[The morphology of sensory corpuscles in the joint capsule--ultrastructural and histochemical study].

Sensory corpuscles in the cat elbow joint were observed by light and electron microscopy. Two types of corpuscles were identified, i.e. Pacini-type and Ruffini-type corpuscles. Silver impregnation revealed a single straight axon terminal in Pacini-type and highly-ramified fine axons in Ruffini-type corpuscles. Pacini-type corpuscles, 100-200 microns long and 30 microns wide, consisted of dense lamellae of lamellar cells and thick capsule. The lamellar portion contained a centrally-located axon terminal, and was similar in organization to the inner core of the typical Pacini corpuscle. The capsule was the continuation of perineurial sheath. This corpuscle was devoid of outer core structure as seen in a typical Pacini corpuscle. Ruffini-type corpuscles, 50-150 microns long and 25-50 microns wide, had the branched axon terminals with varicosities under the incomplete capsule. Axons, which were surrounded by thin Schwann cell processes, were embedded in the dense layers of collagen fibrils. The interior of the corpuscle was separated into small compartments by cell processes extended from the capsule. The axon varicosities contained numerous mitochondria. These fine structures of the corpuscles were similar to those of Ruffini corpuscles reported so far in other regions. Both Pacini-type and Ruffini-type corpuscles were clearly demonstrated by histochemistry for ChE. Inasmuch as the staining feature of corpuscles was different from each other, the distribution pattern of corpuscles in the joint capsules could be obtained by examining semi-serial sections. Pacini-type corpuscles were mainly found in the synovial layer, while Ruffini-type corpuscles were mainly located in the fibrous layer of the joint capsule. Both types of corpuscles were located near the median nerve on the flexor side of the joint. The reaction products of ChE activity were located in the peri-axonal as well as inter-lamellar spaces of Pacini-type corpuscles, and in the peri-axonal region as well as around Schwann cell processes of Ruffini-type corpuscles. No definite reaction product was found within axon terminals. Some reaction products were also found in the rough endoplasmic reticulum and/or nuclear envelope, suggesting that ChE is synthesized by Schwann cells. The significance of these sensory corpuscles with regard to the deep sensation in the joint capsule was discussed from the point of view of the electro-physiological characteristics of the corpuscles.