abortion in Immunodeficient SCID Mice

PROBLEM: Immunodeficient SCID mice on the CB-17 have been used to test the role of “rejection” in a xenogeneic blastocyst transfer model of recurrent miscarriage, but interpretation of the data requires knowing syngeneic within-species matings have a high success rate and do not require immunotrophic factors expected only in immunocompetent non-T-cell deficient mice. METHOD: Resorption rates were studied in a SCID CB-17 barrier facility that provided the mice used to test the role of immunology in the resorption model. RESULTS: Spontaneous resorption in syngeneically mated immunodeficient SCID mice on the CB-17 background occurred at an unexpectedly high rate and could not be prevented by treatment with anti-asialo GM1 antibody or GM-CSF, both of which are effective in ameliorating abortion in DBA/2J-mated CBA/J mice. Immunocompetent CB-17 +/+ mice showed an even higher rate of loss. The latter was also not affected by treatment with anti-asialo GM1 antibody or by GM-CSF and was not prevented by tetracycline (which is effective in the DBA/2-CBA/J system) or progesterone treatment. Mating experiments showed a scid/+ × scid//+ cross gave the highest rate of loss, and it appeared that the presence of +/+-type embryos in the uterus could be augmenting abortion with selective discrimination against scid/scid embryos. High abortion rates were associated both with appearance of a coagulase-negative Staphylococcus sp. in feces and with loss of one component of the SPF flora. Decidual tissue from mated CB-17 +/+ mice showed premature release of TNF-cc in absence of TGF-β2-related suppressor activity, and vascular lesions (fibrinoid necrosis), varying in extent, were associated with both scid/scid × scid/scid and +/+ × +/+ pregnancies. TNF-α also appeared prematurely in pregnant scid/scid mice, but the levels were lower (and areas of necrosis smaller than in +/+ × +/+ pregnancies). Outcrossing onto a C57B1/6 background dramatically reduced the abortion rate, indicating an important genetic effect on susceptibility with heterogeneity protecting against abortion. CONCLUSIONS: SCID mice on the CB-17 background do not have a high rate of successful syngeneic pregnancies, and a TNF-α induced vasculopathy may be responsible. Abortion was not caused by immunodeficiency leading to loss of immunotrophism because immunocompetent non-SCID CB-17 mice had a higher rate of loss. Factors augmenting the abortion rate included the presence of embryos of the +/+ genotype in the uterus and treatment with anti-asialo GM1 antibody. Abortion rates were not reduced by treatments effective in the DBA/2-mated CBA/J mouse model but were reduced by re-establishing a new colony with defined flora (a temporary effect) and by outcrossing mice with a different (C57B1/6) background. Together, the data suggest an infectious trigger (identity uncertain) of the vasculopathy and an important genetic influence on susceptibility with heterozygosity and a SCID mouse mutation providing against abortion a degree of protection.     

High IgE secretion capacity of human plasma cells

In accordance with results obtained in another culture system, it has previously been shown that human B cells frequently switch to immunoglobulin E (IgE) when they are co-cultured with irradiated mutant EL4 thymoma cells (which provide a CD40 ligand-mediated B cell activation signal), T cell supernatant and recombinant interleukin (IL)-4. However, because of the potentially severe side effects of IgE, such as anaphylaxis, B cells could have a limited capacity to produce this isotype. The IgE secretion rate of plasma cells is not known. In the present study, we compared the secretion rates for different Ig classes by means of limiting dilution analysis of plasmocytic cells that were harvested after 8 to 9 days from primary EL4/B cell cultures and titrated into secondary cultures in the presence of a cell proliferation-blocking concentration of hydroxyurea. These cells secreted Ig at constant rates for periods of up to 2 weeks; IgE secretion was IL-4 independent. The mean cellular secretion rates were similarly high for IgE (150 pg/cell/24 h) and other isotypes (IgM 273 pg, IgG 112 pg, IgA 136 pg/cell/24 h). In terms of molecules per min this represents 3.3 × 10⁵ for IgE versus 1.2 × 10⁵ for IgM, 3.1 × 10⁵ for IgG and 3.6 × 10⁵ for IgA. The relative frequency of IgE-secreting cells was only 0.3 % of the total number of Ig-secreting cells, suggesting a small size of IgE-producing clones in this in vitro system. Whether this is relevant regarding an in vivo response is not known. Clearly, the Ig secretion capacity of plasma cells would not limit an IgE response in the absence of extrinsic control.