Postmortem imaging reveals patterns of medial temporal lobe vulnerability to tau pathology in Alzheimer's disease.

Our current understanding of the spread and neurodegenerative effects of tau neurofibrillary tangles (NFTs) within the medial temporal lobe (MTL) during the early stages of Alzheimer's Disease (AD) is limited by the presence of confounding non-AD pathologies and the two-dimensional (2-D) nature of conventional histology studies. Here, we combine ex vivo MRI and serial histological imaging from 25 human MTL specimens to present a detailed, 3-D characterization of quantitative NFT burden measures in the space of a high-resolution, ex vivo atlas with cytoarchitecturally-defined subregion labels, that can be used to inform future in vivo neuroimaging studies. Average maps show a clear anterior to poster gradient in NFT distribution and a precise, spatial pattern with highest levels of NFTs found not just within the transentorhinal region but also the cornu ammonis (CA1) subfield. Additionally, we identify granular MTL regions where measures of neurodegeneration are likely to be linked to NFTs specifically, and thus potentially more sensitive as early AD biomarkers.

Ex vivo, in situ perfusion protocol for human brain fixation compatible with microscopy, MRI techniques, and anatomical studies.

We present a method for human brain fixation based on simultaneous perfusion of 4% paraformaldehyde through carotids after a flush with saline. The left carotid cannula is used to perfuse the body with 10% formalin, to allow further use of the body for anatomical research or teaching. The aim of our method is to develop a vascular fixation protocol for the human brain, by adapting protocols that are commonly used in experimental animal studies. We show that a variety of histological procedures can be carried out (cyto- and myeloarchitectonics, histochemistry, immunohistochemistry, intracellular cell injection, and electron microscopy). In addition, ex vivo, ex situ high-resolution MRI (9.4T) can be obtained in the same specimens. This procedure resulted in similar morphological features to those obtained by intravascular perfusion in experimental animals, provided that the postmortem interval was under 10 h for several of the techniques used and under 4 h in the case of intracellular injections and electron microscopy. The use of intravascular fixation of the brain inside the skull provides a fixed whole human brain, perfectly fitted to the skull, with negligible deformation compared to conventional techniques. Given this characteristic of ex vivo, in situ fixation, this procedure can probably be considered the most suitable one available for ex vivo MRI scans of the brain. We describe the compatibility of the method proposed for intravascular fixation of the human brain and fixation of the donor's body for anatomical purposes. Thus, body donor programs can provide human brain tissue, while the remainder of the body can also be fixed for anatomical studies. Therefore, this method of human brain fixation through the carotid system optimizes the procurement of human brain tissue, allowing a greater understanding of human neurological diseases, while benefiting anatomy departments by making the remainder of the body available for teaching purposes.

Study of the human hippocampal formation: a method for histological and magnetic resonance correlation in perinatal cases.

Little information is available on the magnetic resonance imaging (MRI) determination of the hippocampal formation (HF) during the perinatal period. However, this exploration is increasingly used, which requires defining visible HF landmarks on MRI images, validated through histological analysis. This study aims to provide a protocol to identify HF landmarks on MRI images, followed by histological validation through serial sections of the temporal lobe of the samples examined, to assess the longitudinal extent of the hippocampus during the perinatal period. We examined ex vivo MRI images from nine infant control brain samples. Histological validation of the hippocampal formation MRI images was obtained through serial sectioning and examination of Nissl-stained sections at 250 µm intervals along the entire length of the hippocampal formation. Up to six landmarks were identified both in MRI images and the serial histological sections. Proceeding in an anterior to posterior (rostrocaudal) direction, these were as follows: 1) the limen insulae (fronto-temporal junction); 2) the beginning of the amygdaloid complex; 3) the beginning of the lateral ventricle; 4) the caudal limit of the uncus, indicated by the start of the lateral geniculate nucleus (at the level of the gyrus intralimbicus); 5) the end of the lateral geniculate nucleus (beginning of the pulvinar); and 6) the beginning of the fornix. After histological validation of each of these landmarks, the full longitudinal length of the hippocampal formation and distances between landmarks were calculated. No statistically significant differences were found in total length or between landmarks. While the HF is anatomically organized at birth, its annotation is particularly challenging to perform. The histological validation of HF landmarks allows a better understanding of MRI images. The proposed protocol could be useful to assess MRI hippocampal quantification in children and possible variations due to different neurological diseases.

Methacrylate Cationic Nanoparticles Activity against Different Gram-Positive Bacteria.

Nanotechnology is a developing field that has boomed in recent years due to the multiple qualities of nanoparticles (NPs), one of which is their antimicrobial capacity. We propose that NPs anchored with 2-(dimethylamino)ethyl methacrylate (DMAEMA) have antibacterial properties and could constitute an alternative tool in this field. To this end, the antimicrobial effects of three quaternised NPs anchored with DMAEMA were studied. These NPs were later copolymerized using different methylmethacrylate (MMA) concentrations to evaluate their role in the antibacterial activity shown by NPs. Clinical strains of Staphylococcus aureus, S. epidermidis, S. lugdunensis and Enterococcus faecalis were used to assess antibacterial activity. The minimal inhibitory concentration (MIC) was determined at the different concentrations of NPs to appraise antibacterial activity. The cytotoxic effects of the NPs anchored with DMAEMA were determined in NIH3T3 mouse fibroblast cultures by MTT assays. All the employed NPs were effective against the studied bacterial strains, although increasing concentrations of the MMA added during the synthesis process diminished these effects without altering toxicity in cell cultures. To conclude, more studies with other copolymers are necessary to improve the antibacterial effects of NPs anchored with DMAEMA.

Nursing Student Satisfaction with the Teaching Methodology Followed during the COVID-19 Pandemic.

Background: Halfway through the 2019−2020 academic year, the entire university system was affected by an exceptional situation caused by the COVID-19 pandemic. Online learning was globally implemented for all degrees to finish the course and to meet academic objectives. This unforeseen change in teaching and subsequent evaluations meant teachers and students had to invest significant effort. Student satisfaction is used to measure the evaluation of teaching/learning processes in higher education. Our objective was to know and compare the satisfaction of nursing students taught at a Spanish public university after making changes to the teaching methodology. Methods: A descriptive observational study that measures student satisfaction. Study population: 240 students registered in academic years 2019−2020 and 2020−2021 answered the survey. The survey contained 30 items answered on a Likert-type scale. The main variables: the learning methodology (online or blended) was the independent variable; student satisfaction was the dependent variable. Descriptive and bivariate analyses were performed. Results: A response rate between 37.4% and 41.2%. Overall satisfaction was 2.75 points (SD 0.56) and 2.94 points (SD 0.49) with online learning and bimodal learning, respectively (maximum score 4 points) (p < 0.004). Conclusions: Student satisfaction was moderate−high for both learning methodologies. Students found that the b-learning methodology was the most valued.

Three-dimensional mapping of neurofibrillary tangle burden in the human medial temporal lobe.

Tau protein neurofibrillary tangles are closely linked to neuronal/synaptic loss and cognitive decline in Alzheimer's disease and related dementias. Our knowledge of the pattern of neurofibrillary tangle progression in the human brain, critical to the development of imaging biomarkers and interpretation of in vivo imaging studies in Alzheimer's disease, is based on conventional two-dimensional histology studies that only sample the brain sparsely. To address this limitation, ex vivo MRI and dense serial histological imaging in 18 human medial temporal lobe specimens (age 75.3 ± 11.4 years, range 45 to 93) were used to construct three-dimensional quantitative maps of neurofibrillary tangle burden in the medial temporal lobe at individual and group levels. Group-level maps were obtained in the space of an in vivo brain template, and neurofibrillary tangles were measured in specific anatomical regions defined in this template. Three-dimensional maps of neurofibrillary tangle burden revealed significant variation along the anterior-posterior axis. While early neurofibrillary tangle pathology is thought to be confined to the transentorhinal region, we found similar levels of burden in this region and other medial temporal lobe subregions, including amygdala, temporopolar cortex, and subiculum/cornu ammonis 1 hippocampal subfields. Overall, the three-dimensional maps of neurofibrillary tangle burden presented here provide more complete information about the distribution of this neurodegenerative pathology in the region of the cortex where it first emerges in Alzheimer's disease, and may help inform the field about the patterns of pathology spread, as well as support development and validation of neuroimaging biomarkers.

Neuropeptides in the developing human hippocampus under hypoxic-ischemic conditions.

The perinatal period, sensitive for newborn survival, is also one of the most critical moments in human brain development. Perinatal hypoxia due to reduced blood supply to the brain (ischemia) is one of the main causes of neonatal mortality. Brain damage caused by perinatal hypoxia-ischemia (HI) can lead to neuro- and psychological disorders. However, its impact seems to be region-dependent, with the hippocampus being one of the most affected areas. Among the neuronal populations of the hippocampus, some interneuron groups - such as somatostatin- or neuropeptide Y-expressing neurons - seem to be particularly vulnerable. The limited information available about the effects of HI in the hippocampus comes mainly from animal models and adult human studies. This article presents an immunohistochemical analysis of somatostatin (SOM) and neuropeptide Y (NPY) expression in the developing human hippocampus after perinatal HI. Two rostrocaudal sections of the body of the hippocampus were analysed, and the number of immunostained cells in the polymorphic layer of the dentate gyrus (DG) and the pyramidal cell layer and stratum oriens of the CA3, CA2 and CA1 fields of the hippocampus proper were quantified. The results showed a lower density of both neuropeptides in hypoxic compared to control cases. In the HI group, the number of SOM-immunoreactive cell bodies was statistically significantly lower in the pyramidal cell layer and stratum oriens of CA1, while the number of NPY-expressing neurons was statistically lower in the pyramidal cell layer of CA2. Besides, the number of SOM-expressing neurons was significantly higher in the stratum oriens of CA1 compared to that in CA2. In sum, we observed a different vulnerability of SOM- and NPY-containing neurons in the developing human hippocampus following perinatal HI damage. Our results could contribute to a better understanding of the behaviour of these neuronal populations under stressful conditions during the perinatal period.

Quantitative assessment of amygdala in Macaca fascicularis monkeys.

The amygdaloid complex (AC) is involved in very relevant cognitive and emotional pathways and exhibits changes in aging and in some neurological and psychiatric disorders. The quantitative estimators of AC could be useful to understand the impact of amygdaloid pathology in these processes, both globally and for each nucleus in particular, and their neurons. The present study analyzes morphometric and stereological estimators in the whole AC and its three main nuclei (lateral [La], basal [Ba], and accessory basal [AB]) in six Macaca fascicularis monkeys. All the brains were fixed and sectioned in the coronal plane; Nissl-stained sections were used for estimation of size and form parameters in both, the AC, and the La, Ba, and AB nuclei separately. The study includes stereological estimates of the volume and surface area of the AC; also, volume of the neurons in the amygdaloid nuclei was estimated using the point-sampled intercepts method. Our results show that the AB nucleus is smaller than both the La and Ba nuclei in both morphometric and stereological estimators. Brain hemispheric side had not significant influence on any of quantitative estimates. The neuron volume was higher in the AB nucleus relative to LA and Ba of the nuclei. These data describe some quantitative parameters of the amygdaloid complex and their main nuclei that could help us to detect small changes in neurodegenerative and other pathological processes.

Neuronal volume of the hippocampal regions in ageing.

The hippocampal formation (HF) has an important role in different human capacities, such as memory processing and emotional expression. Both extensive changes and limited variations of its components can cause clinically expressed dysfunctions. Although there remains no effective treatment for diseases caused by pathological changes in this brain region, detection of these changes, even minimally, could allow us to develop early interventions and establish corrective measures. This study analysed the neuronal islands of layer II of the entorhinal cortex (EC), the neuronal clumps of the external principal layer of the presubiculum (PrS) and the dentate granule cells of the dentate gyrus (DG), which represent the prominent structural regions within the HF circuit. Subjects from two age groups (younger or older than 65 years) were studied and their neuronal size assessed by the point-sampled intercepts stereological method. The quantitative v¯v(soma) estimate was a volume of roughly 8,500 µm3 for EC layer II neurons, and DG granule neurons and presubicular neurons were five and 10 times smaller, respectively. The older age group showed a v¯v(soma) increase of 2%, 18% and 28% with respect to the younger group in the PrS, DG and EC regions, respectively. None of these regions showed interhemispheric differences. This quantitative estimation is relevant because the observed variance in the v¯v(soma) estimates suggests that biological variation is the main contributory factor, with intercepts and measurements having a smaller impact. Therefore, we suggest that age has a limited influence on neuronal volume variation in these HF regions, which needs to be compared with similar measurements in neurodegenerative disorders such as Alzheimer's.

Postnatal Development of NPY and Somatostatin-28 Peptidergic Populations in the Human Angular Bundle.

The angular bundle is a white matter fiber fascicle, which runs longitudinally along the parahippocampal gyrus. It is best known for carrying fibers from the entorhinal cortex (EC) to the hippocampus through the perforant and alvear pathways, as well as for carrying hippocampal output to the neocortex, and distributing fibers to polysensory cortex. The angular bundle is already present prenatally at the beginning of the fetal period. Connections between the EC and the hippocampus are established by the 20th gestational week (gw). In the postnatal period, it shows increasing myelination. The angular bundle, as well as other white matter portions of gyral surfaces in the brain, presents interstitial neurons, a remnant of subplate neurons. Those interstitial neurons show neurochemical phenotypes both prenatally and postnatally, among which, neuropeptide Y (NPY) and Somatostatin-28 (SOM-28) peptidergic populations are noticeable, and accompany the fiber connections in the maturation of the hippocampal formation. We sought to investigate the topography of the postnatal distribution and relative density of neurons immunoreactive for NPY or SOM in the angular bundle along the rostrocaudal axis of the hippocampus. The study was carried out in 15 cases, ranging from 35 gws, up to 14 year old. All cases showed positive neurons showing a polygonal or spindle shaped morphology for both peptides, scattered throughout the angular bundle. The highest number of positive neurons appeared around birth and the ensuing weeks. Up to one and a half years, the density of both peptidergic populations decreased slightly. However, cases older than 2 years of age showed a substantial decrease in density of immunolabeled neurons, density that did not showed a minor decrease in density of positive neurons in cases older than 2 years. In addition, a topography from caudal to rostral levels of the angular bundle was detected at all ages. The functional significance of interstitial cells is unknown, but the existence of SOM and NPY peptidergic neurons, presumably inhibitory, in the white matter of the angular bundle, could contribute to the basic wiring of the hippocampal formation, through which autobiographical and spatial memories can begin to be stored in the infant brain.

Prefrontal cortex afferents to the anterior temporal lobe in the Macaca fascicularis monkey.

The anatomical organization of the lateral prefrontal cortex (LPFC) afferents to the anterior part of the temporal lobe (ATL) remains to be clarified. The LPFC has two subdivisions, dorsal (dLPFC) and ventral (vLPFC), which have been linked to cognitive processes. The ATL includes several different cortical areas, namely, the temporal polar cortex and rostral parts of the perirhinal, inferotemporal, and anterior tip of the superior temporal gyrus cortices. Multiple sensory modalities converge in the ATL. All of them (except the rostral inferotemporal and superior temporal gyrus cortices) are components of the medial temporal lobe, which is critical for long-term memory processing. We studied the LPFC connections with the ATL by placing retrograde tracer injections into the ATL: the temporal polar (n = 3), perirhinal (areas 35 and 36, n = 6), and inferotemporal cortices (area TE, n = 5), plus one additional deposit in the posterior parahippocampal cortex (area TF, n = 1). Anterograde tracer deposits into the dLPFC (A9 and A46, n = 2), the vLPFC (A46v, n = 2), and the orbitofrontal cortex (OF; n = 2) were placed for confirmation of those projections. The results showed that the vLPFC displays a moderate projection to rostral area TE and the dorsomedial portion of the temporal polar cortex; in contrast, the dLPFC connections with the ATL were weak. By comparison, the OFC and medial frontal cortices (MFC) showed dense connectivity with the ATL, namely, A13 with the temporopolar and perirhinal cortices. All areas of the MFC projected to the temporopolar cortex, albeit with a lower intensity. The functional significance of such paucity of LPFC afferents is unknown.

Postnatal development of the human hippocampal formation.

The postnatal development of the human hippocampal formation (HF) is subject of increasing interest due to its implication in important pathologies that hamper the normal development of children. In this work, we present a glimpse of the main events that constitute important milestones in the development and shaping of some of the most important psychological capabilities such as autobiographical memory. We analyzed a total of 21 brains ranging from 27 gestational weeks to 14 years. Although we examined some cases in the last trimester of gestation, our description starts at birth, around 40 gestational weeks. Serial sections stained with thionin for Nissl analysis revealed that all fields of the HF were present and identifiable at birth. However, the relative growth of the cortical mantle was much higher relative to the HF. The main structural changes took place during the first postnatal year, in particular in the dentate gyrus and in the entorhinal cortex. At subsequent ages, a growth in size was noted in all components of the HF. This growth was more evident at the body and tail of the hippocampus, as evidenced by measurements of the neuroanatomical series. In addition, we examined in some cases the MRI appearance of the HF at different postnatal ages obtained by postmortem imaging. MRI neuroanatomical series provided anatomically identified landmarks useful for the MRI identification of different components of the HF during postnatal development.