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PubMed2001

Institutional and legislative issues of emergency management policy in Russia.

The emergency management policy as an organic component of the national development policy in contemporary Russia exists only for a slight more than a decade. However, its basic trends and directions could be revealed. In the legislative area covering technological accidents involving hazardous materials these include increasing differentiation of acts in terms of issue coverage, gradual integration of legislation via enforcement of the so-called systemic (umbrella) acts and increasing incorporation of specific acts, and keeping dominance of federal emergency acts. In addition, emergency legislation and policy programs on communities' protection against major hazards drift from alleviation-oriented towards more mitigation-focused. Meanwhile, the bulk of the existing acts are still specific laws and regulations, which consider most emergency response. In institutional realms the key direction of emergency policy development involved organization and progress of the Unified State System for Emergency Prevention and Elimination of the Russian Federation (USEPE) with EMERCOM as a key coordinator and actor in handling technological hazards and accidents. The detailed analysis of USEPE organizational pattern and operation modes including institutional structure, key functions, means and forces and operation routines is provided. It is argued that the system's logic and flexible organizational framework only to some extent contribute to effective mitigation of the major emergencies and/or disasters. In no less extent it depends on the existing socioeconomic conditions, which have been for a long time unfavorable in Russia and thus seriously constrain the USEPE effectiveness. This provides for ambiguous integral evaluation of the emergency management policy in the 1990s and early 2000s.

Disaster Planning↗
PubMed1997

Nitric oxide, prostaglandin, and sensory neurons in gastric mucosal blood flow response during acid secretion in rats.

1. The mechanism underlying the increase of gastric mucosal blood flow (GMBF) during acid secretion induced by pentagastrin was investigated in anesthetized rats, in relation to nitric oxide (NO), prostaglandin (PG), and sensory neurons. 2. An intravenous infusion of pentagastrin at 60 micrograms/kg/h (submaximal dose) produced an increase of acid secretion and GMBF as determined by laser Doppler flowmetry, and the GMBF response was totally attenuated when the acid secretion was inhibited by omeprazole or when the luminal H+ was removed by mucosal perfusion with glycine (200 mM). 3. Prior administration of NG-nitro-L-arginine methyl ester (L-NAME, 5 mg/kg, IV), a NO synthase inhibitor, significantly mitigated the GMBF response to pentagastrin, without any influence on acid secretion, and this effect was antagonized by coadministration of L-arginine (500 mg/kg IP). 4. The increase of GMBF during pentagastrin infusion also was significantly mitigated by indomethyacin (5 mg/kg, SC) or sensory deafferentation following capsaicin pretreatment, had no effect on the acid secretion, and was totally inhibited by the combined treatments with indomethacin plus L-NAME in addition to sensory deafferentation. 5. Pentagastrin infusion for 8 hr did not by itself cause any macroscopic damage in the stomach, but additional treatments with L-NAME, and indomethacin plus sensory deafferentation provoked severe lesions in the gastric mucosa. 6. These results suggest that the increase of GMBF induced by submaximal dose of pentagastrin totally depends on luminal H+. This process seems to be mediated by endogenous NO and PGs, as well as capsaicin-sensitive sensory neurons, and to play a pivotal role in maintaining mucosal integrity during acid secretion.

Animals↗
PubMed2003

Hyperprolactinemia in response to antipsychotic drugs: characterization across comparative clinical trials.

BACKGROUND: Atypical antipsychotic drugs for the treatment of schizophrenia provide effective treatment of psychotic symptoms with a safety profile superior to conventional antipsychotic medications. Neuroendocrine abnormalities in patients with schizophrenia, such as chronic hyperprolactinemia, may now potentially be minimized by the use of newer prolactin-sparing antipsychotic drugs. A discrimination of prolactin-sparing versus prolactin-elevating antipsychotic drugs may provide the clinician with treatment choices in order to avoid or mitigate hyperprolactinemia-associated morbidity. METHODS: Results from five clinical trials were used to characterize factors that may influence antipsychotic drug effects on levels of serum prolactin. Factors investigated included drug treatment, gender, time course, potential for reduction or reversibility, and age. RESULTS: Factors that influenced the risk of hyperprolactinemia included gender, with females appearing to be more sensitive than males, and drug treatment, with risperidone and conventional antipsychotic agents increasing prolactin more than olanzapine. Patients of all ages demonstrated sensitivity to increased prolactin. Furthermore, patients with hyperprolactinemia sustained the effect over time. Hyperprolactinemia reversed when patients were switched to a prolactin-sparing antipsychotic medication. CONCLUSION: Effects of antipsychotic medications on serum prolactin are multi-factorial. Evidence for sexual, reproductive, and general medical consequences of antipsychotic-induced hyperprolactinemia is developing, and identifying antipsychotic drugs with a favorable prolactin profile would be important in mitigating these consequences. Most notably for women, atypical or novel antipsychotic drugs with a prolactin-sparing profile may offer effective clinical treatment with preservation of physiological hormonal function.

Adult↗
PubMedDate not supplied

Therapy effect of antiulcer agents on new chronic cysteamine colon lesion in rat.

After demonstration that cysteamine induced duodenal lesions in gastrectomized rats, while a number of antiulcer drugs mitigated these lesions, it was shown that one single intrarectal (i.r.) cysteamine application produced severe colon lesions in acute studies in rats. Thus, the further focus was on the protracted effect of cysteamine challenge (400 mg/kg b.w. i.r.) and therapy influence in chronic experiments in female rats. Regularly, cysteamine colon lesions were markedly mitigated by ranitidine (10), omeprazole (10), atropine (10), methylprednisolone (1), sulphasalazine (50; mg/kg), pentadecapeptide BPC 157 (PL-10, PLD-116; 10 microg or 10 ng/kg). Specifically, after 1 or 3 months following initial challenge (cysteamine 400 mg/kg i.r.) in female rat, the therapy [BPC 157 (PL-10, PLD-116 (10.0 microg or 10.0 ng/kg; i.g., i.p., i.r.), ranitidine, omeprazole, atropine, methylprednisolone, sulphasalazine (i.p.)] reversed the protracted cysteamine colon injury: the 1 week-regimen (once daily application) started after 1 month post-cysteamine, as well as the 2 weeks-regimen (once daily application), which started after 3 months. The effect on recidive lesion was also tested. These cysteamine lesions may reappear after stopping therapy (after stopping therapy for 3 weeks at the end of 2-weeks regimen started in 3 months-cysteamine female rats) in sulphasalazine group, while this reappearance is markedly antagonized in pentadecapeptide BPC 157 (PL-10, PLD-116)-rats (cysteamine-colon lesion still substantially low).

Animals↗
PubMed2003

Management of municipal solid waste incineration residues.

The management of residues from thermal waste treatment is an integral part of waste management systems. The primary goal of managing incineration residues is to prevent any impact on our health or environment caused by unacceptable particulate, gaseous and/or solute emissions. This paper provides insight into the most important measures for putting this requirement into practice. It also offers an overview of the factors and processes affecting these mitigating measures as well as the short- and long-term behavior of residues from thermal waste treatment under different scenarios. General conditions affecting the emission rate of salts and metals are shown as well as factors relevant to mitigating measures or sources of gaseous emissions.

Air Pollution↗
PubMed2002

Potential protective effect of melatonin against dibromoacetonitrile-induced oxidative stress in mouse stomach.

Dibromoacetonitrile (DBAN) is a disinfection by-product following chlorination of drinking water. Epidemiological studies indicate that it might present a potential hazard to human health. DBAN was previously found to induce oxidative stress in rat stomach as manifested by perturbation of some enzymatic and nonenzymatic antioxidant parameters. Therefore, we have investigated the oxidative stress possibly induced by DBAN in mouse stomach and possible protection by melatonin (MLT) as a free radical scavenger. In a dose-response study, mice were administered a single oral dose of DBAN (30, 60 and 120 mg kg(-1)) and were sacrificed after 1 h. DBAN significantly reduced glutathione (GSH) content that was somehow dose-related, and inhibited glutathione-S-transferase (GST) activity in gastric tissues. The highest dose of DBAN (120 mg kg(-1)) lowered GSH by 74% and induced a significant elevation of lipid peroxidation products, determined as thiobarbituric acid reactive substances (TBARS) by 69%. The same dose inhibited the gastric activities of GST, superoxide dismutase (SOD) and catalase (CAT) by 70, 57 and 23%, respectively. In a time-course study, mice were administered DBAN (60 mg kg(-1) p.o.) and sacrificed 0.5, 1, 3, 6, 12 and 24 h after treatment. GSH was dramatically depleted at 0.5, 1, 3 and 6 h (45, 38, 39 and 49% of control, respectively) and remained significantly low at 12 and 24 h. Also, DBAN caused an accumulation of TBARS in gastric tissues starting from 3 h and was maximum at 6 h (133% of the control). The enzymatic activities of GST and SOD were maximally inhibited by DBAN treatment at 0.5 h (32% for GST and 37% for SOD of the respective control). The activities of both enzymes returned to control values at 24 h. CAT activity was not affected by DBAN administration at all. Pretreatment of another group of mice with melatonin (10 mg kg(-1) per day p.o. 12 days) before administration of DBAN (60 mg kg(-1) p.o.) completely mitigated the aforementioned parameters. In conclusion, the present study indicates that DBAN induces a marked oxidative stress in mouse stomach as evidenced by GSH depletion, TBARS accumulation and GST, SOD and CAT inhibition. Melatonin could mitigate DBAN-induced oxidative stress in mouse stomach as it did almost normalize both the enzymatic and nonenzymatic antioxidant parameters.

Acetonitriles↗
PubMed2006

Efficacy of fexofenadine in the prophylactic control of cat allergen-induced allergic rhinitis.

BACKGROUND: To date, it is unknown whether fexofenadine mitigates the worsening of symptoms induced by the cat allergen Felis domesticus allergen 1. OBJECTIVE: To determine the effects of a single dose of fexofenadine hydrochloride, 180 mg, in preventing and controlling cat allergen-induced allergic rhinitis symptoms using the cat room challenge model. METHODS: This single-center, randomized, double-blind, placebo-controlled, 2-way crossover study consisted of a screening visit, 1 or 2 qualifying visits, and 2 treatment periods separated by a mean +/- SD washout period of 14 +/- 3 days. Patients were randomized to treatment sequence 1 (placebo followed by fexofenadine) or sequence 2 (fexofenadine followed by placebo). Baseline end points were obtained before study drug administration, and allergen challenges were initiated 1 1/2 hours after dosing. The primary end point was the change from predose baseline in the total symptom score (sum of rhinorrhea, itchy nose/palate/ throat, sneezing, and itchy/watery/red eyes) after 30 minutes of allergen exposure compared with placebo. RESULTS: Of 211 patients screened, 66 were randomized and 63 completed the study. Mean change in the total symptom score from predose baseline was significantly less with fexofenadine compared with placebo 30 minutes after initiation of the cat allergen challenge (2 hours after dosing) (P = .03). The overall incidence of treatment-emergent adverse events was low and comparable for both groups. CONCLUSION: Prophylactic treatment with a single dose of fexofenadine hydrochloride, 180 mg, significantly mitigated the worsening of allergic rhinitis symptoms induced by exposure to cat allergen compared with placebo use.

Adolescent↗
PubMed2003

Spatial spectra of scalp EEG and EMG from awake humans.

OBJECTIVE: Evaluate spectral scaling properties of scalp electroencephalogram (EEG) and electromyogram (EMG), optimal spacing of electrodes, and strategies for mitigating EMG. METHODS: EEG was recorded referentially from 9 subjects with a 64 channel linear array (electrodes 3mm apart) placed parasagittally or transversely on forehead or occiput, at rest with eyes open or closed, or with deliberate EMG. Temporal (PSD(t)) and spatial (PSD(x)) power spectral densities were calculated with one-dimensional fast Fourier transform (FFT) for comparison with earlier analyses of intracranial EEG. RESULTS: Scaling of PSD(t) from scalp resembled that from pia: near-linear decrease in log power with increasing log frequency (1/f(alpha)). Scalp PSD(x) decreased non-linearly and more rapidly than PSD(x) from pia. Peaks in PSD(t) (especially 4-12Hz) and PSD(x) (especially 0.1-0.4 cycles/cm) revealed departures from 1/f(alpha). EMG power in PSD(t) was more "white" than 1/f(alpha). CONCLUSIONS: Smearing by dura-skull-scalp distorts PSD(x) more than PSD(t) of scalp EEG from 1/f(alpha) scaling at the pia. Spatial spectral peaks suggest that optimal scalp electrode spacing might be approximately 1cm to capture non-local EEG components having the texture of gyri. Mitigation of EMG by filtering is unsatisfactory. A criterion for measuring EMG may support biofeedback for training subjects to reduce their EMG. SIGNIFICANCE: High-density recording and log-log spectral display of EEG provide a foundation for holist studies of global human brain function, as an alternative to network approaches that decompose EEG into localized, modular signals for correlation and coherence.

Brain↗
PubMed2006

Can venlafaxine in breast milk attenuate the norepinephrine and serotonin reuptake neonatal withdrawal syndrome.

A newborn infant whose mother had used venlafaxine, a selective inhibitor of both norepinephrine and serotonin reuptake, throughout pregnancy exhibited signs consistent with the norepinephrine and serotonin reuptake withdrawal syndrome. Is it possible that mother's milk can help mitigate the effects of norepinephrine and serotonin reuptake withdrawal? Pharmacokinetic analysis and review of the only published case with active treatment of a baby with venlafaxine suggest that breastfeeding may mitigate the neonatal withdrawal syndrome.

Breast Feeding↗
PubMed2025

Candida auris outbreak in a cardiothoracic transplant intensive care unit: implications for infection prevention practices and keeping pace with an evolving landscape.

OBJECTIVE: To describe the mitigation strategies for a Candida auris outbreak in a cardiothoracic transplant intensive care unit (CTICU) and its implications for infection prevention practices. DESIGN: Retrospective cohort study from July 2023 to February 2024. SETTING: A large academic medical center. METHODS: A multidisciplinary team convened to conduct the outbreak investigation and develop mitigation strategies in the CTICU. RESULTS: From July 2023 to February 2024, 34 possible hospital-onset cases of C. auris were identified in our CTICU. Whole-genome sequencing and phylogenetic analysis based on pairwise single nucleotide polymorphism (WG-SNP) distance revealed two distinct outbreak clusters. Of the 34 patients, 11 (32.3%) were solid organ transplant recipients and 12 (35.3%) had a mechanical circulatory support device. Of the cohort, only 11/34 (32.3%) had prior exposure to high-risk healthcare facilities within six months prior to admission, as follows: acute inpatient rehabilitation facilities (AIRs) (n = 5, 14.7%), skilled nursing facilities (SNFs) (n = 3, 8.8%), and long-term acute care hospitals (LTACHs) (n = 3, 8.8%). The cohort had a median of 22.0 antibiotic-days prior to their positive results. Five (14.7%) patients had C. auris candidemia, three of whom expired likely due to infection. Infection Prevention (IP) interventions addressed several modes of transmission, including healthcare personnel hands, shared patient equipment, and the environment. CONCLUSION: Our experience suggests that the epidemiology of C. auris may be changing, pointing towards a rising prevalence in acute care settings. IP interventions targeting hand hygiene behavior and promoting centralizing cleaning and disinfection of shared patient equipment may have contributed to outbreak resolution.

Humans↗
PubMedDate not supplied

Counting crises: US hospital evacuations, 1971-1999.

OBJECTIVES: To investigate the relative distribution of hazards causing hospital evacuations, thereby to provide rudimentary risk information for hospital disaster planning. METHODS: Cases of hospital evacuations were retrieved from newspaper and publication databases and classified according to hazard type, proximate and original cause, duration, and casualties. Both partial and full evacuations were included. The total number of evacuation incidents for all hazards were compared to the total number of hospital incidents for the one hazard, fire, for which national data is available. RESULTS: There were 275 reported evacuation incidents from 1971-1999, with an annual average of 21 in the 1990s, the period for which databases were more reliable. The most, 33, were recorded in 1994, the year of the Northridge Earthquake. Of all incidents, 63 (23%) were attributable primarily to internal fire, followed by internal hazardous materials (HazMat) events (18%), hurricane (14%), human threat (13%), earthquake (9%), external fire (6%), flood (6%), utility failure (5%), and external HazMat (4%). CONCLUSIONS: More than 50% of the hospital evacuations occurred because of hazards originating in the hospital facility itself or from human intruders. While natural disasters were not the preponderant causes of evacuations, they caused severe problems when multiple hospitals in the same urban area were incapacitated simultaneously. Clearly, as hospitals are vulnerable to many hazards, mitigation investments should be assessed not in terms of single-hazard risk-cost-benefit analysis, but in terms of capacity to mitigate multiple hazards. In view of the many qualifications and limitations of the dataset used here, but value of such data for disaster planning, hospitals should be asked to submit standardized incident reports to permit national data gathering on major disruptions.

Databases as Topic↗
PubMedDate not supplied

Health aspects of the Tsunami disaster in Asia.

This is a summary of the proceedings of the Conference on the Health Aspects of the Tsunami Disaster in Asia that was convened by the World Health Organization in Phuket, Thailand from 04-06 May 2005. It contains reviews of the experiences of the health sector and early recovery following the Earthquake and Tsunami with emphasis on what was done well and what could have been done better and the lessons learned that can be incorporated into actions that will mitigate the damage created by future events. It outlines the national and international responses and recovery and the actions taken and not taken by the international community in support of the countries affected. Specific issues addressed include: (1) needs assessments; (2) coordination; (3) filling gaps in essential services, and (4) capacity building at the country level. Each of these aspects is analyzed as to its: (1) appropriateness; (2) adequacy; (3) effectiveness; (4) efficiency; and (5) connectedness. Much of what occurred provided benefits to the stricken population, but there is substantial room for improvement through implementation of the lessons learned. These lessons must be converted into actions in order to mitigate the damage sustained and to enhance our responses to the damage from future events.

Disaster Planning↗
PubMedDate not supplied

Sharing international experiences in disasters: summary and action plan.

INTRODUCTION: The discussions in this theme provided an opportunity to share specific experiences with disasters that occurred outside of the Asia-Pacific Rim. METHODS: Details of the methods used are provided in the preceding paper. The chairs moderated all presentations and produced a summary that was presented to an assembly of all of the delegates. Since the findings from the Theme 7 and Theme 3 groups were similar, the chairs of both groups presided over one workshop that resulted in the generation of a set of action plans that then were reported to the collective group of all delegates. RESULTS: The main points developed during the presentations and discussion included: (1) disaster response planning, (2) predetermined command and organizational structure, (3) rapid response capability, (4) mitigation, and (5) communications and alternatives. DISCUSSION: The action plans presented are in common with those presented by Theme 3, and include: (1) plan disaster responses including the different types, identification of hazards, training based on experiences, and provision of public education; (2) improving coordination and control; (3) maintaining communications assuming infrastructure breakdown; (4) maximizing mitigation through standardized evaluations, creation of a legal framework, and recognition of advocacy and public participation; and (5) providing resources and knowledge through access to existing therapies, using the media, and increasing decentralization of hospital inventories. CONCLUSIONS: Most of the problems that occurred outside the Asia-Pacific rim relative to disaster management are similar to those experienced within it. They should be addressed in common with the rest of the world.

Communication↗
PubMed2004

Co-control of urban air pollutants and greenhouse gases in Mexico City.

This study addresses the synergies of mitigation measures to control urban air pollutant and greenhouse gas (GHG) emissions, in developing integrated "co-control" strategies for Mexico City. First, existing studies of emissions reduction measures--PROAIRE (the air quality plan for Mexico City) and separate GHG studies--are used to construct a harmonized database of options. Second, linear programming (LP) is developed and applied as a decision-support tool to analyze least-cost strategies for meeting co-control targets for multiple pollutants. We estimate that implementing PROAIRE measures as planned will reduce 3.1% of the 2010 metropolitan CO2 emissions, in addition to substantial local air pollutant reductions. Applying the LP, PROAIRE emissions reductions can be met at a 20% lower cost, using only the PROAIRE measures, by adjusting investments toward the more cost-effective measures; lower net costs are possible by including cost-saving GHG mitigation measures, but with increased investment. When CO2 emission reduction targets are added to PROAIRE targets, the most cost-effective solutions use PROAIRE measures for the majority of local pollutant reductions, and GHG measures for additional CO2 control. Because of synergies, the integrated planning of urban-global co-control can be beneficial, but we estimate that for Mexico City these benefits are often small.

Air Pollutants↗
PubMed2005

Impact of vegetation on sedimentary organic matter composition and polycyclic aromatic hydrocarbon attenuation.

Results from natural and engineered phytoremediation systems provide strong evidencethatvegetated soils mitigate polycyclic aromatic hydrocarbon (PAH) contamination. However, the mechanisms by which PAH mitigation occurs and the impact of plant organic matter on PAH attenuation remain unclear. This study assessed the impact of plant organic matter on PAH attenuation in labile and refractory sediments fractions from a petroleum distillate waste pit that has naturally revegetated. Samples were collected in distinct zones of barren and vegetated areas to assess changes to organic matter composition and PAH content as vegetation colonized and became established in the waste pit. Sediments were fractionated into bulk sediment and humin fractions and analyzed for organic matter composition by isotope ratio mass spectrometry (delta (13)C), 13C nuclear magnetic resonance (13C NMR), delta 14C AMS (accelerator mass spectrometry), and percent organic carbon (%TOC). Gas chromatography mass spectrometry (GC/ MS) of lipid extracts of SOM fractions provided data for PAH distribution histograms, compound weathering ratios, and alkylated and nonalkylated PAH concentrations. Inputs of biogenic plant carbon, PAH weathering, and declines in PAH concentrations are most evidentfor vegetated SOM fractions, particularly humin fractions. Sequestered PAH metabolites were also observed in vegetated humin. These results show that plant organic matter does impact PAH attenuation in both labile and refractory fractions of petroleum distillate waste.

Biodegradation, Environmental↗
PubMed2004

Influence of total organic carbon and UV-B radiation on zinc toxicity and bioaccumulation in aquatic communities.

The effects of total organic carbon (TOC) and UV-B radiation on Zn toxicity and bioaccumulation in a Rocky Mountain stream community were assessed in a 10-d microcosm experiment. We predicted that TOC would mitigate Zn toxicity and that the combined effects of Zn and UV-B would be greater than Zn alone. However, TOC did not mitigate Zn toxicity in this study. In fact, treatments with TOC plus Zn had significantly lower community respiration as compared with the controls and Zn concentrations associated with the periphyton increased in the presence of TOC. UV-B had no additive effect on periphyton Zn accumulation or community respiration. Heptageniid mayflies (Ephemeroptera) were particularly sensitive to Zn, and reduced abundances were observed in all Zn treatments. UV-B did not additionally impact Heptageniid abundances; however UV-B did have a greater effect on macroinvertebrate drift than Zn alone. Ephemeroptera, Plecoptera, and Trichoptera (groups typically classified as sensitive to disturbance) were found in highest numbers in the drift of UV-B + Zn treatments. Measures of Zn accumulation in the caddisfly Arctopsyche grandis, periphyton biomass, and total macroinvertebrate abundance were not sufficiently sensitive to differentiate effects of TOC, UV-B, and Zn. These results indicate that UV-B and TOC affect Zn bioavailability and toxicity by impacting species abundance, behavior, and ecosystem processes.

Animals↗
PubMed1998

Role of nitric oxide in IL-2 therapy-induced capillary leak syndrome.

Nitric oxide (NO) is a potent short-lived and short range bioactive molecule, which plays a key role in physiological and pathological processes including inflammation and cancer. Detrimental effects of excessive NO production during septic shock have been well recognized. We tested the hypothesis that 'capillary leak syndrome' following systemic interleukin-2 (IL-2) therapy resulted from a cascade of events leading to the induction of NO which, directly or indirectly, injured capillaries and caused fluid leakage. Our results provided the first direct evidence that the induction of active NO synthase (NOS) leading to the overproduction of NO is instrumental in IL-2-induced capillary leakage in mice and that successful blocking of this overproduction with chronic oral administration of NOS inhibitors can mitigate this leakage without interfering with the beneficial antitumor effects of IL-2 therapy. NO blocking agents can, in fact, improve IL-2-induced antitumor effector cell activation, as well as tumor regression. In our studies, NO blocking agents alone reduced the growth and metastasis of a murine mammary carcinoma, at least in part, by mitigating the invasion and angiogenesis-stimulating role of tumor-derived NO. Thus, NOS inhibitors may be useful in treating certain tumors and serve as valuable adjuncts to systemic IL-2 based immunotherapy of cancer and infectious diseases.

Animals↗
PubMedDate not supplied

A model of ocular dominance column development by competition for trophic factor: effects of excess trophic factor with monocular deprivation and effects of antagonist of trophic factor.

Recent experimental evidence has implicated neurotrophic factors (NTs) in the competitive process believed to drive the development of ocular dominance (OD) columns. Application of excess amounts of particular NTs can prevent the segregation process, suggesting that they could be the substance for which geniculocortical afferents compete during development. We have previously presented a model that accounts for normal OD development as well as the prevention of that development with excess NT. The model uses a Hebbian learning rule in combination with competition for a limiting supply of cortical trophic factor to drive OD segregation, without any weight normalization procedures. Subsequent experimental evidence has further suggested that NTs may be causally involved in the competitive process. Application of NT antagonist can prevent OD columns by causing inputs from both eyes to be eliminated, suggesting that NTs may be the substance for which geniculocortical afferents compete. Also, excess NT can mitigate the shift to the open eye normally caused by monocular deprivation (MD). In this article, we show that the current model can account for these subsequent experiments. We show that deprivation of NT causes inputs from both eyes to decay and that excess NT can mitigate the shift to the open eye normally seen with MD. We then present predictions of the model concerning the effects of NT on the length of the critical period during which MD is effective. The model presents a novel mechanism for competition between neural populations inspired by particular biological evidence. It accounts for three specific experimental results, and provides several testable predictions.

Age Factors↗