Compartmental and topographical distributions of axons in nerves to the amphibian (Bufo marinus) glutaeus muscle

Abstract

The present work seeks to determine if axons to an amphibian muscle are segregated in nerve trunks between the spinal cord and muscle according to their primary nerve destination or their topographical projection in the muscle. The distribution of axons to different compartments and subcompartments of the amphibian (Bufo marinus) glutaeus muscle has been determined in transverse sections of spinal and limb nerves after retrogradely labelling the axons with horseradish peroxidase. Glutaeus axons were dispersed widely through spinal nerves 8 and 9 but loosely gathered together in one quadrant of the sciatic nerve after passing through the lumbar plexus. Glutaeus axons became tightly clustered to the exclusion of other axons along the length of the triceps femoris nerve after it divides from the sciatic nerve. Furthermore, axons destined for one of the two glutaeus primary nerve branches segregate from those of the other branch at the level of the triceps femoris nerve before the glutaeus nerve forms. On the other hand, motoneurones that subserve a primary branch are not segregated, but are found throughout the rostrocaudal extent of the glutaeus motoneurone pool. Injection of horseradish peroxidase under the epimysium of either the ventral or the dorsal surfaces of the glutaeus muscle labelled motoneurones preferentially in either the rostral or caudal part of the motoneurone pool, respectively. This confirms studies that have shown a topographical projection from the spinal motoneurone pool onto the glutaeus muscle. However, there was no segregation of dorsally projecting axons in the glutaeus and primary nerve branches. Thus, glutaeus axons segregate according to their muscle compartmental projections well before entering the muscle, but they show no organization in nerves with respect to their topographical projections within a compartment.

Topographical distribution of motor fascicles in the sciatic‐tibial nerve of the rat

“…Several studies in different animal species, including monkeys, based on retrograde tracing,9–13 support the view of a systematic topography of fascicles in the peripheral nerve. In fact, it has been described that, although there is a plexiform structure of fascicles in more proximal parts of the nerve, the nerve fibers of a discrete distal fascicle remain together over distances of several centimeters, even as they zigzag from one fascicle to another and maintain the somatotopic clustering along the nerve 7, 14.…”

Spatial clustering analysis in neuroanatomy: Applications of different approaches to motor nerve fiber distribution

“…Consequently, it was assumed that fiber topography is in general disorganized (Sunderland, 1945). Evidence contradicting this view started to accumulate from subsequent anatomical tracing studies in amphibians (Brown et al, 1989) and primates (Brushart, 1991), and from microneurographical studies in man (Schady et al, 1983;Hallin, 1990). No study, to date, established the topography of the proximal nerve levels, such as the ventral roots (Stewart, 2003).…”

Polysialylated Neural Cell Adhesion Molecule Is Necessary for Selective Targeting of Regenerating Motor Neurons

“…The absence of PMR in NCAM (؊/؊) mice is not attributable to an abnormal distribution of femoral motor axons in mice lacking NCAM Normally, motor axons preferentially cluster in major limb nerves before they exit as a coherent group at the level of their appropriate muscle in birds (Lance-Jones and Landmesser, 1981;Milner et al, 1998), amphibians (Wilson et al, 1988;Brown et al, 1989), and mammals (Browne, 1950;Brown and Booth, 1983). Whether the same degree of motor axon compartmentalization occurs in NCAM (Ϫ/Ϫ) mice is not known.…”