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Biomedical subjects

O Steward

Publications and source records attributed to O Steward.

At least 127 records · Page 7Linked to original sources
PubMed1983

Distribution and subcellular localization of calmodulin in adult and developing brain tissue.

The distribution and subcellular localization of calmodulin in adult and developing cerebellum was studied in rats by immunocytochemistry. Calmodulin immunoreactivity was found both in neurons and in glial cells. Within neurons the staining was particularly intense in the cell nucleus and in dendrites, the cytoplasm of the cell body was more lightly stained than the nucleus, and light immunoreactivity was observed in axons. Electron microscopic analysis confirmed the association of calmodulin with the nuclear chromatin, while the nucleolus remained unstained. The reaction product was also found overlying the membranes of several organelles, in postsynaptic densities and decorating both dendritic and axonal microtubules. In developing Purkinje cells, calmodulin immunoreactivity was found as early as 5 days after birth. During the initial phases of dendritic development (5-10 days post-natal), the reaction product was associated with the organelles of the apical cone, while little or no staining was observed in the elongating dendrites or in the cell nucleus. Later in development, calmodulin was found in primary and secondary dendrites, and by 20 days after birth immunoreactivity appeared in the cell nucleus, and in the postsynaptic densities of immature spines located in dendrites. The presence of calmodulin in the apical cone suggests the possibility that this protein may participate in the regulation of microtubule formation during the initial stages of dendritic development. Its presence in dendrites at later stages (during the period of synaptogenesis) may indicate that it also participates in the formation of synapses between the parallel fibres and dendritic spines.

Animals↗
PubMed1983

Increases in protein-precursor incorporation in the denervated neuropil of the dentate gyrus during reinnervation.

Cellular metabolic events accompanying postlesion synaptogenesis in the hippocampus were studied by analyzing incorporation of protein precursor ([3H]leucine) in the dentate gyrus. Adult rats were injected intravenously with [3H]leucine at periods from 2 to 60 days following unilateral destruction of the entorhinal cortex, and were killed 30 min later. Precursor incorporation was quantified autoradiographically by counting silver grains over the cell bodies and dendrites of dentate granule cells ipsi- and contralateral to the lesion. The relative grain density was increased over the denervated portion of the neuropil at 6-12 days postlesion, corresponding to the early phase of terminal proliferation and reactive synaptogenesis. Whereas incorporation was increased over the denervated neuropil, the availability of [3H]leucine was decreased relative to the contralateral side in autoradiographic preparations designed to reveal the concentration of the unincorporated 3H-labeled precursor and its diffusible degradation products. Silver grains were not selectively associated with glial cells bodies or vascular elements, but rather were distributed diffusely throughout the neuropil. Increases in grain density over the denervated zone were observed when animals were killed 8 min after the leucine injection, suggesting that the increases were not due solely to rapid transport from granule cell bodies to dendrites. We propose that an increased incorporation of protein precursor occurs primarily within the denervated dendrites of granule cells during the early phase of reinnervation, and that protein synthetic activity in these cells might be involved in the process of reinnervation.

Animals↗
PubMed1983

Immunocytochemical localization of actin and microtubule-associated protein MAP2 in dendritic spines.

To determine whether dendritic spines contain actin, we evaluated the immunocytochemical localization of actin in the hippocampal formation and cerebral cortex of the rat. Monoclonal hybridoma antibodies were prepared against adult quail breast muscle actin. The culture supernatant of two cell lines (QAB1 and QAB2) was examined. Both antibodies bound only actin in crude brain homogenates, and neither exhibited species specificity. Electron microscopic analyses of sections reacted with QAB1 revealed staining of postsynaptic densities and dendritic microtubules but little staining of the cytoplasmic compartment of spines. However, sections reacted with QAB2 exhibited staining at the cytoplasmic compartment of spines as well as the sites stained by QAB1. We also evaluated the immunocytochemical distribution of beta-tubulin and high molecular weight microtubule-associated protein (MAP2) utilizing monoclonal antibodies. MAP2 was found in the dendritic spine as well as in the parent dendrite. However, beta-tubulin was found only in the postsynaptic density and in the microtubules of the parent dendrite. The combined results indicate that actin is present in the spine along with MAP2 and that there is a difference in the actin (or the state of actin) in the spine in comparison with other neuronal compartments.

Actins↗
PubMed1982

Neurotoxic effects of colchicine: differential susceptibility of CNS neuronal populations.

Colchicine injected into the dentate gyrus of the hippocampus in adult rats preferentially destroys dentate granule cells. In the present study, we examine the light- and electron-microscopic correlates of the degeneration and evaluate whether the selectivity is preserved across the range of doses between 0.18 and 25 micrograms. Colchicine in a similar dose range was also injected into the cerebellum, olfactory bulb, striatum and cerebral cortex to examine local and regional differences in susceptibility to colchicine. The morphological changes accompanying degeneration in the dentate gyrus include fragmentation of the granule cell layer, appearance of small dark staining bodies in the cell layer, massive microglial invasion and profound disruption of granule cell axons and dendrites. Electron-microscopic observations suggest that the small dark bodies are probably condensed nuclei. The preferential vulnerability of dentate granule cells following intrahippocampal injection was observed at all doses. At doses between 0.18 and 2.5 micrograms there was little evidence of damage to neurons other than dentate granule cells. At the highest dose tested (25 micrograms) some pyramidal cells of regio superior near the injection site were destroyed, while granule cell destruction extended several mm from the injection site. Injection of 0.5-25 micrograms into the cerebellum resulted in the destruction of both granule cells and Purkinje cells, while cells which appeared to be neurons in the molecular layer were less affected. Following injection of 0.5 microgram into the olfactory bulb, granule cells were extensively destroyed and there appeared to be some loss of mitral cells and an overall shrinkage of the injected bulb. Neuronal destruction in the striatum was observed with colchicine injections ranging from 2.5 to 25 micrograms, but at a given dose, the destruction was less extensive than for any other region tested except cerebral cortex. A possible application of this method and the implications of these results for other investigators using colchicine in the brain are discussed.

Animals↗
PubMed1982

Reduction in caffeine toxicity by acetaminophen.

A patient who allegedly consumed 100 tablets of an over-the-counter analgesic containing sodium acetylsalicylate, caffeine, and acetaminophen displayed no significant CNS stimulation despite the presence of 175 micrograms of caffeine per mL of serum. Because salicylates have been reported to augment the stimulatory effects of caffeine on the CNS, attention was focused on the possibility that the presence of acetaminophen (52 micrograms/mL) reduced the CNS toxicity of caffeine. Studies in DBA/2J mice showed that: 1) pretreatment with acetaminophen (100 mg/kg) increased the interval between the administration of caffeine (300 to 450 mg/kg IP) and the onset of fatal convulsions by a factor of about two; and 2) pretreatment with acetaminophen (75 mg/kg) reduced the incidence of audiogenic seizures produced in the presence of caffeine (12.5 to 75 mg/kg IP). The frequency of sound-induced seizures after 12.5 or 25 mg/kg caffeine was reduced from 50 to 5% by acetaminophen. In the absence of caffeine, acetaminophen (up to 300 mg/kg) did not modify the seizures induced by maximal electroshock and did not alter the convulsant dose of pentylenetetrezol in mice (tests performed by the Anticonvulsant Screening Project of NINCDS). Acetaminophen (up to 150 micrograms/mL) did not retard the incorporation of radioactive adenosine into ATP in slices of rat cerebral cortex. Thus the mechanism by which acetaminophen antagonizes the actions of caffeine in the CNS remains unknown.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗
PubMed1982

Preferential localization of polyribosomes under the base of dendritic spines in granule cells of the dentate gyrus.

Electron microscopic studies of the dentate gyrus of the rat have revealed an apparent association between polyribosomes and dendritic spines. The present study was designed to elucidate the nature of this association. Our qualitative observations revealed that polyribosomes appeared primarily in two locations within the dendrite: (1) beneath the base of identified spines just subjacent to the intersection of the spine neck with the main dendritic shaft and (2) beneath mounds in the dendritic membrane which had the appearance of the base of a spine which extended out of the plane of section. To quantitatively define the nature of the apparent association, we attempted to determine (1) the proportion of spines with associated polyribosomes and (2) the proportion of the polyribosomes within dendrites which are associated with spine bases. Evaluation of profiles which were identifiable as spine neck-dendritic shaft intersections in a single section revealed that an average of 12.2% had associated polyribosomes. A serial section analysis revealed a somewhat higher incidence, however. Of a collection of 34 through-sectioned spines, 29% had polyribosomes which were revealed in one or more of the sections comprising the series. To evaluate what proportion of polyribosomes within the dendrite was associated with spines, we evaluated a series of photographs covering approximately 1250 micrometer2 of the dentate molecular layer from five animals, identifying all polyribosomes within dendrites and scoring their location as being (1) under spines, (2) under mounds, or (3) other. An average of 9.6% of the polyribosomes were found under processes identifiable as spine neck-dendritic shaft intersections, while 71.4% of the polyribosomes were found under mounds. Only 19% were not obviously associated with spines or mounds. Spine bases and mounds comprise only 3 of 35%, respectively, of the outline of dendritic profiles, however, indicating that the high incidence of polyribosomes under these elements cannot be accounted for by chance. To attempt to determine whether the mounds represent the base of dendritic spines, 68 mounds in 21 dentritic profiles were selected from the middle of the series of 20 serial sections. Ninetine of these mounds (28%) were continuous with an identified spine, and an additional 31% were continuous with thin processes of the size and appearance of spine necks. Thus, most of the mounds probably do represent the base of spines which extend out of the plane of a single section.

Animals↗
PubMed1982

Medial septal area lesions disrupt theta rhythm and cholinergic staining in medial entorhinal cortex and produce impaired radial arm maze behavior in rats.

This study was designed to determine (1) which brain area paces the theta rhythm in the medial entorhinal cortex (MEC) of rats and (2) the extent to which the behavioral effects of lesions in the medial septal area (MSA), which disrupt the cholinesterase-related pathway to the hippocampal formation, resemble the effects previously reported to result from fimbria-fornix lesions. MSA lesions abolished or decreased theta rhythm in dorsal hippocampus (DHPC) and MEC; acetylcholinesterase (AChE) staining was depleted or diminished in all of the hippocampus and entorhinal cortex. Rats with MSA lesions were impaired on acquisition of a radial arm maze task. Unilateral fimbria lesions left theta rhythm and AChE staining essentially unaltered in ipsilateral DHPC and MEC but depleted AChE in ipsilateral ventral hippocampus (VHPC) and ventral lateral entorhinal cortex (LEC). A lesion of the dorsal fornix at the level of the hippocampal flexure left ipsilateral DHPC theta rhythm and AChE stain unaltered while causing a substantial reduction in theta rhythm and depletion of AChE in ipsilateral MEC. AChE staining was complete in VHPC and LEC. These results suggest tha MSA paces MEC theta rhythm and that the presumed cholinergic projection which mediates this function travels in the dorsal fornix. The fimbria carries a presumed cholinergic projection to ventral LEC. Rats with MSA lesions can learn a radial arm maze task, unlike rats with fimbria-fornix lesions, but they learn significantly slower than normal rats.

Acetylcholinesterase↗
PubMed1981

Sprouting in the avian brainstem auditory pathway: dependence on dendritic integrity.

The brainstem auditory pathway of the chicken were used to examine the relationship between the maintenance of dendrites following denervation and the successful reinnervation (sprouting) by surviving afferents. In the system the third-order cells in n. laminaris receive spatially segregated binaural innervation from n. magnocellularis. Afferents from the ipsilateral n. magnocellularis innervate the dendrites on the dorsal aspect of n. laminaris cells, while afferents from contralateral magnocellular neurons innervate ventral dendrites via the crossed dorsal cochlear tract. Denervation of the ventral dendrites of n. laminaris cells by transection at the midline results in rapid and severe atrophy of the denervated dendrite. Unilateral cochlea removal induces transneuronal degeneration of 30-45% of the ipsilateral magnocellular cells, thereby partially denervating one dendrite of the n. laminaris cells on each side of the brain. In animals with long-standing transections of the crossed dorsal cochlear tract there is no evidence of sprouting the fibers from the ipsilateral n. magnocellularis when the projections of the surviving magnocellular neurons are traced with degeneration methods after a secondary cochlea removal. However, when dendrites of n. laminaris are partially denervated dendrites do not disappear. Furthermore, secondary lesions of the crossed dorsal cochlear tract or secondary cochlea removal reveal that these denervated dendrites are reinnervated by the afferents from the opposite n. magnocellularis which are normally restricted to the opposite dendrite of the n. laminaris cells.

Animals↗
PubMed1980

The effect of unilateral basilar papilla removal upon nuclei laminaris and magnocellularis of the chick examined with [3H]2-deoxy-D-glucose autoradiography.

The effect of unilateral basilar papilla removal on glucose uptake in the 2nd and 3rd order auditory nuclei in the chick's brain stem, nucleus magnocellularis and nucleus laminaris, respectively, was examined with [3H]2-deoxy-D-glucose (2-DG) autoradiography. The tissue was processed according to a thaw-mount technique, and the number of grains in the resulting autoradiographs was counted to assess changes in glucose uptake. It was observed that there is a greater density of grains over the neuropil regions of nucleus laminaris which receive input from the normal ear than over the corresponding regions which receive input from the operated ear. Similarly, differences in grain density are found between the normally innervated and deafferented magnocellular nuclei although these differences are not as great as those in nucleus laminaris. Differences in grain density were also apparent between the glial/fiber regions which bound the neuropil areas of nucleus laminaris; there is a greater density of grains overlying those glial/fiber regions through which fibers receiving input from the normal ear course than over those regions through which fibers which normally carry input from the operated ear travel. It is likely that this difference mainly reflects glucose uptake in the fibers although a possible contribution of glial tissue cannot be excluded. All these effects of basilar papilla removal are seen with survival times as short as 70 min and thus likely reflect the reduction of neural activity rather than the degeneration of pre- or postsynaptic elements. Finally, the same pattern of results as described above was found when using the more common [14C]2-DG procedure or when using [3H]2-DG but processing the tissue using the freeze-dried technique. The present results thus show the neuropil regions of nucleus laminaris and the adjacent glial/fiber areas to be areas of high glucose utilization. Unilateral basilar papilla removal results in the removal of an excitatory input to these regions, and this results in a reduction of glucose utilization that is specific to those neuropil regions and glial/fiber areas that receive input from the operated ear. These findings are contrasted with another study in which removal of a major excitatory input to the dentate gyrus of the rat results in a reduced glucose utilization which is not specific to the deafferented region and which largely reflects post- rather than presynatic events.

Animals↗
PubMed1980

Trajectory of contralateral entorhinal axons which reinnervate the fascia dentata of the rat following ipsilateral entorhinal lesions.

Unilateral destruction of the entorhinal area in the rat results in the proliferation of a pathway from the surviving contralateral entorhinal area to the fascia dentata denervated by the lesions (the crossed temporodentate pathway). The present study analyzes the point of entry of these reinnervating fibers into the fascia dentata, and their trajectory within the reinnervated zones utilizing orthograde transport of tritiated proline or horseradish peroxidase (HRP). Following injections of tritiated proline or HRP into the surviving entorhinal area in animals with long standing unilateral entorhinal lesions labeled axons could be visualized entering the contralateral fascia dentata via two routes. Labeled fibers could be traced from the dorsal hippocampal commissure (the dorsal psalterium) into the rostral tip of the fascia dentata (the fasciola cinerea) and from the terminal field of the crossed temporo-ammonic tract in regio superior into adjacent portions of the stratum moleculare of the fascia dentata. Within the stratum moleculare, most of the labeled axons had predominantly a caudal and lateral orientation. Exceptions to this predominant trajectory were found in the case of some of the axons which entered the ventral blade of the rostral fascia dentata, and coursed laterally from their point of entry. Comparisons of the trajectory of the crossed temporodentate projections with that of the normal ipsilateral pathway indicated that while the predominant trajectory of the fibers was roughly comparable, the polarity of the projections was in part opposite. Specifically, the normal ipsilateral pathway travels in a caudorostral direction, while the majority of fibers of the crossed temporodentate pathway apparently project rostrocaudally. The significance of this difference in the pattern of innervation is discussed with respect to the normal functioning of the temporodentate circuitry.

Animals↗