Muscle Spindle Density of Lateral Rotators of the Thigh in Japanese Macaques and a Gibbon

Abstract

We examined the six small lateral rotators of the hip joint, which is one of the most flexible joints and allows kinematically complex motions of the hindlimb, to elucidate the functional differentiation among these muscles and to test the hypothesis that species-specific characteristics in hindlimb use during locomotion are reflected in the muscle spindle density and in other parameters of the deep small hip joint rotators. For these purposes, we estimated the number of muscle spindles of the superior gemellus muscle (SG), inferior gemellus muscle, quadratus femoris muscle, obturator internus muscle (OI), obturator externus muscle, and piriformis muscle in three Japanese macaques and a gibbon, using 30-µm-thick serial sections throughout each muscle length after azan staining. The numbers of muscle spindles per 10,000 muscle fibers were determined to compare inter-muscle variation. The spindle density was highest in the SG and lowest in the OI in the Japanese macaques, suggesting that the SG, which is attached to the tendon of the OI, functions as a kinesiological monitor of the OI. On the other hand, SG the was missing in the gibbon, and the OI in the gibbon contained more spindles than that in the Japanese macaques. This suggests that the SG and the OI fused into one muscle in the gibbon. We postulate that the relative importance of the deep small hip rotator muscles differs between the Japanese macaques and gibbon and that the gibbon’s muscles are less differentiated in terms of the spindle density, probably because this brachiating species uses its hindlimbs less frequently.

Mammalian facial muscles contain muscle spindles

“…Previous studies focusing on identifying muscle spindle presence have used traditional histochemistry staining techniques, such as trichromes (Boyd-Clark et al, 2002;Cobo et al, 2017;Takeuchi et al, 2019) and hematoxylin & eosin staining (Cobo et al, 2017;May et al, 2018May et al, , 2022Mayer et al, 2021). May et al (2018May et al ( , 2022 and Cobo et al (2017) successfully used H&E staining and trichrome staining with the human and rhesus macaque platysma muscle and zygomaticus major Note that, in species where more than one section was examined, we examined sections that were far removed from one another to ensure that we were not counting the same muscle spindle multiple times.…”

Topographical anatomy of the albino rat’s ischiotrochanteric muscle group

“…For this reason, they are also the focus of research [8][9][10][11] . Animal models are often used for this purpose 12,13 .…”