Subpallial Telencephalon Research Articles

The brain of the tree pangolin (Manis tricuspis). VIII. The subpallial telencephalon.

The current study provides a detailed architectural analysis of the subpallial telencephalon of the tree pangolin. In the tree pangolin, the subpallial telencephalon was divided into septal and striatopallidal regions. The septal region contained the septal nuclear complex, diagonal band of Broca, and the bed nuclei of the stria terminalis. The striatopallidal region comprised of the dorsal (caudate, putamen, internal and external globus pallidus) and ventral (nucleus accumbens, olfactory tubercle, ventral pallidum, nucleus basalis, basal part of the substantia innominata, lateral stripe of the striatum, navicular nucleus, and the major island of Calleja) striatopallidal complexes. In the tree pangolin, the organization and numbers of nuclei forming these regions and complexes, their topographical relationships to each other, and the cyto‐, myelo‐, and chemoarchitecture, were found to be very similar to that observed in commonly studied mammals. Minor variations, such as less nuclear parcellation in the bed nuclei of the stria terminalis, may represent species‐specific variations, or may be the result of the limited range of stains used. Given the overall similarity across mammalian species, it appears that the subpallial telencephalon of the mammalian brain is highly conserved in terms of evolutionary changes detectable with the methods used. It is also likely that the functions associated with these nuclei in other mammals can be translated directly to the tree pangolin, albeit with the understanding that the stimuli that produce activity within these regions may be specific to the life history requirements of the tree pangolin.

Integrated Behavioral, Genetic and Brain Circuit Visualization Methods to Unravel Functional Anatomy of Zebrafish Amygdala.

The mammalian amygdala is a complex forebrain structure consisting of a heterogeneous group of nuclei derived from the pallial and subpallial telencephalon. It plays a critical role in a broad range of behaviors such as emotion, cognition, and social behavior; within the amygdala each nucleus has a distinct role in these behavioral processes. Topological, hodological, molecular, and functional studies suggest the presence of an amygdala-like structure in the zebrafish brain. It has been suggested that the pallial amygdala homolog corresponds to the medial zone of the dorsal telencephalon (Dm) and the subpallial amygdala homolog corresponds to the nuclei in the ventral telencephalon located close to and topographically basal to Dm. However, these brain regions are broad and understanding the functional anatomy of the zebrafish amygdala requires investigating the role of specific populations of neurons in brain function and behavior. In zebrafish, the highly efficient Tol2 transposon-mediated transgenesis method together with the targeted gene expression by the Gal4-UAS system has been a powerful tool in labeling, visualizing, and manipulating the function of specific cell types in the brain. The transgenic resource combined with neuronal activity imaging, optogenetics, pharmacology, and quantitative behavioral analyses enables functional analyses of neuronal circuits. Here, we review earlier studies focused on teleost amygdala anatomy and function and discuss how the transgenic resource and tools can help unravel the functional anatomy of the zebrafish amygdala.

MAP'ing CNS Development and Cognition: An ERKsome Process

The ERK MAP kinase signaling cascade plays critical roles in brain development, learning, memory, and cognition. It has recently been appreciated that mutation or deletion of elements within this signaling pathway leads to developmental syndromes in humans that are associated with impaired cognitive function and autism. Here, we review recent studies that provide insight into the biological roles of the ERKs in the brain that may underlie the cognitive deficits seen in these syndromes.

Developmental Mechanisms Underlying the Generation of Cortical Interneuron Diversity

GABAergic interneurons are critical components of cortical circuits. However, understanding their function has become extremely challenging because they constitute one of the most diverse groups of cells in the central nervous system. Indeed, cortical GABAergic interneurons are heterogeneous in so many different ways--morphology, molecular profiling, electrical properties--that even attempts to discern what parameters should be used to identify cortical interneuron subtypes have failed to generate broad consensus among experts in the field. The extent to which cortical interneuron diversity emerges during development is largely unknown, but it is likely that insights on how this process takes place may help us understand their role as integrative and synchronizing elements in cortical function. Here, we review recent data on how the large variety of distinct classes of cortical interneurons may arise during development.

The vertebrate ortholog of Aristaless is regulated by Dlx genes in the developing forebrain

The Dlx transcription factors have a central role in controlling the development of gamma-aminobutyric acid (GABA)-ergic neurons in the forebrain. However, little is known about how they control the properties of GABAergic neurons. One candidate is the Aristaless (Arx) homeobox gene, which lies genetically downstream of the fly Dlx gene (Distal-less, Dll). The expression of Arx in the mouse forebrain includes Dlx-expressing territories, such us the ventral thalamus, parts of the hypothalamus, and the ganglionic eminences and their derivatives in the subpallial telencephalon, and is expressed, as with the Dlx genes, in cortical GABAergic neurons. By using gain-of-function and loss-of-function assays in mouse and chicken embryos, we show that the Dlx genes have a conserved role in regulating the expression of Arx in the forebrain of vertebrates. Ectopic expression of Dlx genes with electroporation in brain slices from mouse embryos and in the neural tube of chick embryos shows that Dlx genes are sufficient to induce Arx ectopically. Moreover, we provide evidence that the Dlx genes exert a functionally relevant role in regulating Arx in vivo, as shown by the severe reduction in the expression of Arx in Dlx1/2 double-knockout mice. Therefore, our results suggest evolutionarily conserved functions of Dlx genes in regulating Arx expression between Drosophila and vertebrates.

Fgf signalling through MAPK cascade is required for development of the subpallial telencephalon in zebrafish embryos.

The telencephalon is formed in the most anterior part of the central nervous system (CNS) and is organised into ventral subpallial and dorsal pallial domains. In mice, it has been demonstrated that Fgf signalling has an important role in induction and patterning of the telencephalon. However, the precise role of Fgf signalling is still unclear, owing to overlapping functions of Fgf family genes. To address this, we have examined, in zebrafish embryos, the activation of Ras/mitogen-activated protein kinase (MAPK), one of the major downstream targets of Fgf signalling. Immunohistochemical analysis reveals that an extracellular signal-regulated kinase (ERK), a vertebrate MAPK is activated in the anterior neural boundary (ANB) of the developing CNS at early segmentation stages. Experiments with Fgf inhibitors reveal that ERK activation at this stage is totally dependent on Fgf signalling. Interestingly, a substantial amount of ERK activation is observed in ace mutants in which fgf8 gene is mutated. We then examine the function of Fgf signalling in telencephalic development by use of several inhibitors to Fgf signalling cascade, including dominant-negative forms of Ras (Ras(N17)) and the Fgf receptor (Fgfr), and a chemical inhibitor of Fgfr, SU5402. In treated embryos, the induction of telencephalic territory normally proceeded but the development of the subpallial telencephalon was suppressed, indicating that Fgf signalling is required for the regionalisation within the telencephalon. Finally, antisense experiments with morpholino-modified oligonucleotides suggest that zebrafish fgf3, which is also expressed in the ANB, co-operates with fgf8 in subpallial development.

A tecto-rotundo-telencephalic pathway in the rattlesnake: evidence for a forebrain representation of the infrared sense

Rattlesnakes possess a sensory system specialized for the detection of infrared (IR) radiation. IR signals ascend as far as the optic tectum, where they generate a spatiotopic map. It is unknown if such signals reach the forebrain, but the existence of prominent tectothalamic pathways in other vertebrates makes this a distinct possibility. In nonmammalian forms, the major target of ascending tectal visual signals is nucleus rotundus, a thalamic nucleus that projects in turn to the subpallial telencephalon. We sought to determine whether a tecto-rotundo-telencephalic system exists in rattlesnakes and, if so, whether it carries IR as well as visual information. We have identified a thalamic nucleus in the rattlesnake Crotalus viridis that matches the n. rotundus of other reptiles in its topographic location, cytoarchitecture, and connections. Using anterograde and retrograde transport of HRP, we have demonstrated a strong ipsilateral and weaker contralateral tectorotundal projection. Tectorotundal cells lay primarily in the deeper tectal layers, which receive input from the IR system, but also in the superficial, visual layers. In n. rotundus, single units recorded extracellularly invariably responded to visual stimuli, but many were also sensitive to unimodal IR stimuli. IR and visual receptive fields were very large and often bilateral. Some rotundal units appeared sensitive to substrate vibration. Most habituated rapidly. Nucleus rotundus was found to project to a sector of the ipsilateral anterior dorsal ventricular ridge (ADVR) of the telencephalon. Single units in this region of the ADVR resembled those in rotundus, responding to visual, IR, and/or vibrational stimuli and possessing large, often bilateral receptive fields. These findings demonstrate the existence of a tecto-rotundo-telencephalic pathway in rattlesnakes and suggest that this system conveys IR as well as visual information to the forebrain. Ascending tectofugal pathways have been implicated in the discrimination of form. Thus, pattern recognition may have to be added to orientation as a proper function of the IR system of pit vipers.

Topologic and connectional analysis of the dorsal thalamus of Triturus alpestris (amphibia, urodela, salamandridae).

A morphological and connectional analysis was performed on the dorsal thalamus of the alpine newt, Triturus alpestris. We have used a graphic reconstruction technique for the evaluation of the connectional (HRP) data. On the basis of these reconstructions, we propose a subdivision of the salamandrid dorsal thalamus into subhabenular, anteroventral, and posterodorsal zones. Each of these zones is defined by its telencephalic projections ("ascending thalamofugal systems"). The posterodorsal zone projects to the striatum, the anteroventral zone to the pallium. The subhabenular zone projects to the subpallial telencephalon and to the tegmentum. This zonal subdivision allows a more detailed comparison of the salamandrid dorsal thalamic features with ranid dorsal thalamic structures. We compare our dorsal thalamic zones to the ones proposed by Herrick (J. Comp. Neurol. 62:239-261, '35, The Brain of the Tiger Salamander. Chicago: The University of Chicago Press, '48). Furthermore, using the same reconstructive technique, we undertook an analysis of the spatial relations of various inputs to the salamandrid dorsal thalamus ("thalamopetal systems"). Besides the well-known retinal inputs, we identified the tectum and the tegmentum as sources of inputs to the thalamus. We provide evidence that there is no extensive multi- or unimodal overlap of these thalamopetal systems.

Role of the paleostriatum in species-typical display behavior of the lizard ( Anolis carolinensis)

In a comparative study of forebrain mechanisms of species-typical behavior, unilateral lesions were placed in the subpallial telencephalon of male green anolis lizards ( Anolis carolinensis), in which there is an almost complete decussation of the optic nerve. Responses to a conspecific male antagonist in a territorial confrontation were then tested when the subject's vision was limited to an eye leading to either the normal or lesioned hemisphere. In lizards with lesions involving the paleostriatum and lateral forebrain bundle, there was an elimination of or marked deficit in the performance of the challenge display while signature displays and measures of general activity were not significantly affected. Lesions predominantly in anterior or posterior dorsal ventricular ridge resulted in no significant deficit in any behavioral measure.