Showing papers by "Neeraj Jain published in 1995"

Limits on plasticity in somatosensory cortex of adult rats: hindlimb cortex is not reactivated after dorsal column section.

Abstract: 1. To better understand the limits and extents of plasticity in sensory systems of adult mammals, we unilaterally sectioned the dorsal funiculus at thoracic levels in nine adult rats to deactivate ascending afferents from the hindpaw and lower body. After postsurgical recovery periods of 3 h to 3 mo, the region of primary somatosensory cortex (S1) representing the limbs and trunk was extensively mapped with microelectrodes. 2. Recording sites were later identified as being within the hindlimb representation and other parts of S1 by relating locations of microlesions to the cytochrome oxidase pattern in sections of cortex cut tangential to the pial surface. The extent and effectiveness of spinal cord lesions were evaluated by injecting cholera toxin B subunit conjugated with horseradish peroxidase (B-HRP) at various sites in the deafferented hindpaw. 3. In five animals with complete section of the dorsal funiculus, we failed to detect any response to cutaneous stimulation of any part of the body in the deafferented hindlimb cortex. In four other animals with incomplete lesions, neurons in some penetrations could be activated by hindlimb stimulation, but not by stimulating other body parts. In those cases without activation of hindlimb cortex, B-HRP was detected in the spinal cord only caudal to the lesion, and it was not transported to the nucleus gracilis. Limited transport past the lesion to nucleus gracilis was detected in cases with incomplete lesions. 4. The results indicate that forelimb inputs do not substitute for missing hindlimb inputs in primary somatosensory cortex in rats and that the potential for somatotopic reorganization is more limited than previously thought.

Cell free ascitic fluid prevents loss of cell surface sialic acid from Zajdela Ascitic Hepatoma cells in culture.

Abstract: In the Zajdela Ascitic Hepatoma (ZAH), a rat tumor, high levels of cell surface sialic acid residues are present which masked the immunogenicity of the cells. We have shown here that cell surface sialic acid level goes down rapidly when ZAH cells are put in culture. The reduction in surface sialic acid levels is due to a decrease in sialic acid residues on the major sialylated glycoprotein, gp 120, as well as a decrease in gp 120 polypeptide. The loss of sialic acid from the cultured cells is reduced if the cells are cultured in the presence of cell free ascitic fluid from ZAH tumor.