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M Conley

Publications and source records attributed to M Conley.

At least 37 records · Page 2Linked to original sources
PubMed1991

Evidence for separate pathways within the tecto-geniculate projection in the tree shrew.

Two layers (3 and 6) in the dorsal lateral geniculate nucleus (GLd) of the tree shrew (Tupaia belangeri) receive projections from the superficial layers of the superior colliculus. The goal of this study was to determine whether the same or different cells in the superior colliculus give rise to the projections to layers 3 and 6 by following individual axons labeled with biocytin from the superior colliculus to the GLd. The results show that the terminal fields differ in the two layers--those in layer 3 are restricted to a line of projection, whereas those in layer 6 are elongated along the dimension orthogonal to a line of projection. Another important difference between axons that project to GLd layers 3 and 6 is that those that project to layer 6 give off collaterals to the posterior pretectal nucleus, whereas at least some axons that project to layer 3 send a collateral to the ventral lateral geniculate nucleus (GLv). These results suggest that the superior colliculus exerts separate influences on these two GLd layers, both of which project to separate targets above layer IV in the striate cortex. The biocytin method has proved useful by showing the dendritic trees of the superior colliculus cells of origin, the pathways taken by the axons (including the presence of collaterals), and the terminal fields both within and outside the GLd.

Animals↗
PubMed1990

Sublaminar organization within layer VI of the striate cortex in Galago.

In this study we examined the organization of projections from the striate cortex to the dorsal lateral geniculate (GL) and pulvinar (PUL) nuclei in the prosimian Galago by using retrograde transport methods. Injections of wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) into the PUL labeled two bands of cells in the striate cortex: the first consisted of large pyramidal cells in the upper half of layer V; the second consisted of small and medium-size pyramidal cells located in the deepest part of layer VI. The location of cells within layer VI coincided with a clear cytoarchitectonic sublayer, VIb, which contains fewer and paler staining cells than VIa. Injections of WGA-HRP involving all layers of the GL produced an uninterrupted band of pyramidal cells distributed throughout layer VI (a and b), including the region labeled after injections into the PUL. Thus as a first approximation, layer VI can be divided into an upper tier (VIa) that projects only to the GL and a lower tier (VIb) that projects to both the GL and PUL. Injections of WGA-HRP that were restricted to one or a few GL layers revealed a further refinement of the subdivisions within layer VI. Injections into the parvicellular and intercalated (or koniocellular) layers of the GL labeled neurons predominantly in the upper half of layer VIa, whereas injections restricted to the magnocellular layers labeled neurons in the lower half of layer VIa and in layer VIb. In order to determine whether individual neurons in layer VIb send axon collaterals to both the GL and PUL, we injected WGA-HRP into one nucleus and fluorescent rhodamine latex beads into the other. In three experiments, we found only one double-labeled cell. In sum, the results provide evidence that layer VI is divided into at least three sublayers: upper VIa, which projects to the intercalated and parvicellular GL layers; lower VIa, which projects to the magnocellular GL layers; and VIb, which sends separate projections to the magnocellular layers of the GL and to the PUL. The segregation observed is sufficiently discrete to propose the existence of multiple, descending pathways from layer VI of the striate cortex that complement those ascending from the GL and PUL.

Animals↗
PubMed1989

Morphology of retinogeniculate axons in the macaque.

The size, pattern of terminal arborizations, and laminar specificity of individual retinogeniculate axons were studied in the macaque following injections of HRP into the optic tract. Axons that terminated in the magnocellular layers had significantly larger fiber diameters and wider terminal fields than those that terminated in the parvocellular layers. Terminal fields of magnocellular fibers spanned most of the width of their target layer, whereas those of parvocellular fibers were restricted to approximately one-half the width of their target layers; almost all terminal fields were oriented along lines of projection. All of the optic tract fibers that we examined terminated in only one layer of the lateral geniculate nucleus (GL), including a population of fine caliber fibers that project to the intercalated layers, and none had collateral projections outside the GL. The results suggest that each layer--magnocellular, parvocellular, and intercalated--receives projections from a morphologically distinct population of optic tract fibers.

Animals↗
PubMed1988

Cholinergic projections from the midbrain reticular formation and the parabigeminal nucleus to the lateral geniculate nucleus in the tree shrew.

The distribution and sources of putative cholinergic fibers within the lateral geniculate nucleus (GL) of the tree shrew have been examined by using the immunocytochemical localization of choline acetyltransferase (ChAT). ChAT-immunoreactive fibers are found throughout the thalamus but are particularly abundant in the GL as compared to other principal sensory thalamic nuclei (medial geniculate nucleus, ventral posterior nucleus). Individual ChAT-immunoreactive fibers are extremely fine in caliber and display numerous small swellings along their lengths. Within the GL, ChAT-immunoreactive fibers are more numerous in the layers than in the interlaminar zones and, in most cases, the greatest density is found in layers 4 and 5. Two sources for the ChAT-immunoreactive fibers in the GL have been identified--the parabigeminal nucleus (Pbg) and the pedunculopontine tegmental nucleus (PPT)--and the contribution that each makes to the distribution of ChAT-immunoreactive fibers in GL was determined by combining immunocytochemical, axonal transport, and lesion methods. The projection from the Pbg is strictly contralateral, travels via the optic tract, and terminates in layers 1, 3, 5, and 6 as well as the interlaminar zones on either side of layer 5. The projection from PPT is bilateral (ipsilateral dominant) and terminates throughout the GL as well as in other thalamic nuclei. Lesions of the Pbg eliminate the ChAT-immunoreactive fibers normally found in the optic tract but have no obvious effect on the density of ChAT-immunoreactive fibers in the contralateral GL. In contrast, lesions of PPT produce a conspicuous decrease in the number of ChAT-immunoreactive fibers in the GL and in other thalamic nuclei on the side of the lesion but have no obvious effect on the number of ChAT-immunoreactive fibers in the optic tract. These results suggest that there are two sources of cholinergic projections to the GL in the tree shrew which are likely to play different roles in modulating the transmission of visual activity to the cortex. The Pbg is recognized as a part of the visual system by virtue of its reciprocal connections with the superficial layers of the superior colliculus, while the PPT is a part of the midbrain reticular formation and is thought to play a non-modality-specific role in modulating the activity of neurons throughout the thalamus and in other regions of the brainstem.

Animals↗
PubMed1988

Laminar organization of geniculostriate projections. A common organizational plan based on layers rather than individual functional classes.

The types of laminar segregation of neuronal classes found in the lateral geniculate nucleus (GL) of mammals are almost as varied as the groups themselves which exhibit lamination. This essay deals with the question of whether, in spite of the differences in which classes are segregated by layer in different species, one rule might apply to the laminar distribution of projections from the GL to the striate cortex. Until recently, the weight of experimental evidence suggested that the laminar or sublaminar distribution of such projections was organized so as to segregate functional classes (i.e. W, X, Y, on center, off center). While this model appears to be consistent with the organization of geniculostriate projections in many species (especially primates), recent studies on species other than primates suggest that the laminar distribution of geniculostriate projections is not based on a segregation of functional classes per se, but on the segregation of projections from whole GL layers (or layer pairs) including all of their constituent cell classes.

Animals↗
PubMed1988

Delivery room management of meconium staining of the amniotic fluid and the development of meconium aspiration syndrome.

A 1-year prospective survey of obstetric and pediatric management of meconium staining of the amniotic fluid in 464 patients was undertaken. Pharyngeal suctioning before delivery was performed using bulb syringe (N = 130), De Lee suction catheter (N = 186), or both (N = 98); endotracheal intubation after delivery was also done in 413 instances. Using any of the three suctioning techniques, no differences were seen in Apgar scores, respiratory rates, presence or absence of meconium on or below the vocal cords, or development of meconium aspiration syndrome (MAS). If meconium was present on the vocal cords, it was present below the vocal cords in 76% of the cases. If no meconium was visualized, it was found below the vocal cords in only 7% of the cases. Of the 142 infants with meconium below the vocal cords, 10% developed MAS and all 14 survived.

Amniotic Fluid↗
PubMed1987

Terminations of individual optic tract fibers in the lateral geniculate nuclei of Galago crassicaudatus and Tupaia belangeri.

The morphology and laminar distribution of individual optic fibers projecting to the lateral geniculate nucleus (GL) of Galago and Tupaia were studied following iontophoretic injections of horseradish peroxidase (HRP) into the optic tract. In Galago the GL is composed of three functionally matched pairs of layers, each characterized by cells of a given size, one large, one medium-sized, and one small. The results show that there is a close correspondence between the size of the afferent fibers and the size of the neurons in the target layer: large axons project to the magnocellular layers, medium-sized axons project to the parvicellular layers, and small fibers project to the intercalated layers. In Tupaia the GL is composed of two functionally matched pairs and two unmatched layers. Optic fibers that project to the medial matched pair (1 and 2) are only slightly larger than those that project to the lateral matched pair (4 and 5), but both are larger than those that project to the unmatched layers (3 and 6). In both species terminal arbors and the distribution of terminal boutons within layers corresponded closely with the organization of dendritic processes of cells in the target layer. This correspondence was particularly evident in the parvicellular layers in Galago and in layer 6 in Tupaia: parvicellular terminal arbors, like the dendrites of parvicellular cells, are organized in narrow columns oriented along lines of projection, whereas layer 6 terminal arbors, like the dendrites of layer 6 cells, are oriented in elongated strips perpendicular to lines of projection. In both species there was evidence for sublaminar terminations in some layers. These were restricted to the parvicellular layers in Galago and layers 4 and 5 in Tupaia. With the exception of a small number of fine fibers in the intercalated layers in Galago, optic fibers in both species terminated in one and only one layer in a set. The significance of this result depends on the relation between ganglion cell classes and what is being segregated in different GL layers. Lateral geniculate lamination varies even in closely related species and has evolved independently in such distantly related lines as carnivores and primates. It is not surprising, therefore, that what is being segregated varies from species to species.

Animals↗
PubMed1986

Laminar asymmetry in the distribution of choline acetyltransferase-immunoreactive neurons in the retina of the tree shrew (Tupaia belangeri).

Cholinergic neurons in the retina of the tree shrew were identified immunocytochemically using a monoclonal antibody directed against choline acetyltransferase (ChAT). The chief result is that roughly 4 times as many ChAT-immunoreactive neurons are found in the inner nuclear layer (INL) as in the ganglion cell layer (GCL). In the INL, two classes of cholinergic neuron can be distinguished on the basis of soma size, one large and one small. The large neurons correspond closely in size and number to the displaced cholinergic neurons in the GCL, suggesting that these are the matching populations of cholinergic amacrine cells reported in other species. The small ChAT-immunoreactive neurons, on the other hand, which make up 60% of the total number of ChAT-positive neurons in the retina, appear to have no counterpart in the GCL. Whether these small neurons are a separate class of amacrine cell or some other cell type (e.g. bipolar, interplexiform, etc.) remains to be determined.

Animals↗
PubMed1986

Ocular dominance columns and retinal projections in New World spider monkeys (Ateles ater).

Retinal projections and the degree of ocular segregation in the striate cortex were examined by transneuronal autoradiography following unilateral intraocular injections of 3H-proline in a New World primate, the spider monkey (Ateles ater). The results show that, within the lateral geniculate nucleus (LGN), retinal fibers terminate in six principal layers and within the interlaminar spaces adjacent to the magnocellular layers, as well as the S layers ventral to the magnocellular layers. Projections to the superior colliculus, both ipsilateral and contralateral to the injected eye, were patchy and restricted to the superficial gray layer. Our main result shows that, in the striate cortex, LGN projections terminate in well-defined ocular dominance columns in layer IV. Labelled columns were most clearly delimited in layer IVb, where they averaged 373 + 42 micron in width in both the ipsilateral and contralateral hemispheres, slightly smaller than those reported originally from electrophysiological studies of striate cortex in spider monkeys (Hubel and Wiesel, '68). Unlabelled intercolumns were significantly narrower than labelled columns, which suggests that there may be overlap between input from the two eyes between columns. Quantitative measures showed above-background label also in cortical layers IIIb, V, and VI. Our results support the idea that among primates, ocular dominance columns are not limited to Old World species. At the same time, it is apparent that spider monkeys are exceptional among New World primates in having sharply delimited columns. The functional significance of the variation in the degree of ocular segregation in the cortex and its relation to primate evolution are discussed.

Animals↗
PubMed1986

Long-range focal collateralization of axons arising from corticocortical cells in monkey sensory-motor cortex.

Small extracellular injections of HRP were placed into a stratum of corticocortical axons situated immediately deep to area 3b of the monkey somatic sensory cortex. This stratum had previously been demonstrated to contain corticocortical fibers linking the cytoarchitectonic fields of the somatic sensory cortex to one another and certain of them to the motor cortex. This method resulted in extremely successful filling of pyramidal cells, their axons, collateral axon branches, and terminations in areas 3b, 1, and 2 posterior to the injection and in areas 3a and 4 anterior to it. The major finding was that cells with somata situated in any one of these fields and with principal axons traversing the injection site have long collaterals, primarily in layers III and V, which can extend throughout their own cytoarchitectonic field and into one or more other fields. In these fields they give off focused, columnlike concentrations of terminal boutons, which can be separated from one another by 800 micron or more. The anterogradely labeled, primary corticocortical fibers, traced forwards into areas 3a and 4, have virtually identical focal terminations. These findings indicate that interareal connectivity in the sensory-motor cortex can be effected by the axon branches of single cells rather than by separate groups of cells, and this may form a basis for the convergence of place and modality information on single cells in the sensorimotor cortex, a convergence that is not seen in the thalamic input to this cortex.

Animals↗
PubMed1985

Neuronal classes and their relation to functional and laminar organization of the lateral geniculate nucleus: a Golgi study of the prosimian primate, Galago crassicaudatus.

The neuronal organization of the lateral geniculate nucleus of the prosimian primate, Galago crassicaudatus, was studied in Golgi-Kopsch-impregnated material. On the basis of cytoarchitecture, electrophysiology, and connections the nucleus is divisible into three pairs of layers--one magnocellular, one parvocellular, and one koniocellular--each part of a separate retinogeniculate and geniculostriate pathway (Itoh et al., '82; Norton and Casagrande, '82). In Macaca and Saimiri, which have equally distinct geniculate subdivisions, it has been reported that, outside of cell size, no one morphological attribute differentiates magnocellular from parvocellular neurons (Campo-Ortega et al., '68; Wong-Riley, '72; Saini and Garey, '81; Wilson and Hendrickson, '81). Results presented here are not inconsistent with this conclusion. However, when the results are analyzed from the standpoint of the collective traits that distinguish the cell groups that make up the layers, clear morphological differences are evident. Using this approach we find the following differences between presumed projection neurons and interneurons in each pair of layers. The projection neurons of the magnocellular layers, as a group, exhibit large cell bodies with radially arranged dendrites which often extend beyond laminar borders. The magnocellular interneurons are larger than their counterparts in the other layers and, like the magnocellular projection neurons, exhibit radially arranged dendrites. The former, however, also share characteristics in common with other interneurons such as relatively small somata, few proximal dendrites, and complex distal dendritic appendages. In contrast, the projection neurons and interneurons of the parvocellular layers have smaller somata and more restricted dendritic spreads than their counterparts in the magnocellular layers. Dendritic arbors of parvocellular neurons are typically oriented perpendicular to laminar borders and remain confined to their layer of origin. The koniocellular neurons represent a more diverse population but collectively are distinct in that the dendrites of almost all neurons in these layers run parallel to the layers. The fact that presumed interneurons and projection neurons in a single layer share a number of related dendritic features suggests that both groups together are responsible for the structural and, hence, functional architecture of a layer.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

Laminar organization of geniculocortical projections in Galago senegalensis and Aotus trivirgatus.

The projections of the lateral geniculate nucleus to striate cortex were traced by anterograde and retrograde transport of WGA-HRP in two primates, Galago and Aotus. The goal was to determine the laminar organization of the terminals of individual layers of the lateral geniculate nucleus. The results show that in both species the magnocellular layers project to cortical layer IV alpha, the parvicellular layers project to IV beta, and the intercalated geniculate layers (which term includes layers 4 and 5 in Galago) project to layers III and I. The distribution of terminals in layer III is periodic, which is to say, there are regularly spaced regions of terminals separated by regions devoid of terminals. When the two species are compared to Saimiri, it is clear that the basic organization of the three pathways relaying in the lateral geniculate nucleus is common to all three primates. At the same time, there are some significant species differences. The total pattern of projections in Galago is compressed in comparison to that in the monkey, and this compression seems to be related to the poorer differentiation of cortical layers in the prosimian. For example, layer IIIC is distinct only in the two monkeys and at the same time it is spared from geniculate terminations. Both Galago and Aotus differ from Saimiri in that they lack a projection from the parvicellular geniculate layers to the layer IIIB. These species comparisons are relevant to the questions of the functional significance of the three pathways and the evolution of the primate striate cortex.

Animals↗
PubMed1985

Demonstration of ipsilateral retinocollicular projections in the tree shrew (Tupaia glis).

Ipsilateral retinocollicular projections labeled by anterograde transport of wheatgerm agglutinin-horseradish peroxidase (HRP) conjugate in the tree shrew were examined. For those animals in which this pathway was demonstrated (4 of 14) ipsilateral collicular labeling extended across approximately the anterior two-thirds of the colliculus, with the exception of the extreme rostral pole. Labeling was invariably punctuate and spaced at regular intervals in the lower stratum griseum superficiale. The laminar distribution and patchy terminations of ipsilateral projections are discussed in relation to two apparently independent pathways originating in the temporal retina, the crossed and uncrossed collicular pathways.

Animals↗
PubMed1985

Morphological and functional types of neurons in cat ventral posterior thalamic nucleus.

Neurons in the thalamic ventral posterior (VB) nucleus of the cat were investigated by extracellular and intracellular recording and by anatomical methods involving either the retrograde transport of horseradish peroxidase (HRP) or the intracellular injection of HRP. Two morphological types of neurons could be detected by retrograde labeling from small injections of HRP in the internal capsule adjacent to VB. These two and one other type, judged to be an interneuron, could also be identified by intracellular staining. Type I cells are large, have thick proximal dendrites which branch in a tuft-like manner, and thick, rapidly conducting axons. They possess few or no dendritic appendages. Type II cells are smaller and have slender proximal dendrites which branch dichotomously and thin, slower conducting axons. Those injected intracellularly are covered in fine, hair-like dendritic appendages. Type III cells are small and have thin processes that give rise to many bulbous dilatations and no obvious axon. Type I and type II cells give off slender axon collaterals in the thalamic reticular nucleus but not in VB. Examples of both types of cell could be antidromically activated from the somatic sensory cortex. Type I and type II cells recovered histologically after intracellular recording included examples of most types of receptive field, including several forms of cutaneous and deep fields, as classified by us in a parallel intra- and extracellular study of unit responses. All but one type I cell, however, responded in a transient manner to peripheral stimulation. The remaining type I cell and all members of an admittedly small sample of type II cells responded in a sustained manner. The sample of recovered interneurons and of units that could not be driven antidromically from the cerebral cortex suggested that they, too, included all receptive field types. We conclude that submodality specificity in VB is not represented by morphological specificity in thalamocortical relay cells or interneurons. Some other functional parameter, such as tonic or phasic responsiveness, may be more obviously correlated with relay cell morphology.

Action Potentials↗
PubMed1985

The morphology of physiologically identified GABAergic neurons in the somatic sensory part of the thalamic reticular nucleus in the cat.

Neurons with somatic sensory receptive fields were examined electrophysiologically in the thalamic reticular nucleus of the cat. All cells had receptive fields much larger than those of neurons in the ventral posterior nucleus and were driven by less readily defined somesthetic stimuli. Response latencies to peripheral or medial lemniscal stimulation were, on average, longer than in the ventral posterior nucleus and suggested activation of the reticular nucleus cells by collaterals of thalamocortical relay cell axons arising in the ventral posterior nucleus. When injected intracellularly with horseradish peroxidase, reticular nucleus cells displayed thin axons with intrareticular collaterals and diffuse branches through much of the ventral posterior and posterior thalamic nuclei. Dendrites ended in processes resembling synaptic terminals. Electron microscopic immunocytochemistry of the same part of the reticular nucleus revealed processes immunoreactive for glutamic acid decarboxylase and identifiable as both collateral axon terminals and presynaptic dendrites of GABAergic reticular nucleus cells. These synaptically linked reticular nucleus cells and, in addition, immunoreactive somata and presynaptic dendrites received synapses from at least three varieties of nonimmunoreactive profiles.

Animals↗
PubMed1984

The distribution of glutamic acid decarboxylase immunoreactivity in the diencephalon of the opossum and rabbit.

We have examined the distribution of neurons and terminals immunoreactive for glutamic acid decarboxylase (GAD) in the thalamus and adjacent structures of the opossum (Didelphis virginiana) and the rabbit and have compared this distribution with the distributions we described previously for the cat and bushbaby (Galago senegalensis). The significance of these experiments depends, first, on the fact that GAD is the synthetic enzyme for GABA, and therefore that GAD immunoreactivity is a marker for GABAergic inhibitory neurons, and second, on previous findings that suggest that GABAergic neurons in the dorsal thalamus are local circuit neurons. In both cat and Galago, GAD-immunoreactive neurons are distributed essentially throughout the entire thalamus. In the opossum, GAD neurons are chiefly confined to the dorsal lateral geniculate nucleus and the lateral extremity of the lateral posterior nucleus. The distribution of GAD neurons in the rabbit is intermediate between that found in the opossum on the one hand and cat and Galago on the other. Like opossum, about 25% of the neurons in the lateral geniculate nucleus of rabbit are GAD immunoreactive. Unlike opossum, however, as many as 18% of the cells in the ventral posterior nucleus of the rabbit are GAD immunoreactive, and scattered cells are also labeled in other thalamic areas, such as the medial geniculate and the lateral group. Aside from the findings in the dorsal thalamus, the chief observation is that GAD-immunoreactive neurons and/or terminals densely fill all principal targets of the optic tract, including the ventral lateral geniculate nucleus; the superficial gray layer of the superior colliculus; the anterior, posterior, and olivary pretectal nuclei; the nucleus of the optic tract; and the medial and lateral terminal nuclei of the accessory optic tract. These results support the idea first put forward by Cajal that local circuit neurons increase in number during the course of the evolution of complex mammalian brains. If we can assume that the conservative opossum retains characteristics reflecting an early stage of mammalian evolution, the results suggest that thalamic local circuit neurons arose first in the visual system and only later in evolution spread throughout the thalamus.

Animals↗