Morphofunctional restoration of a nerve trunk by filling the defect with a blood vessel

Dynamics of morphologic and functional restoration of the nerve trunk and separate receptive skin formations have been investigated in white rats after a sutureless connection of the cut nerve by means of the implanted artery. For testing the reparative processes neurohistological and electrophysiological techniques have been used. In spite of a relatively early restoration of the integrity of the injured nerve and reaching the nervous fibers up to the skin, functional organization of the dermal sensory apparatus is observed only in a year after the operation.     

Dynamics of the recovery of the structure and function of the sciatic nerve and skin receptors in reinnervation of the hindlimb of white rats

The dynamics of the structural and functional repair of nerve trunks and receptor endings in the rat foot skin was studied on the model of sutureless connection of the damaged nerve by and implanted arterial vessel. Neurohistological and neurophysiological methods were used to show that the anatomical repair of the nerve integrity, maturation of nerve fibers and formation of receptor endings preceded their functional restoration. Terms of myelinization of regenerating axons, their diameters and initial stages of the formation of receptors in the foot skin were established. The restoration of the skin receptor function was shown to occur within 11-13 months after operation.     

Development of methods of connecting severed nerve trunks to restore their integrity

An experimental model of a seamless end-to-end joining of severed sciatic nerve (with gaps between the two ends 5-8 mm-wide) using an implanted arterial vessel was elaborated on random bred and inbred Wistar rats. Histological examination showed that nerve regeneration along the implanted arterial lumen was directly oriented and was not accompanied by neuroma formation which was always the case in the control. It took some nerve fibers 20 days to join the gap between the cut nerve ends. In 4 months myelination of regenerating fibers was observed in the blood vessel lumen, in 3 months the lumen was filled with bundles of myelinated fibers, and in 9 months the structure of the regenerating nerve was similar to that of the mature trunk observed in animals. The elaborated experimental model is to be employed in the studies of reparatory histogenesis in peripheral nervous tissues. The data obtained may be used in neurosurgery.     

Neurofilament-like and glial fibrillary acidic protein-like immunoreactivities in rat and guinea-pig sympathetic ganglia in situ and after perturbation

Summary The presence of neurofilament (NF)-like and glial fibrillary acidic protein (GFAP)-like immunoreactivities was studied in sympathetic ganglia of adult rats and guinea pigs during normal conditions and after perturbation. In the superior cervical ganglion (SCG) of normal rats, many ganglion cells and nerve fibers show NF immunoreactivity. Some of these nerve fibers disappear after preganglionic decentralization of SCG; this indicates the presence of a mixture of preand postganglionic NF-positive nerves in the ganglion. Cuts in both preand postganglionic nerves result in a marked increase in GFAP immunoreactivity in SCG, whereas NF immunoreactivity increases in nerve cell bodies after preganglionic cuts. Only a few ganglion cells show NF immunoreactivity in the normal SCG of guinea pig. All intraganglionic NF-positive nerves are of preganglionic origin; decentralization abolishes NF immunoreactivity in these nerve fibers. The inferior mesenteric ganglion, the hypogastric nerves and colonic nerves in guinea pigs contain large numbers of strongly NF-immunoreactive nerve fibers.When the SCG of adult rat is grafted to the anterior eye chamber of adult rat recipients, both ganglionic cell bodies and nerve fibers, forming on the host iris from the grafted ganglion, are NF-positive. As only the perikarya of these neurons normally exhibit NF immunoreactivity, and the terminal iris arborizations are NF-negative, it appears that the grafting procedure causes NF immunoreactivity to become more widespread in growing SCG neurons.     

Chick heart peptidergic innervation: localization and development

Localization and development of chick heart peptidergic innervation (Substance P, VIP and Somatostatin) were investigated by means of immunofluorescence technique. The peptidergic component of the heart innervation was observed, for the first time, in older than 11 day chick embryos, i.e., subsequently to the appearance of the cholinergic component. The peptidergic structures achieve nearly full development in about 16-17 day embryos. Substance P is the most represented of the three peptides. It is localized both in nerve bundle fibers and in isolated fibers within the myocardium, the pericardium, the vessel walls; it is also present in fibers of some heart base ganglia. VIP is mostly contained in some thick single fibers travelling along the vessel walls of the heart base, the myocardium and the pericardium. Some VIP immunoreactive cells were also observed in the base ganglia. Somatostatin is mostly contained in some ganglia cells, whilst thin Somatostatin-immunoreactive fibers form a rich plexus among the atrial and ventricular myofibers, without contacting the vessel walls.     

Implantation of embryonic brain tissue into regenerating peripheral nerve

Dynamics of development of the cerebral cortex tissue anlage in 17-day-old embryos of Wistar rats, implanted into the sciatic nerve of mature rats with the aim to establish new relay and trophic centers in the regenerating nerve have been studied. By means of certain morphological methods (silver nitrate impregnation after Bielschowsky-Gros, Sudan black, hematoxylin-eosin, toluidine blue after Nissl stainings) it has been stated that the implanted nerve cells not only preserve their viability, but also differentiate from neuroblasts up to young and mature neurons during 2 months. Already in 14 days after the operation there are blood vessels in the implants; by the 2d month massive myelinization of axons begins in the implant. A part of the regenerating myelin fibers of the nerve gets into the implant and branches. In similar cases connections between the implanted neurons and the host peripheral nervous fibers are supposed to be established.     

Study of neuropeptide Y-containing nerve fibers in the human penis

Summary Neuropeptide Y 1–36 (IR-NPY) immunoreactive nerve-fiber processes have been observed in tunicae of veins and arteries and in smooth muscles of the human penis taken at autopsy or during surgery by use of light-and electron-microscopic immunohistochemical techniques. Numerous IR-NPY nerve fibers were mostly concentrated in the inner part of the adventitia close to the media of the arterial and venous vessels and among the intracavernous smooth muscle cells. IR-NPY nerve fibers were less abundant in veins than in arteries. Positive somata were not observed in the penises. At the ultrastructural level, IR-NPY were localized exclusively in large, dense granules of nerve terminals by means of the postembedding immunogold technique. In the deep dorsal vein, IR-NPY nerve fibers were also located in the media formed by an outer circular and an inner longitudinal layer. In the intracavernous and dorsal arteries, they showed the highest density in the inner part of the adventitia. In the corpora cavernosa and in the corpus spongiosum, IR-NPY nerve processes were intermingled between the smooth-muscle fibers around the sinusoid spaces. IR-NPY nerve fibers were present in the cavernous nerves close to the central arteries. The urethra did not show any IR-NPY-positive nerve fibers. This peculiar distribution of IR-NPY nerve fibers suggested that they could participate in regulating arterial and venous blood flow and intracavernous smooth-muscle tone. NPY may therefore be of importance in some of the mechanisms of penile erection especially during detumescence.     

Three dimensional observation of the nerve fibers along the cerebral blood vessels

Three dimensional observation of the nerve fibers along the cerebral blood vessels was investigated by scanning electron microscopy. Electron probe X-ray microanalysis was also performed in the cerebral blood vessels treated with peroxidase-antiperoxidase immunohistochemistry intensified by nickel ammonium sulfate. Nerve fibers (2-8 microns in diameter) formed a plexus on the outer surface of the adventitia. After branching, the nerve fibers penetrated the blood vessel adventitia. Substance P-immunoreactive nerve fibers showed a meshwork pattern in the outer layer of the adventitia, and vasoactive intestinal polypeptide (VIP)-immunoreactive nerve fibers revealed a spiral running pattern in the inner layer of the adventitia. Taken together with previous studies, these findings suggest that substance P nerve fibers in the cerebral arteries may not be related to arterial dilatation or constriction, but VIP nerve fibers may be vasodilative.     

Neurofilament phosphorylation in development. A sign of axonal maturation?

Monoclonal antibodies to the 200K neurofilament (NF) protein selectively decorated axons in tissue sections. Dilution of the antibodies in phosphate buffer and digestion with phosphatase abolished the stain. With conventional monoclonal and polyclonal NF antibodies, i.e. antibodies decorating NF regardless of their location (axons, perikarya and dendrites), the staining was not affected by this treatment. With all antibodies, axon-specific and conventional, the staining was abolished by trypsin digestion. Subsequent digestion with phosphatase did not restore the staining. Compared with conventional NF antibodies, staining with axon-specific anti-NF 200K was a late phenomenon in chick embryo development. NF 200K immunoreactivity was first observed in peripheral nerves and in the anterior columns of the spinal cord on day 10. Sensory ganglia and optic nerve fibers were negative. With conventional NF antibodies these structures were stained on days 4 and 5, respectively. In the following days of development the study was confined to the retina, optic nerves, cranial peripheral nerves and sensory ganglia. Up to day 16, bundles of thin peripheral nerve fibers, strongly decorated by conventional NF antibodies, did not stain with anti-NF 200K in double labelling experiments. Nerve bundles emerging from the ganglia were also negative, although some thick nerve fibers within the ganglia were stained. NF 200K immunoreactivity was first observed on day 17 in the optic nerve and in the layer of optic nerve fibers. At this time, staining was confined to the bundle emerging from the temporal side of the retina. In newborn chicken, only few fibers stained with anti-NF 200K in the nasal bundle, while the temporal bundle was well stained. It is suggested that the NF 200K antibodies reacted with a phosphorylated epitope in the axon, and that NF phosphorylation is a late event in ontogenesis probably related to axonal maturation.     

Implantation of embryonic neocortex and spinal cord into injured peripheral nerve of adult rats

Spinal cord and cerebral cortex of 14-day-old embryos of Wistar rats were implanted into the sciatic nerve of mature rats in order to study dynamics of the development of neuronal and neuroglial elements in ectopic sites. By means of light and electron microscopy it has been stated that the implanted nerve cells of the cortex and spinal cord survive during 5 month and differentiate from neuroepithelial cells and neuroblasts up to young and mature neurons. It was found that thirty days after operation the spinal cord implants contained myelinated nerve fibers and numerous synapses. The data obtained suggest that the implants of fetal spinal cord are more favorable for regeneration of the injured nervous stems than the cerebral cortex.     

Three dimensional observation of the nerve fibers along the cerebral blood vessels

Summary Three dimensional observation of the nerve fibers along the cerebral blood vessels was investigated by scanning electron microscopy. Electron probe X-ray microanalysis was also performed in the cerebral blood vessels treated with peroxidase-antiperoxidase immunohistochemistry intensified by nickel ammonium sulfate.Nerve fibers (2–8 m in diameter) formed a plexus on the outer surface of the adventitia. After branching, the nerve fibers penetrated the blood vessel adventitia. Substance P-immunoreactive nerve fibers showed a meshwork pattern in the outer layer of the adventitia, and vasoactive intestinal polypeptide (VIP)-immunoreactive nerve fibers revealed a spiral running pattern in the inner layer of the adventitia. Taken together with previous studies, these findings suggest that substance P nerve fibers in the cerebral arteries may not be related to arterial dilatation or constriction, but VIP nerve fibers may be vasodilative.     

Regeneration of the peripheral nerves in the lumen of implanted vessels

Regeneration of the rat peripheral nerve in the lumen of implanted aorta was examined over 4 months. The nerve invaded the vessel with its entire trunk and went out of the distal vessel to the adjacent muscles. Inflammatory infiltrations were observed only outside the implant. Only insignificant number of inflammatory elements were inside the lumen. These conditions favored good regeneration of the nerve without forming a neuroma at the end of the cut nerve. The regenerating myelinized fibers formed spiral-like or bush-like terminals on muscle fibers. The model of directed regeneration of the peripheral nerves in the vascular lumen holds promise for rapid and accurate reinnervation of tissues and organs.     

Equilibria of frog nerve with different external concentrations of sodium ions

Using the ability of the nerve fibers to conduct impulses as indicator of changes in the concentration of sodium ions in the interstitial spaces of nerve an evaluation has been made of the diffusion constant of sodium ions. The calculated minimal value (0.62 x 10(-4) cm.(2)/min.) undoubtedly is much too low; nevertheless, it is still so high that as a rule the diffusion of sodium ions is far more rapid than the establishment of excitability changes; therefore, diffusion times need not be taken into account in the interpretation of ordinary experiments. By measurements of the changes in the longitudinal conductivity of nerve which result from changes in the external concentration of sodium chloride an evaluation has been made of the diffusion constant of sodium chloride in the interstitial spaces of nerve. A minimal value for this constant is 1.4 x 10(-4) cm.(2)/min. The evidence presented would be compatible with the assumption that the permeability of the connective tissue sheath for sodium ions decreases slightly after the concentration of sodium ions in the interstitial spaces of the nerve has become negligible; the evidence, however, shows that changes in the permeability of the sheath cannot play a significant role in determining the temporal courses of the development of inexcitability in a sodium-free medium and of the restoration of excitability by added sodium ions. If a decrease in the permeability of the sheath should take place in a sodium-free medium, the change would be small and would occur after the nerve fibers have become inexcitable; on the other hand the action of a moderate concentration of sodium ions would be sufficient to restore the permeability of the sheath. As measured by the recovery by A fibers of the ability to conduct impulses the restoration by 0.1 N sodium ions of nerve that has been deprived of sodium for 15 to 20 hours, i.e. for several hours after the nerve fibers have become inexcitable, begins after a significant delay, since no A fiber begins to conduct impulses in less than 8 or 10 minutes. The delay is referable to the fact that, before the A fibers can regain the ability to conduct impulses, those changes in their properties have to be reversed, which have taken place in the absence of sodium ions. Usually within 1 minute after sodium ions are made available to the nerve the polarizability of the membrane by the anodal current begins to increase; the A fibers soon begin to produce unconducted impulses in response to the break of the anodal current; then, they produce unconducted impulses in response to the closure of the cathodal current, and finally they become able to conduct impulses, although at a markedly reduced speed. The C fibers, that become inexcitable in a sodium-free medium later than the A fibers, begin to conduct impulses within 1 minute or 2 after 0.1 N sodium ions are made available to the nerve. Treatment of a nerve, that has been kept in a sodium-free medium, for 15 to 20 hours, with a moderate concentration of sodium ions (0.015, 0.02 N), acting for 1 hour or 2, is not sufficient to restore the ability to conduct impulses to more than a few A fibers, but it produces in a relatively large number of fibers a partial restoration, so that when the concentration of sodium ions outside the epineurium is increased by 0.005 or 0.01 N a significant number of A fibers begin to conduct impulses within less than 5 seconds. Initially the recovery progresses with great rapidity, but after a small number of minutes the height of the conducted spike remains practically stationary. Increase of the external concentration of sodium ions by a small amount again causes a rapid enhancement of the recovery, but once more, after a few minutes the height of the spike remains practically stationary, etc. A subnormal concentration of sodium ions may restore to all the A fibers the ability to conduct impulses, but only 0.1 N sodium ions are able to produce a complete restoration of the speed of conduction, and only after they have been allowed to act for a considerable period of time. The ability of all the C fibers to conduct impulses may be restored by relatively small concentrations of sodium ions, 0.02 to 0.025 N. Nerve fibers that have become inexcitable in a sodium-free medium and have been restored by sodium ions are far more sensitive to the effect of the lack of sodium than the fibers of untreated nerve. Repeated removal and addition of sodium ions may bring the nerve fibers, especially those of spinal roots, to a state in which the sensitivity to the lack of sodium is exceedingly great; spinal root fibers may then begin to become inexcitable in a sodium-free medium within a few seconds. Treatment of the nerve with 0.1 N sodium ions for 1 hour or 2 is sufficient to bring about a marked increase in the resistance to the lack of sodium. On the other hand keeping a nerve in Ringer's solution or in the presence of 0.04 N sodium ions does not produce a readily detectable increase in the sensitivity to the lack of sodium. Even the resistance of nerve kept in the presence of 0.025 N sodium ions for 23 hours is very high, since after 2 hours in a sodium-free medium more than two-thirds of the initially conducting fibers will be able to conduct impulses. Frog nerve reaches different states of equilibrium with different external concentrations of sodium ions. The states are characterized by the degree of effectiveness of the nerve reaction, the speed of conduction of impulses, and the number of conducting fibers. Approximately the same equilibrium state may be reached by (a) leaving the nerve for 20 to 24 hours in the presence of a subnormal concentration of sodium ions and (b) by leaving the nerve in a sodium-free medium for 15 to 20 hours, restoring it with 0.1 N sodium ions acting for a short period of time, rendering it inexcitable again in a sodium-free medium, and finally restoring it with a moderate concentration of sodium ions. If, however, the nerve that has been kept in a sodium-free medium for 15 to 20 hours is restored directly by a moderate concentration of sodium ions the state will not be reached, at least not for several hours, which corresponds to equilibrium with that concentration. The role of sodium in nerve physiology is discussed. Sodium participates in at least four processes, (a) The regulation of the concentration of water outside the nerve fibers; (b) the regulation of the total value of the membrane potential; (c) the production of the nerve impulse, and (d) the establishment of the nerve reaction. In so far as processes (c) and (d) are concerned only the sodium present inside the nerve fibers plays a role; the presence of sodium ions outside the nerve fibers is important only because in the absence of interstitial sodium ions the nerve fibers lose a part of their internal sodium content. The nerve impulse and the nerve reaction may be produced for long periods of time after the concentration of sodium ions outside the nerve fibers has become negligible. A working hypothesis is put forward according to which the internal sodium content and the interstitial concentration of sodium ions are in equilibrium in so far as a different internal sodium content corresponds to each interstitial concentration. The properties of the nerve fibers are determined by the internal sodium content. The change in properties, i.e. in the state of the nerve fibers, results from processes that take place inside the nerve fibers after the interstitial concentration of sodium ions and consequently also the internal sodium content have been changed.     

Neurofilament Proteins Are Distributed in a Diminishing Proximodistal Gradient Along Rat Sciatic Nerve

Neurofilament (NF) proteins are distributed in a diminishing proximodistal gradient along rat sciatic nerve when compared with total noncollagen or other proteins in nerve. About a twofold decline of NF proteins can be detected by quantitating nerve proteins that have been separated by gel electrophoresis. A similar decrease of immunoreactivity to each NF subunit is seen in distal nerve segments when noncollagen nerve proteins are immunoblotted. Parallel decreases occur in all three NF proteins, thereby maintaining neurofilament subunit stoichiometry along the neuraxis. The same NF gradient can be detected when the NF contents in nerve branches to the gluteus and gastrocnemius muscles are compared with each other and with those in nerve segments taken from the same proximodistal levels of the parent sciatic nerve. The gradient of NF proteins increases during postnatal development and is readily detected by postnatal day 16. During the same period of development, the heavy NF subunit appears for the first time and is rapidly incorporated throughout the sciatic nerve. Hence, the NF gradient becomes manifest during the development and maturation of the adult form of the axonal cytoskeleton. The basis for the proximodistal gradient of NF proteins in peripheral nerve is presently unknown. The extent of the gradient cannot be accounted for on the basis of diminishing numbers of nerve fibers or increasing amounts of other nerve proteins, e.g., collagen, in distal nerve. An alternative interpretation is that the gradient reflects a low level of NF protein turnover during axonal transport.     

Efficiency of reinnervation of neonatal rat muscle of original and foreign nerves

Formation of neuromuscular connections in mammals may involve a hierarchy of efficiency of synapse formation at a stage when motor nerves have already contacted muscle fibers and during the transitional period of multiple innervation. In an attempt to test for such a hierarchy, we examined, in neonatal rats, the relative efficiency of reinnervation by foreign or original nerves implanted simultaneously in a large muscle so that competition for muscle fibers was minimized. The tibial nerve, containing gastrocnemius nerve fibers, and the “foreign” peroneal nerve were implanted into the denervated lateral gastrocnemius muscle. One to five months later, indirect tetanic tensions obtained upon stimulating the implanted nerves were measured by isometric techniques and were compared to contralateral control muscles. When both nerves were implanted side by side at the end-plate region, approximately equal tetanic tensions were obtained at the time of testing. The same result was also obtained when the tibial and common peroneal nerves were implanted into non-end-plate and end-plate regions, respectively. However, in the reverse experiment, the tibial nerve implanted at the end-plate region produced significantly higher tetanic tension than the peroneal nerve at the non-end-plate site in the same muscle. Thus, the original nerve, compared to a foreign nerve, appeared to reinnervate neonatal muscle more effectively, but this was only revealed under conditions where access to former end-plate regions was unequal.     

Structure of the endothelium of the thoracic and abdominal aorta of intact rats studied by various methods of preparation and handling of the specimens

By means of scanning and transmissive electron microscopy structural peculiarities of endothelium of the thoracic and abdominal parts of the intact rat aorta have been studied at various regimens of preparation and making specimens . The greatest changes endotheliocytes (EC) undergo at using immersion fixation after dissection of the aortal segments. These changes are less pronounced at immersion fixation in situ. A decreased perfusion pressure results in appearance of intimal folds and microfolds on the surface of EC. Increasing time for washing more than 1 min results in appearance of inflations and craters on the surfice of EC. For analysis by means of transmissive electron microscopy it is not necessary to remove blood completely out of the vascular bed. The most essential factor is to maintain perfusion pressure at the average systolic level in the given area of the vessel. However, to make the analysis by means of scanning electron microscopy this method is not suitable. The most optimal condition for initial stages of preparing vessels for morphological investigation is their washing for 1 min in the medium 199 with addition of heparin (10 units/ml) during no more than 1 min with a subsequent perfusive fixation in 2.5% solution of glutaraldehyde in the medium 199 no less than 5 min under the average arterial pressure in the given area of the vessel.     

Some physiological and biochemical features of striated muscles reinnervated by preganglionic sympathetic fibers

Skeletal muscle fibers can be reinnervated by motor cholinergic fibers, that is, functional connection can be achieved. However, functional connection implies not only the capacity of the nerve impulse to elicit a contractile response but also the capability of the reinnervating neurons to evoke particular modifications of the physiological and biological features of the muscles. In order to search for some of the modifications due to reinnervation by preganglionic sympathetic fibers, muscle contraction time was studied in three different preparations of adult cats: a) cricothyroid muscle reinnervated by preganglionic fibers; b) cricothyroideus reinnervated by its own nerve; and c) the corresponding normal neuromuscular preparation. The activities of malic dehydrogenase, of aldolase and pyruvic kinase were studied in these three preparations as well as in the denervated cricothyroid muscles. Reinnervation by preganglionic fibers prolonged the twich contraction time, whereas, self-reinnervation did not alter it. On the other hand, the activities of the three enzymes decreased as a result of denervation. In contrast, the muscle reinnervated with sympathetic preganglionic fibers partially recovered the normal level of malic dehydrogenase and the aldolase activities; but showed no modification in the level of pyruvic kinase activity. Conversely, in the muscle fibers reinnervated by their own nerve, the activity of the three enzymes returned to normal levels. The shortening of contraction time of the preganglionic reinnervated muscle correlates well with the features of the enzymic activities found in these muscles. It can be concluded: a) preganglionic sympathetic axons are able to achieve functional connections with striated muscles and b) considering the trophic effect, preganglionic fibers resemble the motor nerve supplying slow muscles.     

Analysis of nerve supply pattern in thoracic duct in young and elderly men

BACKGROUND: Analysis of the innervation pattern of the thoracic duct in young and elderly human subjects has been performed. The subdivision of the vessels in cervical and lumbar region were taken in consideration. MeTHODS AND RESULTS: Immunostaining for general nerve fibers with a PGP 9.5 marker disclosed a diffuse innervation of the thoracic duct in young subjects, which was strongly reduced in elderly subjects. In young subjects, tyrosine hydroxylase (TH) and neuropeptide Y (NPY) immunoreactive fibers, markers of noradrenergic postganglionic sympathetic fibers, were frequent; choline acetyltransferase (ChAT) immunoreactive fibers, marker of cholinergic parasympathetic nerve fibers, were also well represented. Therefore, the influence of sympathetic and parasympathetic nerve systems on the thoracic duct can be confirmed. The immunoreactivity of vasoactive intestinal peptide (VIP), a neuropeptide frequently present in cholinergic parasympathetic nerve fibers, was scarcely present. Dopamine-positive fibers were observed in few short nerve fibers. Substance P (SP)-positive fibers were widely distributed in the medial and intimal smooth muscle layers, suggesting their involvement as contractile modulating fibers and sensitive fibers. In elderly subjects, an evident reduction of all specific nerve fibers analyzed was detected, the ChAT-positive fibers being the most affected. CONCLUSIONS: The lymphatic vessel thoracic duct is able to regulate hydrodynamic lymph flow by intrinsic contraction of its smooth muscle layer. Therefore, analysis of the thoracic duct innervation pattern may be important in assessing the regulation of vessel contraction. These findings called attention to the reduction of lymphatic drainage functionality affecting fluid balance in the elderly.     

Nonacceptance of innervation by innervated neonatal rat muscle

Denervated adult muscle accepts innervation and has high levels of extrajunctional acetylcholine (ACh) receptor, compared to innervated adult muscle. If the high receptor density or any externally oriented part of the receptor molecule permitted or triggered functional synaptogenesis, then innervated neonatal muscle, with its known high extrajunctional sensitivity, should also accept extra synapses from implanted motor nerves. This prediction was tested by implanting the common peroneal nerve into innervated lateral gastrocnemius muscle in 25 neonatal rats and studying the innervation achieved 1–8 weeks later. With one exception, zero or negligible twitch tensions were obtained when the implanted nerve was stimulated. Intracellular recording in two cases showed no evidence of subthresholdevoked potentials in surface muscle fibers. In contrast, when the original motor nerve was cut at the time of common peroneal nerve implantation, reinnervation occurred as soon as 4 days later, and substantial indirect twitches (most observed qualitatively) were invariably found 6–7 days after operation. Four to eight weeks after nerve implantation into denervated muscle, substantial twitch tensions were obtained upon stimulation of the implanted nerve. α-Bungarotoxin binding to extrajunctional ACh receptors per unit surface area was similar in innervated neonatal and denervated adult muscle. Therefore, nonacceptance of additional functional innervation in neonatal muscle implies that a high average density of extrajunctional ACh receptor is not sufficient to permit or trigger functional neuromuscular junction formation.     

Neurogenic inflammation of gingivomucosal tissue in streptozotocin-diabetic rat

Previously it was assumed that nerve fibres are involved in the neurogenic inflammation induced by mechanical or chemical irriations. It has been also suggested that in diabetes mellitus the unmyelinated small diameter fibers are impaired as a result of diabetic neuropathy. Therefore, our aim was to study the alterations of the nerve processes in the gingivomucosal tissue in streptozotocin (STZ)-diabetic rats. Light- and electronmicroscopical examinations were made to analyze the changes in nerve fibres. After one week of steptozotocin treatment, the gingivomucosal tissue had inflammatory cell infiltration and some degenerated nerve fibres were also observed. Dense mitochondria, disorganization of cell organelles, and appearance of myelin-like dense bodies were found in the axons of degenerared nerve fibres. Semiquantitative analysis showed that 14 +/- 4% of the unmyelinated nerve fibres degenerated after one week of STZ treatment. However, degeneration of the myelinated nerve fibers was not observed. Two weeks after STZ treatment, most of the unmyelinated and myelinated nerve fibers showed degeneration (86 +/- 5%) and the placement of the ligature revealed a non-inflammatory connective tissue adjacent to a normal epithelium. The myelin sheath was disrupted and dark axoplasm with cytolysosomes became manifest. These findings demonstrated that both unmyelinated and myelinated nerve fibers are altered and inflammatory reaction exists in the gingivomucosal tissue only in the early stage of diabetes mellitus.