All animals evaluate the salience of external stimuli and integrate them with internal physiological information into adaptive behavior. Natural and sexual selection impinge on these processes, yet our understanding of behavioral decision-making mechanisms and their evolution is still very limited. Insights from mammals indicate that two neural circuits are of crucial importance in this context: the social behavior network and the mesolimbic reward system. Here we review evidence from neurochemical, tract-tracing, developmental, and functional lesion/stimulation studies that delineates homology relationships for most of the nodes of these two circuits across the five major vertebrate lineages: mammals, birds, reptiles, amphibians, and teleost fish. We provide for the first time a comprehensive comparative analysis of the two neural circuits and conclude that they were already present in early vertebrates. We also propose that these circuits form a larger social decision-making (SDM) network that regulates adaptive behavior. Our synthesis thus provides an important foundation for understanding the evolution of the neural mechanisms underlying reward processing and behavioral regulation. J. Comp. Neurol. 519:3599–3639, 2011.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/cne.22735

The Vertebrate mesolimbic reward system and social behavior network: A comparative synthesis

A major challenge for fluorescence imaging of living mammalian cells is maintaining viability following prolonged exposure to excitation illumination. We have monitored the dynamics of mitochondrial distribution in hamster embryos at frequent intervals over 24 h using two-photon microscopy (1,047 nm) while maintaining blastocyst, and even fetal, developmental competence. In contrast, confocal imaging for only 8 h inhibits development, even without fluorophore excitation. Photo-induced production of H2O2 may account, in part, for this inhibition. Thus, two-photon microscopy, but not confocal microscopy, has permitted long-term fluorescence observations of the dynamics of three-dimensional cytoarchitecture in highly photosensitive specimens such as mammalian embryos.

Long-term two-photon fluorescence imaging of mammalian embryos without compromising viability

The mammalian telencephalon is considered the most complex of all biological structures. It comprises a large number of functionally and morphologically distinct types of neurons that coordinately control most aspects of cognition and behavior. The subpallium, for example, not only gives rise to multiple neuronal types that form the basal ganglia and parts of the amygdala and septum but also is the origin of an astonishing diversity of cortical interneurons. Despite our detailed knowledge on the molecular, morphological, and physiological properties of most of these neuronal populations, the mechanisms underlying their generation are still poorly understood. Here, we comprehensively analyzed the expression patterns of several transcription factors in the ventricular zone of the developing subpallium in the mouse to generate a detailed molecular map of the different progenitor domains present in this region. Our study demonstrates that the ventricular zone of the mouse subpallium contains at least 18 domains that are uniquely defined by the combinatorial expression of several transcription factors. Furthermore, the results of microtransplantation experiments in vivo corroborate that anatomically defined regions of the mouse subpallium, such as the medial ganglionic eminence, can be subdivided into functionally distinct domains.

https://www.jneurosci.org/content/jneuro/27/36/9682.full.pdf

Delineation of multiple subpallial progenitor domains by the combinatorial expression of transcriptional codes.

THIS interesting monograph appears in Dr. J. W. Spengel's “Ergebnisse und Fortschritte der Zoologie.” It gives an excellent account of the structure and mechanism of the central nervous system founded on morphological and physiological facts, as these have been laboriously collected by the most modern methods by which the nervous elements have been examined. The author deals with the plan of reflex mechanisms, he describes the architecture and localisation of the central ganglia and nerve-roots, and his illustrations are drawn from morphological studies of the simpler types. One of the most important sections is No. vii., in which he discusses the functions of the great divisions of the nervous system. Nowhere have we seen a better discussion of the relations and functions of the cerebellum, or a more lucid account of the remarkable deep connections of the auditory nerves. The author has evidently received illumination from the researches and constructive criticism of Sherrington, while, as indicated by a good bibliography, he is acquainted with the literature of this vast subject. The work is a valuable contribution to human and comparative neurology. The Central Nervous System of Vertebrates. By J. B. Johnston. Pp. 170. (Jena: G. Fischer, 1909.)

/pdf/the-central-nervous-system-of-vertebrates-2mr75r8ao0.pdf

The Central Nervous System of Vertebrates

Brain res bull

Publisher Summary
Neuroanatomical concepts of the hypothalamus, the forebrain territory that controls homeostasis and drives in vertebrates, are over 100 years old. Neuroanatomists of the 19th century generally considered the hypothalamus to consist of the tuberal or infundibular area, a median prominence at the brain ventral surface at the location of the pituitary gland, framed in front and at the sides by the optic chiasm and tracts. The neural plate fate maps of amniotes and anamniotes are strictly comparable from a topological point of view. The relative positions of the prospective brain areas can be extrapolated from one species to another. The prospective longitudinal or axial dimension of the brain is best represented by the neural/non-neural border of the neural plate, which will transform into the longitudinal roof plate of the closed neural tube. This developmental analysis suggests that all adult median forebrain derivatives found between the anterior commissure and the mamillary area are equally rostralmost loci in the brain. At the open neural plate, the rostral forebrain primordium contains the prospective hypothalamus as a large area centered upon the alar, basal, and floor portions of the terminal wall, its caudal part covering as well a rostral part of the lateral wall, whereas the prospective telencephalon forms a thin band at the dorsal periphery of the alar portion of these domains, including the corresponding roof area. A handful of genes, coding either for transcription factors or secreted protein morphogens, participate in early patterning and regional identity specification along the AP and DV dimensions of the whole forebrain, including the hypothalamus. The complex networked interplay of many molecular signals that control brain development represents a dynamic ontogenetic system that tends to reach different equilibrium states in different parts of the neuroepithelial wall.

Chapter 8 – Hypothalamus

The hypothalamus comprises alar, basal, and floor plate developmental compartments. Recent molecular data support a rostrocaudal subdivision into rostral (terminal) and caudal (peduncular) halves. In this context, the distribution of neuronal populations expressing somatostatin (Sst) mRNA was analyzed in the developing mouse hypothalamus, comparing with the expression pattern of the genes Orthopedia (Otp), Distal-less 5 (Dlx5), Sonic Hedgehog (Shh), and Nk2 homeobox 1 (Nkx2.1). At embryonic day 10.5 (E10.5), Sst mRNA was first detectable in the anterobasal nucleus, a Nkx2.1-, Shh-, and Otp-positive basal domain. By E13.5, nascent Sst expression was also related to two additional Otp-positive domains within the alar plate and one in the basal plate. In the alar plate, Sst-positive cells were observed in rostral and caudal ventral subdomains of the Otp-positive paraventricular complex. An additional basal Sst-expressing cell group was found within a longitudinal Otp-positive periretromamillary band that separates the retromamillary area from tuberal areas. Apart of subsequent growth of these initial populations, at E13.5 and E15.5 some Sst-positive derivatives migrate tangentially into neighboring regions. A subset of cells produced at the anterobasal nucleus disperses ventralward into the shell of the ventromedial hypothalamic nucleus and the arcuate nucleus. Cells from the rostroventral paraventricular subdomain reach the suboptic nucleus, whereas a caudal contingent migrates radially into lateral paraventricular, perifornical, and entopeduncular nuclei. Our data provide a topologic map of molecularly defined progenitor areas originating a specific neuron type during early hypothalamic development. Identification of four main separate sources helps to understand causally its complex adult organization.

/pdf/topography-of-somatostatin-gene-expression-relative-to-1dy0vitiom.pdf

Topography of Somatostatin Gene Expression Relative to Molecular Progenitor Domains during Ontogeny of the Mouse Hypothalamus

Conserved pattern of OTP-positive cells in the paraventricular nucleus and other hypothalamic sites of tetrapods.

Early pretectal gene expression pattern shows a conserved anteroposterior tripartition in mouse and chicken.

Ten years ago, we published the first detailed prosomeric map of the forebrain in lampreys. In the interim, the prosomeric model has been modified and simplified to better explain numerous data on the

Sylvia M. Bardet

Papers

Chapter 8 – Hypothalamus

Topography of Somatostatin Gene Expression Relative to Molecular Progenitor Domains during Ontogeny of the Mouse Hypothalamus

Conserved pattern of OTP-positive cells in the paraventricular nucleus and other hypothalamic sites of tetrapods.

Early pretectal gene expression pattern shows a conserved anteroposterior tripartition in mouse and chicken.

New and old thoughts on the segmental organization of the forebrain in lampreys.