Hospital wastewater (HWW) treatment in low- and middle-income countries: A systematic review of microbial treatment efficacy

BACKGROUND

Proper treatment of hospital wastewater (HWW) is crucial to minimize the long-term effects on human health and aquatic ecosystems. However, the majority of HWW generated in low and middle-income countries (LMICs), is discharged without adequate treatment. This systematic review aims to fill the knowledge gap in LMICs by examining the efficacy of HWW treatment and the types of technologies used.

METHODS

Studies included in the review offered valuable insights into the current state of HWW management in LMICs. Between 2000 and 2022, only 36 research studies focused on hospital-based wastewater treatment within LMICs. Data were extracted on wastewater treatment technologies in hospitals or healthcare settings in LMICs. Data on sampling techniques, effectiveness, microorganisms and risk of bias of included studies were recorded.

RESULTS

A total of 36 articles met the eligibility criteria: mentioned about 1) hospitals 2) wastewater treatment 3) LMICs and 4) treatment efficacy. Twenty-two studies were conducted in Asia (22/36), 17 were conducted in countries with high Human Development Index. Constructed wetland, and activated sludge process were the most common technologies used in LMICs. A few studies utilized membrane bioreactors and ozone/UV treatment. Fourteen studies reported the concentration reduction to assess the microbial efficacy of the treatment process, 29/36 studies did not meet the national standards for effluent discharge. Reporting on sampling methods, wastewater treatment processes and efficacy of HWW treatment were at high risk of bias. Extreme heterogeneity in study methods and outcomes reporting precluded meta-analysis.

CONCLUSIONS

The existing evidence indicates inadequate microbial treatment in low- and middle-income country hospitals, with this systematic review emphasizing the need for improvement in healthcare waste management. It underscores the importance of long-term studies using innovative treatment methods to better understand waste removal in LMIC hospitals and calls for further research to develop context-specific healthcare waste treatment approaches in these regions.

Gender and water, sanitation, and hygiene: Three opportunities to build from recent reporting on global progress, 2000-2022

In this Perspective, Juliet Willetts and colleagues discuss opportunities to stimulate progress in gender-related aspects of water, sanitation and hygiene.

A method for correcting underestimation of enteric pathogen genome quantities in environmental samples

Exposure to enteric pathogens in the environment poses a serious risk for infection and disease. The accurate detection and quantification of enteric pathogens in environmental samples is critical for understanding pathogen transport and fate and developing risk assessment models. In this study, we successfully applied TaqMan real-time PCR assays to quantitatively detect five human-specific pathogens (Shigella/EIEC, Salmonella Typhi, Vibrio cholera, Norovirus, and Giardia) in samples from open drains, canals, floodwater, septic tanks, and anaerobic baffled reactors (ABR) collected in Mirpur, Dhaka, Bangladesh from April to October 2019. Overall, the grab and sediment samples showed low inhibition but the ultrafiltration samples collected from open drain had significantly higher (P = 0.0049) degree of PCR inhibition (median Ct = 31.06) compared to the extraction controls (Ct = 28.54). We developed a two-step method to adjust underestimation of pathogen quantities due to PCR inhibition and non-optimum PCR efficiency. Compared to other sample types, ultrafiltration samples demonstrated a wide range of concentration increase (1.0%-182.5%) by pathogens after adjusting for PCR inhibition and non-optimum efficiencies. These quantitative qPCR assays are successful in quantifying multiple enteric pathogens in environmental samples, and the adjustment method would be useful for correcting underestimates of pathogen quantities due to partial PCR inhibition and non-optimum efficiency.

Faecal contamination of groundwater self-supply in low- and middle income countries: Systematic review and meta-analysis

Self-supply is a ubiquitous response by households to the public water supply inadequacies found worldwide. Self-supply is invested in and managed by an individual household, accessible on-premises and unregulated. Vulnerability to faecal contamination is a concern due to reliance on low-cost technologies and shallow groundwater. This review aims to evaluate the evidence base on the safety of groundwater self-supply in low- and middle income countries in relation to faecal contamination. Differences in microbial water quality between source types, settings, countries and ownership were investigated. A search of peer-reviewed studies in low- and middle income countries was conducted in online databases, including PubMed, Web of Science, ProQuest and Environmental Complete. Studies were included if they had sufficient detail about the water samples to be related to groundwater self-supply, contained extractable data on faecal indicator bacteria (FIB) including thermotolerant coliform or Escherichia coli and were published in English between 1990 and April 2020. A total of 30 studies were included, resulting in 100 datasets and 26,981 water samples across the studies. FIB were present in 36% self-supply samples. The odds of FIB being detected was significantly higher for unimproved sources (OR=8.19, 95% CI [4.04-16.59], p<0.001) and for sources in low income countries (OR=3.85, 95% CI [1.85-7.69], p<0.001). Self-supply was significantly more likely to be contaminated than piped supply (OR=3.45, 95% CI [1.52-7.82], p=0.003). However, water quality was highly heterogeneous (I²=90.9%). Egger's test found no evidence of small study publication bias for self-supply compared to public supply. No evidence of bias due to lack of randomization or season was found, but study design and quality could potentially bias the results. To achieve Sustainable Development Goal 6.1 on safe drinking water for all, more attention is needed from governments to engage with self-supply and formulate balanced policy responses.

Modelling faecal pathogen flows and health risks in urban Bangladesh: Implications for sanitation decision making

Faecal-oral infections are a major component of the disease burden in low-income contexts, with inadequate sanitation seen as a contributing factor. However, demonstrating health effects of sanitation interventions - particularly in urban areas - has proved challenging and there is limited empirical evidence to support sanitation decisions that maximise health gains. This study aimed to develop, apply and validate a systems modelling approach to inform sanitation infrastructure and service decision-making in urban environments by examining enteric pathogen inputs, transport and reduction by various sanitation systems, and estimating corresponding exposure and public health impacts. The health effects of eight sanitation options were assessed in a low-income area in Dhaka, Bangladesh, with a focus on five target pathogens (Shigella, Vibrio cholerae, Salmonella Typhi, norovirus GII and Giardia). Relative to the sanitation base case in the study site (24% septic tanks, 5% holding tanks and 71% toilets discharging directly to open drains), comprehensive coverage of septic tanks was estimated to reduce the disease burden in disability-adjusted life years (DALYs) by 48-72%, while complete coverage of communal scale anaerobic baffled reactors was estimated to reduce DALYs by 67-81%. Despite these improvements, a concerning health risk persists with these systems as a result of effluent discharge to open drains, particularly when the systems are poorly managed. Other sanitation options, including use of constructed wetlands and small bore sewerage, demonstrated further reductions in local health risk, though several still exported pathogens into neighbouring areas, simply transferring risk to downstream communities. The study revealed sensitivity to and a requirement for further evidence on log reduction values for different sanitation systems under varying performance conditions, pathogen flows under flooding conditions as well as pathogen shedding and human exposure in typical low-income urban settings. Notwithstanding variability and uncertainties in input parameters, systems modelling can be a feasible and customisable approach to consider the relative health impact of different sanitation options across various contexts, and stands as a valuable tool to guide urban sanitation decision-making.

COVID-19: urgent actions, critical reflections and future relevance of 'WaSH': lessons for the current and future pandemics

The COVID-19 pandemic placed hygiene at the centre of disease prevention. Yet, access to the levels of water supply that support good hand hygiene and institutional cleaning, our understanding of hygiene behaviours, and access to soap are deficient in low-, middle- and high-income countries. This paper reviews the role of water, sanitation and hygiene (WaSH) in disease emergence, previous outbreaks, combatting COVID-19 and in preparing for future pandemics. We consider settings where these factors are particularly important and identify key preventive contributions to disease control and gaps in the evidence base. Urgent substantial action is required to remedy deficiencies in WaSH, particularly the provision of reliable, continuous piped water on-premises for all households and settings. Hygiene promotion programmes, underpinned by behavioural science, must be adapted to high-risk populations (such as the elderly and marginalised) and settings (such as healthcare facilities, transport hubs and workplaces). WaSH must be better integrated into preparation plans and with other sectors in prevention efforts. More finance and better use of financing instruments would extend and improve WaSH services. The lessons outlined justify no-regrets investment by government in response to and recovery from the current pandemic; to improve day-to-day lives and as preparedness for future pandemics.

Global Water, Sanitation and Hygiene Research Priorities and Learning Challenges under Sustainable Development Goal 6

MOTIVATION

Sanitation and Water for All (SWA) is a global partnership addressing challenges to universal water, sanitation, and hygiene (WaSH) access. Shortly following adoption of the United Nations' Sustainable Development Goals, the Research and Learning (R&L) constituency of SWA undertook a systematic study to determine global research priorities and learning needs.

PURPOSE

We aimed to identify priority topics where improved knowledge would aid achievement of Goal 6, by developing a global WaSH research agenda, and to describe evidence-use challenges among WaSH professionals.

APPROACH AND METHODS

We delivered a tailored, semi-structured electronic questionnaire to representatives from countries, R&L institutions, and other SWA partners (external support agencies, civil society, and private sector). The survey gathered views from 76 respondents working in an estimated 36 countries across all world regions. Data were analyzed quantitatively and qualitatively to identify patterns and themes.

FINDINGS

Most responses indicated lowered confidence on at least one Goal 6 target area, especially managing untreated wastewater and faecal sludge. Both brief and lengthy information formats were valued. WaSH information was perceived as conflicting or unreliable among non-R&L constituencies, suggesting differences in perceptions and information-seeking approaches. While the R&L constituency appeared saturated with learning and training opportunities, others perceived barriers to participating (e.g. not receiving notice or invitation). Research and other WaSH activities were frequently constrained by upward accountability to funders, while stakeholders were inconsistently included in research processes.

POLICY IMPLICATIONS

This study offers insight into perceived research and decision challenges related to Goal 6 targets. It develops a unified research agenda focused on high priority topics, and recommends renewed attention to evidence synthesis, learning and implementation support, research engagement, and multisectoral coordination.

Faecal contamination of groundwater in rural Vanuatu: prevalence and predictors

Groundwater is an important source of water for coastal communities in Pacific Island Countries. This study assessed the prevalence and predictors of faecal contamination in groundwater sources across 11 islands in Vanuatu. Escherichia coli was detected in 49% of sources and E. coli concentration exceeded 10 MPN (most probable number)/100 mL for 23% of sources. When adjusting for other variables, the detection of E. coli was significantly associated with severe pump stand corrosion, suggestive of contaminated run-off directly entering boreholes. E. coli concentration >10 MPN/100 mL was also significantly associated with: (i) hand-dug wells (as compared to drilled boreholes); (ii) severe pump stand corrosion; (iii) water points underlain by volcanic rocks (as compared to coral limestone); and (iv) rainfall in the previous 24 h. Encasing pump stands in concrete - as some communities had done - was found to have a significant protective effect. While baseline statistics for Sustainable Development Goal target 6.1 suggest that 87% of Vanuatu's rural population have access to at least a basic (improved) water source, the results from this study point to extensive microbial water quality concerns linked to degraded water supply infrastructure in need of rehabilitation.

Are piped water services reaching poor households? Empirical evidence from rural Viet Nam

The delivery of water services to the poor is lagging, yet local causes and manifestations of this are not well understood. Better data is needed to identify inequalities where they occur, explore underlying reasons, and develop strategies to achieve more equitable access. A focus on the local scale is important because this is where water services are delivered, and inequalities in access can be best observed. This paper presents a mixed-methods study of poor households' access to piped water in rural Viet Nam, providing insight into local dynamics of the water/poverty nexus. Findings pointed to lower rates of piped water access for poor households across areas served by government, private and community service providers. Connection fees were found to be the primary barrier to poor households accessing available piped services. The study also found that where financial support is provided, poor households can achieve comparable or even higher rates of access. Key implications of the study are the demonstrated value of, and yet challenges associated with, rigorous local-level monitoring to ensure equitable, quality service delivery.

Multiple water source use in rural Vanuatu: are households choosing the safest option for drinking?

Households in low- and middle-income countries commonly make use of multiple water sources. However, it remains unclear to what extent their drinking water choices are optimal from a health perspective. This matched cohort study across 10 islands in Vanuatu examined communities with both a groundwater and rainwater source to determine whether their preferred drinking option was the safest in microbial terms. In communities that preferred to drink rainwater, 56.5% of rainwater sources had 'high-risk' or 'very high risk' Escherichia coli contamination (> 10 MPN/100 mL) compared with 26.1% of groundwater sources (p = 0.092). Moreover, a preference for drinking rainwater was significantly associated with rainwater sources having 'high-risk' or 'very high risk' levels of E. coli contamination (p = 0.045). Results show that communities do not necessarily choose the safest water source for drinking. Findings also highlight the need to bolster local capacity to manage water quality risks and for Sustainable Development Goal monitoring to distinguish between protected and unprotected rainwater tanks.

Risk factors associated with rural water supply failure: A 30-year retrospective study of handpumps on the south coast of Kenya

An improved understanding of failure risks for water supplies in rural sub-Saharan Africa will be critical to achieving the global goal of safe water for all by 2030. In the absence of longitudinal biophysical and operational data, investigations into water point failure risk factors have to date been limited to cross-sectional research designs. This retrospective cohort study applies survival analysis to identify factors that predict failure risks for handpumps installed on boreholes along the south coast of Kenya from the 1980s. The analysis is based on a unique dataset linking attributes of >300 water points at the time of installation with their operational lifespan over the following decades. Cox proportional hazards and accelerated failure time models suggest water point failure risks are higher and lifespans are shorter when water supplied is more saline, static water level is deeper, and groundwater is pumped from an unconsolidated sand aquifer. The risk of failure also appears to grow as distance to spare part suppliers increases. To bolster the sustainability of rural water services and ensure no community is left behind, post-construction support mechanisms will need to mitigate heterogeneous environmental and geographical challenges. Further studies are needed to better understand the causal pathways that underlie these risk factors in order to inform policies and practices that ensure water services are sustained even where unfavourable conditions prevail.

Faecal Pathogen Flows and Their Public Health Risks in Urban Environments: A Proposed Approach to Inform Sanitation Planning

Public health benefits are often a key political driver of urban sanitation investment in developing countries, however, pathogen flows are rarely taken systematically into account in sanitation investment choices. While several tools and approaches on sanitation and health risks have recently been developed, this research identified gaps in their ability to predict faecal pathogen flows, to relate exposure risks to the existing sanitation services, and to compare expected impacts of improvements. This paper outlines a conceptual approach that links faecal waste discharge patterns with potential pathogen exposure pathways to quantitatively compare urban sanitation improvement options. An illustrative application of the approach is presented, using a spreadsheet-based model to compare the relative effect on disability-adjusted life years of six sanitation improvement options for a hypothetical urban situation. The approach includes consideration of the persistence or removal of different pathogen classes in different environments; recognition of multiple interconnected sludge and effluent pathways, and of multiple potential sites for exposure; and use of quantitative microbial risk assessment to support prediction of relative health risks for each option. This research provides a step forward in applying current knowledge to better consider public health, alongside environmental and other objectives, in urban sanitation decision making. Further empirical research in specific locations is now required to refine the approach and address data gaps.

A qualitative examination of the health workforce needs during climate change disaster response in Pacific Island Countries

BACKGROUND

There is a growing body of evidence that the impacts of climate change are affecting population health negatively. The Pacific region is particularly vulnerable to climate change; a strong health-care system is required to respond during times of disaster. This paper examines the capacity of the health sector in Pacific Island Countries to adapt to changing disaster response needs, in terms of: (i) health workforce governance, management, policy and involvement; (ii) health-care capacity and skills; and (iii) human resources for health training and workforce development.

METHODS

Key stakeholder interviews informed the assessment of the capacity of the health sector and disaster response organizations in Pacific Island Countries to adapt to disaster response needs under a changing climate. The research specifically drew upon and examined the adaptive capacity of individual organizations and the broader system of disaster response in four case study countries (Fiji, Cook Islands, Vanuatu and Samoa).

RESULTS

'Capacity' including health-care capacity was one of the objective determinants identified as most significant in influencing the adaptive capacity of disaster response systems in the Pacific. The research identified several elements that could support the adaptive capacity of the health sector such as: inclusive involvement in disaster coordination; policies in place for health workforce coordination; belief in their abilities; and strong donor support. Factors constraining adaptive capacity included: weak coordination of international health personnel; lack of policies to address health worker welfare; limited human resources and material resources; shortages of personnel to deal with psychosocial needs; inadequate skills in field triage and counselling; and limited capacity for training.

CONCLUSION

Findings from this study can be used to inform the development of human resources for health policies and strategic plans, and to support the development of a coordinated and collaborative approach to disaster response training across the Pacific and other developing contexts. This study also provides an overview of health-care capacity and some of the challenges and strengths that can inform future development work by humanitarian organizations, regional and international donors involved in climate change adaptation, and disaster risk reduction in the Pacific region.

Non-government organisation engagement in the sanitation sector: opportunities to maximise benefits

Non-government organisations (NGOs) have long played a role in delivering sanitation services to communities in Southeast Asia and Pacific countries, particularly in rural areas. In contrast with large scale infrastructure focused initiatives, NGO programs commonly focus on building linkages between technical and social realms. Drawing on the breadth and depth of NGO experiences, there are opportunities for NGOs to play a greater role in the sanitation sector and to work in partnership with other actors including utilities and government agencies to ensure both 'hardware' and 'software' components of sanitation are built in to project design and delivery to maximise community benefits and ensure longer term system sustainability. This paper discusses these issues and considers how the contribution of NGOs to the sanitation sector in developing countries might be enhanced. The paper is based on recent research for the Australian Agency for International Development (AusAID) intended to guide investment in the water and sanitation sectors of Asia and Pacific partner countries, exploring the potential for increased NGO engagement. The paper presents findings of the research concerning NGO roles and approaches, discusses existing NGO activities in the sanitation sector in Vietnam and Timor Leste and identifies strategies for NGOs and for other sector actors including utilities and government agencies to maximise the benefits of NGO engagement in the sanitation sector.

Making decentralised systems viable: a guide to managing decentralised assets and risks

Decentralised systems have the potential to provide a viable option for long term sustainable management of household wastewater. Yet, at present, such systems hold an uncertain status and are frequently omitted from consideration. Their potential can only be realised with improved approaches to their management, and improved methods to decision-making in planning of wastewater systems. The aim of this paper is to demonstrate the value of a novel framework to guide the planning of decentralised systems so that asset management and risk management are explicitly considered. The framework was developed through a detailed synthesis of literature and practice in the area of asset management of centralised water and wastewater systems, and risk management in the context of decentralised systems. Key aspects of the framework are attention to socio-economic risks as well as engineering, public health and ecological risks, the central place of communication with multiple stakeholders and establishing a shared asset information system. A case study is used to demonstrate how the framework can guide a different approach and lead to different, more sustainable outcomes, by explicitly considering the needs and perspectives of homeowners, water authorities, relevant government agencies and society as a whole.

Case studies of change--addressing family support needs of rural GPs

The National Rural Faculty of the Royal Australian College of General Practitioners received commonwealth funding between 2000-2002 to develop a rural medical family support project. There were three elements to this project: a counselling and communication skills or mentoring workshop for rural GP spouses in each state. The development of a resource kit of existing rural medical family support strategies, and the piloting of a range of strategies designed to address family support needs in collaboration with rural GPs, registrars and their families. This article focusses on the last of these three elements.

The selective glycine antagonist gavestinel lacks phencyclidine-like behavioral effects

Gavestinel [GV150526A; ( E)-3[(phenylcarbamoil)ethenyl]-4,6-dichloroindole-2-carboxylic acid sodium salt] is a selective antagonist at the strychnine-insensitive glycine site of the -methyl-D-aspartate (NMDA) receptor. It was tested for its ability to substitute for phencyclidine (PCP) in rats and rhesus monkeys trained to discriminate PCP from saline, under a two-lever fixed-ratio (FR) food reinforcement schedule, and for its ability to maintain responding in rhesus monkeys trained to self-administer PCP under a FR reinforcement schedule. No PCP-lever responding was observed after gavestinel (1-56 mg/kg i.p.) administration to rats discriminating PCP (2.0 mg/kg i.p.) from saline. The highest dose of gavestinel (100 mg/kg i.p.) tested eliminated responding. Likewise, no PCP-lever responding was observed after gavestinel (1-30 mg/kg s.c.) administration to rhesus monkeys discriminating PCP (0.08 or 0.1 mg/kg i.m.) from saline; the highest dose of gavestinel (30 mg/kg s.c.) tested reduced response rates to approximately 50% of those observed after its vehicle ( -cyclodextrin in 0.9% saline). Gavestinel (0.1-1 mg/kg per i.v. infusion) was not self-administered by rhesus monkeys that reliably self-administered PCP (0.0056 or 0.01 mg/kg per i.v. infusion). Infusion rates at the highest dose were typically lower than those for vehicle or saline, suggesting behavioral activity. Together, these results suggest that at behaviorally active doses gavestinel is not PCP-like and is likely to have low abuse liability.

(+)-N-Allylnormetazocine (NANM)-like discriminative stimulus effects of N-methyl-D-aspartate (NMDA) antagonists

The effects of the competitive NMDA antagonists, 2-amino-4,5-(1,2-cyclohexyl)-7-phosphonoheptanoic acid (NPC 12626) and 3-(2-carboxypiperazin-4-yl) propyl-l-phosphonic acid (CPP), were compared to those of the noncompetitive NMDA antagonists, phencyclidine (PCP) and (+)-5-methyl-10, 11-dihydro-5H-dibenzo (a,d) cyclohepten-5, 10-imine maleate (MK-801), in male Sprague-Dawley rats trained to discriminate 5 mg/kg (+)-N-allyl-normetazocine (NANM) from saline under a standard two-lever fixed-ratio 32 schedule of food reinforcement. (+) - NANM, PCP and MK-801 dose-dependently substituted for the training dose of (+) - NANM in all rats tested. Conversely, NPC 12626 and CPP produced no more than an average of 73% (+) - NANM-lever responding at doses that also reduced response rates by more than 50% of corresponding control response rates. Methohexital also produced an average of 50% (+) - NANM-lever responding at doses that reduced response rates. In addition to supporting a role for the PCP receptor in transducing the discriminative stimulus effects of (+) - NANM, these results lend further evidence for differences in the behavioral effects of competitive and noncompetitive NMDA antagonists.

A common strategic language for clinicians and senior managers

Effective strategic analysis of existing and potential services requires a framework which is relevant and understandable to both clinicians and senior managers. Our work with NHS trusts has developed a framework based on analysis of services into four principal service streams--emergency general hospital, non-emergency general hospital, specialist general hospital and tertiary. Relating service streams to clinical specialties provides a matrix which can provide a basis for an initial analysis of the current and prospective clinical services portfolio, allowing drilling down into the detail and back up to the overall picture. Portfolio effectiveness is assessed by considering overall viability consisting of three interrelated elements--clinical, market and financial viability. The interrelationship of service streams, clinical specialties and viability allows the trust board and key clinicians to share insights into the current and potential systemic linkages between these three elements and to develop a vision of future strategic direction.

Generation of stable test atmospheres of cocaine base and its pyrolyzate, methylecgonidine, and demonstration of their biological activity

Generating controlled test atmospheres of known chemical identity and airborne concentration upon demand is a significant technical obstacle that limits the scope and repeatability of studies of inhaled substances. We addressed this problem as applied to the generation of atmospheres that result from heating crack cocaine, which include both cocaine and its pyrolyzate methylecgonidine (MEG). A condensation aerosol generator was used to generate atmospheres comprised of monodisperse particles of cocaine, MEG, or mixtures of both that are of submicron size suitable for deposition in the alveolar region of primates. Compressed air seeded with nanometer-size sodium chloride particles was passed through a constant depth of molten cocaine or MEG in a bead bed, reheated, and condensed to an aerosol within an annulus of cold air. To achieve control of a mixture of both compounds, MEG was condensed onto cocaine particles in a separate coating step. On-line analytical instruments provided verification of airborne concentration, estimates of particle size, and dispersion as well as chemical identity. Specific airway conductance (SGaw), heart rate, and rectal and skin temperatures were measured in squirrel monkeys breathing atmospheres containing condensation aerosols of cocaine or MEG free base. SGaw was reduced after inhalation of either base, and both induced temperature and cardiovascular changes, demonstrating that the aerosols so generated had biological activity.

Effects of methylecgonidine on acetylcholine-induced bronchoconstriction and indicators of lung injury in guinea pigs

The fumarate salt of methylecgonidine (MEG; anhydroecgonine methylester), a pyrolysis product of cocaine, has previously been shown to antagonize contractions of guinea pig isolated trachea induced by acetylcholine (ACh) and other spasmogenics. We determined the effects of MEG fumarate on ACh-induced bronchoconstriction in vivo. Specific airway conductance (SGaw) was measured in guinea pigs receiving 30-300 mg/kg s.c. MEG fumarate and exposed one hour later to nebulized ACh (0.2-3.2%; by inhalation). MEG fumarate did not induce any changes in SGaw; neither did it antagonize dose-dependent decreases in SGaw induced by ACh. However, tremors, salivation, startle and increased numbers of fecal boli were observed after MEG administration. Thus, unlike antagonism of ACh-induced contractions of guinea pig isolated trachea observed in vitro, MEG fumarate does not antagonize ACh-induced bronchoconstriction in vivo, even at doses which induced changes in grossly-observable behavior. Inhalation of a condensation aerosol of MEG base induced lung damage as evidenced by the presence of blood and higher levels of protein and lactate dehydrogenase in the lung lavage fluid of MEG-treated animals than of control animals. Aerosols of MEG fumarate, on the other hand, did not induce lung damage when inhaled. These results extend previous observations that MEG base may contribute to detrimental pulmonary effects of crack smoking.

Pulmonary effects of the cocaine pyrolysis product, methylecgonidine, in guinea pigs

The pulmonary effects of the cocaine pyrolysis product, methylecgonidine (MEG; anhydroecgonine methyl ester), were assessed in guinea pigs. Specific airway conductance (SGaw), which decreases during bronchoconstriction, was measured in guinea pigs exposed to atmospheres containing a condensation aerosol of MEG free base (13 +/- 1 mg/liter of air), nebulized MEG fumarate (3 and 12% in phosphate buffered saline) or nebulized acetylcholine chloride (0.2 and 0.4% in phosphate buffered saline). A decrease in SGaw to 24.0 +/- 4.2% (mean +/- 2 S.E.M.) of baseline levels was observed in guinea pigs breathing MEG free base. A decrease to 28.4 +/- 4.5% of baseline was observed following administration of 0.4% acetylcholine. No change in SGaw was measured in guinea pigs exposed to 3% MEG fumarate but SGaw was reduced to 69.3 +/- 5.3% of baseline after exposure to 12% MEG fumarate. MEG free base poses an alkaline challenge to the lung, 3% MEG fumarate is neutral (pH approximately 7.4) and 12% MEG fumarate is acidic (pH approximately 4.3); thus, MEG free-base and 12% MEG fumarate might provoke a reflex bronchoconstriction due to direct pulmonary irritant effects. These results suggest that MEG free base produced during crack pyrolysis may play a role in bronchoconstriction observed in crack smokers.

Behavioral pharmacology of NPC 17742, a competitive N-methyl-D-aspartate (NMDA) antagonist

The behavioral effects of the competitive N-methyl-D-aspartate (NMDA) antagonist 2R,4R,5S-2-amino-4,5-(1,2-cyclohexyl)-7-phosphonoheptanoate (NPC 17742) were compared with those of its parent compound, 2-amino-4,5-(1,2-cyclohexyl)-7-phosphonoheptanoate (NPC 12626), and other reference agents in a variety of operant-based tasks in rodents. In mice trained to lever press under a fixed-ratio (FR) 20 reinforcement schedule, NPC 17742 was 6.2 times more potent than NPC 12626 and equipotent with the competitive NMDA antagonist [E]-2-amino-4-methyl-5-phosphono-3-penteneoic acid (CGP 37849) in reducing rates of responding. NPC 17742 was also 3.5 and 4.5 times more potent than [+-]cis-4-phosphonomethyl-2-piperidine carboxylate (CGS 19755) and [+-] 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonate (CPP), respectively, and half as potent as 3SR, 4aRS, 6SR, 8aRS-6-(phosphonomethyl)-1,2,3,4,4a,5,6,7,8,8a- decahydroisoquinoline-3-carboxylate (LY 274614) in this paradigm. In rats trained to discriminate 4.0 mg/kg NPC 17742 from saline, NPC 17742 was 5.7 times more potent than NPC 12626 in substituting for NPC 17742. CGS 19755 also substituted for NPC 17742, but a maximum of only 50% NPC 17742 lever responding was observed after LY 274614 administration. In rats trained to lever press in a modified Geller-Seifter procedure, NPC 17742 and NPC 12626, like the benzodiazepine chlordiazepoxide, increased rates of punished responding. Neither tolerance nor sensitization to the anti-punishment effects were observed upon administration of NPC 17742 for 5 consecutive days. The results are consistent with NPC 17742 being a potent, systemically active compound whose behavioral effects are mediated through interaction with the NMDA receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacological specificity of N-methyl-D-aspartate discrimination in rats

The purpose of this study was to provide further information on the usefulness of N-methyl-D-aspartate (NMDA) discrimination in rats as a behavioral model for NMDA receptor activation. The pharmacological specificity of the NMDA discriminative stimulus was examined in rats trained to discriminate 30 mg/kg, i.p. NMDA from saline using a 2-lever fixed-ratio (FR) 32 food reinforcement schedule. Pharmacologically diverse centrally-acting agents were examined for their ability to substitute for NMDA. Morphine did not substitute for NMDA; neither did the central stimulants, caffeine and (+)-amphetamine, which produced a maximum mean of only 16 and 35% NMDA-lever responding, respectively. Pentylenetetrazol and picrotoxin also did not substitute for NMDA. Compounds interacting with cholinergic neurotransmission including nicotine, physostigmine, arecoline and mecamylamine, produced at best, only intermediate levels of NMDA-lever responding (32-61%), with the highest levels of NMDA-lever responding generally occurring at doses that also reduced rates of responding. These results suggest that the discriminative stimulus properties of NMDA are dissimilar from those of a number of centrally-acting drugs. Combined with the results of studies indicating that the NMDA discriminative stimulus can be antagonized by competitive NMDA antagonists, these results provide further evidence that NMDA receptor activation is the basis of NMDA discrimination and that this model may be useful for studying site-selective NMDA agonists and antagonists.

Pharmacological profile of NPC 17742 [2R,4R,5S-(2-amino-4,5-(1, 2-cyclohexyl)-7-phosphonoheptanoic acid)], a potent, selective and competitive N-methyl-D-aspartate receptor antagonist

2R,4R,5S-(2-amino-4,5-(1,2-cyclohexyl)-7-phosphonoheptanoic acid) (NPC 17742), the most potent isomer of the mixture 2-amino-4,5-(1,2-cyclohexyl)-7-phosphonoheptanoic acid (NPC 12626), was evaluated for activity in tests associated with receptors for excitatory amino acids. In receptor binding assays, NPC 17742 was selective for the N-methyl-D-aspartate (NMDA) receptor with a potency comparable to that of D(-, -3-(2-carboxypiperazine-4-yl)propyl-1-phosphonic acid. Like (+/-)cis-4-phosphono-methyl-2-piperidine carboxylic acid (CGS 19755) and (+/-)(E)-2-amino-4-methyl-5-phosphono-3-penteneoic acid (CGP 37849), NPC 17742 competitively inhibited NMDA-induced enhancement of 1-[(2-thienyl)cyclohexyl]piperidine binding to the NMDA receptor ionophore and partially inhibited [3H]glycine binding to strychnine-insensitive sites. In contrast, NPC 17742 and CGP 37849 inhibited Mg(++)-stimulated 1-[(2-thienyl)cyclohexyl]piperidine binding in a noncompetitive fashion. In voltage-clamped Xenopus oocytes expressing excitatory amino acid receptors, NPC 17742 (pKB = 6.91) was equipotent with CGP 37849 (pKB = 7.17) in inhibiting NMDA-induced inward currents. Likewise, NPC 17742 (ED50 = 2.68 mg/kg) was equipotent with CGP 37849 and CGS 19755 in blocking NMDA-induced convulsions, but was less potent than these two compounds in the maximal electroshock test. Unlike CGP 37849 or CGS 19755, NPC 17742 potently antagonized seizures induced by pentylenetetrazol. In a model of global ischemia, low doses of NPC 17742 given either before or after ischemic result were effective in blocking damage to hippocampal CA1 neurons. The pharmacologic responses to NPC 17742 occurred at doses 30- to 300-fold lower than the acute lethal dose.(ABSTRACT TRUNCATED AT 250 WORDS)

Systemic magnesium chloride administration fails to produce phencyclidine-like discriminative stimulus effects in rats

Systemic administration of magnesium chloride was evaluated for phencyclidine (PCP)-like discriminative stimulus effects. Six rats were trained to discriminate PCP (1.25 mg/kg, i.p.) from saline under a two-lever fixed-ratio 32 schedule of food reinforcement. Magnesium chloride (10-80 mg/kg, i.p.) failed to substitute for PCP, with no dose producing greater than an average of 21% PCP-lever responding. At doses greater than 40 mg/kg, magnesium chloride decreased rates of responding, providing evidence that it was evaluated over a behaviorally-relevant dose range. The results provide further evidence for differences in the behavioral effects of drugs which antagonize N-methyl-D-aspartate receptor-mediated neurotransmission by different mechanisms.

NMDA antagonists: lack of antipunishment effect in squirrel monkeys

Effects of the noncompetitive N-methyl-D-aspartate (NMDA) antagonist phencyclidine (PCP) and competitive antagonists 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP) and 2-amino-4,5-(1,2-cyclohexyl)-7-phosphonoheptanoic acid (NPC 12626) were studied in 6 squirrel monkeys trained under a multiple schedule of unpunished and punished lever pressing. PCP (0.03-0.3 mg/kg, IM) failed to produce increases in punished responding, even at doses that produced extreme response-rate decreases in nonpunishment components. Similarly, CPP (1-17 mg/kg) and NPC 12626 (3-30 mg/kg) did not produce increases in punished responding at any dose tested. Repeated administration of NPC 12626 (17 mg/kg) for 4 consecutive days did not result in increased rates of punished responding. The benzodiazepine anxiolytic midazolam (0.3 mg/kg) and, to a lesser extent, the barbiturate pentobarbital (5.6 mg/kg), produced increases in punished responding in the same subjects at doses that did not markedly affect unpunished responding. Coadministration of PCP (0.03 mg/kg) with doses of midazolam ranging from 0.03-3 mg/kg did not produce changes in the midazolam dose-response curve for either unpunished or punished responding. These results fail to support findings in rats that NMDA antagonists produce antipunishment effects similar to those of benzodiazepine anxiolytics.

Pentobarbital-like effects of N-methyl-D-aspartate antagonists in mice

The effects of the competitive N-methyl-D-aspartate (NMDA) antagonist, 3-[(+/-)-2-carboxypiperazin-4-yl]propyl-1-phosphonic acid (CPP), and of the noncompetitive NMDA antagonist, dizocilpine (MK-801), were determined in mice trained to discriminate pentobarbital (20 mg/kg i.p.) from saline under a standard two-lever fixed-ratio 20 schedule of sweetened milk reinforcement. CPP substituted for pentobarbital; however, pentobarbital-lever responding was usually associated with decreases in response rates. Dizocilpine produced a maximum average of only 62% pentobarbital-lever responding, accompanied by a 50% decrease in response rates. These results suggest that pentobarbital-like discriminative stimulus effects are more likely to be produced by competitive than by noncompetitive NMDA antagonists. This extends previous observation in rats and provides further evidence for differences in the behavioral effects of competitive and noncompetitive NMDA antagonists and for an overlap in the behavioral pharmacology of NMDA antagonists and classical CNS depressants.

The behavioral pharmacology of NMDA receptor antagonists

There is considerable interest in the development of NMDA antagonists as potential therapeutic agents in the treatment of convulsant, neurodegenerative and anxiety disorders. Because the clinical use of phencyclidine (PCP) has been precluded by its psychotomimetic effects and abuse potential, there has been concern that other NMDA antagonists including those acting competitively might produce similar untoward effects. However, the studies in animals, reviewed here by Joyce Willetts, Robert Balster and David Leander, suggest that while there are certain similarities in the behavioral effects of PCP-like and competitive antagonists, there are also differences. These differences have implications for the development of NMDA antagonists with less likelihood for producing PCP-like side-effects.

Effects of competitive and noncompetitive N-methyl-D-aspartate (NMDA) antagonists in rats trained to discriminate NMDA from saline

Competitive and noncompetitive N-methyl-D-aspartate (NMDA) antagonists and other central nervous system depressants were assessed for their ability to antagonize the discriminative stimulus effects of NMDA in rats trained under a standard two-lever fixed ratio schedule of food reinforcement. The competitive NMDA antagonists, 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonate and NPC 12626 [2-amino-4,5-(1,2-cyclohexyl)-7-phosphonoheptanoate], dose-dependently antagonized NMDA-lever selection at doses that did not affect rates of responding. Conversely, the noncompetitive NMDA antagonists, phencyclidine, MK-801 [(+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d)cyclohepten-5,10-imine maleate] and (+)-N-allylnormetazocine, as well as pentobarbital and diazepa, all reduced response rates dose-dependently without antagonism of NMDA-lever responding. In stimulus generalization tests, NPC 12626 and 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonate at doses higher than those required to antagonize NMDA, often elicited NMDA-lever responding. The mechanisms underlying the similarities in the interoceptive stimuli produced by NMDA and its competitive antagonists remain to be determined. These results indicate that although competitive NMDA antagonists antagonize effects of NMDA without concomitant behavioral disruption, noncompetitive NMDA antagonists and central nervous system depressants are behaviorally disruptive at doses that do not antagonize NMDA. The results provide further evidence for differences in the behavioral profiles of competitive and noncompetitive NMDA antagonists.

Cholinergic effects on spinal dorsal horn neurons in vitro: an intracellular study

The cholinoceptive properties of dorsal horn neurons (lamina III-V) were investigated by means of intracellular recordings from the rat isolated spinal cord slice preparation. In half of the neurons investigated, acetylcholine (ACh) evoked a dose-dependent slow depolarization and increase in excitability; hyperpolarization was observed in 10% of neurons. Acetyl-beta-methylcholine (MCh) similarly depolarized 39% and hyperpolarized 25% of neurons tested; depolarization was also observed following bethanechol. Responses to the muscarinic agonists were abolished by atropine (10(-5) M). Nicotine depolarized 84% of tested neurons; dihydro-beta-erythroidine (5 x 10(-5) M) and (+)-tubocurarine (10(-6) M) antagonized this depolarization. ACh-, MCh- and nicotine-induced depolarizations, associated with changes in input resistance, were maintained in the presence of tetrodotoxin (10(-6) M). Substance P, as well as repetitive electrical stimulation of the dorsal root, also evoked depolarization in ACh-sensitive neurons. Atropine, but not (+)-tubocurarine, diminished responses to both substance P and dorsal root stimulation. These results indicate that dorsal horn neurons are ACh-sensitive and possess both muscarinic and nicotinic receptors. In addition, the parallel sensitivity of neurons to muscarinic agonists, substance P and dorsal root stimulation, as well as the parallel antagonistic effect of atropine, are supportive of a common ionic mechanism underlying the activation of muscarinic and substance P receptors.

Pentobarbital-like discriminative stimulus effects of N-methyl-D-aspartate antagonists

The discriminative stimulus effects of competitive and noncompetitive N-methyl-D-aspartate (NMDA) antagonists were compared in rats trained to discriminate sodium pentobarbital (5.0 mg/kg i.p.) from saline under a two-lever fixed ratio 32 schedule of food reinforcement. The competitive NMDA antagonist 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP) substituted for pentobarbital at doses that did not disrupt rates of responding. The proposed competitive NMDA antagonist NPC 12626 [2-amino-4,5-(1,2-cyclohexyl)-7-phosphonoheptanoic acid] also substituted for pentobarbital. The benzodiazepine antagonist Ro15-1788 did not antagonize the pentobarbital-like discriminative stimulus effects of CPP. The noncompetitive NMDA antagonists phencyclidine and MK-801 [(+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d)cyclohepten-5,10-imine maleate] produced a maximum average of only 42 and 38%, respectively, pentobarbital-lever responding at doses that also substantially reduced response rates. These results suggest that the competitive NMDA antagonists CPP and NPC 12626 share discriminative stimulus properties with pentobarbital. However, the pentobarbital-like discriminative stimulus effects of CPP are probably not mediated through interaction with benzodiazepine receptors sensitive to Ro15-1788. In addition, because phencyclidine and MK-801 did not fully substitute for pentobarbital, these results provide further evidence for differences in the discriminative stimulus properties of competitive and noncompetitive NMDA antagonists.

Drug discrimination based on the competitive N-methyl-D-aspartate antagonist, NPC 12626

The discriminative stimulus effects of the N-methyl-D-aspartate (NMDA) antagonists 3-([+/-]-2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP) and phencyclidine were assessed in a drug discrimination based on the competitive NMDA antagonist 2-amino-4,5-(1,2-cyclohexyl)-7-phosphonoheptanoic acid (NPC 12626). Adult male Sprague-Dawley rats were trained to discriminate NPC 12626 from saline using a standard two-lever fixed ratio 32 schedule of food reinforcement. NPC 12626 dose-dependently substituted for the training dose (20 mg/kg IP) with an ED50 of 9.5 mg/kg. The competitive NMDA antagonist CPP completely substituted for NPC 12626 (ED50 = 1.4 mg/kg IP). The non-competitive NMDA antagonist phencyclidine, as well as pentobarbital and NMDA, failed to substitute completely for NPC 12626, even at doses of these drugs that reduced response rates. These data indicate that the discriminative stimulus properties of NPC 12626 are selective and shared by CPP but not by phencyclidine, pentobarbital or NMDA. The emerging evidence for differences in the discriminative stimulus effects of competitive NMDA antagonists and phencyclidine suggests that competitive antagonists such as NPC 12626 and CPP may not have phencyclidine-like abuse liability.

The discriminative stimulus effects of N-methyl-D-aspartate antagonists in phencyclidine-trained rats

The discriminative stimulus effects of two competitive N-methyl-D-aspartate (NMDA) antagonists, 2-amino-7-phosphonoheptanoate (APH) and 3-[(+-)-2-carboxypiperazin-4-yl]propyl-1-phosphonate (CPP), were assessed in rats trained to discriminate phencyclidine from saline. Systemically administered APH (10-60 mg/kg i.p.) failed to elicit phencyclidine-lever responding; however, partial generalization from phencyclidine occurred following intracerebroventricular (i.c.v.) administration of APH (1.5-30 micrograms). Systemic and central administration of CPP (3-30 mg/kg i.p.; 0.1-10 micrograms i.c.v.) also resulted in partial generalization from phencyclidine. Partial generalization was also obtained with methohexital (5-30 mg/kg i.p.). However, generalization to APH, CPP and methohexital was usually accompanied by decreased response rates, and response rate decreases frequently occurred without appreciable phencyclidine-lever selection, indicating that these drugs also had no phencyclidine-like behavioral effects. The drug di-ortho-tolyl guanidine (DTG) which binds with high-affinity to sigma receptors failed to elicit phencyclidine-lever responding, even at doses which reduced response rates. These findings suggest that although competitive NMDA antagonists share some discriminative stimulus properties with phencyclidine, there is not a complete overlap in the discriminative stimulus properties of competitive and non-competitive NMDA antagonists. Furthermore, the discriminative stimulus effects of APH and CPP were no more similar to phencyclidine than those of methohexital.

Phencyclidine-like discriminative stimulus properties of MK-801 in rats

The discriminative stimulus properties of the N-methyl-D-aspartate (NMDA) antagonist MK-801 ((+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d)cyclohepten-5,10-imine) were investigated in rats trained to discriminate phencyclidine (PCP; 1.25 mg/kg i.p.) from saline on a standard two-lever fixed ratio 32 schedule of food reinforcement. MK-801 was generalized from PCP in a dose-dependent manner, with an ED50 of 0.10 mg/kg i.p. The ED50 for PCP was 0.7 mg/kg io.p. MK-801 is, therefore, a very potent PCP-like drug which may share cellular mechanisms and other effects with PCP, including the antagonism of NMDA.

Receptor mediation of the discriminative stimulus properties of phencyclidine and sigma-opioid agonists

Evidence has accumulated that the discriminative stimulus effects of phencyclidine (PCP) may be transduced by a specific receptor in mammalian brain. Two major lines of evidence support this hypothesis. One is the structure-activity correlation that arylcyclohexylamine analogs of PCP have for PCP-like discriminative effects and displacement of [3H]PCP binding. The other, even stronger, evidence is that representatives of some nonarylcyclohexylamine classes of drugs are both generalized from PCP and have activity at PCP-binding sites. These include the psychotomimetic sigma-agonist opioids such as (+)-N-allylnormetazocine (NANM), the 1,3-substituted dioxolanes dexoxadrol and etoxadrol and some benz(f)isoquinolines. Early evidence suggested that there may be a complete overlap in the discriminative effects and receptor systems for PCP and sigma-agonists, and there continues to be evidence to support the commonality of these drug groups. On the other hand, binding studies with radiolabeled sigma agonists have revealed a non-PCP site. The role of this site in the behavioral actions of sigma-agonists is at present unknown. PCP analogs and other PCP-like drugs also can function as reinforcers for self-administration behavior, suggesting that the same cellular mechanisms may be responsible for both discriminative and reinforcing stimulus effects of these drugs. PCP has been shown to block many of the in vitro and in vivo effects of N-methyl-D-aspartate (NMDA), a putative specific agonist for a subtype of excitatory amino acid receptor. Recent evidence that NMDA antagonists are generalized from PCP in rats and pigeons provides evidence that modification of excitatory amino neurotransmission may be a physiological function of the PCP receptor and that this receptor complex may be involved in PCP's discriminative stimulus effects.

The acute and chronic effects of capsaicin on slow excitatory transmission in rat dorsal horn

The acute and chronic effects of capsaicin on rat spinal dorsal horn neurons and the excitatory transmission in the dorsal horn were investigated by means of intracellular recording techniques in the spinal cord slice preparation. Bath application of capsaicin (1-2 X 10(-5) M) produced in a majority of cells a prolonged depolarization associated with an increase in synaptic activity and intense neuronal discharges. During and immediately following the capsaicin depolarization, repetitive stimulation of a dorsal root failed to elicit the slow depolarization. After neonatal capsaicin treatment the proportion of dorsal horn neurons exhibiting the slow excitatory transmission was markedly reduced, however, the fast excitatory postsynaptic potentials were present in all examined cells. In addition, the proportion and sensitivity of the cells responding with a slow depolarization to substance P increased.

Fine structural changes in cat L7 ventral horn neurones after chronic sub LD50 DFP

The fine structural changes in the ventral anterior horn of spinal segment L7, have been studied in adult cats after single and chronic sub LD50 (0.1 to 0.75 mg/kg SC with a cumulative range of 1.3 mg/kg to 10.5 mg/kg) low dose exposure to diisopropylfluorophosphate (DFP). Only the motoneurons of the chronically treated animals show an increase in the number of lysosomes, neurofilaments and vesicle-like structures. A large number of coated vesicles is observed within axons and axon terminals of both acute and chronically treated animals. Morphological evidence of axon and terminal degeneration is seen only in chronically treated animals. The present study shows that chronic sub LD50 low dose administration of DFP over periods from 5 to 21 days results in degenerative changes of presynaptic terminals and axons, with the severity of the changes being dependent on dose and duration of treatment. The data are interpreted by comparison with single high dose exposure reported in the literature with a discussion of acute and delayed neurotoxic effects of DFP, on the central nervous system.