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Biomedical subjects

P Levitt

Publications and source records attributed to P Levitt.

At least 91 records · Page 5Linked to original sources
PubMed1991

Access to gastric tissue promotes the survival of axotomized neurons in the dorsal motor nucleus of the vagus in neonatal rats.

Lesioning the vagus nerve in the neck (cervical vagotomy) results in a rapid and virtually complete loss of motoneurons in the dorsal motor nucleus of the vagus in neonatal rats. The present study sought to determine whether access to gastric target tissue will promote the survival of these motoneurons after axotomy. Quantitative analysis demonstrates that subdiaphragmatic vagotomy, which leaves the cut vagal axons in close proximity to their normal gastric targets, results in significantly less motoneuron loss than cervical vagotomy. Furthermore, the loss of motoneurons after cervical vagotomy can be significantly reduced by transplanting embryonic gastric tissue to the neck of vagotomized neonatal host rats, in the vicinity of the cut axons. The survival effect of transplanted gastric tissue appears specific because control transplants of embryonic bladder tissue fail to reduce motoneuron death after cervical vagotomy. Injections of the neural tracers Fluoro-Gold and cholera toxin-horseradish peroxidase into gastric transplants labeled surviving motoneurons in cervically vagotomized rats, whereas tracer injections into bladder transplants or into host cervical tissues did not. These results indicate that neonatal vagal motoneurons are capable of making the adjustments necessary to survive axotomy if they have access to gastric target cells. The apparent dependence of injured neonatal vagal motoneurons on gastric tissue offers a new system in which to examine in vivo the trophic interactions between neurons and their targets.

Animals↗
PubMed1991

Early in vitro genesis and differentiation of axons and dendrites by hippocampal neurons analyzed quantitatively with neurofilament-H and microtubule-associated protein 2 antibodies.

Differentiating neurons initially extend neurites that are the precursors of axons and dendrites. The temporal pattern of neurite outgrowth has been studied extensively, but mostly qualitative analyses have been used to study this phenomenon. We have examined neurite outgrowth of hippocampal neurons in primary cultures using a polyclonal antibody against microtubule-associated protein 2 (MAP2) and a novel monoclonal antibody against the phosphorylated form of high neurofilament subunit (NF-H). These antibodies serve as markers for dendrites and axons, respectively. The neurite staining patterns were quantified during the first 10 days in culture and the analysis revealed that primary processes undergo three phases of differentiation: (i) in the first 24 h, the majority of primary neurites express MAP2 only and a small percentage express both MAP2 and NF-H; (ii) between 24 and 48 h, NF-H expression increases and it is coexpressed with MAP2 in many neurites as they begin to lengthen; and (iii) between 48 h and 4 days, MAP2 and NF-H protein expression occurs in separate populations of neurites. While most of the earliest forming primary neurites appear to be dendritic (MAP2 only), the coexpression of dendritic and axonal protein markers in a group of early forming processes suggests that these neurites may not be predetermined to become a dendrite or an axon. Our data also indicate that NF-H is detectable early in primary neurite development and that, based on in vivo localization and morphology of cultured neurites, the phosphorylated form of NF-H is concentrated in axons.

Animals↗
PubMed1991

Heterogeneous distribution of the limbic system-associated membrane protein in the caudate nucleus and substantia nigra of the cat.

The limbic system-associated membrane protein is a glycoprotein selectively associated, in the adult, with dendrites and cell bodies of neurons of the limbic system and related brain regions. In the present study, the distribution of the limbic system-associated membrane protein was studied by immunohistochemistry in the caudate nucleus and substantia nigra of the cat to determine how its expression relates to the compartmentalization of these areas. In all areas of the caudate nucleus, the pattern of limbic system-associated membrane protein immunoreactivity was highly heterogeneous, labeling zones that were in register with areas expressing neurochemical markers that classically identify striosomes. The extrastriosomal matrix exhibited low levels of staining. The results show that the limbic system-associated membrane protein is expressed by neurons within the target areas (striosomes) of subsets of limbic afferents (originating mainly from the basolateral nucleus of the amygdala and the prefrontal cortex), whereas regions of the caudate nucleus (extrastriosomal matrix) receiving inputs from other subdivisions of the limbic system, such as the cingulate cortex and the ventral tegmental area, contain relatively low levels of limbic system-associated membrane protein immunoreactivity. Thus the expression of this antigen may reflect the targeting of specific groups of limbic afferents to regions that are intimately associated with distinct components of the limbic system. The presence of limbic system-associated membrane protein in neurons of the substantia nigra pars compacta does not appear to be related to the presence or absence of the protein in their striatal target areas.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗
PubMed1991

Persistence of fluoro-gold following degeneration of labeled motoneurons is due to phagocytosis by microglia and macrophages.

When the neural tracer Fluoro-Gold is used to retrogradely label a population of axotomized neurons, cellular labeling can persist in the axotomized nucleus even when Nissl staining indicates that the injured neurons have degenerated. In order to determine the identity of the labeled cells that remain, this study combines retrograde transport of Fluoro-Gold with immunocytochemical methods for identification of specific non-neuronal cell types following peripheral axotomy and Fluoro-Gold labeling of motoneurons in the dorsal motor nucleus of the vagus in neonatal and adult rats. Fourteen days following cervical vagotomy in neonatal rats, Nissl staining revealed a virtually complete loss of vagal motoneurons. Fourteen days after cervical vagotomy in adult rats, vagal motoneuronal loss was not yet extensive but chromatolysis had clearly begun. Injection of Fluoro-Gold into the vagus nerve just prior to the vagotomy led to Fluoro-Gold labeling of remaining vagal motoneurons. In addition, many other small, brightly labeled cells were present in the lesioned vagal nuclei of all rats. Immunofluorescent identification of astrocytes with anti-glial fibrillary acidic protein and microglia and macrophages with OX42 (anti-C3bi complement receptor) and ED1 (anti-monocyte/macrophage cytoplasmic antigen) demonstrated that the small, bright Fluoro-Gold-labeled cells were non-neuronal, non-astrocytic phagocytes, including microglia. These results indicate that phagocytic microglia and other macrophages sequester Fluoro-Gold in the axotomized dorsal motor nucleus of the vagus of neonatal and adult rats, leading to persistence of fluorescent cellular labeling following the loss of retrogradely labeled axotomized neurons.

Age Factors↗
PubMed1991

The early commitment of fetal neurons to the limbic cortex.

The limbic-system-associated membrane protein (LAMP) is expressed early in cerebral cortical development by migrating and postmigratory neurons in limbic regions such as the prefrontal and perirhinal cortices (Horton and Levitt, 1988), but not by nonlimbic neurons such as in the primary sensory and motor cortices. In the present study, we used LAMP expression to evaluate the timing and potential cell-lineage and environmental determinants of the commitment of cerebral cortical neurons to limbic and nonlimbic phenotypes. The cerebral wall, containing either presumptive perirhinal or sensorimotor cortex, was removed prior to [embryonic day (E) 12, 14] or just after (E17) the onset of LAMP expression, labeled with fast blue, and placed into cavities in either perirhinal or sensorimotor regions of postnatal day (P) 1 hosts. Host animals were allowed to survive until at least P10, and surviving transplanted cells were counted and evaluated for LAMP expression. Sensorimotor cortical neurons transplanted at E14 or E17, in either homotopic or heterotopic locations, did not express LAMP. In contrast, a high percentage of perirhinal cortical neurons transplanted at either E14 or E17, whether situated in sensorimotor or perirhinal regions of the host, expressed the limbic marker protein. Surprisingly, neurons from E12 donors exhibited patterns of LAMP expression that reflected their new location in the host rather than their embryonic origin. The data suggest that there is an early pliant period in which precursor and early differentiating cells remain uncommitted to a particular cortical regional phenotype. After this period, one aspect of the molecular phenotype (determined by LAMP expression) of neurons destined for sensorimotor and allo- and mesocortical regions has become immutable by environmental factors in the host.

Animals↗
PubMed1990

Modification of astrocytes in the spinal cord following dorsal root or peripheral nerve lesions.

Glial fibrillary acidic protein (GFAP) immunocytochemistry was used to monitor the response of astrocytes in the rat spinal cord to either dorsal root or sciatic nerve lesions. Image analysis methods were used to provide a quantitative correlate of the reactive gliosis. Multiple dorsal root section elicited a rapid increase in GFAP immunoreactivity of astrocytes unilaterally within the spinal cord along the pathway of the degenerating dorsal root axons in the dorsal and ventral horns and this gliosis persisted in the dorsal horn beyond the time at which active phagocytosis of degenerative debris occurred. Labeling of proliferating cells using [3H]thymidine revealed that none of the dividing cells contained detectable GFAP, suggesting that the increased GFAP labeling represents primarily a hypertrophy rather than a proliferation of astrocytes. Comparison of animals that had been deafferented in the early neonatal period with those deafferented as adults indicated that the GFAP immunoreactive response persisted following neonatal lesions but that it was markedly less intense than after adult lesions. Sciatic nerve section in adults does not result in extensive frank degeneration but it does evoke a rapid and marked increase in staining of astrocytes both in the dorsal horn and in the ventral horn. Transganglionic changes in GFAP staining in the dorsal horn occur by 3 days post-operatively, which is much earlier than the time of dorsal root ganglion neuron death caused by the sciatic nerve lesion. These experiments indicate that astrocytes can respond to signals from a variety of changes in neurons, including not only Wallerian degeneration, but also retrograde and transganglionic changes.

Animals↗
PubMed1990

Isolation, biochemical characterization and ultrastructural analysis of the limbic system-associated membrane protein (LAMP), a protein expressed by neurons comprising functional neural circuits.

The limbic system-associated membrane protein (LAMP) is a cell surface glycoprotein expressed by cortical and subcortical regions of the mammalian CNS that comprise or receive direct projections from limbic system structures. The early and restricted expression of LAMP has led to its postulated role in neural development. Purification and biochemical characterization of LAMP was performed in order to ascertain its relationship to other, well-defined cell surface proteins in the nervous system. Subcellular fractionation, immunoaffinity chromatography, and Western blots of rodent and bovine hippocampus revealed that LAMP is an integral membrane protein with a molecular mass of 64-68 kDa and a pI of 5.2-5.5. Deglycosylation of LAMP indicates that it contains N-linked high mannose or hybrid sugars and a minor amount of sialic acid. The LAMP protein exhibits an identical molecular mass in developing hippocampus and in several different brain regions in the adult. No cross-reactivity was obtained using the monoclonal antibody that recognizes the HNK-1 carbohydrate epitope, a complex sulfated moiety expressed on members of a large family of glycoproteins. Immunocytochemical analysis at the ultrastructural level reveals that LAMP immunoreactivity is exhibited by neurons in a stereotyped pattern throughout limbic system areas. Glial cells are not immunoreactive. In the adult, LAMP-immunoreactive membrane patches are present exclusively postsynaptically on neuronal somata and dendrites. Myelinated and unmyelinated axons are not stained in any brain region examined. Analysis of LAMP expression in the developing CNS during synaptogenesis demonstrates that LAMP is located on growing axons and both pre- and postsynaptically at forming terminal complexes. Double-labeling studies of the hippocampal neurons grown in vitro reveal that the LAMP epitope is extracellular and is expressed on neurofilament- and microtubule-associated protein 2-positive neurites. Cells expressing glial fibrillary acidic protein are not LAMP-immunoreactive. These results demonstrate that in the adult brain, LAMP is expressed almost exclusively by the postsynaptic (target) elements in limbic circuits, but that during development, all components of the surface of the growing neuron contain LAMP. The stereotyped anatomical pattern of expression of LAMP in the developing and mature brain and its biochemical characteristics suggest that LAMP is a unique, system-associated membrane glycoprotein that is distinct from previously identified, developmentally important cell surface proteins.

Animals↗
PubMed1989

Developmental and regeneration-associated regulation of the limbic system associated membrane protein in explant cultures of the rat brain.

In the present study we have examined the topographic and temporal patterns of expression of the limbic system associated membrane protein by light and electron microscopic immunocytochemistry in organotypic cultures of the rat brain. The regional, cellular and subcellular distribution of staining in young cultures was similar to that in the intact brain of corresponding age. Since the tissue in vitro is isolated both from afferents and targets, short-term protein expression appears to be regulated by factors intrinsic to the neuron. In culture, the protein was present on the surface of neurons which are physiologically interconnected, such as neurons belonging to the septohippocampal system (cholinergic neurons in the septum and pyramidal and granule cells in the hippocampus). It was also present on the surface of axons and growth cones during process outgrowth. Thus, the limbic system associated membrane protein is expressed in an appropriate spatial and temporal pattern for mediating interactions between growing axons and their targets. The expression of the protein in culture showed some important differences as compared to the intact brain. With increasing age, there was an increasing scattering and disappearance of immunoreactivity in cultures fixed with paraformaldehyde/glutaraldehyde. The decreased immunoreactivity in aged cultures does not appear to reflect decreased protein synthesis, because unfixed and acetone-fixed explants continued to show immunostaining. Furthermore, dot-blot assays showed similar amounts of immunoreactivity in culture as in the intact brain of corresponding age. Thus, the age-dependent decrease of immunoreactivity may reflect altered insertion of the protein into the membrane or a modification of the epitope recognized by the antibody. There was a rapid increase (within 1 hour) of immunostaining on the surface of sprouting processes following mechanical lesion of mature, unstained axons. The altered distribution after tissue injury could be a means of ensuring specificity of connectivity during nerve fiber regeneration. On the basis of the reported findings, we suggest that system-specific membrane proteins, including the limbic system associated membrane protein, may mediate the formation of specific connections in the brain. Furthermore, we suggest that the reinnervation processes taking place after central nervous system injury may exhibit a similar molecular basis to the development of neural pathways.

Animals↗
PubMed1989

A membrane glycoprotein associated with the limbic system mediates the formation of the septo-hippocampal pathway in vitro.

The ability of a neuronal surface glycoprotein to mediate the formation of neuronal connections was tested in an explant culture system. A monoclonal antibody against the limbic system-associated membrane protein (LAMP) was used in co-cultures containing cholinergic neurons of the septum and their hippocampal target neurons. Antibody treatment had no effect on general axon outgrowth, but significantly diminished the ability of septal cholinergic axons to invade and collateralize in the hippocampus. The results suggest that factors regulating general axon outgrowth may be distinct from those regulating the patterns of outgrowth that define the formation of neural circuits.

Animals↗
PubMed1988

Normal pharmacological and morphometric parameters in the noradrenergic hyperinnervated mutant mouse, "tottering".

Pharmacological and anatomical analyses of central monoaminergic and cholinergic neurons were performed in the "tottering" mouse, an autosomal recessive neurologic gene mutation that results in an overproduction of axons of the locus coeruleus and an increase in norepinephrine content in specific terminal fields. Except for the previously reported increase in norepinephrine content, all pharmacological parameters measured, including tyrosine hydroxylase activity, norepinephrine turnover, serotonin content, and choline acetyltransferase activity, in targets hyperinnervated by the locus coeruleus were normal. Immunocytochemical staining for tyrosine hydroxylase demonstrated the pronounced hyperinnervation in the "tottering" brain, whereas both serotonin and choline acetyltransferase immunostaining were similar between "tottering" and wild type. The volume of 3 target areas that are hyperinnervated by the locus coeruleus in the "tottering" mouse, the hippocampus, cerebellum, and cochlear nuclei, were normal. In addition, neuronal number and somal size in the locus coeruleus were found to be unchanged in the mutant genotype. These data demonstrate several features of the effects of the "tottering" gene: 1) compensatory changes in several adrenergic pharmacological parameters do not occur in response to the hyperinnervation of targets by locus coeruleus axons; 2) neither direct effects of the "tottering" gene on, nor compensatory changes in, the extent of cholinergic or serotonergic innervation of several targets of the locus coeruleus appear to occur; and 3) the lack of changes in size of the targets of the locus coeruleus suggest that the hyperinnervation in the "tottering" mouse is due to a direct genetic alteration of axonal growth by the locus coeruleus neurons, rather than to selective shrinkage of targets in the presence of normal terminal arbors.

Animals↗
PubMed1988

Sleep apnea and the Chiari I malformation: case report.

The authors report the case of an ambulatory patient who presented with sleep apnea episodes of the central and obstructive types and an associated Chiari Type I malformation. The central episodes stopped and the obstructive episodes decreased markedly after decompression. The improvement in the so-called obstructive episodes was unexpected and indicates that they may have been on a central basis.

Adult↗
PubMed1988

A unique membrane protein is expressed on early developing limbic system axons and cortical targets.

The limbic system-associated membrane protein (LAMP) is a 64 kDa protein that, in the adult brain, is present in cortical and subcortical regions comprising the limbic system (Levitt, 1984). The developmental expression of LAMP was studied in fetal rat brains to determine the specific patterns of distribution and the cellular elements that exhibit LAMP immunoreactivity. Light microscopic immunocytochemical analysis revealed that LAMP is expressed on neurons and their growing axons early in fetal development, at a time coincident with pathway formation and differentiation of limbic system nuclei. In the forebrain, where limbic system structures are heavily concentrated, immunoreactivity appears on subpopulations of axons in a temporal sequence that correlates with the time of formation of pathways carrying limbic system axons. Thus, staining is evident first at embryonic day (E) 15 on fibers within the internal capsule coursing from the diencephalon to cortex. LAMP immunoreactivity appears over the next 3 d in the anterior commissure, fornix, and corpus callosum. Ultrastructural immunocytochemical analysis reveals dense surface staining of fascicles of developing axons and growth cones. The axonal staining is transient, disappearing during the second postnatal week of development. In cerebral cortex, cells in presumptive limbic cortical regions such as lateral perirhinal sulcal cortex and prefrontal cortex are LAMP immunoreactive from the inception of the cortical plate. These cortical regions are clearly delineated from surrounding unstained nonlimbic areas as early as E15. Thus, LAMP expression in the cortex may represent one of the earliest markers of specific cytoarchitectonic areas.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Central adrenergic receptor changes in the inherited noradrenergic hyperinnervated mutant mouse tottering.

Adrenergic receptor binding characteristics were analyzed in the mutant mouse tottering (tg/tg), a single gene locus autosomal recessive mutation causing hyperinnervation by locus coeruleus neurons of their target regions, which results in epilepsy. Instead of the expected down-regulation of receptors due to the hyperinnervation, both [3H]prazosin (alpha 1-receptor) and [125I]iodopindolol (beta-receptor) binding were normal in the tg/tg hippocampus, spinal cord and slightly increased in the cerebellum. This lack of postsynaptic receptor modulation in the target cells, combined with increased levels of norepinephrine due to the aberrant axon growth, may the critical factors in the expression of the abnormal spike-wave absence seizures in the tg/tg mouse.

Animals↗
PubMed1986

Selective infection of astrocytes by Chlamydia trachomatis in primary mixed neuron-glial cell cultures.

Both human biovars of Chlamydia trachomatis were able to productively infect primary cultures of fetal rat brain cells. Infected brain cells released bacteria that reinfected McCoy cells well as other cultured brain cells. The chlamydiae infected cultured astrocytes but were never observed to grow inside neurons, suggesting a selective susceptibility of specific brain cells to chlamydial infections.

Animals↗
PubMed1985

Specific cellular expression of monoamine oxidase B during early stages of quail embryogenesis.

Monoamine oxidase-B (MAO-B) is one of two distinct molecular forms of MAO that in part regulate the cellular levels of biogenic amines. In order to determine whether discrete cell populations known to express aminergic properties in the vertebrate embryo also express MAO-B, the distribution of MAO-B-immunoreactive cells was examined in early developing quail embryos. Two major patterns of staining emerge. First, tissues known to express several aminergic characteristics are initially MAO-B positive at early stages of development and continue to express immunoreactivity through Zacchei stage 20, the oldest stage examined. These include cells of the sympathetic and some cranial and trunk sensory ganglia (beginning at stage 13), the pancreas (stage 14), and the brain stem raphe (stage 14). Second, other structures that contain or accumulate biogenic amines are transiently MAO-B immunopositive during early stages of development. These tissues include extraembryonic yolk sac and presumptive gut endoderm (with most intense staining between stages 8 and 13), the ventral trunk neural tube (stages 14 and 16), and the notochord (stages 8-10). MAO-B immunoreactivity disappears from these regions at different stages, and none are MAO-B positive by stage 19-20. Other structures without known aminergic properties during early development also stain; these include liver (stage 20), mesenchymal cells that surround the Wolffian duct and lung buds (stages 14 and 18), and endothelial cells surrounding the dorsal aorta (stages 14 and 20). In general, however, MAO-B appears to be distributed in embryonic tissues that can use this enzyme to regulate biogenic amine levels either transiently or during initial phenotypic expression of aminergic traits.

Animals↗
PubMed1984

Region-specific distribution of catecholamine afferents in primate cerebral cortex: a fluorescence histochemical analysis.

The density, laminar distribution, spatial orientation, and intrahemispheric pathways of norepinephrine (NE)- and dopamine (DA)- containing axons were analyzed in a wide range of cytoarchitectonically distinct areas of cerebral cortex in the adult rhesus monkey by fluorescence histochemistry. Although the boundaries between most areas were rarely sharp, there were marked regional differences in density and distribution of monoamine afferents in different cortical regions. Fibers exhibiting typical DA-like morphology were found only in the temporal and frontal lobes including motor and premotor areas as well as anterior cingulate and prefrontal cortices. In contrast, NE-containing axons were present in all cerebral lobes, with notably high density in the somatosensory area and low numbers in primary visual cortex. Intracerebral distribution was characterized by a network of large preterminal axons coursing both anteroposteriorly and mediolaterally in layer VI and in the subjacent white matter. In most cytoarchitectonic regions examined, catecholamine (CA)-containing axons exhibited a bilaminar distribution into one superficial and one deep fiber band. The location and width of the two dense bands, as well as the orientation and relative density of fibers within them, was region specific. Although fluorescent axons were found at all cortical depths, layers I, and IV usually contained relatively few fluorescent axons while layers II-III and IV-V were often densely innervated. An observation that may reflect a specialization in gyrencephalic brains is the particularly dense CA innervation around sulcal invaginations in all cerebral lobes. The present results confirm previous biochemical evidence of regional heterogeneity in the concentration of DA and NE in the primate neocortex (Brown and Goldman, '77:Brain Res. 124:576-550) an provide the first anatomical demonstration of corresponding differences in the pattern and density of CA innervation in diverse cytoarchitectonic areas in rhesus monkey. These findings raise the possibility of selective targets and functions for CA fibers in different layers and regions of the primate cortex.

Animals↗