Remak Bundles Research Articles

Degeneration patterns of postganglionic fibers following sympathectomy.

In cats the time course of degeneration following lumbal sympathectomy was studied in the ramus communicans griseus (rcg) and in the nerves to the triceps surae muscle using light and electron microscopic methods. The left lumbar sympathetic trunk including its rami communicantes was removed from L2 to S1 using a lateral approach. The animals were sacrificed between 2 and 48 days after the sympathectomy. Tissue samples were taken (a) one cm proximal to the entrance of the rcg into the spinal nerve, and (b) one cm proximal to the entrance of the nerve into the muscle belly. In the rcg signs of degeneration can already be recognized in the myelinated as well as in the unmyelinated axons 48 h after sympathectomy. The degenerative processes in the axons reach their peak activity at about 4 days p.o. They end a week later. Signs of the reactions of the Schwann cells and of the endoneural cells can first be seen 2 days p.o. They are most pronounced around the 8th day p.o., and last at least up to the third week. Thereafter the cicatrization processes settled to a rather steady state (total observation period 7 weeks). In the muscle nerves the first signs of an axonal degeneration of the sympathetic fibers can be recognized 4 days after surgery. The signs of axonal degeneration are most striking about 8 days p.o. They have more or less disappeared another week later. The reactions of the Schwann cells also start on the fourth day but outlast the degenerative processes by some 8 days. Thus the degenerative and reactive processes in the rcg precede those in the muscle nerves by 2 days early after surgery and by 6 days 3 weeks later. Seven weeks after surgery, fragments of folded basement lamella and Remak bundles with condensed cytoplasm and numerous flat processes are persisting signs of the degeneration. In addition to the differences in time course between the proximal and the distal site of observation, it was also noted that both the axonal degeneration and the reactions of the Schwann cells are more pronounced in the rcg than in the muscle nerve. For example there was abundant mitotic activity in the central endoneural and Schwann cells whereas we could not detect such activity in the periphery.(ABSTRACT TRUNCATED AT 400 WORDS)

Sensory innervation of the Achilles tendon by group III and IV afferent fibers.

In sympathectomized cats the innervation of the Achilles tendon by fine afferent nerve fibers was studied with semithin and ultrathin sections. Several different types of sensory endings of group III and group IV nerve fibers were identified. Of the five different types of endings in the group III range (T III endings), two are located within vessel walls. One of them ends in the circumference of the venous vessels (T III/VV). Its lanceolate terminals have characteristic receptor areas at their edges. The second type ends in the adventitia of lymphatic vessels (T III/LV). Its receptive areas are scattered along their terminal course. Two further group III endings ramify within the connective tissue compartments of the vessel-nerve-fascicles of the peritenonium externum and internum. One type is tightly surrounded by collagen fibrils (T III/PTic); the other terminates between the collagen fiber bundles (T III/PTgc). The latter arrangement recalls the ultrastructural relation between nerve terminals and collagen tissue in Golgi tendon organs. The fifth type innervates the endoneural connective tissue of small nerve fiber bundles (T III/EN). At least some of them come into close contact with bundles of collagen fibers which penetrate the perineural sheath to terminate within the endoneurium. The endings of group IV afferents (T IV endings) show a striking topographic relationship to the blood and lymphatic vessels of all connective tissue compartments of the Achilles tendon. They form penicillate endings which may contain granulated vesicles. In any event, they can easily be discriminated from the T III endings in the vessel walls. In close neighborhood to Remak bundles, a cell has been regularly found which fulfilled all ultrastructural criteria for mast cells. But this cell is not a mast cell proper because it is surrounded by a basal lamina (pseudo mast cell).

Reinnervation of the canine tooth pulp after section of the inferior alveolar nerve in the cat

The apices of lower canine teeth have been examined 9 weeks after unilateral section of the inferior alveolar nerve. The teeth were extensively reinnervated although there was considerable variation in the number of axons present. The myelinated axons were smaller than normal with thinner myelin sheaths. There were fewer axons per non-myelinated fibre (Remak bundle). The proportions of myelinated and non-myelinated fibres were normal.

The characteristics of spontaneous and evoked action potentials recorded from the rabbit's uterine nerves.

1. A method is described for recording in vivo the action potentials of afferent and efferent fibres in whole nerves supplying the rabbit's uterus.2. Examination of these nerves under the light microscope and the electron microscope showed them to be composed almost entirely of non-myelinated fibres.3. Two types of spontaneous action potential were observed; one travelled at about 4 m/sec and probably came from the myelinated fibres, the other travelled at 0.4-1.4 m/sec and certainly came from non-myelinated fibres.4. The efferent fibre spikes were shown to be faster and higher than the spikes from uterine afferent fibres, but slower and smaller than spikes from broad ligament afferent fibres.5. Apart from differences in conduction velocity and height, all spikes were basically similar, lasting about 1.5 msec. The height was related to the square of the velocity. Some more complex spikes were also observed.6. The compound action potential evoked by stimulation of the uterine nerve had three peaks, conducted at 1.3, 0.8 and 0.6 m/sec, respectively, and thought to correspond to the fast afferent fibres, the efferent fibres and the slow afferent fibres, respectively. There were also some late peaks due to reflexion of the antidromic action potentials from the ganglion cells.7. Stimulation of the hypogastric nerve also evoked a compound action potential in the uterine nerves. Stimulation of the pelvic nerves had no effect.8. By means of ganglion blocking agents, the uterine ganglia were shown to lie in the pelvic plexus, peripheral to the hypogastric nerve, but central to the uterine nerves.9. It is argued that the spontaneous action potentials came from individual fibres rather than Remak bundles, and that the recording technique used detected the activity of all but the smallest fibres.