A twin analysis to estimate genetic and environmental factors contributing to variation in weighted gene co-expression network module eigengenes.

Multivariate network-based analytic methods such as weighted gene co-expression network analysis are frequently applied to human and animal gene-expression data to estimate the first principal component of a module, or module eigengene (ME). MEs are interpreted as multivariate summaries of correlated gene-expression patterns and network connectivity across genes within a module. As such, they have the potential to elucidate the mechanisms by which molecular genomic variation contributes to individual differences in complex traits. Although increasingly used to test for associations between modules and complex traits, the genetic and environmental etiology of MEs has not been empirically established. It is unclear if, and to what degree, individual differences in blood-derived MEs reflect random variation versus familial aggregation arising from heritable or shared environmental influences. We used biometrical genetic analyses to estimate the contribution of genetic and environmental influences on MEs derived from blood lymphocytes collected on a sample of N = 661 older male twins from the Vietnam Era Twin Study of Aging (VETSA) whose mean age at assessment was 67.7 years (SD = 2.6 years, range = 62-74 years). Of the 26 detected MEs, 14 (56%) had statistically significant additive genetic variation with an average heritability of 44% (SD = 0.08, range = 35%-64%). Despite the relatively small sample size, this demonstration of significant family aggregation including estimates of heritability in 14 of the 26 MEs suggests that blood-based MEs are reliable and merit further exploration in terms of their associations with complex traits and diseases.

Elective surgery resource utilization.

PURPOSE: Cessation of elective surgery during COVID-19 was partly driven by concern for consumption of hospital resources required by critically ill patients. We aim to determine the extent of resource utilization by elective outpatient surgery to assist in ensuring future resource conservation decisions are data driven. METHODS: The study utilized a retrospective cohort gathered from the American College of Surgeons National Surgical Quality Improvement Program database. Participants were adult patients who underwent elective or non-elective surgery between 2017 and 2018. Outcomes included patient characteristics and post-operative outcomes for elective and non-elective surgeries. Post-operative outcomes were used as a surrogate for the consumption of hospital resources. RESULTS: A total of 1,558,938 (79.8%) elective and 393,339 (20.2%) non-elective surgeries were identified. Elective surgery patients were more likely to be outpatient status, have an ASA class < 3, and exhibited lower rates of prolonged ventilation, 30-day reoperation, and 30-day readmissions, and averaged 5 days less of inpatient stay. Elective outpatient surgery (vs. elective inpatient surgery) averaged shorter operative times and exhibited lower rates of readmissions (2.1% vs. 5.5%; p < 0.001), reoperations (1.1% vs. 2.8%; p < 0.001), prolonged ventilation (0.0% vs. 0.3%; p < 0.001), and 30-day mortality (0.1% vs. 0.5%; p < 0.001) and accounted for 30.2% of the overall relative value units ($339,815,038). CONCLUSION: We evaluated utilization of hospital resources by patients undergoing elective outpatient surgery by identifying surgeries performed in 2017-2018 then stratifying them by outpatient status. Elective outpatient surgeries consumed negligible amounts of hospital resources and should not be considered a threat to resources in the setting of high demand by critically ill COVID-19 patients.

A Case for the Use of the 5-Item Modified Frailty Index in Preoperative Risk Assessment for Tissue Expander Placement in Breast Reconstruction.

BACKGROUND: Preoperative risk assessment is essential in determining which surgical candidates will have the most to gain from an operation. The 5-item modified frailty index (mFI-5) has been validated as an effective way to determine this risk. This study sought to evaluate the performance of the mFI-5 as a predictor of postoperative complications after tissue expander placement. METHODS: Patients who underwent placement of a tissue expander were identified using the 2012 to 2018 American College of Surgeons National Surgical Quality Improvement Project database. Univariate and multivariate regression analysis models were used to assess how mFI-5, the components of the mFI-5 (functional status, diabetes, chronic obstructive pulmonary disease, chronic heart failure, and hypertension), and other factors commonly used to risk stratify (age, body mass index [BMI], American Society of Anesthesiologists (ASA) classification, and history of smoking) were associated with complications. RESULTS: In 44,728 tissue expander placement cases, the overall complication rate was 10.5% (n = 4674). The mFI-5 score was significantly higher in the group that experienced complications (0.08 vs 0.06, P < 0.001). Compared with the mFI-5 individual components and other common variables used preoperatively to risk stratify patients, univariate analysis demonstrated that mFI-5 had the largest effect size (odds ratio [OR], 5.46; confidence interval [CI], 4.29-6.94; P < 0.001). After controlling for age, BMI, ASA classification, and history of smoking, the mFI-5 still remained the predictor of complications with the largest effect size (OR, 2.25; CI, 1.70-2.97; P < 0.001). In assessing specific complications, the mFI-5 is the independent predictor with the largest significant effect size for surgical dehiscence (OR, 12.76; CI, 5.58-28.18; P < 0.001), surgical site infection (OR, 6.68; CI, 4.53-9.78; P < 0.001), reoperation (OR, 5.23; CI, 3.90-6.99; P < 0.001), and readmission (OR, 4.59; CI, 3.25-6.45; P < 0.001) when compared with age, BMI, ASA class, and/or history of smoking alone. CONCLUSIONS: The mFI-5 can be used as an effective preoperative predictor of postoperative complications in patients undergoing tissue expander placement. Not only does it have the largest effect size compared with other historical perioperative risk factors, it is more predictive than each of its individual components.

The 5-Factor Modified Frailty Index as a Predictor of 30-day Complications in Pressure Ulcer Repair.

BACKGROUND: The 5-item modified frailty index (mFI-5) is a validated tool to assess postoperative risks in older surgical candidates. We sought to compare the predictive ability of mFI-5 to its individual components and other established risk factors for complications in flap reconstruction of late-stage pressure ulcer repair. METHODS: The 2012 to 2018 American College of Surgeons National Surgical Quality Improvement Project (ACS-NSQIP) database was queried for pressure ulcer diagnosis and reconstructive flap repair procedures. Univariate and multivariate regression analysis models were used to assess how mFI-5, the components of the mFI-5 (functional status before surgery, diabetes, history of chronic obstructive pulmonary disease, history of congestive heart failure, and history of hypertension requiring medicine), and other factors commonly used to risk-stratify (age, obesity, ASA classification, and history of smoking) were associated with complications. RESULTS: 35.1% of the total 1254 flap reconstructive procedures for pressure ulcer repair experienced complications. Most cases had at least one of the five mFI-5 factors in both the complication (42.7%) and no complication (45.7%) cohorts. Compared with the factors making up the mFI-5 score and other common variables used to risk-stratify, mFI-5 was significantly associated with complications in the univariate (OR 1.17, CI 1.03 - 1.33; P = 0.02) and multivariate analysis (OR 1.16, CI 1.02 - 1.34; P = 0.043). CONCLUSIONS: The mFI-5 is a useful predictor of postoperative outcomes in patients undergoing reconstructive flap surgery for pressure ulcer injuries compared to other historically considered risk factors for surgical complications.

Evaluation of fidaxomicin usage patterns and outcomes for Clostridium difficile infection across the United States Veterans Health Administration.

WHAT IS KNOWN AND OBJECTIVE: Fidaxomicin was recently approved for the treatment of Clostridium difficile infection (CDI). Limited data on its use exist outside of the phase 3 trials. The purposes of this study were to assess the compliance with the Veterans Health Administration (VHA) fidaxomicin criteria for use and describe patient characteristics and outcomes following fidaxomicin treatment for CDI using real-world data within the VHA system. METHODS: This was a multicentre, retrospective, observational study including all adult patients who received at least 1 dose of fidaxomicin at any Veterans Affairs Medical Center. RESULTS AND DISCUSSION: A total of 880 unique patients received 1098 courses of fidaxomicin, resulting in an overall usage rate per C. difficile-positive laboratory test of 1.98%. The rate of fidaxomicin courses per 1000 C. difficile-positive diagnostic tests increased steadily from 2011 through 2015 and plateaued from 2015 to 2016. Compliance with the VHA criteria for use was low (9.1%). The majority of courses were given for a first recurrence (25.0%), followed by an initial episode (23.9%) of CDI. The failure and recurrence rates were 6.8% and 24.4%, respectively. WHAT IS NEW AND CONCLUSION: Although overall use of fidaxomicin was low, compliance with the VHA criteria for use was also low, suggesting that the criteria may need to be revised. Further studies are warranted to clarify the role of fidaxomicin in clinical practice.

BrainGENIE: The Brain Gene Expression and Network Imputation Engine.

In vivo experimental analysis of human brain tissue poses substantial challenges and ethical concerns. To address this problem, we developed a computational method called the Brain Gene Expression and Network-Imputation Engine (BrainGENIE) that leverages peripheral-blood transcriptomes to predict brain tissue-specific gene-expression levels. Paired blood-brain transcriptomic data collected by the Genotype-Tissue Expression (GTEx) Project was used to train BrainGENIE models to predict gene-expression levels in ten distinct brain regions using whole-blood gene-expression profiles. The performance of BrainGENIE was compared to PrediXcan, a popular method for imputing gene expression levels from genotypes. BrainGENIE significantly predicted brain tissue-specific expression levels for 2947-11,816 genes (false-discovery rate-adjusted p < 0.05), including many transcripts that cannot be predicted significantly by a transcriptome-imputation method such as PrediXcan. BrainGENIE recapitulated measured diagnosis-related gene-expression changes in the brain for autism, bipolar disorder, and schizophrenia better than direct correlations from blood and predictions from PrediXcan. We developed a convenient software toolset for deploying BrainGENIE, and provide recommendations for how best to implement models. BrainGENIE complements and, in some ways, outperforms existing transcriptome-imputation tools, providing biologically meaningful predictions and opening new research avenues.

National Trends in Length of Stay for Microvascular Breast Reconstruction: An Evaluation of 10,465 Cases Using the American College of Surgeons National Surgical Quality Improvement Program Database.

BACKGROUND: Decreasing length of stay benefits patients and hospital systems alike. This should be accomplished safely without negatively impacting patient outcomes. The authors hypothesize that in the United States, the average length of stay for patients undergoing microsurgical breast reconstruction has decreased since 2012 without a concurrent increase in complication and readmission rates. METHODS: The authors identified female patients who underwent microvascular breast reconstruction (CPT 19364) from the 2012 to 2018 National Surgical Quality Improvement Program database. Trends in complication and readmission rates and length of stay were examined over 7 years. Multivariable logistic regression models and Mann-Kendall trend tests were used to evaluate associations between length of stay and complication and readmission rates. RESULTS: A total of 10,465 cases were identified. The number of autologous microvascular breast reconstruction procedures performed increased annually between 2012 and 2018. Length of stay decreased significantly from 2012 to 2018 (from 4.47 days to 3.90 days) (p < 0.01). Minor and major complication rates remained constant, although major complications showed a decreasing trend (from 27 percent to 21 percent) (p = 0.07). Thirty-day readmission, surgical-site infection, and wound dehiscence rates remained consistent over the study period, whereas rates of blood transfusion or bleeding decreased (p = 0.02). CONCLUSIONS: Using a national sample from 2012 to 2018, the authors observed a significant decrease in length of stay for patients undergoing microvascular breast reconstruction without a concurrent increase in complication and readmission rates. Current efforts to reduce length of stay have been successful without increasing complication or readmission rates. CLINICAL QUESTION/LEVEL OF EVIDENCE: Risk, III.

An Analysis of the Modified Five-Item Frailty Index for Predicting Complications following Free Flap Breast Reconstruction.

BACKGROUND: The modified five-item frailty index is a validated and effective tool for assessing risk in surgical candidates. The authors sought to compare the predictive ability of the modified five-item frailty index to established risk factors for complications in free flap breast reconstruction. METHODS: The 2012 to 2018 American College of Surgeons National Surgical Quality Improvement Program database was queried for free flap breast reconstructive procedures. Univariate and multivariate regression analysis models were used to assess how modified five-item frailty index and factors commonly used to risk stratify (age, body mass index, American Society of Anesthesiologists classification, and history of smoking) were associated with complications. RESULTS: Of the total 10,550 cases, 24.1 percent experienced complications. A high modified five-item frailty index score is associated with a higher overall rate of postoperative complications (p < 0.001). This significant trend was demonstrated in both surgical (p < 0.001) and medical (p < 0.001) complications. When controlling for other risk factors commonly used for risk stratification such as age, body mass index, American Society of Anesthesiologists classification, and history of smoking, the modified five-item frailty index was significantly associated with medical (OR, 1.75; 95 percent CI, 1.37 to 2.22; p = 0.001) and any complications (OR, 1.58; 95 percent CI, 1.29 to 1.93; p < 0.001) and had the largest effect size. Assessing for specific complications, the modified five-item frailty index is the strongest independent predictor of reoperation (OR, 1.41; 95 percent CI, 1.08 to 1.81; p = 0.009). CONCLUSION: The modified five-item frailty index is a useful predictor of postoperative outcomes in patients undergoing free flap breast reconstruction when compared to other historically considered risk factors for surgical complications. CLINICAL QUESTION/LEVEL OF EVIDENCE: Risk, III.

A population-based study of breast implant illness.

BACKGROUND: Despite evidence supporting the safety of breast implants, some women associate their implants with adverse health effects and have called this syndrome "breast implant illness." We sought to characterize breast implant illness symptoms and to report how implant removal affects their symptoms. METHODS: An anonymous 20 question survey was administered to the Facebook group: "UTAH Breast Implant Illness" to characterize the symptoms these women attributed to their breast implants. Several questions allowed us to evaluate how implant removal affected women's symptoms. RESULTS: Of the 182 respondents, 97% report that implants negatively affect their health and 95% identify these symptoms with breast implant illness. Ninety-six percent of respondents had implants placed for cosmetic reasons and 51% had silicone implants. The most common symptoms associated with breast implant illness are brain fog (95%), fatigue (92%), joint pain (80%), and hair loss (74%). Sixty percent of respondents learned about breast implant illness from family/friends and/or social media platforms (56%), 40% of respondents had their implants removed, and 97% report relief of their symptoms post-removal (23% complete, 74% partial). Following explantation, there was a significant improvement in all but one reported symptom. An association was found between the number of symptoms reported prior to explantation and the number of symptoms resolving following explantation. CONCLUSIONS: Breast implant illness is a syndrome characterized by fatigue, decreased focus, hair loss, and joint pain after the placement of breast implants. Nearly all patients report improvement of symptoms after implant removal. Significant efforts should be made to better understand breast implant illness and its etiology.

Distribution and mobility of lectin receptors on synaptic membranes of identified neurons in the central nervous system.

The distribution and mobility of concanavalin A (Con A) and Ricinus communis agglutinin (RCA) receptors (binding sites) on the external surfaces of Purkinje, hippocampal pyramidal, and granule cells and their attached boutons were studied using ferritin-lectin conjugates. Dendritic fields of these cells were isolated by microdissection and gently homogenized. Cell fragments and pre- and postsynaptic membranes were labeled with the ferritin-lectin conjugates at a variety of temperatures, and the distribution of lectin receptors was determined by electron microscopy. Both classes of these lectin receptors were concentrated at nearly all open and partially open postsynaptic junctional membranes of asymmetric-type synapses on all three neuron types. Con A receptors were most concentrated at the junctional membrane region, indicating that the mature neuron has a specialized nonrandom organization of carbohydrates on its outer surface. Lectin receptors located on postsynaptic junctional membranes appeared to be restricted in their mobility compared to similar classes of receptors on extrajunctional membrane regions. Labeling with ferritin-RCA and -Con A at 37 degrees C produced clustering of lectin receptors on nonjunctional surfaces; however, Con A and RCA receptors retained their nonrandom topographic distribution on the postsynaptic junctional surface. The restricted mobility of lectin receptors was an inherent property of the postsynaptic membrane since the presynaptic membrane was absent. It is proposed that structures in the postsynaptic density may be transmembrane-linked to postsynaptic receptors and thereby determine topographic distribution and limit diffusion of specialized synaptic molecules. Speicalized receptor displays may play an important role in the formation and maintenance of specific synaptic contacts.

Sex pheromones and reproductive isolation of the lesser peachtree borer and the peachtree borer.

(E,Z)-3,13-octadecadien-1-ol acetate, and (Z,Z)-3,13-octadecadien-1-ol acetate, isolated from the female lesser peachtree borer, Synanthedon pictipes (Grote and Robinson), and the female peachtree borer, Sanninoidea exitiosa (Say), respectively, strongly attract the respective males of these species in field bioassays. These compounds are the largest pheromones isolated thus far from a lepidopterous species. Sanninoidea exitiosa males did not respond to the synthesized (E,Z)-isomer, and low concentrations of it in the synthesized (Z,Z)-isomer did not interfere with their response to the (Z,Z)-isomer. In contrast, even very low concentrations of the (Z,Z)-isomer (1 percent) in the (E,Z)-isomer significantly inhibited the response of Synanthedon pictipes males.

Fidaxomicin versus oral vancomycin for severe Clostridium difficile infection: a retrospective cohort study.

OBJECTIVES: This study was conducted to compare clinical outcomes of fidaxomicin versus oral vancomycin in the management of severe Clostridium difficile infection (CDI). METHODS: The investigation was a retrospective, multicentre, propensity score-matched analysis using a national clinical administrative database. Veterans treated for severe CDI from any Veterans Affairs Medical Center between 1 June 2011 and 30 June 2017 were included if they received fidaxomicin or an oral vancomycin regimen for treatment. The two groups were matched by the nearest-neighbour method from a propensity score derived from independent variables associated with the selection of a fidaxomicin course. RESULTS: Propensity score matching resulted in two well-matched cohorts consisting of 213 fidaxomicin and 639 oral vancomycin courses. No statistically-significant difference was found for the primary outcome of combined clinical failure or recurrence (68/213 (31.9%) versus 163/639 (25.5%), respectively, p 0.071). Additionally, no statistically significant differences were found for the secondary outcomes of 30-day (23/213 (10.8%) versus 75/639 (11.7%), respectively, p 0.71), 90-day (48/213 (22.5%) versus 140/639 (21.9%), respectively, p 0.85), and 180-day mortality (62/213 (29.1%) versus 186/639 (29.1%), respectively, p 1.0) between the two treatment groups. CONCLUSIONS: Courses of fidaxomicin or oral vancomycin for severe CDI resulted in similar treatment outcomes. Study findings are consistent with current treatment guideline recommendations for the use of either agent in the management of severe CDI.

Epilepsy, hyperalgesia, impaired memory, and loss of pre- and postsynaptic GABA(B) responses in mice lacking GABA(B(1)).

GABA(B) (gamma-aminobutyric acid type B) receptors are important for keeping neuronal excitability under control. Cloned GABA(B) receptors do not show the expected pharmacological diversity of native receptors and it is unknown whether they contribute to pre- as well as postsynaptic functions. Here, we demonstrate that Balb/c mice lacking the GABA(B(1)) subunit are viable, exhibit spontaneous seizures, hyperalgesia, hyperlocomotor activity, and memory impairment. Upon GABA(B) agonist application, null mutant mice show neither the typical muscle relaxation, hypothermia, or delta EEG waves. These behavioral findings are paralleled by a loss of all biochemical and electrophysiological GABA(B) responses in null mutant mice. This demonstrates that GABA(B(1)) is an essential component of pre- and postsynaptic GABA(B) receptors and casts doubt on the existence of proposed receptor subtypes.

Prevalence of the Clostridium difficile BI/NAP1/027 strain across the United States Veterans Health Administration.

OBJECTIVES: The increased incidence and severity of Clostridium difficile infection (CDI) are thought to result partly from the emergence of the hypervirulent BI/NAP1/027 strain. Limited recent data are available on the prevalence of BI/NAP1/027 in the United States (US). The objective of this study was to assess the recent prevalence of BI/NAP1/027 within the US Veterans Health Administration (VHA). METHODS: Patients with CDI at any Veterans Affairs Medical Center found to routinely test for the presence of BI/NAP1/027 during the study period were included between 1 June 2011 and 30 June 2016 in this retrospective, observational, nationwide study. RESULTS: In total, 7571 patients had 8224 positive C. difficile tests that had a corresponding BI/NAP1/027 test. Of those, there were 1810 (22.0%) presumptive positive for BI/NAP1/027. The overall prevalence of BI/NAP1/027 decreased from a high of 26.2% in 2013 to 16.9% in 2016. Statistically significant reductions in rates from 2012 to 2016 occurred in seven of nine US Census Bureau regions. CONCLUSIONS: The prevalence of C. difficile with the BI/NAP1/027 strain was 22.0% across the VHA between 2012 and 2016. Further studies are needed to confirm these results and for continued monitoring of the trends in BI/NAP1/027 prevalence.

Poly(ethylene glycol) on the liposome surface: on the mechanism of polymer-coated liposome longevity.

The hypothetical model is built explaining the molecular mechanism of protective action of poly(ethylene glycol) on liposomes in vivo. The protective layer of the polymer on the liposome surface is considered as a statistical 'cloud' of polymer possible conformations in solution. Computer simulation was used to demonstrate that relatively a small number of liposome-grafted molecules of hydrophilic and flexible polymer can create a dense protective conformational cloud over the liposome surface preventing opsonizing protein molecules from contacting liposome. A more rigid polymer fails to form this dense protective cloud, even when hydrophilic. Computer simulation was also used to reveal possible heterogeneity of reactive sites on a polymer-coated liposome surface, and to estimate the optimal polymer-to-lipid ratio for efficient liposome protection. Experiments have been performed with the quenching of liposome-associated fluorescent label (nitrobenzoxadiazole or fluorescein) with protein (rhodamine-ovalbumin or anti-fluorescein antibody) from solution. It was shown that poly(ethylene glycol) grafting to liposomes hinders protein interaction with the liposome surface, whereas liposome-grafted dextran (more rigid polymer) in similar quantities does not affect protein-liposome interaction. Highly-reactive and low-reactive populations of chemically identical reactive sites have been found on polymer-coated liposomes. Experimental data satisfactory confirm the suggested mechanism for the longevity of polymer-modified liposome.

Degeneration of hippocampal CA3 pyramidal cells induced by intraventricular kainic acid.

Degeneration of hippocampal CA3 pyramidal cells was investigated by light and electron microscopy after intraventricular injection of the potent convulsant, kainic acid. Electron microscopy revealed evidence of pyramidal cell degeneration within one hour. The earliest degenerative changes were confined to the cell body and proximal dendritic shafts. These included an increased incidence of lysosomal structures, deformation of the perikaryal and nuclear outlines, some increase in background electron density, and dilation of the cisternae of the endoplasmic reticulum accompanied by detachment of polyribosomes. Within the next few hours the pyramidal cells atrophied and became electron dense. Then these cells became electron lucent once more as ribosomes disappeared and their membranes and organelles broke up and disintegrated. Light microscopic changes correlated with these ultrastructural observations. The dendritic spines and the initial portion of the dendritic shaft became electron dense within four hours and degenerated rapidly, whereas the intermediate segment of the dendrites swelled moderately and became more electron lucent. No degenerative changes were evident in pyramidal cell axons and boutons until one day after kainic acid treatment. Less than one hour after kainic acid administration, astrocytes in the CA3 area swelled, initially in the vicinity of the cell body and mossy fiber layers. It is suggested that the paroxysmal discharges initiated in CA3 pyramidal cells by kainic acid served as the stimulus for this response. Phagocytosis commenced between one and three days after kainic acid administration, but remained incomplete at survival times of 6-8 weeks. Astrocytes, microglia, and probably oligodendroglia phagocytized the degenerating material. These results point to the pyramidal cell body and possibly also the dendritic spines as primary targets of kainic acid neurotoxicity. In conjunction with other data, they support the view that lesions made by intraventricular kainic acid can serve as models of epileptic brain damage.

Fate of the hippocampal mossy fiber projection after destruction of its postsynaptic targets with intraventricular kainic acid.

Intraventricular injections of kainic acid were used to create a model of selective cell death in order to study the fate of afferent projections that are deprived of their postsynaptic targets. This treatment rapidly destroyed hippocampal CA3 pyramidal cells, but not those neurons that give rise to their mossy fiber and entorhinal afferents. Light microscopic studies with the Timm's sulfide silver stain indicated that half or more of the mossy fiber boutons in area CA3b were lost within the first 1-3 days after kainic acid administration. This finding was confirmed by electron microscopy. Electron-dense, usually vacuolated mossy fiber boutons accounted for about 10-20% of the total population present at a 4-hour survival time, but were not encountered in control rats nor at survival times longer than 1 day. Other mossy fiber boutons remained electron lucent, but enlarged, became more rounded in shape, and suffered an apparent loss of synaptic vesicles. It is suggested that degeneration of some mossy fiber boutons and resorption of others into the axon may have accounted for the precipitous decline in their number. The dendritic excrescences contacted by these boutons were nearly all undergoing electron-dense degeneration 4 hours after kainic acid administration. In rats that survived 6-8 weeks mossy fiber boutons remained somewhat scarce, individual boutons appeared relatively small, and only one-third the normal percentage were observed to be engaged in more than one synaptic contact within a single cross section. A qualitative electron microscopic study of the entorhinal projection to area CA3 suggested a response to kainic acid treatment similar to that of the mossy fiber projection, except that no entorhinal boutons were seen to become electron dense. These findings suggest that presynaptic fibers in the mature hippocampus adjust the size of their terminal arborizations and number of synaptic contacts to accommodate a reduction in the target cell population. The rapid loss of mossy fiber boutons may be attributable to an unusual fragility of these structures when they are deprived of the mechanical support normally provided by the pyramidal cell. Finally, the ability of kainic acid administration to alter the number and distribution of presynaptic elements must be taken into account whenever this toxin is used to make selective lesions of postsynaptic cells.

Ultrastructure of the olfactory organ in the clawed frog, Xenopus laevis, during larval development and metamorphosis.

Development of the olfactory epithelia of the African clawed frog, Xenopus laevis, was studied by scanning and transmission electron microscopy. Stages examined ranged from hatching through the end of metamorphosis. The larval olfactory organ consists of two chambers, the principal cavity and the vomeronasal organ (VNO). A third sensory chamber, the middle cavity, arises during metamorphosis. In larvae, the principal cavity is exposed to water-borne odorants, but after metamorphosis it is exposed to airborne odorants. The middle cavity and the VNO are always exposed to waterborne odorants. Electron microscopy reveals that in larvae, principal cavity receptor cells are of two types, ciliated and microvillar. Principal cavity supporting cells are also of two types, ciliated and secretory (with small, electron-lucent granules). After metamorphosis, the principal cavity contains only ciliated receptor cells and secretory supporting cells, and the cilia on the receptor cells are longer than in larvae. Supporting cell secretory granules are now large and electron-dense. In contrast, the middle cavity epithelium contains the same cell types seen in the larval principal cavity. The VNO has microvillar receptor cells and ciliated supporting cells throughout life. The cellular process by which the principal cavity epithelium changes during metamorphosis is not entirely clear. Morphological evidence from this study suggests that both microvillar and ciliated receptor cells die, to be replaced by newly generated cells. In addition, ciliated supporting cells also appear to die, whereas there is evidence that secretory supporting cells transdifferentiate into the adult type. In summary, significant developmental additions and neural plasticity are involved in remodeling the olfactory epithelium in Xenopus at metamorphosis.

Regulation of nicotinic acetylcholine receptor numbers and function by chronic nicotine exposure.

Recent advances concerning effects of chronic nicotine exposure on nicotinic acetylcholine receptor (nAChR) expression are reviewed. Implications are assessed of these findings for roles of nAChR in health and disease and for design of drugs for treatment of neurological and psychiatric disorders. Most studies continue to show that chronic nicotine exposure induces increases in numbers of nAChR-like binding or antigenic sites ("upregulation") across all nAChR subtypes investigated, but with time- and dose-dependencies and magnitudes for these effects that are unique to subsets of nAChR subtypes. These effects appear to be post-transcriptionally based, but mechanisms involved remain obscure. With notable exceptions, most studies also show that chronic nicotine exposure induces several phases of nAChR functional loss ("desensitization" and longer-lasting "persistent inactivation") assessed in response to acute nicotinic agonist challenges. Times for onset and recovery and dose-dependencies for nicotine-induced functional loss also are nAChR subtype-specific. Some findings suggest that upregulation and functional loss are not causally- or mechanistically-related. It is suggested that upregulation is not as physiologically significant in vivo as functional effects of chronic nicotine exposure. By contrast, brain levels of nicotine in tobacco users, and perhaps levels of acetylcholine in the extracellular space, clearly are in the range that would alter the balance between nAChR in functionally ready or inactivated states. Further work is warranted to illuminate how effects of chronic nicotinic ligand exposure are integrated across nAChR subtypes and the neuronal circuits and chemical signaling pathways that they service to produce nicotine dependence and/or therapeutic benefit.

Regulation and function of spinal and peripheral neuronal B1 bradykinin receptors in inflammatory mechanical hyperalgesia.

Activation of either B1 or B2 bradykinin receptors by kinins released from damaged tissues contributes to the development and maintenance of inflammatory hyperalgesia. Whereas B2 agonists activate sensory neurones directly, B1 agonists were thought only to have indirect actions on sensory neurones. The recent discovery of constitutive B1 receptor expression in the rat nervous system lead us to re-investigate the role of neuronal B1 receptors in inflammatory hyperalgesia. Therefore we have examined B1 bradykinin receptor regulation in rat dorsal root ganglia in a model of inflammatory hyperalgesia, and correlated it with hyperalgesic behaviour. Twenty-four hours after injection of Freund's complete adjuvant into one hindpaw, there was a significant increase in B1 protein expression (measured by immunohistochemistry) in both ipsilateral and contralateral dorsal root ganglion neurones, whereas axotomy resulted in reduction of B1 protein in ipsilateral dorsal root ganglia. In behavioural experiments, the B1 antagonist desArg10HOE140, administered by either intrathecal or systemic routes, attenuated Freund's complete adjuvant-induced mechanical hyperalgesia in the inflamed paw, but did not affect mechanical allodynia. The B1 agonist, desArg9BK, did not affect paw withdrawal thresholds in nai;ve rats following intraplantar administration into the paw, whilst intrathecal administration elicited mechanical hyperalgesia. However, after Freund's complete adjuvant-induced inflammation, desArg9BK caused a marked mechanical hyperalgesia, by either route, of the contralateral, uninflamed hindpaw, correlating with the observed contralateral and ipsilateral increases in receptor levels. Our results suggest a functional role for B1 receptors expressed both in the periphery and in the spinal cord, in mechanical hyperalgesia during inflammation.