Cognitive domains affected post-COVID-19; a systematic review and meta-analysis

BACKGROUND AND PURPOSE

This review aims to characterize the pattern of post-COVID-19 cognitive impairment, allowing better prediction of impact on daily function to inform clinical management and rehabilitation.

METHODS

A systematic review and meta-analysis of neurocognitive sequelae following COVID-19 was conducted, following PRISMA-S guidelines. Studies were included if they reported domain-specific cognitive assessment in patients with COVID-19 at >4 weeks post-infection. Studies were deemed high-quality if they had >40 participants, utilized healthy controls, had low attrition rates and mitigated for confounders.

RESULTS

Five of the seven primary Diagnostic and Statistical Manual of Mental Disorders (DSM-5) cognitive domains were assessed by enough high-quality studies to facilitate meta-analysis. Medium effect sizes indicating impairment in patients post-COVID-19 versus controls were seen across executive function (standardised mean difference (SMD) -0.45), learning and memory (SMD -0.55), complex attention (SMD -0.54) and language (SMD -0.54), with perceptual motor function appearing to be impacted to a greater degree (SMD -0.70). A narrative synthesis of the 56 low-quality studies also suggested no obvious pattern of impairment.

CONCLUSIONS

This review found moderate impairments across multiple domains of cognition in patients post-COVID-19, with no specific pattern. The reported literature was significantly heterogeneous, with a wide variety of cognitive tasks, small sample sizes and disparate initial disease severities limiting interpretability. The finding of consistent impairment across a range of cognitive tasks suggests broad, as opposed to domain-specific, brain dysfunction. Future studies should utilize a harmonized test battery to facilitate inter-study comparisons, whilst also accounting for the interactions between COVID-19, neurological sequelae and mental health, the interplay between which might explain cognitive impairment.

Para-infectious brain injury in COVID-19 persists at follow-up despite attenuated cytokine and autoantibody responses

To understand neurological complications of COVID-19 better both acutely and for recovery, we measured markers of brain injury, inflammatory mediators, and autoantibodies in 203 hospitalised participants; 111 with acute sera (1-11 days post-admission) and 92 convalescent sera (56 with COVID-19-associated neurological diagnoses). Here we show that compared to 60 uninfected controls, tTau, GFAP, NfL, and UCH-L1 are increased with COVID-19 infection at acute timepoints and NfL and GFAP are significantly higher in participants with neurological complications. Inflammatory mediators (IL-6, IL-12p40, HGF, M-CSF, CCL2, and IL-1RA) are associated with both altered consciousness and markers of brain injury. Autoantibodies are more common in COVID-19 than controls and some (including against MYL7, UCH-L1, and GRIN3B) are more frequent with altered consciousness. Additionally, convalescent participants with neurological complications show elevated GFAP and NfL, unrelated to attenuated systemic inflammatory mediators and to autoantibody responses. Overall, neurological complications of COVID-19 are associated with evidence of neuroglial injury in both acute and late disease and these correlate with dysregulated innate and adaptive immune responses acutely.

Pre-existing neurological conditions and COVID-19 co-infection: Data from systematic reviews, meta-analyses, and scoping reviews

BACKGROUND

Pre-existing neurological diseases have been identified as risk factors for severe COVID-19 infection and death. There is a lack of comprehensive literature review assessing the relationship between pre-existing neurological conditions and COVID-19 outcomes. Identification of high risk groups is critical for optimal treatment and care.

METHODS

A literature review was conducted for systematic reviews, meta-analyses, and scoping reviews published between January 1, 2020 and January 1, 2023. Literature assessing individuals with pre-existing neurological diseases and COVID-19 infection was included. Information regarding infection severity was extracted, and potential limitations were identified.

RESULTS

Thirty-nine articles met inclusion criteria, with data assessing >3 million patients from 51 countries. 26/51 (50.9%) of countries analyzed were classified as high income, while the remaining represented middle-low income countries (25/51; 49.0%). A majority of evidence focused on the impact of cerebrovascular disease (17/39; 43.5%) and dementia (5/39; 12.8%) on COVID-19 severity and mortality. 92.3% of the articles (36/39) suggested a significant association between neurological conditions and increased risk of severe COVID-19 and mortality. Cerebrovascular disease, dementia, Parkinson's disease, and epilepsy were associated with increased COVID severity and mortality.

CONCLUSION

Pre-existing neurological diseases including cerebrovascular disease, Alzheimer's disease and other dementias, epilepsy, and Parkinson's disease are significant risk factors for severity of COVID-19 infection and mortality in the acute infectious period. Given that 61.5% (24/39) of the current evidence only includes data from 2020, further updated literature is crucial to identify the relationship between chronic neurological conditions and clinical characteristics of COVID-19 variants.

Global uncertainty in the diagnosis of neurological complications of SARS-CoV-2 infection by both neurologists and non-neurologists: An international inter-observer variability study

INTRODUCTION

Uniform case definitions are required to ensure harmonised reporting of neurological syndromes associated with SARS-CoV-2. Moreover, it is unclear how clinicians perceive the relative importance of SARS-CoV-2 in neurological syndromes, which risks under- or over-reporting.

METHODS

We invited clinicians through global networks, including the World Federation of Neurology, to assess ten anonymised vignettes of SARS-CoV-2 neurological syndromes. Using standardised case definitions, clinicians assigned a diagnosis and ranked association with SARS-CoV-2. We compared diagnostic accuracy and assigned association ranks between different settings and specialties and calculated inter-rater agreement for case definitions as "poor" (κ ≤ 0.4), "moderate" or "good" (κ > 0.6).

RESULTS

1265 diagnoses were assigned by 146 participants from 45 countries on six continents. The highest correct proportion were cerebral venous sinus thrombosis (CVST, 95.8%), Guillain-Barré syndrome (GBS, 92.4%) and headache (91.6%) and the lowest encephalitis (72.8%), psychosis (53.8%) and encephalopathy (43.2%). Diagnostic accuracy was similar between neurologists and non-neurologists (median score 8 vs. 7/10, p = 0.1). Good inter-rater agreement was observed for five diagnoses: cranial neuropathy, headache, myelitis, CVST, and GBS and poor agreement for encephalopathy. In 13% of vignettes, clinicians incorrectly assigned lowest association ranks, regardless of setting and specialty.

CONCLUSION

The case definitions can help with reporting of neurological complications of SARS-CoV-2, also in settings with few neurologists. However, encephalopathy, encephalitis, and psychosis were often misdiagnosed, and clinicians underestimated the association with SARS-CoV-2. Future work should refine the case definitions and provide training if global reporting of neurological syndromes associated with SARS-CoV-2 is to be robust.

Addressing vaccine-preventable encephalitis in vulnerable populations

PURPOSE OF REVIEW

Vaccinations have been pivotal in lowering the global disease burden of vaccine-preventable encephalitides, including Japanese encephalitis, tick-borne encephalitis, measles encephalitis, and rabies encephalitis, among others.

RECENT FINDINGS

Populations vulnerable to vaccine-preventable infections that may lead to encephalitis include those living in endemic and rural areas, military members, migrants, refugees, international travelers, younger and older persons, pregnant women, the immunocompromised, outdoor, healthcare and laboratory workers, and the homeless. There is scope for improving the availability and distribution of vaccinations, vaccine equity, surveillance of vaccine-preventable encephalitides, and public education and information.

SUMMARY

Addressing these gaps in vaccination strategies will allow for improved vaccination coverage and lead to better health outcomes for those most at risk for vaccine-preventable encephalitis.

Consensus Clinical Guidance for Diagnosis and Management of Adult COVID-19 Encephalopathy Patients

Encephalopathy, a common condition among patients hospitalized with COVID-19, can be a challenge to manage and negatively affect prognosis. While encephalopathy may present clinically as delirium, subsyndromal delirium, or coma and may be a result of systemic causes such as hypoxia, COVID-19 has also been associated with more prolonged encephalopathy due to less common but nevertheless severe complications, such as inflammation of the brain parenchyma (with or without cerebrovascular involvement), demyelination, or seizures, which may be disproportionate to COVID-19 severity and require specific management. Given the large number of patients hospitalized with severe acute respiratory syndrome coronavirus-2 infection, even these relatively unlikely complications are increasingly recognized and are particularly important because they require specific management. Therefore, the aim of this review is to provide pragmatic guidance on the management of COVID-19 encephalopathy through consensus agreement of the Global COVID-19 Neuro Research Coalition. A systematic literature search of MEDLINE, medRxiv, and bioRxiv was conducted between January 1, 2020, and June 21, 2021, with additional review of references cited within the identified bibliographies. A modified Delphi approach was then undertaken to develop recommendations, along with a parallel approach to score the strength of both the recommendations and the supporting evidence. This review presents analysis of contemporaneous evidence for the definition, epidemiology, and pathophysiology of COVID-19 encephalopathy and practical guidance for clinical assessment, investigation, and both acute and long-term management.

Increased volume of cerebral oedema is associated with risk of acute seizure activity and adverse neurological outcomes in encephalitis - regional and volumetric analysis in a multi-centre cohort

BACKGROUND

Seizures can occur unpredictably in patients with acute encephalitis syndrome (AES), and many suffer from poor long-term neurological sequelae. Establishing factors associated with acute seizures risk and poor outcomes could support clinical care. We aimed to conduct regional and volumetric analysis of cerebral oedema on magnetic resonance imaging (MRI) in patients with AES. We assessed the relationship of brain oedema with acute seizure activity and long-term neurological outcome.

METHODS

In a multi-centre cohort study, adults and children presenting with an AES were recruited in the UK. The clinical and brain MRI data were retrospectively reviewed. The outcomes variables were inpatient acute seizure activity and neurological disability at six-months post-discharge. A poor outcome was defined as a Glasgow outcome score (GOS) of 1-3. We quantified regional brain oedema on MRI through stereological examination of T2-weighted images using established methodology by independent and blinded assessors. Clinical and neuroimaging variables were analysed by multivariate logistic regression to assess for correlation with acute seizure activity and outcome.

RESULTS

The study cohort comprised 69 patients (mean age 31.8 years; 53.6% female), of whom 41 (59.4%) had acute seizures as inpatients. A higher Glasgow coma scale (GCS) score on admission was a negative predictor of seizures (OR 0.61 [0.46-0.83], p = 0.001). Even correcting for GCS on admission, the presence of cortical oedema was a significant risk factor for acute seizure activity (OR 5.48 [1.62-18.51], p = 0.006) and greater volume of cerebral oedema in these cortical structures increased the risk of acute seizures (OR 1.90 [1.12-3.21], p = 0.017). At six-month post-discharge, 21 (30.4%) had a poor neurological outcome. Herpes simplex virus encephalitis was associated with higher risk of poor outcomes in univariate analysis (OR 3.92 [1.08-14.20], p = 0.038). When controlling for aetiology, increased volume of cerebral oedema was an independent risk factor for adverse neurological outcome at 6 months (OR 1.73 [1.06-2.83], p = 0.027).

CONCLUSIONS

Both the presence and degree of cerebral oedema on MRIs of patients with AES may help identify patients at risk of acute seizure activity and subsequent long-term morbidity.

Reliability of multi-site UK Biobank MRI brain phenotypes for the assessment of neuropsychiatric complications of SARS-CoV-2 infection: The COVID-CNS travelling heads study

INTRODUCTION

Magnetic resonance imaging (MRI) of the brain could be a key diagnostic and research tool for understanding the neuropsychiatric complications of COVID-19. For maximum impact, multi-modal MRI protocols will be needed to measure the effects of SARS-CoV-2 infection on the brain by diverse potentially pathogenic mechanisms, and with high reliability across multiple sites and scanner manufacturers. Here we describe the development of such a protocol, based upon the UK Biobank, and its validation with a travelling heads study. A multi-modal brain MRI protocol comprising sequences for T1-weighted MRI, T2-FLAIR, diffusion MRI (dMRI), resting-state functional MRI (fMRI), susceptibility-weighted imaging (swMRI), and arterial spin labelling (ASL), was defined in close approximation to prior UK Biobank (UKB) and C-MORE protocols for Siemens 3T systems. We iteratively defined a comparable set of sequences for General Electric (GE) 3T systems. To assess multi-site feasibility and between-site variability of this protocol, N = 8 healthy participants were each scanned at 4 UK sites: 3 using Siemens PRISMA scanners (Cambridge, Liverpool, Oxford) and 1 using a GE scanner (King's College London). Over 2,000 Imaging Derived Phenotypes (IDPs), measuring both data quality and regional image properties of interest, were automatically estimated by customised UKB image processing pipelines (S2 File). Components of variance and intra-class correlations (ICCs) were estimated for each IDP by linear mixed effects models and benchmarked by comparison to repeated measurements of the same IDPs from UKB participants. Intra-class correlations for many IDPs indicated good-to-excellent between-site reliability. Considering only data from the Siemens sites, between-site reliability generally matched the high levels of test-retest reliability of the same IDPs estimated in repeated, within-site, within-subject scans from UK Biobank. Inclusion of the GE site resulted in good-to-excellent reliability for many IDPs, although there were significant between-site differences in mean and scaling, and reduced ICCs, for some classes of IDP, especially T1 contrast and some dMRI-derived measures. We also identified high reliability of quantitative susceptibility mapping (QSM) IDPs derived from swMRI images, multi-network ICA-based IDPs from resting-state fMRI, and olfactory bulb structure IDPs from T1, T2-FLAIR and dMRI data.

CONCLUSION

These results give confidence that large, multi-site MRI datasets can be collected reliably at different sites across the diverse range of MRI modalities and IDPs that could be mechanistically informative in COVID brain research. We discuss limitations of the study and strategies for further harmonisation of data collected from sites using scanners supplied by different manufacturers. These acquisition and analysis protocols are now in use for MRI assessments of post-COVID patients (N = 700) as part of the ongoing COVID-CNS study.

Acute seizure risk in patients with encephalitis: development and validation of clinical prediction models from two independent prospective multicentre cohorts

Objective

In patients with encephalitis, the development of acute symptomatic seizures is highly variable, but when present is associated with a worse outcome. We aimed to determine the factors associated with seizures in encephalitis and develop a clinical prediction model.

Methods

We analysed 203 patients from 24 English hospitals (2005-2008) (Cohort 1). Outcome measures were seizures prior to and during admission, inpatient seizures and status epilepticus. A binary logistic regression risk model was converted to a clinical score and independently validated on an additional 233 patients from 31 UK hospitals (2013-2016) (Cohort 2).

Results

In Cohort 1, 121 (60%) patients had a seizure including 103 (51%) with inpatient seizures. Admission Glasgow Coma Scale (GCS) ≤8/15 was predictive of subsequent inpatient seizures (OR (95% CI) 5.55 (2.10 to 14.64), p<0.001), including in those without a history of prior seizures at presentation (OR 6.57 (95% CI 1.37 to 31.5), p=0.025).A clinical model of overall seizure risk identified admission GCS along with aetiology (autoantibody-associated OR 11.99 (95% CI 2.09 to 68.86) and Herpes simplex virus 3.58 (95% CI 1.06 to 12.12)) (area under receiver operating characteristics curve (AUROC) =0.75 (95% CI 0.701 to 0.848), p<0.001). The same model was externally validated in Cohort 2 (AUROC=0.744 (95% CI 0.677 to 0.811), p<0.001). A clinical scoring system for stratifying inpatient seizure risk by decile demonstrated good discrimination using variables available on admission; age, GCS and fever (AUROC=0.716 (95% CI 0.634 to 0.798), p<0.001) and once probable aetiology established (AUROC=0.761 (95% CI 0.6840.839), p<0.001).

Conclusion

Age, GCS, fever and aetiology can effectively stratify acute seizure risk in patients with encephalitis. These findings can support the development of targeted interventions and aid clinical trial design for antiseizure medication prophylaxis.

Clinical review of cerebral venous thrombosis in the context of COVID-19 vaccinations: Evaluation, management, and scientific questions

BACKGROUND

Vaccine induced immune mediated thrombocytopenia or VITT, is a recent and rare phenomenon of thrombosis with thrombocytopenia, frequently including cerebral venous thromboses (CVT), that has been described following vaccination with adenovirus vaccines ChAdOx1 nCOV-19 (AstraZeneca) and Ad26.COV2·S Johnson and Johnson (Janssen/J&J). The evaluation and management of suspected cases of CVT post COVID-19 vaccination are critical skills for a broad range of healthcare providers.

METHODS

A collaborative comprehensive review of literature was conducted among a global group of expert neurologists and hematologists.

FINDINGS

Strategies for rapid evaluation and treatment of the CVT in the context of possible VITT exist, including inflammatory marker measurements, PF4 assays, and non-heparin anticoagulation.

Strain differences in the behavioural outcome of neonatal ventral hippocampal lesions are determined by the postnatal environment and not genetic factors

It has been demonstrated that not only do rats neonatally lesioned in the ventral hippocampus (VH) develop behavioural hypersensitivity to amphetamine postpubertally, but also that the expression of the sensitivity is strain specific. For example, excitotoxic VH lesions at postnatal day (PD) 7 lead to significant increases in amphetamine-induced locomotion in postpubertal Fischer rats, but not in Lewis rats. However, as it is likely that the effect of strain differences are due to a combination of genetics and environment, we examined the contributions of the environment of the pups in determining the behavioural outcome following neonatal VH lesions. Fisher and Lewis rat pups were cross-fostered at birth, and then at PD7 lesioned bilaterally in the VH with ibotenic acid. ANOVA analysis of postpubertal amphetamine-induced locomotor data revealed a significant effect of the strain of the dams raising the pups but no effect of the strain of the pup. In addition, a post hoc analysis revealed that lesioned Fisher or Lewis rats raised by Fisher, but not those raised by Lewis, dams demonstrated amphetamine-induced hyperlocomotion relative to nonlesioned controls. Observations of the maternal behaviour of Fischer and Lewis dams revealed significant differences in the frequency of arched-back nursing between the two strains. Interestingly, a correlation of the frequency of arched back nursing vs novelty- or amphetamine-induced locomotion revealed that the lesioned rats were significantly more affected by increases in arched-back nursing compared to the controls. The results suggest that the genetic background of the pups does not significantly affect the behavioural outcome following neonatal VH lesions; however, the results do suggest an important role of early environmental variables on the behavioural outcome of neonatal VH lesions.

Lewis and Fischer rats: a comparison of dopamine transporter and receptors levels

Previous reports have shown that the inbred strains of rat, Lewis (LEW) and Fischer 344 (F344), differ in several behavioural and biochemical indices of mesolimbic dopamine (DA) function. Specifically, these two strains differ in their behavioural and neurochemical response to novel environments, and acute amphetamine or cocaine challenge as well as in their susceptibility to addiction. To investigate if differences in DA D1-like, D2-like, D3 receptors and DA transporter could be correlated with these behavioural differences between strains, a comparative autoradiographic study of DA receptors and transporter within the striatal and accumbal regions was undertaken. We observed strain and region specific differences in binding levels for DA D2-like and D3 receptors and for the DA transporter. Namely, DA transporter levels in the striatum, nucleus accumbens and olfactory tubercle of LEW rats were significantly lower than in F344 rats. DA D3 densities in the shell of the nucleus accumbens and olfactory tubercle of LEW rats were lower than the levels found in the F344 rats. Finally, LEW rats have a lower levels of D2-like receptors in the striatum and the core of the nucleus accumbens compared to F344 rats. These data suggest that differences in DA transporter and DA receptors may in part contribute to differences in DA related behaviour seen between these two strains.

NCAM-180 knockout mice display increased lateral ventricle size and reduced prepulse inhibition of startle

NCAM-180 knockout mice, which have documented deficits in neural migration, were used to determine whether developmental abnormalities could lead to morphological changes and alterations in sensory motor gating mechanisms. Measurement of the lateral ventricle showed that NCAM-180-/- mice had marked increases in both the left and right anterior horns of the lateral ventricle. Furthermore, these mice also displayed a reduction of prepulse inhibition that was differentially affected by the dopamine agonist apomorphine. These results are discussed in light of the known increase in lateral ventricle size and reduction in prepulse inhibition that are seen in schizophrenia.

Cloning and in situ hybridization analysis of the expression of polysialyltransferase mRNA in the developing and adult rat brain

Polysialyltransferase (PST) is an enzyme that catalyzes the addition of polysialic acid (PSA), a homopolymer of alpha-2,8-linked sialic acid residues, onto neural cell adhesion molecule (NCAM). The expression of PSA-NCAM in the brain is developmentally regulated and is of critical importance; however, the temporal and spatial developmental expression of brain PST, a potential key player in the control of PSA-NCAM levels, remains unclear. In the present study, we have cloned the coding region of rat PST cDNA by reverse transcription-polymerase chain reaction, using primers based on the hamster PST-1 cDNA sequence. A 39-mer oligonucleotide complementary to rat PST cDNA was synthesized to investigate the distribution of its mRNA in the developing and adult rat brain by Northern blot and in situ hybridization. In the embryonic rat brain, PST mRNA was detected abundantly throughout the neuroepithelia of most brain regions. At post-natal days 1 and 14, PST was detected throughout the neocortex, in the pyramidal cells (PC) of the hippocampus proper, the granule cell layer (GCL) of the dentate gyrus, the anterior ventral nucleus of the thalamus (AVNT) and the GCL and external germinal layer of the cerebellum. Finally, from PD21 until adulthood, expression of PST mRNA was restricted to the PC layer of the hippocampus proper, the GCL of the dentate gyrus, the AVNT, the GCL of the cerebellum and the dorsal and lateral nucleus of the anterior olfactory bulb. The developmental profile of PST mRNA is paralleled in some structures by that of the PSA-NCAM, there are, however, notable exceptions. Therefore, our results demonstrate that expression of rat PST mRNA is developmentally regulated, is present in the adult rat brain in restricted areas and may be involved in regulating temporal and spatial expression of PSA-NCAM.

Behavioral changes in rats with early ventral hippocampal damage vary with age at damage

Our previous work demonstrated that neonatal (on postnatal day 7, PD7) excitotoxic damage of the ventral hippocampus (VH) results in delayed emergence of behaviors related to dopaminergic (DA) transmission. In this study, the developmental effects of VH lesions induced at two other ages were investigated in the rat. Ibotenic acid or artificial cerebrospinal fluid was infused into the VH of 3- (PD3) or 14- (PD14)-day-old rat pups. Amphetamine-induced (1.5 mg/kg, i.p.) locomotor activity was assessed in the sham and lesioned rats prior to (PD35) and after puberty (PD56 and PD86). Apomorphine-induced (0.75 mg/kg s.c.) stereotypic behaviors were measured on PD56. Similar VH lesions resulted in different profiles of behavioral abnormalities depending upon the age at which they were induced. The PD3 lesioned rats displayed hyperlocomotion to amphetamine only after puberty, while the PD14 lesioned rats manifest hyperlocomotion as early as 3 weeks after surgery (at PD35). Moreover, the PD3 lesioned rats tended to show more stereotypic behaviors in response to apomorphine than the sham-operated controls, while the PD14 rats had a profoundly diminished stereotypic response. The behavioral changes in the PD3 lesioned rats are reminiscent of those previously described in animals lesioned at PD7. In contrast, the deficits in the PD14 lesioned animals resemble those seen before in rats lesioned in adulthood. These results indicate that the pattern of impairments associated with the excitotoxic VH lesion varies with age at lesion, i.e. a similar pattern seems to be associated with lesions up to PD7, but not by PD14. To the extent that the neonatal VH lesion in the rat models certain phenomenological aspects of schizophrenia, including the temporal pattern of symptom onset, these results provide evidence that the model requires an early defect in limbic cortical development.

Comparison of single-biphasic versus sequential-biphasic shocks on defibrillation threshold in pigs

Current generation implantable cardioverter defibrillators use monophasic, biphasic, or sequential pulse shocks, most of which truncate after a given time, dumping the remaining charge on the capacitor through an internal resistor. We hypothesized that having an additional current pathway, and delivering the majority of the remaining charge on a single capacitor to the two pathways using additional shock phases, would improve defibrillation efficacy. This hypothesis was tested by comparing DFTs using a simulated single capacitor, single-biphasic shock (two 5-ms pulses separated by 0.2 ms), delivered to coupled pairs of electrodes, to those using a sequential-biphasic shock (four 5-ms pulses separated by 0.2 ms) delivered to separate opposing electrodes, delivered from the same electrodes for both waveforms. In eight open-chest anesthetized pigs, four mesh electrodes (Medtronic TX-7, 6.5 cm2), were sutured on the epicardium of the anterior and posterior surfaces of each ventricle. Shocks were delivered from a 200-microF capacitor bank. Triplicate DFTs were obtained using each waveform in a randomized crossover design. Initial leading edge voltage (mean +/- SEM: 420 +/- 33 V vs 497 +/- 34 V; P < 0.05), initial peak current (4.8 +/- 0.4 A vs 13 +/- 1.1 A; P < 0.001), and delivered energy (16.9 +/- 2.6 J vs 30.4 +/- 5.3 J; P < 0.05) at the DFT were all significantly lower using sequential-biphasic shocks than those using single-biphasic shocks, respectively. We conclude that for direct heart defibrillation, it is worthwhile to combine sequential capability to biphasic shocks and deliver the remaining charge on the capacitor to the two different pathways.

Enhanced amphetamine sensitivity and increased expression of dopamine D2 receptors in postpubertal rats after neonatal excitotoxic lesions of the medial prefrontal cortex

Functional and structural abnormalities in the medial prefrontal cortex (MPFC) and overactive dopamine (DA) neurotransmission are thought to be the key pathologies in schizophrenia. To understand the role of MPFC in the pre- and postpubertal development of the subcortical DA system, the effects of neonatal [postnatal day 7 (PD7)] MPFC excitotoxic lesions on locomotor behaviors and the expression of DA receptor subtypes and DA transporter were investigated in Sprague Dawley rats at PD35 and PD56, respectively. No significant differences in the novelty of d-amphetamine-induced locomotion were observed between sham-operated and ibotenic acid-lesioned rats at PD35. Postpubertally (at PD56), however, the locomotor activity of lesioned rats in the novel environment and after d-amphetamine administration was enhanced significantly compared with controls. The expressions of DA D1, D2, D3, and D4 receptors and DA transporter were then estimated in MPFC-lesioned and sham-operated rats at PD59 and PD60. The levels of DA D2 receptors, measured using [3H]-YM-09151-2 binding, and its mRNA by in situ hybridization, were observed to be significantly increased at PD60 in striatal and limbic areas of lesioned rats. Levels of other DA receptor subtypes were not significantly affected at any time points. Lesioned rats at PD39 show a small increase in DA transporter level in the shell of nucleus accumbens; however, this effect seems to wear off at PD60. The data suggest that neonatal MPFC lesions may alter the functional development and maturation of mesolimbic/nigrostriatal DA systems in that neonatally lesioned rats grow into a behavioral/neurochemical deficit.

Amphetamine-induced c-fos mRNA expression is altered in rats with neonatal ventral hippocampal damage

To further characterize the mechanisms underlying enhanced dopamine-related behaviors expressed during adulthood in rats with neonatal excitotoxic ventral hippocampal (VH) damage, we studied the expression of c-fos mRNA in these rats after a single saline or amphetamine (AMPH) (10 mg/kg, i.p.) injection using in situ hybridization. The VH of rat pups was lesioned with ibotenic acid on postnatal day 7 (PD7). At the age of 90 days, rats were challenged with AMPH or saline, and the expression of c-fos mRNA using an oligonucleotide probe was assessed 30, 90, and 180 min later. AMPH significantly increased c-fos mRNA expression in medial prefrontal cortex, piriform cortex, cingulate cortex, septal region, and dorsolateral and ventromedial striatum in control and lesioned rats. However, this response to AMPH was attenuated 30 min after AMPH injection in all of these regions in the lesioned as compared to the sham-operated rats. No significant changes were seen at other time points. These results indicate that the neonatal VH lesion alters time-dependent intracellular signal transduction mechanisms measured by AMPH-induced c-fos mRNA expression in cortical and subcortical brain regions. Changes in c-fos mRNA expression in this putative animal model of schizophrenia may have implications for long-term alterations in cellular phenotype because of altered regulation of certain target genes.

Measurement of blood-retinal barrier breakdown in endotoxin-induced endophthalmitis

PURPOSE

Endophthalmitis is a severe inflammatory disorder with profound visual consequences. Treatment of this disorder has been limited by the lack of quantitative information regarding retinal responses to severe inflammation. The purpose of this study was to measure the effect of endotoxin-induced endophthalmitis on blood-retinal barrier (BRB) function in vivo using contrast-enhanced magnetic resonance imaging (MRI).

METHODS

Endophthalmitis was produced by injecting Escherichia coli endotoxin into the midvitreous of pigmented rabbits. Contrast-enhanced MRI was performed at selected intervals thereafter. In all cases, a clinical grading system was used to assess the severity of inflammation before imaging. In a dose-response experiment, total vitreous protein was measured from vitreous specimens obtained 1 day after endotoxin injection and immediately after the imaging procedure.

RESULTS

At 1 day after injection, endotoxin produced a selective breakdown of the inner BRB at all doses evaluated (0.01 microgram to 500 micrograms). Permeability-surface area product normalized to the area of leaky retina (PS') increased from 1.35 +/- 0.78 x 10(-4) cm/minute (mean +/- SEM, n = 4 eyes) at a dose of 0.01 microgram to 8.15 +/- 2.22 x 10(-4) cm/minute n = 4) eyes) at a dose of 10 micrograms. Inner BRB integrity was restored by day 28 after injection. In general, changes in PS', blood-aqueous barrier leakage, mean clinical score, and vitreous protein concentration were found, but the correlation between any two of these parameters was poor.

CONCLUSION

Leakage of contrast appears early in the course of endotoxin-induced endophthalmitis and is a self-limited process. In future studies, these quantifiable changes in BRB permeability should prove useful in the assessment of various therapeutic interventions.

Visualization of subtle contrast-related intensity changes using temporal correlation

Contrast-enhanced magnetic resonance imaging (MRI) is a promising method for investigating the breakdown of the blood-retinal barrier (BRB). However, subtle intensity changes due to low concentrations of contrast agent can be difficult to detect without observer bias. In this study, we developed a temporal correlation method for detecting these subtle signal intensity changes. The method was evaluated in eyes with chemically induced retinal lesions of known size. A time series of MRI data were collected following i.v. administration of different doses of gadolinium-diethylaminetriaminepentaacetic acid (0.05, 0.1, 0.5 mmol/kg). These time course images were analyzed by temporal correlation to a reference enhancement curve. The reference curve was generated based on a validated theoretical enhancement curve. The temporal correlation method detected signal intensity changes in cases where the changes were too subtle to be visible on a postinjection image or a subtraction image (obtained by subtracting the precontrast image from the final image in the time course set). In addition, assessment of leakage was performed by viewing each image in the set with an eight gray-level palette. Areas of leakage identified in this manner corresponded to those identified by temporal correlation, a finding which supports the validity of the temporal correlation method. These results suggest that temporal correlation may be a time-efficient way to screen large numbers of image data sets using an objective, user-independent criterion.

Effects of flecainide on defibrillation threshold in pigs

Flecainide has been reported to decrease defibrillation efficacy in pentobarbital-anesthetized dogs. Conversely, flecainide did not alter defibrillation energy requirements in halothane-anesthetized pigs. We wished to determine whether these discrepancies were related to defibrillation technique, interaction with the anesthetic regimen, or animal species. The effects of three doses of flecainide on defibrillation threshold (DFT) were determined using single- and sequential-pulse shocks in halothane-anesthetized open-chest pigs. Triplicate DFTs were obtained before and after three doses of flecainide (n = 34) or saline (n = 13) infusion. Similarly, the effects of the highest dose of flecainide were determined using barbiturate-anesthetized animals (n = 10). Flecainide did not alter DFT at any dose with either the single-pulse shock (control 17.7 +/- 2.1 J, highest dose of flecainide 19.1 +/- 3.2 J, p = NS) or sequential-pulse shock (control 9.2 +/- 1.0 J, highest dose of flecainide 8.4 +/- 1.4 J, p = NS) when halothane anesthesia was used. Similar results were obtained using barbiturate anesthesia either with sequential (control 8.7 +/- 0.9 vs. 8.2 +/- 0.6 J, p = NS) or single shocks (control 13.2 +/- 0.8 vs. 13.7 +/- 1.0 J, p = NS). Flecainide did not alter DFT in our model, regardless of defibrillation technique or anesthetic regimen.

Biphasic versus sequential pulse defibrillation: a direct comparison in pigs

It has recently been demonstrated that both biphasic and sequential pulse defibrillation shocks are superior to monophasic defibrillation shocks in animals and humans. There is little information directly comparing these two waveforms when pulse characteristics, subject, and total electrode surface area are kept constant. Pigs were randomized in a cross-over design for triplicate determinations of defibrillation threshold using biphasic and sequential pulse shocks and both large and small epicardial electrodes. Anesthetized pigs weighing 18 to 28 kg had sets of defibrillating electrodes (TX-7) with total surface areas of 13 cm2 (group 1, n = 16) and 26 cm2 (group 2, n = 16), respectively, attached to the heart. Leading edge delivered voltage, current, and energy were significantly lower with sequential pulse shocks than with biphasic shocks for both electrode sets (delivered energy means +/- standard error of the mean: 13.3 +/- 1.6 versus 22.4 +/- 3.0 joules, and 9.9 +/- 1.5 versus 14.2 +/- 1.6 joules, respectively). In addition, six of the pigs could not be defibrillated with 900 stored V using biphasic shocks, although all pigs were defibrillated with less than 800 stored V using sequential pulse defibrillation. We conclude that sequential pulse defibrillation using three defibrillating electrodes provides an important current delivery system not matched by biphasic shocks using two electrodes when subject, waveform characteristics, and total electrode surface area are kept constant.

Congenital ocular fibrosis syndrome associated with the Prader-Willi syndrome

We report an 11-year-old boy with both the congenital ocular fibrosis and the Prader-Willi syndromes. Since birth he has had bilateral blepharoptosis and fixed ocular misalignment in downward gaze. Pathological examination of the extraocular muscles showed replacement by fibrous tissue. Additionally, the child had the typical clinical features of the Prader-Willi syndrome including mental retardation, hypotonia, short stature, hypogonadism, and obesity. The Prader-Willi syndrome has been consistently associated with interstitial deletions of the long arm of chromosome 15. Although our patient appeared to have normal chromosomes, he may indeed have an undetectable deletion which may be responsible for both syndromes. We believe that the gene(s) for the congenital ocular fibrosis syndrome may be located near the gene(s) for the Prader-Willi syndrome on the long arm of chromosome 15.