ThermoCyte: an inexpensive open-source temperature control system for in vitro live-cell imaging

Live-cell imaging is a common technique in microscopy to investigate dynamic cellular behaviour and permits the accurate and relevant analysis of a wide range of cellular and tissue parameters, such as motility, cell division, wound healing responses and calcium (Ca2+) signalling in cell lines, primary cell cultures and ex vivo preparations. Furthermore, this can occur under many experimental conditions, making live-cell imaging indispensable for biological research. Systems which maintain cells at physiological conditions outside of a CO2 incubator are often bulky, expensive and use proprietary components. Here we present an inexpensive, open-source temperature control system for in vitro live-cell imaging. Our system 'ThermoCyte', which is constructed from standard electronic components, enables precise tuning, control and logging of a temperature 'set point' for imaging cells at physiological temperature. We achieved stable thermal dynamics, with reliable temperature cycling and a standard deviation of 0.42°C over 1 h. Furthermore, the device is modular in nature and is adaptable to the researcher's specific needs. This represents simple, inexpensive and reliable tool for laboratories to carry out custom live-cell imaging protocols, on a standard laboratory bench, at physiological temperature.

A finite element model of contusion spinal cord injury in rodents

Traumatic spinal cord injuries result from high impact forces acting on the spine and are proceeded by an extensive secondary inflammatory response resulting in motor, sensory, and autonomic dysfunction. Experimental in vivo traumatic spinal cord injuries in rodents using a contusion model have been extremely useful in elucidating the underlying pathophysiology of these injuries. However, the relationship between the pathophysiology and the biomechanical factors is still not well understood. Therefore, the aim of this research is to provide a comprehensive analysis of the biomechanics of traumatic spinal cord injury in a rat contusion model. This is achieved through the development and validation of a finite element model of the thoracic rat spinal cord and subsequently simulating controlled cortical impact-induced traumatic spinal cord injury. The effects of impactor velocity, depth, and geometry on the resulting stresses and strains within the spinal cord are investigated. Our results show that increasing impactor depth results in larger stresses and strains within the spinal cord tissue as expected. Further, for the first time ever our results show that impactor geometry (spherical versus cylindrical) plays an important role in the distribution and magnitude of stresses and strains within the cord. Therefore, finite element modelling can be a powerful tool used to predict stresses and strains that occur in spinal cord tissue during trauma.

Evaluation of physical activity calorie equivalent (PACE) labels' impact on energy purchased in cafeterias: A stepped-wedge randomised controlled trial

BACKGROUND

A recent meta-analysis suggested that using physical activity calorie equivalent (PACE) labels results in people selecting and consuming less energy. However, the meta-analysis included only 1 study in a naturalistic setting, conducted in 4 convenience stores. We therefore aimed to estimate the effect of PACE labels on energy purchased in worksite cafeterias in the context of a randomised study design.

METHODS AND FINDINGS

A stepped-wedge randomised controlled trial (RCT) was conducted to investigate the effect of PACE labels (which include kcal content and minutes of walking required to expend the energy content of the labelled food) on energy purchased. The setting was 10 worksite cafeterias in England, which were randomised to the order in which they introduced PACE labels on selected food and drinks following a baseline period. There were approximately 19,000 workers employed at the sites, 72% male, with an average age of 40. The study ran for 12 weeks (06 April 2021 to 28 June 2021) with over 250,000 transactions recorded on electronic tills. The primary outcome was total energy (kcal) purchased from intervention items per day. The secondary outcomes were: energy purchased from non-intervention items per day, total energy purchased per day, and revenue. Regression models showed no evidence of an overall effect on energy purchased from intervention items, -1,934 kcals per site per day (95% CI -5,131 to 1,262), p = 0.236, during the intervention relative to baseline, equivalent to -5 kcals per transaction (95% CI -14 to 4). There was also no evidence for an effect on energy purchased from non-intervention items, -5 kcals per site per day (95% CI -513 to 504), p = 0.986, equivalent to 0 kcals per transaction (95% CI -1 to 1), and no clear evidence for total energy purchased -2,899 kcals per site (95% CI -5,810 to 11), p = 0.051, equivalent to -8 kcals per transaction (95% CI -16 to 0). Study limitations include using energy purchased and not energy consumed as the primary outcome and access only to transaction-level sales, rather than individual-level data.

CONCLUSION

Overall, the evidence was consistent with PACE labels not changing energy purchased in worksite cafeterias. There was considerable variation in effects between cafeterias, suggesting important unmeasured moderators.

TRIAL REGISTRATION

The study was prospectively registered on ISRCTN (date: 30.03.21; ISRCTN31315776).

Acceptability of policies to reduce consumption of red and processed meat: A population-based survey experiment

Policies to reduce meat consumption are needed to help achieve climate change targets, and could also improve population health. Public acceptability can affect the likelihood of policy implementation. This study estimated the acceptability of policies to reduce red and processed meat consumption, and whether acceptability differed when policies were framed as benefitting health or the environment. In an online experiment, 2215 UK adults rated the acceptability of six policies, presented in a randomised order. Prior to rating policies, participants were randomised to one of two framing conditions, with policy outcomes described either as benefitting health or the environment. Regression models examined differences in the primary outcome - policy acceptability (rated on a 7-point scale) - by framing. Labels were the most accepted policy (48% support), followed by a media campaign (45%), reduced availability (40%) and providing incentives (38%). Increasing price (27%) and banning advertising (26%) were the least accepted. A substantial proportion of participants neither supported nor opposed most policies (26-33%), although this fell to 16% for increasing price. There was no evidence that framing policy benefits from a health or environment perspective influenced acceptability (-0.06, 95%CIs: 0.18,0.07). Fewer than half of the UK sample expressed support for any of six policies to reduce meat consumption, regardless of framing measures as benefitting health or the environment. Conversely, fewer than half expressed opposition, with the exception of price, suggesting considerable scope to influence public opinion in support of meat reduction measures to meet environmental and health goals.

Public support for policies to improve population and planetary health: A population-based online experiment assessing impact of communicating evidence of multiple versus single benefits

Background

Effective interventions for reducing the consumption of products that harm population and planetary health often lack public support, impeding implementation. Communicating evidence of policies’ effectiveness can increase public support but there is uncertainty about the most effective ways of communicating this evidence. Some policies have multiple benefits such as both improving health and the environment. This study assesses whether communicating evidence of multiple versus single benefits of a policy increases its support.

Method

Participants (n = 4616) nationally representative of the British population were randomised to one of 24 groups in an online experiment with a 4 × 3 × 2 between-subjects factorial design. The messages that participants viewed differed according to the evidence they communicated (no message, effectiveness for changing behaviour, effectiveness for changing behaviour + one policy benefit, effectiveness for changing behaviour + three policy benefits), type of policy (taxation, availability) and the target behaviour (consumption of energy-dense food, alcohol, or meat). The primary outcome was policy support.

Results

In a full factorial ANOVA, there was a significant main effect of communicating evidence of effectiveness on policy support, which was similar across policies and behaviours. Communicating three benefits increased support relative to communicating one benefit (d = 0.15; p = 0.01). Communicating one benefit increased support compared to providing evidence for changing behaviour alone (d = 0.13; p = 0.004) or no message (d = 0.11 p = 0.022).

Conclusion

Communicating evidence of a policy's benefits increases support for policy action across different behaviours and policies. Presenting multiple benefits of policies enhances public support.

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Providing evidence of policies effectiveness at achieving policy goals increases public support.

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Uncertainty exists about the most effective ways of communicating this evidence.

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Evidence about multiple policy benefits increases support more than evidence for a single benefit.

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Effects are evident across behaviours and policies.

Impact of decreasing the proportion of higher energy foods and reducing portion sizes on food purchased in worksite cafeterias: A stepped-wedge randomised controlled trial

BACKGROUND

Overconsumption of energy from food is a major contributor to the high rates of overweight and obesity in many populations. There is growing evidence that interventions that target the food environment may be effective at reducing energy intake. The current study aimed to estimate the effect of decreasing the proportion of higher energy (kcal) foods, with and without reducing portion size, on energy purchased in worksite cafeterias.

METHODS AND FINDINGS

This stepped-wedge randomised controlled trial (RCT) evaluated 2 interventions: (i) availability: replacing higher energy products with lower energy products; and (ii) size: reducing the portion size of higher energy products. A total of 19 cafeterias were randomised to the order in which they introduced the 2 interventions. Availability was implemented first and maintained. Size was added to the availability intervention. Intervention categories included main meals, sides, cold drinks, snacks, and desserts. The study setting was worksite cafeterias located in distribution centres for a major United Kingdom supermarket and lasted for 25 weeks (May to November 2019). These cafeterias were used by 20,327 employees, mainly (96%) in manual occupations. The primary outcome was total energy (kcal) purchased from intervention categories per day. The secondary outcomes were energy (kcal) purchased from nonintervention categories per day, total energy purchased per day, and revenue. Regression models showed an overall reduction in energy purchased from intervention categories of -4.8% (95% CI -7.0% to -2.7%), p < 0.001 during the availability intervention period and a reduction of -11.5% (95% CI -13.7% to -9.3%), p < 0.001 during the availability plus size intervention period, relative to the baseline. There was a reduction in energy purchased of -6.6% (95% CI -7.9% to -5.4%), p < 0.001 during the availability plus size period, relative to availability alone. Study limitations include using energy purchased as the primary outcome (and not energy consumed) and the availability only of transaction-level sales data per site (and not individual-level data).

CONCLUSIONS

Decreasing the proportion of higher energy foods in cafeterias reduced the energy purchased. Decreasing portion sizes reduced this further. These interventions, particularly in combination, may be effective as part of broader strategies to reduce overconsumption of energy from food in out-of-home settings.

TRIAL REGISTRATION

ISRCTN registry ISRCTN87225572.

Release probability increases towards distal dendrites boosting high-frequency signal transfer in the rodent hippocampus

Dendritic integration of synaptic inputs involves their increased electrotonic attenuation at distal dendrites, which can be counterbalanced by the increased synaptic receptor density. However, during network activity, the influence of individual synapses depends on their release fidelity, the dendritic distribution of which remains poorly understood. Here, we employed classical optical quantal analyses and a genetically encoded optical glutamate sensor in acute hippocampal slices of rats and mice to monitor glutamate release at CA3-CA1 synapses. We find that their release probability increases with greater distances from the soma. Similar-fidelity synapses tend to group together, whereas release probability shows no trends regarding the branch ends. Simulations with a realistic CA1 pyramidal cell hosting stochastic synapses suggest that the observed trends boost signal transfer fidelity, particularly at higher input frequencies. Because high-frequency bursting has been associated with learning, the release probability pattern we have found may play a key role in memory trace formation.

LTP Induction Boosts Glutamate Spillover by Driving Withdrawal of Perisynaptic Astroglia

Extrasynaptic actions of glutamate are limited by high-affinity transporters expressed by perisynaptic astroglial processes (PAPs): this helps maintain point-to-point transmission in excitatory circuits. Memory formation in the brain is associated with synaptic remodeling, but how this affects PAPs and therefore extrasynaptic glutamate actions is poorly understood. Here, we used advanced imaging methods, in situ and in vivo, to find that a classical synaptic memory mechanism, long-term potentiation (LTP), triggers withdrawal of PAPs from potentiated synapses. Optical glutamate sensors combined with patch-clamp and 3D molecular localization reveal that LTP induction thus prompts spatial retreat of astroglial glutamate transporters, boosting glutamate spillover and NMDA-receptor-mediated inter-synaptic cross-talk. The LTP-triggered PAP withdrawal involves NKCC1 transporters and the actin-controlling protein cofilin but does not depend on major Ca2+-dependent cascades in astrocytes. We have therefore uncovered a mechanism by which a memory trace at one synapse could alter signal handling by multiple neighboring connections.

Communicating evidence about the environment's role in obesity and support for government policies to tackle obesity: a systematic review with meta-analysis

Public support for many policies that tackle obesity by changing environments is low. This may reflect commonly held causal beliefs about obesity, namely that it is due to failures of self-control rather than environmental influences. Several studies have sought to increase public support by changing these and similar causal beliefs, with mixed results. The current review is the first systematic synthesis of these studies. Searches of PsycInfo, Medline, Web of Science, Scopus, and Open Grey yielded 20 eligible studies (N = 8977) from 11,776 abstracts. Eligible studies were controlled experiments with an intervention group that communicated information about the environment’s role in obesity, and a measure of support for environment-based obesity policies. The protocol was prospectively registered on PROSPERO. Meta-analyses showed no evidence that communicating information about the environment’s influence on obesity changed policy support or the belief that the environment influences obesity. A likely explanation for this null effect is the ineffectiveness of interventions that were designed to change the belief that the environment influences obesity. The possibility remains, however, that the association observed between beliefs about the causes of obesity and attitudes towards obesity policies is correlational and not causal.

Communicating Evidence about the Causes of Obesity and Support for Obesity Policies: Two Population-Based Survey Experiments

Public support for numerous obesity policies is low, which is one barrier to their implementation. One reason for this low support is the tendency to ascribe obesity to failings of willpower as opposed to the environment. Correlational evidence supports this position. However, the experimental evidence is mixed. In two experimental studies, participants were randomised to receive no message, messages about the environment's influence on obesity (Study 1 & 2), or messages about the environment's influence on human behaviour (Study 1). We investigated whether communicating these messages changed support for obesity policies and beliefs about the causes of obesity. Participants were recruited from nationally representative samples in Great Britain (Study 1 & 2) and the USA (Study 2) (total n = 4391). Study 2 was designed to replicate existing research. Neither study found evidence that communicating the messages increased support for obesity policies or strengthened beliefs about the environment's role in obesity. Study 2, therefore, did not replicate two earlier experimental studies. Instead, the studies reported here suggest that people's beliefs about the causes of obesity are resistant to change in response to evidence and are, therefore, not a promising avenue to increase support for obesity policies.

Increasing the proportion of healthier foods available with and without reducing portion sizes and energy purchased in worksite cafeterias: protocol for a stepped-wedge randomised controlled trial

BACKGROUND

Overconsumption of energy from food contributes to high rates of overweight and obesity in many populations. A promising set of interventions tested in pilot studies in worksite cafeterias, suggests energy intake may be reduced by increasing the proportion of healthier - i.e. lower energy - food options available, and decreasing portion sizes. The current study aims to assess the impact on energy purchased of i. increasing the proportion of lower energy options available; ii. combining this with reducing portion sizes, in a full trial.

METHODS

A stepped-wedge randomised controlled trial in 19 worksite cafeterias, where the proportion of lower energy options available in targeted food categories (including main meals, snacks, and cold drinks) will be increased; and combined with reduced portion sizes. The primary outcome is total energy (kcal) purchased from targeted food categories using a pooled estimate across all sites. Follow-up analyses will test whether the impact on energy purchased varies according to the extent of intervention implementation.

DISCUSSION

This study will provide the most reliable estimate to date of the effect sizes of two promising interventions for reducing energy purchased in worksite cafeterias.

TRIAL REGISTRATION

The study was prospectively registered on ISRCTN (date: 24.05.19; TRN: ISRCTN87225572; doi: https://doi.org/10.1186/ISRCTN87225572).

Author Correction: Disentangling astroglial physiology with a realistic cell model in silico

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Self-regulatory consequences of observing others making goal progress: A longitudinal field study in weight loss groups

OBJECTIVE

What happens when people see others making progress toward a goal that they also hold? Is it motivating or could it undermine goal pursuit because people feel that they have made progress themselves (i.e., they experience vicarious goal satiation)?

METHODS

We investigated these questions in a longitudinal field context - a group weight loss programme. N = 132 participants who were overweight or obese and attended weekly weight loss classes completed questionnaires over 11 weeks to investigate the consequences of observing other people making progress toward their goal of losing weight RESULTS: Observing others making good progress was associated with participants holding stronger intentions to lose weight themselves (B = 0.04, p = .012), positive goal-related affect (B = 0.27, p = .017), and feeling that they were also making progress themselves (B = 0.22, p < .001). However, observing others making good progress was also associated with losing a smaller amount of weight over the following week (B = .13, p = .005). Mediation analyses showed a significant indirect effect of observing others making good progress, via feelings about their own progress, on changes in weight, B = .02, 95% CI [.00, .04].

CONCLUSIONS

People who view others making progress tend to be less successful at losing weight themselves over the following week. The findings suggest that this is, in part, explained by the person feeling as if they have made progress themselves; thereby providing the first demonstration of vicarious goal satiation in a field context. Statement of contribution What is already known on this subject? Many people strive toward health goals (e.g., try to lose weight) with other people. However, research into vicarious goal satiation (VGS) suggests that seeing someone else achieve their goal may lead people to believe that they have made progress themselves and undermine goal pursuit. What does this study add? A longitudinal test of VGS in a field context, namely weight loss groups. Observing other people do well was motivating for the observer. They also believed that they had made progress themselves and were less successful at losing weight.

Public acceptability of nudging and taxing to reduce consumption of alcohol, tobacco, and food: A population-based survey experiment

There is growing evidence for the effectiveness of choice architecture or 'nudge' interventions to change a range of behaviours including the consumption of alcohol, tobacco and food. Public acceptability is key to implementing these and other interventions. However, few studies have assessed public acceptability of these interventions, including the extent to which acceptability varies with the type of intervention, the target behaviour and with evidence of intervention effectiveness. These were assessed in an online study using a between-participants full factorial design with three factors: Policy (availability vs size vs labelling vs tax) x Behaviour (alcohol consumption vs tobacco use vs high-calorie snack food consumption) x Evidence communication (no message vs assertion of policy effectiveness vs assertion and quantification of policy effectiveness [e.g., a 10% change in behaviour]). Participants (N = 7058) were randomly allocated to one of the 36 groups. The primary outcome was acceptability of the policy. Acceptability differed across policy, behaviour and evidence communication (all ps < .001). Labelling was the most acceptable policy (supported by 78%) and Availability the least (47%). Tobacco use was the most acceptable behaviour to be targeted by policies (73%) compared with policies targeting Alcohol (55%) and Food (54%). Relative to the control group (60%), asserting evidence of effectiveness increased acceptability (63%); adding a quantification to this assertion did not significantly increase this further (65%). Public acceptability for nudges and taxes to improve population health varies with the behaviour targeted and the type of intervention but is generally favourable. Communicating that these policies are effective can increase support by a small but significant amount, suggesting that highlighting effectiveness could contribute to mobilising public demand for policies. While uncertainty remains about the strength of public support needed, this may help overcome political inertia and enable action on behaviours that damage population and planetary health.

Computed tomography confirmation of component rotation in nanosensor-balanced total knee arthroplasty

Balanced gaps and proper rotation are felt to be essential for optimum range of motion, stability, and patellar tracking in total knee arthroplasty. The purpose of this study is to assess, using computed tomography, the rotation of femoral and tibial components in fresh-frozen human cadaver knees that have been balanced using nanosensor trials while also observing how this rotation affects measured compartment loads and requirement for ligament balancing adjustment. We found that minor degrees of rotational malalignment of the femur and tibia were common using standard instrumentation and measured resection technique. Quantitative balance and rotational congruence are aided by nanosensor guidance, and femoral malrotation of up to 8° does not appear to affect compartment loads significantly as long as rotational congruity is present.

Multiplexed calcium imaging of single-synapse activity and astroglial responses in the intact brain

All-optical registration of neuronal and astrocytic activities within the intact mammalian brain has improved significantly with recent advances in optical sensors and biophotonics. However, relating single-synapse release events and local astroglial responses to sensory stimuli in an intact animal has not hitherto been feasible. Here, we present a multiplexed multiphoton excitation imaging approach for assessing the relationship between presynaptic Ca2+ entry at thalamocortical axonal boutons and perisynaptic astrocytic Ca2+ elevations, induced by whisker stimulation in the barrel cortex of C57BL/6 mice. We find that, unexpectedly, Ca2+ elevations in the perisynaptic astrocytic regions consistently precede local presynaptic Ca2+ signals during spontaneous brain activity associated with anaesthesia. The methods described here can be adapted to a variety of optical sensors and are compatible with experimental designs that might necessitate repeated sampling of single synapses over a longitudinal behavioural paradigm.

Disentangling astroglial physiology with a realistic cell model in silico

Electrically non-excitable astroglia take up neurotransmitters, buffer extracellular K+ and generate Ca2+ signals that release molecular regulators of neural circuitry. The underlying machinery remains enigmatic, mainly because the sponge-like astrocyte morphology has been difficult to access experimentally or explore theoretically. Here, we systematically incorporate multi-scale, tri-dimensional astroglial architecture into a realistic multi-compartmental cell model, which we constrain by empirical tests and integrate into the NEURON computational biophysical environment. This approach is implemented as a flexible astrocyte-model builder ASTRO. As a proof-of-concept, we explore an in silico astrocyte to evaluate basic cell physiology features inaccessible experimentally. Our simulations suggest that currents generated by glutamate transporters or K+ channels have negligible distant effects on membrane voltage and that individual astrocytes can successfully handle extracellular K+ hotspots. We show how intracellular Ca2+ buffers affect Ca2+ waves and why the classical Ca2+ sparks-and-puffs mechanism is theoretically compatible with common readouts of astroglial Ca2+ imaging.

Proteomic Analysis After Status Epilepticus Identifies UCHL1 as Protective Against Hippocampal Injury

Brief, non-harmful seizures (preconditioning) can temporarily protect the brain against prolonged, otherwise injurious seizures. Following focal-onset status epilepticus (SE) in preconditioned (tolerance) and sham-preconditioned (injury) mice, we screened for protein changes using a proteomic approach and identified several putative candidates of epileptic tolerance. Among SE-induced changes to both proteomic screens, proteins clustered in key regulatory pathways, including protein trafficking and cytoskeletal regulation. Downregulation of one such protein, ubiquitin carboxyl-terminal hydrolase isozyme L1 (UCHL1), was unique to injury and not evident in tolerance. UCHL1 inhibition decreased hippocampal ubiquitin, disrupted UPS function, interfered with seizure termination and exacerbated seizure-induced cell death. Though UCHL1 transcription was maintained after SE, we observed downregulation of the pro-translational antisense Uchl1 (AsUchl1) and confirmed that both AsUchl1 and rapamycin can increase UCHL1 expression in vivo. These data indicate that the post-transcriptional loss of UCHL1 following SE is deleterious to neuronal survival and may contribute to hyperexcitability, and are suggestive of a novel modality of rapamycin therapy.

Monitoring single-synapse glutamate release and presynaptic calcium concentration in organised brain tissue

Brain function relies in large part on Ca²⁺-dependent release of the excitatory neurotransmitter glutamate from neuronal axons. Establishing the causal relationship between presynaptic Ca²⁺ dynamics and probabilistic glutamate release is therefore a fundamental quest across neurosciences. Its progress, however, has hitherto depended primarily on the exploration of either cultured nerve cells or giant central synapses accessible to direct experimental probing in situ. Here we show that combining patch-clamp with time-resolved imaging of Ca²⁺ -sensitive fluorescence lifetime of Oregon Green BAPTA-1 (Tornado-FLIM) enables readout of single spike-evoked presynaptic Ca²⁺ concentration dynamics, with nanomolar sensitivity, in individual neuronal axons in acute brain slices. In parallel, intensity Tornado imaging of a locally expressed extracellular optical glutamate sensor iGluSnFr provides direct monitoring of single-quantum, single-synapse glutamate releases in situ. These two methods pave the way for simultaneous registration of presynaptic Ca²⁺ dynamics and transmitter release in an intact brain at the level of individual synapses.

Astrocytes mediate neurovascular signaling to capillary pericytes but not to arterioles

Active neurons increase their energy supply by dilating nearby arterioles and capillaries. This neurovascular coupling underlies BOLD functional imaging signals, but its mechanism is controversial. Canonically, neurons release glutamate to activate metabotropic glutamate receptors (mGluR5) on astrocytes, evoking Ca²⁺ release from internal stores, activating phospholipase A₂ and generating vasodilatory arachidonic acid derivatives. However, adult astrocytes lack mGluR5, and knock-out of the IP₃ receptors that release Ca²⁺ from stores does not affect neurovascular coupling. We now show that buffering astrocyte Ca²⁺ inhibits neuronally-evoked capillary dilation, that astrocyte [Ca²⁺]_i is raised not by release from stores but by entry through ATP-gated channels, and that Ca²⁺ generates arachidonic acid via phospholipase D2 and diacylglycerol kinase rather than phospholipase A₂. In contrast, dilation of arterioles depends on NMDA receptor activation and Ca²⁺-dependent NO generation by interneurons. These results reveal that different signalling cascades regulate cerebral blood flow at the capillary and arteriole levels.

Validation of a portable pneumatic captive bolt device as a one-step method of euthanasia for use in depopulation of feedlot cattle

OBJECTIVE

To validate the effectiveness of a penetrating captive bolt device with a built-in low-pressure air channel pithing mechanism (PCBD) as a 1-step method for euthanasia of cattle.

DESIGN

Clinical trial.

ANIMALS

66 feedlot steers and heifers (weight, 227 to 500 kg [500 to 1,100 lb]) that were not expected to survive or finish the feeding period with their cohorts.

PROCEDURES

Cattle were transported to a university facility and euthanized with the PCBD. For each calf, clinical variables were monitored and recorded immediately before and for at least 10 minutes after application of the PCBD. Following euthanasia, the head of each calf was removed and trauma to the brain and skull was assessed and scored.

RESULTS

Death was successfully achieved with the PCBD without application of an ancillary technique in all 66 cattle; however, 4 (6%) cattle required a second or third shot from the PCBD because of technical errors in its placement. All shots from the PCBD that entered the cranial vault successfully rendered cattle unconscious without a return to sensibility.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that the PCBD was an effective 1-step method of euthanasia for use in mass depopulation of feedlot cattle.

Time-Resolved Imaging Reveals Heterogeneous Landscapes of Nanomolar Ca(2+) in Neurons and Astroglia

Maintaining low intracellular calcium is essential to the functioning of brain cells, yet the phenomenology and mechanisms involved remain an enigma. We have advanced a two-photon excitation time-resolved imaging technique, which exploits high sensitivity of the OGB-1 fluorescence lifetime to nanomolar Ca²⁺ concentration ([Ca²⁺]) and enables a high data acquisition rate in situ. The [Ca²⁺] readout is not affected by dye concentration, light scattering, photobleaching, micro-viscosity, temperature, or the main known concomitants of cellular activity. In quiescent tissue, standard whole-cell configuration has little effect on resting [Ca²⁺] inside neuronal dendrites or inside astroglia dye-filled via gap junctions. Mapping basal [Ca²⁺] in neurons and astrocytes with submicron resolution unveils heterogeneous concentration landscapes that depend on age and preceding activity. The rich information content represented by such landscapes in acute slices and in vivo promises to unveil the hitherto unexplored, potentially fundamental aspects of brain cell physiology.

Video Abstract

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OGB-1 lifetime readout is specific to low [Ca²⁺] and enables 100 Hz acquisition rate

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Neurons and astrocytes maintain uneven landscapes of resting [Ca²⁺]

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Resting [Ca²⁺] patterns in neurons and astroglia are age and activity dependent

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Astroglia in situ split into two sub-groups with respect to their resting [Ca²⁺]

Comparison of short-term effects of midazolam and lorazepam in the intra-amygdala kainic acid model of status epilepticus in mice

Benzodiazepines remain as the first-line treatment for status epilepticus (SE), but debate continues as to the choice and delivery route of pharmacotherapy. Lorazepam is currently the preferred anticonvulsant for clinical use, but midazolam has become a popular alternative, particularly as it can be given by nonintravenous routes. Anticonvulsants are also commonly used to terminate SE in animal models. Here, we aimed to compare the efficacy of midazolam with that of lorazepam in an experimental model of focal-onset SE. Status epilepticus was induced by intra-amygdala microinjection of kainic acid in 8week old C57Bl/6 mice. Forty minutes later, mice were treated with an intraperitoneal injection of either lorazepam or midazolam (8mg/kg). Electroencephalogram (EEG) activity, histology, and behavioral tests assessing recovery of function were evaluated and compared between groups. Intraperitoneal injection of either lorazepam or midazolam resulted in similar patterns of reduced EEG epileptiform activity during 1-hour recordings. Damage to the hippocampus and presentation of postinsult anxiety-related behavior did not significantly differ between treatment groups at 72h. However, return of normal behaviors such as grooming, levels of activity, and the evaluation of overall recovery of SE mice were all superior at 24h in animals given midazolam compared with lorazepam. Our results indicate that midazolam is as effective as lorazepam as an anticonvulsant in this model while also providing improved animal recovery after SE. These data suggest that midazolam might be considered by researchers as an anticonvulsant in animal models of SE, particularly as it appears to satisfy the requirements of refining procedures involving experimental animals at early time-points after SE.

Transcriptional Response of Polycomb Group Genes to Status Epilepticus in Mice is Modified by Prior Exposure to Epileptic Preconditioning

Exposure of the brain to brief, non-harmful seizures can activate protective mechanisms that temporarily generate a damage-refractory state. This process, termed epileptic tolerance, is associated with large-scale down-regulation of gene expression. Polycomb group (PcG) proteins are master controllers of gene silencing during development that are re-activated by injury to the brain. Here, we explored the transcriptional response of genes associated with polycomb repressive complex (PRC) 1 (Ring1A, Ring1B, and Bmi1) and PRC2 (Ezh1, Ezh2, and Suz12), as well as additional transcriptional regulators Sirt1, Yy1, and Yy2, in a mouse model of status epilepticus (SE). Findings were contrasted to changes after SE in mice previously given brief seizures to evoke tolerance. Real-time quantitative PCR showed SE prompted an early (1 h) increase in expression of several genes in PRC1 and PRC2 in the hippocampus, followed by down-regulation of many of the same genes at later times points (4, 8, and 24 h). Spatio-temporal differences were found among PRC2 genes in epileptic tolerance, including increased expression of Ezh2, Suz12, and Yy2 relative to the normal injury response to SE. In contrast, PRC1 complex genes including Ring 1B and Bmi1 displayed differential down-regulation in epileptic tolerance. The present study characterizes PcG gene expression following SE and shows prior seizure exposure produces select changes to PRC1 and PRC2 composition that may influence differential gene expression in epileptic tolerance.

Differential DNA methylation profiles of coding and non-coding genes define hippocampal sclerosis in human temporal lobe epilepsy

Temporal lobe epilepsy is associated with large-scale, wide-ranging changes in gene expression in the hippocampus. Epigenetic changes to DNA are attractive mechanisms to explain the sustained hyperexcitability of chronic epilepsy. Here, through methylation analysis of all annotated C-phosphate-G islands and promoter regions in the human genome, we report a pilot study of the methylation profiles of temporal lobe epilepsy with or without hippocampal sclerosis. Furthermore, by comparative analysis of expression and promoter methylation, we identify methylation sensitive non-coding RNA in human temporal lobe epilepsy. A total of 146 protein-coding genes exhibited altered DNA methylation in temporal lobe epilepsy hippocampus (n = 9) when compared to control (n = 5), with 81.5% of the promoters of these genes displaying hypermethylation. Unique methylation profiles were evident in temporal lobe epilepsy with or without hippocampal sclerosis, in addition to a common methylation profile regardless of pathology grade. Gene ontology terms associated with development, neuron remodelling and neuron maturation were over-represented in the methylation profile of Watson Grade 1 samples (mild hippocampal sclerosis). In addition to genes associated with neuronal, neurotransmitter/synaptic transmission and cell death functions, differential hypermethylation of genes associated with transcriptional regulation was evident in temporal lobe epilepsy, but overall few genes previously associated with epilepsy were among the differentially methylated. Finally, a panel of 13, methylation-sensitive microRNA were identified in temporal lobe epilepsy including MIR27A, miR-193a-5p (MIR193A) and miR-876-3p (MIR876), and the differential methylation of long non-coding RNA documented for the first time. The present study therefore reports select, genome-wide DNA methylation changes in human temporal lobe epilepsy that may contribute to the molecular architecture of the epileptic brain.

MicroRNA-34a upregulation during seizure-induced neuronal death

MicroRNAs (miRNAs) are short, noncoding RNAs that function as posttranscriptional regulators of gene expression by controlling translation of mRNAs. A subset of miRNAs may be critical for the control of cell death, including the p53-regulated miRNA, miR-34a. Because seizures activate p53, and p53-deficient mice are reportedly resistant to damage caused by prolonged seizures, we investigated the role of miR-34a in seizure-induced neuronal death in vivo. Status epilepticus was induced by intra-amygdala microinjection of kainic acid in mice. This led to an early (2 h) multifold upregulation of miR-34a in the CA3 and CA1 hippocampal subfields and lower protein levels of mitogen-activated kinase kinase kinase 9, a validated miR-34a target. Immunoprecipitation of the RNA-induced silencing complex component, Argonaute-2, eluted significantly higher levels of miR-34a after seizures. Injection of mice with pifithrin-α, a putative p53 inhibitor, prevented miR-34a upregulation after seizures. Intracerebroventricular injection of antagomirs targeting miR-34a reduced hippocampal miR-34a levels and had a small modulatory effect on apoptosis-associated signaling, but did not prevent hippocampal neuronal death in models of either severe or moderate severity status epilepticus. Thus, prolonged seizures cause subfield-specific, temporally restricted upregulation of miR-34a, which may be p53 dependent, but miR-34a is probably not important for seizure-induced neuronal death in this model.

Immune responses during pregnancy in heifers naturally infected with Neospora caninum with and without immunization

This study was designed to identify changes in parasite-specific immune responses that occur during vertical transmission of Neospora caninum and can be used as indicators of parasite reactivation in naturally infected heifers. Ten heifers were unimmunized and 11 immunized with killed tachyzoites. One unimmunized heifer, which aborted at week 19 of gestation, had an increase in parasite-specific antibodies, mainly IgG(2), from week 15 to week 19 and a concomitant decline in parasite-specific cell-mediated immune (CMI) responses. Eight unimmunized heifers, which had live full-term congenitally infected calves, had an increase in antibodies, mainly IgG(2), from week 21 onwards. All immunized heifers delivered live full-term congenitally infected calves, and had a bimodal increase in antibodies; primarily IgG(1) following immunization and predominantly IgG(2) from week 17 onwards. Immunized heifers had significantly greater overall mean humoral and CMI responses than unimmunized heifers. Nine uninfected control heifers and their calves were seronegative. These results indicate that reactivation of a latent infection occurred in the naturally infected heifers, regardless of their immunization status, and was associated with increased parasite-specific antibodies, mainly IgG(2).

Factors affecting conception rate after artificial insemination and pregnancy loss in lactating dairy cows

Objectives were to determine factors associated with conception rate (CR) and pregnancy loss (PL) in high producing lactating Holstein cows. In Study 1, CR was evaluated in 7633 artificial inseminations (AI) of 3161 dairy cows in two dairy farms. Pregnancy diagnosis was performed by palpation per rectum 39+/-3 days after AI. Environmental temperature was recorded at different intervals prior to and after AI. In Study 2, 1465 pregnancies from 1393 cows diagnosed at 31+/-3 days after AI by ultrasonography on three dairy farms were re-examined 14 days later to determine PL. Temperature > or =29 degrees C was considered to be heat stress (HS). Exposure to HS was defined as following: NH, no heat stress; HS1, exposure to at least 1 day of maximum temperature > or =29 degrees C and average daily maximum temperature (ADMT) <29 degrees C; and HS2, exposure to ADMT > or =29 degrees C. In Study 1, exposure of cows to HS1 and HS2 from 50 to 20 prior to AI was associated with reduced CR compared to cows not exposed to HS (28.8, 23.0, and 31.3%, respectively). Post-AI HS was not associated with CR. Cows inseminated following estrus detection or timed AI had similar CR. As the number of AI increased, CR decreased. Multiparous cows had lower CR than primiparous cows, and occurrence of milk fever and retained placenta was associated with decreased CR. In Study 2, PL was not associated with exposure to HS either prior to or after AI. Cows diagnosed with clinical mastitis experienced increased PL, but parity, number of AI, AI protocol, milk production, and days postpartum at AI were not associated with PL. In conclusion, CR was affected by HS prior to AI, parity, number of AI, and postparturient diseases, whereas PL was affected by clinical mastitis.

Evaluation of flunixin meglumine as an adjunct treatment for diarrhea in dairy calves

OBJECTIVE

To assess the use of flunixin meglumine as an adjunct treatment for diarrhea in calves.

DESIGN

Clinical trial.

ANIMALS

115 calves with diarrhea that were 1 to 21 days old at enrollment.

PROCEDURE

Calves that developed diarrhea were randomly assigned to receive no flunixin meglumine (controls), a single dose of flunixin meglumine (2.2 mg/kg [1.0 mg/lb]), or 2 doses of flunixin meglumine administered 24 hours apart. Serum IgG concentration and PCV were measured prior to enrollment in the trial. Calves were evaluated daily to determine rectal temperature, fecal consistency, demeanor, and skin elasticity score. The primary analytic outcome was days of sickness (morbid-days).

RESULTS

Calves with fecal blood and treated with a single dose of flunixin meglumine had fewer morbid-days and antimicrobial treatments, compared with controls. Although not significant, calves given 2 doses of flunixin meglumine in 24 hours had fewer morbid-days than untreated control calves. Regardless of severity of diarrhea, calves without fecal blood did not benefit from the use of flunixin. For calves with fecal blood, failure of passive transfer (low serum IgG concentration) was an independent risk factor for increased morbid-days.

CONCLUSIONS AND CLINICAL RELEVANCE

Treatment with a single dose of flunixin meglumine resulted in fewer antimicrobial treatments and morbid-days in calves with fecal blood. As observed in other studies, calves with failure of passive transfer were at high risk for poor outcomes. This emphasizes the importance of developing and implementing effective colostrum delivery programs on dairy farms.

Evaluation of effect of estradiol cypionate administered prophylactically to postparturient dairy cows at high risk for metritis

OBJECTIVE

To determine whether 4 mg of estradiol cypionate (ECP) administered prophylactically to high-risk postparturient dairy cows decreases incidence of postpartum metritis.

DESIGN

Randomized, placebo-controlled, triple-masked clinical trial.

ANIMALS

250 postparturient dairy cows in a herd with postparturient hypocalcemia, retained fetal membranes, dystocia, stillbirth, or twins.

PROCEDURE

Cows were given 4 mg of ECP (treatment) or 2 mL of vegetable oil (control) by i.m. injection within 24 to 36 hours of calving. Monitoring rectal temperatures and evaluation for metritis was performed once daily for 10 days. Cows with fever > or = 39.7 degrees C (103.5 degrees F) were treated with 1.5 g of ceftiofur hydrochloride.

RESULTS

When assessed by ordinal logistic regression, there were no differences between groups in incidence of mild or severe metritis. Cows that calved during the second or third quarter of the year were at increased risk of metritis, compared with those that calved during the fourth quarter. Following stratification by lactation (first and > or = 2), it was observed that multiparous cows that did not receive antimicrobials during the first 3 days of the postparturient period were 5 times as likely to have metritis, compared with cows treated with antimicrobials on the basis of fever or other concurrent disease.

CONCLUSIONS AND CLINICAL RELEVANCE

Prophylactic administration of ECP to dairy cows at high risk for metritis did not reduce risk for metritis. Treating multiparous cows with antimicrobials on the basis of fever during the early postpartum period was associated with decreased incidence of metritis.

Influence of arrival weight, season and calf supplier on survival in Holstein beef calves on a calf ranch in California, USA

On a yearly basis, large calf ranches rear thousands of neonatal cattle for replacement heifers, veal or dairy beef. Dairy beef ranches obtain bull-calves from multiple sources and with questionable colostrum intake histories. Such ranches accumulate large amounts of data that could be used to help them with calf purchasing and on-farm management practices to avoid losses. Our purpose was to describe some calf purchase factors associated with mortality in neonatal calves raised on a single large calf ranch. Computerized records describing 120,197 bull-calves purchased between January 1997 and November 1998 were used in a survival analysis. Risk factors for mortality within the first 4 weeks after arrival on the ranch included body weight on arrival, month of arrival, and the calf supplier. The strength of the effects was conditional on the week after arrival to the ranch.

Adherens junctions and beta-catenin-mediated cell signalling in a non-metazoan organism

Mechanical forces between cells have a principal role in the organization of animal tissues. Adherens junctions are an important component of these tissues, connecting cells through their actin cytoskeleton and allowing the assembly of tensile structures. At least one adherens junction protein, beta-catenin, also acts as a signalling molecule, directly regulating gene expression. To date, adherens junctions have only been detected in metazoa, and therefore we looked for them outside the animal kingdom to examine their evolutionary origins. The non-metazoan Dictyostelium discoideum forms a multicellular, differentiated structure. Here we describe the discovery of actin-associated intercellular junctions in Dictyostelium. We have isolated a gene encoding a beta-catenin homologue, aardvark, which is a component of the junctional complex, and, independently, is required for cell signalling. Our discovery of adherens junctions outside the animal kingdom shows that the dual role of beta-catenin in cell-cell adhesion and cell signalling evolved before the origins of metazoa.

Use of chlorhexidine-releasing nylon fibres to reduce device-related uterine infections

Implantation of intrauterine devices (IUDs) is associated with an increased incidence of uterine infection, probably as a result of vaginal bacteria entering the uterus at the time of insertion. To reduce the incidence of IUD-related infections, the incorporation of antimicrobial agents into the tail of the device was studied. Chlorhexidine was shown to be released from within nylon hollow fibres at a rate of approximately 114 microg x day(-1) for 10 days. This rate of release was sufficient to exhibit a biocidal effect on bacteria embedded within a mucus gel in vitro. When these devices were implanted transcervically into the guinea-pig uterus they significantly reduced the extent of uterine bacterial contamination within 24 h. These findings indicate that chlorhexidine-releasing devices are potentially useful in the reduction of device-related infections.

Effects of antimicrobial treatment at the end of lactation on milk yield, somatic cell count, and incidence of clinical mastitis during the subsequent lactation in a dairy herd with a low prevalence of contagious mastitis

OBJECTIVE

To determine whether treating cows with antimicrobials at the end of lactation would lower the incidence of clinical mastitis, improve milk production, and decrease somatic cell count (SCC) in the subsequent lactation.

DESIGN

Randomized blind field trial.

ANIMALS

233 Holstein cows from a single herd. All cows were in lactation 2 or greater.

PROCEDURE

Cows were randomly assigned to treatment groups. Treated cows were given procaine penicillin G and novobiocin by intramammary infusion. Control cows were not treated. Farm personnel recorded cases of clinical mastitis. Milk yield and SCC were recorded during the subsequent lactation.

RESULTS

Treatment did not significantly reduce the incidence of clinical mastitis when data for all cows were grouped or when data were stratified by lactation groups (lactation 2 vs lactation > or = 3) or by last SCC (< or = 500,000 cells/ml vs > 500,000 cells/ml). Somatic cell counts (first, mean of first 5, maximum of first 5) for treated and control cows were similar, and proportions of treated and control cows with SCC > 500,000 cells/ml at least once were not significantly different. Treated cows produced 179 kg (394 lb) more milk during the first 17 weeks of lactation than did control cows.

CLINICAL IMPLICATIONS

Treating cows with antimicrobials at the end of lactation increased 17-week milk production during the subsequent lactation and, at current milk prices, was financially preferable to not treating them.

Evidence of vertical transmission of Neospora sp infection in dairy cattle

OBJECTIVE

To determine whether heifers with naturally acquired congenital exposure to Neospora sp would transmit the infection to their offspring during gestation.

DESIGN

Prospective cohort study.

ANIMALS

Neonatal heifers on a dairy with a history of Neospora sp infections were selected for the study on the basis of their serum titers to Neospora sp, as determined by the use of indirect fluorescent antibody testing. Seropositive heifers (n = 25) had titers > or = 1:5,120 and seronegative heifers (25) had titers < or = 1:80. All heifers were raised and bred on the dairy, and samples were obtained from heifers and their calves at the time of calving.

PROCEDURE

Blood samples were tested for Neospora sp antibodies. Histologic evaluations, Neospora sp immunohistochemical examinations, and protozoal culturing were performed on samples obtained from selected offspring (second-generation calves).

RESULTS

Seropositive heifers gave birth to calves with titers > or = 1:1,280 to Neospora sp. All offspring from seropositive heifers that were necropsied had evidence of Neospora sp infection. All seronegative heifers and their offspring had titers < 1:80 to Neospora sp.

CLINICAL IMPLICATIONS

Congenitally acquired Neospora sp infection can persist in clinically normal heifers and be transmitted transplacentally to their offspring. Vertical transmission can be a way by which neosporosis is maintained in herds.

Preservative efficacy tests in formulated nasal products: reproducibility and factors affecting preservative activity

Preservative efficacy tests were performed in triplicate on each of three batches of three formulated nasal spray preparations to assess the inter- and intra-batch variation in preservative performance which typically results from these procedures, and to assess the relative importance of factors influencing preservative performance in nasal products. Tests were conducted using procedures conforming, as far as possible, to both the European and the US pharmacopoeias and the results interpreted using the performance criteria of both. Despite the adoption of practices designed to maximize reproducibility, a marked variation in the degree of microbial inactivation was observed, both within and between batches of product. A preservative system comprising benzalkonium chloride and phenylethyl alcohol was found to be far superior to combinations of either benzalkonium chloride plus disodium edetate or potassium sorbate plus disodium edetate, both of which failed to satisfy the EP performance criteria on a number of occasions. Proposals are made for the adoption of inactivation criteria which incorporate realistic error limits reflecting the inherent problems of reproducibility of the viable counting procedures involved.

Sensitivity and specificity analysis for somatic cell count (SCC) used to predict bacteriologically positive subclinical mastitis at calving in a dairy herd with low SCC

OBJECTIVE

Validate, by sensitivity and specificity analyses, use of somatic cell count (SCC) to predict bacteriologically positive subclinical mastitis in a California dairy herd with low SCC.

DESIGN

Study of monthly dairy herd improvement SCC obtained from the immediate preceding lactation and individual cow composite milk sample microbiologic isolates collected at calving.

ANIMALS

515 California dairy cows with SCC and culture data.

PROCEDURE

Somatic cell count sensitivity and specificity analyses with combinations of SCC parameter and at various thresholds were done, using the bacterial isolates as the standard.

RESULTS

Combination of SCC threshold and SCC parameters could not be developed that had sufficient sensitivity and specificity to be a useful predictor of cows that would calve with subclinical mastitis.

CLINICAL IMPLICATIONS

Under the conditions at this particular dairy, SCC could not be used as a basis of prediction of cows that would calve with bacteriologically positive subclinical mastitis or require selective nonlactating-cow antibiotic treatment.

Patterns of uterine prolapse in dairy cows and prognosis after treatment

A 12-month study was undertaken in a 9-veterinarian dairy practice to determine patterns of uterine prolapse and factors associated with posttreatment survival. Of 220,000 cows in herds visited by veterinarians from the practice, 200 (0.09%) developed prolapses mostly (155/169 with data) in the first 24 hours after calving. Most cows (130/200) had prolapses during fall and winter months, and assistance was required in 47 of 200 calvings that resulted in prolapses. Treatment of affected cows (n = 196) consisted of cleansing and replacement of the uterus, insertion of perivulvar retention sutures, local and systemic administration of antibiotics, and parenteral administration of dexamethasone and oxytocin. Calcium was administered to cows with milk fever (n = 117) and to multiparous cows without milk fever attended by veterinarian 9 (n = 8). Crude recovery rate after 2 weeks was 72.4%, but recovery was significantly better if the calf was born alive (P = 0.001), the cow was primiparous (P = 0.03), the cow did not have stage-3 milk fever (P = 0.003), or if the cow was attended by veterinarian 9 (P = 0.01). Time to treatment was not significantly associated with recovery, but affected cows were treated mostly (127/156) within 2 hours of occurrence of the prolapse. By multivariable analysis, presence of a liveborn calf, parity, and lack of stage-3 milk fever, but not attending veterinarian, were significant (P less than 0.05) prognostic indicators of 2-week survival.

Uterine prolapse and hypocalcemia in dairy cows

Blood samples were collected from 53 dairy cows with uterine prolapse and from 53 cows with normal parturition (no uterine prolapse) matched by dairy as controls for various management programs among dairies. Cows with uterine prolapse had significantly lower total serum calcium content than did controls (P less than 0.01). Mean (+/- SEM) serum calcium content (mg/dl) for affected cows and controls were 6.08 (+/- 0.25) and 6.96 (+/- 0.20), respectively. Severe hypocalcemia (less than 4 mg/dl) was found in 10 (19%) of the affected cows, compared with 1 (1.8%) of the controls. Fifteen (28%) of the affected cows had moderate hypocalcemia (4.1 to 6.0 mg/dl), compared with 14 (26%) of the controls; 19 (36%) of the affected cows were mildly hypocalcemic (6.1 to 7.9 mg/dl), compared with 25 (47%) of the controls. Nine (17%) of the affected cows and 13 (25%) of the controls were within the normal range of calcium content (greater than 8 mg/dl). Nine of the affected cows were first-calf cows. The serum of these animals did not have significantly lower calcium concentrations, compared with controls matched by parity. Serum calcium values (mg/dl) for 9 first-calf cows and the 9 matched controls were 7.24 (+/- 0.42) and 7.00 (+/- 0.39), respectively. It was concluded that hypocalcemia was associated with uterine prolapse in multiparous dairy cows and, along with other factors, is involved as an etiologic factor for this puerperal condition.

Clot retraction: evaluation in dilute suspensions of platelet-rich plasma and gel-separated platelets

Suspensions of platelet-rich plasma (PRP) or gel-separated platelets (GSP) can be used to evaluate clot retraction subsequent to platelet aggregation and fibrin formation. PRP (200,000 per cubic millimeter) or GSP (200,000 or 100,000 per cubic millimeter) are diluted 1:10 (PRP) or 1:8 (GSP) in phosphate buffer, pH 7.4, and clotted with a high concentration (2.5 U. per milliliter) of thrombin. Human fibrinogen (25 mg. per cent) is added to GSP prior to dilution. Clot retraction is 91 to 100 per cent completed in 1 hour and is quantified by measurement of residual fluid volume. Test conditions are unfavorable for fibrinolysis. Very low concentrations of fibrin/fibrinogen degradation products D and E are detected in residual fluid, and no erythrocyte fall-out occurs. Furthermore, the extent of retraction in the dilute systems is related only to platelet numbers and platelet function. The dilute PRP and GSP methods allow evaluation of clot retraction in the presence of PGE1, the most potent inhibitor of platelet aggregation induced by conventional concentrations of collagen, ADP, epinephrine, and thrombin (0.1 to 0.5 U. per milliliter). High concentrations of PGE1 (to 6 x 10(-6) M) do not inhibit aggregation of GSP, fibrin formation, or platelet-fibrin interaction induced by 2.5 U. per milliliter of thrombin. In contrast, PGE1 concentrations as low as 1.5 to 3.0 x 10(-8) M inhibit clot retraction in both the dilute PRP and GSP systems. Thus, using dilute PRP or GSP the effects of platelet aggregation inhibitors on clot retraction can be determined independently of effects on platelet aggregation.