Single-Nucleus Transcriptional Profiling of GAD2-Positive Neurons From Mouse Lateral Habenula Reveals Distinct Expression of Neurotransmission- and Depression-Related Genes

Background

Glutamatergic projection neurons of the lateral habenula (LHb) drive behavioral state modulation by regulating the activity of midbrain monoaminergic neurons. Identifying circuit mechanisms that modulate LHb output is of interest for understanding control of motivated behaviors.

Methods

A small population of neurons within the medial subnucleus of the mouse LHb express the GABAergic (gamma-aminobutyric acidergic)-synthesizing enzyme GAD2, and they can inhibit nearby LHb projection neurons; however, these neurons lack markers of classic inhibitory interneurons, and they coexpress the vesicular glutamate transporter VGLUT2. To determine the molecular phenotype of these neurons, we genetically tagged the nuclei of GAD2-positive cells and used fluorescence-activated nuclear sorting to isolate and enrich these nuclei for single-nucleus RNA sequencing.

Results

Our data confirm that GAD2+/VGLUT2+ neurons intrinsic to the LHb coexpress markers of both glutamatergic and GABAergic transmission and that they are transcriptionally distinct from either GABAergic interneurons or habenular glutamatergic neurons. We identify gene expression programs within these cells that show sex-specific differences in expression and that are implicated in major depressive disorder, which has been linked to LHb hyperactivity. Finally, we identify the Ntng2 gene encoding the cell adhesion protein netrin-G2 as a marker of LHb GAD2+/VGLUT2+ neurons and a gene product that may contribute to their target projections.

Conclusions

These data show the value of using genetic enrichment of rare cell types for transcriptome studies, and they advance understanding of the molecular composition of a functionally important class of GAD2+ neurons in the LHb.

Single-nucleus transcriptional profiling of GAD2-positive neurons from mouse lateral habenula reveals distinct expression of neurotransmission- and depression-related genes

Glutamatergic projection neurons of the lateral habenula (LHb) drive behavioral state modulation by regulating the activity of midbrain monoaminergic neurons. Identifying circuit mechanisms that modulate LHb output is of interest for understanding control of motivated behaviors. A small population of neurons within the medial subnucleus of the mouse LHb express the GABAergic synthesizing enzyme GAD2, and they can inhibit nearby LHb projection neurons; however, these neurons lack markers of classic inhibitory interneurons and they co-express the vesicular glutamate transporter VGLUT2. To determine the molecular phenotype of these neurons, we genetically tagged the nuclei of GAD2-positive cells and used fluorescence-activated nuclear sorting to isolate and enrich these nuclei for single nuclear RNA sequencing (FANS-snRNAseq). Our data confirm that GAD2+/VGLUT2+ neurons intrinsic to the LHb co-express markers of both glutamatergic and GABAergic transmission and that they are transcriptionally distinct from either GABAergic interneurons or habenular glutamatergic neurons. We identify gene expression programs within these cells that show sex-specific differences in expression and that are implicated in major depressive disorder (MDD), which has been linked to LHb hyperactivity. Finally, we identify the Ntng2 gene encoding the cell adhesion protein Netrin-G2 as a marker of LHb GAD2+/VGLUT+ neurons and a gene product that may contribute to their target projections. These data show the value of using genetic enrichment of rare cell types for transcriptome studies, and they advance understanding of the molecular composition of a functionally important class of GAD2+ neurons in the LHb.

Mutations of the histone linker H1-4 in neurodevelopmental disorders and functional characterization of neurons expressing C-terminus frameshift mutant H1.4

Rahman syndrome (RMNS) is a rare genetic disorder characterized by mild to severe intellectual disability, hypotonia, anxiety, autism spectrum disorder, vision problems, bone abnormalities and dysmorphic facies. RMNS is caused by de novo heterozygous mutations in the histone linker gene H1-4; however, mechanisms underlying impaired neurodevelopment in RMNS are not understood. All reported mutations associated with RMNS in H1-4 are small insertions or deletions that create a shared frameshift, resulting in a H1.4 protein that is both truncated and possessing an abnormal C-terminus frameshifted tail (H1.4 CFT). To expand understanding of mutations and phenotypes associated with mutant H1-4, we identified new variants at both the C- and N-terminus of H1.4. The clinical features of mutations identified at the C-terminus are consistent with other reports and strengthen the support of pathogenicity of H1.4 CFT. To understand how H1.4 CFT may disrupt brain function, we exogenously expressed wild-type or H1.4 CFT protein in rat hippocampal neurons and assessed neuronal structure and function. Genome-wide transcriptome analysis revealed ~ 400 genes altered in the presence of H1.4 CFT. Neuronal genes downregulated by H1.4 CFT were enriched for functional categories involved in synaptic communication and neuropeptide signaling. Neurons expressing H1.4 CFT also showed reduced neuronal activity on multielectrode arrays. These data are the first to characterize the transcriptional and functional consequence of H1.4 CFT in neurons. Our data provide insight into causes of neurodevelopmental impairments associated with frameshift mutations in the C-terminus of H1.4 and highlight the need for future studies on the function of histone H1.4 in neurons.

The NMDA receptor subunit GluN3A regulates synaptic activity-induced and myocyte enhancer factor 2C (MEF2C)-dependent transcription

N-Methyl-d-aspartate type glutamate receptors (NMDARs) are key mediators of synaptic activity-regulated gene transcription in neurons, both during development and in the adult brain. Developmental differences in the glutamate receptor ionotropic NMDA 2 (GluN2) subunit composition of NMDARs determines whether they activate the transcription factor cAMP-responsive element-binding protein 1 (CREB). However, whether the developmentally regulated GluN3A subunit also modulates NMDAR-induced transcription is unknown. Here, using an array of techniques, including quantitative real-time PCR, immunostaining, reporter gene assays, RNA-Seq, and two-photon glutamate uncaging with calcium imaging, we show that knocking down GluN3A in rat hippocampal neurons promotes the inducible transcription of a subset of NMDAR-sensitive genes. We found that this enhancement is mediated by the accumulation of phosphorylated p38 mitogen-activated protein kinase in the nucleus, which drives the activation of the transcription factor myocyte enhancer factor 2C (MEF2C) and promotes the transcription of a subset of synaptic activity-induced genes, including brain-derived neurotrophic factor (Bdnf) and activity-regulated cytoskeleton-associated protein (Arc). Our evidence that GluN3A regulates MEF2C-dependent transcription reveals a novel mechanism by which NMDAR subunit composition confers specificity to the program of synaptic activity-regulated gene transcription in developing neurons.

Automated Live-Cell Imaging of Synapses in Rat and Human Neuronal Cultures

Synapse loss and dendritic damage correlate with cognitive decline in many neurodegenerative diseases, underlie neurodevelopmental disorders, and are associated with environmental and drug-induced CNS toxicities. However, screening assays designed to measure loss of synaptic connections between live cells are lacking. Here, we describe the design and validation of automated synaptic imaging assay (ASIA), an efficient approach to label, image, and analyze synapses between live neurons. Using viral transduction to express fluorescent proteins that label synapses and an automated computer-controlled microscope, we developed a method to identify agents that regulate synapse number. ASIA is compatible with both confocal and wide-field microscopy; wide-field image acquisition is faster but requires a deconvolution step in the analysis. Both types of images feed into batch processing analysis software that can be run on ImageJ, CellProfiler, and MetaMorph platforms. Primary analysis endpoints are the number of structural synapses and cell viability. Thus, overt cell death is differentiated from subtle changes in synapse density, an important distinction when studying neurodegenerative processes. In rat hippocampal cultures treated for 24 h with 100 μM 2-bromopalmitic acid (2-BP), a compound that prevents clustering of postsynaptic density 95 (PSD95), ASIA reliably detected loss of postsynaptic density 95-enhanced green fluorescent protein (PSD95-eGFP)-labeled synapses in the absence of cell death. In contrast, treatment with 100 μM glutamate produced synapse loss and significant cell death, determined from morphological changes in a binary image created from co-expressed mCherry. Treatment with 3 mM lithium for 24 h significantly increased the number of fluorescent puncta, showing that ASIA also detects synaptogenesis. Proof of concept studies show that cell-specific promoters enable the selective study of inhibitory or principal neurons and that alternative reporter constructs enable quantification of GABAergic or glutamatergic synapses. ASIA can also be used to study synapse loss between human induced pluripotent stem cell (iPSC)-derived cortical neurons. Significant synapse loss in the absence of cell death was detected in the iPSC-derived neuronal cultures treated with either 100 μM 2-BP or 100 μM glutamate for 24 h, while 300 μM glutamate produced synapse loss and cell death. ASIA shows promise for identifying agents that evoke synaptic toxicities and screening for compounds that prevent or reverse synapse loss.

HIV gp120 upregulates tonic inhibition through α5-containing GABAARs

HIV-Associated Neurocognitive disorder (HAND) affects nearly half of infected patients. The HIV envelope protein gp120 is shed by infected cells and is a potent neurotoxin in vitro that reproduces many aspects of HAND when expressed in vivo. Here, we show that HIV gp120 increases the amplitude of a tonic current mediated by γ-aminobutyric acid type-A receptors (GABA_ARs). Treating rat hippocampal cultures with 600 pM gp120_IIIB for 4 h increased a tonic bicuculline-sensitive current, which remained elevated for 24 h. The increased current resulted from upregulation of extrasynaptic α5-containing GABA_ARs, as indicated by inhibition with the selective inverse agonist basmisanil. Treatment with gp120 increased α5-GABA_AR immunoreactivity on the cell surface without new protein synthesis. The increase in tonic inhibition was prevented by a C-X-C chemokine receptor type 4 (CXCR4) antagonist or elimination of microglia from the culture. Treatment with interleukin-1β (IL-1β) increased the tonic current and an IL-1 receptor antagonist blocked the gp120-evoked response. Pharmacological or genetic inhibition of p38 mitogen-activated protein kinase (MAPK) prevented the gp120-evoked increase in tonic current and direct activation of a mutant form of p38 MAPK expressed in neurons increased the current. Collectively, these data show that gp120 activates CXCR4 to stimulate microglia to release IL-1β. Subsequent stimulation of IL-1 receptors activates p38 MAPK in neurons leading to the upregulation of α5-containing GABA_ARs. Increased tonic inhibition impairs neuroplasticity and inhibition of α5-containing GABA_ARs improves cognitive function in disease models. Thus, gp120-induced upregulation of α5-containing GABA_ARs presents a novel therapeutic target for HAND.

HIV gp120-induced neuroinflammation potentiates NMDA receptors to overcome basal suppression of inhibitory synapses by p38 MAPK

HIV-associated neurocognitive disorder affects about half of HIV-infected patients. HIV impairs neuronal function through indirect mechanisms mainly mediated by inflammatory cytokines and neurotoxic viral proteins, such as the envelope protein gp120. HIV gp120 elicits a neuroinflammatory response that potentiates NMDA receptor function and induces the loss of excitatory synapses. How gp120 influences neuronal inhibition remains unknown. In this study, we expressed a green fluorescent protein (GFP)-tagged recombinant antibody-like protein that binds to the post-synaptic scaffolding protein gephyrin to label inhibitory synapses in living neurons. Treatment with 600 pM gp120 for 24 h increased the number of labeled inhibitory synapses. HIV gp120 evoked the release of interleukin-1β (IL-1β) from microglia to activate IL-1 receptors on neurons. Subsequent activation of the tyrosine kinase Src and GluN2A-containing NMDA receptors increased the number of inhibitory synapses via a process that required protein synthesis. In naïve cultures, inhibition of neuronal p38 mitogen-activated protein kinase (p38 MAPK) increased the number of inhibitory synapses suggesting that p38 MAPK produces a basal suppression of inhibitory synapses that is overcome in the presence of gp120. Direct activation of a mutant form of p38 MAPK expressed in neurons mimicked basal suppression of inhibitory synapses. This study shows for the first time that gp120-induced neuroinflammation increases the number of inhibitory synapses and that this increase overcomes a basal suppression of synaptic inhibition. Increased inhibition may be an adaptive mechanism enabling neurons to counteract excess excitatory input in order to maintain network homeostasis. OPEN SCIENCE BADGES: This article has received a badge for *Open Materials* because it provided all relevant information to reproduce the study in the manuscript. The complete Open Science Disclosure form for this article can be found at the end of the article. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/.

Scaling Synapses in the Presence of HIV

A defining feature of HIV-associated neurocognitive disorder (HAND) is the loss of excitatory synaptic connections. Synaptic changes that occur during exposure to HIV appear to result, in part, from a homeostatic scaling response. Here we discuss the mechanisms of these changes from the perspective that they might be part of a coping mechanism that reduces synapses to prevent excitotoxicity. In transgenic animals expressing the HIV proteins Tat or gp120, the loss of synaptic markers precedes changes in neuronal number. In vitro studies have shown that HIV-induced synapse loss and cell death are mediated by distinct mechanisms. Both in vitro and animal studies suggest that HIV-induced synaptic scaling engages new mechanisms that suppress network connectivity and that these processes might be amenable to therapeutic intervention. Indeed, pharmacological reversal of synapse loss induced by HIV Tat restores cognitive function. In summary, studies indicate that there are temporal, mechanistic and pharmacological features of HIV-induced synapse loss that are consistent with homeostatic plasticity. The increasingly well delineated signaling mechanisms that regulate synaptic scaling may reveal pharmacological targets suitable for normalizing synaptic function in chronic neuroinflammatory states such as HAND.

Interleukin-1β activates an Src family kinase to stimulate the plasma membrane Ca2+ pump in hippocampal neurons

The plasma membrane Ca(2+) ATPase (PMCA) plays a major role in clearing Ca(2+) from the neuronal cytoplasm. The cytoplasmic Ca(2+) clearance rate affects neuronal excitability, synaptic plasticity, and neurotransmission. Here, we examined the modulation of PMCA activity by PTKs in hippocampal neurons. PMCA-mediated Ca(2+) clearance slowed in the presence of pyrazolopyrimidine 2, an inhibitor of Src family kinases (SFKs), and accelerated in the presence of C2-ceramide, an activator of PTKs. Ca(2+) clearance kinetics were attenuated in cells expressing a dominant-negative Src mutant, suggesting that the pump is tonically stimulated by a PTK. Tonic stimulation was reduced in hippocampal neurons expressing short hairpin (sh)RNA directed to mRNA for Yes. shRNA-mediated knockdown of PMCA isoform 1 (PMCA1) removed tonic stimulation of Ca(2+) clearance, indicating that the kinase stimulates PMCA1. IL-1β accelerated Ca(2+) clearance in a manner blocked by an IL-1β receptor antagonist or by an inhibitor of neutral sphingomyelinase, the enzyme that produces ceramide. Thus IL-1β activates an SFK to stimulate the plasma membrane Ca(2+) pump, decreasing the duration of Ca(2+) transients in hippocampal neurons.

HIV-1 Tat-induced changes in synaptically-driven network activity adapt during prolonged exposure

HIV-associated neurocognitive disorders (HAND) afflict approximately half of HIV-infected patients. The HIV-1 transactivator of transcription (Tat) protein is released by infected cells and contributes to the pathogenesis of HAND, but many of the underlying mechanisms remain poorly understood. Here we used fura-2-based Ca(2+) imaging and whole-cell patch-clamp recording to study the effects of Tat on the spontaneous synaptic activity that occurs in networked rat hippocampal neurons in culture. Tat triggered aberrant network activity that exhibited a decrease in the frequency of spontaneous action potential bursts and Ca(2+) spikes with a simultaneous increase in burst duration and Ca(2+) spike amplitude. These network changes were apparent after 4 h treatment with Tat and required the low-density lipoprotein receptor-related protein (LRP). Interestingly, Tat-induced changes in network activity adapted during 24 h exposure. The activity returned to control levels in the maintained presence of Tat for 24 h. These observations indicate that Tat causes aberrant network activity, which is dependent on LRP, and adapts following prolonged exposure. Changes in network excitability may contribute to Tat-induced neurotoxicity in vitro and seizure disorders in vivo. Adaptation of neural networks may be a neuroprotective response to the sustained presence of the neurotoxic protein Tat and could underlie the behavioral and electrophysiological changes observed in HAND.

Experiment assessment of mass effects in the rat: implications for small animal PET imaging

In vivo imaging using positron emission tomography (PET) is important in the development of new radiopharmaceuticals in rodent animal models for use as biochemical probes, diagnostic agents, or in drug development. We have shown mathematically that, if small animal imaging studies in rodents are to have the same "quality" as human PET studies, the same number of coincidence events must be detected from a typical rodent imaging "voxel" as from the human imaging voxel. To achieve this using the same specific activity preparation, we show that roughly the same total amount of radiopharmaceutical must be given to a rodent as to a human subject. At high specific activities, the mass associated with human doses, when administered to a rodent, may not decrease the uptake of radioactivity at non saturable sites or sites where an enzyme has a high capacity for a substrate. However, in the case of binding sites of low density such as receptors, the increased mass injected could saturate the receptor and lead to physiologic effects and non-linear kinetics. Because of the importance of the mass injected for small animal PET imaging, we experimentally compared high and low mass preparations using ex vivo biodistribution and phosphorimaging of three compounds: 2-fluoro-2-deoxyglucose (FDG), 6-fluoro-L-metatyrosine (FMT) and one receptor-directed compound, the serotonin 5HT1A receptor ligand, trans-4-fluoro-N-[2-[4-(2-methoxylphenyl) piperazino]ethyl]-N-(2-pyridyl) cyclohexane- carboxamide (FCWAY). Changes in the mass injected per rat did not affect the distribution of FDG, FMT, and FCWAY in the range of 0.6-1.9 nmol per rat. Changes in the target to nontarget ratio were observed for injected masses of FCWAY in the range of approximately 5-50 nmol per rat. If the specific activity of such compounds and/or the sensitivity of small animal scanners are not increased relative to human studies, small animal PET imaging will not correctly portray the "true" tracer distribution. These difficulties will only be exacerbated in animals smaller than the rat, e.g., mice.

Monitoring the correction of glycogen storage disease type 1a in a mouse model using [(18)F]FDG and a dedicated animal scanner

Monitoring gene therapy of glycogen storage disease type 1a in a mouse model was achieved using [(18)F]FDG and a dedicated animal scanner. The G6Pase knockout (KO) mice were compared to the same mice after infusion with a recombinant adenovirus containing the murine G6Pase gene (Ad-mG6Pase). Serial images of the same mouse before and after therapy were obtained and compared with wild-type (WT) mice of the same strain to determine the uptake and retention of [(18)F]FDG in the liver. Image data were acquired from heart, blood pool and liver for twenty minutes after injection of [(18)F]FDG. The retention of [(18)F]FDG was lower for the WT mice compared to the KO mice. The mice treated with adenovirus-mediated gene therapy had retention similar to that found in age-matched WT mice. These studies show that FDG can be used to monitor the G6Pase concentration in liver of WT mice as compared to G6Pase KO mice. In these mice, gene therapy returned the liver function to that found in age matched WT controls as measured by the FDG kinetics in the liver compared to that found in age matched wild type controls.

A novel approach using transcomplementing adenoviral vectors for gene therapy of adrenocortical cancer

Current therapies for adrenocortical carcinomas do not improve the life expectancy of patients. In this study, we tested whether a gene-transfer therapy based upon a suicide gene/prodrug system would be effective in an animal model of the disease. We employed E4- and E1A/B-depleted, herpes simplex virus-thymidine kinase-expressing adenoviral mutants that transcomplement each other within tumor cells, hereby improving transgene delivery and efficacy by viral replication in situ. Transcomplementation of vectors increased the fraction of transduced of tumor cells. This increase was accompanied by greater tumor volume reduction compared to non-transcomplementing approaches. Survival time improved with non-replicating vectors plus GCV compared to controls. However, transcomplementation/replication of vectors led to a further significant increment in anti-tumor activity and survival time (p < 0.02). In treated animals, we observed a high number of apoptotic nuclei both adjacent to and distant from injection sites and sites of viral oncolysis. Ultrastructural analyses exhibited nuclear inclusion bodies characteristic of virus production in situ, and provided further evidence that this therapy induced apoptotic cell death within tumor cells. We conclude that the efficacy of suicide gene therapy is significantly amplified by viral replication and, in combination with GCV, significantly reduces tumor burden and increases survival time.

High resolution PET, SPECT and projection imaging in small animals

Positron emission tomography, single photon emission computed tomography and planar projection imaging of radioactive tracers have long been in use for detecting and diagnosing disease in human subjects. More recently, advanced versions of these same technologies have begun to be used across the breadth of modern biomedical research to study non-invasively small laboratory animals in a myriad of experimental settings. In this report, we describe some of the new instruments and techniques that make these measurements possible and illustrate, with a few examples, the potential power of these methods in modern biomedical research.

Performance characteristics of the 3-D OSEM algorithm in the reconstruction of small animal PET images. Ordered-subsets expectation-maximixation

Rat brain images acquired with a small animal positron emission tomography (PET) camera and reconstructed with the three-dimensional (3-D) ordered-subsets expectation-maximization (OSEM) algorithm with resolution recovery have better quality when the brain is imaged by itself than when inside the head with surrounding background activity. The purpose of this study was to characterize the dependence of this effect on the level of background activity, attenuation, and scatter. Monte Carlo simulations of the imaging system were performed. The coefficient of variation from replicate images, full-width at half-maximum (FWHM) from point sources and image profile fitting, and image contrast and uniformity were used to evaluate algorithm performance. A rat head with the typical levels of five and ten times the brain activity in the surrounding background requires additional iterations to achieve the same resolution as the brain-only case at a cost of 24% and 64% additional noise, respectively. For the same phantoms, object scatter reduced contrast by 3%-5%. However, attenuation degraded resolution by 0.2 mm and was responsible for up to 12% nonuniformity in the brain images suggesting that attenuation correction is useful. Given the effects of emission and attenuation distribution on both resolution and noise, simulations or phantom studies should be used for each imaging situation to select the appropriate number of OSEM iterations to achieve the desired resolution-noise levels.

Evaluation of 99mTc-mercaptoacetyltriglycine-biocytin as a new hepatobiliary imaging agent in mice coinjected with bilirubin

We evaluated 99mTc-labeled mercaptoacetyltriglycine (99mTc-MAG3)-biocytin as a hepatobiliary imaging agent in the absence and presence of bilirubin in mice. We then compared its pharmacokinetic parameters; peak liver/heart activity ratio (rmax) and half clearance time (HCT) with those of 99mTc-labeled diisopropyl-iminodiacetic acid (99mTc-disofenin). Balb/c mice were injected intravenously with hepatobiliary agent (99mTc-MAG3-biocytin or 99mTc-disofenin) alone or in combination with bilirubin at two doses (7 and 14 mg/kg) dissolved in 5% human serum albumin. Images were acquired every 15 s for 30 min with a gamma-camera equipped with a pinhole collimator. Dynamic images showed rapid hepatic uptake of 99mTc-MAG3-biocytin, with rapid clearance from the blood and rapid excretion via the biliary system. Its hepatic uptake was not affected by bilirubin coinjection, whereas 99mTc-disofenin coinjected with bilirubin showed a higher blood background than 99mTc-disofenin alone. These qualitative findings were reflected in pharmacokinetic parameters, rmax and HCT. The rmax was obtained from plots of time versus liver/heart activity ratios obtained in equal-area regions of interest over the heart and liver. The HCT was calculated from the hepatic clearance curve from plots of time versus liver activity. 99mTc-MAG3-biocytin without bilirubin coinjection showed an rmax of 8.9+/-1.3 and an HCT of 399+/-36 s. These values did not change even when 14 mg/kg of bilirubin were coinjected. By contrast, the parameters for 99mTc-disofenin with bilirubin were significantly (p < 0.01) affected by 14 mg/kg of bilirubin coinjection: rmax was decreased from 7.9+/-2.5 to 1.4+/-0.2 and HCT was increased from 292+/-32 s to 782+/-133 s. 99mTc-MAG3-biocytin hepatobiliary scintigraphy in mice is not affected by bilirubin coinjection, and this hepatobiliary agent appears to offer promise for estimating hepatic function in patients with high bilirubin levels.

Performance characteristics of a compact position-sensitive LSO detector module

We assembled a compact detector module comprised of an array of small, individual crystals of lutetium oxyorthosilicate:Ce (LSO) coupled directly to a miniature, metal-can, position-sensitive photomultiplier tube (PSPMT). We exposed this module to sources of 511-keV annihilation radiation and beams of 30- and 140-keV photons and measured spatial linearity; spatial variations in module gain, energy resolution, and event positioning; coincidence timing; the accuracy and sensitivity of identifying the crystal-of-first-interaction at 511 keV; and the effects of intercrystal scatter and LSO background radioactivity. The results suggest that this scintillator/phototube combination should be highly effective in the coincidence mode and can be used, with some limitations, to image relatively low-energy single photon emitters. Photons that are completely absorbed on their first interaction at 511 keV are positioned by the module at the center of a crystal. Intercrystal scatter events, even those that lead to total absorption of the incident photon, are placed by the module in a regular "connect-the-dot" pattern that joins crystal centers. As a result, the accuracy of event positioning can be made to exceed 90%, though at significantly reduced sensitivity, by retaining only events that occur within small regions-of-interest around each crystal center and rejecting events that occur outside these regions in the connect-the-dot pattern.

Use of 99mTc-mercaptoacetyltriglycine (MAG3)-biocytin hepatobiliary scintigraphy to study the protective effect of a synthetic enzyme inhibitor on acute hepatotoxicity in mice

Recent data suggest that inhibitors of ethanol-inducible cytochrome P450 (CYP2E1) can protect the liver from injury caused by various substrates of CYP2E1. In this study, we measured the protective effect of isopropyl-2-(1,3-dithioetane-2-ylidene)-2[N-(4-methylthiazol -2-yl)-carbamoyl]acetate (YH439), a transcriptional inhibitor of CYP2E1, against carbon tetrachloride (CCl4)-induced hepatotoxicity by using various conventional methods and dynamic scintigraphy with 99mTc-mercaptoacetyltriglycine (MAG3)-biocytin, a recently developed scintigraphic agent. Balb/c mice were pretreated with two doses of YH439 (50 or 150 mg/kg per day) at 48 h and 24 h and one dose of CCl4 (0.25 mL/kg) at 18 h before scintigraphy. The results were compared with those of two other groups, one that received CCl4 but not YH439, and the other that received neither (control). Scintigraphic images were acquired continuously at 15-sec intervals for 30 min. Pharmacokinetic parameters, such as peak liver/heart ratio (r(max)), peak liver uptake time (t(max)), and hepatic half-clearance time (HCT), were obtained from time-activity curves derived from regions-of-interest (ROI) over the liver and the heart. Acute administration of CCl4 alone caused centrilobular necrosis and serum transaminase levels to rise more than 5 times higher than those of the control group. Pharmacokinetic parameters also changed significantly from those of the control group. Administration of YH439 prevented centrilobular necrosis and significantly improved pharmacokinetic parameters. This study demonstrates for the first time that hepatobiliary scintigraphy can be used to study in vivo biochemistry of the CYP2E1 inhibitor (YH439) against liver toxicity.

The case of Mr. Martinez: ethical conflicts in home care

Mr. Martinez recently was accepted into the Valley Hospice Program with a diagnosis of end-stage lung cancer. He currently lives with his daughter, Amelia, after moving from Puerto Rico 2 years ago after his wife died. His two sons and another daughter live within 20 minutes of Amelia's home. They are a close-knit family, and the children are committed to honoring Martinez' wishes to die in his room in Amelia's home.

A head motion measurement system suitable for emission computed tomography

Subject motion during brain imaging studies can adversely affect the images through loss of resolution and other artifacts related to movement. We have developed and tested a device to measure head motion externally in real-time during emission computed tomographic (ECT) brain imaging studies, to be used eventually to correct ECT data for that motion. The system is based on optical triangulation of three miniature lights affixed to the patient's head and viewed by two position-sensitive detectors. The computer-controlled device converts the three sets of lamp positions into rotational and translational coordinates every 0.7 seconds. When compared against a mechanical test fixture, the optical system was found to be linear and accurate with minimal crosstalk between the coordinates. In a study of two subjects, comparing the angular motions measured by the optical device and a commercially available electromagnetic motion detector, the two systems agreed well, with an root mean square (rms) difference of less than 0.6 degree for all rotations.

Dynamic circular buffering: a technique for equilibrium gated blood pool imaging

We have devised a software technique called "dynamic circular buffering" (DCB) with which we create a gated blood pool image sequence of the heart in real time using the best features of LIST and FRAME mode methods of acquisition/processing. The routine is based on the concept of independent "agents" acting on the timing and position data continuously written into the DCB. This approach allows efficient asynchronous operation on PC-type machines and enhanced capability on systems capable of true multiprocessing and multithreading.

Head movement in normal subjects during simulated PET brain imaging with and without head restraint

Head movement during brain imaging is recognized as a source of image degradation in PET and most other forms of medical brain imaging. However, little quantitative information is available on the kind and amount of head movement that actually occurs during these studies. We sought to obtain this information by measuring head movement in normal volunteers.

METHODS

Head position data were acquired for 40 min in each of 13 supine subjects with and without head restraint. These data were then used to drive a mathematically simulated head through exactly the same set of movements. The positions of point sources embedded in this head were computed at each location and these data summarized as movement at FWHM in each of the three coordinate directions.

RESULTS

Head movement increased with the length of the sampling interval for studies of either type (with or without head restraint), but the amount and rate of increase with restraint was much smaller. In contrast, head movement during consecutive, short sampling intervals was small and did not increase with time. Spatial gradients in head movement were detected within each study type, and significant spatial differences in head movement were found between study types.

CONCLUSIONS

Head movements in normal, supine subjects, though small, can cause the effective resolution of a brain imaging study to appear to vary in space and time. These effects can be reduced significantly with head restraint and may also be reduced by dividing the acquisition of a single image into a sequence of short images (instead of a single long image), aligning these images spatially and summing the result.

Assessment of coronary artery disease by radionuclide cineangiography. History, current applications, and new directions

In recent years, the utility of radionuclide cineangiography in prognostication has made it a mainstay of management decision making. With evolution of therapeutic modalities and concomitant alteration in management strategies, however, the technique and its application are undergoing parallel evolution to optimize response to current needs. Thus, in addition to standard planar rest and exercise assessment of left ventricular function, newer approaches are involving combined perfusion and function assessment, application of pharmacological stress to permit technically advantageous variations in imaging protocols, and application of SPECT technology in collecting blood pool data for tomographic display and analysis.

Performance characteristics of a 511-keV collimator for imaging positron emitters with a standard gamma-camera

Line-source experiments were conducted to assess the performance of a gamma-camera equipped with a specially designed 511-keV collimator for the planar imaging of positron emitters. The results were compared with the camera performance with routinely used collimators and radionuclides (thallium-201, technetium-99m and gallium-67). With positron emitters, scatter contributed less to the widening of the line spread function than with radionuclides emitting lower photon energies. These observations can be explained by the relative deterioration in the discrimination power of the gamma-camera to reject scattered radiation at low energies. Planar 511-keV imaging may provide relevant clinical information, as we showed by fluorodeoxyglucose studies in a patient with a myocardial infarction and in a patient with a malignant lymphoma. It is concluded that positron emitters can be effectively applied for planar imaging with the generally available gamma-cameras. This study implies that radiotracers developed for positron emission tomography may find a place in the practice of conventional nuclear medicine.

A theoretical comparison of first-pass and gated equilibrium methods in the measurement of systolic left ventricular function

First-pass and gated equilibrium radionuclide studies of left ventricular function have proven extremely useful in the detection and management of patients with heart disease. Despite this practical experience, however, comparison of these methods generally has been confined to procedural differences that do not reflect the intrinsic properties of the methods. Here, we describe the results of a simple theoretical calculation from first principles that compares the methods based on their relative statistical precision. This analysis assumes that each procedure is carried out with the same tracer dose in the same hypothetical patient under identical conditions and with the same ideal imaging equipment. Results obtained with this model suggest that the imaging time required for a gated equilibrium study to achieve the same statistical precision as a first-pass study is typically less than 2 min in resting subjects and less than 1 min during stress. The analysis also indicates that gated equilibrium studies will tend to possess the greater statistical precision when cardiac output is elevated, such as when the heart is imaged during exercise. On the other hand, this analysis indicates that the first-pass method will tend to possess the greater precision when cardiac output is low and when imaging time is highly constrained.

Coronary vasoconstriction induced by vasopressin. Production of myocardial ischemia in dogs by constriction of nondiseased small vessels

BACKGROUND

We studied the effect of intracoronary administration of arginine-8-vasopressin on blood flow in nondiseased coronary arteries and determined whether this vasoconstriction was severe enough to produce ischemia in 30 dogs.

METHODS AND RESULTS

In group 1 (n = 6), after vasopressin administration coronary blood flow was decreased by 41% (p less than 0.002) without changes in heart rate or aortic pressure, and left ventricular ejection fraction measured by radionuclide angiocardiography was decreased by 18% (p less than 0.0005). In group 2 (n = 6), ischemia was confirmed by measurement of transmural pH changes. Administration of vasopressin decreased subendocardial pH of the infused zone from 7.40 +/- 0.03 to 7.31 +/- 0.07 (p less than 0.01). The subendocardial pH of the zone not infused with vasopressin did not change. To overcome the intrinsic regulation of blood flow, operating primarily in small coronary arteries, we hypothesized that vasopressin must increase resistance primarily in large rather than small coronary arteries. After intracoronary infusion in group 3 (n = 6), however, most (94%) of the increase in resistance during vasopressin administration was explained by an increase of resistance in small coronary arteries. In group 4 (n = 9), vasopressin decreased coronary blood flow by 50% and decreased local shortening by 90% at a time when systemic hemodynamics were unchanged. Coronary constriction induced by vasopressin, or the recovery from it, also was not altered by cyclooxygenase blockade.

CONCLUSIONS

Thus, vasopressin produces myocardial ischemia by constricting small, nondiseased coronary arteries severely enough to overcome the competition from normal coronary regulation, and this ischemic event is not mediated by prostaglandin products.

Comparison of fixed and variable temporal resolution methods for creating gated cardiac blood-pool image sequences

In each of 50 resting subjects, two gated blood-pool image sequences were created from the same LIST mode data set. One sequence was created using a sorting method that spans each individual cardiac cycle with the same number of images (the "variable temporal" or VT method), while the other (the "fixed temporal" or FT method) spans the average cardiac cycle with images of fixed temporal duration. Left ventricular time-activity curves were extracted from each sequence using identical regions-of-interest and analyzed with identical methods to obtain estimates of ejection fraction, peak ejection rate, peak filling rate, and the times of occurrence of these peak rates. Differences among certain of these parameters in kind and amount support the hypothesis that estimates of resting cardiac function are more accurately portrayed by the FT method. The magnitudes of these differences are small for systolic parameters but large for early diastolic parameters. Thus, although both methods might be used for measuring systolic function, the FT method will yield a more accurate estimate of peak filling rate in resting subjects.

Diagnosis of coronary artery disease by radionuclide angiography: effect of combining indices of left ventricular function

The aim of this study was to determine whether the diagnostic capability of radionuclide angiography (RNA) in detecting coronary artery disease (CAD) might be improved by using several indices of left ventricular (LV) function in concert. Three different models (rest data, exercise data, and rest plus exercise data) were derived by stepwise multivariate discriminant analysis of RNA data in 65 normal volunteers and 111 patients with CAD and normal ejection fraction (EF) at rest. The model with only resting indices yielded a diagnostic capability comparable to the simple measure of EF response to exercise (area under receiver operating characteristic curve = 89% and 91%, respectively). Both the exercise and rest plus exercise models gave better results (area = 94% and 97%, respectively), but only the rest plus the exercise model was better than the EF response alone (p less than 0.001). Thus (a) if resting studies alone are performed, the diagnostic potential of RNA may be improved by combining several indices of resting function; and (b) combined rest and exercise data may improve the sensitivity of RNA in detecting CAD over what could be obtained with the EF response to exercise alone.

Influence of temporal smoothing on quantitation of left ventricular function by gated blood pool scintigraphy

Frequently, indexes of systolic and diastolic left ventricular (LV) function obtained from radionuclide angiography are computed after the LV time-activity curve has been temporally smoothed. This smoothing process may introduce important systematic errors into the analysis. To assess this potential effect, high temporal resolution time-activity curves (20 ms/point) were obtained in 113 normal subjects, 175 patients with coronary artery disease and 171 patients with hypertrophic cardiomyopathy. The curves were then subjected to 0-, 3-, 5-, 7- and 9-point temporal smoothing. In each group, increased smoothing progressively and consistently underestimated ejection fraction by up to 5% (p less than 0.001) and peak ejection rate by up to 14% (p less than 0.001). A greater effect on peak filling rate was observed: 5-point and 9-point smoothing reduced peak filling rate by 10% and 23% in normal subjects, 3% and 10% in patients with coronary artery disease and 7% and 15%, respectively, in patients with hypertrophic cardiomyopathy (all p less than 0.001). These errors were compounded further when the same data obtained at lower temporal resolution (40 ms/point) were analyzed: 5-point and 9-point smoothing resulted in underestimation of peak filling rate by 20% and 46% in normal subjects, 13% and 43% in coronary artery disease and 16% and 34% in hypertrophic cardiomyopathy. The underestimation was not uniform, and its magnitude varied considerably among individuals in each of the 3 groups. Thus, smoothing of LV time-activity curves may result in significant systematic errors in computation of indexes of LV systolic and diastolic function, especially in data with poor temporal resolution. These concepts apply to other imaging methods, such as magnetic resonance imaging and cine-computed tomography, that assess LV function from the LV volume curve. Although ejection fraction is affected only mildly by these errors, both peak filling rate and peak ejection rate may be severely underestimated.

A method for postinjection PET transmission measurements with a rotating source

A method is presented for obtaining accurate positron emission tomography transmission measurements after tracer injection. A transmission scan is performed using a rotating source immediately before or after a conventional emission scan. Sinogram windowing, which removes most scattered and random coincidences, also removes most of the emission counts contaminating the transmission measurement. Data from the emission scan can be used to subtract the remaining emission counts to produce accurate transmission measurements. For studies with moderate to low emission count rates (e.g., fluorodeoxyglucose) there is little increase in noise in the resulting attenuation correction factors. This method was tested in experiments with phantoms and a rotating source simulator and validated against conventional ring transmission measurements. Applications of the technique can significantly shorten the time between transmission and emission studies, and thereby reduce the likelihood of patient motion and increase scanning throughput.

The effect of coronary artery bypass grafting on left ventricular systolic function at rest: evidence for preoperative subclinical myocardial ischemia

Successful coronary artery bypass grafting (CABG) improves exercise-induced left ventricular (LV) dysfunction in patients with coronary artery disease (CAD), but its potential for improving resting LV function remains controversial. To assess the influence of CABG on LV function at rest, 31 CAD patients without previous myocardial infarction were studied before and 6 months after CABG by radionuclide angiography after all cardiac medicines were withdrawn. No patient had angina or ischemic electrocardiographic changes at rest. In 27 patients with patent bypass grafts, CABG significantly increased LV ejection fraction during exercise (47 +/- 11% before to 63 +/- 9% after operation, p less than 0.001), indicating reduction in exercise-induced LV ischemia. Moreover, LV ejection fraction at rest also increased (55 +/- 9 to 60 +/- 8%, p less than 0.001), with 20 of 27 patients manifesting an increase compared with preoperative values. Eleven of these 20 patients had apparently normal LV function at rest (ejection fraction and regional wall motion) before CABG. LV regional ejection fraction was computed by dividing the LV region of interest into 20 sectors. Regional analysis indicated that improved ejection fraction at rest after CABG occurred in regions developing ischemia during exercise before CABG. In 4 patients with occluded grafts, the ejection fraction at rest was unchanged by CABG globally (59 +/- 8 to 58 +/- 9%, difference not significant) and regionally. Thus, LV global and regional function at rest improved after successful CABG, even in patients with normal global LV ejection fraction and no visually detectable wall motion abnormality before surgery.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of energy window on cardiac ejection fraction

ECG gated gamma-ray energy spectra from the left ventricle were created each 50 msec during the cardiac cycle. Nine of ten subjects were studied with a nonimaging Nal probe, and the tenth with a high-resolution Germanium detector. Placing multiple energy windows over the energy spectra, EF was found to vary with the energy window selected. Moving a 20% window across the photopeak produced a roughly linear increase in EF with energy (2.3 EF units per 10 keV increase in energy) in eight of the ten subjects. Dividing the photopeak into a low (126-140 keV) and high-energy (140-154 keV) portion gave significantly different EFs (high energy exceeding low energy by 17%). Increasing the width of a narrow window centered about the photopeak produced negligible change in EF. Examining the energy spectra showed that the small-angle scattered radiation (126-139 keV) was proportionately greater at end systole than at end diastole, after normalizing the spectra to the same photopeak area.

Effects of aging on asynchronous left ventricular regional function and global ventricular filling in normal human subjects

In many patients with coronary artery disease or hypertrophic cardiomyopathy, reduced left ventricular rapid diastolic filling is related to asynchronous left ventricular regional diastolic function. Because left ventricular filling also declines with aging in normal subjects, in this study the influence of regional ventricular diastolic asynchrony on global ventricular filling as a function of age was investigated in 66 normal volunteers aged 19 to 77 years (mean 42) by radionuclide angiography. No subject had systemic hypertension or left ventricular hypertrophy. Indexes of left ventricular systolic function at rest did not vary with age, but rapid diastolic filling significantly declined with age: peak filling rate decreased (r = 0.69), time to peak filling rate increased (r = 0.53) and magnitude of rapid filling (% of left ventricular end-diastolic volume) decreased (r = 0.76) with aging. Left ventricular synchrony was assessed from regional volume curves derived by dividing the global ventricular region of interest into four quadrants. Indexes of systolic synchrony were unaffected by age, but regional variation in time to peak filling rate, an index of diastolic asynchrony, increased with aging (r = 0.51, p less than 0.001). Moreover, variation in time to peak filling rate correlated with global peak filling rate and magnitude of rapid filling (r = 0.48 and 0.54, p less than 0.001 for both). Multivariate analysis indicated that these effects were independent of age-related changes in blood pressure. Thus, aging alters left ventricular diastolic function, with reduced rate and extent of the rapid filling phase related to increased regional diastolic asynchrony.(ABSTRACT TRUNCATED AT 250 WORDS)

Prognostic implications of symptomatic versus asymptomatic (silent) myocardial ischemia induced by exercise in mildly symptomatic and in asymptomatic patients with angiographically documented coronary artery disease

Patients with coronary artery disease (CAD) may undergo periods of reversible myocardial ischemia without experiencing angina. To study the prognostic implications of "silent" myocardial ischemia induced by exercise, exercise electrocardiography and radionuclide angiography were performed in 131 consecutive patients with CAD, preserved left ventricular (LV) function at rest and mild or no symptoms during medical therapy. All patients who died during medical therapy were in the subgroup of patients with 3-vessel CAD in whom exercise-induced ischemia developed, which was characterized by both a decrease in LV ejection fraction and ST-segment depression. Patients in whom angina pectoris developed during exercise (54% of all patients) had a greater prevalence of this combined ischemic response to exercise than patients without angina (61% vs 27%, p less than 0.001) and also a greater prevalence of left main or 3-vessel CAD (59% vs 25%, p less than 0.001). However, when inducible ischemia was demonstrated, risk stratification and prognosis were the same whether the ischemic episode was symptomatic or silent. Among patients having both a reduction in ejection fraction and a positive ST-segment response, the likelihood of significant left main narrowing (13% vs 26%), 3-vessel CAD (56% vs 51%) and death during subsequent medical therapy (16% vs 9%) was similar in patients with silent compared to those with symptomatic ischemia. These data indicate that patients in whom angina develops during exercise have a greater prevalence of high-risk coronary anatomy and of inducible ischemia than patients without angina. However, once inducible ischemia is documented, the symptomatic response to exercise appears irrelevant for prognostic or risk stratification considerations.

Regional left ventricular asynchrony and impaired global left ventricular filling in hypertrophic cardiomyopathy: effect of verapamil

Left ventricular relaxation and filling are impaired in many patients with hypertrophic cardiomyopathy. To investigate the influence of regional heterogeneity on these global abnormalities, 48 patients with hypertrophic cardiomyopathy and sinus rhythm were studied by radionuclide angiography before and after 1 to 2 weeks of verapamil therapy (320 to 640 mg/day, median 480). Left ventricular regional function was assessed by subdividing the ventricular region of interest into 20 sectors and into four quadrants from which regional time-activity curves were derived. Diastolic asynchrony was measured as the regional variation in timing between minimal volume and peak filling rate, and heterogeneity in the magnitude of rapid diastolic filling was measured as the regional variation in percent contribution of atrial systole to end-diastolic volume. Compared with 28 normal subjects, the patients with hypertrophic cardiomyopathy had greater regional variation in both timing (35 +/- 24 versus 12 +/- 6 ms, p less than 0.001) and magnitude (10 +/- 6 versus 7 +/- 4%, p less than 0.02) of rapid filling. Verapamil reduced the regional variation in timing (to 21 +/- 16 ms, p less than 0.001) and magnitude (to 7 +/- 3%, p less than 0.001) of rapid filling. These regional changes, indicating more uniform regional diastolic performance after verapamil, were associated with improved global diastolic filling: global rapid filling increased in both rate and magnitude and time to peak filling rate decreased. These findings indicate that the beneficial effect of verapamil on left ventricular diastolic function in hypertrophic cardiomyopathy may be mediated by reduction in regional asynchrony.

Functional consequences and intracoronary localization of alpha-adrenergic stimulation of the canine coronary circulation

Although alpha-adrenergic stimulation can increase coronary vascular resistance, it remains unknown whether the vasoconstriction can override intrinsic coronary regulatory influences to produce ischemia. Methoxamine, 2 to 4 mg, was infused into the circumflex coronary artery of 23 chloralose-anesthetized open chest dogs, and resulted in a 68% increase in coronary vascular resistance. The functional consequence of this increased coronary vascular resistance was assessed by gated radionuclide ventriculography and ST-T wave changes on the electrocardiogram. In six dogs (Group I), aortic pressure changed trivially (less than 5 mm Hg) to allow distinction between direct effects of the flow reduction and indirect effects of increased aortic pressure. In this group, coronary blood flow decreased 33% from a control value of 44 +/- 10 ml/min (p less than 0.001) and left ventricular ejection fraction decreased from 0.54 +/- 0.12 to 0.46 +/- 0.10 (p less than 0.025). In eight dogs (Group II) in which aortic pressure increased by more than 5 mm Hg, left ventricular ejection fraction decreased from 0.46 +/- 0.07 to 0.39 +/- 0.09 (p less than 0.002). Pressure gradients were measured between the aorta and a distal coronary artery branch to calculate small and large vessel resistances separately in four other dogs (Group III). The resistance of small coronary arteries accounted for 92% of the total increase in coronary vascular resistance produced by methoxamine. In five other dogs (Group IV), intracoronary methoxamine, 2 mg, produced ST-T wave changes suggestive of ischemia as it increased coronary vascular resistance by 33%.(ABSTRACT TRUNCATED AT 250 WORDS)

Prospective evaluation of doxorubicin cardiotoxicity by rest and exercise radionuclide angiography

The role of rest and exercise radionuclide angiography (RNA) in predicting the cardiotoxic effects of doxorubicin was assessed prospectively in 48 patients who received a mean total doxorubicin dose of 522 mg/m2 (range 480 to 600). Thirty-three of these patients also received cyclophosphamide (mean 5,220 mg/m2). Left ventricular (LV) ejection fraction (EF) at rest progressively decreased from the baseline value of 55 +/- 9% to 52 +/- 8% after 338 mg/m2 to 47 +/- 8% after completion of doxorubicin therapy (p less than 0.001). In 42 patients (88%) EF at rest decreased after doxorubicin administration. Although no patient had known prior heart disease, the EF response to exercise was abnormal in 11 patients before doxorubicin. EF at rest after doxorubicin was significantly lower (41 +/- 6% vs 49 +/- 8%, p less than 0.02) in these 11 patients than in the 29 patients in whom the pretreatment EF response to exercise was normal, and in 4 of the 11 patients congestive heart failure developed. While age was an independent risk factor, cyclophosphamide did not appear to enhance the cardiotoxicity of doxorubicin. By multivariate analysis, age (p = 0.01) and EF at the midcourse of doxorubicin therapy (p less than 0.001) were the most significant predictors of final EF after completion of doxorubicin therapy; neither rest nor exercise EF before doxorubicin appreciably improved the predictive value of age and EF at midcourse of therapy. Thus, some depression of LV function occurs in most patients receiving doxorubicin, and patients with abnormal baseline function appear to be at greater risk of clinical congestive heart failure after doxorubicin therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Weighted integration method for local cerebral blood flow measurements with positron emission tomography

A new technique called the weighted integration method for the measurement of local CBF (LCBF) in humans with positron emission tomography (PET) is presented. LCBF is calculated from weighted time integrals of the blood and tissue radioactivity curves. This method is computationally efficient and achieves nearly optimal statistical estimation of LCBF. The predicted root mean squared error of the weighted integration method is verified by simulation studies and is only 1-2% larger than the minimum possible error that can be achieved by an ideal estimation algorithm. For LCBF of greater than 30 ml/min/100 g, the weighted integration method provides reduced noise compared with the integrated projection technique, the PET autoradiographic method, and the steady-state technique. In addition, an error analysis is performed to study the sensitivity of the weighted integration method to tissue mixtures, blood sample timing errors, and changes in LCBF during the data collection period.

Isovolumic relaxation period in hypertrophic cardiomyopathy: assessment by radionuclide angiography

Left ventricular isovolumic relaxation and the relation between relaxation and filling were studied in 90 patients with hypertrophic cardiomyopathy and 29 control subjects using radionuclide angiography. The isovolumic relaxation period was determined automatically on left ventricular time-activity curves as the interval between minimal volume and onset of rapid filling. In 17 patients, M-mode echocardiography performed simultaneously with radionuclide angiography demonstrated that onset of mitral valve opening correlated well with onset of rapid filling (r = 0.84, p less than 0.001). The isovolumic relaxation period was longer in patients with hypertrophic cardiomyopathy than in control subjects (95 +/- 44 versus 50 +/- 23 ms, p less than 0.01) and was longer in patients without an outflow tract gradient at rest than in patients with a gradient (109 +/- 37 versus 86 +/- 35 ms, p less than 0.05). In these patients without obstruction, a weak linear relation between duration of the isovolumic period and peak filling rate was found (r = 0.48, p less than 0.02). Filling was impaired in patients with hypertrophic cardiomyopathy, as assessed by lower peak filling rate (3.2 +/- 1.2 versus 3.5 +/- 0.5 end-diastolic volume/s, p less than 0.05) and prolonged time to peak filling rate (185 +/- 44 versus 145 +/- 20 ms, p less than 0.01) compared with values in control subjects. The delay in time to peak filling rate was caused primarily by the prolonged isovolumic period, because the interval from onset of rapid filling to peak filling rate was similar in patients with hypertrophic cardiomyopathy and control subjects (87 +/- 31 versus 95 +/- 25 ms, NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Parabiotic transfer of cancer anorexia/cachexia in male rats

To demonstrate that the anorexia and depletion of cachexia reverses on tumor removal, F344 rats underwent sarcoma resection when their food intake fell to 0 g/day. In survivors of surgery, reversal in food intake was apparent within 3 days postoperatively, followed after 2 days by gain in host weight. To detect whether the transmission of anorexia/cachexia in these tumor-bearing (TB) rats was via the circulation, four groups were studied: single non-tumor bearing (NTB); single TB; parabiotic NTB; and parabiotic TB. The measured blood exchange rate between parabiotic halves was 1.2-1.5%/min. No cachectic effect was detected in either half of the NTB parabionts. There was no evidence of sarcoma metastases in the tumor-free half of the parabiotic TB pair. All the rats associated with the presence of tumor showed cachectic effects but the degree and timing of effect varied among the three conditions, single TB, parabiotic TB half, and parabiotic tumor-free half. In all variables examined (fall in food intake, time of first fall in food intake, host weight loss, elevation of blood urea nitrogen) the severities were always in the same sequence: single TB greater than parabiotic TB half greater than parabiotic tumor-free half greater than NTB. In addition, the TB parabiotic pair had a significantly longer survival time and grew a significantly larger tumor than did the single TB animal. The parabiotic tumor had a slower initial growth rate and a slower deceleration rate than the singlet tumor. These results provide evidence for the humoral mediation of cancer-associated cachexia.

Verapamil-induced improvement in left ventricular diastolic filling and increased exercise tolerance in patients with hypertrophic cardiomyopathy: short- and long-term effects

Verapamil improves exercise tolerance and decreases symptoms in many patients with hypertrophic cardiomyopathy. The mechanisms responsible for these effects are not completely understood, although previous studies indicate that verapamil enhances left ventricular relaxation and diastolic filling in such patients. To investigate the association between changes in left ventricular filling and exercise tolerance after verapamil, we studied 55 patients with hypertrophic cardiomyopathy by radionuclide angiography and graded treadmill testing before and after 1 to 4 weeks of therapy with orally administered verapamil, 320 to 640 mg/d. The verapamil-induced increase in peak left ventricular filling rate at rest (from 3.1 +/- 1.3 to 3.7 +/- 1.3 end-diastolic volumes/sec; p less than .001) was associated with an increase in exercise tolerance (from 5.9 +/- 3.6 to 8.7 +/- 4.7 min; p less than .001); exercise capacity increased in 34 of 43 patients (79%) manifesting an increase in peak filling rate but only one of 12 patients (8%) with unchanged or decreased peak filling rate (p less than .001). This initial trend persisted in 25 patients studied after 1 year of therapy; 11 of 16 patients (69%) with a persistent increase in peak filling rate had persistent improvement in exercise tolerance relative to preverapamil values, compared with only one of nine patients (11%) in whom peak filling rate was unchanged or decreased relative to preverapamil levels (p less than .02). Verapamil withdrawal after 1 to 2 years in 24 patients resulted in reduction in peak filling rate (p less than .001) and was associated with deterioration in exercise tolerance in 17 patients (71%). Hence, verapamil-induced changes in left ventricular peak filling rate were associated significantly with objective symptomatic improvement. These data support the concept that enhanced left ventricular diastolic filling is an important mechanism contributing to the clinical improvement experienced by many patients with hypertrophic cardiomyopathy during therapy with verapamil.

Asynchronous left ventricular regional function and impaired global diastolic filling in patients with coronary artery disease: reversal after coronary angioplasty

Left ventricular diastolic filling is impaired in many patients with coronary artery disease and normal left ventricular systolic function, and is improved in many patients after coronary angioplasty (PTCA). To investigate the mechanisms for this improvement, we studied regional asynchrony by radionuclide angiography in 26 patients with single-vessel coronary artery disease before and after successful PTCA. Before PTCA, all patients had normal ejection fractions at rest and normal qualitative left ventricular regional wall motion, as determined by radionuclide and contrast angiography. Quantitative left ventricular regional function was assessed by dividing the left ventricular region of interest into 20 sectors. Phase analysis was performed on each sector's time-activity curve, and the average intersector phase difference was used as an index of left ventricular regional synchrony. Before PTCA, average intersector phase difference was increased compared with normal (6.0 +/- 2.2 vs 4.0 +/- 1.7 degrees, p less than .005), indicating asynchronous regional function. After PTCA, ejection fraction at rest was unchanged, but peak left ventricular filling rate at rest increased from 2.5 +/- 0.6 to 3.0 +/- 0.6 end-diastolic volume/sec (p less than .001) and was associated with a decrease in average intersector phase difference from 6.0 +/- 2.2 to 5.1 +/- 2.3 degrees (p less than .05). Average intersector phase difference decreased in 16 of 21 patients in whom peak filling rate increased after PTCA (p less than .005), compared with one of five patients in whom peak filling rate was unchanged or decreased. Hence, improved global left ventricular filling after PTCA was associated with more synchronous left ventricular regional behavior. To identify the cause of regional asynchrony before PTCA, we then generated time-activity curves from each of four left ventricular quadrants. These data indicated that the asynchrony was caused by regional variation in timing of diastolic rather than systolic events and that PTCA resulted in reduction in regional diastolic asynchrony. These data suggest that in many patients with coronary artery disease and normal left ventricular systolic function, impaired global diastolic filling may result from asynchronous left ventricular regional diastolic function, which is a reversible manifestation of myocardial ischemia or reduced coronary flow.

Left ventricular dysfunction in patients with angina pectoris, normal epicardial coronary arteries, and abnormal vasodilator reserve

Thirty-three patients with chest pain despite angiographically normal coronary arteries underwent both coronary flow studies during pacing and resting and exercise gated blood pool scintigraphy. During atrial pacing after administration of ergonovine, those patients developing their typical chest pain demonstrated significantly lower great cardiac vein flow (97 +/- 31 vs 150 +/- 33 ml/min, p less than .001), higher coronary resistance (1.27 +/- 0.43 vs 0.77 +/- 0.18 mm Hg/ml/min, p less than .005), and less lactate consumption (30.5 +/- 22.0 vs 69.7 +/- 41.1 mM . ml/min, p less than .005) and a higher left ventricular end-diastolic pressure after pacing (20 +/- 4 vs 12 +/- 1, p less than .001) compared with those without pain and in the absence of significant luminal narrowing of the epicardial coronary arteries. The 26 patients with abnormal vasodilator reserve demonstrated reduced left ventricular ejection fraction during exercise (58 +/- 8%) compared with the seven patients with appropriate vasodilator reserve (66 +/- 4%, p less than .05) and with a group of 52 control patients of similar age and sex distribution and free of known heart disease (66 +/- 10%, p less than .001). In addition, 12 of the 26 patients with abnormal vasodilator reserve demonstrated exercise-induced regional wall motion abnormalities. Many of these patients also manifested impaired left ventricular diastolic filling at rest compared with the control subjects (peak filling rate 2.6 +/- 0.7 vs 3.2 +/- 0.7 end-diastolic volume/sec, p less than .005). Thus, patients with chest pain resulting from abnormal vasodilator reserve demonstrate abnormalities of left ventricular systolic and diastolic function suggestive of myocardial ischemia.

Exercise-induced ischemia in mildly symptomatic patients with coronary-artery disease and preserved left ventricular function. Identification of subgroups at risk of death during medical therapy

To determine prospectively whether the severity of reversible left ventricular ischemia provides prognostic information in mildly symptomatic patients with coronary-artery disease and preserved left ventricular function at rest (ejection fraction greater than 40 per cent), we studied 117 patients by means of exercise electrocardiography and radionuclide angiography. No patient had stenosis of the left main coronary artery. Mortality during subsequent medical therapy was significantly associated (by univariate life-table analysis) with three-vessel coronary-artery disease and the magnitude of the ejection fraction during exercise. In patients with three-vessel disease who had both ST-segment depression of 1 mm or more and a decrease in ejection fraction during exercise, in association with an exercise tolerance of 120 W or less, the probability of survival at four years was only 71 +/- 11 per cent (S.E.). All deaths occurred in this subgroup. Thus, objective evidence of left ventricular ischemia during exercise and exercise capacity identify one subgroup of minimally symptomatic patients with three-vessel disease with an excellent prognosis and another subgroup at relatively high risk of dying during subsequent medical therapy.

Reversal of left ventricular dysfunction after aortic valve replacement for chronic aortic regurgitation: influence of duration of preoperative left ventricular dysfunction

Preoperative left ventricular systolic function is an important predictor of postoperative prognosis in patients with aortic regurgitation. Although left ventricular dysfunction is reversible after aortic valve replacement to a greater extent in patients with good preoperative exercise capacity compared with patients with impaired exercise capacity, not all patients with preserved exercise capacity demonstrate improved left ventricular function after aortic valve replacement. To determine the influence of duration of preoperative left ventricular dysfunction on postoperative reversal of left ventricular dysfunction, we studied 37 patients with aortic regurgitation who preoperatively had left ventricular dysfunction, defined as subnormal echocardiographic fractional shortening (less than 29%), and good preoperative exercise capacity, defined as completion of stage I of the NIH treadmill protocol without limiting symptoms. Eight patients were asymptomatic. In 11 patients left ventricular dysfunction was documented 18 to 57 months preoperatively (prolonged); in 10 patients left ventricular dysfunction developed in an interval of 14 months or less preoperatively (brief); in 16 patients duration of left ventricular dysfunction was unknown. Patients with brief vs those with prolonged left ventricular dysfunction did not differ with respect to severity of preoperative symptoms or exercise tolerance, echocardiographically determined left ventricular dimensions or fractional shortening (25 +/- 3% [SD] vs 25 +/- 3%), or radionuclide angiographic ejection fraction (42 +/- 5% vs 42 +/- 5%).(ABSTRACT TRUNCATED AT 250 WORDS)

Scintigraphic quantification of asynchronous myocardial motion during the left ventricular isovolumic relaxation period: a study in the dog during acute ischemia

Asynchronous motion of left ventricular myocardium during the period of left ventricular isovolumic relaxation has often been observed in patients with coronary artery disease. Detection and quantitation of this abnormality with noninvasive nuclear tracer methods, however, have not yet been reported. Thus, functional images of regional left ventricular time to minimum counts (or volume), computed from gated blood pool image sequences, were analyzed to detect and quantitate myocardial asynchrony during this interval. The method was tested by comparing regional with global time to minimum counts before and after coronary artery occlusion in the awake dog. After occlusion, minimum counts in the ischemic region occurred later in the cardiac cycle than did global minimum counts (average difference 69 +/- 37 ms, p less than 0.001). Before occlusion, however, minimum counts in the same region occurred at the same moment as global minimum counts (average difference 4 +/- 12 ms, NS). Thus, acute ischemia in dogs produces a pronounced asynchrony in myocardial motion during the earliest moments of diastole. The magnitude of this asynchrony (69 ms) probably corresponds to the length of the global isovolumic relaxation period in these animals after occlusion. This method might be useful in detecting and quantitating isovolumic asynchrony in ischemia and changes in this asynchrony with therapy (verapamil therapy, for example).

Profound but reversible myocardial depression in patients with septic shock

To characterize the role of cardiac function in septic shock, serial radionuclide cineangiographic and hemodynamic evaluations were done on 20 patients with documented septic shock. Although all patients had a normal or elevated cardiac index, 10 patients had moderate to severe depression of their ejection fraction with values below 0.40. Thirteen of twenty patients survived their episode. Paradoxically, 10 of 13 survivors, but none of the 7 nonsurvivors, had an initial ejection fraction less than 0.40 (p less than 0.005). The mean initial ejection fraction for the survivors was 0.32 +/- 0.04, and their mean end systolic and end diastolic ventricular volumes were substantially increased with a normal stroke volume. The survivors' serial scans showed a gradual return to normal ejection fraction and ventricular volume by 10 days after the onset of shock. Nonsurvivors had normal initial ejection fractions and ventricular volumes that did not change during serial studies.

Comparative effects of verapamil, diltiazem, and nifedipine on hemodynamics and left ventricular function during acute myocardial ischemia in dogs

The calcium channel-blocking drugs verapamil, diltiazem, and nifedipine are being used with increasing frequency in patients with angina pectoris due to coronary artery disease. Although each of these agents possesses negative inotropic potential, their relative effects on myocardial function in relation to their vasodilator potencies are unknown. We understood to study this in 20 conscious dogs that had partial occlusions of their circumflex coronary arteries during therapy with placebo, verapamil, nifedipine, or diltiazem. Myocardial blood flow was measured by use of microspheres, and left ventricular function was measured by radionuclide angiography. Drug effects were compared at doses causing equal decreases in mean arterial pressure and coronary vascular resistance of nonischemic myocardium. Global ejection fraction and ejection fraction of the ischemic region were significantly decreased by verapamil (p less than .01) and increased by nifedipine (p less than .001); diltiazem caused no significant changes. Verapamil significantly increased peak diastolic filling rate (p less than .001); nifedipine also increased diastolic filling rate, but only at doses that markedly decreased mean arterial pressure and coronary vascular resistance. The effect of diltiazem on diastolic filling rate was not significantly different than placebo. For doses causing an equal decrease in mean arterial pressure, verapamil decreased heart rate (p less than .001), and diltiazem and nifedipine increased heart rate (p less than .001). We conclude that the relative potencies of these three calcium channel blocking agents on left ventricular systolic and diastolic function during myocardial ischemia are different when compared with their relative vasodilator potencies. These differences may have important clinical implications.