Afferent control of neuron numbers in the developing brain

In this study we tested whether the quantitative matching of developing neuronal populations may depend on the size of the afferent supply. Partial deafferentation of the middle division of the parabigeminal nucleus (PBm) was produced before the period of naturally occurring cell death, by reducing the neuronal population of the superior colliculus following partial lesions or eye removal. The number of neurons surviving cell death in the PBm was linearly related to the number of its afferent neurons. This result supports the hypothesis that neurotrophic control by the afferent supply during the period of natural neuronal death is a major determinant of the number of neurons in the developing brain.

Dual control by targets and afferents of developmental neuronal death in the mammalian central nervous system: a study in the parabigeminal nucleus of the rat

Natural and induced cell degeneration were studied in the mesencephalic parabigeminal nucleus of postnatally developing rats. Natural cell death in the normal parabigeminal nucleus had already started at birth, was maximal at 3 days, and proceeded with a declining rate until postnatal days 8-10 in the dorsal, middle, and ventral divisions that compose the nucleus. The number of neurons declined by approximately one-third between birth and postnatal day 15. A unilateral lesion of the superior colliculus made at birth modified this pattern. In the deafferented ipsilateral middle division, the rate of cell death was above normal from day 1 to day 10, and the number of neurons at day 15 was 60% less than in unoperated controls. In the contralateral middle division, in which at least some of the neurons were axotomized by the lesion, the rate of cell death increased at days 1-2 and decreased below normal at days 3-5. Induced changes in the number of neurons were consistent with this pattern, and at day 15 the number was similar to the control value. In the ipsilateral dorsal and ventral divisions, which suffered simultaneous axotomy and deafferentation, the rate of cell death increased in 2 peaks at days 1-2 and 4-6, and the numbers of neurons dropped to negligible values at day 15. The frequency curves of degenerating cells were poor predictors of the absolute changes in neuron numbers, and evidence was found of continued postnatal migration of neurons into the developing parabigeminal nucleus.(ABSTRACT TRUNCATED AT 250 WORDS)

Superior vena cava Doppler: a non-invasive method for the diagnosis of pericardial disease

Superior vena cava Doppler flow velocities were assessed in two patients presenting with cardiac tamponade. Abnormal Doppler flow patterns correlated with right atrial pressure abnormalities characteristic of tamponade and constriction. During tamponade diastolic superior vena cava flow was abolished, and only systolic flow occurred. After pericardiocentesis diastolic flow reappeared. In one patient dominant diastolic flow velocities after pericardiocentesis suggested residual constriction. The flow pattern returned to normal after pericardiectomy, with systolic velocity exceeding diastolic velocity. Serial studies in these patients suggest that Doppler evaluation of superior vena cava blood flow is a useful method for evaluating pericardial disease.

Displaced ganglion cells in the retina of the rat

The distribution, laterality of projection, and perikaryal sizes of displaced ganglion cells (DGCs) were examined in whole-mounted retinae after massive unilateral injections of horseradish peroxidase along the optic tract in pigmented rats. The DGCs were found predominantly in the lower temporal periphery of the retina. Nearly all DGCs labeled had contralaterally projecting axons. The sizes of the labeled DGCs spanned the range of ordinary ganglion cells, but few middle-sized DGCs were labeled. The results support the hypothesis that displaced ganglion cells are late-developing neurons that do not complete their migration toward the ganglion cell layer during retinal histogenesis.

Displaced amacrine cells in the ganglion cell layer of the hamster retina

Neuronal populations were estimated in the ganglion cell layer (GCL) of the adult hamster retina. The total number of neurones averaged 128,000 in Nissl-stained whole-mounts. Following injections of horseradish peroxidase into the brain, an average of 72,000 cells were labeled (mostly above 8 micron in diameter), indicating that 56% of the neurones in the GCL are ganglion cells. Forty-one percent of the neurones (mostly below 8 micron diameter) of the GCL survived for 5 months after optic nerve transection at 12 days after birth. The results indicate that more than 40% of the neurones in the GCL of the hamster retina are displaced amacrine cells.

Materials management's role in product line development

Product line management and product line cost accounting are terms that are appearing more frequently in the literature, and on hospital management and board meeting agendas. As regulatory and competitive pressures continue to shape the health care market, health provider organizations will put increasing emphasis on defining, developing and managing their product lines. (Product lines are much more than DRGs.) Product line management and cost accounting present the materials manager with an opportunity to become more involved with the

Mononuclear phagocytes in the retina of developing rats

Mononuclear phagocytes were labeled with colloidal carbon injected into the circulation or stained with cytochemical techniques for the detection of marker enzymes in whole-mounted retinae of rats from birth to 10 days after birth. Positive cells were found apposed to or scattered among the blood vessels of the immature vascular network located just vitread to the developing retina. A few cells only had carbon distributed in the cytoplasm, but all retinae tested had positive cells. The enzymes located cytochemically in the phagocytes were non-specific esterase, acid phosphatase and endogenous peroxidase. When stained with aniline dyes, the phagocytes had a morphology similar to blood monocytes. Such cells were not found in the retina of adult rats. It is concluded that mononuclear phagocytes reside just vitread to the ganglion cell layer during the period of natural cell death in that layer. The phagocytes are probably associated with the removal of cell debris during the late period of retinal histogenesis.

Developmental genetics of the retina: evidence that the pearl mutation in the mouse affects the time course of natural cell death in the ganglion cell layer

The time course of natural cell death was studied postnatally in the ganglion cell and inner plexiform layers of the retina in the developing mouse. We examined congenic wild-type, albino and pearl mutants from birth to 12 days of age. In both wild-type and albino mice, natural cell death proceeded with an increasing rate from birth to a peak 6 days after birth, and with a decreasing rate thereafter. In contrast, cell death in pearl mutants proceeded with essentially a decreasing rate postnatally. The populations of neurones and glial cells in the ganglion cell and inner plexiform layers of the retina were also determined in adult mice. It was shown that pearl mutants had a slightly smaller number of cells in those layers than both wildtype and albino mice, and that the difference was probably due entirely to the numbers of neurones. We conclude that the pearl mutation in the mouse affects the timing of developmental cell death, but the effect is not directly related to the amount of pigment in the eye.

Transient populations of presumptive macrophages in the brain of the developing hamster, as indicated by endocytosis of blood-borne horseradish peroxidase

During postnatal development, clusters of cells associated with the mononuclear phagocytic system appear within the white matter of rodents and cats. We studied the distribution and morphology of these cells in the hamster's brain during the first 2 weeks after birth. In animals of different ages, horseradish peroxidase was injected into the heart. After 3-6 h survival, the animals were perfused with aldehydes and had their brains removed, cut and reacted. In another series, fixed brain sections from horseradish peroxidase-injected and non-injected animals were reacted for a non-specific esterase expressed by monocytes and macrophages. The horseradish peroxidase reaction-product was seen throughout the nervous tissue at the first postnatal day, appearing more concentrated in certain brain sectors from postnatal day 3 through 10, to finally become restricted to a few regions at postnatal day 16. Horseradish peroxidase-labeled cells appeared in increasing numbers from postnatal day 1 to 8, decreasing thereafter to disappear completely at postnatal day 16. Some labeled cells were roundish or elliptical with few, if any, processes; others had several clearly detectable processes. Horseradish peroxidase-labelled cells formed clusters within the dorsal subventricular zone, dorsal cortical white matter, corpus callosum and several other prosencephalic fiber tracts. The morphology of esterase-reactive cells was less clearly outlined but their distribution and relative density correlated with those of horseradish peroxidase-labeled cells. Also, many horseradish peroxidase-labeled cells were esterase-positive in most clusters. We conclude that (1) some cells in the developing brain selectively endocytose and accumulate blood-borne horseradish peroxidase in their cytoplasm, (2) these cells do not appear to be neurons but a particular cell type associated to the mononuclear phagocytic system and (3) they cluster transiently in particular sectors of the cortical and subcortical white matter during the first 2 weeks after birth.

Evidence for differential effects of terminal and dendritic competition upon developmental neuronal death in the retina

Retinal ganglion cells with ipsilaterally projecting axons were labelled with horseradish peroxidase injected unilaterally along the optic pathway in adult rats. Unoperated controls were compared with three groups of animals operated at birth, given (a) contralateral enucleation, (b) contralateral lesion to the optic tract or (c) both lesions simultaneously. The numbers of ipsilaterally projecting cells were increased in all three operated groups, presumably because of a reduction in natural neuronal death following diminished terminal and dendritic competition. The pattern of increase of labelled cell density varied with the type of lesion: enucleation led to a major increase within lower temporal retina; optic tract lesion caused its major increase in upper temporal retina, centred at the location of the area centralis; and the double lesion combined both effects above. The distribution of cell-body sizes was differentially affected by the lesions: enucleation led to a shift in the distribution towards the small cell side of the spectrum, when compared with the controls; optic tract lesion shifted the distribution towards the large cell side of the spectrum, but only outside the temporal crescent; and the double lesion led to a shift towards small cells within the temporal crescent and towards large cells outside the crescent, again combining the effects of the single lesions. Large alpha-like neurones with ipsilateral axons were common in the nasal retina of both groups given optic tract lesions but they were rare in the nasal retina of unoperated and, especially, of enucleated rats. The limits of the temporal crescent were unchanged, notwithstanding the large numbers of cells outside the crescent in operated rats. It is suggested that postnatal competitive interactions at the level of terminals and of dendrites control natural neuronal death in the rat retina with different requirements regarding retinal topography and ganglion cell types. The postnatal regulation of neuronal numbers is not responsible for the generation of the nasotemporal division but may be involved in the development of differential distributions of specific ganglion cell types across the retina.

Observations on postnatal neurogenesis in the superior colliculus and the pretectum in the opossum

Postnatal neurogenesis has been detected in the superior colliculus (CS) and caudal pretectum of the opossum in the period ranging from 2 to 13 days ( PND2 to PND13 ) of life in the pouch. Examination of the pattern of labeling in specimens exposed to a pulse of tritiated thymidine ( [3H]T) in PND4 or PND7 and allowed 1.5 h survival reveals that postnatal cell proliferation for the CS is virtually confined to the ventricular zone with no evidence for in situ[3H]T uptake in the collicular plate. Semi-quantitative analysis in long survival animals shows that postnatal neurogenesis peaks later in the CS ( PND7 ) than in the caudal pretectum ( PND4 ) and also persists longer in the former than in the latter. Comparisons of the numerical density of heavily labeled neurons suggest the occurrence of ventro-dorsal and rostro-caudal gradients of neurogenesis in the CS. Separate analysis of superficial, intermediate and deep layers shows, in addition, a combined rostrolateral-to-caudomedial gradient of neurogenesis in the superficial layers. Comparisons of the time schedules of neurogenesis for the superficial layers and of the deployment of optic fibers suggest that migration of neurons to their eventual destination is completed at or after the arrival of afferents.

Organization of the visual thalamus: corticothalamic projections from the primary visual area in the opossum

The projections from the visual cortex to thalamic nuclei in the opossum were investigated by degeneration and radioautographic methods. Efferent axons from the striate cortex course from the internal capsule to the thalamus in two bundles, one of which innervates the reticular and dorsal lateral geniculate nuclei, while the other bundle innervates the external layer of the ventral lateral geniculate nucleus. Both bundles course along and through terminal fields found in the lateral posterior nucleus. The visuotopic organization inferred from the corticofugal pathway shows that projection lines in the dorsal lateral geniculate nucleus (DLGN) run along medio-lateral strips including both the beta and alpha segments, across the quasi-laminae of retino-geniculate projection, and that naso-temporal axes in the visual field run in a dorso-ventral direction through the DLGN. The external layer of the ventral lateral geniculate nucleus receives a projection from the striate cortex and bilateral projections from the retina, and naso-temporal axes in the visual field are represented along a dorso-ventral direction in this layer. The striate cortical projections cover approximately the lateral two-thirds of the lateral posterior nucleus, overlapping a small retinal terminal field, and naso-temporal axes in the visual field are represented onto the cortico-recipient zone in a mirror-symmetric direction to that of the adjoining DLGN. In all these three cortico-recipient zones, dorso-ventral axes in the visual field are represented in a rostro-caudal direction.

Postnatal changes in retinal ganglion cell and optic axon populations in the pigmented rat

The number of ganglion cells in the retina of the postnatal rat has been examined. We estimated both the number of axons in the optic nerve and the number of cells which can be retrogradely labelled with horseradish peroxidase from injections into the brain. In the retina of the newborn rat there are at least twice as many ganglion cells as in the adult rat. By retrograde labelling of the ganglion cells and following transection of their axons 24-48 hrs later we can find no evidence that ganglion cells withdraw their axon without degeneration of the patent cell body. We have found that the excess ganglion cells are lost over the first ten postnatal days and during this period we observe pyknotic nuclei in the ganglion cell layer. From our estimates of the total number of neurones in the ganglion cell layer and the number of ganglion cells found at different ages we conclude that the migration of amacrine cells into the ganglion cell layer occurs in the first five postnatal days.

Retrograde and anterograde-transneuronal degeneration in the parabigeminal nucleus following tectal lesions in developing rats

Degenerative effects in the parabigeminal nucleus were studied in adult rats that had received lesions of the superior colliculus at different postnatal ages. Unilateral lesions lead to complete degeneration of the dorsal and ventral divisions of the parabigeminal nucleus, which connect reciprocally with the damaged tectum, and produce effects on the middle division which receives afferents from the ipsilateral and projects to the contralateral tectum. On the side contralateral to the lesion there was a reduction in the cross-sectional area of the division as a consequence of retrograde degeneration, except in rats operated on at birth or when adults; ipsilateral to the lesion there was a reduction in the cross-sectional area of the division as a result of anterograde-transneuronal degeneration, except in animals operated on when adults. The reduction in cross-sectional area is partly due to a decrease in the number of neurones in the middle division. The maximal effects in both cases occurred in animals operated on at 10 days after birth, and the sensitivity to retrograde degeneration follows a U-shaped curve. Bilateral tectal lesions performed at birth or 5 days after birth produce virtually complete degeneration of the whole parabigeminal nuclei. Anterograde radioautographic tracing showed that all parabigeminal divisions received topographically organized projections from the ipsilateral superior colliculus. Ipsilateral projections from the dorsal and ventral divisions and crossed projections from the middle division were identified in the tectum of newborn rats with fluorescent retrograde tracers. Possible explanations for the cases in which tectal lesions failed to produce an effect on the architecture of the middle division include increased resistance to axonal damage and regulative processes over natural neuronal death. The results also indicate that the two forms of degeneration are additive with regard to the whole population of developing parabigeminal neurones.

Massive retinotectal projection in rats

Retinal ganglion cells were labeled with horseradish peroxidase injected into the superior colliculus of normal pigmented rats. It is shown that virtually all ganglion cells with crossed axons project to the tectum, thus including all cell types described so far in the rat. The results contrast with the conclusion that only one-third of the ganglion cell population project to the tectum in normal hamsters.

Ganglion cell death within the developing retina: a regulatory role for retinal dendrites?

The effects of neonatal midbrain lesions on populations of retinal ganglion cells with ipsilateral or contralateral projections were investigated in hooded rats with the use of horseradish peroxidase. After bilateral lesions of the superior colliculus performed at birth, the number of contralaterally projecting ganglion cells is reduced but the number of ipsilaterally projecting cells is increased. Bilateral tectal lesions performed 5 days after birth reduce the number of both contralaterally and ipsilaterally projecting ganglion cells. Unilateral tecto-pretectal lesions performed at birth lead to extensive retrograde degeneration of contralaterally projecting ganglion cells in the opposite retina: but both the ipsilateral terminal fields of the same retina and its population of ipsilaterally projecting ganglion cells are increased. Cells located at the border between the temporal crescent and the nasal areas of the retina opposite an unilateral tecto-pretectal lesion were found to have their dendrites pointing towards the severely depleted nasal areas more frequently than in normal rats. These observations suggest that competitive interactions between retinal dendrites may play a role in regulating ganglion cell death in the developing retina. The increased population of ipsilaterally projecting ganglion cells would reflect the survival of neurones which would otherwise normally degenerate, resulting from reduced local interactions as a consequence of the massive removal of neighbouring contralaterally projecting cells.

The pretectal complex in the opossum: projections from the striate cortex and correlation with retinal terminal fields

Two terminal fields were revealed in the pretectal complex of the opossum by the Fink-Heimer method after striate cortical lesions. A rostral field is located within a rostrolateral strip of the compact part of the anterior pretectal nucleus, where a partial topographic arrangement of this projection is present. A caudal field is located within the sub-brachial nucleus of the optic tract, located between the brachium of the superior colliculus and the posterior pretectal nucleus. The corticotopic projection to this field is mirror-symmetric to that found in the superior colliculus and overlaps a bilateral projection from the retina. Based on neural pathway evidence, it is concluded that the nucleus of the optic tract in the opossum can be subdivided in (a) an intrabrachial nucleus receiving a direct projection from the contralateral retina and (b) a sub-brachial nucleus receiving projections from both retinae and from the striate cortex. The pretectal complex, as the superior colliculus, can be anatomically subdivided in a superficial region receiving visual input (the optic pretectum) and a deep region only remotely connected to the visual system. The optic pretectum, however, differs from the superior colliculus in displaying a multiple-map arrangement within its constituent nuclei, instead of a single continuous representation of the visual field.

Alcohol and rape in Winnipeg, 1966-1975

Either victim or rapist or both were drinking prior to 72% of the rapes occurring in Winnipeg from 1966 through 1975, and the presence of alcohol increased the likelihood that the victim would be injured prior to sexual intercourse.

Receptive field properties of single units in the opossum striate cortex

On the basis of their trigger-features, 98 units out of 127 recorded in striate cortex of immobilized opossums, under forced breathing of a nitrous oxide/oxygen mixture, were classified into 5 receptive field groups. Group 1 units (20/127) responding to small stationary spots were shown to be made up of regions of opposite response type and mutual antagonism, separate by linear boundaries. The optimal discharge was elicited by a stimulus configuration consisting of rectilinear regions of opposite contrast positioned and oriented in the visual field so as not to elicit antagonism while maximizing the overlap with regions responsive to that contrast. To edges in motion these units were shown to be made up of light and dark discharge centers, the locations of which could not be predicted from the map to stationary spots. In addition to position and orientation, direction was another important stimulus parameter. Group 2 units (34/127) had uniform requirements of stimulus orientation, direction of motion or both, througout the receptive field. Width was rarely a significant variable. Three subgroups were detected: orientation selective, directional selective and orientation-direction sensitive. Group 3 units (18/127) required stopped stimuli. In most instances (14/18) this property was attributed to a suppressive surround with relatively non-specific stimulus requirements. Oriented and non-oriented responsive receptive fields were observed. Group 3 units with no surround (4/18) responded best to properly positioned and oriented wedges, usually of 90 degrees. Group 4 units (24/127) had uniform fields with little stimulus specificity and were often responsive to diffuse light. Although not sensitive to stimulus orientation and direction, motion was frequently a requisite for optimal responses. Group 5 receptive fields (2/127) had concentrically arranged regions of distinct response type which displayed mutual antagonism. No sensitivity to orientation or direction was detected. Twenty-nine units remained unclassified. Other group distinctions were the relatively higher spontaneous activity of group 4 units and the large field sizes encountered among groups 1 and 4 when compared to group 2. Based on their properties and receptive field type distribution, we propose that striate receptive fields in the opossum have a similar organization to those of other mammals.