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Occurrence of phospholipase A1-A2 and lysophosphatidylcholine acyltransferase activities in axolemma-enriched fractions of brain stem, optic pathway, and cranio-spinal nerves of the rabbit.

An axolemma-enriched fraction was isolated and characterized from homogenates of brain stem, pooled optic nerve and tract, and sciatic and hypoglossal nerves of adult rabbits. In these fractions, the phospholipase A1 and A2, as well as the activity of acyl-CoA:1-acyl-sn-glycero-3-phosphorylcholine and acyl-CoA:2-acyl-sn-glycero-3-phosphorylcholine acetyl transferase, using 1-acyl- and 2-acyl-GPC as acyl acceptors, were studied. The activity of the four enzymes was clearly detectable in the central nervous system (CNS) and peripheral nervous system (PNS) axolemmatic preparations, as well as in other subcellular fractions examined. The axolemma fractions, in which acetylcholinesterase displayed the highest activities, were particularly enriched in the acylation reaction enzymes. These latter showed specific activities about twofold higher compared with those of the homogenates and significant correlation with acetylcholinesterase. The noticeable presence of these enzyme activities in both CNS and PNS axolemma suggests that a deacylation-reacylation system for phospholipids may be operative in this membrane.

1-Acylglycerophosphocholine O-Acyltransferase↗

Experimental traction injuries of cervical spinal nerve roots: a scanning EM study of rupture patterns in fresh tissue.

This study examines the levels at which fresh rat ventral and dorsal C4 to T1 spinal roots rupture under traction stress. Rupture rarely occurs at the CNS-PNS transitional zone. Despite its delicate appearance this is strengthened in a number of ways, so that it is less vulnerable than the roots and their constituent rootlets and aggregated rootlet bundles (ARBs). Ventral roots commonly rupture either where the rootlets join to form the ARBs, along the course of the latter, or where these in turn join to form the ventral root. Dorsal root rupture shows a similar pattern but has a higher frequency of rupture within the root proper than is the case with the ventral roots. The level of rupture also varies systematically over the series of roots examined: rupture points tend to be located at more distal levels in caudal roots. This may occur because of mechanical differences in the distribution of traction stress along roots, related to their courses through the vertebral canal. Upper roots run transversely and the traction force is transmitted directly to rootlet levels, while more caudal roots run obliquely and tend to rupture where they are drawn taut against the pedicle. Many of the morphological features of ruptured roots would tend to inhibit regeneration of fibres distally. Differences in the pattern of rupture between fresh and fixed roots are examined. The latter tend to rupture at levels closer to the CNS than the former.

Animals↗

Injured nerve block alters adjacent nerves spinal interaction in neuropathic rats.

Baseline activity and responses to simultaneous saphenous stimulation of pairs of neurones recorded from sciatic (L5-6) and saphenous (L2) spinal cord segments, in rats with thermal hyperalgesia following sciatic constriction, were analysed before, during and after a sciatic nerve block with a local anaesthetic. In sciatic neurones, during the block, reductions of baseline activity (p < 0.001), increases in threshold of saphenous electrical stimulation (p < 0.01) and reductions of responses to electrical and to natural noxious saphenous stimuli (p < 0.001) were consistently found. The neuronal baseline and evoked activities remained unmodified in saphenous neurones. The contribution of input from injured periphery to central neurone circuitry mechanisms underlying the unmasking of improper afferents is discussed.

Afferent Pathways↗

Regulation of tadpole spinal nerve fiber growth by the regenerating limb blastema in tissue culture.

Explants of frog tadpole spinal cord cocultured with blastemas of regenerating hindlimbs provide in vitro evidence that the mesenchymelike cells of the blastema may serve to elicit nerve fiber growth and sprouting into the limb stump. The present study indicates that (1) blastemal mesenchyme results in enhanced, directed nerve fiber growth and its extended survival in defined tissue culture medium; (2) the amount of nerve growth decreases in the presence of blastemas from limbs incapable of complete regeneration; and (3) the quantity of nerve fiber outgrowth decreases as the developmental stage of the spinal cord increases. It is hypothesized that one of the requisites for limb regeneration is the production of a distal population of dedifferentiated cells capable of eliciting nerve fiber outgrowth from competent neural tissue in an amount that is sufficient to promote nerve-dependent regeneration.

Animals↗