Lateral inhibition in V1 controls neural & perceptual contrast sensitivity

Lateral inhibition is a central principle for sensory system function. It is thought to operate by the activation of inhibitory neurons that restrict the spatial spread of sensory excitation. Much work on the role of inhibition in sensory systems has focused on visual cortex; however, the neurons, computations, and mechanisms underlying cortical lateral inhibition remain debated, and its importance for visual perception remains unknown. Here, we tested how lateral inhibition from PV or SST neurons in mouse primary visual cortex (V1) modulates neural and perceptual sensitivity to stimulus contrast. Lateral inhibition from PV neurons reduced neural and perceptual sensitivity to visual contrast in a uniform subtractive manner, whereas lateral inhibition from SST neurons more effectively changed the slope (or gain) of neural and perceptual contrast sensitivity. A neural circuit model identified spatially extensive lateral projections from SST neurons as the key factor, and we confirmed this with direct subthreshold measurements of a larger spatial footprint for SST versus PV lateral inhibition. Together, these results define cell-type specific computational roles for lateral inhibition in V1, and establish their unique consequences on sensitivity to contrast, a fundamental aspect of the visual world.

Narrowband gamma oscillations propagate and synchronize throughout the mouse thalamocortical visual system

Oscillations of neural activity permeate sensory systems. In the visual system, broadband gamma oscillations (30-80 Hz) are thought to act as a communication mechanism underlying perception. However, these oscillations show widely varying frequency and phase, providing constraints for coordinating spike timing across areas. Here, we examined Allen Brain Observatory data and performed causal experiments to show that narrowband gamma (NBG) oscillations (50-70 Hz) propagate and synchronize throughout the awake mouse visual system. Lateral geniculate nucleus (LGN) neurons fired precisely relative to NBG phase in primary visual cortex (V1) and multiple higher visual areas (HVAs). NBG neurons across areas showed a higher likelihood of functional connectivity and stronger visual responses; remarkably, NBG neurons in LGN, preferring bright (ON) versus dark (OFF), fired at distinct NBG phases aligned across the cortical hierarchy. NBG oscillations may thus serve to coordinate spike timing across brain areas and facilitate communication of distinct visual features during perception.

Calcium imaging and analysis of the jugular-nodose ganglia enables identification of distinct vagal sensory neuron subsets

Objective.Sensory nerves of the peripheral nervous system (PNS) transmit afferent signals from the body to the brain. These peripheral nerves are composed of distinct subsets of fibers and associated cell bodies, which reside in peripheral ganglia distributed throughout the viscera and along the spinal cord. The vagus nerve (cranial nerve X) is a complex polymodal nerve that transmits a wide array of sensory information, including signals related to mechanical, chemical, and noxious stimuli. To understand how stimuli applied to the vagus nerve are encoded by vagal sensory neurons in the jugular-nodose ganglia, we developed a framework for micro-endoscopic calcium imaging and analysis.Approach.We developed novel methods forin vivoimaging of the intact jugular-nodose ganglion using a miniature microscope (Miniscope) in transgenic mice with the genetically-encoded calcium indicator GCaMP6f. We adapted the Python-based analysis package Calcium Imaging Analysis (CaImAn) to process the resulting one-photon fluorescence data into calcium transients for subsequent analysis. Random forest classification was then used to identify specific types of neuronal responders.Results.We demonstrate that recordings from the jugular-nodose ganglia can be accomplished through careful surgical dissection and ganglia stabilization. Using a customized acquisition and analysis pipeline, we show that subsets of vagal sensory neurons respond to different chemical stimuli applied to the vagus nerve. Successful classification of the responses with a random forest model indicates that certain calcium transient features, such as amplitude and duration, are important for encoding these stimuli by sensory neurons.Significance.This experimental approach presents a new framework for investigating how individual vagal sensory neurons encode various stimuli on the vagus nerve. Our surgical and analytical approach can be applied to other PNS ganglia in rodents and other small animal species to elucidate previously unexplored roles for peripheral neurons in a diverse set of physiological functions.

High-frequency electrical stimulation attenuates neuronal release of inflammatory mediators and ameliorates neuropathic pain

BACKGROUND

Neuroinflammation is an important driver of acute and chronic pain states. Therefore, targeting molecular mediators of neuroinflammation may present an opportunity for developing novel pain therapies. In preclinical models of neuroinflammatory pain, calcitonin gene-related peptide (CGRP), substance P and high mobility group box 1 protein (HMGB1) are molecules synthesized and released by sensory neurons which activate inflammation and pain. High-frequency electrical nerve stimulation (HFES) has achieved clinical success as an analgesic modality, but the underlying mechanism is unknown. Here, we reasoned that HFES inhibits neuroinflammatory mediator release by sensory neurons to reduce pain.

METHODS

Utilizing in vitro and in vivo assays, we assessed the modulating effects of HFES on neuroinflammatory mediator release by activated sensory neurons. Dorsal root ganglia (DRG) neurons harvested from wildtype or transgenic mice expressing channelrhodopsin-2 (ChR2) were cultured on micro-electrode arrays, and effect of HFES on optogenetic- or capsaicin-induced neuroinflammatory mediator release was determined. Additionally, the effects of HFES on local neuroinflammatory mediator release and hyperalgesia was assessed in vivo using optogenetic paw stimulation and the neuropathic pain model of chronic constriction injury (CCI) of the sciatic nerve.

RESULTS

Light- or capsaicin-evoked neuroinflammatory mediator release from cultured transgenic DRG sensory neurons was significantly reduced by concurrent HFES (10 kHz). In agreement with these findings, elevated levels of neuroinflammatory mediators were detected in the affected paw following optogenetic stimulation or CCI and were significantly attenuated using HFES (20.6 kHz for 10 min) delivered once daily for 3 days.

CONCLUSION

These studies reveal a previously unidentified mechanism for the pain-modulating effect of HFES in the setting of acute and chronic nerve injury. The results support the mechanistic insight that HFES may reset sensory neurons into a less pro-inflammatory state via inhibiting the release of neuroinflammatory mediators resulting in reduced inflammation and pain.

Thalamic bursting and the role of timing and synchrony in thalamocortical signaling in the awake mouse

The thalamus controls transmission of sensory signals from periphery to cortex, ultimately shaping perception. Despite this significant role, dynamic thalamic gating and the consequences for downstream cortical sensory representations have not been well studied in the awake brain. We optogenetically modulated the ventro-posterior-medial thalamus in the vibrissa pathway of the awake mouse and measured spiking activity in the thalamus and activity in primary somatosensory cortex (S1) using extracellular electrophysiology and genetically encoded voltage imaging. Thalamic hyperpolarization significantly enhanced thalamic sensory-evoked bursting; however, surprisingly, the S1 cortical response was not amplified, but instead, timing precision was significantly increased, spatial activation more focused, and there was an increased synchronization of cortical inhibitory neurons. A thalamocortical network model implicates the modulation of precise timing of feedforward thalamic population spiking, presenting a highly sensitive, timing-based gating of sensory signaling to the cortex.

China Pakistan Economic Corridor Digital Transformation

The China-Pakistan Economic Corridor (CPEC) vision and mission are to improve the people's living standards of Pakistan and China through bilateral investments, trade, cultural exchanges, and economic activities. To achieve this envisioned dream, Pakistan established the China-Pakistan Economic Corridor Authority (CPECA) to further its completion, but Covid-19 slowed it down. This situation compelled the digitalization of CPEC. This article reviews the best practices and success stories of various digitalization and e-governance programs and, in this light, advises the implementation of the Ajman Digital Governance (ADG) model as a theoretical framework for CPEC digitalization. This article concludes that the Pakistani government needs to transform CPEC digitalization by setting up the CPEC Digitalization and Transformation Center (DTC) at the CPECA office to attract more investors and businesses.

Belt and Road Environmental Implications for South Asia

The Belt and Road Initiative (BRI) can play a significant role in the sustainable development of South Asia if appropriately implemented. Apart from the economic, trade, and cultural benefits of this colossal infrastructure, less is known about its environmental impact on South Asia. This study looks closely at the potential impact of the BRI on the South Asian environment. This research is based on the government-issued environmental policies, peer-reviewed literature, media articles, and reports. It has been suggested that the BRI could have a negative impact on the South Asian environment, which provided if does not consider the Paris agreement with its partners in the region. The study suggests that partner countries should adopt the BRI project to the principles of environmental impact assessment.

MRI analysis of simple and aneurysmal bone cysts in the proximal humerus: what actually matters in clinical routine

OBJECTIVE

To evaluate magnetic resonance imaging (MRI) characteristics of simple and aneurysmal bone cysts (SBC/ABC) of the proximal humerus and the intermittent difficulty in the imaging differentiation between the two in daily clinical routine.

MATERIALS AND METHODS

MR images of 26 patients with suspected SBC/ABC in the proximal humerus were retrospectively assessed by two independent radiologists blinded to the final histological result. Based on a standard MRI protocol, different morphologic features and signal intensities of the lesion on non-enhanced and enhanced sequences were documented. The radiological diagnosis was correlated with histology.

RESULTS

Eighteen patients had the image-based diagnosis of an SBC, yet the histology confirmed only 12, the residual 6 were identified as an ABC, despite the imaging criteria corresponding unambiguously to the former. One of the main reasons was the unicameral morphology of lesions, found in 9/14 (64.3%) cases of all ABCs, i.e., in 19/26 cases in total. Therefore, the sensitivity of the radiological diagnosis was moderate (57.14%), yet specificity very high (100%). In total, 69.2% (18/26) presented with a pathological fracture at admission, which correlated strongly with both circumferential (MCC = 0.65, p = 0.01) and septal (MCC = 0.42, p = 0.06) enhancement patterns. Circumferential enhancement was also found to correlate strongly with the histological diagnosis, being recognized in all cases of ABC (MCC = 0.44, p = 0.06).

CONCLUSION

MRI characteristics of ABCs/SBCs in the proximal humerus are indifferent and ABCs may morphologically present as SBCs. Radiologists should be aware of the different, often confusing presentation of both entities in daily clinical routine.

Development and evaluation of pH-sensitive biodegradable ternary blended hydrogel films (chitosan/guar gum/PVP) for drug delivery application

pH responsive hydrogels have gained much attraction in biomedical fields. We have formulated ternary hydrogel films as a new carrier of drug. Polyelectrolyte complex of chitosan/guar gum/polyvinyl pyrrolidone cross-linked via sodium tripolyphosphate was developed by solution casting method. Fourier transform infrared spectroscopy, scanning electron microscopy and thermogravimetric analysis were conducted to examine the interactions between the polymeric chains, surface morphology and thermal stability, respectively. The swelling tests resulted that the swelling was reduced with the increase in the concentration of crosslinker due to the more entangled arrangement and less availability of pores in hydrogels. Ciprofloxacin hydrochloride was used as a model drug and its release in simulated gastric fluid, simulated intestinal fluid and phosphate buffer saline solution was studied. pH responsive behaviour of the hydrogels have subjected these hydrogels for drug release applications.

Probing mechanisms of visual spatial attention in mice

The role of spatial attention for visual perception has been thoroughly studied in primates, but less so in mice. Several behavioral tasks in mice reveal spatial attentional effects, with similarities to observations in primates. Pairing these tasks with large-scale, cell-type-specific techniques could enable deeper access to underlying mechanisms, and help define the utility and limitations of resolving attentional effects on visual perception and neural activity in mice. In this Review, we evaluate behavioral and neural evidence for visual spatial attention in mice; assess how specializations of the mouse visual system and behavioral repertoire impact interpretation of spatial attentional effects; and outline how several measurement and manipulation techniques in mice could precisely test and refine models of attentional modulation across scales.

Spatial modulation of dark versus bright stimulus responses in the mouse visual system

A fundamental task of the visual system is to respond to both increases and decreases of luminance with action potentials (ON and OFF responses1-4). OFF responses are stronger, faster, and more salient than ON responses in primary visual cortex (V1) of both cats5,6 and primates,7,8 but in ferrets9 and mice,10 ON responses can be stronger, weaker,11 or balanced12 in comparison to OFF responses. These discrepancies could arise from differences in species, experimental techniques, or stimulus properties, particularly retinotopic location in the visual field, as has been speculated;9 however, the role of retinotopy for ON/OFF dominance has not been systematically tested across multiple scales of neural activity within species. Here, we measured OFF versus ON responses across large portions of visual space with silicon probe and whole-cell patch-clamp recordings in mouse V1 and lateral geniculate nucleus (LGN). We found that OFF responses dominated in the central visual field, whereas ON and OFF responses were more balanced in the periphery. These findings were consistent across local field potential (LFP), spikes, and subthreshold membrane potential in V1, and were aligned with spatial biases in ON and OFF responses in LGN. Our findings reveal that retinotopy may provide a common organizing principle for spatial modulation of OFF versus ON processing in mammalian visual systems.

Diminished Cortical Excitation and Elevated Inhibition During Perceptual Impairments in a Mouse Model of Autism

Sensory impairments are a core feature of autism spectrum disorder (ASD). These impairments affect visual perception and have been hypothesized to arise from imbalances in cortical excitatory and inhibitory activity. There is conflicting evidence for this hypothesis from several recent studies of transgenic mouse models of ASD; crucially, none have measured activity from identified excitatory and inhibitory neurons during simultaneous impairments of sensory perception. Here, we directly recorded putative excitatory and inhibitory population spiking in primary visual cortex (V1) while simultaneously measuring visual perceptual behavior in CNTNAP2-/- knockout (KO) mice. We observed quantitative impairments in the speed, accuracy, and contrast sensitivity of visual perception in KO mice. During these perceptual impairments, stimuli evoked more firing of inhibitory neurons and less firing of excitatory neurons, with reduced neural sensitivity to contrast. In addition, pervasive 3-10 Hz oscillations in superficial cortical layers 2/3 (L2/3) of KO mice degraded predictions of behavioral performance from neural activity. Our findings show that perceptual deficits relevant to ASD may be associated with elevated cortical inhibitory activity along with diminished and aberrant excitatory population activity in L2/3, a major source of feedforward projections to higher cortical regions.

Effect of Varying Amount of Polyethylene Glycol (PEG-600) and 3-Aminopropyltriethoxysilane on the Properties of Chitosan based Reverse Osmosis Membranes

Chitosan and polyethylene glycol (PEG-600) membranes were synthesized and crosslinked with 3-aminopropyltriethoxysilane (APTES). The main purpose of this research work is to synthesize RO membranes which can be used to provide desalinated water for drinking, industrial and agricultural purposes. Hydrogen bonding between chitosan and PEG was confirmed by displacement of the hydroxyl absorption peak at 3237 cm-1 in pure chitosan to lower values in crosslinked membranes by using FTIR. Dynamic mechanical analysis revealed that PEG lowers Tg of the modified membranes vs. pure chitosan from 128.5 °C in control to 120 °C in CS-PEG5. SEM results highlighted porous and anisotropic structure of crosslinked membranes. As the amount of PEG was increased, hydrophilicity of membranes was increased and water absorption increased up to a maximum of 67.34%. Permeation data showed that flux and salt rejection value of the modified membranes was increased up to a maximum of 80% and 40.4%, respectively. Modified films have antibacterial properties against Escherichia coli as compared to control membranes.

Novel Maleic Acid, Crosslinked, Nanofibrous Chitosan/Poly (Vinylpyrrolidone) Membranes for Reverse Osmosis Desalination

Fresh and clean water is consistently depleting and becoming a serious problem with rapid increases in population, so seawater desalination technology has captured global attention. For an efficient desalination process, this work proposes a novel, nanofibrous, thin-film composite membrane (NF-TFC) based on the deposition of the nanofibrous active layer of a blend of chitosan (CS) and poly (vinylpyrrolidone) (PVP) crosslinked with maleic acid on a 3-triethoxysilylpropylamine functionalized cellulose acetate substrate. FTIR analysis demonstrated the development of chemical and physical interactions and confirmed the incorporation of functional groups present in the NF-TFC. Scanning electron microscopy (SEM) micrographs depict the fibrous structure of the active layers. The reverse osmosis (RO) desalination characteristics of NF-TFC membranes are elevated by increasing the concentration of the crosslinker in a CS/PVP blend. Cellulose acetate (CA)-S4 attained an optimal salt rejection of 98.3% and permeation flux of 42.9 L/m2h, suggesting that the NF-TFC membranes could be favorable for seawater desalination.

Cortical State Fluctuations across Layers of V1 during Visual Spatial Perception

Many factors modulate the state of cortical activity, but the importance of cortical state variability for sensory perception remains debated. We trained mice to detect spatially localized visual stimuli and simultaneously measured local field potentials and excitatory and inhibitory neuron populations across layers of primary visual cortex (V1). Cortical states with low spontaneous firing and correlations in excitatory neurons, and suppression of 3- to 7-Hz oscillations in layer 4, accurately predicted single-trial visual detection. Our results show that cortical states exert strong effects at the initial stage of cortical processing in V1 and can play a prominent role for visual spatial behavior in mice.

Spatial attention enhances network, cellular and subthreshold responses in mouse visual cortex

Internal brain states strongly modulate sensory processing during behaviour. Studies of visual processing in primates show that attention to space selectively improves behavioural and neural responses to stimuli at the attended locations. Here we develop a visual spatial task for mice that elicits behavioural improvements consistent with the effects of spatial attention, and simultaneously measure network, cellular, and subthreshold activity in primary visual cortex. During trial-by-trial behavioural improvements, local field potential (LFP) responses to stimuli detected inside the receptive field (RF) strengthen. Moreover, detection inside the RF selectively enhances excitatory and inhibitory neuron responses to task-irrelevant stimuli and suppresses noise correlations and low frequency LFP fluctuations. Whole-cell patch-clamp recordings reveal that detection inside the RF increases synaptic activity that depolarizes membrane potential responses at the behaviorally relevant location. Our study establishes that mice display fundamental signatures of visual spatial attention spanning behavioral, network, cellular, and synaptic levels, providing new insight into rapid cognitive enhancement of sensory signals in visual cortex.

Extensive research in primates shows that attention to space improves behavioural performance as well as neural responses to stimuli in that location. Here, the authors establish a visual spatial attention task in mice and report on attentional modulation of behaviour, as well as neural correlates from subthreshold responses in single cells to spikes and LFP at network level.

Autonomous patch-clamp robot for functional characterization of neurons in vivo: development and application to mouse visual cortex

Patch clamping is the gold standard measurement technique for cell-type characterization in vivo, but it has low throughput, is difficult to scale, and requires highly skilled operation. We developed an autonomous robot that can acquire multiple consecutive patch-clamp recordings in vivo. In practice, 40 pipettes loaded into a carousel are sequentially filled and inserted into the brain, localized to a cell, used for patch clamping, and disposed. Automated visual stimulation and electrophysiology software enables functional cell-type classification of whole cell-patched cells, as we show for 37 cells in the anesthetized mouse in visual cortex (V1) layer 5. We achieved 9% yield, with 5.3 min per attempt over hundreds of trials. The highly variable and low-yield nature of in vivo patch-clamp recordings will benefit from such a standardized, automated, quantitative approach, allowing development of optimal algorithms and enabling scaling required for large-scale studies and integration with complementary techniques. NEW & NOTEWORTHY In vivo patch-clamp is the gold standard for intracellular recordings, but it is a very manual and highly skilled technique. The robot in this work demonstrates the most automated in vivo patch-clamp experiment to date, by enabling production of multiple, serial intracellular recordings without human intervention. The robot automates pipette filling, wire threading, pipette positioning, neuron hunting, break-in, delivering sensory stimulus, and recording quality control, enabling in vivo cell-type characterization.

A novel device for real-time measurement and manipulation of licking behavior in head-fixed mice

The mouse has become an influential model system for investigating the mammalian nervous system. Technologies in mice enable recording and manipulation of neural circuits during tasks where they respond to sensory stimuli by licking for liquid rewards. Precise monitoring of licking during these tasks provides an accessible metric of sensory-motor processing, particularly when combined with simultaneous neural recordings. There are several challenges in designing and implementing lick detectors during head-fixed neurophysiological experiments in mice. First, mice are small, and licking behaviors are easily perturbed or biased by large sensors. Second, neural recordings during licking are highly sensitive to electrical contact artifacts. Third, submillisecond lick detection latencies are required to generate control signals that manipulate neural activity at appropriate time scales. Here we designed, characterized, and implemented a contactless dual-port device that precisely measures directional licking in head-fixed mice performing visual behavior. We first determined the optimal characteristics of our detector through design iteration and then quantified device performance under ideal conditions. We then tested performance during head-fixed mouse behavior with simultaneous neural recordings in vivo. We finally demonstrate our device's ability to detect directional licks and generate appropriate control signals in real time to rapidly suppress licking behavior via closed-loop inhibition of neural activity. Our dual-port detector is cost effective and easily replicable, and it should enable a wide variety of applications probing the neural circuit basis of sensory perception, motor action, and learning in normal and transgenic mouse models. NEW & NOTEWORTHY Mice readily learn tasks in which they respond to sensory cues by licking for liquid rewards; tasks that involve multiple licking responses allow study of neural circuits underlying decision making and sensory-motor integration. Here we design, characterize, and implement a novel dual-port lick detector that precisely measures directional licking in head-fixed mice performing visual behavior, enabling simultaneous neural recording and closed-loop manipulation of licking.

Millisecond Coupling of Local Field Potentials to Synaptic Currents in the Awake Visual Cortex

The cortical local field potential (LFP) is a common measure of population activity, but its relationship to synaptic activity in individual neurons is not fully established. This relationship has been typically studied during anesthesia and is obscured by shared slow fluctuations. Here, we used patch-clamp recordings in visual cortex of anesthetized and awake mice to measure intracellular activity; we then applied a simple method to reveal its coupling to the simultaneously recorded LFP. LFP predicted membrane potential as accurately as synaptic currents, indicating a major role for synaptic currents in the relationship between cortical LFP and intracellular activity. During anesthesia, cortical LFP predicted excitation far better than inhibition; during wakefulness, it predicted them equally well, and visual stimulation further enhanced predictions of inhibition. These findings reveal a central role for synaptic currents, and especially inhibition, in the relationship between the subthreshold activity of individual neurons and the cortical LFP during wakefulness.

An excitatory basis for divisive normalization in visual cortex

Neurons in visual cortex are connected not only locally, but also through networks of distal connectivity. These distal networks recruit both excitatory and inhibitory synapses and result in divisive normalization. Normalization is traditionally thought to result from increases in synaptic inhibition. By combining optogenetic stimulation and intracellular recordings in mouse visual cortex, we found that, on the contrary, normalization is a result of a decrease in synaptic excitation.

Inhibition dominates sensory responses in the awake cortex

The activity of the cerebral cortex is thought to depend on the precise relationship between synaptic excitation and inhibition^1-4. In visual cortex, in particular, intracellular measurements have related response selectivity to coordinated increases in excitation and inhibition^5-9. These measurements, however, have all been performed during anaesthesia, which strongly influences cortical state¹⁰ and therefore sensory processing^7,11-15. The synaptic activity evoked by visual stimulation during wakefulness is unknown. Here, we measured visually evoked responses – and the underlying synaptic conductances – in the visual cortex of anaesthetised and awake mice. Under anaesthesia, responses could be elicited from a large region of visual space¹⁶ and were prolonged in time. During wakefulness responses were more spatially selective and much briefer. Whole-cell patch-clamp recordings of synaptic conductances^5,17 revealed a surprising difference in synaptic inhibition during the two conditions. Whereas under anaesthesia inhibition tracked excitation in amplitude and spatial selectivity, during wakefulness it was much stronger than excitation and exhibited extremely broad spatial selectivity. We conclude that during wakefulness cortical responses to visual stimulation are dominated by synaptic inhibition, restricting their spatial spread and temporal persistence. These results provide the first direct glimpse of synaptic mechanisms that control visual responses in the awake cortex.

Routine stress testing after percutaneous coronary interventions

Percutaneous coronary intervention (PCI) is the most frequently performed cardiovascular procedure. Many physicians caring for post-PCI patients have routinely subjected patients to periodic stress testing. In the recent years, due to widespread use of drug eluting stents the combined rates of major adverse cardiac events (MACE) and in-stent restenosis (ISR) dropped <10% in the initial 12 months post-PCI, with only half of these patients bearing symptoms. This has translated into reduced pre-test probability of post-PCI ischemia. Consequently, the beneficial effect of this practice came into question. Moreover, in addition to its financial implications, routine post-PCI stress testing may carry potential harm: medication or exercise induced arrhythmia, infarction and/or death, patient irradiation exposure, false-positive tests resulting in excessive invasive testing or interventions, and the illusion of "wellness" in the face of a somewhat unpredictable disease. This review addresses the role stress testing post-PCI: it is concluded that routine stress testing in clinically stable asymptomatic post-PCI patients should be discouraged. Selective utilization of stress testing in patients with exceptionally high risk of ISR or MACE can be utilized to answer important clinical questions or guide and refine clinical care.

Clinical applicability of coronary atherosclerotic lesion characterization

Native coronary atherosclerosis (CAS) is a diffuse and progressive disease process that is occasionally associated with either clinical atherothrombosis and/or major adverse cardiac events (MACE) including: ST elevation myocardial infarction (STEMI), acute coronary syndromes without ST elevation (ACSWSTE), heart failure, cardiac arrest and sudden cardiac death. Both, the timing and coronary site responsible for the MACE are currently unpredictable. Cardiovascular investigators have engaged in the task of characterizing CAS lesions in order to enhance our knowledge of CAS pathophysiology. It was expected that the knowledge acquired will allow scientists and clinicians to develop effective strategies to detect and treat "vulnerable plaque" (VP) prior to the evolution of MACE. This review discusses the emerging data regarding the pathology and natural history of the VP and vulnerable patient and the progress made in characterizing atherosclerotic plaque instability and vulnerability. Future directions in the field of plaque characterization and their potential clinical and research applications are discussed.

Aspirin for the prevention of cardiovascular morbidity

Aspirin (ASA) use for secondary prevention in patients with cardiovascular (CV) disease is well established through its beneficial effects on the reduction of myocardial infarction, ischemic stroke and CV mortality. This beneficial effect of ASA seems to consistently outweigh the risk in most patient subsets. Current guidelines endorse ASA for primary prevention of CV events in adults who are at moderate-high risk of CV morbidity. Recent emerging data on the efficacy and safety of ASA conflicts with former randomized clinical trials and raises concerns regarding the validity of these recommendations. The following manuscript describes the data emerging from contemporary trials regarding the efficacy and safety of ASA in various patient subsets. The authors propose certain strategies to enhance safety and efficacy in order to augment the beneficial effects of ASA along with other modalities of primary prevention for suitable candidates. When contemplating ASA prescription for primary prevention of CV events, physicians should carefully weigh the potential benefits of risk reduction versus likelihood of harm, mostly related to bleeding complications.

Rapid neocortical dynamics: cellular and network mechanisms

The highly interconnected local and large-scale networks of the neocortical sheet rapidly and dynamically modulate their functional connectivity according to behavioral demands. This basic operating principle of the neocortex is mediated by the continuously changing flow of excitatory and inhibitory synaptic barrages that not only control participation of neurons in networks but also define the networks themselves. The rapid control of neuronal responsiveness via synaptic bombardment is a fundamental property of cortical dynamics that may provide the basis of diverse behaviors, including sensory perception, motor integration, working memory, and attention.

Contributions of Yale neuroscience to Donald O. Hebb's organization of behavior

The neuropsychological concepts found in Donald Hebb's The Organization of Behavior have greatly influenced many aspects of neuroscience research over the last half century. Hebb's ideas arose from a rich tradition of research. An underappreciated contribution came from pioneering studies at Yale University. Here, we wish to reconsider these developments, placing particular emphasis on the roles of the neurophysiologists John Fulton, J.J. Dusser de Barenne, and Warren McCulloch and the psychologists Donald Marquis and Ernest Hilgard. These neuroscientists all contributed significantly to the intellectual climate that gave rise to Hebb's remarkable synthesis.

Enhancement of visual responsiveness by spontaneous local network activity in vivo

Spontaneous activity within local circuits affects the integrative properties of neurons and networks. We have previously shown that neocortical network activity exhibits a balance between excitatory and inhibitory synaptic potentials, and such activity has significant effects on synaptic transmission, action potential generation, and spike timing. However, whether such activity facilitates or reduces sensory responses has yet to be clearly determined. We examined this hypothesis in the primary visual cortex in vivo during slow oscillations in ketamine-xylazine anesthetized cats. We measured network activity (Up states) with extracellular recording, while simultaneously recording postsynaptic potentials (PSPs) and action potentials in nearby cells. Stimulating the receptive field revealed that spiking responses of both simple and complex cells were significantly enhanced (>2-fold) during network activity, as were spiking responses to intracellular injection of varying amplitude artificial conductance stimuli. Visually evoked PSPs were not significantly different in amplitude during network activity or quiescence; instead, spontaneous depolarization caused by network activity brought these evoked PSPs closer to firing threshold. Further examination revealed that visual responsiveness was gradually enhanced by progressive membrane potential depolarization. These spontaneous depolarizations enhanced responsiveness to stimuli of varying contrasts, resulting in an upward (multiplicative) scaling of the contrast response function. Our results suggest that small increases in ongoing balanced network activity that result in depolarization may provide a rapid and generalized mechanism to control the responsiveness (gain) of cortical neurons, such as occurs during shifts in spatial attention.

Properties of action-potential initiation in neocortical pyramidal cells: evidence from whole cell axon recordings

Cortical pyramidal cells are constantly bombarded by synaptic activity, much of which arises from other cortical neurons, both in normal conditions and during epileptic seizures. The action potentials generated by barrages of synaptic activity may exhibit a variable site of origin. Here we performed simultaneous whole cell recordings from the soma and axon or soma and apical dendrite of layer 5 pyramidal neurons during normal recurrent network activity (up states), the intrasomatic or intradendritic injection of artificial synaptic barrages, and during epileptiform discharges in vitro. We demonstrate that under all of these conditions, the real or artificial synaptic bombardments propagate through the dendrosomatic-axonal arbor and consistently initiate action potentials in the axon initial segment that then propagate to other parts of the cell. Action potentials recorded intracellularly in vivo during up states and in response to visual stimulation exhibit properties indicating that they are typically initiated in the axon. Intracortical axons were particularly well suited to faithfully follow the generation of action potentials by the axon initial segment. Action-potential generation was more reliable in the distal axon than at the soma during epileptiform activity. These results indicate that the axon is the preferred site of action-potential initiation in cortical pyramidal cells, both in vivo and in vitro, with state-dependent back propagation through the somatic and dendritic compartments.

Neocortical network activity in vivo is generated through a dynamic balance of excitation and inhibition

The recurrent excitatory and inhibitory connections between and within layers of the cerebral cortex are fundamental to the operation of local cortical circuits. Models of cortical function often assume that recurrent excitation and inhibition are balanced, and we recently demonstrated that spontaneous network activity in vitro contains a precise balance of excitation and inhibition; however, the existence of a balance between excitation and inhibition in the intact and spontaneously active cerebral cortex has not been directly tested. We examined this hypothesis in the prefrontal cortex in vivo, during the slow (<1 Hz) oscillation in ketamine-xylazine-anesthetized ferrets. We measured persistent network activity (Up states) with extracellular multiple unit and local field potential recording, while simultaneously recording synaptic currents in nearby cells. We determined the reversal potential and conductance change over time during Up states and found that the body of Up state activity exhibited a steady reversal potential (-37 mV on average) for hundreds of milliseconds, even during substantial (21 nS on average) changes in membrane conductance. Furthermore, we found that both the initial and final segments of the Up state were characterized by significantly more depolarized reversal potentials and concomitant increases in excitatory conductance, compared with the stable middle portions of Up states. This ongoing temporal evolution between excitation and inhibition, which exhibits remarkable proportionality within and across neurons in active local networks, may allow for rapid transitions between relatively stable network states, permitting the modulation of neuronal responsiveness in a behaviorally relevant manner.

Inhibitory postsynaptic potentials carry synchronized frequency information in active cortical networks

Temporal precision in spike timing is important in cortical function, interactions, and plasticity. We found that, during periods of recurrent network activity (UP states), cortical pyramidal cells in vivo and in vitro receive strong barrages of both excitatory and inhibitory postsynaptic potentials, with the inhibitory potentials showing much higher power at all frequencies above approximately 10 Hz and more synchrony between nearby neurons. Fast-spiking inhibitory interneurons discharged strongly in relation to higher-frequency oscillations in the field potential in vivo and possess membrane, synaptic, and action potential properties that are advantageous for transmission of higher-frequency activity. Intracellular injection of synaptic conductances having the characteristics of the recorded EPSPs and IPSPs reveal that IPSPs are important in controlling the timing and probability of action potential generation in pyramidal cells. Our results support the hypothesis that inhibitory networks are largely responsible for the dissemination of higher-frequency activity in cortex.

Pulse elongation and deconvolution filtering for medical ultrasonic imaging

Range sidelobe artifacts which are associated with pulse compression methods can be reduced with a new method composed of pulse elongation and deconvolution (PED). While pulse compression and PED yield similar signal-to-noise ratio (SNR) improvements, PED inherently minimizes the range sidelobe artifacts. The deconvolution is implemented as a stabilized inverse filter. With proper selection of the excitation waveform an exact inverse filter can be implemented. The excitation waveform is optimized in a minimum mean square error (MMSE) sense. An analytical expression for the power spectrum of the optimal pulse is presented and several techniques to numerically optimize the excitation pulse are shown. The effects of PED are demonstrated in computer simulations as well as ultrasonic images.

Myocardial infarction postpartum in patients taking bromocriptine for the prevention of breast engorgement

Three cases of myocardial infarction (MI) in women taking bromocriptine for milk suppression are presented. The incidents occurred in 1993 and 1994, the last only two weeks before the withdrawal of the drug from the American market as a drug suitable for ablactation. In one patient, the MI presented on the 12 day postpartum and was accompanied by signs and symptoms reminiscent to ergotism. Another mother suffered MI, accompanied by hypertension, six days after a vaginal delivery complicated by postpartum haemorrhage. The third patient began to take bromocriptine more than 2 weeks postpartum and died suddenly 24 days after her childbirth. To the knowledge of the authors, these are the 12th to 14th literary reports describing an apparent association between the use of bromocriptine for ablactation and the occurrence of MI in the puerperium.

A double chamber system for producing constant radon concentration

An experimental arrangement of a radon chamber with an intrinsic constancy of the relative radon concentration is described. The system consists of a reference chamber and an auxiliary storage chamber. The only active device is a timer-controlled pump or valve which feeds radon gas from the storage into the reference chamber. The switching pattern of the timer is extracted from model calculations and theoretically performs an exact compensation of the radon loss by radioactive decay. If the calculations are done in real time and online, every known external event influencing the radon concentration can be compensated. This paper presents a simple timer circuit and a computer code which generates the timer program. The influence of the air flow stability and the leakage of the chambers are discussed. It is planned to apply this theoretical approach to provide a constant radon gas concentration for an actual chamber.

Diabetic cardiomyopathy: experimental and clinical observations

Heart failure, arrhythmia, or chest pain can be a consequence of diabetes independent of coronary disease or hypertension. Diastolic myocardial dysfunction is common, contributing to the high mortality during acute infarction. The authors discuss diabetic cardiomyopathy and its management.

Efficacy and safety of combinations of nitrendipine, atenolol, and hydrochlorothiazide in black hypertensive patients

Twenty-four black hypertensive patients were studied in a randomized, double-blind trial of combinations of nitrendipine, atenolol, and hydrochlorothiazide. After six weeks, blood pressure was normalized in all three treatment groups, i.e. diastolic blood pressure less than 95 mmHg and a decline in diastolic blood pressure of at least 5 mmHg from baseline. The drug combinations containing hydrochlorothiazide were associated with higher incidence of metabolic abnormalities, especially hypokalaemia and hyperuricaemia.

Effects of diabetes on myocardial perfusion in the atherosclerotic monkey

We examined the influence of diabetes on the severity of coronary atherosclerosis, as judged by coronary morphometric and blood flow studies. Cynomolgus monkeys were fed a coconut-peanut oil mixture plus cholesterol to induce the plaque lesions of atherosclerosis in nondiabetic (group 2) and diabetic monkeys (group 3). Group 1 consisted of chow-fed controls. After 18 months of hypercholesterolemia, the animals were anesthetized to assess myocardial blood flow, by use of radioactive microspheres. Transmural and inner/outer wall flow ratios were normal in the two lipid-fed groups in the basal state. Vasodilation after adenosine (0.45 mg/kg/min IV) elicited a more than threefold rise of transmural blood flow in group 1, and a significantly reduced increment in groups 2 and 3. The blood flow ratio was not different from unity in group 1 but declined to 0.69 +/- 0.03 in group 2 and 0.69 +/- 0.06 in group 3, with similar decrements of heart rate and aortic pressure. In contrast to results in group 1, left ventricular filling pressure rose and velocity of contractile elements declined to a similar extent in groups 2 and 3 after adenosine, consistent with myocardial ischemia. Morphometric measurements as well as chemical analyses were performed on the three major coronary arteries. The degree of intimal thickening and increase of cholesterol and collagen content were comparable in groups 2 and 3. Thus, in this model the plaque lesions of atherosclerosis did not appear to be intensified by diabetes. Moreover, the responses to adenosine in terms of myocardial underperfusion and mechanical dysfunction were comparable in the two experimental groups.

Arrhythmia susceptibility and myocardial composition in diabetes. Influence of physical conditioning

Abnormal myocardial composition in diabetes mellitus has been described, but the effects on ventricular vulnerability have not been defined. We have assessed the susceptibility to arrhythmias in a canine model after 1 yr of mild diabetes induced by alloxan. Since physical conditioning can affect metabolic abnormalities in diabetes, this intervention has also been evaluated. Group 1 served as controls and groups 3 and 4 were diabetic. Animals in the latter group as well as nondiabetic controls of group 2 were exercised on a treadmill for the last 8 mo of the experiment. After 1 yr, anesthesia was induced with chloralose for vulnerability studies. The ventricular fibrillation threshold of 24.4 +/- 1.9 mA in group 3 was significantly less than in normals (45.1 +/- 2.2). Spontaneous arrhythmias were also more prevalent in diabetics during acute ischemia (group 3-A). Increased ventricular vulnerability after epinephrine infusion was present in the sedentary diabetes despite normal ventricular function responsiveness. In a superfused preparation of myocardium, resting membrane potential and action potential amplitude were normal in diabetics, and beta-adrenergic stimulation shortened repolarization more than in controls. Myocardial collagen concentrations, which included an interfibrillar distribution on morphologic examination, were increased in group 3. In the trained diabetics of group 4 the basal vulnerability thresholds and responses to epinephrine were normal. While myocardial collagen levels were normal, cholesterol and triglyceride increments persisted. Thus, in mild experimental diabetes, enhanced susceptibility to arrhythmias exists; this susceptibility may be based on a combination of nonhomogenous collagen accumulation affecting local conduction and increased electrophysiologic sensitivity to catecholamines.

Effects of beta-adrenergic inhibition on scar formation after myocardial infarction

In view of clinical interest in the efficacy of beta-adrenergic blockade during acute myocardial infarction (AMI), we have determined the long-term effect of therapy on scar formation after experimental myocardial ischemia. Intact anesthetized dogs underwent acute occlusion of the left anterior descending coronary artery, by means of a balloon catheter, which permitted monitoring of the aortic-peripheral coronary artery pressure gradient during the 4-hour period of balloon inflation. Practolol administration was begun 15 minutes after the onset of ischemia in group A. Control animals (group B) received procainamide to approximate the antiarrhythmic action of beta blockade. Only group A exhibited significant reduction in the ST segments during acute ischemia. Chronic therapy was maintained for 1 month and the mature scar formed in the myocardium was assessed after 4 months. The extent of subendocardial scar was similar in both groups but subepicardial scar formation was significantly less in group A. There was also a significant decrease in the percentage of total myocardium involved with scar in this treatment group. Although thinning of the left ventricular wall was similar for both groups in the central scar region, this process was significantly reduced at the lateral margin in group A. Thus, specific beta-receptor blockade during acute myocardial ischemia and sustained during the repair process can result in a reduced quantity and altered distribution of mature scar.

Intra-aortic balloon counterpulsation in an experimental model of myocardial infarction

The efficacy of intra-aortic balloon counterpulsation for heart failure during acute myocardial infarction has been controversial, and early intervention has been suggested as crucial. We have examined this type of therapy in the intact anesthetized dog during complete occlusion of the proximal left anterior descending coronary artery with a balloon-tipped catheter. Group 1 (n = 8) represented untreated animals undergoing four hours of ischemia. Group 2 (n = 7) consisted of animals undergoing counterpulsation with an intra-aortic balloon after 15 minutes of ischemia. Initially, stroke volume and the mean rate of left ventricular fiber shortening were similarly diminished in both groups, while filling pressure rose proportionately. After four hours, the mean rate of fiber shortening, stroke volume, and left ventricular filling pressure rose to a greater extent in untreated compared to treated animals (p less than 0.01). The degree of swelling in ischemic tissue and the number of sites with ST-segment elevation and their sums were comparable in the two groups. Thus, intra-aortic counterpulsation applied early in the course of ischemia can improve global left ventricular dysfunction without affecting the extent of myocardial injury.

Emetine-induced cardiomyopathy in rabbits

A correlative electrocardiographic and ultrastructural study of myocardium in rabbits, administered 1 mg/kg of emetine hydrochloride intramuscularly for 5 successive days of a week over 2 to 4 week period, was conducted. The study revealed electrocardiographic changes and a spectrum of ultrastructural lesions involving myocardial cells and interstitial neural elements. The severity of these lesions was related to the cumulative dose of the drug. Myocardial cell lesions were characterized by fatty infiltration, increase in glycogen content, myofibrillolysis, focal cytoplasmic degeneration, contraction-band necrosis and intercalated disc disjunction, herniation and fragmentation of the close junction (nexus). Neural lesions included mesaxonal and axonal myelinoid bodies and alterations in dense-core vesicles of biogenic amine containing cells. Atrial myocardial lesions were relatively fewer and less severe than those in the ventricular myocardium. The myocardial cell and neural lesions may be inter-related and underlie the pathogenesis of emetine-induced cardiomyopathy.