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At least 307 records · Page 17Linked to original sources
PubMed1999

Anatomical connections of auditory and lateral line areas of the dorsal telencephalon (Dm) in the osteoglossomorph teleost, Gnathonemus petersii.

Local field potentials evoked either by auditory or by mechanosensory (water displacement) lateral line stimuli were recorded in sensory subregions of the telencephalic nucleus dorsalis pars medialis (Dm) in the weakly electric fish Gnathonemus petersii. The neural tracer Neurobiotin was injected into these two physiologically defined subregions. A reciprocal connection between the two subregions of Dm, as well as cell bodies and terminals in other telencephalic regions, whose distribution was somewhat different for the two injection types, were found. The course of labeled fibers outside the telencephalon was similar after injections in both Dm regions. Fibers were seen running through the lateral forebrain bundle (lfb) to the ventral surface area of the brain within the diencephalic preglomerular region (PGv). Within a narrow streak along the ventral side of the brain densely arranged cell bodies were labeled. The locations of labeled cells within PGv were indistinguishable after tracer was injected into either acoustical or lateral line areas of Dm. Only after injection into the mechanosensory Dm region labeled cell bodies were found in the anterior preglomerular nucleus (PGa), in addition. When crystals of the fluorescent tracer DiI were inserted in the ventral part of PGv, a path of labeled fibers similar to that after telencephalic injections was found. Labeled terminals, but no cell bodies, were located both in the acoustical and in the mechanosensory regions of Dm as well as in several other telencephalic areas. Even though sensory regions in Dm that process acoustical and mechanical stimuli are segregated and unimodal, they both receive input from neurons of PGv. The specificity of the mechanosensory region of Dm might originate from the additional input from PGa and from other endbrain areas.

Animals↗
PubMed1998

Effects of dopaminergic drugs on locomotor activity in teleost fish of the genus Oreochromis (Cichlidae): involvement of the telencephalon.

Single Oreochromis niloticus and O. mossambicus were placed in an unfamiliar white basin for 21 min, and their activity in this open-field situation was recorded from overhead on video. Apomorphine added to the water (2-8 mg/liter) caused a significant increase in locomotor activity, as assessed by the frequency that a fish swam over a rectilinear array of lines drawn on the base. This effect was attenuated by chlorpromazine (2 mg/liter) and abolished by the D1 antagonist SCH-23390 (1 mg/liter); the D2 antagonist metoclopramide (8 mg/liter) had no effect. Removal of both hemispheres of the telencephalon abolished the response to apomorphine, whereas removal of only one hemisphere or cauterization of the nostrils had no effect. It is concluded that the role of the dopaminergic system in the regulation of locomotor activity is reminiscent of the mammalian mesolimbic, rather than the nigrostriatal, system but that further studies are required to determine the source of the dopaminergic innervation and its likely telencephalic targets.

Animals↗
PubMed2005

Unraveling the molecular pathways that regulate early telencephalon development.

The telencephalon, at the rostral end of the developing central nervous system, starts off as a sheet of neuroepithelial cells. During development, this sheet of cells becomes patterned and morphologically partitioned into areas that give rise to the adult cerebral hemispheres. How does this happen? How are telencephalic precursor cells instructed to generate myriad neural cell types in different areas and at different times as well as to change their rates of cell proliferation, differentiation, and death? The molecular pathways required for patterning the telencephalic neuroepithelium and forming the cerebral hemispheres are beginning to be unraveled.

Animals↗
PubMed1999

Visual circuits of the avian telencephalon: evolutionary implications.

Birds and primates are vertebrates that possess the most advanced, efficient visual systems. Although lineages leading to these two classes were separated about 300 million years ago, there are striking similarities in their underlying neural mechanisms for visual processing. This paper discusses such similarities with special emphasis on the visual circuits in the avian telencephalon. These similarities include: (1) the existence of two parallel visual pathways and their distinct telencephalic targets, (2) anatomical and functional segregation within the visual pathways, (3) laminar organization of the telencephalic targets of the pathways (e.g. striate cortex in primates), and (4) possible interactions between multiple visual areas. Additional extensive analyses are necessary to determine whether these similarities are due to inheritance from a common ancestral stock or the consequences of convergent evolution based on adaptive response to similar selective pressures. Nevertheless, such a comparison is important to identify the general and specific principles of visual processing in amniotes (reptiles, birds, and mammals). Furthermore, these principles in turn will provide a critical foundation for understanding the evolution of the brain in amniotes.

Animals↗
PubMed2001

Prepubertal increases in the levels of two salmon gonadotropin-releasing hormone mRNAs in the ventral telencephalon and preoptic area of masu salmon.

Ontogenic changes in the expression levels of two salmon gonadotropin-releasing hormone genes (sGnRH-I and -II) were examined in the forebrain region including the ventral telencephalon and preoptic area of masu salmon by competitive reverse transcription-polymerase chain reaction (RT-PCR). Two genes showed similar expression patterns throughout the lifetime in both sexes, although the levels of sGnRH-II mRNA were about 20 times higher than those of sGnRH-I mRNA. In males, the levels of sGnRH mRNAs increased at the beginning of the second year and reached their maximum in the autumn. The levels decreased gradually until the autumn of the third year when fish sexually matured. In females, the levels reached their maximum in the first autumn and fluctuated considerably along with the seasons in the third year. These results suggest that, in the salmon brain, sGnRH genes are activated long before the sexual maturation under sexually different control mechanisms.

Age Factors↗
PubMed1996

Demonstration of a new dopamine-containing cell group in the primate rostral telencephalon.

The presence of dopaminergic neurons in the rostral forebrain has long been uncertain though the existence of tyrosine-hydroxylase (TH)-containing cells has been known in the region. Using an antibody to dopamine (DA), we demonstrated neurons immunoreactive (ir) to DA in the rostroventral striatum of the Japanese monkey (Macaca fuscata). The DA-ir cells were found at the ventral margin of the rostral part of the caudate nucleus, at the ventral margin of the rostral part of the nucleus accumbens, in the olfactory tubercle, and along the lateral margin of the putamen. These cells were intensely stained, small in size, and fusiform or ovoid in shape, and had one or two short processes. DA-ir cells were far smaller in number than TH-ir ones. The primates may possess a unique dopaminergic system in the rostral telencephalon.

Animals↗
PubMed1999

Changes in binding to muscarinic and nicotinic cholinergic receptors in the chick telencephalon, following passive avoidance learning.

Changes in nicotinic and muscarinic cholinergic receptors 30 min after one-trial passive avoidance training were studied in day-old chicks (Gallus domesticus), by quantitative receptor autoradiography. [3H]-alpha-bungarotoxin (alpha-BgT) and [3H]-quinuclidinyl benzilate (QNB) were used to monitor changes in 15 forebrain regions for nicotinic and muscarinic receptors, respectively. A significant increase occurred bilaterally in the quantity of bound alpha-BgT in the lobus parolfactorius, while the amount of bound QNB decreased significantly, and bilaterally, in the hippocampus, hyperstriatum ventrale, lobus parolfactorius and posterolateral telencephalon, pars dorsalis. The data support an involvement of cholinergic receptor types in the neural mechanisms underlying passive avoidance learning.

Animals↗
PubMedDate not supplied

Understanding the basic circuitry of the cerebral hemispheres: the case of lizards and its implications in the evolution of the telencephalon.

The organization of the cerebral hemispheres of mammals is characterized by corticostriatal glutamatergic projections and striatopallidal GABAergic ones, plus the descending projections of the pallium and subpallium to extratelencephalic targets. The present review of the available neuroanatomical data on the forebrain of lizards suggests that the telencephalon of reptiles also follows this basic pattern of connectivity. In addition, we show that this basic circuitry includes a pallido-cortical projection, therefore forming a cortico-striato-pallido-cortical circuit. The analysis of this circuitry for the medial, dorsal, lateral, and ventral pallial divisions in reptiles and mammals leads to the following conclusions: (1) The medial and dorsal cortices of lizards together appear to be equivalent to the medial pallium of mammals. (2) The projection from the lacertilian dorsal cortex to the striatum proper resembles the subiculo-striatal projection of mammals, rather than the isocortical projection to the caudatus-putamen. (3) Most of the dorsal striatum of reptiles is engaged in the corticostriatal circuit corresponding to the ventral pallium (the anterior dorsal ventricular ridge), and therefore, it is not equivalent to the mammalian caudatus-putamen, which is involved in the circuit of the dorsal pallium. (4) The main and accessory olfactory bulbs also follow this pattern of connections.

Animals↗
PubMed2001

Oligodendrocyte development in the spinal cord and telencephalon: common themes and new perspectives.

There are clear parallels between oligodendrocyte development in the spinal cord and forebrain. However, there is new evidence that in both of these regions oligodendrocyte lineage development may be more complex than we earlier thought. This stems from the recent identification of three new transcription factor genes, Olig1, Olig2 and Sox10, that are expressed from the early stages of oligodendrocyte lineage development. In this article, we highlight the common themes underlying specification and early development of oligodendrocytes in the spinal cord and telencephalon. Then, we discuss recent studies of Sox10 and the Olig genes and their implications for oligodendrocyte specification. We conclude that although the mechanisms of oligodendrogenesis appear to be fundamentally similar at different rostro-caudal levels of the neuraxis, there are still many unanswered questions about the details of oligodendrocyte specification.

Animals↗
PubMed2001

Hepatocyte growth factor/scatter factor is a motogen for interneurons migrating from the ventral to dorsal telencephalon.

Cortical interneurons arise from the proliferative zone of the ventral telencephalon, the ganglionic eminence, and migrate into the developing neocortex. The spatial patterns of migratory interneurons reflect the complementary expression of hepatocyte growth factor/scatter factor (HGF/SF) and its receptor, MET, in the forebrain. Scatter assays on forebrain explants demonstrate regionally specific motogenic activity due to HGF/SF. In addition, exogenous ligand disrupts normal cell migration. Mice lacking the urokinase-type plasminogen activator receptor (u-PAR), a key component of HGF/SF activation, exhibit deficient scatter activity in the forebrain, abnormal interneuron migration from the ganglionic eminence, and reduced interneurons in the frontal and parietal cortex. The data suggest that HGF/SF motogenic activity, which is essential for normal development of other organ systems, is a conserved mechanism that regulates trans-telencephalic migration of interneurons.

Animals↗
PubMed2002

Establishment of the telencephalon during gastrulation by local antagonism of Wnt signaling.

Cells at the anterior boundary of the neural plate (ANB) can induce telencephalic gene expression when transplanted to more posterior regions. Here, we identify a secreted Frizzled-related Wnt antagonist, Tlc, that is expressed in ANB cells and can cell nonautonomously promote telencephalic gene expression in a concentration-dependent manner. Moreover, abrogation of Tlc function compromises telencephalic development. We also identify Wnt8b as a locally acting modulator of regional fate in the anterior neural plate and a likely target for antagonism by Tlc. Finally, we show that tlc expression is regulated by signals that establish early antero-posterior and dorso-ventral ectodermal pattern. From these studies, we propose that local antagonism of Wnt activity within the anterior ectoderm is required to establish the telencephalon.

Animals↗
PubMed2000

A retinoic acid synthesizing enzyme in ventral retina and telencephalon of the embryonic mouse.

Most retinoic acid (RA) in the embryonic mouse is generated by three retinaldehyde dehydrogenases (RALDHs). RALDH1 (also called E1, AHD2 or ALDH1) is expressed in the dorsal retina, and RALDH2 (V2, ALDH11) generates most RA in the embryonic trunk. The third one, RALDH3 (V1), synthesizes the bulk of RA in the head of the early embryo. We show here that RALDH3 is a mouse homologue to ALDH6, an aldehyde dehydrogenase cloned from adult human salivary gland (Hsu, L.C., Chang, W.-C., Hiraoka, L., Hsien, C.-L., 1994. Molecular cloning, genomic organization, and chromosomal localization of an additional human aldehyde dehydrogenase gene, ALDH6. Genomics 24, 333-341), which was recently reported to act as a RALDH (Yoshida, A., Rzhetsky, A., Hsu, L.C., Chang, C., 1998. Human aldehyde dehydrogenase gene family. Eur. J. Biochem. 251, 549-557). RALDH3 expression begins in the surface ectoderm over the optic recess. In rapidly changing expression patterns it labels the appearance of several ectodermal structures: it marks the formation of the lens and the olfactory organ from ectodermal placodes, and it delineates the beginning eyelid field. Within the optic vesicle, RALDH3 is expressed in the ventral retina and the dorsal pigment epithelium. In the telencephalon, RALDH3 is expressed at high levels in the lateral part of the ganglionic eminence. From here it extends via the piriform cortex into the lower part of the septum. Of the three RALDHs, RALDH3 shows the strongest predilection for epithelia.

Aldehyde Dehydrogenase↗
PubMed1997

Expression of a novel aristaless related homeobox gene 'Arx' in the vertebrate telencephalon, diencephalon and floor plate.

We have isolated a novel homeobox gene that is expressed in the vertebrate central nervous system and which shows striking similarity to the Drosophila al gene in the homeodomain (85% identity) and in a 17 amino acid-sequence near the carboxyl-terminus. This gene was designated Arx (aristaless related homeobox gene) in consideration of its structural similarity to the al gene. Arx was highly conserved between mouse and zebrafish. Neuromeric expression in the forebrain and longitudinal expression in the floor plate were observed in mouse and zebrafish. The expression of Arx in the ganglionic eminence and ventral thalamus overlapped regionally with that of Dlx1, but the cell layer where Arx is expressed differed from that of the Dlx1. This gene was also found to be expressed in the dorsal telencephalon (presumptive cerebral cortex) of mouse embryos. The structure and expression pattern of Arx with respect to any possible relationship to al and Dlx1, as well as the function of Arx in the floor plate are discussed.

Amino Acid Sequence↗
PubMed1998

The Xenopus Emx genes identify presumptive dorsal telencephalon and are induced by head organizer signals.

We have isolated and studied the expression pattern of Xemx1 and Xemx2 genes in Xenopus laevis. Xemx genes are the homologues of mouse Emx genes, related to Drosophila empty spiracles. They are expressed in selected regions of the developing brain, particularly in the telencephalon, and, outside the brain, in the otic vesicles, olfactory placodes, visceral arches and the developing excretory system. We also report on experiments concerning the tissue and molecular signals responsible for their activation in competent ectoderm. Xemx genes are activated in ectoderm conjugated with head organizer tissue, but not with tail organizer tissue. Furthermore, they are not activated in animal cap either by noggin or by Xnr3, thus suggesting that a different inducer or the integration of several signals may be responsible for their activation.

Amino Acid Sequence↗
PubMed2002

Molecular mechanisms underlying cell fate specification in the developing telencephalon.

The cellular properties of neural progenitor cells have been best characterized in the telencephalon, the most complex region of the vertebrate brain. In recent years, several transcription factors, including Mash1, Ngn1/2, Pax6 and Emx1/2, and signaling molecules, such as Notch and bone morphogenetic proteins, have emerged as important players in key areas of telencephalic development. These include the specification of positional identity, the proliferation of neural stem cells and their commitment to a neuronal or glial fate, and the differentiation of layer-specific neuronal phenotypes in the cerebral cortex.

Animals↗
PubMed1997

Regionalization in the mammalian telencephalon.

Regionalization in the telencephalon results in the formation of functionally and anatomically distinct territories. Cell fate analysis and gene expression studies suggest these subdivisions arise relatively late in development compared with the spinal cord or hindbrain. The mechanisms underlying the commitment of telencephalic cells to specific regional identities have been examined through recent transplantation experiments.

Animals↗
PubMed2003

Cannabinoid CB1 receptor activation does not prevent the toxicity of glutamate towards embryonic chick telencephalon primary cultures.

Cannabinoids, as a result of their ability to activate cannabinoid CB1 receptors, have been shown to possess neuroprotective properties in vivo. In vitro studies into neuroprotective effects mediated by CB1 receptors have in general used primary neuronal cultures derived from embryonic rodents. In the present study, we have investigated whether embryonic chick telencephalon primary cultures in serum-free medium are a useful alternative for such in vitro studies. The CB agonist CP 55940 reduced the cAMP response to 5 microM forskolin by 40 and 50% at concentrations of 3 nM and 30 nM, respectively. This reduction was blocked by the CB1 receptor antagonist AM251, indicating the presence of functional CB1 receptors in the cultures. Incubation of the cultures with glutamate (100 microM or 1 mM) for 1 h followed by medium change and incubation for 24 h produced a release of the cytoplasmic enzyme lactate dehydrogenase into the medium. This release was prevented by MK-801 confirming the central role of NMDA receptors in the glutamate toxicity. However, 3-30 nM CP 55940 did not produce any neuroprotection in this model regardless as to whether dibutyryl cyclic AMP was added to the culture medium. The endocannabinoid anandamide was also without effect when added either per se or together with the related N-acyl ethanolamines palmitoylethanolamide, oleoylethanolamide and stearoylethanolamide (at relative concentrations matching those seen in rat brain after excitotoxic insult). It is concluded that embryonic chick neurons in primary serum-free culture are not a useful model for the study of neuroprotective effects mediated by CB1 receptors in vitro.

Animals↗
PubMed1990

Visual telencephalon modulates directional selectivity of accessory optic neurons in pigeons.

The directional selectivity of units within the nucleus of the basal optic root (nBOR) of the accessory optic system (AOS) was studied before and after lesions of the visual telencephalon (visual Wulst) in urethane-anesthetized pigeons. In intact pigeons, most nBOR units preferred upward motion with a temporal component or downward motion with a nasal component. The ipsilateral and bilateral telencephalic lesions generated a dramatic reduction in the number of cells with optimal responses to upward motion. The overall distribution of preferred directions was still bimodal following ipsilateral or bilateral Wulst lesions, with most units showing best responses to a straight temporal or to downward-nasal directions. The contralateral Wulst lesions produced, instead, a marked reduction in downward preferences. The nBOR units which were studied in these cases showed mainly upward-temporal and upward-nasal responses. These data suggest an involvement of the visual Wulst in the determination of the directional selectivity of nBOR neurons in the pigeon. Specifically, the responses of nBOR units to upward motion appeared to depend on the integrity of the telencephalic descending systems which impinge, in both direct and indirect ways, upon that AOS nucleus. Taken together with data for the mammalian AOS, the present results indicate that nonretinal afferents to AOS nuclei have an important role in the functional organization of that subcortical visual pathway.

Animals↗