Electron Microscopic Degeneration Research Articles

Effects of Orally Administered 5-Fluorouracil and Its Derivative 5′-Deoxy-5-fluorouridine on 7,12-Dimethylbenz[β]Anthracene-Induced Breast Carcinomas in Rats

Antitumour activity of 20 mg/kg 5-fluorouracil (5-FU) and 100 or 200 mg/kg 5'-deoxy-5-fluorouridine (5'-DFUR) was assessed by tumour regression, light and electron microscopic changes, and immunohistochemical variations in broxuridine labelling in 7,12-dimethyl-benz[a]anthracene- (DMBA-) induced breast carcinomas in rats. The relative regression of tumours was significantly (P less than 0.05) greater in animals receiving 5-FU or 5'-DFUR than in control animals. Light microscopic changes became apparent after 3 or 4 days' treatment and were more evident after 4-21 days. Electron microscopic degeneration of tumours was observed after 1 day. The broxuridine labelling index decreased significantly (P less than 0.05) in rats receiving 5-FU and especially in those receiving 5'-DFUR. Concentrations of 5-FU in DMBA-induced breast carcinomas were significantly (P less than 0.05) higher in rats treated with 5'-DFUR than in those treated with 5-FU, and the histological degeneration was significantly (P less than 0.05) more advanced in 5'-DFUR- than in 5-FU-treated animals, possibly due to the higher pyrimidine nucleoside phosphorylase activity in the former treatment group.

Modification of left-right pairing during the development of individual crest synapses in the rat interpeduncular nucleus.

The synaptic organization of the rat interpeduncular nucleus is highly ordered in the normal adult. By 90 days of age, 90% of crest synapses in its intermediate subnuclei are formed by two cholinergic endings, one from each medial habenula. Stereological calculation of the number of crest synapses per intermediate subnucleus, based on total samples of crest synapses in 3-4 sections through the subnucleus, allows comparisons of afferent pairing among ages without interference by other developmental changes. Between 21 and 90 days of age, the total number of crest synapses per intermediate subnucleus increases tenfold (p less than 10(-8], from 90,000 at 21 days of age, through 130,000 at 28 days, 440,000 at 45 days, to 1,000,000 at 90 days. The volume of the intermediate subnucleus increases fivefold during the same interval. Electron microscopic degeneration was used to estimate the pairing of left and right habenula afferents at crest synapses at the same ages. Through 21 days of age, only one-third of crest synapses are formed with pairing of one left and one right medial habenula afferent, whereas two-third have both afferent endings arising from the same medial habenula. At 28 days of age left-right pairing has increased to 43%, and at 45 days of age 53%, or 240,000, are so paired. The number of same-side paired crest synapses at 45 days, 210,000, is 3.5 times the number so paired at 21 days (p = .003). This indicates continued formation of considerable numbers of crest synapses with this transient mode of airing as late as 45 days of age.(ABSTRACT TRUNCATED AT 250 WORDS)

Organization of retinogeniculate projections in turtles of the genera Pseudemys and Chrysemys.

Organization of retinal projections to the dorsal lateral geniculate complex in turtles has been studied by means of light and electron microscopic axon tracing techniques. Orthograde degeneration studies with Fink-Heimer methods following restricted retinal lesions show the entire retina has a topologically organized projection to the contralateral dorsal lateral geniculate complex. The nasotemporal axis of the retina projects along the rostrocaudal axis of the geniculate complex; the dorsoventral axis of the retina projects along the dorsoventral axis of the geniculate complex. The projection to the ipsilateral dorsal lateral geniculate complex originates from the ventral, temporal and nasal edges of the retina. The nasotemporal axis of the ipsilateral retina projects along the rostrocaudal axis of the geniculate complex. It was not possible to determine the orientation of the dorsoventral axis of the ipsilateral retina on the geniculate complex. Light microscopic autoradiographic tracing experiments and electron microscopic degeneration experiments show the retinogeniculate projection has a laminar organization. Retinogeniculate terminals are found in both the neuropile and cell plate throughout all three subnuclei of the dorsal lateral geniculate complex but have a distinctive distribution in each subnucleus. In the subnucleus ovalis, they are frequent in both the neuropile and cell plate which forms the rostral pole of the complex. In the dorsal subnucleus, they are most prevalent in the outer part of the neuropile layer, less frequent in the inner part of the neuropile, and rare in the cell plate. In the ventral subnucleus, they are frequent in the outer part of the neuropile but are also common in the inner part of the neuropile and cell plate. These observations point to several principles of geniculate organization in turtles. First, the complex receives projections from the entire contralateral retina and a segment of the ipsilateral retina. It thus has monocular and binocular segments that together receive a topologically organized representation of the binocular visual space and the contralateral monocular visual space. Second, the three geniculate subnuclei receive information from different, specialized regions of the retina and visual space. Subnucleus ovalis receives information from the frontal binocular visual field. The ventral subnucleus receives information from the caudal binocular field. The dorsal subnucleus receives input from the contralateral monocular field. Third, there is a lamination of retinal inputs in the geniculate complex which differs in character within the three subnuclei.(ABSTRACT TRUNCATED AT 400 WORDS)

Telencephalic terminals in the major retinal synaptic lamina of the goldfish optic tectum

Light and electron microscopic degeneration studies were used to examine the telencephalotectal pathway in goldfish. Both techniques showed that each telencephalic lobe sent bilateral projections to several tectal laminae. Degenerating synaptic terminals and fibers were observed in the major retinal projection lamina as well as in other tectal laminae. The terminals contained round to oval synaptic vesicles, asymmetric synapses and contacted relatively small postsynaptic profiles.

The synaptic organization of the cat entopeduncular nucleus: A combined electron microscopic degeneration and HRP study

The synaptic organization of the cat entopeduncular nucleus: A combined electron microscopic degeneration and HRP study

The synaptic organization of the cat entopeduncular nucleus: A combined electron microscopic degeneration and HRP study

The synaptic organization of the cat entopeduncular nucleus: A combined electron microscopic degeneration and HRP study

Left-right pairing at the crest synapses of rat interpeduncular nucleus

Synaptic terminals of the habenulo-interpeduncular axons in rat interpeduncular nucleus were demonstrated by electron-microscopic autoradiography following [ 3H]leucine injection into the habenula. The endings are of two types, S and crest synapses. Previous descriptions of the S synapses based on indirect identification were confirmed. The crest synapses in the interpeduncular nucleus consist of two habenular afferents contacting a narrowed dendrite. Injection of both habenulae with radiolabeled amino acid resulted in autoradiographic labeling of both axons at 48% of individual crest synapses, and of one axon at 39%. However, when only one habenula was injected, no more than one axon was labeled at individual crest synapses; this occurred at 59%. Interpretation of unlabeled endings is possible using the “detection rate” of the method (per cent ratio of labeled to total endings). The detection rate, which can be determined for the bilateral injection case, allows recalculation of the raw data for the unilateral injection case. Left-right pairing of habenular afferents actually occurs at approximately 90% of crest synapses. The use of detection rates in this way, additionally exemplified by analysis of an electron-microscopic degeneration study, is also important in many other applications of both of these experimental neuroanatomical methods, especially when comparisons between two sets of data are made. The conclusions of studies which have not taken this problem into account must be interpreted with caution.

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.

Cytoarchitecture, fiber connections, and ultrastructure of nucleus isthmi in a teleost (Navodon modestus) with a special reference to degenerating isthmic afferents from optic tectum and nucleus pretectalis.

Cytoarchitecture and fiber connections of the nucleus isthmi in a teleost (Navodon modestus) were studied by means of Nissl, Bodian, toluidine blue, Golgi, and Fink-Heimer methods. Synaptic terminals were classified by the ultrastructural characteristics, and their origins were determined by electron microscopic degeneration experiments. The nucleus isthmi is composed of an outer cellular area or shell and an inner noncellular area or core. The shell covers anterior, dorsal, and ventral aspects of the core. The cell bodies in the shell are oval (15 x 20 micrometers) with an anteroposterior long axis, and have many somatic spines. Spines are also seen on the initial segment of the axon. Primary dendrites extend posteromedially and branch out in the core. The core contains thin and thick myelinated fibers, which originate in the optic tectum and in the nucleus pretectalis, respectively. At least two types of axon terminal were distinguished in the nucleus isthmi: S type, containing spherical vesicles, and F type, containing flattened vesicles. S terminals are derived from thin myelinated fibers and are only seen in the core where they form asymmetric synapses with dendrites. Frequently a portion of the S terminal membrane near the usual synaptic cleft is in close apposition with the membrane of an adjacent small dendrite or spine. F terminals, which derived from thick myelinated fibers, make symmetric synaptic contacts with both cell bodies in the shell and dendrites in the core. S terminals degenerate after ipsilateral ablation of the optic tectum, whereas F terminals degenerate after destruction of the nucleus pretectalis.

The ultrastructural identification of vagal terminals in the solitary nucleus of the cat after anterograde labelling with horseradish peroxidase

Horseradish peroxidase (HRP) was injected into the nodose ganglion of the cat in order to label the axon terminals of vagal afferent fibres in the solitary nucleus. HRP reaction product was seen in axons, the majority of which were unmyelinated. Axon terminals containing round clear vesicles and an occasional dense-core vesicle were also labelled. These terminals synapsed upon both large and small dendritic elements, the majority of which were less than 1.0 μm in diameter. This labelling method appears not to affect adversely the normal ultrastructural characteristics of terminals or their postsynaptic relationships and in these respects is superior to electron microscopic degeneration methods.

Direct retinal input to the limbic system of the rat

Retinal projections in rats were studied using anterograde horseradish peroxidase (HRP) tracing and electron microscopic (EM) degeneration. HRP-labeled axons were observed to leave the optic tract in the vicinity of the lateral geniculate nucleus and enter the stria terminalis where they coursed anteriorly to the bed nucleus of the stria terminalis (BNST), and the anterodorsal (TAD) and anteroventral (TAV) thalamic nuclei. After enucleation, selected areas studied with EM confirmed that retinal presynaptic terminals are located in the BNST and TAV. These results support the finding of Conrad and Stumpf that the retina has a direct link to the limbic system 2.

Autoradiographic and electron microscopic degeneration evidence for axonal sprouting in the rat corticopontine system

Newborn (2 or 3 days postnatal) rats were subjected to unilateral cerebral cortical lesions involving much of the anterior (sensorimotor) cortical surface in the right hemisphere. Three months later, the survivors were divided into two groups, one group receiving a [ 3H]leucine injection in the left sensorimotor cortex and the other sustaining a lesion involving the left sensorimotor cortex. Routine autoradiographic studies in the first group revealed abnormally dense axonal and terminal labeling in the pontine gray contralateral to the leucine-injected hemisphere, suggesting that much of the label was due to sprouting from intact corticopontine axons into the neonatally deafferented pontine gray. In the group with a second (adult) cortical lesion contralateral to the neonatal ablation, degenerating axons and boutons were abundant in the pontine gray contralateral to the adult lesion and at least some of these were interpreted to represent sprouted corticopontine axons and their terminals.

The organization of the lateral posterior nucleus of the golden hamster after neonatal superior colliculus lesions.

The reorganization of the adult hamster's lateral posterior nucleus after neonatal superior colliculus lesions was studied using primarily light and electron microscopic degeneration techniques. Two types of experiments were conducted. First, the distributions of the remaining afferents from the contralateral superior colliculus, the cotralateral retina, and the ipsilateral posterior neocortex were determined using the Fink-Heimer ('67) technique. Normally the projections from the contralateral superior colliculus and retina are sparse and restricted to small areas in the rostrolateral subdivision. After neonatal lesions of the ipsilateral colliculus, however, these two minor projections greatly increase in density and expand to share a common border. In contrast, the normal projection from the posterior neocortex is dense throughout the rostrolateral subdivision. After a neonatal colliculus lesion, however, this projection is greatly decreased in the region occupied by the optic tract terminals. Second, the ultrastructural organizatin of the rostrolateral subdivision was studied in adult animals whhich had received neonatal colliculus lesions. Normally, this region is characterized by synaptic clusters in which numerous medium-sized terminals (M-terminals), almost all from the ipsilateral colliculus, synapse around the shaft of a large central dendrite. The contralateral colliculus and retina normally contribute only a few M-terminals. After a neonatal colliculus lesion, typical clusters still form, but now the expanded projections from the contralateral colliculus and retina contribute numerous M-terminals. The cortex does not contribute M-terminals in either normal or experimental animals. These results suggest that the afferents to the rostrolateral subdivision normally compete for synaptic space. The various factors that might be involved in determining the outcome of such competition are discussed.

Intrinsic organization of snake lateral cortex.

Lateral cortex is the most laterally placed of the four cortical areas in snakes. Earlier studies suggest that it is composed of several subdivisions but provide no information on their organization. This paper first investigates the structure of lateral cortex in boa constrictors (Constrictor constrictor), garter snakes (Thamnophis sirtalis), and banded water snakes (Natrix sipedon) using Nissl and Golgi preparations; and secondly examines the relation of main olfactory bulb projections to the subdivisions of lateral cortex using Fink-Heimer and electron microscopic preparations. Lateral cortex is divided on cytoarchitectonic grounds into two major parts called rostral and caudal lateral cortex. Each part is further divided into dorsal and ventral subdivisions so that lateral cortex has a total of four subdivisions: dorsal rostral lateral cortex (drL), ventral rostral lateral cortex (vrL), dorsal caudal lateral cortex (dcL) and ventral caudal lateral cortex (vcL). Systematic analyses of Golgi preparations indicate that the rostral and caudal parts each contain distinct populations of neurons. Rostral lateral cortex contains bowl cells whose dendrites arborize widely in the outer cortical layer (layer 1). The axons of some bowl cells can be traced medially into dorsal cortex, dorsomedial cortex and medial cortex. Caudal lateral cortex contains pyramidal cells whose somata occur in layers 2 and 3 and whose dendrites extend radially up to the pial surface. In addition, three populations of neurons occur in both rostral and caudal lateral cortex. Stellate cells occur in all three layers and have dendrites which arborize in all directions. Double pyramidal cells occur primarily in layer 2 and have dendrites which form two conical fields whose long axes are oriented radially. Horizontal cells occur in layer 3 and have dendrites oriented concentric with the ependyma. Fink-Heimer preparations of snakes which underwent lesions of the main olfactory bulb show that the primary olfactory projections to cortex are bilateral and restricted precisely to rostral lateral cortex. Electron microscopic degeneration experiments indicate that the olfactory bulb fibers end as terminals which have clear, spherical vesicles and asymmetric active zones. The majority are presynaptic to dendritic spines in outer layer 1. These studies establish that lateral cortex in snakes is heterogeneous and contains two major parts, each containing two subdivisions. The rostral and caudal parts have characteristic neuronal populations. Primary olfactory input is restricted to rostral lateral cortex and seems to terminate heavily on the distal dendrites of bowl cells. Axons of some of these cells leave lateral cortex, so that the rostral lateral cortex forms a direct route by which olfactory information reaches other cortical areas. The functional role of caudal lateral cortex is not clear.

Synapse formation after injury in the adult rat brain: Failure of fimbrial axons to reinnervate the bed nucleus of the stria terminalis

Selectivity in the reinnervation of denervated postsynaptic sites in the adult rat septal nuclei has been studied by both light and electron microscopic degeneration techniques after lesions of the fimbria and stria terminalis. In the mid-rostrocaudal septum the ventral border of the lateral septal nucleus is coextensive with the dorsal border of the strial bed nucleus. In the normal rat, fimbrial axons establish synapses throughout the lateral septal nucleus of the same side, and also in the dorsal part of the lateral septal nucleus on the opposite side. The stria terminalis establishes synapses in the ipsilateral but not in the contralateral bed nucleus at this level. Both the fimbria and the stria terminalis were completely severed on the left side, and after adequate survival for the removal of all degeneration, the distribution of the remaining fimbria was plotted. Interesting changes were found on the side contralateral to the second lesion, where the fimbria both increases the number of its synaptic terminals within its proper contralateral territory (the dorsal part of the lateral septal nucleus) and also extends its distribution into the ventral part of the lateral septal nucleus — the territory normally reserved for the ipsilateral fimbria. Although completely surrounding the strial bed nucleus, fimbrial axons fail to invade the bed nucleus, and fimbrial terminals are no obvious structural barriers between the neuropil postsynaptic sites. Since there are no obvious structural barriers between the neuropil of the lateral septal nucleus and that of the strial bed nucleus it is suggested that this failure is most likely to be due either to some biochemical incompatibility between fimbrial axons and strial postsynaptic sites, or to the fact that the fimbrial axons are denied access because some other (unidentified) axonal system forms new presynaptic terminals which effectively pre-empt the sites in the strial bed nucleus.

Electron microscopic demonstration of caudal afferents to the rat interpeduncular nucleus

Analysis of the synaptology of the rat interpeduncular nucleus is of interest, amongst other reasons, because of morphological and biochemical evidence for synaptic sprouting following lesions of the habenular nucleus. Thus far only the synapses arising from the habenulointerpeduncular afferent axons have been identified by electron microscopy. The afferents from the midbrain tegmentum, which form a tegmentopeduncular tract, have been studied by the electron microscopic degeneration method in adult rats. Electrolytic lesions were placed stereotaxically so as to destroy the tegmentopeduncular tract, as well as various portions of the dorsal or ventral tegmental nuclei. The degeneration of endings in the interpeduncular nucleus was the same in each case. This consisted of (1) occasional neurofilamentous type degeneration of axons forming axodendritic synapses at 3 days' survival; (2) dense type degeneration of axons in contact with either small (0.4–0.8μm) or large (1.4–2.0μm) dendrites, with synaptic contacts which were symmetrical to moderately asymmetrical; (3) occasional axosomatic synapses also showing dense type degeneration. The projection was apparently greatest in the caudal portion of the interpeduncular nucleus. Equally important were observations of structures which were unaffected by the lesions. These included the S and crest synapses, some somatic synapses, and apparently normal numbers of synapses containing flattened vesicles. The present observations demonstrate the afferents from the tegmentum caudal to the interpeduncular nucleus at the fine structural level. A small number of those synapses previously classified as S or somatic synapses, and possibly as F synapses are of this origin. These afferents may be those which undergo sprouting caused by habenular lesions, with resulting formation of heterologous crest synapses, increase in number of somatic synapses, or both.

Electron microscopic identification of mammillary body terminals in the rats AV thalamic nucleus by means of anterograde transport of HRP. A quantitative comparison with the EM degeneration and EM autoradiographic techniques

A comparison has been made between the number of horseradish peroxidase (HRP)-labeled mammillary body terminals in the antero-ventral (AV) nucleus and the number of such terminals labeled with the electron microscopic (EM) autoradiographic [6] and EM degeneration technique [6]. With the anterograde HRP technique less terminals were labeled than with the autoradiographic technique, but more than with the degeneration technique. Furthermore it may be concluded that the anterograde HRP technique is suitable for determining the type of terminal and does not require the long exposure time of the autoradiographic technique.

LIGHT AI{D ELECTRON MICROSCOPIC STT]I}Y ON TWO OF THE AFFEftEIiIT PROJECTIONS TO THE AMYGDALA

Several studies were made on the level of light microscope to examine the various afferents which termi' nate in the amYgdala' Studies with electron microscopic degeneration methods, however, were very limited in number.Hall (19?2) in her review article on the structural organization of the amygdala described preliminary results dealing with degenerated terminal boutons in the amygdala after lesions involving the pre-optic area and the temporal cortex.Recently, Wakefleld and Hall ( 19?4) demonstrated degenerated terminal boutons containing flattened vesicles in the central, medial and basolateral nuclei after lesions in the lateral pre-optic area.The present work is a combined light and electron microscopie investigation to localize the site and mode of termination of the olfactory flbres from the olfactory bulb, and of the neocortical afferents from the inferior temPoral area to the v+ rious amygdaloicl nuclei.

Prenatal development of central optic pathways in albino rats.

The development of the central optic projections in albino rat fetuses has been studied using light and electron microscopic degeneration techniques and the horseradish peroxidase method for demonstrating axonal projections of neurons. The first optic axons to reach the region of the optic chiasm arrive at day 15. By day 16, a substantial optic chiasm is seen and the optic tract can be traced into the epithalamus, having first passed through the ventral lateral geniculate nucleus and a thin lamina of cells which is thought to correspond to part of the future dorsal geniculate nucleus. A growth rate of 80-100 mum per hour is estimated for the fastest growing axons. By day 16-1/3 the first axons have entered the anterior border of the superior colliculus and in the next day have grown across the entire rostrocaudal extent with the exception of the medial and lateral edges. The optic axons are recognized at day 17 as bundles lying just below the surface, but in older animals they come to lie deeper, as the whole layer of optic innervation broadens. The first synapses to be formed in the superior colliculus (some of them of optic origin) appear on day 17. Subsequently, there is a gradual increase in the number of contacts, the great majority being formed by optic axons. Compared with previous studies on Xenopus and chick, one of the most striking features of the development of the central visual connections in the rat is the relatively long time before the first optic axons reach the brain and the speed with which they innervate the central structures once they have arrived.