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R W Gundersen

Publications and source records attributed to R W Gundersen.

8 recordsLinked to original sources
PubMed1987

Response of sensory neurites and growth cones to patterned substrata of laminin and fibronectin in vitro.

During neurite elongation in the developing peripheral nervous system, the distribution of laminin and fibronectin may provide preferred substrates for neurite elongation. In this study, the response of sensory neurites and growth cones to patterns of laminin or fibronectin applied to a background substrate of Type IV collagen was studied to determine any possible substrate preference. Neurites exhibited elongation restricted to a laminin pattern, but not a fibronectin pattern, indicating that sensory neurites prefer to elongate on laminin compared to Type IV collagen. When polylysine is included in the background substrate, neurite preference for laminin is decreased. Laminin also enhances neurite elongation and defasciculation and stabilizes growth cone protrusions. These results suggest an adhesive as well as a cytoskeletal involvement in the response to laminin, but direct adhesion estimates indicate that laminin decreases overall adhesion, arguing against an adhesive involvement. Regardless of the mechanism involved, the observed neurite preference for laminin is consistent with the hypothesis that spatial and temporal laminin distributions provide preferred pathways for peripheral neurite elongation.

Animals↗
PubMed1985

Sensory neurite growth cone guidance by substrate adsorbed nerve growth factor.

The response of growth cones from embryonic chick dorsal root ganglia to a patterned substrate of adsorbed nerve growth factor (NGF) was studied. The patterned substrate presented growth cones with an adsorbed NGF pattern and NGF-free substrate. NGF-responsive growth cones from 7 and 9 day ganglia could not proceed onto NGF-free substrate, reproducing the adsorbed NGF pattern. NGF-unresponsive growth cones from 17 day ganglia did not display any preference for adsorbed NGF or NGF-free substrata, which resulted in neurites not reproducing the adsorbed NGF pattern. Neurite outgrowth from NGF responsive 7-day ganglia onto a patterned NGF substrate, in NGF-containing medium, was radially symmetrical, exhibiting no growth cone response to the patterned NGF substrate. The lack of NGF-responsive growth cone extension onto NGF-free substrate indicates that NGF is a requirement for neurite elongation. If NGF is withdrawn from growth cones by microperfusion, neurite elongation ceases. Thus, an adsorbed pattern of NGF may be duplicated because growth cones are not able to extend onto NGF-free substrate, since NGF is a requirement for neurite elongation. These results indicate that substrate adsorbed NGF can support neurite formation and elongation as well as guide the direction of neurite elongation.

Adsorption↗
PubMed1984

The effects of conditioned media on spinal neurites: substrate-associated changes in neurite direction and adherence.

The effects of conditioned media and other growth factors on spinal cord neurite adherence, growth rate, and direction were studied. Skeletal muscle-conditioned medium (SMCM) significantly increased neurite adherence and altered the direction of elongation. Lung- and skin-conditioned media, nerve growth factor, and polyornithine binding neurite promoting factor did not affect neurite adherence or direction. The positive effects of SMCM on neurite adherence and direction may be due to substrate-bound substances, since SMCM depleted of poly-L-lysine-adsorbable materials decreased neurite adherence and direction, and the directional response was greatly diminished on SMCM-conditioned substrate. Haptotaxis may be the basis of the turning response, since it appears to involve substrate-bound molecules which slightly increase adherence. It was also observed that the measured length of neurite involved in a turn toward SMCM was much greater than the calculated length of neurite (based on neurite elongation rates). Therefore, it appears as if the growth cone has been displaced, dragging the attached neurite with it. These observations suggest that the growth cone may have extensive locomotive capabilities which affect growth cone migration.

Animals↗
PubMed1984

Neurite growth cone-substratum adherence increases in vitro.

During experiments characterizing the turning response of dorsal root ganglion neurites toward NGF, it was observed that growth cone-substratum adherance increased with time in culture. The experiments reported here indicate that the observed increase in growth cone-substratum adherance is significant and can be detected with both collagen and poly-L-lysine substrates. The increased adherance is apparently due to a substance(s) produced and released by the ganglia which binds to the substrate, increasing adherance. Flow chamber studies indicate that the substrate-bound substance(s) may be necessary for neurite growth onto artificial tissue culture substrata.

Animals↗
PubMed1980

Characterization of the turning response of dorsal root neurites toward nerve growth factor.

This study reports that chick dorsal root ganglion neurites undergo a rapid (20 min) reorientation of their direction of growth in response to nerve growth factor (NGF) concentration gradients in vitro. Dorsal root ganglia from chick embryos were explanted onto a collagen-poly-L-lysine substrate. After 24-48 h in culture, NGF gradients were applied to individual growth cones via a micropipette containing 50 biological units NGF/ml. The growth cones turned and grew toward these NGF sources. This turning response was not caused by the trophic effects of NGF on neurite initiation, survival, or growth rate. Dorsal root neurites also grew toward sources of mono- and dibutyryl cyclic adenosine monophosphate (dB cAMP), cyclic guanosine monophosphate (cGMP), and elevated calcium in the presence of the calcium ionophore A23187. These results are consistent with the hypothesis that intracellular levels of cAMP and /or cGMP and calcium may play a role in the turning response of dorsal root neurites toward NGF, but do not establish a causal relationship between the mechanisms of action of NGF, cyclic nucleotides and calcium. Total growth cone adherence to the substrate was measured using a timed microjet of perfusion medium. NGF increased the adherence of growth cones to the substrate, but caffeine and dB cAMP which also elicit the positive turning response, decreased growth cone adherence. Calcium, which did not elicit the positive turning response, produced a greater growth cone adherence to the substrate than that observed with NGF. Although these results do not rule out a role of adhesion changes in axonal turning to NGF, they show that a general increase in adherence does not correlate well with the rapid turning response observed in this study.

Animals↗
PubMedDate not supplied

Interference reflection microscopic study of dorsal root growth cones on different substrates: assessment of growth cone-substrate contacts.

The contact between dorsal root growth cones and substrates of type IV collagen, fibronectin, poly-L-lysine, and laminin were studied using interference reflection microscopy (IRM) coupled with detaching growth cones from these substrates and observing substrate-associated membrane (SAM). IRM images of growth cones on collagen and fibronectin indicate substantial dark areas of close association between the substrate and basal region of the growth cone. The thin membranous veils and lamellapodia appear bright, indicating a greatly decreased association with the substrate. Filopodia can appear either entirely dark or light but usually are dark interspersed with brighter areas indicating varying degrees of contact. IRM images of growth cones on polylysine and laminin suggest a decreased association between the basal region of the growth cone and the substrate. The appearance of veils and lamellapodia was similar to that observed on collagen and fibronectin. Observations of SAM indicate an increased degree of contact between growth cones and substrates of collagen and fibronectin compared to laminin and polylysine. Collectively these data indicate that simple increases in adhesion are not adequate to explain substrate preference and enhancement of neurite elongation. Overall decreases in adhesion may accomplish the same phenomena, suggesting that it is perhaps more important to consider the regional distribution of adhesive contacts in relation to growth cone movement.

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