Associative and predictive hippocampal codes support memory-guided behaviors

Episodic memory involves learning and recalling associations between items and their spatiotemporal context. Those memories can be further used to generate internal models of the world that enable predictions to be made. The mechanisms that support these associative and predictive aspects of memory are not yet understood. In this study, we used an optogenetic manipulation to perturb the sequential structure, but not global network dynamics, of place cells as rats traversed specific spatial trajectories. This perturbation abolished replay of those trajectories and the development of predictive representations, leading to impaired learning of new optimal trajectories during memory-guided navigation. However, place cell assembly reactivation and reward-context associative learning were unaffected. Our results show a mechanistic dissociation between two complementary hippocampal codes: an associative code (through coactivity) and a predictive code (through sequences).

Targeting ribosome biogenesis reinforces ERK-dependent senescence in pancreatic cancer

Pancreatic adenocarcinomas (PDAC) often possess mutations in K-Ras that stimulate the ERK pathway. Aberrantly high ERK activation triggers oncogene-induced senescence, which halts tumor progression. Here we report that low-grade pancreatic intraepithelial neoplasia displays very high levels of phospho-ERK consistent with a senescence response. However, advanced lesions that have circumvented the senescence barrier exhibit lower phospho-ERK levels. Restoring ERK hyperactivation in PDAC using activated RAF leads to ERK-dependent growth arrest with senescence biomarkers. ERK-dependent senescence in PDAC was characterized by a nucleolar stress response including a selective depletion of nucleolar phosphoproteins and intranucleolar foci containing RNA polymerase I designated as senescence-associated nucleolar foci (SANF). Accordingly, combining ribosome biogenesis inhibitors with ERK hyperactivation reinforced the senescence response in PDAC cells. Notably, comparable mechanisms were observed upon treatment with the platinum-based chemotherapy regimen FOLFIRINOX, currently a first-line treatment option for PDAC. We thus suggest that drugs targeting ribosome biogenesis can improve the senescence anticancer response in pancreatic cancer.

Hippocampo-cortical circuits for selective memory encoding, routing, and replay

Traditionally considered a homogeneous cell type, hippocampal pyramidal cells have been recently shown to be highly diverse. However, how this cellular diversity relates to the different hippocampal network computations that support memory-guided behavior is not yet known. We show that the anatomical identity of pyramidal cells is a major organizing principle of CA1 assembly dynamics, the emergence of memory replay, and cortical projection patterns in rats. Segregated pyramidal cell subpopulations encoded trajectory and choice-specific information or tracked changes in reward configuration respectively, and their activity was selectively read out by different cortical targets. Furthermore, distinct hippocampo-cortical assemblies coordinated the reactivation of complementary memory representations. These findings reveal the existence of specialized hippocampo-cortical subcircuits and provide a cellular mechanism that supports the computational flexibility and memory capacities of these structures.

Over and above frequency: Gamma oscillations as units of neural circuit operations

Gamma oscillations (∼30-150 Hz) are widespread correlates of neural circuit functions. These network activity patterns have been described across multiple animal species, brain structures, and behaviors, and are usually identified based on their spectral peak frequency. Yet, despite intensive investigation, whether gamma oscillations implement causal mechanisms of specific brain functions or represent a general dynamic mode of neural circuit operation remains unclear. In this perspective, we review recent advances in the study of gamma oscillations toward a deeper understanding of their cellular mechanisms, neural pathways, and functional roles. We discuss that a given gamma rhythm does not per se implement any specific cognitive function but rather constitutes an activity motif reporting the cellular substrates, communication channels, and computational operations underlying information processing in its generating brain circuit. Accordingly, we propose shifting the attention from a frequency-based to a circuit-level definition of gamma oscillations.

CA2 orchestrates hippocampal network dynamics

The hippocampus is composed of various subregions: CA1, CA2, CA3, and the dentate gyrus (DG). Despite the abundant hippocampal research literature, until recently, CA2 received little attention. The development of new genetic and physiological tools allowed recent studies characterizing the unique properties and functional roles of this hippocampal subregion. Despite its small size, the cellular content of CA2 is heterogeneous at the molecular and physiological levels. CA2 has been heavily implicated in social behaviors, including social memory. More generally, the mechanisms by which the hippocampus is involved in memory include the reactivation of neuronal ensembles following experience. This process is coordinated by synchronous network events known as sharp-wave ripples (SWRs). Recent evidence suggests that CA2 plays an important role in the generation of SWRs. The unique connectivity and physiological properties of CA2 pyramidal cells make this region a computational hub at the core of hippocampal information processing. Here, we review recent findings that support the role of CA2 in coordinating hippocampal network dynamics from a systems neuroscience perspective.

Global longitudinal strain assessment in long-term survivors of childhood acute lymphoblastic leukemia

Background

The role of global longitudinal strain (GLS) in the long-term cardiac evaluation of childhood acute lymphoblastic leukemia (ALL) survivors is not clearly defined.

Purpose

To assess the prevalence of subclinical left ventricular systolic dysfunction (SLVD) in long-term survivors of ALL. We also aimed to compare echocardiographic measurements with a control group.

Methods

Patients <18 years of age diagnosed with ALL between 1985–2015 at our center were enrolled. Healthy siblings willing to participate were conformed the control group. GLS was measured with an automated software (AutoStrain, Tomtec). SLVD was defined as GLS<18.5% (absolute value) based on the lower limit of the 95% confidence interval in the control group. Group differences were accounted with nverse probability of treatment weighting.

Results

Of the 90 survivors included (37.8% female, time from diagnosis 18 [11–26] years), 24 (26.6%) had SLVD. Left ventricular systolic but not diastolic measurements were reduced compared to the control group (Table 1). Predictors of GLS in the survivors were smoking (p=0.004) and history of hematopoietic stem-cell transplantation (p=0.042) (Table 2).

Conclusions

Over ¼ of childhood ALL survivors had abnormal GLS values after a median follow-up of 18 years. Left-ventricular systolic parameters were reduced compared to a control group.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): Sociedad Española de Cardiología. Sociedad Andaluza de Cardiología.

High-resolution optogenetics in space and time

To understand the neural mechanisms of behavior, it is necessary to both monitor and perturb the activity of ensembles of neurons with high specificity. While neural ensemble recordings have been available for decades, progress in high-resolution manipulation techniques has lagged behind. Optogenetics has enabled the manipulation of genetically defined cell types in behaving animals, and recent developments, including multipoint nanofabricated light sources, provide spatiotemporal resolution on a par with that of physiological recordings. Here we review current advances in optogenetic methods for cellular-resolution stimulation and intervention, as well as their integration with real-time neural recordings for closed-loop experimentation. We discuss how these approaches open the door to new kinds of experiments aimed at dissecting the role of specific neural patterns and discrete cellular populations in orchestrating the activity of brain circuits that support behavior and cognition.

Impact of COVID-19 on heart failure hospitalizations: one year after

Background

Coronavirus disease 2019 (COVID-19) rapidly spread worldwide since it first emerged in December 2019, with more than 100 million cases reported to date, causing a great impact on healthcare systems. Heart failure (HF) is a major health problem. It affects about 10 million people in Europe and is the leading cause of hospitalization for patients older than 65 years. During the first wave of COVID-19 there was an important decrease in HF hospitalizations. Data regarding HF admissions during the second and third waves and inter-waves periods is scarce.

Purpose

To examine the impact of COVID-19 on HF hospitalizations during the first year of the pandemic and to compare the clinical characteristics and in-hospital outcomes of patients admitted during the three pandemic waves with those admitted the previous year during the same periods.

Methods

Data from a tertiary Heart Failure Unit in Southern Spain between 1 March 2020 and 28 February 2021 were compared to the corresponding time period in the previous year. The impact of the pandemic on weekly hospitalizations was assessed using a Poisson Regression model, with year, season and pandemic wave as covariates. Clinical characteristics and in-hospital outcomes of patients admitted during the three waves were compared to those admitted during the same periods one year after.

Results

A significantly lower weekly number of admissions for HF was observed during the three pandemic wave periods compared to all other included periods (inter-wave periods and same periods in the previous year) (p=0.002, IRR 0.81, 0.77–0.86). Figure 1 shows monthly HF admissions between 1 March 2020 and 28 February 2021 (pandemic year) and the previous year, as well as COVID-19 hospitalized cases in our area. Clinical characteristics and in-hospital outcomes of patients admitted during the COVID-19 waves and the same periods in the previous year are shown in Figure 2. Patients admitted during the COVID-19 waves were younger, and fewer had diabetes mellitus (DM), atrial fibrillation (AF) and valvular heart disease (VHD). There were no differences in clinical outcomes (intensive care unit admission, in-hospital mortality).

Conclusion

There was decline in HF hospitalization during the three waves of the pandemic year, but not during the inter-wave periods. Patients admitted during the wave periods had some clinical differences but similar in-hospital outcomes.

Funding Acknowledgement

Type of funding sources: None. Figure 1Figure 2

The continued need for animals to advance brain research

Policymakers aim to move toward animal-free alternatives for scientific research and have introduced very strict regulations for animal research. We argue that, for neuroscience research, until viable and translational alternatives become available and the value of these alternatives has been proven, the use of animals should not be compromised.

Subcircuits of Deep and Superficial CA1 Place Cells Support Efficient Spatial Coding across Heterogeneous Environments

The hippocampus is thought to guide navigation by forming a cognitive map of space. Different environments differ in geometry and the availability of cues that can be used for navigation. Although several spatial coding mechanisms are known to coexist in the hippocampus, how they are influenced by various environmental features is not well understood. To address this issue, we examined the spatial coding characteristics of hippocampal neurons in mice and rats navigating in different environments. We found that CA1 place cells located in the superficial sublayer were more active in cue-poor environments and preferentially used a firing rate code driven by intra-hippocampal inputs. In contrast, place cells located in the deep sublayer were more active in cue-rich environments and used a phase code driven by entorhinal inputs. Switching between these two spatial coding modes was supported by the interaction between excitatory gamma inputs and local inhibition.

Layer-Specific Physiological Features and Interlaminar Interactions in the Primary Visual Cortex of the Mouse

The relationship between mesoscopic local field potentials (LFPs) and single-neuron firing in the multi-layered neocortex is poorly understood. Simultaneous recordings from all layers in the primary visual cortex (V1) of the behaving mouse revealed functionally defined layers in V1. The depth of maximum spike power and sink-source distributions of LFPs provided consistent laminar landmarks across animals. Coherence of gamma oscillations (30-100 Hz) and spike-LFP coupling identified six physiological layers and further sublayers. Firing rates, burstiness, and other electrophysiological features of neurons displayed unique layer and brain state dependence. Spike transmission strength from layer 2/3 cells to layer 5 pyramidal cells and interneurons was stronger during waking compared with non-REM sleep but stronger during non-REM sleep among deep-layer excitatory neurons. A subset of deep-layer neurons was active exclusively in the DOWN state of non-REM sleep. These results bridge mesoscopic LFPs and single-neuron interactions with laminar structure in V1.