Search

The distribution patterns of a set of conserved brain developmental regulatory transcription factors were analyzed in the forebrain of the basal actinopterygian fish Acipenser ruthenus, consistent with the prosomeric model. In the telencephalon, the pallium was characterized by ventricular expression of Pax6. In the subpallium, the combined expression of Nkx2.1/Islet‐1 (Isl1) allowed to propose ventral and dorsal areas, as the septo‐pallidal (Nkx2.1/Isl1+) and striatal derivatives (Isl1+), respectively, and a dorsal portion of the striatal derivatives, ventricularly rich in Pax6 and devoid of Isl1 expression. Dispersed Orthopedia (Otp) cells were found in the supracommissural and posterior nuclei of the ventral telencephalon, related to the medial portion of the amygdaloid complex. The preoptic area was identified by the Nkx2.1/Isl1 expression. In the alar hypothalamus, an Otp‐expressing territory, lacking Nkx2.1/Isl1, was identified as the paraventricular domain. The adjacent subparaventricular domain (Spa) was subdivided in a rostral territory expressing Nkx2.1 and an Isl1+ caudal one. In the basal hypothalamus, the tuberal region was defined by the Nkx2.1/Isl1 expression and a rostral Otp‐expressing domain was identified. Moreover, the Otp/Nkx2.1 combination showed an additional zone lacking Isl1, tentatively identified as the mamillary area. In the diencephalon, both Pax6 and Isl1 defined the prethalamic domain, and within the basal prosomere 3, scattered Pax6‐ and Isl1‐expressing cells were observed in the posterior tubercle. Finally, a small group of Pax6 cells was observed in the pretectal area. These results improve the understanding of the forebrain evolution and demonstrate that its basic bauplan is present very early in the vertebrate lineage. [ABSTRACT FROM AUTHOR]

The early patterning of the thalamus during embryonic development defines rostral and caudal progenitor domains, which are conserved from fishes to mammals. However, the subsequent developmental mechanisms that lead to the adult thalamic configuration have only been investigated for mammals and other amniotes. In this study, we have analyzed in the anuran amphibian Xenopus laevis (an anamniote vertebrate), through larval and postmetamorphic development, the progressive regional expression of specific markers for the rostral (GABA, GAD67, Lhx1, and Nkx2.2) and caudal (Gbx2, VGlut2, Lhx2, Lhx9, and Sox2) domains. In addition, the regional distributions at different developmental stages of other markers such as calcium binding proteins and neuropeptides, helped the identification of thalamic nuclei. It was observed that the two embryonic domains were progressively specified and compartmentalized during premetamorphosis, and cell subpopulations characterized by particular gene expression combinations were located in periventricular, intermediate and superficial strata. During prometamorphosis, three dorsoventral tiers formed from the caudal domain and most pronuclei were defined, which were modified into the definitive nuclear configuration through the metamorphic climax. Mixed cell populations originated from the rostral and caudal domains constitute most of the final nuclei and allowed us to propose additional subdivisions in the adult thalamus, whose main afferent and efferent connections were assessed by tracing techniques under in vitro conditions. This study corroborates shared features of early gene expression patterns in the thalamus between Xenopus and mouse, however, the dynamic changes in gene expression observed at later stages in the amphibian support mechanisms different from those of mammals. [ABSTRACT FROM AUTHOR]

The Pax6 gene encodes a regulatory transcription factor that is key in brain development. The molecular structure of Pax6, the roles it plays and its patterns of expression in the brain have been highly conserved during vertebrate evolution. As neurodevelopment proceeds, the Pax6 expression changes from the mitotic germinal zone in the ventricular zone to become distributed in cell groups in the adult brain. Studies in various vertebrates, from fish to mammals, found that the Pax6 expression is maintained in adults in most regions that express it during development. Specifically, in amphibians, Pax6 is widely expressed in the adult brain and its distribution pattern serves to highlight regional organization of the brain. In the present study, we analyzed the detailed distribution of Pax6 cells in the adult central nervous system of lungfishes, the closest living relatives of all tetrapods. Immunohistochemistry performed using double labeling techniques with several neuronal markers of known distribution patterns served to evaluate the actual location of Pax6 cells. Our results show that the Pax6 expression is maintained in the adult brain of lungfishes, in distinct regions of the telencephalon (pallium and subpallium), diencephalon, mesencephalon, hindbrain, spinal cord, and retina. The pattern of Pax6 expression is largely shared with amphibians and helps to understand the primitive condition that would have characterized the common ancestors to all sarcopterygians (lobe‐finned fishes and tetrapods), in which Pax6 would be needed to maintain specific entities of subpopulations of neurons. [ABSTRACT FROM AUTHOR]

Many of the genes involved in brain patterning during development are highly conserved in vertebrates and similarities in their expression patterns help to recognize homologous cell types or brain regions. Among these genes, Pax6 and Pax7 are expressed in regionally restricted patterns in the brain and are essential for its development. In the present immunohistochemical study we analyzed the distribution of Pax6 and Pax7 cells in the brain of six representative species of tetrapods and lungfishes, the closest living relatives of tetrapods, at several developmental stages.The distribution patterns of these transcription factors were largely comparable across species. In all species only Pax6 was expressed in the telencephalon, including the olfactory bulbs, septum, striatum, and amygdaloid complex. In the diencephalon, Pax6 and Pax7 were distinct in the alar and basal parts, mainly in prosomeres 1 and 3. Pax7 specifically labeled cells in the optic tectum (superior colliculus) and Pax6, but not Pax7, cells were found in the tegmentum. Pax6 was found in most granule cells of the cerebellum and Pax7 labeling was detected in cells of the ventricular zone of the rostral alar plate and in migrated cells in the basal plate, including the griseum centrale and the interpeduncular nucleus. Caudally, Pax6 cells formed a column, whereas the ventricular zone of the alar plate expressed Pax7. Since the observed Pax6 and Pax7 expression patterns are largely conserved they can be used to identify subdivisions in the brain across vertebrates that are not clearly discernible with classical techniques. [ABSTRACT FROM AUTHOR]

The telencephalic basal ganglia (BG) of amniotes consist of two subdivisions, striatum and pallidum, which share many features, including development, cell types, neurotransmitter organization and hodology. In particular, these two subdivisions during development are defined on the basis of discrete gene expression patterns (genoarchitecture or genoarchitectonics). The characterization of the BG in the subpallium of representatives of the different classes of anamniote vertebrates was first approached in studies dealing with their localization, hodology and main neurochemical characteristics. Thus, it was proposed that an impressive degree of conservation exists across species. New insights can be gained by the comparative analysis of the expression of conserved transcription factors that distinctly define the striatal and pallidal components of the BG in all vertebrates. In addition, the expression of other genes that characterize neighboring regions of the BG is also useful to define the boundaries of each subdivision. Following this approach, we have analyzed the BG in the brain of juvenile representatives of amphibians, lungfishes, holosteans, Polypteriformes and Chondrichthyes. In addition, we briefly review previous data in teleosts and agnathans. The markers used include islet 1 and Dlx as striatal markers, whereas Nkx2.1 is essential for the identification of the pallidum. In turn, Pax6 and in particular Tbr1 are expressed in the pallium. These markers have been systematically analyzed in combination with neuronal markers of specific subpallial territories and cell populations, such as tyrosine hydroxylase, γ-aminobutyric acid, nitric oxide synthase, substance P and enkephalin. The results highlight that many genes share common distribution patterns and are arranged in conserved combinations whose identification has served to define homologies between components of the BG in distant species. © 2014 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Pax7 is a member of the highly conserved Pax gene family that is expressed in restricted zones of the central nervous system (CNS) during development, being involved in early brain regionalization and the maintenance of the regional identity. Using sensitive immunohistochemical techniques we have analyzed the spatiotemporal pattern of Pax7 expression in the brain of the anuran amphibian Xenopus laevis, during development. Pax7 expression was first detected in early embryos in the basal plate of prosomere 3, roof and alar plates of prosomere 1 and mesencephalon, and the alar plate of rhombomere 1. As development proceeded, Pax7 cells were observed in the hypothalamus close to the catecholaminergic population of the mammillary region. In the diencephalon, Pax7 was intensely expressed in a portion of the basal plate of prosomere 3, in the roof plate and in scattered cells of the thalamus in prosomere 2, throughout the roof of prosomere 1, and in the commissural and juxtacommissural domains of the pretectum. In the mesencephalon, Pax7 cells were localized in the optic tectum and, to a lesser extent, in the torus semicircularis. The rostral portion of the alar part of rhombomere 1, including the ventricular layer of the cerebellum, expressed Pax7 and, gradually, some of these dorsal cells were observed to populate ventrally the interpeduncular nucleus and the isthmus (rhombomere 0). Additionally, Pax7 positive cells were found in the ventricular zone of the ventral part of the alar plate along the rhombencephalon and the spinal cord. The findings show that the strongly conserved features of Pax7 expression through development shared by amniote vertebrates are also present in the anamniote amphibians as a common characteristic of the brain organization of tetrapods. [ABSTRACT FROM AUTHOR]

ABSTRACT The onset and developmental dynamics of Pax3, Pax6, and Pax7 expressions were analyzed by immunohistochemical techniques in the central nervous system (CNS) of embryos, larvae, and recently metamorphosed juveniles of the urodele amphibian Pleurodeles waltl. During the embryonic period, the Pax proteins start being detectable in neuroepithelial domains. Subsequently, they become restricted to subsets of cells in distinct brain regions, maintaining different degrees of expression in late larvae and juvenile brains. Specifically, Pax6 is broadly expressed all along the urodele CNS (olfactory bulbs, pallium, basal ganglia, diencephalon, mesencephalic tegmentum, rhombencephalon, and spinal cord) and the developing olfactory organ and retina. Pax3 and Pax7 are excluded from the rostral forebrain and were usually observed in overlapping regions during embryonic development, whereas Pax3 expression is highly downregulated as development proceeds. Thus, Pax3 is restricted to the roof plate of prosomere 2, pretectum, optic tectum, rhombencephalon, and spinal cord. Comparatively, Pax7 was more conspicuous in all these regions. Pax7 cells were also found in the paraphysis, intermediate lobe of the hypophysis, and basal plate of prosomere 3. Our data show that the expression patterns of the three Pax genes studied are overall evolutionarily conserved, and therefore could unequivocally be used to identify subdivisions in the urodele brain similar to other vertebrates, which are not clearly discernable with classical techniques. In addition, the spatiotemporal sequences of expression provide indirect evidence of putative migratory routes across neuromeric limits and the alar-basal boundary. J. Comp. Neurol. 521:3913-3953, 2013. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Expression patterns of Pax6, Pax7, and, to a lesser extent, Pax3 genes were analyzed by a combination of immunohistochemical techniques in the central nervous system of adult specimens of the urodele amphibian Pleurodeles waltl. Only Pax6 was found in the telencephalon, specifically the olfactory bulbs, striatum, septum, and lateral and central parts of the amygdala. In the diencephalon, Pax6 and Pax7 were distinct in the alar and basal parts, respectively, of prosomere 3. The distribution of Pax6, Pax7, and Pax3 cells correlated with the three pretectal domains. Pax7 specifically labeled cells in the dorsal mesencephalon, mainly in the optic tectum, and Pax6 cells were the only cells found in the tegmentum. Large populations of Pax7 cells occupied the rostral rhombencephalon, along with lower numbers of Pax6 and Pax3 cells. Pax6 was found in most granule cells of the cerebellum. Pax6 cells also formed a column of scattered neurons in the reticular formation and were found in the octavolateral area. The rhombencephalic ventricular zone of the alar plate expressed Pax7. Dorsal Pax7 cells and ventral Pax6 cells were found along the spinal cord. Our results show that the expression of Pax6 and Pax7 is widely maintained in the brains of adult urodeles, in contrast to the situation in other tetrapods. This discrepancy could be due to the generally pedomorphic features of urodele brains. Although the precise role of these transcription factors in adult brains remains to be determined, our findings support the idea that they may also function in adult urodeles. J. Comp. Neurol. 521:2088-2124, 2013. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Lungfishes are currently considered the closest living relatives of tetrapods and represent an interesting group for the study of evolutionary traits in the transition from fishes to tetrapods. The brains of lungfishes have received little attention in comparative studies probably due to the difficulty of obtaining these unique animals. In the present study the distribution of orexin (hypocretin)-like immunoreactivity was studied in the brain of the African lungfish Protopterus dolloi and the Australian lungfish Neoceratodus forsteri by using antibodies directed against the mammalian orexin-A and orexin-B peptides. Simultaneous detection of orexins and tyrosine hydroxylase or serotonin was used to assess the precise location of the orexins in the brain and to evaluate the possible influence of the orexin system on the monoaminergic cell groups. Although some differences were noted, a common pattern for the distribution of orexins in the two lungfishes studied was observed. In both species, most immunoreactive neurons were observed in the suprachiasmatic nucleus and dorsal hypothalamus. Only in Neoceratodus, however, were important cell populations found in the preoptic area and infundibular hypothalamus, whereas small numbers of faintly reactive neurons were present in the lateral septum and ventral striatum. Fiber labeling was widely distributed in all main brain subdivisions, but was more abundant in regions such as the septum, preoptic area, suprachiasmatic nucleus, lateral hypothalamic area, thalamus, pretectum and tegmentum. Less conspicuous was the innervation of the pallial regions, habenula, optic tectum, rhombencephalic reticular formation and spinal cord. Orexinergic innervation was found in close contact with dopaminergic, noradrenergic and serotoninergic cell groups, homologous to the substantia nigra in the midbrain tegmentum, the locus coeruleus, the nucleus of the solitary tract and the raphe nuclei. Although unique features have been found for lungfishes, the location of orexin immunoreactive elements is largely consistent with that recently reported following a similar approach in amphibians and amniotes, suggesting that the general organization of this peptidergic system occurred in the common ancestor of lungfishes and tetrapods. Copyright © 2010 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Abstract: Previous studies in amphibians yielded contradictory results about the distribution of calbindin-D28k (CB) and calretinin (CR) in retinal neurons, most likely due to the different antibodies used. The present comparative study aimed to characterize the distribution of CB and CR in relation to retinal neurons in six species of anuran and urodele amphibians by using the same immunohistochemical protocol with specific poly- and monoclonal antibodies. CB was specifically found in cones, in subpopulations of bipolar and amacrine cells and in sparse neurons in the ganglion cell layer. All photoreceptors were negative for CR, whereas subpopulations of horizontal, bipolar and amacrine cells as well as cells in the ganglion cell layer contained CR. CB/CR colocalization occurred in some amacrine cells and in cells of the ganglion cell layer, with variable proportions among species. Most of the ganglion cells identified by retrograde labeling from the optic nerve contained CB and/or CR. Cholinergic cells, visualized by choline acetyltransferase (ChAT) immunoreactivity, constituted a subpopulation of the CR-positive amacrine cells in anurans and a high percentage (40–90%) of cholinergic cells were CR immunoreactive in urodeles. CB/ChAT colocalization was between 10 and 30% in anurans and lower in urodeles (7–10%). Finally, CB colocalized in 6–8% of the tyrosine hydroxylase (TH) amacrine cells only in anurans, whereas CR and TH colocalized in 5% of TH cells in the urodele retina. Our data suggest a specific pattern for CB and CR distribution in the retinal neurons of amphibians comparable to amniotes in some cell types showing, however, peculiar features not observed previously in other vertebrates. [Copyright &y& Elsevier]

Abstract: Neuropeptide FF-like immunoreactive (NPFFir) cells and fibers were analyzed through development of Xenopus laevis. The first NPFFir cells appeared in the embryonic hypothalamus, which projected to the intermediate lobe of the hypophysis, the brainstem and spinal cord. Slightly later, scattered NPFFir cells were present in the olfactory bulbs and ventral telencephalon. In the caudal medulla, NPFFir cells were observed in the nucleus of the solitary tract only at embryonic and early larval stages. Abundant NPFFir cells and fibers were demonstrated in the spinal cord. The sequence of appearance observed in Xenopus shares many developmental features with mammals although notable differences were observed in the telencephalon and hypothalamus. In general, NPFF immunoreactivity developed earlier in amphibians than in mammals. [Copyright &y& Elsevier]

Neuropeptide FF (NPFF) is an FMRFamide-related peptide widely distributed in the mammalian brain. NPFF immunohistochemistry labeled cell bodies in a few locations and dense fiber networks throughout the brain. Recently, the distribution of NPFF immunoreactive (NPFF-ir) cells and fibers in the brain of anuran and urodele amphibians was studied and, as in mammals, significant species differences were noted. To further assess general and derived features of the NPFF-containing neuron system in amphibians, we have investigated the distribution of NPFF-ir cell bodies and fibers in the brain of the gymnophionan Dermophis mexicanus by means of an antiserum against bovine NPFF. This distribution was compared to that of FMRFamide immunoreactivity. Major traits shared with anurans and urodeles were the abundant fiber labeling in the ventral telencephalon, hypothalamus, isthmus, ventrolateral medulla and dorsal spinal cord. In addition, in the three amphibian orders the majority of the NPFF-ir cells were located in the preoptic-hypothalamic region. However, distinct particular features were present in the gymnophionan such as the lack of NPFF-ir cells in the telencephalon, brainstem and spinal cord and the absence of NPFF-ir fibers in the hypophysis and the olfactory bulbs. This pattern was distinct from that observed for FMRFamide distribution. Striking differences were noted in the pallium, caudal hypothalamus and midbrain tegmentum where FMRFamide – containing cells were localized. The present results in Dermophis support the idea that data from gymnophionans must be included when stating the amphibian condition of a given system because important variations are obvious when gymnophionans are compared with anurans and urodeles. Copyright © 2006 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Abstract: Immunohistochemistry for calbindin-D28k (CB) revealed that the spinal cord of Xenopus laevis possess a large number of CB-containing neurons widely distributed in both the dorsal and ventral horns, including areas which possess long ascending projections to supraspinal structures. In addition, the presence of CB-immunoreactive axons in the spinal funiculi suggested that descending projections containing this calcium binding protein may originate in different brainstem nuclei. Apart from mapping CB-containing elements in the spinal cord, a double labeling approach was used that combined the retrograde transport of dextran amines with CB immunohistochemistry. Thus, dextran amine injections into the lateral reticular region of the rhombencephalon, the parabrachial region, the mesencephalon and the dorsal thalamus revealed many retrogradely labeled cells in the spinal cord, a few number of which were double labeled for CB and found in the superficial dorsal horn and in the ventral medial region of the ventral horn. Their axons passed mainly via the lateral funiculus. Tracer application into the cervical spinal cord, combined with CB immunohistochemistry, resulted in retrogradely labeled cells throughout the brain, five groups of which showed CB immunoreactivity: (1) the mesencephalic trigeminal nucleus, (2) the laterodorsal tegmental nucleus, (3) the raphe nucleus, (4) the middle reticular nucleus and (5) the inferior reticular nucleus. The presence of CB in spinal pathways suggests that CB may play a role in controlling spinal cells, mainly subserving visceroceptive and nociceptive information to supraspinal levels, and might also modulate reticulospinal pathways. [Copyright &y& Elsevier]

Abstract: By means of double immunohistofluorescence techniques, we have investigated the colocalization of nitric oxide synthase and tyrosine hydroxylase (TH) or serotonin (5-HT) in the central nervous system of the anurans Rana perezi and Xenopus laevis and the urodele Pleurodeles waltl. A wide codistribution of neuronal populations, expressing these markers, was found throughout the brain and spinal cord. In contrast, colocalization of these markers was rather restricted. Only in the caudal portion of the brainstem raphe column in anurans, approximately 80% of the 5-HT-positive cells were also NOS-immunoreactive, whereas in the urodele brain, about 40% of the serotonergic cells at the level of the glossopharyngeal motor nucleus were simultaneously NOS-positive. In various brain regions, a wide codistribution of NOS- and TH-containing neurons was observed, but real colocalization of nitrergic and catecholaminergic cells was only found in a small neuron population in the posterior tubercle of anuran amphibians. Therefore, in amphibians, only a distinct and small cell population within the serotonergic raphe column (anurans and urodele) and in the catecholaminergic posterior tubercle (anurans) seem to produce simultaneously nitric oxide. [Copyright &y& Elsevier]

The ontogeny of cholinergic neurons has been studied in the brain of the urodele amphibian Pleurodeles waltl by means of choline acetyltransferase (ChAT) immunohistochemistry. Embryonic and larval stages were studied. The earliest ChAT immunoreactive (ChATi) cells were the primary motoneurons in the upper spinal cord, at embryonic stage 29. Slightly later, before hatching, the cranial nerve motor nuclei were immunopositive as well as non-motor populations in the developing inferior reticular nucleus, the nucleus of the solitary tract, the dorsal column nucleus and the retina. At initial larval stages, ChATi cells were located for the first time in the suprachiasmatic nucleus and the isthmic tegmentum. In addition, moderate immunoreactivity appeared in the Mauthner cells. During the period of active larval life the cholinergic systems maturated progressively and new ChATi cell groups were found in the caudal telencephalon and the habenula. Also extensive fiber labeling occurred at active larval stages. No transient ChAT expression was observed and even the Mauthner cells maintained their immunoreactivity after metamorphosis. A general caudorostral spatio-temporal sequence of appearance of cholinergic structures was found in the brain. Comparison of the results observed in the urodele with previous data available only in amniotes shows numerous similarities and suggests a conservative developmental pattern of cholinergic systems in vertebrates. [Copyright &y& Elsevier]

The neuropeptide FF (NPFF) is a member of the RFamide related peptides (FaRPs) that share the dipeptide Arg–Phe–NH2 at their C-terminal. It was originally isolated from bovine brain and its wide distribution has been demonstrated in the brain of several mammalian species. By means of an NPFF antiserum we have investigated the distribution pattern of NPFF-like immunoreactive cells and fibers in the brain of anuran and urodele amphibians. In both amphibian orders, the most conspicuous labeled cell population was found in the preoptic area and hypothalamus, primarily in the suprachiasmatic region. Numerous fibers reached the median eminence and the intermediate lobe of the hypophysis. Only in the anuran brain cells were observed in the pallium and septum. In the urodele, cells and fibers of the terminal nerve were distinctly labeled. Cell bodies were widely distributed in the reticular formation of anurans and, in both orders, a large cell population was found in the nucleus of the solitary tract and the spinal cord. Comparable fiber distribution between both orders exists in which the basal telencephalon (mainly the amygdaloid complex), the hypothalamus and the spinal cord are the regions most richly innervated. The distribution pattern of NPFF-like immunorective elements in the brain of amphibians, which only partly overlaps with those of other FaRPs, supports the notion that a NPFF-like peptide exists in amphibians. On the basis of its localization, this peptide may act as a hypophysiotropic neurohormone and be involved in background adaptation. Its wide distribution in similar zones of the brain in amphibians and mammals suggests that functional roles of this peptide have been conserved in vertebrate evolution. [Copyright &y& Elsevier]

The organization of nitrergic systems in the brains of anuran and urodele amphibians was recently studied and significant differences were noted between both amphibian orders. However, comparable data are not available for the third order of amphibians, the gymnophionans (caecilians). In the present study we have investigated the distribution of neuronal elements that express nitric oxide synthase (NOS) in the brain of the gymnophionan amphibian Dermophis mexicanus by means of immunohistochemistry with specific antibodies against NOS and enzyme histochemistry for NADPH-diaphorase. Both techniques yielded identical results and were equally suitable to demonstrate the nitrergic system. In addition, they were useful tools in the identification of cell groups and brain structures, otherwise indistinct in the brains of caecilians. The distribution of nitrergic structures observed in Dermophis conforms to the overall amphibian pattern but numerous distinct peculiarities were also noted. These included a dense innervation of the olfactory bulbs but a lack of reactivity in olfactory and vomeronasal fibers and glomeruli. A large population of nitrergic cells in the striatum and the presence of thalamic neurons, as well as the specific distribution of nitrergic cells in the isthmic region, are some of the differential features in the gymnophionan brain. Given the variability among species in the same class of vertebrates any discussion including amphibians should also include evidence for gymnophionans.Copyright © 2002 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Abstract: The orexins (hypocretins) are peptides found primarily in neurons of the hypothalamus of all vertebrates. Many differences were reported about the precise location of orexin containing cells and their projections throughout the brain in different species. However, there are few direct cross-species comparisons. Previous studies in anuran amphibians have also reported notable species differences. We examined and directly compared the distribution of orexinergic neurons and fibers within the brains of representatives of the three amphibian orders, anurans, urodeles and gymnophionans. Simultaneous detection of orexins and tyrosine hydroxylase was used to assess the precise location of the orexins in the brain and to evaluate the possible influence of the orexin system on the catecholaminergic cell groups. Although some differences were noted, a common pattern for the distribution of orexins in amphibians was observed. In all species, most immunoreactive neurons were observed in the suprachiasmatic nucleus, whereas the cells in the preoptic area and the tuberal region were more variable. Orexin immunoreactive fibers in the brain of all species included abundant fibers throughout the preoptic area and hypothalamus, whereas moderate amounts of fibers were present in the pallium, striatum, septum, thalamus, optic tectum, torus semicircularis, rhombencephalon and spinal cord. The use of double immunohistochemistry in amphibians revealed orexinergic innervation in dopaminergic and noradrenergic cell groups, such as the midbrain tegmentum, locus coeruleus and nucleus of the solitary tract, as was previously reported in mammals. [Copyright &y& Elsevier]

Abstract: The existence of propriospinal cholinergic pathways and the origin of supraspinal cholinergic descending projections have been investigated in anuran and urodele amphibians. Retrograde tract tracing techniques with dextran amines injected in the spinal cord at different levels were combined with immunohistochemistry for choline acetyltransferase (ChAT). The analysis of the brachial, thoracic and lumbar spinal cord demonstrated that doubly labeled cells were present only close to the injection site. Thus, the participation of the spinal cholinergic cells in distant intersegmental connections is not present, or is very limited, in amphibians. In anurans, tracer applications to the brachial cord revealed cholinergic cells of origin of spinal projections located in four distinct brain nuclei. The most rostrally located cells were found bilaterally in the preoptic area, among the magnocellular cells. In the ipsilateral isthmic region, the laterodorsal tegmental nucleus also showed doubly labeled cells. Throughout the brainstem, abundant codistribution was observed but actual coexistence of the tracer and ChAT was only found in the nucleus of the solitary tract and the inferior reticular nucleus. In the case of the urodele, abundant codistribution between retrogradely labeled cells and ChAT-positive neurons in zones like the suprachiasmatic nucleus, the isthmic region and the rhombencephalic reticular formation was observed, but the only doubly labeled cells were the Mauthner neurons. The present results in amphibians contrast with previous data in mammals in which is striking the presence of a widespread intrinsic cholinergic innervation of the spinal cord and the virtual absence of cholinergic projections descending from the brainstem. [Copyright &y& Elsevier]

Highlights: [•] Neurons labeled for Pax6 and Pax7 are widely distributed in the adult Xenopus brain. [•] Labeled cells in the adult are located in the same regions as through development. [•] The localization of the labeled cells shows regionalization within the CNS. [•] Pax6 is mainly expressed in the forebrain and Pax7 prevails in the brainstem. [•] The distribution of Pax6 and Pax7 cells appears very conserved across vertebrates. [ABSTRACT FROM AUTHOR]