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PubMed1981

The structure of the mediodorsal cerebral cortex in the lizard Agama agama: a Golgi study.

A Golgi analysis was made of the cell types present in the mediodorsal cerebral cortex of the lizard Agama agama. Mediodorsal cortex can be divided into two areas, small-celled mediodorsal cortex (sMDC) and large-celled mediodorsal cortex (lMDC). Both sMDC and lMDC are four-layered cortices: superficial plexiform layer, cellular layer, deep plexiform layer and fiber layer, lMDC partially overlaps dorsal cortex (medial superposition). Using characteristics of the dendrites and criteria of location, dendritic field shape and soma size, two classes of neurons can be distinguished in sMDC. The first class consists of two types of solitary cells present in the superficial and deep plexiform layers and in the fiber layer. The second class consists of six types of pyramidal-like candelabra cells, composing the cellular layer. In lMDC solitary cells are also present in the superficial and deep plexiform layers and in the fiber layer. Large pyramidal cells of one type lie in the cellular layer. In addition, neurons of the dorsal cortex and of the ventral cell plate of Unger lie in the medial superposition area of lMDC. Throughout the entire mediodorsal cortex, protoplasmic and fibrous astrocytes and ependymal tanycytes are found.

Animals↗

PubMed1982

Convergence of autonomic and limbic connections in the insular cortex of the rat.

The connections of the insular cortex in the rat were studied by using the anterograde and retrograde transport of wheat germ agglutinin-conjugated-horseradish peroxidase. Both anterograde and retrograde transport were seen in the ipsilateral lateral frontal, infralimbic, piriform, and perirhinal cortical areas and in the contralateral insular cortex. In the thalamus, both types of labeling were seen in the mediodorsal and ventroposteromedial parvocellular nuclei; primarily retrograde labeling was seen in the centromedial and paracentral nuclei. In the basal forebrain, anterograde labeling was seen in the lateral part of the bed nucleus of the stria terminalis and in the central nucleus of the amygdala, while retrogradely labeled neurons were found in the magnocellular basal nucleus and in the lateral and the basolateral amygdaloid nuclei. Both types of labeling were seen in the posterior lateral hypothalamic area; the tuberomammillary nucleus contained retrogradely labeled neurons bilaterally. In the midbrain, retrogradely labeled neurons were found in the ventral tegmental area and in the dorsal and superior central raphe nuclei. In the pons, both retrogradely and anterogradely transported label was seen bilaterally in the parabrachial nucleus, primarily in the ventromedial caudal part of the medial subnucleus. Retrogradely labeled neurons were found bilaterally in the locus coeruleus. Anterograde transport was followed into the medulla, bilaterally but more heavily in the contralateral side. Labeled axons appeared to terminate in a topographic pattern in the nucleus of the solitary tract. These results indicate that the insular cortex of the rat is an important part of the highly interconnected central autonomic system. Furthermore, the autonomic representation in the insular cortex may be organized in a viscerotopic manner. The insular cortex also has connections with the limbic system and with the lateral frontal cortical system. Although it is not yet clear whether these connections converge upon the same neurons within the insular cortex, earlier physiological data suggest that each of the diverse systems of connections of this area receives relayed vagal inputs. The insular cortex of the rat may contain a primary cortical visceral representation, and its connections may underlie autonomic integration with behavioral and emotional events.

Amygdala↗

PubMed1984

Cortical and thalamic afferent connections of the insular and adjacent cortex of the cat.

The thalamo-cortical and cortico-cortical afferents of the cat's insular cortex were investigated with the retrograde horseradish peroxidase technique. The most prominent loci of thalamic labeling were the suprageniculate nucleus and parts of the posterolateral nucleus. Injections into the anterior part of the insular cortex also resulted in labeled cells in the ventromedial posterior nucleus and in the intralaminar nuclei, while injections into posterior parts revealed projections from the medial and dorsal parts of the medial geniculate nucleus. Only the anterior and most ventral parts of the insular cortex overlying the anterior rhinal sulcus were connected with the mediodorsal nucleus of the thalamus. All injections into the gyrus sylvius anterior showed a specific pattern of cortical afferents: With the exception of the labeling in the prefrontal cortex and the inferotemporal region, the labeled cells were very narrowly restricted to the presylvian, the suprasylvian, and the splenial sulcus. The thalamic neurons projecting to the cortex were generally organized in a bandlike pattern which crossed nuclear borders. The majority of the cortico-cortical connections originated from sulcal areas next to the prefrontal, parietal, and cingulate cortex, that is, next to so-called association cortices. In the light of the present results the role of the insular cortex as a multifunctional association area is discussed, as well as its relation to other cortical centers.

Afferent Pathways↗

PubMed1989

Comparative distributions of dopamine D-1 and D-2 receptors in the cerebral cortex of rats, cats, and monkeys.

The distributions and laminar densities of cerebral cortical dopamine D-1 and D-2 receptors were studied in rats, cats, and monkeys. Distributions were determined by using alternate, adjacent tissue sections processed for D-1 and D-2 receptor subtypes and compared to an adjacent, nearly adjacent, or similar sections stained for Nissl substance. [3H]-SCH 23390 and [3H]-spiroperidol (in the presence of 100 nM mianserin) were used to label the D-1 and D-2 receptors, respectively. The regional distribution and laminar density of dopamine receptors were determined by in vitro quantitative autoradiography and video densitometry of selected isocortical and peri-allocortical regions. Granular (prefrontal, primary somatosensory, and primary visual), agranular (primary motor and anterior cingulate), and limbic (entorhinal and perirhinal) cortices were examined. Where possible, homologous areas among the species were compared. The D-1 receptor was present in all regions and laminae of the cerebral cortex of rats, cats, and monkeys. The regional densities for the D-1 receptor were higher in the cat and monkey than in the rat. The rat D-1 receptor displayed a relatively homogeneous laminar pattern in most regions except that the deeper laminae (V and VI) contained more receptors than the superficial layers. The cats and monkeys, however, had distinctly heterogeneous laminar patterns in all regions of cortex that varied from one region to another and were quite different from that seen in the rat. The cats and monkeys had highest densities of the D-1 receptor in layers I and II and lowest densities in layers III and IV, whereas layers V and VI were intermediate. The density of D-1 receptors was greater than the density of D-2 receptors in all regions and laminae of cerebral cortex of the cat and monkey and greater in most regions and laminae of the rat cerebral cortex. The D-2 receptor was also distributed in all regions of the cerebral cortex of rats, cats, and monkeys. The D-2 receptor was very homogeneous in its regional distribution and laminar pattern compared to the D-1 receptor in all 3 species. The D-2 receptor was denser in the superficial layers (I and II) of the cortex than in the deeper layers in the rats, but more homogeneous in the different laminae of the cat and monkey cerebral cortex. The rat cortical D-2 receptor exceeded the D-1 receptor in restricted laminae of selective regions.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1990

Regional distribution of binding sites for neuropeptide Y in cat and monkey visual cortex determined by in vitro receptor autoradiography.

The goal of this study was to elucidate the precise regional and laminar distribution of neuropeptide Y (NPY) binding sites in feline and primate visual cortex. By means of in vitro receptor autoradiography, NPY binding sites in primate and feline visual cortex were specifically labeled with 3H-NPY. In cat area 17, the highest density of NPY-binding sites was present in lamina I and the upper half of lamina II. The density then gradually decreased towards lamina VI. Areas 18 and 19 exhibited a similar binding site-density profile. The decrease in density from superficial to deep layers was more gradual in area 18 than in areas 17 and 19. In monkey primary visual cortex (V1), layer IVc presented a high concentration of NPY binding sites, in addition to a dense zone of binding sites in layer I. Monkey secondary visual cortex (V2) displays a similar dense zone in layer I, but lacks such high density of NPY binding sites in layer IV. Therefore, the border between primary and secondary visual cortex coincides with the abrupt disappearance of this latter high density in layer IV. In cat as well as in monkey visual cortex, no significant differences were found between regions representing central vision and those representing the peripheral parts of the visual field. Comparison of our results for NPY binding sites with the distribution of alpha 1-adrenergic receptors, as recently described by Rakic et al. (J. Neurosci. 8(10):3670-3690, 1988) for primate and Parkinson et al. (Brain Res. 457:70-78, 1988) for feline visual cortex, revealed that those two patterns are very similar.

Animals↗

PubMed1990

Ventral temporal cortex in the rat: connections of secondary auditory areas Te2 and Te3.

The present study in the rat deals with the hodological organization of two cytoarchitectonically distinct areas lying caudoventrally (Te2) or ventrally (Te3) to the primary auditory area (Te1). The afferent and efferent systems of connections were identified by using the properties of retrograde and anterograde transport of wheat germ agglutinin conjugated with horseradish peroxidase (WGA-HRP). Large tracer deposits in the ventral temporal cortex involving Te2, Te3, and the dorsal bank of the perirhinal cortex induced a dense retrograde and anterograde pattern of labeling in the following nuclei of the medial geniculate (MG) complex: caudodorsal (MGCD), dorsal (MGD), medial (MGM), suprageniculate (SG), and peripeduncular area (PPA). The ventral nucleus (MGV) was only slightly labeled in its caudal division. Several extrageniculate structures were also labeled. Retrograde cell labeling occurred in centers giving rise to ascending systems of diffuse projections: locus coeruleus (LC), dorsal raphe nucleus (DR), and basal magnocellular nucleus (B). Slight anterograde labeling was present in the dorsal and external cortices of the inferior colliculus (IC), central gray, deep layers of the superior colliculus (SC), reticular thalamic nucleus (RT), and caudate putamen (CPU). Callosal connections were also noted with the contralateral homotopic cortex. In the cases in which there was a notable extension of the zone of diffusion of the tracer into the dorsal bank of the perirhinal cortex, a characteristic pattern of labeling in the subparafascicular, reuniens and paraventricular thalamic nuclei, mammillary complex, lateral and dorsal hypothalamic nuclei, amygdaloid complex, laterodorsal tegmental nucleus, subiculum, and retrosplenial cortex was displayed. Tracer deposits restricted to Te2 induced a dense labeling of the caudal, ventrolateral MGD, lateral PPA and, to a lesser extent, MGCD. The MGM and SG were only slightly labeled. Extrageniculate afferents essentially consist of sparse projections from LC, DR, and B, whereas efferent fibers are directed to the dorsal cortex of the IC, central gray, deep SC layers, and CPU. Callosal connections were also identified. Following tracer deposits restricted to Te3, dense labeling occurred in the MGD, mostly in its medial division, in the caudal MGM, and in the PPA. The MGCD, SG, and MGV were only sparsely labeled. Extrageniculate afferents arise from LC, DR, and B, and efferents are directed to the RT and dorsal cortex of the IC. Contralateral connections with the homotopic cortical area were also noted. Te2 and Te3 share some degree of similitude in their pattern of connections with the MG complex.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1991

Architectonics of the parietal and temporal association cortex in the strepsirhine primate Galago compared to the anthropoid primate Macaca.

A number of higher order association areas have been described in the parietal and temporal cortex of large-brained anthropoid primates such as Macaca. 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 anthropoid Macaca to that of the small-brained, strepsirhine ("prosimian") primate Galago. Our results suggest that Galago possesses many, if not most, of the areas present in Macaca. We were able to identify regions in Galago which resemble Macaca posterior 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 in Macaca, and for most of these subdivisions we were able to identify counterparts in Galago. However, we could not distinguish as many divisions of ST cortex in Galago as in Macaca, 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, with Macaca exhibiting greater development of pyramidal layer IIIc and of the internal granular layer (IV) across much of the parieto-temporal cortex. These findings suggest that many, although possibly not all, of the parietal and temporal association areas present in the modern anthropoid Macaca evolved early in primate history, prior to the divergence of the lineages leading to strepsirhines and anthropoids.

Animals↗

PubMed1991

Ipsilateral cortical connections of granular frontal cortex in the strepsirhine primate Galago, with comparative comments on anthropoid primates.

Modern studies of granular frontal cortex (GFC) in large-brained, anthropoid primates, such as Macaca, 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 primate Galago, 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 acids. Our results indicate that Galago GFC 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 in Galago, as in Macaca. However, we also found that the pattern of parietofrontal connections is simpler in Galago than in Macaca. Specifically, parietal areas project to fewer discrete zones within the GFC of Galago, consistent with the view that these animals have fewer GFC areas than Macaca. In addition, Galago GFC possesses connections that specifically resemble those of Macaca arcuate cortex, but lacks connectional patterns that are characteristic of principalis cortex. These results are in accord with our previous architectonic studies, which indicated that Galago does 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 specializations.

Animals↗

PubMed1991

Appearance of putative amino acid neurotransmitters during differentiation of neurons in embryonic turtle cerebral cortex.

Pyramidal 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 glutamate. 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 cells. 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 differ. 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.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1991

Serotoninergic innervation of the ferret cerebral cortex. II. Postnatal development.

We have investigated the serotoninergic innervation of the ferret cortex from the day of birth to adulthood with immunohistochemical techniques. Due to the premature birth of ferrets, this period spans the entire generation of cells located within the upper cortical layers and their subsequent migration to their final positions. Already at birth, serotoninergic fibers innervate the developing cortex. This innervation is most dense within the marginal zone, the subplate region, and the lower portion of the cortical plate. As long as cell migration continues, serotoninergic fibers enter the expanding portions of the cortex. Only the region just below the marginal zone where newly arriving cells are added to the cortical plate is not innervated by the ingrowing fibers. When the bulk of cell migration ceases, during the third postnatal week, this gap disappears and the fibers gradually form a continuous innervation from the pia to the ventricle. As the cortex matures, the serotoninergic fibers become successively confined to the upper layers, to generate the adult pattern. In the adult ferret cortex, the highest innervation density is found within layers 1, 2, and 3, with a much sparser innervation within the lower layers (Voigt and de Lima, J. Comp. Neurol. 314:403-414, 1991). The dense innervation in the deep cortical layers is only transient, virtually disappearing toward adulthood. These results suggest that serotoninergic axons innervate cortical layers as soon as newly arriving cells reach their final positions within the cortex. This early innervation lends support to the idea that serotonin may play a role during development of the cerebral cortex.

Aging↗

PubMed1991

Development of the projections from the dorsal lateral geniculate nucleus to the lateral suprasylvian visual area of cortex in the cat.

In the study reported in the preceding paper, we used retrograde labeling methods to show that the enhanced projection from the thalamus to the posteromedial lateral suprasylvian (PMLS) visual area of cortex that is present in adult cats following neonatal visual cortex damage arises at least partly from surviving neurons in the dorsal lateral geniculate nucleus (LGN). In the C layers of the LGN, many more cells than normal are retrogradely labeled by horseradish peroxidase (HRP) injected into PMLS cortex ipsilateral to a visual cortex lesion. In addition, retrogradely labeled cells are found in the A layers, which normally have no projection to PMLS cortex in adult cats. The purpose of the present study was to investigate the mechanisms of this enhanced projection by examining the normal development of projections from the thalamus, especially the LGN, to PMLS cortex. Injections of HRP were made into PMLS cortex on the day of birth or at 1, 2, 4, or 8 weeks of age. Retrogradely labeled neurons were present in the lateral posterior nucleus, posterior nucleus of Rioch, pulvinar, and medial interlaminar nucleus, as well as in the LGN, at all ages studied. Within the LGN of the youngest kittens, a small number of retrogradely labeled cells was present in the interlaminar zones and among the cells in the A layers that border these zones. Such labeled cells were virtually absent by 8 weeks of age, and they are not found in normal adult cats. Sparse retrograde labeling of C-layer neurons also was present in newborn kittens.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗

PubMed1993

Histochemical localization of synaptic zinc in the developing cat visual cortex.

The terminal boutons of many neurons in the telencephalon are known to contain a vesicle-bound, chelatable pool of zinc (Zn2+) that can be selectively visualized with histochemical procedures. In this paper, the normal laminar, areal, and ultrastructural distribution of histochemically reactive zinc in the visual cortex of the adult cat as well as its development from birth are described. In the adult cat visual cortex, intense zinc staining was found in layers I, II, III, and V, with layer VI staining only lightly. The primary geniculostriate input zone, layer IV, was conspicuously distinguished by the relative absence of zinc. This distinct pattern was restricted only to areas 17 and 18 and differentiated them from adjacent cortical area 19 laterally and the subadjacent cingulate cortex. The earliest zinc-positive staining in visual cortical areas 17 and 18 was first apparent by postnatal day 2 (P2) and was characterized by staining of a thin layer at the bottom of the cortical plate. By P10, and continuing through P20, synaptic zinc formed a trilaminar pattern of dense staining in areas 17 and 18, which included the top of layer I, and layers III and V. The laminar pattern of synaptic zinc in visual cortex appeared mature by P30, except that the distribution of zinc in layer IV was not uniform. This was most apparent around P50 in tangential sections through layer IV from opened and flattened cortex, where columnar patches of increased zinc staining were apparent in area 17. These columns were approximately 400 microns in diameter, with a centre-to-centre spacing of approximately 900 microns. The distribution of synaptic zinc apparently reflects the process of synaptic maturity of the cat visual cortex and appears to demarcate a particular form of columnar organization in visual cortex.

Animals↗

PubMed1993

Input organization of distal and proximal forelimb areas in the monkey primary motor cortex: a retrograde double labeling study.

The present double-labeling study was designed to demonstrate the morphological framework for motor control in coordinated distal and proximal forelimb movements, which may partly, at least, depend on corticocortical and thalamocortical inputs to the forelimb area in the primary motor cortex. After intracortical microstimulation mapping of the forelimb area in the primary motor cortex of four macaque monkeys, a retrograde tracing study with fluorescent dyes was attempted to label simultaneously neurons in cortical and subcortical sites projecting to the distal forelimb representation area and those projecting to the proximal representation area of the primary motor cortex. Neurons projecting to distal and proximal forelimb parts of the primary motor cortex were largely separate in the following areas: the premotor area, primary somatosensory area, secondary somatosensory area, area 5, and thalamus. In contrast, there was no precise topographic organization of labeled projection neurons in the following areas: the supplementary motor area, cingulate motor area, primary motor cortex adjacent to the injection sites, claustrum, and basal nucleus of Meynert. The present study revealed that the forelimb area of the primary motor cortex receives both segregated and intermixed inputs from cortical and subcortical sources. In particular, the fact that the forelimb area of the primary motor cortex receives topographically organized inputs from the premotor area and nontopographically organized inputs from the supplementary motor area and cingulate motor area indicates possible different functional roles of frontal premotor areas in control of coordinated distal and proximal forelimb movements.

Animals↗

PubMed1994

Pyramidal neurons in layer 5 of the rat visual cortex. I. Correlation among cell morphology, intrinsic electrophysiological properties, and axon targets.

Previous work has established two structure/function correlations for pyramidal neurons of layer 5 of the primary visual cortex of the rat. First, cells projecting to the superior colliculus have thick apical dendrites with a florid terminal arborization in layer 1, whereas those projecting to the visual cortex of the opposite hemisphere have thinner apical dendrites that terminate below layer 1, without a terminal tuft (e.g., Hallman et al.: J Comp Neurol 272:149, '90). Second, intracellular recording combined with dye injection has revealed two classes of cells: the first has a thick, tufted apical dendrite and fires a distinctive initial burst of two or more impulses, of virtually fixed, short interspike interval, in response to current injection; and the other, with a slender apical dendrite lacking a terminal tuft, tends to have a longer membrane time constant and higher input resistance, and does not fire characteristic bursts (e.g., Larkman and Mason: J Neurosci 10:1407, '90). The present study combined intracellular recording in isolated slices of rat visual cortex and injection of carboxyfluorescein, to reveal soma-dendritic morphology, with prior injection of rhodamine-conjugated microspheres into the superior colliculus or contralateral visual cortex to label neurons according to the target of their axons. This permitted a complete correlation of morphology, intrinsic electrophysiological properties, and identity of the projection target for individual pyramidal cells. Neurons retrogradely labeled from the opposite visual cortex were found in all layers except layer 1 while those labeled from the superior colliculus lay exclusively in layer 5. Within layer 5 interhemispheric cells were more concentrated in the lower half of the layer but extensively overlapped the distribution of corticotectal cells. Every cell studied that projected to the superior colliculus was of the bursting type and had a thick apical dendrite with a terminal tuft. Every cell in this study projecting to the opposite visual cortex was a "nonburster" and had a slender apical dendrite with fewer oblique branches that ended without a terminal tuft, usually in the upper part of layer 2/3. Interhemispheric cells also had rounder, less conical somata and generally had fewer basal dendrites than corticotectal neurons. Many cells with the physiological and morphological characteristics of interhemispheric cells were not back-labeled from the opposite visual cortex, implying that pyramidal cells of this type can have other projection targets (e.g., other cortical sites in the ipsilateral hemisphere).(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗

PubMed1995

Development of basal forebrain projections to visual cortex: DiI studies in rat.

We performed experiments using retrograde and anterograde labeling with DiI to examine the development of basal forebrain (BFB) projections to the visual cortex in postnatal rats. DiI placed in occipital cortex led to retrograde labeling of BFB neurons as early as postnatal day 0 (P0); labeled cells were found mainly in the diagonal band complex but also in the medial septum, globus pallidus, and substantia innominata. The retrogradely labeled BFB cells displayed remarkably well-developed dendritic arbors, even in younger animals, and showed increases in soma size, dendritic arbors, and dendritic spines over the first 2 postnatal weeks. DiI placements in the diagonal band led to anterogradely labeled axons in cortex. At early ages (P0-P1), labeled axons were largely confined to white matter. With increasing age, greater numbers of labeled axons were seen in the white matter and in deep cortical layers, and labeled axons extended into superficial layers. The leading edge of labeled fibers reached layer V of visual cortex by P2 and layer IV by P4 and were found throughout the cortical layers by P6. Numbers and densities of labeled axons in visual cortex were greater in older animals, at least through P14. The time of ingrowth of labeled BFB axons into visual cortex indicates that these afferents grow into particular cortical layers after those layers have differentiated from the cortical plate. These data indicate that basal forebrain projections arrive in occipital cortex after cortical lamination is well underway and after the entry of primary thalamocortical projections.

Animals↗

PubMed1995

Two rules for callosal connectivity in striate cortex of the rat.

In the rat, callosal cells occupy lateral as well as medial portions of striate cortex. In the region of the border between areas 17 and 18, which contains a representation of the vertical meridian of the visual field, cells projecting through the corpus callosum are concentrated throughout the depth of the cortex. In contrast, in medial portion of striate cortex, where peripheral portions of the visual field are represented, callosal cells are preferentially found in infragranular layers. These differences in topography and laminar distribution suggest that these callosal regions, referred to as medial and lateral callosal regions in the present study, subserve different functions. We explored this possibility by analyzing the patterns of callosal linkages in these two callosal regions. We charted the location of retrogradely labeled cells within striate cortex of one hemisphere after placing restricted injections of one or more fluorescent tracers into selected sites in the contralateral striate cortex. We found the medial and lateral callosal regions have distinctly different topographic organizations. Injections into medial striate cortex of one hemisphere produced labeled cells predominantly in mirror-symmetric loci in medial portions of contralateral striate cortex. The arrangement of these connections suggests that they mediate direct interactions between cortical regions representing visual fields located symmetrically on opposite sides of the vertical meridian of the visual field. In contrast, the mapping in the lateral callosal region is reversed: injections into the 17/18a border produced labeled fields located medial to the contralateral 17/18a border, while injections slightly medial to the 17/18a border produced labeled fields located at the contralateral 17/18a border.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2003

Posterior cingulate cortex activation by emotional words: fMRI evidence from a valence decision task.

Functional imaging studies consistently find that emotional stimuli activate the posterior cingulate cortex, a region that appears to have memory-related functions. However, prior imaging studies have not controlled for non-emotional stimulus features that might activate this region by engaging memory processes unrelated to emotion. This study examined whether emotional words activated the posterior cingulate cortex when these potentially confounding factors were controlled. Sixty-four pleasant and 64 unpleasant words were matched with neutral words on non-emotional features known to influence memory. Eight subjects underwent block-designed functional magnetic resonance imaging scans while evaluating the valence of these words. The posterior cingulate cortex was significantly activated bilaterally during both unpleasant and pleasant compared to neutral words. The strongest activation peak with both unpleasant and pleasant words was observed in the left subgenual cingulate cortex. Anteromedial orbital and left inferior and middle frontal cortices were also activated by both pleasant and unpleasant words. Right amygdala and auditory cortex were activated only by unpleasant words, while left frontal pole was activated only by pleasant words. The results show that activation of the posterior cingulate cortex by emotional stimuli cannot be attributed to the memory-enhancing effects of non-emotional stimulus features. The findings are consistent with the suggestion that this region may mediate interactions of emotional and memory-related processes. The results also extend prior findings that evaluating emotional words consistently activates the subgenual cingulate cortex, and suggest a means of probing this region in patients with mood disorders.

Acoustic Stimulation↗

PubMed2003

Encoding of novel picture pairs activates the perirhinal cortex: an fMRI study.

It is well established in nonhuman primates that the medial temporal lobe (MTL) structures, the hippocampus and the entorhinal and perirhinal cortices, are necessary for declarative memory encoding. In humans, the neuropathological and neuropsychological changes in early Alzheimer's disease (AD) further support a role for the rhinal cortex in the consolidation of new events into long-term memory. Little is known, however, regarding the function of the rhinal cortex in humans in vivo. To examine the participation of the interconnected MTL structures as well as the whole-brain network of activated brain areas in visual associative long-term memory, functional magnetic resonance imaging (fMRI) was used to determine the brain regions that are activated during encoding and retrieval of paired pictures in 12 young control subjects. The most striking finding in the MTL activation pattern was the consistent activation of the perirhinal cortex in the encoding-baseline and encoding-retrieval comparisons with a strict statistical threshold (P < 0.00001). In contrast, no perirhinal cortex activation was detected in the retrieval-baseline or retrieval-encoding comparisons even with a low statistical threshold (P < 0.05). The location of the perirhinal activation area was in the transentorhinal part of the perirhinal cortex, in the medial bank of the collateral sulcus. The hippocampus and the more posterior parahippocampal gyrus were activated in both encoding and retrieval conditions. During the encoding processing, MTL activations were more consistent and the hippocampal activation area located more anteriorly than during retrieval. The frontal, parietal, temporal, and occipital association cortices were also activated in the encoding-baseline and retrieval-baseline comparisons. The data suggest that encoding, but not retrieval, of novel picture pairs activates the perirhinal cortex. To our knowledge, this is the first fMRI study reporting encoding activation in this transentorhinal part of the perirhinal cortex, the site of the very earliest neuropathological changes in AD.

Adult↗