José Luis Bueno-López

Targets and Laminar Distribution of Projection Neurons with 'Inverted' Morphology in Rabbit Cortex.

This study examines the axonal projections of so‐called inverted pyramids and other neurons with their major dendritic shaft oriented in the direction of the white matter (‘inverted cells’) in the adult rabbit cortex. Single injections of horseradish peroxidase wheat germ agglutinin were made into cortical or subcortical sites. The resulting retrograde labelling in the cortex was analysed and the distribution across areas and layers of inverted cells contributing to each of these projections was estimated. In addition, the radial distribution of inverted cells was independently determined from rapid Golgi‐impregnated and Nissl‐stained material. All three procedures revealed that inverted cells lay overwhelmingly in infragranular layers, but congregated at the border between layers 5 and 6. Inverted cells, identified by retrograde labelling, seldom furnished non‐telencephalic centres; in contrast, these cells constituted a major source for the projections to the ipsi‐ or the contralateral cortex, the claustrum or the nucleus caudatus. In general, each set of inverted cells (when defined by its specific destination as a group) was located below the typically oriented cells whose axons were aimed at the same target. Thus, the inverted cells of the rabbit cortex are characterized not only by their unique morphology and their corticocortical, corticoclaustral and corticostriatal projections, but also by their distinctive radial locations. These findings suggest that inverted cells, even though possibly composed of different cell types, are a specific class of projection neurons.

The underside of the cerebral cortex: layer V/VI spiny inverted neurons

This paper presents an account of past and current research on spiny inverted neurons – alternatively also known as ‘inverted pyramidal neurons’– in rats, rabbits and cats. In our laboratory, we have studied these cells with a battery of techniques suited for light and electron microscopy, including Nissl staining, Golgi impregnation, dye intracellular filling and axon retrograde track‐tracing. Our results show that spiny inverted neurons make up less than 8.5 and 5.5% of all cortical neurons in the primary and secondary rabbit visual cortex, respectively. Infragranular spiny inverted neurons constitute 15 and 8.5% of infragranular neurons in the same animal and areas. Spiny inverted neurons congregate at layers V–VI in all studied species. Studies have also revealed that spiny inverted neurons are excitatory neurons which furnish axons for various cortico‐cortical, cortico‐claustral and cortico‐striatal projections, but not for non‐telencephalic centres such as the lateral and medial geniculate nuclei, the colliculi or the pons. As a group, each subset of inverted cells contributing to a given projection is located below the pyramidal neurons whose axons furnish the same centre. Spiny inverted neurons are particularly conspicuous as a source of the backward cortico‐cortical projection to primary visual cortex and from this to the claustrum. Indeed, they constitute up to 82% of the infragranular cells that furnish these projections. Spiny inverted neurons may be classified into three subtypes according to the point of origin of the axon on the cell: the somatic basal pole which faces the cortical outer surface, the somatic flank and the reverse apical dendrite. As seen with electron microscopy, the axon initial segments of these subtypes are distinct from one another, not only in length and thickness, but also in the number of received synaptic boutons. All of these anatomical features together may support a synaptic‐input integration which is peculiar to spiny inverted neurons. In this way, two differently qualified streams of axonal output may coexist in a projection which arises from a particular infragranular point within a given cortical area; one stream would be furnished by the typical pyramidal neurons, whereas spiny inverted neurons would constitute the other source of distinct information flow.

Percentage incidence of γ-aminobutyric acid neurons in the claustrum of the rabbit and comparison with the cortex and putamen

We describe the incidence of gamma-aminobutyric acid (GABA)ergic neurons after post-embedding immunocytochemistry on semithin sections of the claustrum, putamen and lateral, dorsal and medial cortical areas. Twelve percent of the neurons counted in the claustrum of 11 rabbits were GABAergic. This incidence was significantly higher in the dorsal halves of both the insular and endopiriform claustra than in the ventral (13 vs. 10%). The incidence of GABAergic cells was 4% in the putamen, 14% in the insular cortex, 15% in areas 17 and 18 and 13% in area 29d. Thus, our results indicate that in contrast to the putamen the incidence of GABAergic cells was similar in the claustrum and cortical areas. We interpret this in the light of the pallial origin of the claustrum, which has recently been substantiated.

Widespread Horizontal Connections Arising from Layer 5/6 Border Inverted Cells in Rabbit Visual Cortex.

Herein we describe the inverted cells [defined as those projection neurons having a major dendritic shaft abpially oriented (Bueno‐López et al., Eur. J. Neurosci., 3, 415, 1991)] originating a unique set of cortical connections characterized by extraordinarily widespread horizontal distribution. Single and multiple injections of wheatgerm agglutinin ‐ horseradish peroxidase were made in areas 17 and 18 and the resulting retrograde labelling in the cortex was analysed. The findings were assessed in independent control experiments in which Fluoro‐Gold was used as retrograde tracer. Following single injections in area 17 several separate patches of labelled cells comprising layers 2–6 were consistently found in area 18. In addition to these associational cells a number of labelled cells appeared at the layer 5/6 border but were distributed over most of the tangential extent of the visual occipital cortex. This widespread pattern was particularly striking in brains after multiple injections. In these brains a conspicuous band of labelled cells at the 5/6 border radiated from the injection sites, making up an apparently continuous horizontal sheet that intersected the striate ‐ extrastriate boundary and merged with the patches of labelled cells in area 18 and beyond. Most of the cells in the 5/6 border band were inverted cells (82%; n= 2081). Injections in area 18 failed to produce such a widespread set of labelled cells in area 17. The functional significance of these connections furnished by the 5/6 border inverted cells remains to be determined, but their distribution would allow for convergent/divergent binding interactions both intra‐areally (within area 17) and inter‐areally (from area 18 to area 17).

Spatial compartmentalization of AMPA glutamate receptor subunits at the calyx of Held synapse

The mature calyx of Held ending on principal neurons of the medial nucleus of the trapezoid body (MNTB) has very specialized morphological and molecular features that make it possible to transmit auditory signals with high fidelity. In a previous work we described an increased localization of the ionotropic α‐amino‐3‐hydroxy‐5‐methyl‐4 isoxazolepropionic acid (AMPA) glutamate receptor (GluA) subunits at postsynaptic sites of the calyx of Held‐principal cell body synapses from postnatal development to adult. The aim of the present study was to investigate whether the pattern of the synaptic distribution of GluA2/3/4c and ‐4 in adult MNTB principal cell bodies correlated with preferential subcellular domains (stalks and swellings) of the calyx. We used a postembedding immunocytochemical method combined with specific antibodies to GluA2/3/4c and GluA4 subunits. We found that the density of GluA2/3/4c in calyceal swellings (19 ± 1.54 particles/μm) was higher than in stalks (10.93 ± 1.37 particles/μm); however, the differences for GluA4 were not statistically significant (swellings: 13.84 ± 1.39 particles/μm; stalks: 10.42 ± 1.24 particles/μm). Furthermore, GluA2/3/4c and GluA4 labeling co‐localized to some extent in calyceal stalks and swellings. Taking these data together, the distribution pattern of GluA subunits in postsynaptic specializations are indicative of a spatial compartmentalization of AMPA subunits in mature calyx‐principal neuron synapses that may support the temporally precise transmission required for sound localization in the auditory brainstem. J. Comp. Neurol. 518:163–174, 2010.

GABAergic neurons in the rabbit visual cortex: percentage, layer distribution and cortical projections

6250 neurons yielding either callosal or inter-areal ipsilateral projections extrinsic to area 17 was GABAergic. Comparing these findings with those reported for other mammals, it seems that the incidence and distribution of GABAergic neurons in the visual cortex is similar in rabbits and rats. In contrast to rats but akin to higher mammals, no GABAergic neuron was found to furnish cortico-cortical connections to area 17 other than intrinsic connections.

Antonio Gimbernat y Arbos: An Anatomist-surgeon of the Enlightenment (In the 220th Anniversary of his ''A New Method of Operating the Crural Hernia'')

This article focuses on Antonio de Gimbernat y Arbós (1734–1816), with particular attention paid to his famous publication “Nuevo método de operar en la hernia crural” (2013 marking its 220 anniversary), which was translated into English by Thomas Beddoe two years later (A new method of operating for the femoral hernia Translated from the Spanish of Don Antonio de Gimbernat, To which are added, with plates by the translator, queries respecting a safer method of performing inoculation). Antonio de Gimbernat y Arbós, a Spanish anatomist and surgeon, was one of the pioneers during the “Age of Dissection” (late 18th Century). He was a man of great willpower, bright, thorough, and unique. From his careful anatomical study in the inguinal region, he made a detailed description of the lacunar ligament, which John Hunter called the Gimbernats ligament in his honor. Antonio de Gimbernat y Arbós also proposed an advanced treatment for strangulated femoral hernias. He acquired extraordinarily broad surgical skills with therapeutic orientation, conservative, not aggressive, based on the knowledge he had gained through dissection. Furthermore, though this is less well known nowadays, Antonio de Gimbernat y Arbós was also relevant organizer of education and health‐services — as it was the custom of the great physician of this time. Consequently, Antonio de Gimbernat y Arbós is truly representative of the great figures of the anatomists‐surgeons of the Enlightenment. Clin. Anat. 26:800–809, 2013.

The attitudes of medical students in Europe toward the clinical importance of histology: Attitudes of Medical Students Toward Histology

Many studies have been undertaken to assess the attitudes of medical students to the clinical importance of gross anatomy. However, much less is known about their attitudes toward the clinical importance of histology. Using Thurstone and Chave methods to assess attitudes, over 2,000 early stage medical students across Europe provided responses to a survey that tested the hypothesis that the students have a high regard for histologys clinical relevance. Regardless of the university and country surveyed, and of the teaching methods employed for histology, our findings were not consistent with our hypotheses, students providing a more moderate assessment of histologys importance compared to gross anatomy but more positive than their attitudes toward embryology. Histology should play a significant role in medical education in terms of appreciating not just normal structure and function but also pathology. We conclude that teachers of histology should pay special attention to informing newly‐recruited medical students of the significant role played by histology in attaining clinical competence and in underpinning their status as being learned members of a healthcare profession. This work was conducted under the auspices of the Trans‐European Pedagogic Research Group (TEPARG). Clin. Anat. 30:635–643, 2017.

Projections, Partaken Circuits and Axon Initial Segments of Cortical Principal Neurons

© 2012 Bueno-Lopez et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Projections, Partaken Circuits and Axon Initial Segments of Cortical Principal Neurons