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Decades of hippocampal neurophysiology research have linked the hippocampal theta rhythm to voluntary movement. A consistent observation has been a robust correlation between the amplitude (or power) and frequency of hippocampal theta and running speed. Recently, however, it has been suggested that acceleration, not running speed, is the dominating influence on theta frequency. There is an inherent interdependence among these two variables, as acceleration is the rate of change in velocity. Therefore, we investigated theta frequency and amplitude of the local-field potential recorded from the stratum pyramidale, stratum radiatum, and stratum lacunosum moleculare of the CA1 subregion, considering both speed and acceleration in tandem as animals traversed a circular task or performed continuous alternation. In male and female rats volitionally controlling their own running characteristics, we found that running speed carries nearly all of the variability in theta frequency and power, with a minute contribution from acceleration. These results contradicted a recent publication using a speed-clamping task, where acceleration and movement are compelled through the use of a bottomless car (Kropff et al., 2021a). Therefore, we reanalyzed the speed-clamping data replicating a transient increase in theta frequency during acceleration. Compared with track running rats, the speed-clamped animals exhibited lower velocities and acceleration values but still showed a stronger influence of speed on theta frequency relative to acceleration. As navigation is the integration of many sensory inputs that are not necessarily linearly related, we offer caution in making absolute claims regarding hippocampal physiology from correlates garnered from a single behavioral repertoire.SIGNIFICANCE STATEMENT A long-standing, replicable observation has been the increase of hippocampal theta power and frequency with increasing running speed. Recently, however, an experimental approach that clamps the running speed of an animal has suggested that acceleration is the dominant influence. Therefore, we analyzed data from freely behaving rats as well as data from the speed-clamping experiment. In unrestrained behavior, speed remains the dominant behavioral correlate to theta amplitude and frequency. Positive acceleration in the speed-clamp experiment induced a transient increase in theta frequency and power. However, speed retained the dominant influence over theta frequency, changing with velocity in both acceleration and deceleration conditions.
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Hipocampo , Ritmo Teta , Aceleração , Animais , Feminino , Hipocampo/fisiologia , Masculino , Ratos , Ritmo Teta/fisiologiaRESUMO
Healthcare organisations are hierarchical; almost all are organised around the ranking of individuals by authority or status, whether this be based on profession, expertise, gender or ethnicity. Hierarchy is important for several reasons; it shapes the delivery of care, what is prioritised and who receives care. It also has an impact on healthcare workers and how they work and communicate together in organisations. The purpose of this scoping review is to explore the qualitative evidence related to hierarchy in healthcare organisations defined broadly, to address gaps in macro-level healthcare organisational research, specifically focusing on the (1) impact of hierarchy for healthcare workers and (2) how hierarchy is negotiated, sustained and challenged in healthcare organisations. After a search and screening, 32 papers were included in this review. The findings of this review detail the wide-reaching impacts that hierarchy has on healthcare delivery and health workers. The majority of studies spoke to hierarchy's impact on speaking up, that is, how it shaped communication between staff with differential status: not only what was said, but how it had an impact on what was acceptable to say, by whom and at what time. Hierarchy was also noted to have substantial personal costs, impacting on the well-being of those in less powerful positions. These findings also provide insight into the complex ways in which hierarchy was negotiated, challenged and reproduced. Studies not only detailed the way in which hierarchy was navigated day to day but also spoke to the reasons as to why hierarchy is often entrenched and difficult to shift. A number of studies spoke to the impact that hierarchy had in sustaining gender and ethnic inequalities, maintaining historically discriminatory practices. Importantly, hierarchy should not be reduced to differences between or within the professions in localised contexts but should be considered at a broad organisational level.
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BACKGROUND: Workforce is a fundamental health systems building block, with unprecedented measures taken to meet extra demand and facilitate surge capacity during the COVID-19 pandemic, following a prolonged period of austerity. This case study examines trends in Ireland's publicly funded health service workforce, from the global financial crisis, through the Recovery period and into the COVID-19 pandemic, to understand resource allocation across community and acute settings. Specifically, this paper aims to uncover whether skill-mix and staff capacity are aligned with policy intent and the broader reform agenda to achieve universal access to integrated healthcare, in part, by shifting free care into primary and community settings. METHODS: Secondary analysis of anonymised aggregated national human resources data was conducted over a period of almost 14 years, from December 31st 2008 to August 31st 2021. Comparative analysis was conducted, by professional cadre, across three keys periods: 'Recession period' December 31st 2008-December 31st 2014; 'Recovery period' December 31st 2014-December 31st 2019; and the 'COVID-19 period' December 31st 2019-August 31st 2021. RESULTS: During the Recession period there was an overall decrease of 8.1% (n = 9333) between December 31st 2008 and December 31st 2014, while the Recovery period saw the overall staff levels rebound and increase by 15.2% (n = 16,789) between December 31st 2014 and December 31st 2019. These figures continued to grow, at an accelerated rate during the most recent COVID-19 period, increasing by a further 8.9% (n = 10,716) in under 2 years. However, a notable shift occurred in 2013, when the number of staff in acute services surpassed those employed in community services (n = 50,038 and 49,857, respectively). This gap accelerated during the Recovery and COVID-19 phase. By August 2021, there were 13,645 more whole-time equivalents in acute settings compared to community, a complete reverse of the 2008 situation. This was consistent across all cadres. Workforce absence trends indicate short-term spikes resulting from shocks while COVID-19 redeployment disproportionately impacted negatively on primary care and community services. CONCLUSIONS: This paper clearly demonstrates the prioritisation of staff recruitment within acute services-increasing needed capacity, without the same commitment to support government policy to shift care into primary and community settings. Concerted action including the permanent redistribution of personnel is required to ensure progressive and sustainable responses are learned from recent shocks.
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COVID-19 , COVID-19/epidemiologia , Programas Governamentais , Humanos , Irlanda , Pandemias , Recursos HumanosRESUMO
Theta oscillations in the primary visual cortex (VC) have been observed during running tasks, but the mechanism behind their generation is not well understood. Some studies have suggested that theta in the VC is locally generated, while others have proposed that it is volume conducted from the hippocampus. The present study aimed to investigate the relationship between hippocampal and VC LFP dynamics. Analysis of power spectral density revealed that LFP in the VC was similar to that in the hippocampus, but with lower overall magnitude. As running velocity increased, both the power and frequency of theta and its harmonics increased in the VC, similarly to what is observed in the hippocampus. Current source density analysis triggered to theta did not identify distinct current sources and sinks in the VC, supporting the idea that theta in the VC is conducted from the adjacent hippocampus. Phase coupling between theta, its harmonics, and gamma is a notable feature in the hippocampus, particularly in the lacunosum moleculare. While some evidence of coupling between theta and its harmonics in the VC was found, bicoherence estimates did not reveal significant phase coupling between theta and gamma. Similar results were seen in the cross-region bicoherence analysis, where theta showed strong coupling with its harmonics with increasing velocity. Thus, theta oscillations observed in the VC during running tasks are likely due to volume conduction from the hippocampus.
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Hippocampal theta and gamma rhythms are hypothesized to play a role in the physiology of higher cognition. Prior research has reported that an offset in theta cycles between the entorhinal cortex, CA3, and CA1 regions promotes independence of population activity across the hippocampus. In line with this idea, it has recently been observed that CA1 pyramidal cells can establish and maintain coordinated place cell activity intrinsically, with minimal reliance on afferent input. Counter to these observations is the contemporary hypothesis that CA1 neuron activity is driven by a gamma oscillation arising from the medial entorhinal cortex (MEC) that relays information by providing precisely timed synchrony between MEC and CA1. Reinvestigating this in rats during appetitive track running, we found that theta is the dominant frequency of cross-frequency coupling between the MEC and hippocampus, with hippocampal gamma largely independent of entorhinal gamma.
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The hippocampal local field potential (LFP) exhibits a strong correlation with behavior. During rest, the theta rhythm is not prominent, but during active behavior, there are strong rhythms in the theta, theta harmonics, and gamma ranges. With increasing running velocity, theta, theta harmonics and gamma increase in power and in cross-frequency coupling, suggesting that neural entrainment is a direct consequence of the total excitatory input. While it is common to study the parametric range between the LFP and its complementing power spectra between deep rest and epochs of high running velocity, it is also possible to explore how the spectra degrades as the energy is completely quenched from the system. Specifically, it is unknown whether the 1/f slope is preserved as synaptic activity becomes diminished, as low frequencies are generated by large pools of neurons while higher frequencies comprise the activity of more local neuronal populations. To test this hypothesis, we examined rat LFPs recorded from the hippocampus and entorhinal cortex during barbiturate overdose euthanasia. Within the hippocampus, the initial stage entailed a quasi-stationary LFP state with a power-law feature in the power spectral density. In the second stage, there was a successive erosion of power from high- to low-frequencies in the second stage that continued until the only dominant remaining power was <20 Hz. This stage was followed by a rapid collapse of power spectrum toward the absolute electrothermal noise background. As the collapse of activity occurred later in hippocampus compared with medial entorhinal cortex, it suggests that the ability of a neural network to maintain the 1/f slope with decreasing energy is a function of general connectivity. Broadly, these data support the energy cascade theory where there is a cascade of energy from large cortical populations into smaller loops, such as those that supports the higher frequency gamma rhythm. As energy is pulled from the system, neural entrainment at gamma frequency (and higher) decline first. The larger loops, comprising a larger population, are fault-tolerant to a point capable of maintaining their activity before a final collapse.
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Although the activity from the dentate gyrus is known to have strong connections with other hippocampal layers, the functionality of these connections, that is, the degree to which it drives activity in the downstream regions of the hippocampus, is not well understood. This question is particularly relevant for mesoscale localfield potential (LFP) rhythms such as gamma oscillations. Following the hypothesis that fundamental features of the LFP are consistent with turbulent dynamics, we investigate the crosslayer relationship between the CA1 layers and the dentate gyrus as a function of running speed. In agreement with previous studies, same-layer spectral and bispectral analyses show that increasing input (rat speed) results in an increase of power and nonlinearity (phase coupling) between theta and gamma. The effectiveness of the connection between the 2 regions is investigated using cross-bicoherence analysis. Based on the turbulence interpretation of the evolution of spectra and bispectra as a function of the power input rate, we propose a measure for estimating the strength of the cross-frequency, cross-layer nonlinear forcing, that compares the magnitude of bicoherence (same-layer) and cross-bicoherence (cross-layer). Our results suggest that at moderate speeds gamma in CA1 is mainly driven by local theta, while the coupling of the CA1 gamma to the dentate-gyrus gamma becomes significant. Overall, these data are consistent with the hypothesis of theta-to-gamma energy cascade model for the organization of hippocampal LFP, with theta playing the role of a global pacemaker across the entire hippocampus while gamma is a local oscillation generated by through local anatomical connections. (PsycInfo Database Record (c) 2021 APA, all rights reserved).
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Região CA1 Hipocampal , Giro Denteado , Ritmo Teta , Animais , Feminino , Ritmo Gama , Masculino , RatosRESUMO
The potential for the use of Clostridial neurotoxins as bioweapons makes the development of small-molecule inhibitors of these deadly toxins a top priority. Recently, screening of a random hydroxamate library identified a small-molecule inhibitor of C. botulinum Neurotoxin Serotype A Light Chain (BoNT/A-LC), 4-chlorocinnamic hydroxamate, a derivative of which has been shown to have in vivo efficacy in mice and no toxicity. We describe the X-ray crystal structures of BoNT/A-LC in complexes with two potent small-molecule inhibitors. The structures of the enzyme with 4-chlorocinnamic hydroxamate or 2,4-dichlorocinnamic hydroxamate bound are compared to the structure of the enzyme complexed with L-arginine hydroxamate, an inhibitor with modest affinity. Taken together, this suite of structures provides surprising insights into the BoNT/A-LC active site, including unexpected conformational flexibility at the S1' site that changes the electrostatic environment of the binding pocket. Information gained from these structures will inform the design and optimization of more effective small-molecule inhibitors of BoNT/A-LC.
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Toxinas Bacterianas/antagonistas & inibidores , Clostridium botulinum tipo A/química , Antitoxinas , Sítios de Ligação , Cromatografia Líquida , Clonagem Molecular , Cristalografia por Raios X , DNA Complementar/biossíntese , Glicosídeos/química , Modelos Moleculares , Modelos Estatísticos , Conformação Molecular , Triterpenos/químicaRESUMO
Mesoscale cortical activity can be defined as the organization of activity of large neuron populations into collective action, forming time-dependent patterns such as traveling waves. Although collective action may play an important role in the cross-scale integration of brain activity and in the emergence of cognitive behavior, a comprehensive formulation of the laws governing its dynamics is still lacking. Because collective action processes are macroscopic with respect to neuronal activity, these processes cannot be described directly with methods and models developed for the microscale (individual neurons).To identify the characteristic features of mesoscopic dynamics, and to lay the foundations for a theoretical description of mesoscopic activity in the hippocampus, we conduct a comprehensive examination of observational data of hippocampal local field potential (LFP) recordings. We use the strong correlation between rat running-speed and the LFP power to parameterize the energy input into the hippocampus, and show that both the power and non-linearity of collective action (e.g., theta and gamma rhythms) increase with increased speed. Our results show that collective-action dynamics are stochastic (the precise state of a single neuron is irrelevant), weakly non-linear, and weakly dissipative. These are the principles of the theory of weak turbulence. Therefore, we propose weak turbulence a theoretical framework for the description of mesoscopic activity in the hippocampus. The weak turbulence framework provides a complete description of the cross-scale energy exchange (the energy cascade). It uncovers the mechanism governing major features of LFP spectra and bispectra, such as the physical meaning of the exponent α of power-law LFP spectra (e.g., f -α, where f is the frequency), the strengthening of theta-gamma coupling with energy input into the hippocampus, as well as specific phase lags associated with their interaction. Remarkably, the weak turbulence framework is consistent with the theory of self organized criticality, which provides a simple explanation for the existence of the power-law background spectrum. Together with self-organized criticality, weak turbulence could provide a unifying approach to modeling the dynamics of mesoscopic activity.
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[reaction: see text] Botulinum neurotoxins (BoNTs), etiological agents of the deadly food poisoning disease botulism, are the most toxic proteins currently known. By using in situ lead identification chemistry, we have uncovered the first class of inhibitors that displays nanomolar potency. From a 15 microM lead compound, structure-activity relationship studies were performed granting the most potent BoNT/A inhibitor reported to date that displays an inhibition constant of 300 nM.
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Toxinas Botulínicas Tipo A/antagonistas & inibidores , Toxinas Botulínicas Tipo A/toxicidade , Técnicas de Química Combinatória , Inibidores de Proteases/síntese química , Botulismo/etiologia , Estrutura Molecular , Inibidores de Proteases/química , Inibidores de Proteases/farmacologia , Relação Estrutura-AtividadeRESUMO
BACKGROUND: The prevalence of obesity has increased dramatically worldwide. The obesity epidemic begs for novel concepts and therapeutic targets that cohesively address "food-abuse" disorders. We demonstrate a molecular link between impairment of a central kinase (Akt) involved in insulin signaling induced by exposure to a high-fat (HF) diet and dysregulation of higher order circuitry involved in feeding. Dopamine (DA) rich brain structures, such as striatum, provide motivation stimuli for feeding. In these central circuitries, DA dysfunction is posited to contribute to obesity pathogenesis. We identified a mechanistic link between metabolic dysregulation and the maladaptive behaviors that potentiate weight gain. Insulin, a hormone in the periphery, also acts centrally to regulate both homeostatic and reward-based HF feeding. It regulates DA homeostasis, in part, by controlling a key element in DA clearance, the DA transporter (DAT). Upon HF feeding, nigro-striatal neurons rapidly develop insulin signaling deficiencies, causing increased HF calorie intake. METHODOLOGY/PRINCIPAL FINDINGS: We show that consumption of fat-rich food impairs striatal activation of the insulin-activated signaling kinase, Akt. HF-induced Akt impairment, in turn, reduces DAT cell surface expression and function, thereby decreasing DA homeostasis and amphetamine (AMPH)-induced DA efflux. In addition, HF-mediated dysregulation of Akt signaling impairs DA-related behaviors such as (AMPH)-induced locomotion and increased caloric intake. We restored nigro-striatal Akt phosphorylation using recombinant viral vector expression technology. We observed a rescue of DAT expression in HF fed rats, which was associated with a return of locomotor responses to AMPH and normalization of HF diet-induced hyperphagia. CONCLUSIONS/SIGNIFICANCE: Acquired disruption of brain insulin action may confer risk for and/or underlie "food-abuse" disorders and the recalcitrance of obesity. This molecular model, thus, explains how even short-term exposure to "the fast food lifestyle" creates a cycle of disordered eating that cements pathological changes in DA signaling leading to weight gain and obesity.
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Dopamina/metabolismo , Proteínas Proto-Oncogênicas c-akt/metabolismo , Animais , Transporte Biológico , Biotinilação , Encéfalo/metabolismo , Membrana Celular/metabolismo , Corpo Estriado/metabolismo , Dieta Hiperlipídica , Homeostase , Insulina/metabolismo , Locomoção , Masculino , Obesidade/metabolismo , Ratos , Ratos Sprague-Dawley , Transdução de Sinais , Substância Negra/metabolismoRESUMO
Small molecules based upon a 2-acylguanidine-5-phenyl thiophene scaffold that can activate the light chain metalloprotease of botulinum neurotoxin serotype A (BoNT LC/A) by an apparent reduction in Km are reported. On the basis of structure-activity relationships and the activation profile, one or more molecules of activator specifically bind to a defined site on the toxin, causing the observed rate enhancement. With the ever-growing clinical uses of BoNT, compounds such as those reported here may provide a method for combating the emerging adaptive immune responses to BoNT.
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Toxinas Botulínicas Tipo A/química , Toxinas Botulínicas Tipo A/metabolismo , Metaloproteases/química , Metaloproteases/metabolismo , Tiofenos/farmacologia , Toxinas Botulínicas Tipo A/antagonistas & inibidores , Catálise , Ativação Enzimática/efeitos dos fármacos , Cinética , Relação Estrutura-Atividade , Tiofenos/químicaRESUMO
Botulinum neurotoxins (BoNTs), etiological agents of the deadly food poisoning disease botulism, are the most toxic proteins currently known. Although only a few hundred cases of botulism are reported in the United States annually, there is growing interest in BoNTs attributable to their potential use as biological warfare agents. Neurotoxicity results from cleavage of the soluble NSF-attachment protein receptor complex proteins of the presynaptic vesicles by the BoNT light chain subunit, a Zn endopeptidase. Few effective inhibitors of BoNT/A LC (light chain) activity are known, and the discovery process is hampered by the lack of an efficient high-throughput assay for screening compound libraries. To alleviate this bottleneck, we have synthesized the peptide SNAPtide and have developed a robust assay for the high-throughput evaluation of BoNT/A LC inhibitors. Key aspects for the development of this optimized assay include the addition of a series of detergents, cosolvents, and salts, including 0.01% w/v Tween 20 to increase BoNT/A LC catalysis, stability, and ease of small molecule screening. To evaluate the effectiveness of the assay, a series of hydroxamate-based small molecules were synthesized and examined with BoNT/A LC. The methodology described is superior to other assays reported to date for the high-throughput identification of BoNT/A inhibitors.
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Toxinas Botulínicas Tipo A/antagonistas & inibidores , Inibidores de Proteases/síntese química , Proteínas SNARE/síntese química , Catálise , Substâncias para a Guerra Química/toxicidade , Detergentes/química , Metaloendopeptidases/antagonistas & inibidores , Fármacos Neuromusculares/toxicidade , Inibidores de Proteases/farmacologia , Proteínas SNARE/farmacologia , Sais/química , Solventes/química , Espectroscopia de Infravermelho com Transformada de Fourier , Estireno/química , Fatores de TempoRESUMO
Protein-protein interactions are of critical importance in biological systems, and small molecule modulators of such protein recognition and intervention processes are of particular interest. To investigate this area of research, we have synthesized small-molecule libraries that can disrupt a number of biologically relevant protein-protein interactions. These library members are designed upon planar motif, appended with a variety of chemical functions, which we have termed "credit-card" structures. From two of our "credit-card" libraries, a series of molecules were uncovered which act as inhibitors against the HIV-1 gp41 fusogenic 6-helix bundle core formation, viral antigen p24 formation, and cell-cell fusion at low micromolar concentrations. From the high-throughput screening assays we utilized, a selective index (SI) value of 4.2 was uncovered for compound 2261, which bodes well for future structure activity investigations and the design of more potent gp41 inhibitors.