Distribution of sensory nerves in the levator ani muscle of young and aged male Wistar rats

Abstract

Distribution of sensory nerves in the levator ani muscle of young and aged male Wistar rats Robert M. Santer, Andrew P. Carson-Stevens: School of Biosciences, Cardiff University, Cardiff CF10 3US, United Kingdom We have mapped the distribution of free nerve endings and muscle spindles by immunohistochemistry in the levator ani (LA) muscle of young and aged rats in order to investigate force transmission within this muscle. We have previously measured a near 40% decrease in tetanic and specific force generation in the rat LA in old age. The entire LA was removed bilaterally from terminally anaesthetised male rats (n = 6 per age group) of 3 and 24-27 month male Wistar rats, fixed in 4% paraformaldehyde and cryosectioned longitudinally or transversely at 12μm. Sections were incubated with primary polyclonal antisera against calretinin and neurofilament 200 followed by appropriate FITC-conjugated secondary antisera. The distribution of muscle spindles and free nerve endings was subsequently mapped in both the longitudinal and transverse planes. Muscle spindles were localised close to the LA’s myotendinous attachment to the penile bulb and also in the region of the midline raphé where the right and left LAs unite. Spindles were located deep within the LA whereas free nerve endings were distributed more widely in the muscle. In the aged animals the pattern of spindle distribution was unchanged but increased endomysial collagen(I) and decreased muscle fibre size did not permit quantitative assessment of nerve and muscle spindle numbers to be made. However, in spite of the expected signs of age-associated changes in LA muscle fibres, similar changes in the sensory innervation were not noted. Support of the Wellcome Trust is gratefully acknowledged.