Luis Puelles

• Doctor in Medicine and Surgery
• Professor Emeritus at University of Murcia

3D brain atlases are key resources to understand the brain’s spatial organization and promote interoperability across different studies. However, unlike the adult mouse brain, the lack of developing mouse brain 3D reference atlases hinders advancements in understanding brain development. Here, we present a 3D developmental common coordinate framewo...

Data mining was performed at the databases of the Allen Institute for Brain Science ( RRID:SCR_017001 ) searching for genes expressed selectively throughout the adult mouse mesocortex (transitional cortex ring predicted within the concentric ring theory of mammalian cortical structure, in contrast with central isocortex [ICx] and peripheral allocor...

Classical studies of the avian diencephalon hardly mention the habenulo-interpeduncular tract (a.k.a. retroflex tract), although both the habenula (HB) (its origin) and the interpeduncular nuclear complex (its target) are present. Retroflex tract fibers were described at early embryonic stages but seem absent in the adult in routine stains. However...

At the end of 2023, the Whole Mouse Brain Atlas was announced, revealing that there are about 5300 molecularly defined neuronal types in the mouse brain. We ask whether brain models exist that contemplate how this is possible. The conventional columnar model, implicitly used by the authors of the Atlas, is incapable of doing so with only 20 brain c...

At the end of 2023 the Whole Mouse Brain Atlas was announced, revealing that there are about 5,300 molecularly defined neuronal types in the mouse brain. We ask whether brain models exist that contemplate how this is possible. The conventional columnar model, implicitly used by the authors of the Atlas, is incapable of doing so with only 20 brain c...

Brain models present a viewpoint on the fundamental structural components of the brain and their mutual organization, generally relative to a particular concept of the brain axis. A model may be based on adult brain structure or on developmental morphogenetic aspects. Brain models usually have functional implications, depending on which functional...

Brain models present a viewpoint on the fundamental structural components of the brain and their mutual organization, generally relative to a particular concept of the brain axis. A model may be based on adult brain structure or on developmental morphogenetic aspects. Brain models usually have functional implications, depending on which functional...

3D standard reference brains serve as key resources to understand the spatial organization of the brain and promote interoperability across different studies. However, unlike the adult mouse brain, the lack of standard 3D reference atlases for developing mouse brains has hindered advancement of our understanding of brain development. Here, we prese...

The globus pallidus (GP) of primates is divided conventionally into distinct internal and external parts. The literature repeats since 1930 the opinion that the homolog of the primate internal pallidum in rodents is the hypothalamic entopeduncular nucleus (embedded within fiber tracts of the cerebral peduncle). To test this idea, we explored its hi...

This essay reexamines molecular evidence supporting the existence of the ‘preisthmus’, a caudal midbrain domain present in vertebrates (studied here in the mouse). It is thought to derive from the embryonic m2 mesomere and appears intercalated between the isthmus (caudally) and the inferior colliculus (rostrally). Among a substantial list of gene e...

This essay reexamines molecular evidence supporting the existence of the ‘preisthmus’, a caudal midbrain domain present in vertebrates (studied here in the mouse). It is held to derive from the embryonic m2 mesomere and appears intercalated between the isthmus (caudally) and the inferior colliculus (rostrally). Among a substantial list of gene expr...

Simple Summary A key question in embryonic development is to determine the molecular and cellular mechanisms involved in the early specification and differentiation of neuroblast populations and the final disposition of mature neurons in the central and peripheral nervous system. These embryonic developmental events are governed by genetic factors...

The ventromedial hypothalamic nucleus (VMH) is one of the most distinctive hypothalamic tuberal structures, subject of numerous classic and modern functional studies. Commonly, the adult VMH has been divided in several portions, attending to differences in cell aggregation, cell type, connectivity, and function. Consensus VMH partitions in the lite...

The lateral hypothalamus (LH) has a heterogeneous cytoarchitectonic organization that has not been elucidated in detail. In this work, we analyzed within the framework of the prosomeric model the differential expression pattern of 59 molecular markers along the ventrodorsal dimension of the medial forebrain bundle in the mouse, considering basal an...

Most of the studies on neurochemical mapping, connectivity, and physiology in the hypothalamic region were carried out in rats and under the columnar morphologic paradigm. According to the columnar model, the entire hypothalamic region lies ventrally within the diencephalon, which includes preoptic, anterior, tuberal, and mamillary anteroposterior...

The retina is known to target many superficial areas in the brain. These have always been studied under the tenets of the classic columnar brain model, which was not designed to produce causal explanations, being functionally oriented. This has led over the years to a remarkable absence of understanding or even hypothetical thinking about why the o...

Significance During brain development, neurons are generated by spatially and temporally distinct processes that remain to be fully characterized. The ganglionic eminences (GEs) in the embryonic subpallium give rise to GABAergic and cholinergic neuron lineages that form the basal ganglia or migrate to the cerebral cortex. Beyond a limited set of ca...

In the developing brain, the phenomenon of neurogenesis is manifested heterotopically, that is, much the same neurogenetic steps occur at different places with a different timetable. This is due apparently to early molecular regionalization of the neural tube wall in the anteroposterior and dorsoventral dimensions, in a checkerboard pattern of more...

This essay re-examines the singular case of the supposedly unique rostrally elongated notochord described classically in amphioxus. We start from our previous observations in hpf 21 larvae [Albuixech-Crespo et al., 2017] indicating that the brain vesicle has rostrally a rather standard hypothalamic molecular configuration. This correlates with the...

The prosomeric model was postulated jointly by L. Puelles and J. L. R. Rubenstein in 1993 and has been developed since by means of minor changes and a major update in 2012. This article explains the progressive academic and scientific antecedents leading LP to this collaboration and its subsequent developments. Other antecedents due to earlier neur...

The trigeminal column is a hindbrain structure formed by second order sensory neurons that receive afferences from trigeminal primary (ganglionic) nerve fibers. Classical studies subdivide it into the principal sensory trigeminal nucleus located next to the pontine nerve root, and the spinal trigeminal nucleus which in turn consists of oral, interp...

The author worked before on the wide problem of the evolution of the vertebrate pallium. He proposed various Bauplan models based in the definition of a set of pallial sectors with characteristic (topologically invariant) mutual relationships and distinct molecular profiles. Out of one of these models, known as the ‘updated tetrapartite pallium mod...

Neurons can change their classical neurotransmitters during ontogeny, sometimes going through stages of dual release. Here, we explored the development of the neurotransmitter identity of neurons of the avian nucleus isthmi parvocellularis (Ipc), whose axon terminals are retinotopically arranged in the optic tectum (TeO) and exert a focal gating ef...

The tuberal hypothalamic ventral premamillary nucleus (VPM) described in mammals links olfactory and metabolic cues with mating behavior and is involved in the onset of puberty. We offer here descriptive and experimental evidence on a migratory phase in the development of this structure in mice at E12.5–E13.5. Its cells originate at the retromamill...

The purinergic system is one of the oldest cell-to-cell communication mechanisms and exhibits relevant functions in the regulation of the central nervous system (CNS) development. Amongst the components of the purinergic system, the iono-tropic P2X7 receptor (P2X7R) stands out as a potential regulator of brain pathology and physiology. Thus, P2X7R...

The prethalamic eminence (PThE), a diencephalic caudal neighbor of the telencephalon and alar hypothalamus, is frequently described in mammals and birds as a transient embryonic structure, undetectable in the adult brain. Based on descriptive developmental analysis of Tbr1 gene brain expression in chick embryos, we previously reported that three mi...

We focus this report on the nucleus of the lateral olfactory tract (NLOT), a superficial amygdalar nucleus receiving olfactory input. Mixed with its Tbr1-expressing layer 2 pyramidal cell population (NLOT2), there are Sim1-expressing cells whose embryonic origin and mode of arrival remain unclear. We examined this population with Sim1-ISH and a Sim...

The amygdala in mammals plays a key role in emotional processing and learning, being subdivided in pallial and subpallial derivatives. Recently, the cortical ring model and the pallial amygdalar radial model (Puelles et al. 2019; Garcia-Calero et al. 2020) described the pallial amygdala as an histogenetic field external to the allocortical ring, an...

The interpeduncular nucleus (IPN) is a highly conserved limbic structure in the vertebrate brain, located in the isthmus and rhombomere 1. It is formed by various populations that migrate from different sites to the distinct domains within the IPN: the prodromal, rostral interpeduncular, and caudal interpeduncular nuclei. The aim here was to identi...

Enhancers integrate transcription factor signaling pathways that drive cell fate specification in the developing brain. We used single cell RNA-sequencing (scRNA-seq) to capture enhancer activity at single cell resolution and delineate specification of cells labeled by enhancers in mouse medial, lateral, and caudal ganglionic eminences (MGE, LGE, a...

The hypothalamus is a heterogeneous rostral forebrain region that regulates physiological processes essential for survival, energy metabolism, and reproduction, mainly mediated by the pituitary gland. In the updated prosomeric model, the hypothalamus represents the rostralmost forebrain, composed of two segmental regions (terminal and peduncular hy...

The radial dimension expands during central nervous system development after the proliferative neuroepithelium is molecularly patterned. The process is associated with neurogenesis, radial glia scaffolding, and migration of immature neurons into the developing mantle stratum. Radial histogenetic units, defined as a delimited neural polyclone whose...

The interpeduncular nucleus (IPN) is a hindbrain structure formed by three main subdivisions, the prodromal (Pro) domain located at the isthmus (Ist), and the rostral and caudal interpeduncular domains (IPR, IPC) within rhombomere 1 (r1). Various cell populations can be detected in the IPN through the expression of the Nkx6.1, Otp, Otx2, Pax7, and/...

Conventional anatomic models of the rodent (mammalian) amygdala are based on section planes oblique to its intrinsic radial glial organization. As a result, we still lack a model of amygdalar histogenesis in terms of radial units (progenitor domains and related radial migration and layering patterns). A radial model of the mouse pallial amygdala is...

We present here a thorough and complete analysis of mouse P0‐P140 prethalamic histogenetic subdivisions and corresponding nuclear derivatives, in the context of local tract landmarks. The study used as fundamental material brains from a transgenic mouse line that expresses LacZ under the control of an intragenic enhancer of Dlx5 and Dlx6 (Dlx5/6‐La...

The human claustrum, a major hub of widespread neocortical connections, is a thin, bilateral sheet of grey matter located between the insular cortex and the striatum. The subplate is a largely transient cortical structure that contains some of the earliest generated neurons of the cerebral cortex and has important developmental functions to establi...

The prethalamic eminence (PThE) is the most dorsal subdomain of the prethalamus, which corresponds to prosomere 3 (p3) in the prosomeric model for vertebrate forebrain development. In mammalian and avian embryos, the PThE can be delimited from other prethalamic areas by its lack of Dlx gene expression, as well as by its expression of glutamatergic-...

The inner ear is a complex three-dimensional sensory structure with auditory and vestibular functions. It originates from the otic placode, which generates the sensory elements of the membranous labyrinth and all the ganglionic neuronal precursors. Neuroblast specification is the first cell differentiation event. In the chick, it takes place over a...

The prosomeric brain model contemplates progressive regionalization of the central nervous system (CNS) from a molecular and morphological ontogenetic perspective. It defines the forebrain axis relative to the notochord, and contemplates intersecting longitudinal (zonal, columnar) and transversal (neuromeric) patterning mechanisms. A checkboard pat...

The components of the claustrum have been identified by gene expression in mice, but there is still uncertainty about the location of homologous components in primates. To aid interpretation of homologous elements between rodents and primates, we used a current understanding of pallial topology, species-specific telencephalic deformation, and gene...

The traditional subdivision of the brain stem into midbrain, pons, and medulla oblongata is based purely on the external appearance of the human brain stem. There is an urgent need to update the names of brain stem structures to be consistent with the discovery of rhomobomeric segmentation based on gene expression. The most important mistakes are t...

Recent neuroanatomic concepts and terms referring to the non-telencephalic forebrain are presented and discussed, in context with the present scenario in which the old columnar paradigm is being substituted by the prosomeric model, largely on the basis of novel molecular and experimental evidence.

Use of a segmental approach in the study of vestibular centers in the hindbrain improves morphological and functional understanding of this region controlled by Hox genes, among other molecular determinants. Here, we review accrued data about segmental organization of vestibular afferents and efferents. Inner ear‐originated vestibular fibers enter...

The classic columnar model of cranial nerve central representation assumes that all motor and sensory hindbrain neurons develop within four radial migration domains, held to be separated by a sulcal alar–basal boundary (sulcus limitans). This essay reviews a number of developmental data that challenge these concepts. These results are interpreted w...

Amphioxus is the living chordate closest to the ancestral form of vertebrates, and in a key position to reveal essential aspects of the evolution of the brain Bauplan of vertebrates. The dorsal neural cord of this species at the larval stage is characterized by a small cerebral vesicle at its anterior end and a large posterior region. The latter is...

Avian brain organization or brain Bauplan is identical with that of vertebrates in general. This essay visits avian studies that contained advances or discussions about brain organization, trying to explain critically what they contributed. In order to start from a specific background, the new prevailing paradigm as regards brain organization, the...

The r4-derived territory is located in the pontine region of the brainstem, forming a wedge-shaped slice that broadens from the choroidal roof to the ventral midline. R4-derived neuronal populations migrate radially inside and tangentially outside this rhombomere, forming nuclei of the sensorimotor auditory, vestibular, trigeminal and reticular sys...

This essay reviews step by step the conceptual changes of the updated tetrapartite pallium model from its tripartite and early tetrapartite antecedents. The crucial observations in mouse material are explained first in the context of assumptions, tentative interpretations, and literature data. Errors and the solutions offered to resolve them are ma...

The vertebrate inner ear is a complex three-dimensional sensorial structure with auditory and vestibular functions. The molecular patterning of the developing otic epithelium creates various positional identities, consequently leading to the stereotyped specification of each neurosensory and non-sensory element of the membranous labyrinth. The Iroq...

The isthmus is recognized as the most rostral segment of the hindbrain in non-mammalian vertebrates . In mammalian embryos, transient Fgf8 expression defines the developing isthmic region, lying between the midbrain and the first rhombomere, but there has been uncertainty about the existence of a distinct isthmic segment in postnatal mammals. We at...

We examined in detail the distribution of AZIN2 (antizyme inhibitor 2) expression in the adult mouse hindbrain and neighboring spinal cord. AZIN2, similar to previously known AZIN1, is a recently-discovered, a functional paralog of ornithine decarboxylase (ODC). Due to their structural similarity to ODC, both AZIN1 and AZIN2 counteract the inhibito...

All vertebrate brains develop following a common Bauplan defined by anteroposterior (AP) and dorsoventral (DV) subdivisions, characterized by largely conserved differential expression of gene markers. However, it is still unclear how this Bauplan originated during evolution. We studied the relative expression of 48 genes with key roles in vertebrat...

Temporal expression of Nk2.1 during amphioxus development. Lateral views (A-F, F’), dorsal views (A’-E’), and schematic drawings (A”-F”) of the neural component of Nk2.1 gene expression pattern from 15 to 36 hours post-fertilization. Anterior is to the left except in F. Somites are indicated using red dotted lines. Scale bar = 50μm. (TIF)

Additional gene markers used in this study. Other markers with neural expression used in this study in lateral (A-G) or dorsal views (A’-G’), and drawings of the neural component of each gene expression pattern with the relative position of somites (A”-G’). Markers with no expression in the amphioxus developing CNS at this stage are showed in later...

Probes of amphioxus used for in situ hybridization. (XLSX)

Expression of key gene markers at early neural stage. (TIF)

Information on the neural expression of genes used in this study. (XLSX)

Probes of zebrafish used for in situ hybridization. (XLSX)

Our previous analysis of progenitor domains in the pretectum of Xenopus revealed three molecularly distinct anteroposterior subdivisions, identified as precommissural (PcP), juxtacommissural (JcP), and commissural (CoP) histogenetic domains (Morona et al. [2011] J Comp Neurol 519:1024–1050). Here we analyzed at later developmental stages the nuclei...

The inner ear is a morphologically complex sensory structure with auditory and vestibular functions. The developing otic epithelium gives rise to neurosensory and non-sensory elements of the adult membranous labyrinth. Extrinsic and intrinsic signals manage the patterning and cell specification of the developing otic epithelium by establishing line...

The pallium of birds and reptiles is analyzed in detail with regard to the classification of its natural subdivisions on the basis of the tetrapartite pallium model proposed in 2014 by the first author. The possibility to use genoarchitectural data for this task is connected with the fundamental criteria of homology, namely conserved topological po...

Traditional attempts to classify the relationships between parts of the central nervous system of vertebrates have been almost entirely based on the external appearance of structures in the adult brain. Developmental gene expression and fate mapping have enabled researchers to derive a causally based natural ascription of parts to particular region...

The study of developmental gene expression has exposed major errors in traditional representations of brain stem organization. The major misunderstandings concern the status of the isthmus, the pons, and the pretectal area. The isthmus is the most rostral segment of the hindbrain, separating the midbrain from the first rhombomere, whereas tradition...

Neuromorphological concepts have stood and evolved upon methodological foundations.

The mature brain contains more than a hundred types of neurons. These may differ in the size and shape of their cell bodies or somata, in the size, shape and complexity of their dendritic trees, in the length and destination of their axons, in receptor repertoire, in neurotransmitter profile , in their mode of influencing other neurons (excitation...

The centres or grisea in the brain discussed in the previous section are interconnected by fibres, which commonly assemble in fibre systems, bundles or tracts.

By way of introduction, we present here two figures that have been shown before (see Plates 24 and 34).

Plate 17 presents dorsal views of early frog and human embryos (Fig. A, B). In the frog embryo, the neural plate is surrounded by a distinct ridge (neural fold). In the human embryo, such a demarcation is lacking and the neural plate can only be arbitrarily delimited morphologically from the remainder of the external germ layer , though a precise n...

At the beginning of this new section it may be recalled that: 1. The CNS consists of fundamental morphological units (FMUs), which are centres of neuronal and glial proliferation, migration and differentiation (Plate 93, Fig. A). 2. All of these FMUs are radial entities, the ventricular/ependymal surfaces of which occupy a specific area of the vent...

All fundamental morphological units (FMUs) in the CNS occupy their own, specific locus at the ventricular surface of the neural tube, and hence their position can be fully characterized in flat maps of the ventricular surface of the CNS (see Plate 68). However, the CNS is a three-dimensional structure and so are the FMUs. The third dimension, which...

The transformation of the neural plate into the neural tube is known as neurulation. During this process, the bilateral outer borders of the neural plate fuse together point-to-point along the median line, forming the roof plate. The neural crest population is released into the mesenchyme at the same time, and the skin also fuses, covering the whol...

This chapter explores the advantages of studying the evolution of vertebrate forebrain structures from the perspective provided by secondary organizers. The bauplan of vertebrate brains is captured schematically by morphological models, which must be tested for validity across phylogeny. The orthogonal longitudinal and transverse boundaries define...

This paper deals with a recent revision of the terminology of the Sections Central Nervous System (CNS; Systema nervosum centrale) and Peripheral Nervous System (PNS; Systema nervosum periphericum) of the Terminologia Anatomica (TA, 1998) and the Terminologia Histologica (TH, 2008). These sections were extensively updated by the Federative Internat...

Elucidating the transcriptional circuitry controlling forebrain development requires an understanding of enhancer activity and regulation. We generated stable transgenic mouse lines that express CreERT2 and GFP from ten different enhancer elements with activity in distinct domains within the embryonic basal ganglia. We used these unique tools to ge...

Our previous analysis of progenitor domains in the pretectum of Xenopus revealed three molecularly distinct anteroposterior subdivisions identified as precommissural (PcP), juxtacommissural (JcP), and commissural (CoP) histogenetic domains (Morona et al. [2011] J Comp Neurol 519:1024-1050). Here we analyzed at later developmental stages the nuclei...

Chapters provides overview of pathways of development and reviews of dysmorphic syndromes for which the causative gene has been identified. For each disorder, an analysis of the role of the gene in the relevant developmental pathway is provided, along with the mechanism by which mutations in the gene cause the developmental pathology. Emphasis is p...

Studies on gene expression in the developing claustrum of the mouse have clarified the relationships and identity of the claustrum proper and related endopiriform nuclei. The cells of the claustrum primordium express Nr4a2; they are formed in combination with the Nr4a2-labeled subplate cells in the lateral pallium at the site of the future insular...

This book demonstrates that the systematic study of gene expression patterns in embryonic and adult brains, in combination with selected data from earlier studies, can pave the way for a new neuromorphology, the most salient features of which may be summarized as follows: (1) Causal analysis of molecular patterning at neural plate and early neural...