The human periallocortex: layer pattern in presubiculum, parasubiculum and entorhinal cortex. A review

The cortical mantle is not homogeneous, so that three types of cortex can be distinguished: allocortex, periallocortex and isocortex. The main distinction among those three types is based on morphological differences, in particular the number of layers, overall organization, appearance, etc., as well as its connectivity. Additionally, in the phylogenetic scale, this classification is conserved among different mammals. The most primitive and simple cortex is the allocortex, which is characterized by the presence of three layers, with one cellular main layer; it is continued by the periallocortex, which presents six layers, although with enough differences in the layer pattern to separate three different fields: presubiculum (PrS), parasubiculum (PaS), and entorhinal cortex (EC). The closest part to the allocortex (represented by the subiculum) is the PrS, which shows outer (layers I–III) and inner (V–VI) principal layers (lamina principalis externa and lamina principalis interna), both separated by a cell poor band, parallel to the pial surface (layer IV or lamina dissecans). This layer organization is present throughout the anterior-posterior axis. The PaS continues the PrS, but its rostrocaudal extent is shorter than the PrS. The organization of the PaS shows the layer pattern more clearly than in the PrS. Up to six layers are recognizable in the PaS, with layer IV as lamina dissecans between superficial (layers I–III) and deep (V–VI) layers, as in the PrS. The EC presents even more clearly the layer pattern along both mediolateral and rostrocaudal extent. The layer pattern is a thick layer I, layer II in islands, layer III medium pyramids, layer IV as lamina dissecans (not present throughout the EC extent), layer V with dark and big pyramids and a multiform layer VI. The EC borders laterally the proisocortex (incomplete type of isocortex). Variations in the appearance of its layers justify the distinction of subfields in the EC, in particular in human and nonhuman primates. EC layers are not similar to those in the neocortex. The transition between the periallocortical EC and isocortex is not sharp, so that the proisocortex forms an intervening cortex, which fills the gap between the periallocortex and the isocortex

The influence of semantic and phonological factors on syntactic decisions: An event-related brain potential study

During language production and comprehension, information about a word's syntactic properties is sometimes needed. While the decision about the grammatical gender of a word requires access to syntactic knowledge, it has also been hypothesized that semantic (i.e., biological gender) or phonological information (i.e., sound regularities) may influence this decision. Event-related potentials (ERPs) were measured while native speakers of German processed written words that were or were not semantically and/or phonologically marked for gender. Behavioral and ERP results showed that participants were faster in making a gender decision when words were semantically and/or phonologically gender marked than when this was not the case, although the phonological effects were less clear. In conclusion, our data provide evidence that even though participants performed a grammatical gender decision, this task can be influenced by semantic and phonological factors

Comparison of histological delineations of medial temporal lobe cortices by four independent neuroanatomy laboratories

The medial temporal lobe (MTL) cortex, located adjacent to the hippocampus, is crucial for memory and prone to the accumulation of certain neuropathologies such as Alzheimer's disease neurofibrillary tau tangles. The MTL cortex is composed of several subregions which differ in their functional and cytoarchitectonic features. As neuroanatomical schools rely on different cytoarchitectonic definitions of these subregions, it is unclear to what extent their delineations of MTL cortex subregions overlap. Here, we provide an overview of cytoarchitectonic definitions of the entorhinal and parahippocampal cortices as well as Brodmann areas (BA) 35 and 36, as provided by four neuroanatomists from different laboratories, aiming to identify the rationale for overlapping and diverging delineations. Nissl-stained series were acquired from the temporal lobes of three human specimens (two right and one left hemisphere). Slices (50 μm thick) were prepared perpendicular to the long axis of the hippocampus spanning the entire longitudinal extent of the MTL cortex. Four neuroanatomists annotated MTL cortex subregions on digitized slices spaced 5 mm apart (pixel size 0.4 μm at 20× magnification). Parcellations, terminology, and border placement were compared among neuroanatomists. Cytoarchitectonic features of each subregion are described in detail. Qualitative analysis of the annotations showed higher agreement in the definitions of the entorhinal cortex and BA35, while the definitions of BA36 and the parahippocampal cortex exhibited less overlap among neuroanatomists. The degree of overlap of cytoarchitectonic definitions was partially reflected in the neuroanatomists' agreement on the respective delineations. Lower agreement in annotations was observed in transitional zones between structures where seminal cytoarchitectonic features are expressed less saliently. The results highlight that definitions and parcellations of the MTL cortex differ among neuroanatomical schools and thereby increase understanding of why these differences may arise. This work sets a crucial foundation to further advance anatomically-informed neuroimaging research on the human MTL cortex

Application of the fractionator and vertical slices to estimate total capillary length in skeletal muscle

A new stereological method is proposed which combines vertical slice projections with the fractionator to estimate the total capillary length in a skeletal muscle. The method was demonstrated on the soleus muscle of a Wistar rat. The implementation required capillary highlighting, tissue sampling, and data acquisition in the form of intersection counts between capillary projections and cycloid test lines. The capillaries were demonstrated using vascular perfusion (with gelatine) of the hind leg of the rat. The sampling procedure followed the fractionator design, namely a multistage systematic sampling design with a known sampling fraction at each stage. To make the design unbiased, vertical slices were used; for efficiency, the vertical axis was chosen parallel to the main axis of the muscle. As prescribed to avoid bias, the cycloid test lines were superimposed on the slice projections, viewed under the light microscope, with their minor axes normal to the vertical axis. The estimation precision was compared for different sampling and subsampling fractions. The proposed method was globally highly efficient, unbiased, and easy to implement

Identification of the human medial temporal lobe regions on magnetic resonance images

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Quantitative modification of the testicular structure in pigs fed with anabolic doses of clenbuterol

Morphological and structural data of the testes of thirty male pigs were recorded in order to evaluate the effects of an anabolic clenbuterol treatment. Pigs aged 6 months were randomly allocated to one of three experimental groups. In two treated groups, the animals were fed with anabolic doses of clenbuterol (1 ppm); in the CLB group ($n = 10$) clenbuterol was given until they were slaughtered (treatment period = 3 months) whereas in the CLBW group ($n = 10$) the clenbuterol was withdrawn two weeks before slaughter (treatment period = 2.5 months); clenbuterol was not given to the pigs of the control group ($n = 10$). Stereological estimations of the tissular volume fraction and tubular volume density were applied to quantify the structural constituents of the testes. The results showed an increased volume fraction of the testicular interstitium especially in the Leydig cell population, as a result of the clenbuterol treatment. The increase in the nuclear volume fraction of the Leydig cells was the more persistent change in the variations recorded in both treated groups with respect to the control. A regression of the seminal epithelium was also recorded in the treated animals. The rest of the structural parameters were closer to the normal figures in the CLBW group, suggesting a recovery of the testicular structure when clenbuterol was withdrawn.Modification quantitative de la structure testiculaire chez des porcs nourris avec des doses anabolisantes de clenbutérol. Les données morphologiques et structurales des testicules de trente porcs ont été recueillies afin d'évaluer les effets d'un traitement anabolisant à base de clenbutérol. Les porcs ont été distribués de façon aléatoire dans chacun des trois groupes expérimentaux : dans deux des groupes traités les animaux ont été nourris avec des doses anabolisantes de clenbutérol (1 ppm); dans le groupe CLB ($n = 10$) le clenbutérol a été administré aux animaux jusqu'à l'abattage (période de traitement = 3 mois) alors que dans le groupe CLBW ($n = 10$) le clenbutérol a été retiré de l'alimentation deux semaines avant l'abattage (période de traitement = 2,5 mois); le clenbutérol n'a pas été administré aux porcs du groupe témoin ($n = 10$). Les estimations stéréologiques de la fraction du volume tissulaire et de la densité du volume tubulaire ont été utilisées pour quantifier les constituants structuraux des testicules. Un accroissement de la fraction du volume de l'interstitium testiculaire et surtout de la population des cellules de Leydig (fraction de volume occupée par les noyaux) a été la modification la plus persistante des variations recueillies dans les deux groupes traités par rapport au groupe témoin. Une régression de l'épithélium séminal a également été notée chez les animaux traités. Le reste des paramètres structuraux étaient plus proches des schémas normaux dans le groupe CLBW suggérant un retour à la normale des structures testiculaires lorsque le clenbutérol est retiré

The parahippocampal gyrus in the baboon: anatomical, cytoarchitectonic and magnetic resonance imaging (MRI) studies

The parahippocampal gyrus, located at the medial temporal lobe, is a key structure in declarative memory processing. We have analyzed the general organization of the parahippocampal gyrus in the baboon, a nonhuman primate species relatively close to human. This region is rostrocaudally made up of the temporopolar, perirhinal, entorhinal (divided into seven subfields) and posterior parahippocampal (areas TH and TF) cortices. The basic analysis has been performed in three brains, serially sectioned and stained with thionin, myelin stain, acetylcholinesterase and parvalbumin, to determine cytoarchitectonic boundaries. Borders of all subfields were charted onto camera lucida drawings, and two-dimensional maps of the surface and topography of the parahippocampal gyrus were made. Finally, the limits of each parahippocampal area were then transposed on corresponding MR images (commonly used for in vivo PET or functional MRI activation studies) of two animals for precise identification. The general cytoarchitectonic features of the baboon parahippocampal gyrus are similar to macaques, but the size of temporopolar cortex and the laminar organization of perirhinal and posterior parahippocampal cortices resemble humans more than macaque species. In conclusion, the size and structure of the baboon parahippocampal cortex makes this species very appropriate for experimental studies on memory function

Gross anatomy dissections and self-directed learning in medicine

The Medical School of the University of Castilla-La Mancha (UCLM, Albacete Spain) was launched in 1998 and is the most recent one in Spain. Teaching is based on small groups of students (20–25 students/group). An objective-oriented self-learning approach provides maximal autonomy and independence in the achievement of objectives by the students in close association with academic staff. Gross Anatomy courses take place in the first and second years. The one in the first year is a single 10-credit course, where one credit equals 10 hr of teaching activity. In the second year, Anatomy and Embryology are integrated with Physiology and Histology, and comprise 70 credits altogether. In addition, all students carry out two mandatory gross anatomical dissections per year, in groups of three students, to allow direct handling of human anatomical material. Students are provided with handouts containing general instructions on how to perform the dissection and the structures (items) that they must expose in a given period of time (4 hr). Afterward, a Faculty member checks the number of items demonstrated and the quality of the dissection. Each group submits a written report that contributes to the final score. We evaluated the number of items shown in each of two consecutive dissections for first and second year medical students. The data obtained indicate that students engaged in self-directed learning through small groups working with Faculty staff are able to self-improve their anatomical skills