Histochemical evidence for the existence of skeletofusimotor (β) innervation in the primate

Abstract

A total of ten alpha motor axons which innervated the peroneus brevis muscle were isolated in two cynomolgus monkeys. In each experiment, the isolated alpha axons were stimulated collectively to deplete glycogen from their muscle units. The muscle was then frozen quickly , cut serially, and stained for glycogen. Of the 52 muscle spindles that were examined, zones of glycogen depletion were found in the intrafusal fibres of 32 spindles. The glycogen-depleted motor units included both fast-twitch and slow-twitch types. Depleted zones were observed in all three types of intrafusal muscle fibres. It was concluded that skeletofusimotor (beta) efferents were among the stimulated motor axons. This finding constitutes the first anatomical evidence for the existence of beta innervation in the primate.

The mammalian muscle spindle and its central control

“…3-Innervation has now been found in a number of different muscles and species (cat, monkey, rat, rabbit, man;Cooper and Daniel 1963;Bessou et al 1963Bessou et al , 1965Adal and Barker 1965;Emonet-D~nand et al 1966Emonet-D~nand et al , 1970Emonet-D~nand et al , 1975Swash and Fox 1972;Andrew and Part 1974;Barker 1974a;Emonet-D~nand and Laporte 1975;Mc William 1975;Laporte and Emonet-DOnand 1976;Cheney and Preston 1976b;Harker et al 1977;Murthy et al 1982;Murthy 1983).…”

Age-dependent decline in density of human nerve and spinal ganglia neurons expressing the α3 isoform of Na/K-ATPase

“…We found no α3-NKA-positive large myelinated fibers in human L4-L5 ventral root, suggesting a paucity of β-motor neurons at these spinal levels (Romanovsky et al, 2007). Nonetheless, 39% and 62% of spindles in human peroneus brevis muscle and extensor capri radialis muscles are reported as receiving βinnervation, respectively (Kakuda et al, 1998; Murthy et al, 1982). Therefore, the presence of some processes of β-motor neurons among α3NKA-positive tibial nerve fibers in our samples cannot be excluded.…”