ISSN:0006-8977    

DOI:10.1159/000113271

出版商:S. Karger AG    

年代:1995

数据来源: Karger

ISSN:0006-8977    

DOI:10.1159/000113272

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

There are several reasons why we lack detailed and comprehensive theories of how isocortex evolved in the various lines of mammalian evolution. Although current methods allow cortical areas to be defined with a high degree of assurance, few taxa have been studied in detail, and even the most-studied taxa are incompletely understood. In addition, concepts persist from early studies, based on limited data, that confound current theories, and some theories of isocortical evolution have been based on questionable premises. Nevertheless, some conclusions are clearly supportable. Early mammals had small brains with proportionately little isocortex. Mammals with larger brains and proportionately more isocortex evolved in several lines of descent. All mammals appear to have roughly 20 cortical areas, 'the organs of the brain', in common as retentions from an early ancestor, with primary and secondary sensory fields occupying much of cortex. Some of these cortical areas have been greatly modified in some taxa to become significantly expanded in size, highly laminated structurally, or both. Numbers of areas have increased independently in several branches of mammalian evolution, and the functioning of large brains may be enhanced by having more subdivisions. Finally, over many generations new areas may emerge from old by the formation of functionally distinct modules within areas, followed by the fusion of modules to ultimately form separate areas.

ISSN:0006-8977    

DOI:10.1159/000113273

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

Certain aspects of thalamic organization in reptiles and mammals are reviewed. Features shared by the dorsal thalamus of reptiles and that of mammals include projection to the telencephalon, specific and non-specific non-telencephalic afferents, and input from the thalamic reticular nucleus. Differences between the dorsal thalamus of reptiles and that of mammals are the absence of reciprocal telencephalic efferents to the dorsal thalamus and lack of local circuit neurons in reptiles (with the exception of the dorsal geniculate complex in turtles) and their presence in mammals. A thalamic reticular nucleus is present in both reptiles and mammals. In both of these classes of vertebrates, this neuronal aggregate surrounds the dorsal thalamus along its lateral surface, projects to the dorsal thalamus, and is organized into sectors. In one group of reptiles, Caiman crocodilus, the sole reptilian group in which immunocytochemical features have been investigated in detail, the reticular nucleus contains at least three neuronal subpopulations: neurons immunoreactive for glutamic acid decarboxylase (GAD); neurons immunoreactive for parvalbumin; and cells that are not immunoreactive for parvalbumin or, probably, GAD. On the other hand, the reticular nucleus of mammals contains a single population of neurons immunoreactive for GAD, gamma amino butyric acid, and parvalbumin.

ISSN:0006-8977    

DOI:10.1159/000113274

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

In anamniotes, the dorsal thalamus comprises: (1) a caudal division, the collothalamus, which receives its predominant input from the midbrain roof and projects ipsilaterally to the telencephalon, predominantly to the striatum, and (2) a rostral division, the lemnothalamus, which predominantly receives a direct retinal (Iemniscal) input and projects bilaterally to the telencephalon, predominantly to the pallium. In amniotes, collothalamic nuclei relay visual, auditory, and somatosensory-multisensory inputs from the midbrain roof to the ipsilateral telencephalon, terminating in both striatum and pallium. For example, the collothalamic visual nuclei consist of the LP-pulvinar complex in mammals and nucleus rotundus in diapsid reptiles, birds, and turtles. Among amniotes, the latter nuclei are homologous to each other as discrete nuclei, as are the collothalamic auditory and collothalamic somatosensory-multisensory nuclei. Lemnothalamic nuclei (and nuclear groups) in amniotes predominantly (and/or plesiomorphically) receive Iemniscal inputs; some project to the telencephalon bilaterally, and most, in contrast to collothalamic nuclei, do not project to the striatum. In mammals, the lemnothalamic nuclei include most of those in the anterior, medial, intralaminar, and ventral nuclear groups and the dorsal lateral geniculate nucleus. In diapsid reptiles, they include the dorsomedial and dorsolateral anterior nuclei and the dorsal lateral optic nucleus; comparable nuclei are present in birds and turtles, with birds additionally having a discrete somatosensory Iemniscal relay nucleus. These lemnothalamic nuclei in each amniote radiation are homologous as a field to the lemnothalamus (i.e., nucleus anterior) in anamniotes. Both divisions of the dorsal thalamus were elaborated to some degree in the common ancestral amniote stock. A further major elaboration of the lemnothalamus characterized the ancestral stock of mammals and may have been one of the key events in early mammalian evolution. Birds have independently, to a lesser degree, elaborated the lemnothalamus.

ISSN:0006-8977    

DOI:10.1159/000113275

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

Recent studies of the limbic system of tetrapods have made data available that challenge some of the long-held tenets of forebrain evolution. Using the basic principle of parsimony – that the best hypotheses concerning homologies are those requiring the fewest number of evolutionary changes – we have reevaluated comparisons of tetrapod limbic systems. Given the current data, the following points appear to be justified: (1) the common ancestors of reptiles and mammals had a well-developed limbic system in which the basic subdivisions and connections of the amygdalar nuclei were established; (2) the ventral part of the lateral pallium in amphibians appears to be a single structure which corresponds to at least four areas in reptiles: centromedial DVR, ventral anterior amygdala, lateral amygdala, and part of the lateral cortex; (3) the medial pallium in amphibians appears to be homologous with the dorsal and medial cortices in reptiles and with the general and hippocampal cortices in mammals; (4) the cortical targets of the main olfactory bulb in reptiles and mammals appear to be homologous, and their common ancestor probably had a corresponding olfactory pallial field; (5) the targets of the accessory olfactory bulb in amphibians, reptiles, and mammals appear to be homologous, with the exception of nucleus sphericus in reptiles, which lacks an obvious homologue in non-reptiles.

ISSN:0006-8977    

DOI:10.1159/000113276

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

The basal ganglia in modern mammals, birds and reptiles (i.e. modern amniotes) are very similar in connections and neurotransmitters, suggesting that the evolution of the basal ganglia in amniotes has been very conservative. For example, the basal ganglia in all amniotes possess a dorsal striatum containing two main populations of projection neurons, substance P-containing (SP+) and enkephalin-containing (ENK+) neurons, which have major projections to the dorsal pallidum and the tegmentum (ventral tegmental area and substantia nigra, or VTA/SN). The VTA/SN, in turn, has a major dopaminergic (DA+) projection to the striatum in all amniotes. In this paper, we review these data on the basal ganglia in amniotes and note points of similarity and difference in the functional circuitry of the basal ganglia among amniotes. In addition, we review recent findings on the neurotransmitter organization and connectivity of the basal ganglia in amphibians and fishes, with the goal of assessing whether a basal ganglia showing the same basic features as in amniotes is observed in anamniotes. Published data indicate that in at least two groups of fishes (cartilaginous fishes and lungfishes) and apparently in amphibians, the basal ganglia is present and consists of a distinct striatum and pallidum. The striatum of amphibians, cartilaginous fishes, and lungfishes contain SP+ and ENK+ neurons that seem to project to the pallidum as well as to a brainstem cell group that appears comparable to the VTA/SN of amniotes. Data for ray-finned fishes also suggest the presence of a striatum containing SP+ and ENK+ neurons that projects to VTA/SN-like brainstem cell group. In the basal ganglia of ray-finned fishes, however, a distinct pallidum had not been identified. Finally, the brainstem cell group receiving striatal input in all anamniotes contains DA+ neurons that seem to project to the striatum. The present analysis suggests that a rudimentary basal ganglia was already present in the brain of the ancestral jawed vertebrates. This rudimentary basal ganglia likely consisted of a striatum and a pallidum, and the striatum probably already possessed the same basic connections and some of the same basic cell types as the basal ganglia of modern jawed vertebrates.

ISSN:0006-8977    

DOI:10.1159/000113277

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

The basal ganglia in modern mammals, birds and reptiles (i.e. modern amniotes) are very similar in connections and neurotransmitters, suggesting that the evolution of the basal ganglia in amniotes has been very conservative. For example, the basal ganglia in all amniotes possess a dorsal striatum containing two main populations of projection neurons, substance P-containing (SP+) and enkephalin-containing (ENK+) neurons, which have major projections to the dorsal pallidum and the tegmentum (ventral tegmental area and substantia nigra, or VTA/SN). The VTA/SN, in turn, has a major dopaminergic (DA+) projection to the striatum in all amniotes. In this paper, we review these data on the basal ganglia in amniotes and note points of similarity and difference in the functional circuitry of the basal ganglia among amniotes. In addition, we review recent findings on the neurotransmitter organization and connectivity of the basal ganglia in amphibians and fishes, with the goal of assessing whether a basal ganglia showing the same basic features as in amniotes is observed in anamniotes. Published data indicate that in at least two groups of fishes (cartilaginous fishes and lungfishes) and apparently in amphibians, the basal ganglia is present and consists of a distinct striatum and pallidum. The striatum of amphibians, cartilaginous fishes, and lungfishes contain SP+ and ENK+ neurons that seem to project to the pallidum as well as to a brainstem cell group that appears comparable to the VTA/SN of amniotes. Data for ray-finned fishes also suggest the presence of a striatum containing SP+ and ENK+ neurons that projects to VTA/SN-like brainstem cell group. In the basal ganglia of ray-finned fishes, however, a distinct pallidum had not been identified. Finally, the brainstem cell group receiving striatal input in all anamniotes contains DA+ neurons that seem to project to the striatum. The present analysis suggests that a rudimentary basal ganglia was already present in the brain of the ancestral jawed vertebrates. This rudimentary basal ganglia likely consisted of a striatum and a pallidum, and the striatum probably already possessed the same basic connections and some of the same basic cell types as the basal ganglia of modern jawed vertebrates.

ISSN:0006-8977    

DOI:10.1159/000316270

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

The comparative interpretation of forebrain organization of the ray-finned fishes presents a number of challenges. The telencephalon develops by an eversion process, and much of its surface is ventricular rather than pial. A topological map of the ventricular surface shows that the area ventralis (presumed subpallium) is bordered dorsally by the dorsomedial (DM) zone of the area dorsalis, which is, in turn, bordered by the olfactory-recipient dorsoposterior (DP) zone of the area dorsalis. Within the diencephalon small dorsal and ventral thalami and a large group of migrated nuclei assigned to the posterior tuberculum (but of uncertain status) are present. Both the dorsal thalamus and the migrated nuclei of the posterior tuberculum project to the telencephalon. A review of the known connections of the four major zones of the area dorsalis together with their topological positions leads to the following tentative interpretations. Zone DP is homologous to the primary olfactory cortex. There is not enough information concerning the dorsodorsal zone (DD) to speculate on its comparative relationships. Zone DM is a limbic-like area lying between the subpallium and the olfactory pallium and is possibly homologous to the pallial amygdala. The dorsolateral zone (DL) displays a pattern of connectivity with the cerebellum and the optic tectum suggesting a possible homology with non-olfactory, non-limbic pallial areas. Caveats are raised concerning the above interpretations of DM and DL. One or both of them may have evolved independently of the telencephalic zones in tetrapods and may thus represent examples of homoplasy.

ISSN:0006-8977    

DOI:10.1159/000113278

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

A morphotype of the forebrain of gnathostomes, i.e. those characters that must have been present in the forebrain of ancestral gnathostomes, was generated by using out-group analysis to identify the shared primitive characters present in the forebrains of extant gnathostomes. The nature of morphotypes and the steps in generating a morphotype are described. Because hypotheses of phylogenetic relationships profoundly affect the resulting morphotype, current hypotheses of gnathostome interrelationships are reviewed, and particular attention is paid to the problematic relationships of lobe-finned fishes. Ontogenetic studies provide the most common basis for how neural characters are grouped, and a review of the developmental literature indicates that gnathostome forebrains are segmented, with the diencephalon arising from a rostral parencephalic neuromere, which subsequently forms anterior and posterior divisions, and a more caudal synencephalic neuromere. Unfortunately, there is no agreement concerning the number of segments that form the secondary prosencephalon (telencephalon and hypothalamus). For this reason, the characters of the secondary prosencephalon must be analyzed in a topological manner. An out-group analysis of the characters of the diencephalon of extant gnathostomes reveals that the diencephalon of ancestral gnathostomes must have arisen from three segments: an anterior parencephalic segment, which gave rise to intermediate, ventrolateral and ventromedial thalamic nuclei; a posterior parencephalic segment, which gave rise to dorsal and ventral habenular nuclei, anterior, dorsal posterior, dorsal central, and, possibly, lateral posterior thalamic nuclei, and posterior tubercular nuclei; a synencephalic segment, which gave rise to pretectal nuclei, accessory optic nuclei and the nucleus of the medial longitudinal fascicle. The pretectal and posterior tubercular regions of ray-finned fishes appear to be highly derived, due to extensive cellular proliferations that give rise to numerous nuclei. The secondary prosencephalon of ancestral gnathostomes was probably divided rostrally into inverted and evaginated cerebral hemispheres, with paired olfactory bulbs arising directly from the hemispheres, and caudally into preoptic and hypothalamic areas. The cerebral hemispheres likely comprised a dorsally situated pallium divided into medial, dorsal and lateral pallial formations, as well as an intercalated pallial nucleus situated ventrolateral to the lateral pallium, and a ventrally situated subpallium divided medially into septal nuclei and a medial amygdalar nucleus and laterally into a corpus striatum. Both pallial and subpallial centers of ancestral gnathostomes probably received ascending thalamic and posterior tubercular inputs, with telencephalic efferent pathways terminating primarily in the hypothalamus, posterior tubercle and midbrain tegmentum. An out-group analysis further indicates that some taxa in each gnathostome radiation exhibit highly derived telencephalic characters due to the independent expansion of one or more pallial formations.

ISSN:0006-8977    

DOI:10.1159/000113279

出版商:S. Karger AG    

年代:1995

数据来源: Karger