Anterior Dorsal Ventricular Ridge Research Articles

Functional MRI in the Nile crocodile: a new avenue for evolutionary neurobiology.

Crocodilians are important for understanding the evolutionary history of amniote neural systems as they are the nearest extant relatives of modern birds and share a stem amniote ancestor with mammals. Although the crocodilian brain has been investigated anatomically, functional studies are rare. Here, we employed functional magnetic resonance imaging (fMRI), never tested in poikilotherms, to investigate crocodilian telencephalic sensory processing. Juvenile Crocodylus niloticus were placed in a 7 T MRI scanner to record blood oxygenation level-dependent (BOLD) signal changes during the presentation of visual and auditory stimuli. Visual stimulation increased BOLD signals in rostral to mid-caudal portions of the dorso-lateral anterior dorsal ventricular ridge (ADVR). Simple auditory stimuli led to signal increase in the rostromedial and caudocentral ADVR. These activation patterns are in line with previously described projection fields of diencephalic sensory fibres. Furthermore, complex auditory stimuli activated additional regions of the caudomedial ADVR. The recruitment of these additional, presumably higher-order, sensory areas reflects observations made in birds and mammals. Our results indicate that structural and functional aspects of sensory processing have been likely conserved during the evolution of sauropsids. In addition, our study shows that fMRI can be used to investigate neural processing in poikilotherms, providing a new avenue for neurobiological research in these critical species.

Core-and-belt organisation of the mesencephalic and forebrain auditory centres in turtles: Expression of calcium-binding proteins and metabolic activity

The distribution of immunoreactivity to the calcium-binding proteins parvalbumin, calbindin and calretinin and of cytochrome oxidase activity was studied in the mesencephalic (torus semicircularis), thalamic (nucleus reuniens) and telencephalic (ventromedial part of the anterior dorsal ventricular ridge) auditory centres of two chelonian species Emys orbicularis and Testudo horsfieldi. In the torus semicircularis, the central nucleus (core) showed intense parvalbumin immunoreactivity and high cytochrome oxidase activity, whereas the laminar nucleus (belt) showed low cytochrome oxidase activity and dense calbindin/calretinin immunoreactivity. Within the central nucleus, the central and peripheral areas could be distinguished by a higher density of parvalbumin immunoreactivity and cytochrome oxidase activity in the core than in the peripheral area. In the nucleus reuniens, the dorsal and ventromedial (core) regions showed high cytochrome oxidase activity and immunoreactivity to all three calcium-binding proteins, while its ventrolateral part (belt) was weakly immunoreactive and showed lower cytochrome oxidase activity. In the telencephalic auditory centre, on the other hand, no particular region differed in either immunoreactivity or cytochrome oxidase activity. Our findings provide additional arguments in favour of the hypothesis of a core-and-belt organisation of the auditory sensory centres in non-mammalian amniotes though this organisation is less evident in higher order centres. The data are discussed in terms of the evolution of the auditory system in amniotes.

Metabolic activity of the thalamic and telencephalic auditory centers of reptiles

329 The lemniscal (classical projection) and extralemniscal parts of mammalian sensory systems, including the auditory system have different levels of metabolic activity. The lemniscal parts have a higher activity of cytochrome oxidase (CO) and an increased ability to accumulate 2-deoxyglucose (2-DG), whereas the extralemniscal parts are characterized by a lower level of metabolic activity [1]. A similar distribution of metabolic activity was observed in the auditory system of birds (in the mesencephalic, thalamic, and telencephalic auditory centers) [2‐4]. Earlier, we showed that the mesencephalic auditory center, torus semicircularis (TS), of some reptiles, such as turtles and lizards, has a higher CO activity in the central nucleus of the lemniscal pathway than in the peripheral extralemniscal part [5]. However, it is not clear whether the metabolic activity in the rostral centers of reptilian auditory system, viz. the auditory relay thalamic nucleus (n. reuniens, Re) and its projection zone in the telencephalon (the ventromedial part of anterior dorsal ventricular ridge, Advr), have selective distribution. In this work, we studied the distribution of the activity of the mitochondrial oxidative enzyme CO in the rostral auditory centers of two turtle species, Testudo horsfieldi and Emys orbicularis. The experiments were performed with four T. horsfieldi and four E. orbicularis. The CO activity was measured by the standard histochemical method [6] with the use of bovine heart cytochrome Σ (Sigma). The CO activity was estimated by the density of histochemical staining of frozen frontal brain slices with a thickness of 50 µ m. Thalamus. The distribution of the CO activity in the Re in both turtle species was similar and heterogeneous. In the rostral level of the thalamus, we found a CO-active band-shaped structure that continuously spread from the ventricle in the lateral direction below the ventral border of the thalamic center of the tectofugal visual system (Rot) and coincided with the location of the n. anterior (nA). The medial part of this structure is a rostral pole of Re (Figs. 1a and 2a). The middle Re level had two areas with a high CO activity. The larger dorsocentral area occupied almost the entire nucleus except for a small ventrolateral part and extended to the somatic nucleus n. ventralis (nV) below the Rot. This area was continuously connected with the rostral bandshaped structure (Figs. 1b and 2b). Like the rostral part of the Re, this area was filled with stained punctuate terminals with sparse CO-positive cells located in the lat

Level of metabolic activity (cytochrome oxidase) as an index of functional significance of tectofugal and thalamofugal channels of the reptilian visual system

Using histochemical determination of activity of the mitochondrial oxidative enzyme cytochrome oxidase (CO) in brain structures, metabolic activity both in turtles and in lizards has been shown to be higher in centers of the tectofugal channel (the tectal stratum griseum centrale, SGC; nucleus pretectalis ventralis, Ptv; thalamic nucleus rotundus, Rot; telencephalic visual area of the anterior dorsal ventricular ridge, Advr) than in the thalamofugal channel centers (the thalamic nucleus geniculatus lateralis pars dorsalis, GLd; cortex dorsolateralis, Cxdl; and pallial thickening, Path) of the visual system. Some interspecies differences in distribution of the CO activity in the tectal, thalamic, and telencephalic visual centers between terrestrial and pond turtles and lizards were revealed. The obtained data confirm the idea on the dominating role of the tectofugal channel over the thalamofugal channel of the visual system in information processing and organization of the day-to-day behavior of reptiles.

The turtle thalamic anterior entopeduncular nucleus shares connectional and neurochemical characteristics with the mammalian thalamic reticular nucleus

Neurochemical and key connectional characteristics of the anterior entopeduncular nucleus (Enta) of the turtle ( Testudo horsfieldi) were studied by axonal tracing techniques and immunohistochemistry of parvalbumin, γ-aminobutyric acid (GABA) and glutamic acid decarboxylase (GAD). We showed that the Enta, which is located within the dorsal peduncle of the lateral forebrain bundle (Pedd), has roughly topographically organized reciprocal connections with the dorsal thalamic visual nuclei, the nucleus rotundus (Rot) and dorsal lateral geniculate nucleus (GLd). The Enta receives projections from visual telencephalic areas, the anterior dorsal ventricular ridge and dorsolateral cortex/pallial thickening. Most Enta neurons contained GABA and parvalbumin, and some of them were retrogradely labeled when the tracer was injected into the visual dorsal thalamic nuclei. Further experiments using double immunofluorescence revealed colocalization of GAD and parvalbumin in the vast majority of Enta neurons, and many of these cells showed retrograde labeling with Fluoro-gold injected into the Rot and/or GLd. According to these data, the Enta may be considered as a structural substrate for recurrent inhibition of the visual thalamic nuclei. Based on morphological and neurochemical similarity of the turtle Enta, caiman Pedd nucleus, the superior reticular nucleus in birds, and the thalamic reticular nucleus in mammals, we suggest that these structures represent a characteristic component which is common to the thalamic organization in amniotes.

The ascending tectofugal visual system in amniotes: New insights

Ascending tectal axons carrying visual information constitute a fiber pathway linking the mesencephalon with the dorsal thalamus and then with a number of telencephalic centers. The sauropsidian nucleus rotundus and its mammalian homologue(s) occupy a central position in this pathway. The aim of this study was analyzing the rotundic connections in reptiles and birds in relation with comparable connections in mammals, by using biotinylated dextran amines and the lipophilic carbocyanine dye DiI as tracing molecules. In general, rotundic connections in reptiles and birds are quite similar, especially with regards to pretectal and tectal afferences; as a novel finding, we describe varicose fibers arising from nucleus rotundus that reached the developing chick striatum. In addition, this study described the dorsal claustrum as a novel telencephalic target for the suprageniculate nucleus in mammals. Overall, telencephalic projections from the posterior/intralaminar complex of the mammalian thalamus can be compared with the telencephalic projections of the reptilian nucleus rotundus. With the exception of the isocortical connections, the mouse suprageniculate nucleus shares a number of afferent and efferent connections with the sauropsidian nucleus rotundus. Especially significant were the suprageniculate fibers reaching the striatum and then following to reach pallial derivatives such as the lateral amygdala (ventral pallium) and the dorsal claustrum (lateral pallium). These connections can be compared with the rotundic fibers reaching the ventromedial part of the anterior dorsal ventricular ridge in reptiles/entopallium in birds (ventral pallium) and the dorsolateral part of the anterior dorsal ventricular ridge in reptiles (lateral pallium), and probably the mesopallium in birds.

Amygdalostriatal projections in reptiles: a tract-tracing study in the lizard Podarcis hispanica.

Whereas the lacertilian anterior dorsal ventricular ridge contains unimodal sensory areas, its posterior part (PDVR) is an associative center that projects to the hypothalamus, thus being comparable to the amygdaloid formation. To further understand the organization of the reptilian cerebral hemispheres, we have used anterograde and retrograde tracing techniques to study the projections from the PDVR and adjoining areas (dorsolateral amygdala, DLA; deep lateral cortex, dLC; nucleus sphericus, NS) to the striatum in the lizard Podarcis hispanica. This information is complemented with a detailed description of the organization of the basal telencephalon of Podarcis. The caudal aspect of the dorsal ventricular ridge projects nontopographically mainly (but not exclusively) to the ventral striatum. The NS projects bilaterally (with strong ipsilateral dominance) to the nucleus accumbens, thus recalling the posteromedial cortical amygdala of mammals. The PDVR (especially its lateral aspect) and the dLC project massively to a continuum of structures connecting the striatoamygdaloid transition area (SAT) and the nucleus accumbens (rostrally), the projection arising from the dLC being probably bilateral. Finally, the DLA projects massively and bilaterally to both the ventral and dorsal striatum, including the SAT. Our findings lend further support to the view that the PDVR and neighboring structures constitute the reptilian basolateral amygdala and indicate that an emotional brain was already present in the ancestral amniote. These results are important to understand the comparative significance of the caudal aspect of the amniote cerebral hemispheres, and specifically challenge current views on the nature of the avian caudal neostriatum.

Toward the answer, but still far to go

The target article about the origin and evolution of the isocortex triggers questions about unresolved issues that still need to be dealt with, including: (1) the evolutionary scenario of the origin of the lateral isocortex, (2) the expansion of the dorsal pallium in nonmammals, and (3) the heterogeneity of the anterior dorsal ventricular ridge.

Development and evolution of the collopallium in amniotes: a new hypothesis of field homology

Embryological development is uniquely positioned to illuminate both hodology in adult brains and its inherited genetic bases. The lateral corner of the lateral ventricle in mammals is a particularly crucial region where cell migration patterns, transiently formed connections, axonal growth kinetics, and fasciculation patterns are complex and interactive. Based on hodology, the sauropsid anterior dorsal ventricular ridge (ADVR) has been proposed as the homologue on a one-to-one basis of the mammalian lateral neocortex (LNC), the basolateral amygdalar complex (BLA), or the claustrum-endopiriform nucleus (CE). Data on gene expression patterns during development have indicated ADVR homology with parts of the latter two structures rather than with LNC. Collothalamic nuclei (the set of dorsal thalamic nuclei that receive their predominant input from the midbrain roof) project to part of BLA and to LNC. Recent findings demonstrate a complex pattern of mutually overlapping but noncongruent gene expression territories and collothalamic projections, which suggests a new, collopallial field hypothesis that the ADVR is homologous as a field to all three structures LNC, BLA, and CE. This hypothesis accounts for current hodological and developmental data as well as for lack of a CE in monotremes and for an abnormal subcortical lamina of gray matter that results from a genetic abnormality in humans.

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.

Light and electron microscopic evidence for projections from the thalamic nucleus rotundus to targets in the basal ganglia, the dorsal ventricular ridge, and the amygdaloid complex in a lizard

To elucidate the organization and evolution of the tectorotundotelencephalic pathways in birds and reptiles, we reinvestigated at both light and electron microscopic levels the efferent projections of nucleus rotundus in a lizard, using the sensitive tracer biotinylated dextran amine. Our results indicate that nucleus rotundus projects to targets in the basal ganglia (lateral parts of striatum and olfactory tubercle and possibly the globus pallidus), the anterior dorsal ventricular ridge (ADVR), and the amygdaloid complex (the central and possibly lateral amygdaloid nuclei). In these targets, the rotundal axon terminals establish asymmetric, presumably excitatory synaptic contacts, usually with dendrites of local cells. In the ADVR, the rotundal projection terminates in two separate radial regions showing distinct cytoarchitecture: 1) a dorsolateral region that extends radially from the dorsolateral ADVR ventricular surface to the ventral part of the lateral cortex and 2) the lateral part of a ventromedial region that extends radially from the dorsomedial and medial ADVR ventricle to a superficial area interposed between the dorsolateral ADVR and the striatum. These two ADVR regions have different connections with the thalamus and telencephalon, which suggests that they may be involved in different degrees of integration. Our study also suggests that the rotundal projection to the ventromedial ADVR field of lizards may be comparable to the rotundoectostriatal/periectostriatal projection of birds. The connections and pathways involving nucleus rotundus suggest that this nucleus conveys visual information which may play a role in visuomotor, emotional, and visceral functions.

Identification of the reptilian basolateral amygdala: an anatomical investigation of the afferents to the posterior dorsal ventricular ridge of the lizard Podarcis hispanica.

The presence of multimodal association in the telencephalon of reptiles has been investigated by tracing the afferent connections to the posterior dorsal ventricular ridge (PDVR) of the lizard Podarcis hispanica. The PDVR receives telencephalic afferents from the lateral (olfactory) and dorsal cortices, and from the three unimodal areas of the anterior dorsal ventricular ridge, in a convergent manner. From the diencephalon, it receives afferents from the dorsomedial anterior and medial posterior thalamic nuclei, and from several hypothalamic nuclei. Brainstem afferents to the PDVR originate in the dorsal interpeduncular nucleus, the nucleus of the lateral lemniscus and parabrachial nucleus. The afferents to the thalamic nuclei that project to the PDVR have also been studied. The dorsomedial anterior thalamic nucleus receives projections mainly from limbic structures, whereas the medial posterior thalamic nucleus is the target of projections from structures with a clear sensory significance (optic tectum, torus semicircularis, nuclei of the lateral and spinal lemniscus, superior olive and trigeminal complex). As a result, the PDVR appears as an associative centre that receives visual, auditory, somatosensory and olfactory information from several telencephalic and non-telencephalic centres, and a multimodal projection from the medial posterior thalamic nucleus. This pattern of afferents of the PDVR is similar to that of the caudal neostriatum in birds and the basolateral division of the mammalian amygdala. These results indicate that a multimodal amygdala is already present in reptiles, and has probably played a key role in the evolution of the vertebrate brain.

3-Acetylpyridine-induced degeneration and regeneration in the adult lizard brain: a qualitative and quantitative analysis

The neurotoxin 3-acetylpyridine (3AP) produces highly selective neuronal damage in specific areas of the lizard brain. Following 3AP intoxication, proliferation and migration of replacement neurons born in the ventricular walls lead to regeneration of the lesioned areas. Earlier studies established the time course of 3AP-induced degeneration and subsequent regeneration in the medial cerebral cortex of adult lizards (Font, E., Garcı́a-Verdugo, J.M., Alcántara, S. and López-Garcı́a, C., Neuron regeneration reverses 3-acetylpyridine-induced cell loss in the cerebral cortex of adult lizards, Brain Res., 551 (1991) 230–235 [13]). Complementary to our previous studies, we now provide a qualitative and quantitative account of the extent and distribution of neurotoxic damage in the brain as a whole of lizards treated with 3AP using Nissl and Golgi stains, a degeneration-sensitive reduced-silver method, and electron microscopy. Additionally, [ 3H]thymidine autoradiography was used to assess changes in the rate of neurogenesis caused by the 3AP treatment. Single doses of 3AP caused degenerative changes in all the cortical areas, anterior dorsal ventricular ridge, deep layers of the lateral cortex, lateral amygdaloid nucleus, and nucleus sphericus, while sparing other brain areas. The most frequent neuropathic change after 3AP treatment was clumping of the nuclear chromatin with formation of pyknotic nuclei. Occasionally, a second type of injury was observed in neurons of the cell layer of the dorsomedial cortex (DMC). 3AP also caused a conspicuous loss of dendritic spines in bipyramidal neurons of the dorsomedial and dorsal cortices possibly representing transneuronal degeneration. Numbers of [ 3H]thymidine-labeled cells were higher in lizards previously treated with 3AP than in controls. These results demonstrate that the neurotoxic lesion is capable of inducing an increase in the normal rate of adult neurogenesis. Whereas regeneration in the remaining areas was morphologically and histologically complete, in some animals, cell proliferation in the DMC resulted in formation of an abnormal cell plate.

The Telencephalon of Tetrapods in Evolution; pp. 195–204

Numerous scientists have sought a homologue of mammalian isocortex in sauropsids (reptiles and birds) and a homologue of sauropsid dorsal ventricular ridge in mammals. Although some of the proposed theories were enormously influential, alternative theories continued to coexist, primarily because the striking differences in pallial organization between adult mammals, sauropsids, and amphibians enabled different authors to enlist different subsets of similarity data in support of different hypotheses of putative homology. A phylogenetic analysis based on parsimony cannot discriminate between such alternative hypotheses of putative homology, because sauropsids and mammals are sister groups. One solution to this dilemma is to include embryological patterns of telencephalic organization in the comparative analysis. Because early developmental stages in different taxa tend to resemble each other more than the adults do, the embryological data may reveal intermediate patterns of organization that provide unambiguous support for a single hypothesis of putative homology. The validity of this putative homology may then be supported by means of a phylogenetic analysis based on parsimony. A comparative analysis of pallial organization that includes embryological data suggests the following set of homologies. The lateral cortex in reptiles is homologous to the piriform cortex in birds and mammals. The anterior dorsal ventricular ridge in reptiles is probably homologous to the neostriatum and ventral hyperstriatum in birds and to the endopiriform nucleus in mammals. The posterior dorsal ventricular ridge in reptiles is most likely homologous to the archistriatum in birds and to the pallial amygdala in mammals. The pallial thickening in reptiles is probably homologous to the dorsal and intercalated portions of the hyperstriatum in birds and to the claustrum proper in mammals. Finally, the dorsal cortex in reptiles is probably homologous to the accessory hyperstriatum and parahippocampal area in birds and to the isocortex in mammals. These hypotheses of homology imply relatively minor evolutionary changes in development but major changes in neuronal connections. Most significantly, they imply the independent elaboration of thalamic sensory projections to derivatives of the lateral and dorsal pallia in sauropsids and mammals, respectively. They also imply the independent evolution of lamination in the pallium of birds and mammals.

The Telencephalon of Tetrapods in Evolution; pp. 205–213

Numerous scientists have sought a homologue of mammalian isocortex in sauropsids (reptiles and birds) and a homologue of sauropsid dorsal ventricular ridge in mammals. Although some of the proposed theories were enormously influential, alternative theories continued to coexist, primarily because the striking differences in pallial organization between adult mammals, sauropsids, and amphibians enabled different authors to enlist different subsets of similarity data in support of different hypotheses of putative homology. A phylogenetic analysis based on parsimony cannot discriminate between such alternative hypotheses of putative homology, because sauropsids and mammals are sister groups. One solution to this dilemma is to include embryological patterns of telencephalic organization in the comparative analysis. Because early developmental stages in different taxa tend to resemble each other more than the adults do, the embryological data may reveal intermediate patterns of organization that provide unambiguous support for a single hypothesis of putative homology. The validity of this putative homology may then be supported by means of a phylogenetic analysis based on parsimony. A comparative analysis of pallial organization that includes embryological data suggests the following set of homologies. The lateral cortex in reptiles is homologous to the piriform cortex in birds and mammals. The anterior dorsal ventricular ridge in reptiles is probably homologous to the neostriatum and ventral hyperstriatum in birds and to the endopiriform nucleus in mammals. The posterior dorsal ventricular ridge in reptiles is most likely homologous to the archistriatum in birds and to the pallial amygdala in mammals. The pallial thickening in reptiles is probably homologous to the dorsal and intercalated portions of the hyperstriatum in birds and to the claustrum proper in mammals. Finally, the dorsal cortex in reptiles is probably homologous to the accessory hyperstriatum and parahippocampal area in birds and to the isocortex in mammals. These hypotheses of homology imply relatively minor evolutionary changes in development but major changes in neuronal connections. Most significantly, they imply the independent elaboration of thalamic sensory projections to derivatives of the lateral and dorsal pallia in sauropsids and mammals, respectively. They also imply the independent evolution of lamination in the pallium of birds and mammals.

Intrinsic connections in the anterior dorsal ventricular ridge of the lizard psammodromus algirus

We have studied the intrinsic connections of the anterior dorsal ventricular ridge (ADVR) in the lacertid lizard Psammodromus algirus by means of retrograde transport of horseradish peroxidase (HRP) and fluorescent labeling with the lipophilic carbocyanine dye DiI. We injected HRP into different regions in the ADVR arrayed in a medial-to-lateral sequence, with each consisting of three distinct superficial-to-deep zones. When HRP was injected into a given region, many labeled neurons (always located ipsilateral to the injection site) were found at all mediolateral regions of ADVR in locations rostrally distant from the injection site. DiI crystals were applied on different superficial-to-deep zones within each region. Two patterns could be recognized: DiI crystals applied on the periventricular (most superficial) zone resulted in a labeling of cells widely distributed throughout the ADVR independently of the mediolateral region of the application site, whereas DiI crystals applied on deeper zones resulted in a staining of cells mostly restricted to a narrow radial area. Results from both types of labeling confirm that the ADVR has a prominent radial component in its intrinsic organization, but they also demonstrate that some areas of the ADVR receive projections from distant, rostrally located neurons in every ipsilateral region of the ridge itself, which establishes a clear non-radial component. This organization may have important functional properties with regard to a putative integration of different sensory modalities conveyed by thalamic afferent fibers to the ADVR. Last, we analyzed some evolutionary implications of our results. © 1996 Wiley-Liss, Inc.

Intrinsic connections in the anterior dorsal ventricular ridge of the lizard Psammodromus algirus.

We have studied the intrinsic connections of the anterior dorsal ventricular ridge (ADVR) in the lacertid lizard Psammodromus algirus by means of retrograde transport of horseradish peroxidase (HRP) and fluorescent labeling with the lipophilic carbocyanine dye DiI. We injected HRP into different regions in the ADVR arrayed in a medial-to-lateral sequence, with each consisting of three distinct superficial-to-deep zones. When HRP was injected into a given region, many labeled neurons (always located ipsilateral to the injection site) were found at all mediolateral regions of ADVR in locations rostrally distant from the injection site. DiI crystals were applied on different superficial-to-deep zones within each region. Two patterns could be recognized: DiI crystals applied on the periventricular (most superficial) zone resulted in a labeling of cells widely distributed throughout the ADVR independently of the mediolateral region of the application site, whereas DiI crystals applied on deeper zones resulted in a staining of cells mostly restricted to a narrow radial area. Results from both types of labeling confirm that the ADVR has a prominent radial component in its intrinsic organization, but they also demonstrate that some areas of the ADVR receive projections from distant, rostrally located neurons in every ipsilateral region of the ridge itself, which establishes a clear non-radial component. This organization may have important functional properties with regard to a putative integration of different sensory modalities conveyed by thalamic afferent fibers to the ADVR. Last, we analyzed some evolutionary implications of our results.

Adult neurogenesis in the telencephalon of a lizard: a [ 3H]thymidine autoradiographic and bromodeoxyuridine immunocytochemical study

A qualitative and quantitative evaluation of adult neurogenesis in the telencephalon of a lizard was conducted using [ 3H]thymidine autoradiography and immunocytochemical detection of 5′-bromodeoxyuridine (BrdU). The sites of cell proliferation, the fate, and the phenotype of cells born in adulthood were determined by short and long survival experiments (7 and 30 days). Adult specimens of the Moorish gecko, Tarentola mauritanica (Sauria, Gekkonidae), received subcutaneous injections of either BrdU or [ 3H]thymidine. Seven days after BrdU administration most labelled cells were in the walls (ventricular zone; VZ) of the lateral ventricles, particularly close to the sulcal zones. Labelled cells in the VZ of other ventricles were practically absent. Following 30 days, labelled cells outside the VZ were seen in most telencephalic regions: olfactory bulbs (OB), medial, dorsal, and lateral cortices (MC, DC, LC), anterior dorsal ventricular ridge (ADVR), nucleus sphericus (NS), and striatum (St). Electron microscopic examination of [ 3H]thymidine labelled cells found in these areas revealed their neuronal identity. No labelled neurons were detected in the dorsomedial cerebral cortex (DMC), septum (Sp), or elsewhere in the telencephalon. We conclude that neurogenesis occurs in most regions of the adult lizard telencephalon. The most intense neuronal production occurs in the MC. Other telencephalic regions, such as the OB, ADVR, and NS, also show a considerable rate of adult neurogenes. We infer from our results that the new neurons are born in the walls of the lateral ventricles and then migrate to their destinations. Furthermore, we report some evidence suggesting that neurons formed in adulthood in the olfactory bulbs are generated in the distant proliferative VZ. The functional significance of neurogenesis in the telencephalon of adult lizards in unclear, but it seems to be restricted to areas that have been implicated in olfactory plasticity, learning, and memory.

Multivariate statistical analysis of golgi stained neurons

The multivariate statistical analysis provides a useful method to study neuronal populations. It allows both the objective classification of neuronal types and the study of the morphological variation within a neuronal population. We report a particular example of the use of these techniques on a Golgi study of a complex telencephalic structure, the reptilian anterior dorsal ventricular ridge (aDVR). We present a R-mode factor analysis and a cluster analysis on the results of the factor analysis. Sixteen original variables were chosen for the study in order to obtain the greatest information about the cell body, the dendritic field and the location of 96 Golgi-stained cells. Six factors were obtained after the R-mode factor analysis, the interpretation of which was clear in five of them. This contributed to explain the morphological variation of the neuronal types within the aDVR. The cluster analysis classified the 96 cells into eight groups. Some groups could be ascribed to specific regions of the aDVR.

Monoaminergic innervation patterns in the anterior dorsal ventricular ridge of a lacertid lizard, Psammodromus algirus.

In contrast to the view of a diffuse monoaminergic innervation of the telencephalon, studies on the monoaminergic innervation in certain mammalian isocortical regions have shown a high degree of regional and laminar specificity. The present study was designed to examine the distribution patterns of dopamine, noradrenaline and serotonin in a telencephalic structure, the anterior dorsal ventricular ridge, of the sand lizard Psammodromus algirus (Lacertidae) using specific antibodies against each monoamine. The anterior dorsal ventricular ridge receives an abundant monoaminergic innervation compared to that of cortical telencephalic regions. The distribution of the different monoamines presented zonal and regional patterns throughout the ridge. The cell cluster zone was profusely innervated by catecholamines, whereas no serotoninergic fibers innervated the cell bodies in the cluster zone. On the other hand, the periventricular zone was heavily innervated by serotonin, but catecholaminergic fibers were almost lacking. With regard to regional patterns, dopamine exhibited major differences in the mediolateral axis of the anterior dorsal ventricular ridge: dopaminergic innervation was densest in the lateral region, which in other reptiles is described as a target of visual thalamic projections. Whereas the zonal pattern of the monoaminergic innervation of the anterior dorsal ventricular ridge seems to be a constant feature in the reptiles studied to date, the regional pattern varies among reptilian groups, especially taking into account the density of monoaminergic innervation.