NO IS NOT SUBSTANTIALLY INVOLVED IN AFFERENT SIGNALING IN RAT MUSCLE-SPINDLES

As intrafusal nuclear bag and chain fibers of muscle spindles take par t in both sensory and motor functions, these stretch receptors may rep resent a useful model to answer the question whether nitric oxide (NO) signalling is involved in sensory and motor functions or motor events only, as has already been shown for ordinary extrafusal fibers. To an swer these questions, we have applied immunohistochemical and enzyme h istochemical methods to serial transverse sections of the rat gastroso leus muscle for determining the presence or absence of NOS I, NOS-asso ciated diaphorase (NOSaD), AChE and proteins related to the dystrophin complex. NOS I, NOSaD, and AChE were practically absent from the equa torial (central) region of intrafusal fibers, i. e. the site of termin ation of the primary and secondary afferents. These regions showed wea k staining for dystrophin, beta-dystroglycan as well as alpha- and gam ma-sarcoglycan. By contrast, all of these molecules were found enriche d in the polar (peripheral) regions of the intrafusal fiber sarcolemma . NOS I, NOSaD, dystrophin, beta-dystroglycan and the two sarcoglycans showed a general presence in the sarcolemma, whereas AChE was limited to the endplate region and other circumscribed areas. From these obse rvations we would like to conclude that NO does not appear to be signi ficantly or even not involved in signal transfer to the sensory nerve endings in the intrafusal fibers.