Biomedical subjects

R Lent

Publications and source records attributed to R Lent.

At least 37 records · Page 2Linked to original sources

PubMed1992

Bicommissural neurones in the cerebral cortex of developing hamsters.

The trajectory, developmental time course, and origin of callosal fibres that recross through the anterior commissure were studied in developing hamsters, using carbocyanines in fixed brains on different ages. The bicommissural fibres were found in hamsters from E15 through P7, but disappeared after P7. By double labelling it was found that the neurones of origin of these bicommissural fibres were located in the lateral cortex within the region where the callosal zone of origin overlaps that of the anterior commissure. From these experiments, it was concluded that the axons of a group of cells in the lateral cortex of developing rodents are branched and grow transiently through both the callosum and the anterior commissure.

Animals↗

PubMed1991

Development of paleocortical projections through the anterior commissure of hamsters adopts progressive, not regressive, strategies.

The perinatal development of anterior commissure projections was studied in hamsters by use of carbocyanine crystals implanted either into the commissure or into the ventrolateral prosencephalon. The earliest fascicles of growing commissural fibers had reached the midline on day 14 of gestation (E14). On E15, these fibers had entered the opposite hemisphere and reached the borders of their target regions. No waiting period was observed, since on E16 axons were already collateralizing into most targets. On P1, labelled cells were seen in all regions projecting through the anterior commissure in adults, namely, the anterior olfactory nucleus, olfactory tubercle, piriform cortex, nucleus of the lateral olfactory tract, bed nucleus of the stria terminalis, insular, perirhinal, entorhinal, and temporal cortices, as well as the amygdaloid complex. No evidence of topographical exuberance was detected. Counts of labelled neurons showed that the number of commissural cells increased gradually after birth. It is concluded that the development of paleocortical connections through the anterior commissure employs progressive strategies, lacking the regressive phenomena that are characteristic of the neocortical projections through the corpus callosum.

Aging↗

PubMed1991

Pioneer axons in the anterior commissure of hamster embryos.

The existence and the morphological characteristics of pioneer axons in the anterior commissure (AC) were investigated in hamster embryos using fluorescent carbocyanine crystals implanted into the paleocortex. On embryonic days 12-13 (E12-E13), a group of tortuous fibers was seen close to the midline. After this group of fibers reached the midline on E13.5-E14, pioneer axons were seen in the AC, and from E14.5 to E15.5 both pioneers and followers approached the targets, the former ahead of the latter by about 500 microns. Arborization took place as soon as the followers reached the targets (E15.5-E16). The pioneer cells were labeled retrogradely and were seen in the most superficial layers of the paleocortex, along the rostrocaudal extent of the hemisphere. The fact that pioneers appear only during or after crossing suggests the existence of factors either in the midline region and/or in the opposite hemisphere, which selectively accelerate the growth of the pioneers or decelerate the growth of the followers.

Animals↗

PubMed1991

The effects of total and partial callosal agenesis on the rotatory behavior of BALB/cCF mice.

We report a study on rotational behavior (free swim test) of 30 adult male mice of an inbred strain in which about 20% of the animals are born with callosal defects (the BALB/cCF strain). The experiment was designed to study the relationship between the development of the corpus callosum and the degree of lateralization in rotatory behavior. Most of the BALB/cCF mice (77%) were lateralized rotators. Although most animals with a normal callosal area presented individual asymmetry, there was no significant tendency for a populational asymmetry toward one side in this group. In contrast, 75% of the animals with abnormally small callosal areas were left rotators. These animals, therefore, presented not only individual asymmetry, but also a tendency for a populational asymmetry. It was concluded that disturbances in the development of the corpus callosum are related to the appearance of directional populational asymmetry in rotatory behavior.

Agenesis of Corpus Callosum↗

PubMed1990

Neurogenesis and development of callosal and intracortical connections in the hamster.

The developmental time-course of callosal and ipsilateral corticocortical projections was studied in embryonic and postnatal hamsters, from the time of neurogenesis until the appearance of adult patterns. Callosal neurogenesis was determined by combining the incorporation of [3H]thymidine injected on specific embryonic days with retrograde labelling of callosal neurons in the adult animal. The development of both callosal and corticocortical projections was studied by the transport of wheat germ agglutinin conjugated to horseradish peroxidase. Despite a significant radial disperson of postmigratory neurons born on the same day, it was found that the birthdates of callosally-projecting neurons in the frontal cortex were not restricted to a short period of time, but extended between embryonic days 13 and 15. This period covers the neurogenesis of cells in cortical layers III-V. Elongation of callosal axons (and possibly also of corticocortical fibres) started a couple of days before birth in the frontal cortex, and continued through the first postnatal days. After a "waiting period" of a few days, axons from both sets of projections were seen innervating restricted target sectors of the cortex. The zones of origin of these projections were initially exuberant, but were subsequently trimmed to overlap completely with the corresponding terminal fields. It is concluded that callosal and ipsilateral corticocortical projections undergo similar sequences of ontogenetic stages, suggesting that the development of neocortical connectivity as a whole may be governed by one and the same set of rules.

Animals↗

PubMed1990

Development of interhemispheric connections through the anterior commissure in hamsters.

The development of interhemispheric connections through the anterior commissure was studied in hamsters by use of the postmortem fluorescent tracer diI. Labelled commissural axons were seen to approach midline and cross it on E14 (E1, day of conception), extend into the opposite hemisphere and reach the terminal targets on E15, and start to arborize on E16. On P1 (day of birth), a few labelled neurons could already be seen in the anterior olfactory nucleus, olfactory tubercle, piriform and insular cortices, nucleus of the lateral olfactory tract, bed nucleus of the stria terminalis, amygdaloid complex, temporal, perirhinal and entorhinal cortices. In all these regions, labelled neurons became progressively more numerous on P3, P5 and P10, but their distribution did not change. Since no evidence of topographical exuberance of connections could be found, it is hypothesized that the development of anterior commissure connections is entirely progressive, lacking the regressive events that characterize callosal ontogenesis.

Animals↗

PubMed1988

The development of callosal and corticocortical innervation in the neocortex of the hamster.

The development of cortical afferentation by callosal and ipsilateral corticocortical fibers was studied in hamsters by transport of wheat germ agglutinin conjugated to horseradish peroxidase. Elongation of callosal axons (and possibly also of corticocortical fibers) started a couple of days before birth and extended through the first postnatal days. After a "waiting" period of a few days, axons were seen innervating restricted target sectors of the cortex. The zones of origin of these projections were initially exuberant, but they were subsequently trimmed down to overlap with the corresponding terminal fields.

Afferent Pathways↗

PubMed1988

The neurogenesis of the callosal population of cortical cells in hamsters.

The neurogenesis of the callosal subpopulation of cortical cells was determined in hamsters by associating incorporation of [3H]-thymidine injected on different embryonic days with horseradish peroxidase retrograde labelling in adulthood. Despite the great radial dispersion of migratory destinations of neurons born simultaneously, it was found that callosal birthdates in cortical area 6 extend from day E13 to day E15, a period that corresponds to the neurogenesis of layers III-V, where most callosal neurons come to be located in adults.

Animals↗

PubMed1987

Effects of prenatal irradiation on the development of cerebral cortex and corpus callosum of the mouse.

Defects of the cerebral cortex and corpus callosum of mice subjected prenatally to gamma irradiation were evaluated as a function of dose and of embryonic age at irradiation. Pregnant mice were exposed to a gamma source at 16, 17, and 19 days of gestation (E16, E17, and E19, respectively), with total doses of 2 Gy and 3 Gy, in order to produce brain defects on their progeny. At 60 postnatal days, the brains of the offspring were analyzed qualitatively and quantitatively and compared with those of nonirradiated animals. Mice irradiated at E16 were all acallosal. Those that were exposed to 2 Gy displayed an aberrant longitudinal bundle typical of other acallosals, but this was not the case in those irradiated with 3 Gy. The corpus callosum of animals irradiated at E17 with 3 Gy was pronouncedly hypotrophic, but milder effects were observed in the other groups. Quantitative analysis confirmed a dependence of callosal midsagittal area upon dose and age at irradiation, and, in addition, indicated an interaction between these variables. The neocortex of irradiated animals was hypotrophic: layers II-III were much more affected than layer V, and this was more affected than layer VI. Quantitative analysis indicated that this effect also depended on dose and age at irradiation and that it was due to a loss of cortical neurons. Furthermore, a positive correlation was found between the number of neurons within layers II-III, and V and the midsagittal area of the corpus callosum. Ectopic neurons were found in the white matter and in layer I of animals irradiated at E16 and E17, indicating that fetal exposure to ionizing radiation interfered with the migration of cortical neuroblasts.

Abnormalities, Radiation-Induced↗

PubMed1986

Dose-dependent occurrence of the aberrant longitudinal bundle in the brains of mice born acallosal after prenatal gamma irradiation.

Two groups of pregnant mice were gamma-irradiated at the 16th gestation day with doses of 2 or 3 Gy. All litters were born acallosal, but while the 3-Gy mice showed a severely hypotrophic neocortex without the aberrant longitudinal bundle typical of early disconnected rodents, in the 2-Gy group the cortex was less deranged and the aberrant bundle appeared consistently underneath the white matter.

Agenesis of Corpus Callosum↗

PubMed1985

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.

Age Factors↗

PubMed1984

Neuroanatomical effects of neonatal transection of the corpus callosum in hamsters.

Newborn hamsters were subjected to surgical transection of their corpora callosa under hypothermic anesthesia. After completion of their development, one group of animals had their brains prepared for cyto- and myeloarchitectonic analysis. Another group had a small pellet of polyacrylamide gel containing horseradish peroxidase (HRP) implanted in different cortical loci. All were perfused with fixatives and had their brains cut into serial sections. The operated brains showed the following anatomical features: (1) The corpus callosum was partially or totally absent; (2) an abnormal longitudinal bundle was present bilaterally underneath the white matter; and (3) except for the physical displacement of some medial structures, the general architecture of the brain appeared unchanged. Analysis of HRP material revealed that (1) the longitudinal bundle contains cortical fibers, of which at least some are commissural; (2) these cortical fibers display a topographic arrangement within the bundle. Results suggest that brain anatomy of "surgical" acallosal hamsters compares closely with that observed in mice with congenital defects of the corpus callosum, a spontaneous condition which also occurs in humans.

Animals↗

PubMed1983

Cortico-cortical connections reorganize in hamsters after neonatal transection of the callosal bridge.

Neonatal hamsters were subjected to transection of the callosal bridge. Later examination of the brains showed complete or partial absence of the corpus callosum and an anomalous bilateral longitudinal bundle of fibers. In addition, aberrant commissural fibers were seen to connect heterotopically the parietal cortex with the contralateral frontal cortex through a callosal remnant over the septum, and the olfactory cortex with the opposite frontal and parietal cortices through the anterior commissure.

Aging↗

PubMed1982

The organization of subcortical projections of the hamster's visual cortex.

The subcortical projections of the hamster's visual cortex were determined by use of injections of tritiated proline and heat lesions placed in different cortical loci. The brains were processed for autoradiography and silver impregnation of degenerating axons. Striate cortex was shown to project ipsilaterally to the dorsocaudal region of the caudate nucleus, a dorsolateral area within the thalamic reticular nucleus (RT), a laterodorsal region of the nucleus lateralis anterior (LA), the rostral half of nucleus lateralis posterior (LP), the whole territory of the dorsal (dLGN) and ventral (vLGN) geniculate nuclei, the anterior (PA) and posterior (PP) pretectal nuclei, the superior colliculus (SC), and the precerebellar pontine nuclei. In addition, the medial visual area (18b) was shown to project to a medial band of LA and part of the caudal half of LP, while the adjoining parietal cortex was seen to terminate in a lateral part of the caudate, a ventral band of LA, and the ventral half of rostral LP. Segregation of different cortical inputs was clear in LA, LP, caudate, and pons. The projections to dLGN, vLGN, SC, LP, and PA were retinotopically organized. Clear evidence of some topography was found within RT, PP, and the pons, although a consistent map could not be derived from the data.

Animals↗

PubMed1981

Chemical debridement of burns: mercaptans.

Experiments were conducted using non-enzymatic chemical agents (with emphasis on certain mercaptans), alone, in conjunction with enzymatic agents and/or other nonenzymatic chemicals for debridement of burns. Both in vitro (rats, pigs, humans) and in vivo (rats, pigs) tests were carried out. N-acetylcysteine, penicillamine and cysteine ethyl ester in low to moderate concentrations accelerate the debriding action of bromelain (an enzymatic preparation from pineapple stems) and in higher concentrations, N-acetylcysteine and penicillamine (cysteine ethyl ester was not tested) cause ready separation of the burn eschar from the underlying tissue before solubilization of the eschar is complete (rat) or has occurred (pig). Debridement of 3 degree burns of rats is complete within 4-6 hours; the take of immediately applied syngeneic skin grafts is complete and permanent. This is first time rapid debridement of 3 degree burns permitting immediate successful skin grafting has been accomplished with known defined chemicals. In pigs there is softening of the 3 degree burn eschar by N-acetylcysteine but little, if any, dissolution of the eschar. However, mechanical separation of the eschar from the underlying tissue is accomplished readily with a wooden throat stick with no bleeding. There is a change in color of the superficial layer of the underlying subcutaneous tissue from yellow-light brown to dark brown-black. The debrided areas begin to granulate promptly. The healing of deep dermal burns of pigs is hastened by the application of N-acetylcysteine for a day (beginning 24 hours after burning) while the healing of moderately deep dermal burns is not modified. Unburned skin is not damaged. There is no apparent systemic toxicity associated with the use of N-acetylcysteine for debridement of 10-15% b.s.a. 3 degree burns of rats or 15-20% b.s.a. 3 degree burns of pigs. Major emphasis has been on N-acetylcysteine because of the potential adverse secondary effect of penicillamine and cysteine ethyl ester; N-acetylcysteine is readily metabolized. The use of a keratolytic agent prior to the application of N-acetylcysteine hastens the latter's action. Sulfamylon and sulfadiazine can be used with N-acetylcysteine without interfering with its debriding action. The effects of the mercaptans are likely due largely to their ability to depolymerize connective tissue proteoglycans and proteins, especially at the interface between living and dead tissue.

Acetylcysteine↗

PubMed1980

Plasticity of the ipsilateral retinotectal projection in early enucleated opossums: changes in retinotopy and magnification factors.

The aberrant ipsilateral retinocollicular projection in early enucleated opossums was studied with both electrophysiological and radioautographic techniques. It was shown that the expanded projection originates from the same restricted region of temporal retina that gives origin to the normal ipsilateral projection. Furthermore, it was observed that the aberrant projection conveys a well-ordered retinotopy, with changes of the magnification factors compatible with the interpretation that ganglion cells at the borders of the ipsilaterally-projecting region display the most intense plastic response after enucleation.

Animals↗

PubMed1976

Retinofugal projections in the opossum, An anterograde degeneration and radioautographic study.

A study of anterograde degeneration and anterograde transport was undertaken in the opossum primary optic system in order to clarify several points regarding fiber organization and patterns of terminal fields. Through the radioautographic technique of axon tracing, it was demonstrated that the accessory optic system follows the generalized scheme of Hayhow, consisting of two fascicles the three terminal nuclei.

Animals↗

PubMed1976

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.

Animals↗