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M Behan

Publications and source records attributed to M Behan.

At least 55 records · Page 3Linked to original sources
PubMed1991

Cortical barrelfields in organotypic slice cultures from rat somatosensory cortex.

We are attempting to determine the factors that influence both the formation and maintenance of barrels in the rodent somatosensory cortex. Cytochrome oxidase histochemistry and Nissl staining were used to identify the presence of barrels in slice cultures of rat cortex. Barrels were observed in sagittally cut slices, in cortical layer IV, from animals aged postnatal day 5-10 that were cultured for at least 10 days. No differences were observed in the barrel pattern from animals at different postnatal ages, or from cortex that was cultured for different lengths of time. In contrast, cortical barrels in tangentially cut sections from similarly aged animals were clearly visible after one day in culture, but they disappeared after two days in culture. These results suggest that intact connections within cortical columns are sufficient to sustain the functional architecture of the somatosensory cortex in vitro.

Animals↗
PubMed1990

Sources of subcortical GABAergic projections to the superior colliculus in the cat.

The goal of this study was to identify GABAergic input to the cat superior colliculus from neurons located in the caudal diencephalon, mesencephalon, pons and medulla. Cells efferent to the superior colliculus were labeled retrogradely with the tracer horseradish peroxidase, and an antibody to gamma-aminobutyric acid was used to label GABAergic neurons in the same sections. The results indicate that neurons in several distinct areas of the caudal diencephalon and brainstem are both immunocytochemically labeled for GABA and retrogradely labeled with horseradish peroxidase. These areas include zona incerta, nucleus of the posterior commissure, anterior and posterior pretectal nuclei, nucleus of the optic tract, superior colliculus, cuneiform nucleus, subcuneiform area, substantia nigra pars reticulata and pars lateralis, periparabigeminal area, external nucleus of the inferior colliculus, the area ventral to the external nucleus of the inferior colliculus, mesencephalic reticular formation, dorsal and ventral nuclei of the lateral lemniscus, and the perihypoglossal nucleus. The role that such diverse inhibitory input to the superior colliculus might play, particularly in influencing eye movements, is discussed.

Animals↗
PubMed1989

Synaptic connections between corticogeniculate axons and interneurons in the dorsal lateral geniculate nucleus of the cat.

Anatomical evidence is provided for direct synaptic connections by axons from visual cortex with interneurons in lamina A of the cat's dorsal lateral geniculate nucleus. Corticogeniculate axon terminals were labeled selectively with 3H-proline and identified by means of electron microscopic autoradiography. Interneurons in the lateral geniculate nucleus were stained with antibodies that had been raised against gamma aminobutyric acid (GABA). We found that corticogeniculate terminals synapsed with dendrites stained positively for GABA about three times as often as with unstained dendrites. Of the corticogeniculate terminals that contacted GABA-positive dendrites, 97% made synaptic connections with dendritic shafts. Only 3% synapsed with F profiles, the vesicle-filled dendritic appendages characteristic of lateral geniculate interneurons. These results suggest that the corticogeniculate pathway in the cat is directed primarily at interneurons and is organized synaptically to influence the integrated output of these cells, rather than the local interactions in which their dendritic specializations participate.

Animals↗
PubMed1988

Ultrastructural study of large efferent neurons in the superior colliculus of the cat after retrograde labeling with horseradish peroxidase.

The ultrastructure of large neurons in the stratum griseum intermedium of the cat superior colliculus was examined following injections of horseradish peroxidase (HRP) into the dorsal tegmental decussation. Four HRP-labeled cells were selected, and the synaptology of their cell bodies and selected regions of proximal and distal dendrites was examined. The four neurons represent four morphologically distinct cell types: multipolar radiating, tufted, large vertical, and medium-sized trapezoid radiating. These four neurons correspond with cell types X1, X2, X3, and T1 respectively, according to the recent classification of neurons in the superior colliculus of the cat by Moschovakis and Karabelas (J. Comp Neurol. 239:276-308, '85). The three X type neurons are similar in having 83% of their somata and over 74% of their proximal dendrites contacted by synaptic profiles. Distal dendrites of the X type neurons, however, receive fewer synaptic contacts. In contrast, in the T1 cell, only 69% of the soma membrane is contacted by synaptic profiles, and the synaptic coverage on proximal and distal dendrites does not vary much from this. Of the eight types of synaptic terminals described in the stratum griseum intermedium of the cat superior colliculus by Norita (J. Comp. Neurol. 190:29-48, '80), only five are found in contact with the X and T type efferent neurons described here. There are some regional differences in terminal distribution, although each terminal is represented on each cell. Type III terminals (small, contain mostly pleomorphic vesicles, and make symmetrical contacts) are the most abundant on cell bodies and dendrites of all four cell types. Terminal types II (medium-sized, containing round and flattened vesicles, and making asymmetrical contacts), and IV (medium to large in size, containing flattened vesicles, and making symmetrical contacts) are well represented. In general, terminal types I (small, containing densely packed round vesicles, and making asymmetrical contacts) and VI (small and irregular in shape, containing flattened vesicles and making symmetrical contacts) are found infrequently. The identity of different types of synaptic terminal is discussed.

Animals↗
PubMed1987

Synaptic reorganization in the dorsal lateral geniculate nucleus following damage to visual cortex in newborn or adult cats.

We have studied the effects of making large lesions of visual cortex on the synaptic organization of the dorsal lateral geniculate nucleus (LGN) in the cat. Visual cortex was removed at birth in one group of cats and during adulthood in a second group. Following survival periods of 6 months to 2 years, the organization of synapses made by afferents from the retina in the LGN was investigated quantitatively with the electron microscope. In single thin sections we determined the percentage of retinal axon terminals that made synapses in the LGN, the average number of synapses made by each retinal axon terminal, and the identity of each postsynaptic process. These measurements were made separately for retinogeniculate connections in the A and C laminae of the LGN. For comparison, similar sets of measurements were made in adult cats that had been reared normally. When single thin sections from the A or C laminae of the LGN in normal cats are examined, about 60% of the axon terminals from the retina are seen to make at least one synaptic contact. These contacts can be with dendrites or F profiles or both. On average, each retinogeniculate terminal makes approximately 1.4 synapses in the plane of a single section and contacts dendrites three times as often as F profiles. In the A laminae of the LGN in cats that received a visual cortex lesion at birth or in adulthood, the percentage of retinal terminals that make synapses is the same as in normal cats. Similarly, the average number of synaptic contacts made by each retinogeniculate terminal is not changed by a lesion of visual cortex. In contrast, the number of contacts made with dendrites is reduced markedly, by about 29% after a lesion at birth and 53% after a lesion as an adult. However, these reductions are offset by compensatory increases in the number of contacts made with F profiles, and thus the mean number of contacts made by each retinogeniculate terminal is stabilized at a normal value. In the C laminae of the LGN, retinogeniculate terminals also reapportion their synaptic contacts. In cats with a lesion during adulthood, the redistribution of synapses is compensatory, as in the A laminae. When a lesion is made at birth, however, the number of new retinal contacts made with F profiles exceeds the number of dendritic contacts that are lost. As a result, each retinogeniculate terminal makes about 26% more synapses, in total, than normal.(ABSTRACT TRUNCATED AT 400 WORDS)

Age Factors↗
PubMed1987

The nigrotectal projection in the cat: an electron microscope autoradiographic study.

Recent evidence indicates that the nigrotectal tract plays an important role in regulating the premotor responses of cells in the in the intermediate gray layer of the superior colliculus. The purpose of the present study was to characterize the ultrastructure of nigrotectal terminals and of their postsynaptic targets in the intermediate gray layer. Nigrotectal terminals were identified in the electron microscope by labeling them autoradiographically, following injections of tritiated proline into the substantia nigra pars reticulata. The majority of nigrotectal terminals contain a high proportion of pleomorphic vesicles and form symmetrical synaptic contacts. Most of these terminals synapse with small dendritic profiles (2.00 micron +/- 0.83 SD), which may be the distal dendrites of neurons in the intermediate gray layer. Less than 10% of the labeled contacts are made with cell bodies or initial axonal segments.

Animals↗
PubMed1985

An EM-autoradiographic and EM-HRP study of the commissural projection of the superior colliculus in the cat.

Terminals of the commissural projection in the cat were characterized ultrastructurally by autoradiographic and horseradish peroxidase methods. The results of the two studies are complementary. Terminals of commissural cells are present in the intermediate and deep layers of the cat superior colliculus. Two distinct populations of terminals are present: one containing mostly round vesicles and forming asymmetric specializations, and a second containing mostly pleomorphic vesicles and forming symmetric specializations. Both populations contact small dendrites or dendritic appendages. The two populations, mostly round and mostly pleomorphic, are present in the ratio of 2:1. Terminals measure approximately 1.1 micron in mean diameter and contact profiles ranging in size from 0.2 to 4.6 micron. There is no significant difference between the two populations in either pre- or postsynaptic profile size. The colocalization of terminals of commissural neurons with other afferent and efferent projections of the intermediate layers of the superior colliculus is discussed.

Animals↗
PubMed1985

Glutamate decarboxylase immunoreactivity in the intermediate grey layer of the superior colliculus in the cat.

Recent evidence suggests that gamma-aminobutyrate has a profound influence on the activity of premotor neurons in the intermediate grey layer of the superior colliculus. In the present study an antibody to glutamate decarboxylase, the synthesizing enzyme for gamma-aminobutyrate, was used to identify and characterize the structures in the intermediate grey layer of the cat that use gamma-aminobutyrate as a transmitter. The material was examined with both the light and electron microscope. Glutamate decarboxylase immunoreactivity was confined, for the most part, to axon terminals. Glutamate decarboxylase positive terminals almost completely cover the soma and proximal dendrites of the large neurons that are characteristic of this layer. Other glutamate decarboxylase positive terminals contact smaller, presumably more distal dendrites. By combining the glutamate decarboxylase immunocytochemistry with the retrograde transport of horseradish peroxidase in single animals, it was demonstrated that the cells of origin of the major descending efferent pathway from the intermediate grey layer, the predorsal bundle, are heavily contacted by glutamate decarboxylase immunoreactive terminals.

Animals↗
PubMed1984

An EM-autoradiographic analysis of the projection from cortical areas 17, 18, and 19 to the superior colliculus in the cat.

The electron microscopic autoradiographic method was used to identify terminals of axons from cortical areas 17, 18, and 19 in the superficial layers of the superior colliculus. The results show that terminals of area 17 neurons contain round vesicles and made asymmetrical synaptic contacts predominantly onto one or more dendrites or dendritic appendages. Some profiles postsynaptic to labeled terminals contain vesicles and presumably are involved in serial synaptic arrangements. Terminals of area 18 and 19 neurons in the superficial collicular layers appear to comprise two populations, one similar in most respects to area 17 terminals, containing round vesicles and making asymmetrical contacts. The other contains pleomorphic vesicles and makes symmetrical contacts upon dendrites and dendritic appendages. These terminals rarely contact more than one postsynaptic profile, and rarely do the postsynaptic profiles contain vesicles. The two populations of area 18 and 19 terminals containing round and pleomorphic vesicles, respectively, are present in the ratio of approximately 3:1, although this ratio varies throughout the sublaminae of the superficial collicular layers. The presence of two distinct types of cortical terminals in the colliculus suggests that cortical modulation of collicular processing is more complex than was previously conceived.

Animals↗
PubMed1984

Computed tomographic arteriography in the pre-surgical evaluation of hepatic tumours.

Five patients with hepatic neoplasms considered suitable for surgical resection were examined by computed tomography (CT), hepatic angiography and then a combination of angiography and CT (CTA). In each patient the tumour was more clearly defined and its extent more accurately determined than by routine CT. Three patients were spared surgery when further hepatic tumour was shown by CTA. The left lobe was shown to be free of tumour in the other two patients and surgical resection was carried out. Examination by CTA is recommended in all patients with hepatic tumours considered suitable for hepatic resection.

Aged↗
PubMed1983

Structure of the piriform cortex of the opossum. III. Ultrastructural characterization of synaptic terminals of association and olfactory bulb afferent fibers.

Terminals of olfactory bulb afferent (OB) and association (ASSN) fibers within the piriform cortex were characterized ultrastructurally. Identification was by electron microscopic (EM) autoradiography following injections of tritiated amino acids into the olfactory bulb and anterior piriform cortex. The results show that terminals of both fiber systems contain round vesicles and make asymmetrical synaptic contacts predominantly onto dendritic spines. Profiles with pleomorphic vesicles do not appear to be labeled from either site. Since there is strong evidence that both fiber systems generate excitatory postsynaptic potentials (EPSPs) in pyramidal cells, these results provide additional examples in the mammalian CNS of terminals with round vesicles and asymmetrical contacts that mediate an excitatory effect. Percentage density analysis and quantitative study of a large number of heavily labeled terminals revealed that while OB and ASSN terminals are similar in terms of vesicle shape and contact type, they differ in many morphological details including pre- and postsynaptic profile size, the packing density and distribution of synaptic vesicles, synaptic contact shape, and the presence of overlying neuroglial lamellae. However, large variations in appearance of different terminals of the same type are also present so that a small percentage of OB and ASSN terminals are indistinguishable morphologically in the absence of label. An important finding of the quantitative analysis is that spines contacted by lateral olfactory tract (LOT) terminals appear to be of two types based on a bimodal distribution in size and differences in morphology, while spines contacted by ASSN terminals appear to be of a single type. Comparison of these data with results from Golgi analysis indicates that ASSN terminals predominantly contact pyramidal cell spines while OB terminals contact both pyramidal and semilunar cell spines. Quantitative analysis of synaptic vesicles revealed that histograms of vesicle size for OB and ASSN terminals are virtually identical in shape, but peaks are slightly displaced (ASSN vesicles are 5% larger; significant with P less than .002). An analysis of the laminar distribution of OB and ASSN synaptic terminals revealed that while most OB terminals are segregated in layer Ia and most ASSN terminals in layer Ib, occasional OB terminals are observed up to approximately 50 micro deep to the Ia-Ib boundary and occasional ASSN terminals up to approximately 50 micro superficial to this boundary.

Afferent Pathways↗
PubMed1982

A quantitative analysis of the ipsilateral retinocollicular projection in the cat: an EM degeneration and EM autoradiographic study.

The ipsilateral projection to the binocular segment of the superior colliculus in the cat was quantified by means of electron microscopic (EM) degeneration and electron microscopic autoradiography. Because of the patchy distribution of ipsilateral terminals, contiguous samples were taken across the mediolateral extent of the colliculus. The results from both EM degeneration and EM autoradiography are in substantial agreement: In the binocular segment, the ipsilateral projection represents 5.3% and 5.6%, respectively, of the total retinal input to the superior colliculus. As the contralateral projection extends over the whole colliculus but is greatest in the caudal region, while the ipsilateral projection is restricted to the middle one-third of the colliculus, it follows that the total ipsilateral retinocollicular projection is less than earlier estimates (5--10%, Kanaseki and Sprague, '74) and probably closer to 1%, as suggested by Sterling ('73) on the basis of an electron microscopic degeneration study. A significant finding is that there are many more terminals per axon in the contralateral than in the ipsilateral superficial gray. The ratio of degenerated terminals in SGS1 and SGS2 to degenerated axons in SGS3 is 3.1 contralaterally, while in the ipsilateral colliculus the figure is 1.2. This may reflect a difference in the arborization pattern of Y-type and W-type retinal ganglion cells in the colliculus.

Animals↗
PubMed1981

Identification and distribution of retinocollicular terminals in the cat: an electron microscopic autoradiographic analysis.

The electron microscopic (EM) autoradiographic method has been used to determine the size, distribution, and ultrastructure of retinocollicular axon terminals following intraocular injection of either (3H)-leucine or (3H)-proline. In the contralateral colliculus, retinal terminals are most numerous in the uppermost sublamina of the superficial grey, SGS1. The mean diameter of terminals in the contralateral SGS1 and SGS2 is 1.3 micron +/- 0.33, and 1.45 micron +/- 0.37, respectively. The mean diameter of terminals in the deepest contralateral sublamina, SGS3 (1.85 micron +/- 0.62), is significantly larger than the mean diameter of those in the contralateral SGS1 or SGS2. By contrast, the mean diameter of terminals in different sublayers of the ipsilateral superficial grey is relatively constant, ranging from 1.56 micron +/- 0.45 to 1.63 micron +/- 0.60. Most ipsilateral retinal terminals are located in the uppermost part of SGS2. It is postulated that there are two populations of retinal terminals in the superficial grey: a population of smaller terminals present in the contralateral SGS1 and SGS2, and a population of larger terminals present in the contralateral SGS3. Both populations appear to be present in the ipsilateral sublaminae. While all labeled retinocollicular terminals contain round vesicles and asymmetric membrane thickenings, two morphological features appear to be correlated with retinal terminal size: (1) the population of smaller retinal terminals more frequently contacts postsynaptic profiles containing scattered round vesicles; and (2) large, dense-core vesicles are more commonly associated with the presynaptic profiles of the population of larger terminals. A comparison of these morphological findings with available physiological data (Hoffman, '73; Fukuda and Stone, '74; McIlwain and Lufkin, '76 McIlwain, '78) suggests that the smaller terminals may be those of W-retinal ganglion cells, and the larger terminals those of Y-retinal ganglion cells.

Animals↗
PubMed1979

Sonographic evaluation of the nonfunctioning kidney.

The results of B-mode ultrasound examinations in 113 consecutive patients with unilateral renal nonfunction or severe azotemia were reviewed. The causes of nonfunction included the following: hydronephrosis; renal parenchymal disease; renal agenesis; atrophy or dysplasia; multicystic, medullary cystic, and polycystic kidneys; renal arterial or venous occlusive disease; extensively infiltrating neoplasm. The sonographic findings were consistent with the final diagnosis in 92 percent of the cases. A coronal view of the kidney for diagnosing hydronephrosis is described. This view demonstrates the dilated calyces in continuity with the renal pelvis and, when combined with transverse views, improves the reliability of the sonographic diagnosis of hydronephrosis. In cases where the renal landmarks appear totally normal, obstruction can be excluded as a cause of nonfunction, and retrograde pyelography may be avoided. The sonographic manifestations of other parenchymal abnormalities associated with nonfunction, such as cystic renal disease, glomerulonephritis, and renal transplant rejection, are also discussed.

Abscess↗
PubMed1979

The precise origin of the tectospinal pathway in three common laboratory animals: a study using the horseradish peroxidase method.

The horseradish peroxidase tracing method has been used to study the cells of origin of the tectospinal projections in the opossum, the tree shrew, and the cat. The present data show that only those collicular neurons which occupy the deep (ventral to the stratum opticum) tectal laminae send axons to the cervical spinal cord. In particular, layer IV contains the greatest number of spinal projecting neurons. Our results also reveal that while only the large sized collicular neurons project upon the cervical spinal cord in the opossum and the tree shrew, neurons comprising several different size categories do so in the cat. We thus suggest that several different descending channels exist over which the superior colliculus can influence the neck musculature in the cat.

Animals↗