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.