Epigenetic predictors of lifestyle traits applied to the blood and brain

Modifiable lifestyle factors influence the risk of developing many neurological diseases. These factors have been extensively linked with blood-based genome-wide DNA methylation, but it is unclear if the signatures from blood translate to the target tissue of interest-the brain. To investigate this, we apply blood-derived epigenetic predictors of four lifestyle traits to genome-wide DNA methylation from five post-mortem brain regions and the last blood sample prior to death in 14 individuals in the Lothian Birth Cohort 1936. Using these matched samples, we found that correlations between blood and brain DNA methylation scores for smoking, high-density lipoprotein cholesterol, alcohol and body mass index were highly variable across brain regions. Smoking scores in the dorsolateral prefrontal cortex had the strongest correlations with smoking scores in blood (r = 0.5, n = 14, P = 0.07) and smoking behaviour (r = 0.56, n = 9, P = 0.12). This was also the brain region which exhibited the largest correlations for DNA methylation at site cg05575921 - the single strongest correlate of smoking in blood-in relation to blood (r = 0.61, n = 14, P = 0.02) and smoking behaviour (r = -0.65, n = 9, P = 0.06). This suggested a particular vulnerability to smoking-related differential methylation in this region. Our work contributes to understanding how lifestyle factors affect the brain and suggest that lifestyle-related DNA methylation is likely to be both brain region dependent and in many cases poorly proxied for by blood. Though these pilot data provide a rarely-available opportunity for the comparison of methylation patterns across multiple brain regions and the blood, due to the limited sample size available our results must be considered as preliminary and should therefore be used as a basis for further investigation.

Tissue-Specific Immunopathology in Fatal COVID-19

Rationale: In life-threatening coronavirus disease (COVID-19), corticosteroids reduce mortality, suggesting that immune responses have a causal role in death. Whether this deleterious inflammation is primarily a direct reaction to the presence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) or an independent immunopathologic process is unknown.

Objectives: To determine SARS-CoV-2 organotropism and organ-specific inflammatory responses and the relationships among viral presence, inflammation, and organ injury.

Methods: Tissue was acquired from 11 detailed postmortem examinations. SARS-CoV-2 organotropism was mapped by using multiplex PCR and sequencing, with cellular resolution achieved by in situ viral S (spike) protein detection. Histologic evidence of inflammation was quantified from 37 anatomic sites, and the pulmonary immune response was characterized by using multiplex immunofluorescence.

Measurements and Main Results: Multiple aberrant immune responses in fatal COVID-19 were found, principally involving the lung and reticuloendothelial system, and these were not clearly topologically associated with the virus. Inflammation and organ dysfunction did not map to the tissue and cellular distribution of SARS-CoV-2 RNA and protein between or within tissues. An arteritis was identified in the lung, which was further characterized as a monocyte/myeloid-rich vasculitis, and occurred together with an influx of macrophage/monocyte-lineage cells into the pulmonary parenchyma. In addition, stereotyped abnormal reticuloendothelial responses, including excessive reactive plasmacytosis and iron-laden macrophages, were present and dissociated from viral presence in lymphoid tissues.

Conclusions: Tissue-specific immunopathology occurs in COVID-19, implicating a significant component of the immune-mediated, virus-independent immunopathologic process as a primary mechanism in severe disease. Our data highlight novel immunopathologic mechanisms and validate ongoing and future efforts to therapeutically target aberrant macrophage and plasma-cell responses as well as promote pathogen tolerance in COVID-19.

Furosemide in the treatment of phosgene induced acute lung injury

METHOD

Using previously validated methods, 16 anaesthetised large white pigs were exposed to phosgene (target inhaled dose 0.3 mg kg(-1)), established on mechanical ventilation and randomised to treatment with either nebulised furosemide (4 ml of 10 mg x ml(-1) solution) or saline control. Treatments were given at 1, 3, 5, 7, 9, 12, 16 and 20 hours post phosgene exposure; the animals were monitored to 24 hours following phosgene exposure.

RESULTS

Furosemide treatment had no effect on survival, and had a deleterious effect on PaO2: FiO2 ratio between 19 and 24 hours. All other measures investigated were unaffected by treatment.

CONCLUSION

Nebulised furosemide treatment following phosgene induced acute lung injury does not improve survival and worsens PaO2: FiO2 ratio. Nebulised furosemide should be avoided following phosgene exposure.

Tissue and organ donation for research in forensic pathology: the MRC Sudden Death Brain and Tissue Bank

Novel methodological approaches to the investigation of brain and non-central nervous system disorders have led to increased demand for well-characterized, high quality human tissue samples, particularly from control cases. In the setting of the new Human Tissue legislation, we sought to determine whether relatives who have been suddenly bereaved are willing to grant authorization for research use of post mortem tissue samples and organs in sufficient numbers to support the establishment of a brain and tissue bank based in the forensic service. Research authorization was sought from families on the day prior to forensic post mortem examination followed up by written confirmation. We have to date selected individuals who have died suddenly (age range 1-89 years) and who were likely to have normal brains or who had displayed symptoms of a CNS disorder of interest to researchers, including psychiatric disorders. One hundred and eleven families have been approached during the first 2 years of this project. Research use of tissue samples was authorized by 96% of families and 17% agreed to whole brain donation. Audit of families' experience does not suggest that they are further distressed by being approached. Respondents expressed a clear view that the opportunity for research donation should be open to all bereaved families. Despite the sometimes long post mortem intervals, the quality of tissue samples is good, as assessed by a range of markers including Agilent BioAnalyzer quantification of RNA integrity (mean value 6.4). We conclude that the vast majority of families are willing to support research use of post mortem tissues even in the context of sudden bereavement and despite previous adverse publicity. The potential for acquisition of normal CNS and non-CNS tissues and of various hard-to-get CNS disorders suggests that efforts to access the forensic post mortem service for research material are eminently worthwhile.

The dynamics of heroin use; implications for intervention

STUDY OBJECTIVE

To use a readily available dataset to detect periods of epidemic change and to examine the progression of heroin epidemics in different geographical areas. To consider the implications of epidemic change for strategies to tackle drug misuse.

DESIGN

Comparison of trends in new treatment demand, observed incidence, and age specific population rates for treated heroin users in two geographical areas.

PARTICIPANTS

Heroin users recorded to have sought treatment.

MAIN RESULTS

The areas studied seem to show differences with respect to trends in new treatment demand, incidence of heroin use and distribution of age specific population rates; indicating that they may be at different epidemic stages.

CONCLUSIONS

These analyses show how areas may differ with respect to epidemic progression of heroin use. It is essential that government strategies, and local responses to these, should be cognisant of these dynamics.

Hidden need for drug treatment services: measuring levels of problematic drug use in the North West of England

BACKGROUND

In the North West of England, data on drug users are routinely collected from a variety of agencies including specialist treatment centres, police and probation services. However, the covert nature of drug use means that alone, these conventional monitoring systems cannot provide the epidemiology required to target and develop drug treatment and prevention initiatives.

METHODS

Utilizing surveillance data and capture-recapture techniques we estimate the rates of problematic drug users by age and sex in five North West health authorities and one local authority.

RESULTS

Analyses show concentrations of problematic drug use in large metropolitan areas (Liverpool and Manchester) with levels as high as 34.5 and 36.5 per 1000 population (ages 15-44), respectively, and, for males, levels exceed 50 per 1000 in three authorities. Patterns of prevalence for those aged 25 and over differed from those in the younger age groups, with disproportionate levels of young users outside metropolitan areas. The proportion of young users already in treatment (21.3 per cent) was lower (older users, 35.3 per cent), with overall proportions in treatment varying between health authorities (range 26.2-46.5 per cent).

CONCLUSION

With a multi-agency approach, established monitoring systems can be used to measure hidden populations of drug users. Estimates of the current populations of such users in the North West of England suggest that planned increases of people in treatment by 100 per cent would fail to accommodate even current level of problematic users. A holistic approach to new initiatives must ensure that the high level of relapse once drug users are discharged are reduced and that the needs of young users are addressed before prolonged treatment is required.

Cocaine misuse treatment in England

Three methods were used to identify the treatments given to cocaine misusers in England, and to make a preliminary assessment of effectiveness. First, a postal survey of all known drug misuse treatment services ascertained approximate numbers of cocaine misusers presenting and receiving a specified range of treatments. Secondly, staff at selected services were interviewed regarding treatment policies, and asked to subjectively rate short-term and long-term effectiveness. Thirdly, a cohort of individuals in treatment were studied prospectively to assess changes in drug usage and associated problems. Fifty percent of services responded to the survey, but there was known to be significant duplication in service listings and it is considered that a representative pattern of clinical activity has been detected. Approximately half those services had recently treated cocaine misusers, mainly using counselling, residential rehabilitation, and pharmacological treatments, in which 32 different medications were identified. Acupuncture was prominent in a minority of services. Staff interviews suggested several principles in managing cocaine misusers, while all treatments were rated as being more effective in short-term relief of withdrawal features than in enabling longer-term abstinence. The treatment cohort were mostly in residential rehabilitation, and marked reductions in drug use and related clinical and social problems were demonstrated.

Regulation of cell cycle re-entry by growth, survival and stress signalling pathways

The mitogen-activated and stress-activated protein kinases transduce signals from plasma membrane signalling machinery into the nucleus to modulate gene expression. By regulating the genomic response to environmental cues (growth factors, stresses) these pathways determine whether a cell re-enters the cell cycle, undergoes cell cycle arrest, senescence or apoptosis. We are particularly interested in how these pathways integrate with each other, and interact with the cell cycle machinery to achieve these discrete biological responses.

Inhibition of platelet aggregation with glyceryl trinitrate and xanthine oxidoreductase

Xanthine oxidoreductase (XOR) is a mammalian enzyme that possesses a series of redox centers, which use either NAD(+) or molecular oxygen for oxidation of the purines xanthine and hypoxanthine to uric acid. The ability of XOR to act as an NADH oxidase is a less well recognized function of the enzyme, and it is this function that we used to explore the metabolism of glyceryl trinitrate. The antiplatelet effect of nitric oxide (NO) on platelet aggregation was used as a bioassay to assess the bioconversion of glyceryl trinitrate to NO by XOR. The thromboxane mimetic U46619, 2 microM, was used to stimulate platelet aggregation in platelet-rich plasma prepared from healthy drug-free human volunteers. All incubations were carried out at 37 degrees C for 2 min after the addition of U46619. XOR produced a dose-dependent antiaggregant effect when incubated with glyceryl trinitrate (GTN), 220 microM. This did not occur when GTN or XOR was incubated with platelet-rich plasma independently. The antiaggregant effect of XOR plus GTN was dose dependently inhibited by allopurinol, with an IC(50) of 100 microM. The addition of superoxide dismutase (SOD), 100 U/ml produced a shift to the left in the antiaggregant dose-response curve for XOR. The IC(50) for XOR at 200 U/l without SOD was decreased to 80 U/l with SOD. Oxyhemoglobin, an extracellular NO scavenger, produced a dose-dependent, noncompetitive inhibition of the antiaggregant effect of XOR plus GTN. These findings suggest that GTN may be reduced to NO in vitro by the enzyme XOR in sufficient amounts to inhibit platelet aggregation.

Validation of the University of Manchester Drug Misuse Database

OBJECTIVE

The study was conducted to assess the validity and quality of data held by one of the UK regional drug misuse databases (DMD).

DESIGN

The research was multi-centred and used retrospective analysis to assess the validity of data held on the database.

SETTING

The Regional Database is managed at the University of Manchester Drug Misuse Research Unit and uses data returned by medical and non-medical services within the UK's former North Western Regional Health Authority.

MATERIAL

The research was largely based on analysis of the reporting or non-reporting to DMD of 1526 presentations by drug users to four community drug teams (CDTs) during the course of 1993. Two datasets were used: the DMD dataset, based on returns to the regional database from the agencies in question; and agency client records. Additionally the data included on a random sample of 300 database forms returned by these CDTs were compared with information contained in client records.

MAIN OUTCOME MEASURES

The study reports on how well DMD is functioning in relation to the correct reporting of episodes of problem drug use and the quality of data held.

RESULTS

A very high level of agreement (0.875 +/- 0.017, 95% CI, kappa coefficient 0.728) was established between reports sent in to the database and those expected by examination of agency records. The database figures underestimated the total number of episodes that should have been reported by a factor of 0.008. It was also established that 0.906 (+/- 0.018, 95% CI) of the reports made to the database were made correctly, that 0.178 (+/- 0.030, 95% CI) of eligible presentations were not reported, and that 0.166 (+/- 0.030, 95% CI) of ineligible presentations were mistakenly reported. Lastly, it was established that data were unnecessarily missing or inaccurately recorded in 0.027 of cases and that data entry errors occurred in 0.015 of cases.

CONCLUSIONS

The validation project showed that the DMD system is very reliable, providing accurate measures of the extent and nature of presenting problem drug use in the region under study.

Effect of pergolide on restless legs and leg movements in sleep in uremic patients

Restless legs syndrome (RLS) and periodic limb movements in sleep (PLMS) are disorders that are common and disturbing to uremic patients. The treatment of these is problematic. Eight patients on chronic hemodialysis and continuous peritoneal dialysis completed a double-blind placebo-controlled crossover study using incremental doses of pergolide up to 0.25 mg at bedtime for treatment of RLS and sleep disruption. Five patients (62.5%) noted subjective improvement in restless legs symptoms and sleep quality. Objective results were improved only slightly by treatment. The percentage of the first hour in bed during which leg movements occurred decreased from 20.5 +/- 6.0 to 11.5 +/- 3.3, p < 0.05. However, findings during sleep were less positive. The following measures were not significant between placebo and treatment: leg movements per hour of sleep [53.7 +/- 22.3 vs 35.8 +/- 11.8 (p = 0.2)]; and percentage of sleep time spent with leg movements [5.5% +/- 3.2 vs 4.4% +/- 1.4 (p = 0.37)]. Patients continued to have very disrupted sleep, and we could not document an objective improvement in sleep architecture. Thus, although pergolide at the dose of 0.25 mg at bedtime provided subjective improvement in symptoms of restless legs and quality of sleep, and objectively decreased leg movements during the first hour in bed, objectively sleep continued to be disrupted. In this small patient group, the response to pergolide was not uniform, and further investigation is required to test effectiveness at higher doses.

Development of indices for determining extracellular fluid sodium and water status in acute diabetic ketoacidosis: possible tools for clinical audit

The limitation of plasma sodium concentration as an indicator of extracellular hydration status in cases of acute diabetes is well recognized and could lead to individually inappropriate fluid therapy. However, in view of the small analytical and biological variations exhibited by plasma concentrations of protein, water, and sodium in health, we have developed simple laboratory indices that may better describe the extracellular environment. Preliminary data presented here for 20 patients with acute diabetic ketoacidosis admitted as emergencies to Crosshouse Hospital suggest that the type of approach we describe has the potential to supply meaningful therapeutic data to the managing physician and, therefore, merits further study in a clinical setting.

Development of indices for determining extracellular fluid sodium and water status in acute diabetic ketoacidosis: possible tools for clinical audit

The limitation of plasma sodium concentration as an indicator of extracellular hydration status in cases of acute diabetes is well recognized and could lead to individually inappropriate fluid therapy. However, in view of the small analytical and biological variations exhibited by plasma concentrations of protein, water, and sodium in health, we have developed simple laboratory indices that may better describe the extracellular environment. Preliminary data presented here for 20 patients with acute diabetic ketoacidosis admitted as emergencies to Crosshouse Hospital suggest that the type of approach we describe has the potential to supply meaningful therapeutic data to the managing physician and, therefore, merits further study in a clinical setting.

Nasal continuous positive airway pressure. A new treatment for nocturnal gastroesophageal reflux?

Nasal continuous positive airway pressure (CPAP) reduces nocturnal gastroesophageal reflux (GER) in obstructive sleep apnea syndrome (OSAS) patients. The primary objectives of our investigation were to determine if CPAP could reduce reflux in non-OSAS patients and, if so, by what mechanism. Esophageal pH was monitored for 48 h in six nocturnal reflux patients. During the first 24 h, basal reflux data were collected; the second night, nasal CPAP was administered (pressure = 8 cm H2O). Esophageal manometry was obtained in six healthy adult volunteers both on and off nasal CPAP (pressure = 8 cm H2O) to ascertain CPAP's effects on esophageal pressure and peristalsis. The six reflux patients experienced less nocturnal GER while on CPAP. The mean percent time esophageal pH < 4 was reduced from 27.7 +/- 10.0 to 5.8 +/- 2.6 (p < 0.004); the mean reflux duration dropped from 2.1 +/- 0.6 to 0.9 +/- 0.5 min (p < 0.03); and the mean duration of longest reflux improved from 84.3 +/- 32.6 to 13.8 +/- 6.9 min (p < 0.01). The CPAP raised the mean resting midesophageal pressure by 4.4 cm H2O (p < 0.01) and the mean resting lower esophageal pressure (LES) by 13.2 cm H2O (p < 0.02) in the healthy volunteers. Nasal CPAP effectively reduced nocturnal GER in six patients with nocturnal reflux. The antireflux activity of CPAP is likely due to passive elevation of intraesophageal pressure and possibly to reflex LES constriction.

The ability of trainee general practitioners to identify psychological distress among their patients

It is argued that a general practitioner's ability to make accurate ratings of psychological distress is partly determined by the rate at which patients emit cues that are indicative of such distress. This study addresses the behaviours of doctors which influence the rates at which patients emit such cues. Consultations were videotaped involving six General Practice Vocational Trainees, three of them poor, and three of them able identifiers of emotional illness. Consultations were selected so that each trainee was rated interviewing 4 patients with low GHQ scores, and 4 patients with high scores. Behaviours are described which lead to increased cue emission and which are also practised more frequently by able identifiers, while other behaviours reduce cue emission and are practised less frequently by them. Another set of behaviours is no more frequent among the able identifiers, but when practised by able identifiers is associated with increased cue emission by the patients, and when practised by poor identifiers with unaltered or decreased cue emission. Interviews that are 'patient-led' are associated with increased rates of cue emission, while those that are 'doctor-led' are associated with lower rates. The implications of these findings for training doctors working in general medical settings are discussed.

The effect of short-term nasal CPAP on Cheyne-Stokes respiration in congestive heart failure

We studied male patients (BMI = 27.6 +/- 3.4, mean +/- SD), mean age 54.1 +/- 8.9 years, with stable NYHA class 3-4 congestive heart failure (CHF) (LVEF = 24.3 +/- 11.5 percent) and normal daytime arterial blood gas values. These patients underwent three consecutive nights of full polysomnography; adaptation, control, and treatment with nasal CPAP. Each night's study was followed during the day by cognitive testing and multiple sleep latency tests (MSLT). The purpose of the study was to document the effect of nasal CPAP on these variables. The main findings of the study showed no significant differences between control and treatment nights with respect to the amount of Cheyne-Stokes respiration (CSR) observed, the nocturnal oxygenation, or sleep quality. Both subjective and objective measures of sleep quality showed no change from night to night. In addition, the degree of cognitive functioning and daytime sleepiness (as measured by MSLT) showed no significant differences between control and treatment nights. We conclude that short-term treatment with nasal CPAP in patients with CHF does not improve either CSR, nocturnal oxygenation, or sleep quality. Furthermore, most of our patients did not tolerate nasal CPAP therapy.

Nasal CPAP reduces gastroesophageal reflux in obstructive sleep apnea syndrome

Anecdotal reports suggest that obstructive sleep apnea syndrome (OSAS) patients may suffer from frequent nocturnal gastroesophageal reflux (GER) and that nasal continuous positive airway pressure may be an effective form of antireflux therapy in this population. To confirm these clinical impressions, we performed two consecutive days of 24-h esophageal pH monitoring, nocturnal esophageal pressure recording, and polysomnography on six OSAS patients complaining of regular nocturnal GER. On night one, the patients were untreated. Five of six subjects had abnormal amounts of nocturnal GER. Arousal, movement and swallowing were more frequent (p less than 0.043) and nadir intrathoracic pressure lower (p less than 0.005) in the 30 s prior to precipitous drops in esophageal pH (greater than or equal to 2 pH units) than during random control periods. A direct association between obstructive apneas and GER was not identified. On night two, nasal CPAP was administered and successfully treated apnea in five of six subjects. In these patients, there was also dramatic reduction in GER frequency and duration on CPAP. The mean percentage of time pH less than 4 dropped from 6.3 +/- 2.1 to 0.1 +/- 0.1 percent (p less than 0.025). We believe that OSAS may predispose to nocturnal GER by lowering intrathoracic pressure and increasing arousal and movement frequency. Nasal CPAP can correct these predisposing factors and reduce GER.

Improving the skills of established general practitioners: the long-term benefits of group teaching

This study set out to determine the long-term benefits of teaching psychiatric interview skills. Nine established general practitioners, eight of whom were also trainers, took part some 18 months after attending a problem-based interviewing course. Interview skills were assessed by rating behaviour during 10-minute videorecorded simulated consultations with role-players, recorded before and after training and at follow-up. The finding of an earlier study that, in terms of the course model, training successfully modified the doctor's behaviour, was largely replicated. In addition, not only were acquired skills maintained but further change took place during the follow-up period, change that can be seen as improvement in terms of the course model.

Cheyne-Stokes respiration: Stability of interacting systems in heart failure

Cheyne-Stokes respiration, a breathing pattern found in patients with heart failure, is characterized by periodic changes in ventilation. This pattern of breathing is also associated with oscillations in the arousal state, blood oxygen level, carbon dioxide blood level, and the blood pressure. Although originally described as an irregular breathing pattern or an unstable breathing pattern, Cheyne-Stokes respiration may be quite stable for prolonged periods of time. This breathing pattern may represent a clinical disorder in which disease results in a low-frequency oscillation of the system. Treatment that either reduces or abolishes the oscillation results in clinical improvement because of reduced oscillation of the systems whose function is linked to the changes in ventilation.

Link between the ability to detect and manage emotional disorders: a study of general practitioner trainees

Independent ratings were made of videotaped consultations involving six general practice vocational trainees, of whom three were poor identifiers and three were able identifiers of emotional illness. Taped consultations were selected so that each trainee was rated interviewing five patients with low general health questionnaire scores, and five patients with high scores. It was found that able identifiers of emotional illness were more likely than poor identifiers to offer patients information, advice and treatment relevant to their illness, and that they did so in a manner likely to maximize patient satisfaction and cooperation. This was true for both distressed and non-distressed patients. It is argued that both the ability to identify emotional disturbances and the ability to manage emotional illness are characteristics of a generally superior interview style. This may reflect a common variable: the possession of good communication skills.

Improving the psychiatric skills of the general practice trainee: an evaluation of a group training course

Fourteen general practice trainees took part in a course specifically designed to improve their psychiatric interviewing skills. The trainees were instructed in the problem-based model and were taught in a group setting with the use of videotape feedback. A significant improvement was demonstrated in the trainees' ability to identify psychiatric illness accurately, and there were significant changes in their interview behaviours after training. Those who were below average before training showed the greatest improvement. The implications of these findings are discussed. Group video feedback training is as effective as one-to-one video feedback training in improving the psychiatric interviewing skills of GP trainees, and could be more widely employed in general practice vocational training.

How psychiatric disorders are missed during medical consultations

There is a strong correlation between patients' scores on a psychiatric screening questionnaire and the number of cues indicative of psychological disturbance that patients give during the medical interview. Verbal cues have the strongest correlation with psychological distress as measured by the questionnaire, but movement cues and postural cues are also important. The reason why some doctors are better able than others to detect psychiatric illness is that they are more likely to allow patients to express verbal and vocal cues.

Somatostatin-immunoreactive amacrine cells of chicken retina: retinal mosaic, ultrastructural features, and light-driven variations in peptide metabolism

Somatostatin-like immunoreactive amacrine cells of the chicken retina have been characterized by immunohistochemistry at the light and electron microscope levels. The cell bodies were set back from the junction of the inner nuclear and inner plexiform layers, and prominent fibre plexuses were found in sublaminas 1 and 3-5 of the inner plexiform layer. The cells were distributed across the retinal surface with a centroperipheral gradient of cell density. Locally, the cells were organized in a non-random mosaic. Ultrastructurally, immunohistochemical reaction product was found throughout the cytoplasm of the cell bodies, particularly associated with membranous structures, including the cytoplasmic surfaces of the Golgi apparatus, and within large dense-core vesicles. In dendritic varicosities in the inner plexiform layer, reaction product was associated with the external surfaces of small, clear synaptic vesicles. The synaptic relationships of the somatostatin-immunoreactive terminals in sublamina 1 were distinct from those in sublaminas 3-5. Those in sublamina 1 received input predominantly, possibly exclusively, from bipolar cells. Feedback synapses onto bipolar terminals or to the other amacrine cell process at a synaptic dyad were observed. In sublaminas 3-5, input came predominantly, possibly exclusively, from other, non-immunoreactive amacrine cells, and output was primarily onto other amacrine cells. No synaptic contacts with ganglion cells or with other somatostatin-immunoreactive amacrine cells were identified. Changes in levels of somatostatin-like immunoreactivity in retinas of chicks kept on 12:12 light:dark cycles were detected by radioimmunoassay, and by light and electron microscopic immunohistochemistry. Levels of retinal somatostatin-like immunoreactivity increased in the light and decreased in the dark. The changes appear to be light-driven rather than circadian, since with prolonged exposure to light or dark, the levels of somatostatin-like immunoreactivity continued to increase or decrease until plateaus were reached. The light-driven change in levels of somatostatin-like immunoreactivity may be related to the predominance of bipolar input to the immunoreactive processes in sublamina 1 of the inner plexiform layer. The reduction in peptide levels in the dark may indicate greater release of somatostatin-like immunoreactivity from the amacrine cells in the dark, resulting in an inability of peptide synthesis to keep pace with breakdown. In the light, release of somatostatin-like immunoreactivity may be lower, leading to a net synthesis of peptide.

Cholinergic and acetylcholinesterase-containing neurons of the chicken retina

In the chicken retina, choline acetyltransferase-like immunoreactivity (ChAT-LI) defines three populations of cholinergic amacrine cells and two terminal bands in the inner plexiform layer (IPL). Acetylcholinesterase (AChE) histochemistry defines two prominent bands within the IPL which corresponded to those containing ChAT. Other AChE-positive bands in the IPL are not associated with cholinergic transmission sites. Cholinergic cell bodies contain AChE, but the most intensely AChE-positive cells do not appear to be cholinergic. AChE histochemistry may be used to define the major cholinergic synaptic sites in the IPL, and may be a useful marker of IPL lamination.