From task structures to world models: what do LLMs know?

In what sense does a large language model (LLM) have knowledge? We answer by granting LLMs 'instrumental knowledge': knowledge gained by using next-word generation as an instrument. We then ask how instrumental knowledge is related to the ordinary, 'worldly knowledge' exhibited by humans, and explore this question in terms of the degree to which instrumental knowledge can be said to incorporate the structured world models of cognitive science. We discuss ways LLMs could recover degrees of worldly knowledge and suggest that such recovery will be governed by an implicit, resource-rational tradeoff between world models and tasks. Our answer to this question extends beyond the capabilities of a particular AI system and challenges assumptions about the nature of knowledge and intelligence.

Self-orienting in human and machine learning

A current proposal for a computational notion of self is a representation of one's body in a specific time and place, which includes the recognition of that representation as the agent. This turns self-representation into a process of self-orientation, a challenging computational problem for any human-like agent. Here, to examine this process, we created several 'self-finding' tasks based on simple video games, in which players (N = 124) had to identify themselves out of a set of candidates in order to play effectively. Quantitative and qualitative testing showed that human players are nearly optimal at self-orienting. In contrast, well-known deep reinforcement learning algorithms, which excel at learning much more complex video games, are far from optimal. We suggest that self-orienting allows humans to flexibly navigate new settings.

Methodological changes implemented over time to support accurate and timely COVID-19 vaccine coverage estimates: Ontario, Canada

The COVID-19 vaccination program implementation in Ontario, Canada has spanned multiple years and is ongoing. To meet the challenges of the program, Ontario developed and implemented a new electronic COVID-19 immunization registry, COVaxON, which captures individual-level data on all doses administered in the province enabling comprehensive coverage assessment. However, the need for ongoing COVID-19 vaccine coverage assessments over a multi-year vaccination program posed challenges necessitating methodological changes. This paper describes Ontario's COVID-19 immunization registry, the methods implemented over time to allow for the ongoing assessment of vaccine coverage by age, and the impact of those methodological changes. Throughout the course of the vaccination program, four different methodological approaches were used to calculate age-specific coverage estimates using vaccination data (numerator) obtained from COVaxON. Age-specific numerators were initially calculated using age at time of first dose (method A), but were updated to the age at coverage assessment (method B). Database enhancements allowed for the exclusion of deceased individuals from the numerator (method C). Population data (denominator) was updated to 2022 projections from the 2021 national census following their availability (method D). The impact was most evident in older age groups where vaccine uptake was high. For example, coverage estimates for individuals aged 70-79 years of age for at least one dose decreased from 104.9 % (method B) to 95.0 % (method D). Thus, methodological changes improved estimates such that none exceeded 100 %. Ontario's COVID-19 immunization registry has been transformational for vaccine program surveillance. The implementation of a single registry for COVID-19 vaccines was essential for comprehensive near real-time coverage assessment, and enabled new uses of the data to support additional components of vaccine program surveillance. The province is well positioned to build on what has been achieved as a result of the COVID-19 pandemic and expand the registry to other routine vaccination programs.

Evaluation of the gap in delivery of opioid agonist therapy among individuals with opioid-related health problems: a population-based retrospective cohort study

AIMS

Although opioid-related harms have reached new heights across North America, the size of the gap in opioid agonist therapy (OAT) delivery for opioid-related health problems is unknown in most jurisdictions. This study sought to characterize the gap in OAT treatment using a cascade of care framework, and determine factors associated with engagement and retention in treatment.

DESIGN

A population-based retrospective cohort study.

SETTING

Ontario, Canada.

PARTICIPANTS

Individuals who sought medical care for opioid-related health problems or died from an opioid-related cause between 2005 and 2019.

MEASUREMENTS

Monthly treatment status for buprenorphine/naloxone or methadone OAT between 2013 and 2019 (i.e. 'off OAT', 'retained on OAT < 6 months', 'retained on OAT ≥ 6 months').

FINDINGS

Of 122 811 individuals in the cohort, 97 516 (79.4%) received OAT at least once during the study period. There was decreasing 6-month treatment retention over time. Model results indicated that males had higher odds of being on OAT each month [odds ratio (OR) = 1.26, 95% confidence interval (CI) = 1.23-1.28] but lower odds of OAT retention (OR = 0.90, 95% CI = 0.88-0.92), while the reverse was observed for older individuals (monthly: OR = 0.76 per 10-year increase, 95% CI = 0.76-0.77; retention: OR = 1.36 per 10-year increase, 95% CI = 1.34-1.38) and individuals with higher neighbourhood income (e.g. highest income quintile, monthly: OR = 0.79, 95% CI = 0.77-0.82; highest income quintile, retention: OR = 1.15, 95% CI = 1.11-1.20). Individuals residing in rural areas and with a history of mental health diagnoses had poorer outcomes overall, including lower odds of being on OAT each month (rural: OR = 0.75, 95% CI = 0.73-0.78; mental health: OR = 0.89, 95% CI = 0.87-0.92) and OAT retention (rural: OR = 0.79, 95% CI = 0.77-0.82; mental health: OR = 0.81, 95% CI = 0.78-0.83), as well as higher risk of starting/stopping OAT [rural, starting OAT: hazard ratio (HR) = 1.07, 95% CI = 1.05-1.10; mental health, starting OAT: HR = 1.20, 95% CI: 1.18-1.23; rural, stopping OAT: HR = 1.24, 95% CI: = 1.22-1.26; mental health, stopping OAT: HR = 1.11, 95% CI = 1.09-1.13]. Individuals with a history of mental health diagnoses also had a higher risk of death, regardless of OAT status (off OAT death: HR = 1.49, 95% CI = 1.33-1.66; on OAT death: HR = 1.20, 95% CI = 1.09-1.31).

CONCLUSIONS

Factors influencing engagement and declining retention in treatment with opioid agonist therapy in Ontario's health system include age, sex and neighbourhood income, as well as mental health diagnoses or residing in rural regions.

Omadacycline for a Carbapenem-Resistant Enterobacter cloacae-Associated Wound Infection

Introduction: Carbapenem-resistant Enterobacteriaceae (CRE) are problematic pathogens because infections caused by these organisms are associated with significant morbidity and mortality. These organisms often harbor multiple resistance mechanisms, which makes it difficult to treat their associated infections. Treatment typically consists of intravenous antibiotics that are selected based on the specific susceptibility pattern for the pathogen. Data on the use of oral antibiotics for the treatment of infections caused by CRE are sparse. Case Presentation: In this case, a 62-year-old female presented with a chronic left leg wound infection. She previously underwent surgical debridement and skin grafting, which were unsuccessful. She was initially prescribed minocycline for the infection, but the wound got re-infected. At this time, the wound had significant surrounding erythema, drainage, and slough. A wound culture was obtained and demonstrated growth of carbapenem-resistant Enterobacter cloacae and methicillin-resistant Staphylococcus aureus. The patient was initiated on oral omadacycline, and she responded with resolution of the cellulitis and wound drainage. Conclusion: This case demonstrates that omadacycline may be beneficial as an oral medication for the treatment of complicated acute bacterial skin and skin structure infections caused by carbapenem-resistant Enterobacter cloacae.

Identifying the changing age distribution of opioid-related mortality with high-frequency data

Background

Opioid-related mortality continues to rise across North America, and mortality rates have been further exacerbated by the COVID-19 pandemic. This study sought to provide an updated picture of trends of opioid-related mortality for Ontario, Canada between January 2003 and December 2020, in relation to age and sex.

Methods

Using mortality data from the Office of the Chief Coroner for Ontario, we applied Bayesian Poisson regression to model age/sex mortality per 100,000 person-years, including random walks to flexibly capture age and time effects. Models were also used to explore how trends might continue into 2022, considering both pre- and post-COVID-19 courses.

Results

From 2003 to 2020, there were 11,633 opioid-related deaths in Ontario. A shift in the age distribution of mortality was observed, with the greatest mortality rates now among younger individuals. In 2003, mortality rates reached maximums at 5.5 deaths per 100,000 person-years (95% credible interval: 4.0–7.6) for males around age 44 and 2.2 deaths per 100,000 person-years (95% CI: 1.5–3.2) for females around age 51. As of 2020, rates have reached maximums at 67.2 deaths per 100,000 person-years (95% CI: 55.3–81.5) for males around age 35 and 16.8 deaths per 100,000 person-years (95% CI: 12.8–22.0) for females around age 37. Our models estimate that opioid-related mortality among the younger population will continue to grow, and that current conditions could lead to male mortality rates that are more than quadruple those of pre-pandemic estimations.

Conclusions

This analysis may inform a refocusing of public health strategy for reducing rising rates of opioid-related mortality, including effectively reaching both older and younger males, as well as young females, with health and social supports such as treatment and harm reduction measures.

Characteristics Associated With Household Transmission of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) in Ontario, Canada: A Cohort Study

BACKGROUND

Within-household transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has been identified as one of the main sources of spread of coronavirus disease 2019 (COVID-19) after lockdown restrictions and self-isolation guidelines are implemented. Secondary attack rates among household contacts are estimated to be 5-10 times higher than among non-household contacts, but it is unclear which individuals are more prone to transmit infection within their households.

METHODS

Using address matching, a cohort was assembled of all individuals with laboratory-confirmed COVID-19 residing in private households in Ontario, Canada. Descriptive analyses were performed to compare characteristics of cases in households that experienced secondary transmission versus those that did not. Logistic regression models were fit to determine index case characteristics and neighborhood characteristics associated with transmission.

RESULTS

Between January and July 2020, there were 26 714 individuals with COVID-19 residing in 21 226 households. Longer testing delays (≥5 vs 0 days; odds ratio [OR], 3.02; 95% confidence interval [CI], 2.53-3.60) and male gender (OR, 1.28; 95% CI, 1.18-1.38) were associated with greater odds of household secondary transmission, while being a healthcare worker (OR, .56; 95% CI, .50-.62) was associated with lower odds of transmission. Neighborhoods with larger average family size and a higher proportion of households with multiple persons per room were also associated with greater odds of transmission.

CONCLUSIONS

It is important for individuals to get tested for SARS-CoV-2 infection as soon as symptoms appear, and to isolate away from household contacts; this is particularly important in neighborhoods with large family sizes and/or crowded households.

Association of Age and Pediatric Household Transmission of SARS-CoV-2 Infection

Importance

As a result of low numbers of pediatric cases early in the COVID-19 pandemic, pediatric household transmission of SARS-CoV-2 remains an understudied topic.

Objective

To determine whether there are differences in the odds of household transmission by younger children compared with older children.

Design, Setting, and Participants

This population-based cohort study took place between June 1 and December 31, 2020, in Ontario, Canada. Private households in which the index case individual of laboratory-confirmed SARS-CoV-2 infection was younger than 18 years were included. Individuals were excluded if they resided in apartments missing suite information, in households with multiple index cases, or in households where the age of the index case individual was missing.

Exposures

Age group of pediatric index cases categorized as 0 to 3, 4 to 8, 9 to 13, and 14 to 17 years.

Main Outcomes and Measures

Household transmission, defined as households where at least 1 secondary case occurred 1 to 14 days after the pediatric index case.

Results

A total of 6280 households had pediatric index cases, and 1717 households (27.3%) experienced secondary transmission. The mean (SD) age of pediatric index case individuals was 10.7 (5.1) years and 2863 (45.6%) were female individuals. Children aged 0 to 3 years had the highest odds of transmitting SARS-CoV-2 to household contacts compared with children aged 14 to 17 years (odds ratio, 1.43; 95% CI, 1.17-1.75). This association was similarly observed in sensitivity analyses defining secondary cases as 2 to 14 days or 4 to 14 days after the index case and stratified analyses by presence of symptoms, association with a school/childcare outbreak, or school/childcare reopening. Children aged 4 to 8 years and 9 to 13 years also had increased odds of transmission (aged 4-8 years: odds ratio, 1.40; 95% CI, 1.18-1.67; aged 9-13 years: odds ratio, 1.13; 95% CI, 0.97-1.32).

Conclusions and Relevance

This study suggests that younger children may be more likely to transmit SARS-CoV-2 infection compared with older children, and the highest odds of transmission was observed for children aged 0 to 3 years. Differential infectivity of pediatric age groups has implications for infection prevention within households, as well as schools/childcare, to minimize risk of household secondary transmission. Additional population-based studies are required to establish the risk of transmission by younger pediatric index cases.

Urban green space and the risks of dementia and stroke

INTRODUCTION

It is unknown whether urban green space is associated with reduced risk of major neurological conditions, especially dementia and stroke.

METHODS

Retrospective, population-based cohorts were created for each study outcome, including 1.7 and 4.3 million adults in Ontario, Canada for dementia and stroke, respectively. Residential green space was quantified using the satellite-derived Normalized Difference Vegetation Index. Incidence was ascertained using health administrative data with validated algorithms. Mixed-effects Cox models were used to estimate hazard ratios per interquartile range increase in green space exposure.

RESULTS

Between 2001 and 2013, 219,013 individuals were diagnosed with dementia and 89,958 had a stroke. The hazard ratio per interquartile range increase in green space was 0.97 (95% CI: 0.96-0.98) for dementia and 0.96 (0.95-0.98) for stroke. Estimates remained generally consistent in sensitivity analyses.

DISCUSSION

Increased exposure to urban green space was associated with reduced incidence of dementia and stroke. To our knowledge, this is the first population-based cohort study to assess these relationships.

Ambient air pollution and incidence of early-onset paediatric type 1 diabetes: A retrospective population-based cohort study

BACKGROUND

Studies have reported increasing incidence rates of paediatric diabetes, especially among those aged 0-5 years. Epidemiological evidence linking ambient air pollution to paediatric diabetes remains mixed.

OBJECTIVE

This study investigated the association between maternal and early-life exposures to common air pollutants (NO₂, PM_2.5, O₃, and oxidant capacity [Ox; the redox-weighted average of O₃ and NO₂]) and the incidence of paediatric diabetes in children up to 6 years of age.

METHODS

All registered singleton births in Ontario, Ca nada occurring between April 1st^, 2006 and March 31st^, 2012 were included through linkage from health administrative data. Monthly exposures to NO₂, PM_2.5, O₃, and O_x were estimated across trimesters, the entire pregnancy period and during childhood. Random effects Cox proportional hazards models were used to assess the relationships with paediatric diabetes incidence while controlling for important covariates. We also modelled the shape of concentration-response (CR) relationships.

RESULTS

There were 1094 children out of a cohort of 754,698 diagnosed with diabetes before the age of six. O₃ exposures during the first trimester of pregnancy were associated with paediatric diabetes incidence (hazard ratio (HR) per interquartile (IQR) increase = 2.00, 95% CI: 1.04-3.86). The CR relationship between O₃ during the first trimester and paediatric diabetes incidence appeared to have a risk threshold, in which there was little-to-no risk below 25 ppb of O₃, while above this level risk increased sigmoidally. No other associations were observed.

CONCLUSION

O₃ exposures during a critical period of development were associated with an increased risk of paediatric diabetes incidence.

The impact of air pollution on the incidence of diabetes and survival among prevalent diabetes cases

PURPOSE

Growing evidence implicates ambient air pollutants in the development of major chronic diseases and premature mortality. However, epidemiologic evidence linking air pollution to diabetes remains inconclusive. This study sought to determine the relationships between selected air pollutants (nitrogen dioxide [NO₂], fine particulate matter [PM_2.5], ozone [O₃], and oxidant capacity [Ox; the redox-weighted average of O₃ and NO₂]) and the incidence of diabetes, as well as the risk of cardiovascular or diabetes mortality among individuals with prevalent diabetes.

RESEARCH DESIGN AND METHODS

We followed two cohorts, which included 4.8 million Ontario adults free of diabetes and 452,590 Ontario adults with prevalent diabetes, from 2001 to 2015. Area-level air pollution exposures were assigned to subjects' residential areas, and outcomes were ascertained using health administrative data with validated algorithms. We estimated hazard ratios for the association between each air pollutant and outcome using Cox proportional hazards models, and modelled the shape of the concentration-response relationships.

RESULTS

Over the study period, 790,461 individuals were diagnosed with diabetes. Among those with prevalent diabetes, 26,653 died from diabetes and 64,773 died from cardiovascular diseases. For incident diabetes, each IQR increase in NO₂ had a hazard ratio of 1.04 (95% CI: 1.03-1.05). This relationship was relatively robust to all sensitivity analyses considered, and exhibited a near-linear shape. There were also positive associations between incident diabetes and PM_2.5, O₃, and Ox, but these estimates were somewhat sensitive to different models considered. Among those with prevalent diabetes, almost all pollutants were associated with increased diabetes and cardiovascular mortality risk. The strongest association was observed between diabetes mortality and exposure to NO₂ (HR = 1.08, 95% CI: 1.02-1.13).

CONCLUSIONS

Selected air pollutants, especially NO₂, were linked to an increased risk of incident diabetes, as well as risk of cardiovascular or diabetes mortality among persons with prevalent diabetes. As NO₂ is frequently used as a proxy for road traffic exposures, this result may indicate that traffic-related air pollution has the strongest effect on diabetes etiology and survival after diabetes development.

An LC/MS/MS method for quantitation of chemopreventive sphingadienes in food products and biological samples

Colorectal cancer (CRC) is a leading cause of cancer mortality. Diet has a significant influence on colon cancer risk. Identifying chemopreventive agents, dietary constituents, practices and/or diet supplements that promote gut health and reduce the incidence of intestinal neoplasias and CRC could significantly impact public health. Sphingadienes (SDs) are dietary sphingolipids found in plant-based food products. SDs are cytotoxic to colon cancer cells and exhibit chemopreventive properties. The aim of the present study was to develop a sensitive and robust ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) method for quantifying SDs in food products and biological samples. The assay was linear over a concentration range of 80nM to 50μM and was sensitive to a detection limit of 3.3nM. Post-extraction stability was 100% at 24h. SD content in soy oils was approximately 10nM. SDs were detected transiently in the plasma of adult mice 10min after gavage delivery of a 25mg/kg bolus and declined to baseline by 1h. SD uptake in the gut was maximal in the duodenum and peaked 1h after gavage delivery. Disappearance of SDs in the lower gastrointestinal tract suggests either rapid metabolism to yet unidentified products or potentially luminal export.

Actinoranone, a cytotoxic meroterpenoid of unprecedented structure from a marine adapted Streptomyces sp

The isolation and structure elucidation of a new meroterpenoid, actinoranone (1), produced by a marine bacterium closely related to the genus Streptomyces is reported. Actinoranone is composed of an unprecedented dihydronaphthalenone polyketide linked to a bicyclic diterpenoid. The stereochemistry of 1 was defined by application of the advanced Mosher's method and by interpretation of spectroscopic data. Actinoranone (1) is significantly cytotoxic to HCT-116 human colon cancer cells with an LD50 = 2.0 μg/mL.

Anthracimycin, a potent anthrax antibiotic from a marine-derived actinomycete

Licensed to kill: A new antibiotic, anthracimycin (see scheme), produced by a marine-derived actinomycete in saline culture, shows significant activity toward Bacillus anthracis, the bacterial pathogen responsible for anthrax infections. Chlorination of anthracimycin gives a dichloro derivative that retains activity against Gram-positive bacteria, such as anthrax, but also shows activity against selected Gram-negative bacteria.

Mooreia alkaloidigena gen. nov., sp. nov. and Catalinimonas alkaloidigena gen. nov., sp. nov., alkaloid-producing marine bacteria in the proposed families Mooreiaceae fam. nov. and Catalimonadaceae fam. nov. in the phylum Bacteroidetes

Bacterial strains CNX-216(T) and CNU-914(T) were isolated from marine sediment samples collected from Palmyra Atoll and off Catalina Island, respectively. Both strains were gram-negative and aerobic and produce deep-orange to pink colonies and alkaloid secondary metabolites. Cells of strain CNX-216(T) were short, non-motile rods, whereas cells of strain CNU-914(T) were short, curved rods with gliding motility. The DNA G+C contents of CNX-216(T) and CNU-914(T) were respectively 57.7 and 44.4 mol%. Strains CNX-216(T) and CNU-914(T) contained MK-7 as the predominant menaquinone and iso-C15 : 0 and C16 : 1ω5c as the major fatty acids. Phylogenetic analyses revealed that both strains belong to the order Cytophagales in the phylum Bacteroidetes. Strain CNX-216(T) exhibited low 16S rRNA gene sequence identity (87.1 %) to the nearest type strain, Cesiribacter roseus 311(T), and formed a well-supported lineage that is outside all currently described families in the order Cytophagales. Strain CNU-914(T) shared 97.6 % 16S rRNA gene sequence identity with 'Porifericola rhodea' N5EA6-3A2B and, together with 'Tunicatimonas pelagia' N5DB8-4 and four uncharacterized marine bacteria isolated as part of this study, formed a lineage that is clearly distinguished from other families in the order Cytophagales. Based on our polyphasic taxonomic characterization, we propose that strains CNX-216(T) and CNU-914(T) represent novel genera and species, for which we propose the names Mooreia alkaloidigena gen. nov., sp. nov. (type strain CNX-216(T)  = DSM 25187(T)  = KCCM 90102(T)) and Catalinimonas alkaloidigena gen. nov., sp. nov. (type strain CNU-914(T)  = DSM 25186(T)  = KCCM 90101(T)) within the new families Mooreiaceae fam. nov. and Catalimonadaceae fam. nov.

Chloroisothiocyanatoquinolines as fluorogenic derivatizing agents for primary and secondary amines

Two new prechromatographic LC fluorogenic derivatizing agents, 2- and 4-chloro-3-isothiocyanatoquinoline (4 and 5) have been synthesized and shown to react smoothly with primary and secondary amines to produce fluorescent thiazoloquinolines. Compounds 4 and 5 hydrolyse in aqueous base and the rates of this reaction compared with the rates of derivatizations with amino acids indicate that the hydrolysis reaction interferes with derivatization when UV detection is used. The kinetics of derivatization with ordinary amines indicate that this reaction is quite facile, although less nucleophilic amines, e.g. aniline, react slowly. The pKas for first protonations indicate that derivatives of 4 would be unprotonated and those of 5 would be protonated with typical RP-LC mobile phases. The Stokes shift for protonated derivatives of 5 is nearly 200 nm. The excess of unreacted derivatizing reagent interferes with UV detection of some analytes; but when fluorescence detection is used this excess produces only a small negative peak. With fluorescence detection the sensitivity of this method is about 0.8 microM at S/N of 2, and the response of peak height to concentration is linear over at least two decades of concentration.

Reactive oxygen-mediated damage to murine mammary tumor cells

We have shown, in a preliminary report, that macrophages can induce strand breaks in the DNA of co-cultured tumor cells (Chong et al., 1988). The present study is designed to determine if oxygen-centered species generated by the cell-free enzyme-substrate combination of hypoxanthine and xanthine oxidase can induce similar lesions and to identify the specific mediator(s). We report that co-incubation of murine mammary tumor cell lines with hypoxanthine and xanthine oxidase leads to the induction of DNA-strand breaks as determined by fluorescence analysis of DNA unwinding (FADU) assay or alkaline elution techniques. This damage is preventable by catalase which removes hydrogen peroxide but no protection is provided by agents to remove or prevent the formation of superoxide anion (superoxide dismutase), or hydroxyl radical (mannitol or the iron chelator o-phenanthroline). Likewise, cyclooxygenase or lipoxygenase inhibitors of arachidonate metabolism (indomethacin, nordihydroguaiaretic acid, caffeic acid) or bromophenacyl bromide do not alter the degree of DNA scission. Treatment with higher doses of oxygen species leads to significant toxicity as determined by evaluation of cell growth potential or colony-forming ability. Again, toxicity is prevented only by the presence of catalase. Tumor cells are able to rejoin strand breaks at lower, less toxic doses. When comparing different tumor cell subpopulations at various stages of progression, i.e., metastatic vs. nonmetastatic, for sensitivity to hydrogen peroxide-induced strand breakage, we found that at lower concentrations (less than 5 microM) metastatic populations are sensitive whereas nonmetastatic populations exhibit no significant breakage. At higher concentrations of hydrogen peroxide, all lines were sensitive, suggesting that a lower threshold of sensitivity may exist for more progressed tumor cell lines.

Macrophage-mediated induction of DNA strand breaks in target tumor cells

We have shown previously that macrophages are mutagenic to bacteria (A. M. Fulton et al., Cancer Res., 44: 4308-4311, 1984) and can induce the appearance of drug-resistant variants of murine mammary tumor cells (K. Yamashina et al., Cancer Res., 46: 2396-2401, 1986). The present study asks whether inflammatory macrophages can induce lesions in the DNA of cocultured tumor cells and seeks to determine the mediators of this damage. We quantitated the induction of DNA strand breaks using the technique of fluorometric analysis of DNA unwinding. We report that inflammatory macrophages coincubated with a mammary tumor cell line for 60 min at a 1:1 ratio result in significant numbers of strand breaks in the tumor cell DNA. The degree of damage is equivalent to 300 to 1200 rads of gamma-irradiation. Resident (unstimulated) peritoneal macrophages also induce tumor cell DNA strand breaks. However, inhibitor studies reveal quantitative and qualitative differences in strand breaks induced by inflammatory (elicited) versus resident peritoneal macrophages. Resident macrophages require a longer induction period (60 min) before significant breaks are detected, but induce more breaks than do elicited macrophages, which require only a 5-min coincubation period to induce significant damage. The enzyme catalase, which removes H2O2, protects tumor cells from both macrophage effector populations as does the prostaglandin synthase inhibitor, indomethacin. The superoxide anion scavenger, superoxide dismutase, and the lipoxygenase inhibitor, nordihydroguaiaretic acid, are protective against resident macrophage effects only. The metal chelator, o-phenanthroline, provides limited protection for elicited macrophages but induces total DNA breakage in the presence of resident macrophages. Taken together, our data indicate that the degree of strand breakage is greater for the macrophage population with high arachidonate metabolism and low oxidative metabolism (resident macrophages) and less for the macrophage population with high oxidative and low arachidonate metabolism (MVE-2 elicited macrophages). Inhibitor studies implicate both metabolites of reactive oxygen and arachidonate as mediators of this tumor cell DNA damage, with the relevant mediator dependent upon the particular macrophage population under study.

Selective loss of hippocampal granule cells in the mature rat brain after adrenalectomy

Adrenalectomy of adult male rats resulted in a nearly complete loss of hippocampal granule cells 3 to 4 months after surgery. Nissl and immunocytochemical staining of hippocampal neurons revealed that the granule cell loss was selective; there was no apparent loss of hippocampal pyramidal cells or of gamma-amino butyric acid (GABA)-, somatostatin-, neuropeptide Y-, calcium binding protein-, or parvalbumin-containing hippocampal interneurons. The hippocampal CA1 pyramidal cells of adrenalectomized animals exhibited normal electrophysiological responses to afferent stimulation, whereas responses evoked in the dentate gyrus were severely attenuated. Corticosterone replacement prevented both the adrenalectomy-induced granule cell loss and the attenuated physiological response. Thus, the adrenal glands play a role in maintaining the structural integrity of the normal adult brain.

Diet-induced changes in rabbit serum potassium do not alter size or number of brain capillary endothelial cell mitochondria

Previous studies have shown brain extracellular (EC) [K+] to remain constant during wide variations of the plasma-brain [K+] gradient. High serum [K+] is hypothesized to increase K+ pumping by the blood-brain barrier (BBB) to maintain normal EC levels. This changing metabolic work could be reflected in endothelial cell mitochondria which have been shown to be three to four times more numerous in the BBB than in other capillary endothelial cells. We measured several morphologic parameters of brain capillary endothelial cells in white male New Zealand rabbits following dietary manipulation of their serum [K+] levels. Four groups, based on serum [K+] levels, were formed: Deficient, Low, Normal, and High. Following the final day's weight and blood samples, rabbits were anesthetized and perfused for transmission electron microscopic planimetry. Variables included number and area of mitochondria, areas of capillary lumen and capillary diameter, area of endothelial cell, and proportion of endothelial cell taken up by mitochondria. With the exception of the area of the endothelial cell (P less than 0.01), which decreased with increasing serum [K+] levels, no differences appeared among the variables in any of the four groups. Lack of anticipated differences in mitochondrial number or proportional area indicates either that pumping K+ occupies a minor fraction of cell energy, or changes in mitochondrial size or number are not sufficiently sensitive indicators of metabolic workload in this model.

Dendritic organization of the anterior speech area

Golgi studies revealed significant differences in dendritic patterns between neurons of the left and right opercular regions of the frontal lobe (Broca's speech area on the dominant side) and between cells of the left and right precentral areas (the orofacial motor zones) just behind. Although total dendritic length of the basilar dendritic array seemed characteristic of an area independent of side, a larger proportion of the length on the left (dominant) side was made up of higher order (4, 5, 6) dendrite branches, and lower order (1, 2, 3) segments predominated on the right. The pattern was partially reversed in non-right-handed patients. These findings can be interpreted as indicating an early preponderance of dendrite growth in the non-speech-gifted hemisphere followed by enhanced dendrite growth in the dominant hemisphere coincident with the beginning of conceptualization and speech function.

Scanning electron microscopy of the central nervous system. II. The hippocampus

This study has presented cells, fibers and non-neuronal elements as seen in 3 dimensions using the SEM. Our discussion on possible artifacts which can occur with this method is offered in the hope that others will develop better techniques of dissection and specimen preparation. With the picture of normal tissue in mind, the investigator can undertake studies to determine the effects of various interventions on the structures of interest. Such treatments could include deafferentation or the use of macromolecular probes bound to cell surfaces. We anticipate that improvements in tissue preparation techniques by ourselves and others will open the way to intensive investigation of the nervous system using this powerful tool.

Structural correlates of seizure behavior in the mongolian gerbil

Hippocampi of seizure-sensitive and seizure-resistant Mongolian gerbils were examined in search of structural correlates of seizure behavior. In animals with well-established seizure histories, differences were found in both presynaptic and postsynaptic structures. Seizing animals had less dense dendritic spines, a greater proportion of mossy tuft area devoted to presynaptic vesicles, and a smaller proportion devoted to spines. The possible relationship of these findings to epilepsy is discussed.