Biomedical subjects

R D Madison

Publications and source records attributed to R D Madison.

26 records · Page 2Linked to original sources

PubMed1991

Double-labeling of saphenous nerve neuron pools: a model for determining the accuracy of axon regeneration at the single neuron level.

We have developed a labeling procedure which accurately and consistently labels the original sensory pools projecting to their respective nerve branches as a model to quantify the accuracy of nerve regeneration at the single neuron level. Adult and juvenile rats had the saphenous branch of the femoral nerve transected just distal to the bifurcation of the nerve into a sensory branch (saphenous nerve) and a motor branch (nerve to the quadriceps muscle) and exposed to a 3% solution of 1,1'-di-octadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) for 1 h, and then reanastomosed. Two weeks later the sensory branch was redivided proximal to the previous site and labeled with a second tracer (5% fluorogold) using similar procedures. Five days later the animals were killed and cryostat sections were prepared and analyzed with a fluorescence microscope to score single- and double-labeled primary sensory neurons. The results show that the primary sensory neurons which project into the saphenous nerve can be reliably prelabeled by exposure of the saphenous nerve to DiI, and two weeks later approximately 99% of the same population of neurons can be labeled by exposure of the nerve to a second dye, fluorogold. This model system will be very powerful for future studies concerning target reinnervation following nerve regeneration.

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PubMed1991

Neuroblastoma grafts are noninvasively removed within mouse neocortex by selective laser activation of intracellular photolytic chromophore.

Studies of neural cell transplantation would be aided by the ability to damage or destroy, noninvasively and extremely selectively, grafted cells at defined times following their initial implantation. Mechanisms of graft integration and performance could be investigated, also providing insight into natural injury and repair mechanisms. At long wavelengths between 650 and 850 nm, laser energy can penetrate several millimeters of brain tissue without absorption or damage to the unpigmented tissue. However, targeted cells are selectively damaged by illumination at these long wavelengths if they contain latex nanospheres with incorporated cytolytic chromophores (e.g., chlorin e6). Light penetration allows many thousands of cells to be lesioned simultaneously, noninvasively, and deep within a surrounding matrix of other tissue. Such laser-activated damage has been termed laser photolysis (PL). We studied damage to C1300 neuroblastoma (NB) cells grafted into mouse neocortex in vivo by this process of PL. NB cells provided a simple and reproducible model of neural grafting, allowing direct histologic assessment of cellular growth and viability by distinct morphologic and mitotic criteria. Cells were cultured by standard methods, labeled in vitro by brief exposure to nanospheres containing chlorin e6, and grafted to sites within deep layers of mouse neocortex. Mice were exposed to transcranial, fractionated, unfocused pulses of 670-nm-wavelength energy totaling 90-120 J/cm2. We histologically assessed graft growth and cellular viability over a period from 2 d to 4 weeks, measured graft volumes quantitatively during the period of early rapid growth in controls (2 and 7 d), and generated 3-D reconstructions from serial sections to assist in visual analysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

Progressive incorporation of propidium iodide in cultured mouse neurons correlates with declining electrophysiological status: a fluorescence scale of membrane integrity.

We describe a visual assay of neuronal electrophysiologic status for use with cultured neurons, based on the exclusion of propidium iodide (PI) by intact cellular membranes. We use this fluorescent dye, which binds to nucleic acids, at concentrations suitable for long-term exposure to neurons without toxicity. We correlate the progressive loss of resting membrane potential and the progressive inability to generate stimulated action potentials by cultured mouse dorsal root ganglion neurons with increasing incorporation of PI. The scoring system used to gauge incorporation of PI is rapid and highly reproducible using a standard fluorescence microscope. Applications exist for studies of neuronal toxicity, survival, and electrophysiology in vitro.

Animals↗

PubMed1989

Mapping neuronal inputs to REM sleep induction sites with carbachol-fluorescent microspheres.

The cholinergic agonist carbachol was conjugated to latex microspheres that were fluorescently labeled with rhodamine and used as neuroanatomical probes that show little diffusion from their injection site and retrogradely label neurons projecting to the injection site. Microinjection of this pharmacologically active probe into the gigantocellular field of the cat pontine brain stem caused the awake cats to fall into rapid movement (REM) sleep indistinguishable from that produced by free carbachol. Three-dimensional computer reconstruction of the retrogradely labeled neurons revealed a widely distributed neuronal network in the pontine tegmentum. These pharmacologically active microspheres permit a new precision in the characterization and mapping of neurons associated with the control of behavioral state and of other cholinergic networks.

Animals↗

PubMed1988

Entubulation repair with protein additives increases the maximum nerve gap distance successfully bridged with tubular prostheses.

The major objective of the experiments reported in this paper was to test the hypothesis that the maximum distance that peripheral nervous system (PNS) axons can regenerate through a tubular prosthesis may be increased by specific modifications to the internal environment of the prosthesis. The sciatic nerve of adult male rats was transected and proximal and distal nerve stumps were sutured into a silicone tube 20-25 mm in length. The silicone tubes were implanted empty, or the lumen was filled with collagen or a laminin-containing gel. Following 4-16 weeks survival time animals were sacrificed and the contents of the silicone tubes were processed for histological identification of myelinated and unmyelinated axons. All of the tubes with additives, but one of the initially empty tubes, displayed a regenerated nerve cable within the tube. Retrograde labeling studies were carried out to prove that some of the axons present in the regenerated nerve cables arose from primary motor and sensory neurons. These results show that specific modifications to the microenvironment of regenerating PNS axons can affect the success or failure of tubular prostheses for nerve repair.

Animals↗

PubMed1988

Non-invasive laser microsurgery selectively damages populations of labeled mouse neurons: dependence on incident laser dose and absorption.

Selective photothermolysis (SP) is a novel technique by which brief, unfocused laser pulses are selectively absorbed by, and cause selective thermal damage to, endogenously pigmented structures. This report describes the use of an exogenous non-fluorescent chromophore (Procion blue) to effect cellular damage by SP. Cultured dorsal root ganglia neurons were selectively labeled with Procion blue and subjected to varying doses of laser illumination. Progressive cellular damage was assessed by leakage of propidium iodide through damaged membranes. The neurons targeted via an exogenous chromophore sustained damage which was proportionate to laser dose and chromophore concentration. The results of these experiments demonstrated that the rate and extent of neuronal damage can be controlled by adjusting either the incident dose of laser energy or the amount of target chromophore within cells. Selective photothermolysis will provide an experimental tool for neurobiologists in particular and will find general use within the biomedical field.

Animals↗

PubMed1988

Acidic fibroblast growth factor enhances regeneration of processes by postnatal mammalian retinal ganglion cells in culture.

Postnatal rat retinal ganglion cells (RGCs) were identified with specific fluorescent labels and placed in culture. Under these conditions, the outgrowth of processes by RGCs was found to be promoted to a far greater degree by acidic fibroblast growth factor (aFGF) than by basic fibroblast growth factor (bFGF). The effect of aFGF and bFGF on process extension by solitary RGCs was quantified after 24 hr in culture, a time when neither a FGF nor bFGF enhanced RGC survival. The action of aFGF on process outgrowth was markedly potentiated by the addition of heparin (10 micrograms/ml) to the medium, but heparin alone had no effect. In the presence of heparin, half-maximal process outgrowth occurred at an aFGF concentration of less than 20 pg/ml (1 pM). Since all of the centrally projecting processes have already been formed in the living animal prior to use (at 7-12 days of age), at least a portion of the process outgrowth in culture appears to represent a regenerative phenomenon. Statistical analysis of the increase in process growth revealed that aFGF with heparin contributed to both neurite initiation and elongation. The mean number of glial cells, identified with polyclonal antiserum against glial fibrillary acidic protein, was slightly increased in cultures receiving aFGF plus heparin, but this effect was variable, and these glial cells were not in contact with the solitary RGCs that were scored for regeneration of processes. Thus, glial cells probably did not exert a direct physical influence on the degree of process outgrowth observed in the solitary RGCs, although a humoral effect cannot be totally excluded. These results suggest that aFGF has a potent influence on the outgrowth of processes by a neuron in the mammalian central nervous system. The potentiation of this effect by heparin leads us to speculate that the interaction of aFGF with a heparin-like molecule located in the extracellular matrix (such as heparan sulfate proteoglycan) may produce physiological effects in vivo. Furthermore, the lack of a substantial effect of bFGF in this system under these conditions shows that a specific population of mammalian central neurons may be differentially influenced by these two closely related peptide growth factors.

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PubMed1987

Peripheral nerve regeneration with entubulation repair: comparison of biodegradeable nerve guides versus polyethylene tubes and the effects of a laminin-containing gel.

These experiments present quantitative data concerning peripheral nerve regeneration in vivo. We used entubulation repair as a model to compare two different types of tubular prostheses, one nonbiodegradable and the other biodegradable. We modified the microenvironment of the regenerating axons within the tubular prostheses by adding a laminin-containing gel to the interior of the tube at the time of initial implantation. The data demonstrate that specific manipulations to the microenvironment of regenerating peripheral axons have quantitative effects on the rate and extent of nerve regeneration. Such effects were dependent on the composition of the tubular prosthesis and varied according to the survival time of the animals. For instance, the laminin gel within the biodegradable tubes enhanced nerve regeneration at 2 weeks but was inhibitory at 6 weeks. Furthermore, such manipulations may have different effects on the number of myelinated axons found within the regenerating nerve cable versus the number of primary motor and sensory neurons giving rise to such axons. We concluded that: the presence of a laminin-containing gel significantly increased the initial rate at which axons from primary sensory and motor neurons cross a transection site; an initial delay in axonal outgrowth at early time points did not necessarily predict diminished outgrowth at later times; and because of the potential for axonal branching the number of myelinated axons found in the midportion of a tubular prosthesis did not always correlate with the number of primary motor and sensory neurons which gave rise to those axons.

Animals↗