A Review of Ambulance Terrorism on the African Continent.

BACKGROUND: In recent decades, an increasing number of terrorist attacks have been carried out against medical institutions, hospitals, and health care workers. These attacks, that often result in high numbers of casualties and impaired access to health services, have a more significant impact on people's sense of security than attacks against military and police targets. Attacks on ambulances - especially on the African continent - have been sparsely studied. This study examines attacks on ambulances on the African continent during the period from 1992-2022 (until December 31, 2021). METHODS: Reports of ambulance terrorism were extracted from the Global Terrorism Database (GTD), RAND Database of Worldwide Terrorism Incidents (RDWTI), United Nation's Safeguarding Health in Conflict Coalition (SHCC) database, Armed Conflict Location and Event Data Project (ACLED), Surveillance System for Attacks on Health Care (SSA) database, and Aid Worker Security Database (AWSD). Furthermore, a grey literature search was performed. The date and location of the attacks, perpetrators, weapon and attack types, and the number of victims (dead and wounded) and hostages were collected. Results were exported into an Excel spreadsheet (Microsoft Corp.; Redmond, Washington USA) for analysis. RESULTS: During the 30-year study period, 166 attacks were observed in 18 African countries. The number of attacks significantly increased since 2016, with 81.3% of the attacks taking place from 2016 to 2022. In total, 193 people died and another 208 were injured. Attacks with firearms were most frequently noted (92 cases; 55.4%), followed by attacks with explosive devices (26 cases; 15.7%). A significant number of ambulances were hijacked (26 cases; 15.7%) and subsequently used for other terrorist attacks. In seven attacks, ambulances were used as vehicle-born improvised explosive devices (VBIEDs). CONCLUSION: In this database study on ambulance terrorism in Africa, it was found that the reported occurrence of attacks increased from 2013 onwards, including the rise of ambulances used as VBIEDs. These findings suggest that ambulance terrorism represents a real, significant risk that both governments and health care institutions must address.

Hippocampal sharp wave-ripples and the associated sequence replay emerge from structured synaptic interactions in a network model of area CA3.

Hippocampal place cells are activated sequentially as an animal explores its environment. These activity sequences are internally recreated ('replayed'), either in the same or reversed order, during bursts of activity (sharp wave-ripples [SWRs]) that occur in sleep and awake rest. SWR-associated replay is thought to be critical for the creation and maintenance of long-term memory. In order to identify the cellular and network mechanisms of SWRs and replay, we constructed and simulated a data-driven model of area CA3 of the hippocampus. Our results show that the chain-like structure of recurrent excitatory interactions established during learning not only determines the content of replay, but is essential for the generation of the SWRs as well. We find that bidirectional replay requires the interplay of the experimentally confirmed, temporally symmetric plasticity rule, and cellular adaptation. Our model provides a unifying framework for diverse phenomena involving hippocampal plasticity, representations, and dynamics, and suggests that the structured neural codes induced by learning may have greater influence over cortical network states than previously appreciated.

The NKCC1 ion transporter modulates microglial phenotype and inflammatory response to brain injury in a cell-autonomous manner.

The NKCC1 ion transporter contributes to the pathophysiology of common neurological disorders, but its function in microglia, the main inflammatory cells of the brain, has remained unclear to date. Therefore, we generated a novel transgenic mouse line in which microglial NKCC1 was deleted. We show that microglial NKCC1 shapes both baseline and reactive microglia morphology, process recruitment to the site of injury, and adaptation to changes in cellular volume in a cell-autonomous manner via regulating membrane conductance. In addition, microglial NKCC1 deficiency results in NLRP3 inflammasome priming and increased production of interleukin-1ß (IL-1ß), rendering microglia prone to exaggerated inflammatory responses. In line with this, central (intracortical) administration of the NKCC1 blocker, bumetanide, potentiated intracortical lipopolysaccharide (LPS)-induced cytokine levels. In contrast, systemic bumetanide application decreased inflammation in the brain. Microglial NKCC1 KO animals exposed to experimental stroke showed significantly increased brain injury, inflammation, cerebral edema and worse neurological outcome. Thus, NKCC1 emerges as an important player in controlling microglial ion homeostasis and inflammatory responses through which microglia modulate brain injury. The contribution of microglia to central NKCC1 actions is likely to be relevant for common neurological disorders.

Attitudes towards Participation in a Passive Data Collection Experiment.

In this paper, we present the results of an exploratory study conducted in Hungary using a factorial design-based online survey to explore the willingness to participate in a future research project based on active and passive data collection via smartphones. Recently, the improvement of smart devices has enabled the collection of behavioural data on a previously unimaginable scale. However, the willingness to share this data is a key issue for the social sciences and often proves to be the biggest obstacle to conducting research. In this paper we use vignettes to test different (hypothetical) study settings that involve sensor data collection but differ in the organizer of the research, the purpose of the study and the type of collected data, the duration of data sharing, the number of incentives and the ability to suspend and review the collection of data. Besides the demographic profile of respondents, we also include behavioural and attitudinal variables to the models. Our results show that the content and context of the data collection significantly changes people's willingness to participate, however their basic demographic characteristics (apart from age) and general level of trust seem to have no significant effect. This study is a first step in a larger project that involves the development of a complex smartphone-based research tool for hybrid (active and passive) data collection. The results presented in this paper help improve our experimental design to encourage participation by minimizing data sharing concerns and maximizing user participation and motivation.

Publisher Correction: Distinct synchronization, cortical coupling and behavioral function of two basal forebrain cholinergic neuron types.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Distinct synchronization, cortical coupling and behavioral function of two basal forebrain cholinergic neuron types.

Basal forebrain cholinergic neurons (BFCNs) modulate synaptic plasticity, cortical processing, brain states and oscillations. However, whether distinct types of BFCNs support different functions remains unclear. Therefore, we recorded BFCNs in vivo, to examine their behavioral functions, and in vitro, to study their intrinsic properties. We identified two distinct types of BFCNs that differ in their firing modes, synchronization properties and behavioral correlates. Bursting cholinergic neurons (Burst-BFCNs) fired synchronously, phase-locked to cortical theta activity and fired precisely timed bursts after reward and punishment. Regular-firing cholinergic neurons (Reg-BFCNs) were found predominantly in the posterior basal forebrain, displayed strong theta rhythmicity and responded with precise single spikes after behavioral outcomes. In an auditory detection task, synchronization of Burst-BFCNs to the auditory cortex predicted the timing of behavioral responses, whereas tone-evoked cortical coupling of Reg-BFCNs predicted correct detections. We propose that differential recruitment of two basal forebrain cholinergic neuron types generates behavior-specific cortical activation.

Median raphe controls acquisition of negative experience in the mouse.

Adverse events need to be quickly evaluated and memorized, yet how these processes are coordinated is poorly understood. We discovered a large population of excitatory neurons in mouse median raphe region (MRR) expressing vesicular glutamate transporter 2 (vGluT2) that received inputs from several negative experience-related brain centers, projected to the main aversion centers, and activated the septohippocampal system pivotal for learning of adverse events. These neurons were selectively activated by aversive but not rewarding stimuli. Their stimulation induced place aversion, aggression, depression-related anhedonia, and suppression of reward-seeking behavior and memory acquisition-promoting hippocampal theta oscillations. By contrast, their suppression impaired both contextual and cued fear memory formation. These results suggest that MRR vGluT2 neurons are crucial for the acquisition of negative experiences and may play a central role in depression-related mood disorders.

Brainstem nucleus incertus controls contextual memory formation.

Hippocampal pyramidal cells encode memory engrams, which guide adaptive behavior. Selection of engram-forming cells is regulated by somatostatin-positive dendrite-targeting interneurons, which inhibit pyramidal cells that are not required for memory formation. Here, we found that γ-aminobutyric acid (GABA)-releasing neurons of the mouse nucleus incertus (NI) selectively inhibit somatostatin-positive interneurons in the hippocampus, both monosynaptically and indirectly through the inhibition of their subcortical excitatory inputs. We demonstrated that NI GABAergic neurons receive monosynaptic inputs from brain areas processing important environmental information, and their hippocampal projections are strongly activated by salient environmental inputs in vivo. Optogenetic manipulations of NI GABAergic neurons can shift hippocampal network state and bidirectionally modify the strength of contextual fear memory formation. Our results indicate that brainstem NI GABAergic cells are essential for controlling contextual memories.

Co-transmission of acetylcholine and GABA regulates hippocampal states.

The basal forebrain cholinergic system is widely assumed to control cortical functions via non-synaptic transmission of a single neurotransmitter. Yet, we find that mouse hippocampal cholinergic terminals invariably establish GABAergic synapses, and their cholinergic vesicles dock at those synapses only. We demonstrate that these synapses do not co-release but co-transmit GABA and acetylcholine via different vesicles, whose release is triggered by distinct calcium channels. This co-transmission evokes composite postsynaptic potentials, which are mutually cross-regulated by presynaptic autoreceptors. Although postsynaptic cholinergic receptor distribution cannot be investigated, their response latencies suggest a focal, intra- and/or peri-synaptic localisation, while GABAA receptors are detected intra-synaptically. The GABAergic component alone effectively suppresses hippocampal sharp wave-ripples and epileptiform activity. Therefore, the differentially regulated GABAergic and cholinergic co-transmission suggests a hitherto unrecognised level of control over cortical states. This novel model of hippocampal cholinergic neurotransmission may lead to alternative pharmacotherapies after cholinergic deinnervation seen in neurodegenerative disorders.

The Effects of Realistic Synaptic Distribution and 3D Geometry on Signal Integration and Extracellular Field Generation of Hippocampal Pyramidal Cells and Inhibitory Neurons.

In vivo and in vitro multichannel field and somatic intracellular recordings are frequently used to study mechanisms of network pattern generation. When interpreting these data, neurons are often implicitly considered as electrotonically compact cylinders with a homogeneous distribution of excitatory and inhibitory inputs. However, the actual distributions of dendritic length, diameter, and the densities of excitatory and inhibitory input are non-uniform and cell type-specific. We first review quantitative data on the dendritic structure and synaptic input and output distribution of pyramidal cells (PCs) and interneurons in the hippocampal CA1 area. Second, using multicompartmental passive models of four different types of neurons, we quantitatively explore the effect of differences in dendritic structure and synaptic distribution on the errors and biases of voltage clamp measurements of inhibitory and excitatory postsynaptic currents. Finally, using the 3-dimensional distribution of dendrites and synaptic inputs we calculate how different inhibitory and excitatory inputs contribute to the generation of local field potential in the hippocampus. We analyze these effects at different realistic background activity levels as synaptic bombardment influences neuronal conductance and thus the propagation of signals in the dendritic tree. We conclude that, since dendrites are electrotonically long and entangled in 3D, somatic intracellular and field potential recordings miss the majority of dendritic events in some cell types, and thus overemphasize the importance of perisomatic inhibitory inputs and belittle the importance of complex dendritic processing. Modeling results also suggest that PCs and inhibitory neurons probably use different input integration strategies. In PCs, second- and higher-order thin dendrites are relatively well-isolated from each other, which may support branch-specific local processing as suggested by studies of active dendritic integration. In the electrotonically compact parvalbumin- and cholecystokinincontaining interneurons, synaptic events are visible in the whole dendritic arbor, and thus the entire dendritic tree may form a single integrative element. Calretinin-containing interneurons were found to be electrotonically extended, which suggests the possibility of complex dendritic processing in this cell type. Our results also highlight the need for the integration of methods that allow the measurement of dendritic processes into studies of synaptic interactions and dynamics in neural networks.

Generation of physiological and pathological high frequency oscillations: the role of perisomatic inhibition in sharp-wave ripple and interictal spike generation.

Sharp-wave-ripple complexes (SWRs) and interictal-spikes are physiological and pathological forms of irregularly occurring transient high activity events in the hippocampal EEG. They share similar features and carry high-frequency oscillations with different spectral features. Recent results reveal similarities and differences in the generation of the two types of transients, and argue that parvalbumin containing basket cells (PVBCs) are crucial in synchronizing neuronal activity in both cases. SWRs are generated in the reciprocally connected network of inhibitory PVBCs, while in the pathological case, synchronous failure of perisomatic inhibition triggers massive pyramidal cell burst firing. While physiological ripple oscillation is primarily the result of phasic perisomatic inhibitory currents, pathological high-frequency ripples are population spikes of partially synchronous, massively bursting, uninhibited pyramidal cells.

Quantitative ultrastructural analysis of basket and axo-axonic cell terminals in the mouse hippocampus.

Three functionally different populations of perisomatic interneurons establish GABAergic synapses on hippocampal pyramidal cells: parvalbumin (PV)-containing basket cells, type 1 cannabinoid receptor (CB1)-positive basket cells both of which target somata, and PV-positive axo-axonic cells that innervate axon initial segments. Using electron microscopic reconstructions, we estimated that a pyramidal cell body receives synapses from about 60 and 140 synaptic terminals in the CA1 and CA3 area, respectively. About 60 % of these terminals were PV positive, whereas 35-40 % of them were CB1 positive. Only about 1 % (CA1) and 4 % (CA3) of the somatic boutons were negative for both markers. Using fluorescent labeling, we showed that most of the CB1-positive terminals expressed vesicular glutamate transporter 3. Reconstruction of somatic boutons revealed that although their volumes are similar, CB1-positive boutons are more flat and the total volume of their mitochondria was smaller than that of PV-positive boutons. Both types of boutons contain dense-core vesicles and frequently formed multiple release sites on their targets and innervated an additional soma or dendrite as well. PV-positive boutons possessed small, macular synapses; whereas the total synaptic area of CB1-positive boutons was larger and formed multiple irregular-shaped synapses. Axo-axonic boutons were smaller than somatic boutons, had only one synapse and their ultrastructural parameters were closer to those of PV-positive somatic boutons. Our results represent the first quantitative measurement-using a highly reliable method-of the contribution of different cell types to the perisomatic innervation of pyramidal neurons, and may help to explain functional differences in their output properties.

Mechanisms of sharp wave initiation and ripple generation.

Replay of neuronal activity during hippocampal sharp wave-ripples (SWRs) is essential in memory formation. To understand the mechanisms underlying the initiation of irregularly occurring SWRs and the generation of periodic ripples, we selectively manipulated different components of the CA3 network in mouse hippocampal slices. We recorded EPSCs and IPSCs to examine the buildup of neuronal activity preceding SWRs and analyzed the distribution of time intervals between subsequent SWR events. Our results suggest that SWRs are initiated through a combined refractory and stochastic mechanism. SWRs initiate when firing in a set of spontaneously active pyramidal cells triggers a gradual, exponential buildup of activity in the recurrent CA3 network. We showed that this tonic excitatory envelope drives reciprocally connected parvalbumin-positive basket cells, which start ripple-frequency spiking that is phase-locked through reciprocal inhibition. The synchronized GABA(A) receptor-mediated currents give rise to a major component of the ripple-frequency oscillation in the local field potential and organize the phase-locked spiking of pyramidal cells. Optogenetic stimulation of parvalbumin-positive cells evoked full SWRs and EPSC sequences in pyramidal cells. Even with excitation blocked, tonic driving of parvalbumin-positive cells evoked ripple oscillations. Conversely, optogenetic silencing of parvalbumin-positive cells interrupted the SWRs or inhibited their occurrence. Local drug applications and modeling experiments confirmed that the activity of parvalbumin-positive perisomatic inhibitory neurons is both necessary and sufficient for ripple-frequency current and rhythm generation. These interneurons are thus essential in organizing pyramidal cell activity not only during gamma oscillation, but, in a different configuration, during SWRs.

A flexible, interactive software tool for fitting the parameters of neuronal models.

The construction of biologically relevant neuronal models as well as model-based analysis of experimental data often requires the simultaneous fitting of multiple model parameters, so that the behavior of the model in a certain paradigm matches (as closely as possible) the corresponding output of a real neuron according to some predefined criterion. Although the task of model optimization is often computationally hard, and the quality of the results depends heavily on technical issues such as the appropriate choice (and implementation) of cost functions and optimization algorithms, no existing program provides access to the best available methods while also guiding the user through the process effectively. Our software, called Optimizer, implements a modular and extensible framework for the optimization of neuronal models, and also features a graphical interface which makes it easy for even non-expert users to handle many commonly occurring scenarios. Meanwhile, educated users can extend the capabilities of the program and customize it according to their needs with relatively little effort. Optimizer has been developed in Python, takes advantage of open-source Python modules for nonlinear optimization, and interfaces directly with the NEURON simulator to run the models. Other simulators are supported through an external interface. We have tested the program on several different types of problems of varying complexity, using different model classes. As targets, we used simulated traces from the same or a more complex model class, as well as experimental data. We successfully used Optimizer to determine passive parameters and conductance densities in compartmental models, and to fit simple (adaptive exponential integrate-and-fire) neuronal models to complex biological data. Our detailed comparisons show that Optimizer can handle a wider range of problems, and delivers equally good or better performance than any other existing neuronal model fitting tool.

Physiological sharp wave-ripples and interictal events in vitro: what's the difference?

Sharp wave-ripples and interictal events are physiological and pathological forms of transient high activity in the hippocampus with similar features. Sharp wave-ripples have been shown to be essential in memory consolidation, whereas epileptiform (interictal) events are thought to be damaging. It is essential to grasp the difference between physiological sharp wave-ripples and pathological interictal events to understand the failure of control mechanisms in the latter case. We investigated the dynamics of activity generated intrinsically in the Cornu Ammonis region 3 of the mouse hippocampus in vitro, using four different types of intervention to induce epileptiform activity. As a result, sharp wave-ripples spontaneously occurring in Cornu Ammonis region 3 disappeared, and following an asynchronous transitory phase, activity reorganized into a new form of pathological synchrony. During epileptiform events, all neurons increased their firing rate compared to sharp wave-ripples. Different cell types showed complementary firing: parvalbumin-positive basket cells and some axo-axonic cells stopped firing as a result of a depolarization block at the climax of the events in high potassium, 4-aminopyridine and zero magnesium models, but not in the gabazine model. In contrast, pyramidal cells began firing maximally at this stage. To understand the underlying mechanism we measured changes of intrinsic neuronal and transmission parameters in the high potassium model. We found that the cellular excitability increased and excitatory transmission was enhanced, whereas inhibitory transmission was compromised. We observed a strong short-term depression in parvalbumin-positive basket cell to pyramidal cell transmission. Thus, the collapse of pyramidal cell perisomatic inhibition appears to be a crucial factor in the emergence of epileptiform events.

Input-output features of anatomically identified CA3 neurons during hippocampal sharp wave/ripple oscillation in vitro.

Hippocampal sharp waves and the associated ripple oscillations (SWRs) are implicated in memory processes. These network events emerge intrinsically in the CA3 network. To understand cellular interactions that generate SWRs, we detected first spiking activity followed by recording of synaptic currents in distinct types of anatomically identified CA3 neurons during SWRs that occurred spontaneously in mouse hippocampal slices. We observed that the vast majority of interneurons fired during SWRs, whereas only a small portion of pyramidal cells was found to spike. There were substantial differences in the firing behavior among interneuron groups; parvalbumin-expressing basket cells were one of the most active GABAergic cells during SWRs, whereas ivy cells were silent. Analysis of the synaptic currents during SWRs uncovered that the dominant synaptic input to the pyramidal cell was inhibitory, whereas spiking interneurons received larger synaptic excitation than inhibition. The discharge of all interneurons was primarily determined by the magnitude and the timing of synaptic excitation. Strikingly, we observed that the temporal structure of synaptic excitation and inhibition during SWRs significantly differed between parvalbumin-containing basket cells, axoaxonic cells, and type 1 cannabinoid receptor (CB1)-expressing basket cells, which might explain their distinct recruitment to these synchronous events. Our data support the hypothesis that the active current sources restricted to the stratum pyramidale during SWRs originate from the synaptic output of parvalbumin-expressing basket cells. Thus, in addition to gamma oscillation, these GABAergic cells play a central role in SWR generation.

Extrinsic and local glutamatergic inputs of the rat hippocampal CA1 area differentially innervate pyramidal cells and interneurons.

The two main glutamatergic pathways to the CA1 area, the Schaffer collateral/commissural input and the entorhinal fibers, as well as the local axons of CA1 pyramidal cells innervate both pyramidal cells and interneurons. To determine whether these inputs differ in their weights of activating GABAergic circuits, we have studied the relative proportion of pyramidal cells and interneurons among their postsynaptic targets in serial electron microscopic sections. Local axons of CA1 pyramidal cells, intracellularly labeled in vitro or in vivo, innervated a relatively high proportion of interneuronal postsynaptic targets (65.9 and 53.8%, in vitro and in vivo, respectively) in stratum (str.) oriens and alveus. In contrast, axons of in vitro labeled CA3 pyramidal cells in str. oriens and str. radiatum of the CA1 area made synaptic junctions predominantly with pyramidal cell spines (92.9%). The postsynaptic targets of anterogradely labeled medial entorhinal cortical boutons in CA1 str. lacunosum-moleculare were primarily pyramidal neuron dendritic spines and shafts (90.8%). The alvear group of the entorhinal afferents, traversing str. oriens, str. pyramidale, and str. radiatum showed a higher preference for innervating GABAergic cells (21.3%), particularly in str. oriens/alveus. These data demonstrate that different glutamatergic pathways innervate CA1 GABAergic cells to different extents. The results suggest that the numerically smaller CA1 local axonal inputs together with the alvear part of the entorhinal input preferentially act on GABAergic interneurons in contrast to the CA3, or the entorhinal input in str. lacunosum-moleculare. The results highlight differences in the postsynaptic target selection of the feed-forward versus recurrent glutamatergic inputs to the CA1 and CA3 areas.

New silver-gold intensification method of diaminobenzidine for double-labeling immunoelectron microscopy.

The available methods for double-labeling preembedding immunoelectron microscopy are highly limited because not only should the ultrastructure be preserved, but also the different antigens should be visualized by reaction end products that can be clearly distinguished in gray-scale images. In these procedures, one antigen is detected with 3,3'-diaminobenzidine (DAB) chromogen, resulting in a homogeneous deposit, whereas the other is labeled with either a gold-tagged immunoreagent, or DAB polymer, on the surface of which metallic silver is precipitated. The detection of the second antigen is usually impeded by the first, leading to false-negative results. The authors aimed to diminish this hindrance by a new silver intensification technique of DAB polymer, which converts the deposit from amorphous to granular. The method includes three major postdevelopmental steps: (1) treatment of nickel-enhanced DAB with sulfide, (2) silver deposition in the presence of hydroquinone under acidic conditions, and (3) precious metal replacement with gold thiocyanate. This new sulfide-silver-gold intensification of DAB (SSGI) allows a subsequent detection of other antigens using DAB. In conclusion, the new technique loads fine gold particles onto the DAB deposit at a very low background level, thereby allowing a reliable discernment between the elements stained for the two antigens at the ultrastructural level.

Parvalbumin-containing fast-spiking basket cells generate the field potential oscillations induced by cholinergic receptor activation in the hippocampus.

Gamma frequency oscillations in cortical regions can be recorded during cognitive processes, including attention or memory tasks. These oscillations are generated locally as a result of reciprocal interactions between excitatory pyramidal cells and perisomatic inhibitory interneurons. Here, we examined the contribution of the three perisomatic interneuron types--the parvalbumin-containing fast-spiking basket cells (FSBCs) and axo-axonic cells (AACs), as well as the cholecystokinin-containing regular-spiking basket cells (RSBCs) to cholinergically induced oscillations in hippocampal slices, a rhythmic activity that captures several features of the gamma oscillations recorded in vivo. By analyzing the spiking activities of single neurons recorded in parallel with local field potentials, we found that all three cell types fired phase locked to the carbachol-induced oscillations, although with different frequencies and precision. During these oscillations, FSBCs fired the most with the highest accuracy compared with the discharge of AACs and RSBCs. In further experiments, we showed that activation of µ-opioid receptors by DAMGO ([D-Ala(2),N-Me-Phe(4),Gly(5)-ol]enkephalin acetate), which significantly reduced the inhibitory, but not excitatory, transmission, suppressed or even blocked network oscillations both in vitro and in vivo, leading to the desynchronization of pyramidal cell firing. Using paired recordings, we demonstrated that carbachol application blocked GABA release from RSBCs and reduced it from FSBCs and AACs, whereas DAMGO further suppressed the GABA release only from FSBCs, but not from AACs. These results collectively suggest that the rhythmic perisomatic inhibition, generating oscillatory fluctuation in local field potentials after carbachol treatment of hippocampal slices, is the result of periodic GABA release from FSBCs.