摘要:

AbstractAs the first part of a comparative investigation of primate frontal cortex, we compared the frontal architectonic organization ofGalago, a small‐brained, strepsirhine (or “prosimian”) primate, to that of an anthropoid primate,Macaca, by using myelin‐ and Nissl‐stained material. We were able to distinguish many more areas in both taxa than have been recognized in most previous studies of the primate frontal lobe. In particular, we were able to subdivide many of the areas shown in the commonly cited architectonic map of Walker (J. Comp. Neurol. 73:59–86. 1940). Delineation of areas was greatly facilitated by the use of the Gallyas technique for staining myeli.The areal organization of much of frontal cortex (specifically, the premotor, orbital, and medial regions) appears to be very similar inGalagoandMacaca.In these regions, we were able to recognize the same complement of areas in both taxa, with few exceptions. In the granular frontal cortex (GFC), by contrast, we were able to distinguish about twice as many areas inMacacaas inGalago.For most of the GFC areas ofGalago, there are architectonically similar areas inMacaca; the areas shared by both taxa correspond mainly to the arcuate and superior areas ofMacaca(i.e., the region encompassed by Walker's areas 45, 8A, and 8B). However, there are many additional, more rostral, areas inMacacafor which there are no obvious homologues inGalago.In particular,Galagolacks cortex resembling the distinctive, lightly myelinated cortex of theMacacaprincipal sulcus (Walker's area 46 and its subdivisions)Our results are difficult to reconcile with the view that frontal lobe organization varies little across taxa. Rather, they suggest that granular frontal cortex underwent considerable change during primate evolution, including the addition of new areas in

ISSN:0092-7317    

DOI:10.1002/cne.903100402

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractA number of higher order association areas have been described in the parietal and temporal cortex of large‐brained anthropoid primates such asMacaca.However, little is known about the evolution of these areas, and the existence of homologous areas has not yet been clearly demonstrated in other mammalian groups. We addressed this issue by comparing the myelo‐ and cytoarchitecture of posterior association cortex in the anthropoidMacacato that of the small‐brained, strepsirhine (“prosimian”) primate Galag.Our results suggest thatGalagopossesses many, if not most, of the areas present inMacaca.We were able to identify regions inGalagowhich resembleMacacaposterior parietal area 7, superior temporal polysensory cortex (ST), inferotemporal visual cortex (IT), the temporoparietal auditory area (Tpt), and posterior parahippocampal cortex (areas TH and TF). Area 7, ST, and IT can each be subdivided further inMacaca, and for most of these subdivisions we were able to identify counterparts inGalago.However, we could not distinguish as many divisions of ST cortex inGalagoas inMacaca, and it is possible that new areas arose in this region during anthropoid evolution. There also appear to be general differences in architectonic organization between these animals, withMacacaexhibiting greater development of pyramidal layer IIIc and of the internal granular layer (IV) across much of the parieto‐temporal corte.These findings suggest that many, although possibly not all, of the parietal and temporal association areas present in the modern anthropoidMacacaevolved early in primate history, prior to the divergence of the lineages leading to strepsirhines and

ISSN:0092-7317    

DOI:10.1002/cne.903100403

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractModern studies of granular frontal cortex (GFC) in large‐brained, anthropoid primates, such asMacaca, indicate that this region is comprised of many areal subdivisions. These areas vary in their architectonic appearance and each has a distinctive, diverse set of corticocortical connections. The great extent of the GFC region in anthropoids, and its high degree of areal parcellation, suggest that some GFC areas may be specializations of anthropoids, not found in other mammals. To investigate this possibility, we studied the corticocortical connections of GFC in the relatively small‐brained, strepsirhine primateGalago, with a series of eight tracer injections in the frontal cortex, and an additional eight injections of parietal and temporal cortex. Tracers used were wheat‐germ agglutinin conjugated to horseradish peroxidase and tritiated amino acid.Our results indicate thatGalagoGFC has strong, reciprocal connections with the parietal area‐7 complex and with higher‐order temporal areas; there are additional connections with extrastriate visual cortex, parahippocampal, and cingulate areas, and frontal cortex. Thus GFC has an extremely diverse array of cortical connections inGalago, as inMacaca.However, we also found that the pattern of parietofrontal connections is simpler inGalagothan inMacaca.Specifically, parietal areas project to fewer discrete zones within the GFC ofGalago, consistent with the view that these animals have fewer GFC areas thanMacaca.In addition,GalagoGFC possesses connections that specifically resemble those ofMacacaarcuate cortex, but lacks connectional patterns that are characteristic of principals cortex. These results are in accord with our previous architectonic studies, which indicated thatGalagodoes not possess homologues of principalis areas. We conclude that the arcuate areas are common elements of primate GFC organization, while the areas located within and adjacent to the principal sulcus are anthropoid specia

ISSN:0092-7317    

DOI:10.1002/cne.903100404

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractAs a starting point for understanding the development of the cerebral cortex in reptiles and for determining how reptilian cortical development compares to that in other vertebrate classes, we studied the appearance and morphological differentiation of cerebral cortical neurons in embryonic turtles.3H‐thymidine birthdate labeling and focal injections of horseradish peroxidase (HRP) in in vitro cortical slices revealed that replicating cells occupy the outer ventricular zone, and subsequently migrate to the ventricular surface where they divide. Postmitotic neurons begin differentiating and elaborating neurites while migrating back through the ventricular zone. On their arrival at the top of the ventricular zone, pyramidal and nonpyramidal neurons can be distinguished morphologically. Cells with multipolar apical dendritic tufts ascending in the marginal zone resemble immature pyramidal neurons. Neurons morphologically similar to these early pyramidal cells were retrogradely labeled by injections of the lipophilic tracer 1,1‐dioctadecyl‐3,3,3′,3′‐tetramethyl indocarbocyanine perchlorate (diI) in a known pyramidal cell target, the thalamus. Nonpyramidal neurons, resembling Cajal‐Retzius cells, had horizontally oriented long axons and dendrites coursing in the plexiform primordium, the future marginal zone. With further development morphological differences between cell types became accentuated, and pyramidal cell somata were segregated into a single cellular layer flanked by zones containing predominantly nonpyramidal cell.Axon elaboration occurred early in embryonic development, as pyramidal cells sent axonal branches to the septum, thalamus, and cortical targets soon after their generation, and the intracortical axonal plexus became increasingly dense during embryonic life. Over a similar time course the distribution of projecting neurons labeled by thalamic diI injections changed from an initial homogeneous distribution to a preferential location in the superficial half of the cellular laye.Results from this study demonstrate several features of cortical differentiation that are conserved in reptiles and mammals, including similar early morphological differentiation events, the early distinction of principal cell types, and the parallel development of pyramidal and nonpyramidal neurons. The context in which these similar developmental events occur, however, differs profoundly in reptiles and mammals, with differences in the timing and location of neurite elaboration and differences in the appearance and architectonic organization of the cortex. Comparison of cortical developmental patterns between reptiles and mammals shows that similar functional cortical circuits with balanced excitation and inhibition can emerge in diverse cortic

ISSN:0092-7317    

DOI:10.1002/cne.903100405

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractPyramidal and nonpyramidal neurons can be recognized early in the development of the cerebral cortex in both reptiles and mammals, and the neurotransmitters likely utilized by these cells, glutamate and gamma‐aminobutyric acid, or GABA, have been suggested to play critical developmental roles. Information concerning the timing and topography of neurotransmitter synthesis by specific classes of cortical neurons is important for understanding developmental roles of neurotransmitters and for identifying potential zones of neurotransmitter action in the developing brain. We therefore analyzed the appearance of GABA and glutamate in the cerebral cortex of embryonic turtles using polyclonal antisera raised against GABA and glutamat.Neuronal subtypes become immunoreactive for the putative amino acid neurotransmitters GABA and glutamate early in the embryonic development of turtle cerebral cortex, with nonpyramidal cells immunoreactive for GABA and pyramidal cells immunoreactive for glutamate. The results of controls strongly suggest that the immunocytochemical staining in tissue sections by the GABA and glutamate antisera corresponds to fixed endogenous GABA and glutamate. Horizontally oriented cells in the early marginal zone (stages 15–16) that are GABA‐immunoreactive (GABA‐IR) resemble nonpyramidal cells in morphology and distribution. GABA‐IR neurons exhibit increasingly diverse morphologies and become distributed in all cortical layers as the cortex matures. Glutamate‐immunoreactive (Glu‐IR) cells dominate the cellular layer throughout development and are also common in the subcellular layer at early stages, a distribution like that of pyramidal neurons and distinct from that of GABA‐IR nonpyramidal cell.The early organization of embryonic turtle cortex in reptiles resembles that of embryonic mammalian cortex, and the immunocytochemical results underline several shared as well as distinguishing features. Early GABA‐IR nonpyramidal cells flank the developing cortical plate, composed primarily of pyramidal cells, shown here to be Glu‐IR. The earliest GABA‐IR cells in turtles likely correspond to Cajal‐Retzius cells, a ubiquitous and precocious cell type in vertebrate cortex. Glutamate‐IR projection neurons in vertebrates may also be related. The distinctly different topographies of GABA and glutamate containing cells in reptiles and mammals indicate that even if the basic amino acid transmitter‐containing cell types are conserved in higher vertebrates, the local interactions mediated by these transmitters may diffe.The potential role of GABA and glutamate in nonsynaptic interactions early in cortical development is reinforced by the precocious expression of these neurotransmitters in turtles, well before they are required for synaptic transmission. The glutamate expression observed here provides a potential source of agonist for the spontaneous activation of glutamate receptors recently reported for embryonic cortical plate neurons (Blanton et al., 1990: Proc. Natl. Acad. Sci. USA87:8027–8030). The early emergence of amino acid neurotransmitter expression detailed in this study indicates a potential role for GABA‐ and glutamate‐mediated developmenta

ISSN:0092-7317    

DOI:10.1002/cne.903100406

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.903100401

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY