Silver impregnation of degenerating dendrites, cells and axons central to axonal transection. I. A Nauta study on the hypoglossal nerve in kittens

Suppressive silver methods—a tool for identifying axotomy-induced neuron degeneration

Suppressive silver methods evolved from empirical observations about 50 years ago that argyrophilia of normal nerve fibers can be suppressed by a short period of oxidation of tissue sections, whereas degenerating nerve fibers in the same preparations were still clearly visible. Based on this property, suppressive silver impregnation became the main technique for investigating pathways in the central nervous system until the early 1970s. Suppressive silver methods were also found to visualize degenerating nerve cell bodies, in addition to degenerating nerve fibers. This possibility has given these methods an important place among current tools for identifying neuronal degeneration in trauma, disease and toxicity. In this article we demonstrate and review the usefulness of suppressive silver methods in identifying neurons undergoing degeneration as a result of peripheral or central axon injury in immature animals. The documentation is based on previously published data from experiments in which silver impregnation was used to demonstrate degeneration of motoneurons following pure motor axon injury or mixed peripheral nerve injury, as well as on new results on degeneration-induced argyrophilia in the inferior olive following cerebellar lesions. We find that silver precipitates resulting from these injuries are localized either to the entire neuronal cytoplasm, to a few (typically two) intranuclear bodies, or to both sites. The findings are discussed in relation to morphological features of apoptosis, necrosis and retrograde neuronal responses. We suggest that suppressive silver methods allow visualization of different processes of neuronal degeneration, and therefore may be a useful adjunct for identifying axotomy-induced neuronal degeneration.

Involvement of microtubule integrity in memory impairment caused by colchicine

In order to fully evaluate the effects of colchicine treatment on learning ability in rats, colchicine was administered, and both Morris water maze (MWM) and step-through type passive avoidance (PA) learning tests were conducted. In both learning tests, infusion of colchicine into the rat dentate gyrus, at two distinct bilateral rostrocaudal locations, potently impaired memory function in a dose-dependent manner (0.01-2.0 microg/site), whereas systemic injection of colchicine (50-300 microg/kg) did not. In the MWM test, memory impairment was observed even at doses where there was no evidence of any histological changes in the dentate granule cells. This suggests that functional deterioration, that is, learning impairment was induced by the dysfunction of microtubules and/or axons, was caused by colchicine. Moreover, ameliorated learning behavior was observed with chronic treatment of beta-estradiol 3-benzoate, which has been suggested to have an important role as an adjuvant treatment for younger Alzheimer's disease (AD), immediately after colchicine infusion (0.3 microg). These results indicate that the animal model accompanying the colchicine-induced functional defect showing early tau pathology, but not neuronal cell degeneration, may well mimic comparatively early stage of AD.

R, Silva CFD, Lainetti RD. Estudo experimental comparativo da ação das neurocinas cardiotrofina-1 e oncostatina-m na regeneração nervosa periférica

Os avanços das técnicas microcirúrgicas e o conhecimento detalhado do microambiente da regeneração podem contribuir significativamente na melhoria dos resultados das reparações nervosas periféricas. Nos últimos anos vários autores têm utilizado uma série de tecidos e substâncias interpostos entre os cotos de um nervo periférico seccionado, buscando estimular o crescimento axonal no local da lesão. Através da técnica de tubulização, os autores estudam o efeito de duas neurocinas, a cardiotrofina-1 (CT-1) e a oncostatina-M (OsM), no crescimento axonal e na sobrevida dos neurônios sensitivos nos gânglios da raiz dorsal de L5, após a lesão de nervos ciáticos em camundongos C57BL/6J. Utilizam 3 grupos de 7 animais que tiveram seus nervos seccionados e tubulizados com próteses de polietileno preenchidas com cardiotrofina-1, oncostatina-M e citocromo-C, associadas a um extrato de colágeno. Um quarto grupo de 3 animais, não operados, foi considerado por nós como grupo controle de normalidade. Após 4 semanas da cirurgia, os camundongos foram sacrificados, e realizada a contagem das fibras mielínicas nos cabos de regeneração retirados. Os gânglios das raizes dorsais de L5 também foram dissecados possibilitando a contagem dos neurônios sensitivos. Os dados foram analisados estatisticamente, permitindo concluir que as duas substâncias, utilizadas por nós, foram efetivas no estímulo ao brotamento axonal, porém, as mesmas não conseguiram impedir a morte dos neurônios sensitivos no gânglio da raiz dorsal de L5.

Silver impregnability of ischemia-sensitive neocortical neurons after 15 minutes of cardiac arrest in the dog

The development of postischemic neuronal argyrophilia and the subsequent fate of argyrophilic neurons were studied in dogs after 15 min of complete cerebral ischemia and survival varying from 1 h to 7 days. Histopathological examination of the vulnerable neocortical region was performed using the Nauta degeneration method, and the time course of cellular changes was described. Clear-cut neuronal argyrophilia was found to precede cell body shrinkage and gradual disintegration corresponding to selective neuronal death. To clarify this initial stage of neuronal impregnability, the samples from the animals surviving 8 h postarrest were stained with toluidine blue or processed for electron microscopy, and the distribution of argyrophilic cells was confirmed to be identical with that of hyperchromatic or electron-dense cells. On the other hand, infrequently observed "tissue infarctions" exhibited no silver affinity in spite of apparent cellular damage. These findings indicate that enhanced impregnability is related to cytochemical processes incidental to the phenomenon of "selective neuronal death", which can be readily detected by the Nauta method.

Mapping of the canine lumbosacral spinal cord neurons by Nauta method at the end of the early phase of paraplegia induced by ischemia and reperfusion

The Nauta impregnation method was used to map the neuronal changes in the canine lumbosacral segments following ischemia and reperfusion. The early perikaryal changes ensuing during the first phase after 30 min of thoracic aorta cross-clamping alone or followed by 30 min of reperfusion were mapped. During the second phase (one to six postischemic reperfusion days) the dendritic, preterminal and synaptic degeneration developed. The influence of 30 min cross-clamping immediately followed by perfusion fixation is characterized by the occurrence of flocculent argyrophilic clusters in the cytoplasm of middle-sized and large neurons of L3-S1 segments. Declamping of the thoracic aorta followed by 30 min of reperfusion basically modifies the susceptibility of lumbosacral neurons to Nauta impregnation promoting somatic and dendritic argyrophilia mainly of small (less than 15 microns) neurons, localized mostly in the fifth, sixth and seventh layers, respectively. This early appearing somatic and dendritic argyrophilia is not abolished by a pretreatment of sections with acetone in which cholesterol and its esters are highly soluble, or chloroform-methanol which extracts total lipid. After 24 h of reperfusion the somatic and dendritic argyrophilia is lost but the first signs of drop-like degeneration are detected in all but three superficial dorsal horn layers. At the end of the third reperfusion day, an atypical form of bouton degeneration was found, consisting of massive occurrence of enlarged (greater than 4 microns) boutons encircled by a clear halo. Laminar distribution of enlarged degenerating boutons coincides with laminar quantitative distribution of small argyrophilic neurons detected 30 min after reperfusion. The basic orientation of the many terminal fibres attached to enlarged boutons suggests that they belong to the axons localized mainly in the lateral and anterior columns. Despite a dense argyrophilic network pervading the gray matter of lumbosacral segments only pale shadows of middle-sized and large neurons were found at the end of the sixth reperfusion day and neither somatic nor vessel wall argyrophilia could be detected. All animals surviving one, three and six days postoperatively suffered from fully developed paraplegia.

Elimination of intramedullary axon collaterals of cat spinal alpha-motoneurons following peripheral nerve injury

The motor nerve supplying the medial gastrocnemius (MG) muscle was transected in the popliteal fossa of adult cats. The proximal nerve stump was ligated to prevent reinnervation. Three, six or twelve weeks later, axotomized MG motoneurons were intracellularly labelled with horseradish peroxidase, and the morphology of their intramedullary axon collateral systems was investigated quantitatively. The results were compared with corresponding data obtained from normal MG motoneurons. The peripheral chronic axotomy induced a gradual decrease in the number of recurrent axon collaterals originating from the lesioned MG motoraxons within the spinal cord. At 12 weeks postoperatively, this decrease amounted to 40%. The elimination preferentially involved axon collaterals originating from juxta-somatic regions of the motoraxons. In the axon collateral trees persisting in the axotomized MG neurons the tree size, branching patterns and number of synaptic boutons were all normal. Thus, no signs of a gradual deterioration of individual axon collateral systems were observed at any postoperative stage studied. The results are discussed in relation to other retrograde degenerative and regenerative events induced by axotomy.

A morphological study of glial cells in the hypoglossal nucleus of the cat during nerve regeneration

The cat hypoglossal nerve and nucleus have been used as a model for the study of the occurrence and time course of modifications in the size and composition of the perineuronal glial cell population as they relate to cytological changes in the nerve cell body and the initiation and progress of axon regeneration. Animals were killed at 2, 5, 10, 20, 35, 65, and 115 days after crush injury to the hypoglossal nerve. At 5 days after surgery, growth cones and regenerating unmyelinated axons were present at the lesion site, but no conspicuous changes were apparent in the nerve cell bodies. At 10 days after surgery, the granular endoplasmic reticulum was disaggregated and depleted. The elongation phase appeared to be completed at 20 days, as judged by the bilateral retrograde labeling of the hypoglossal nuclei with horseradish peroxidase. By 35 days, the cytoarchitecture of the nerve cell bodies and maturation of axons, as determined by a comparison of the relative frequency distribution of cross sectional areas proximal and distal to the lesion, were completely restored. Comparative quantitative light microscopic examination of the hypoglossal nuclei of intact and experimental animals failed to reveal any statistically significant differences in the total number of glial cells, number of glial cells/unit area of neuropil, or relative proportions of glial cell types at any of the postoperative time intervals. Moreover, electron microscopic quantitation of the microglial cell population did not reveal any significant alterations in the number, density, location, or morphology of these cells.(ABSTRACT TRUNCATED AT 250 WORDS)

A re-evaluation of the question of ascending fibers in the pyramidal tract

In 1952 we published a study in the cat with the Glees method, demonstrating the occurrence of degenerating fibers in the pyramidal tract rostral to transections of the tract in the spinal cord. These fibers were interpreted as spinocortical fibers, which have also been described in man. However, other authors have disputed the existence of such fibers. In an attempt to provide more information about this subject, multiple injections of horseradish peroxidase (free and lectin-labeled) were made in the sensorimotor cortex of 4 cats. No retrogradely labeled cells were found in the spinal cord in these cases. Our present and previously reported findings are discussed in the light of other studies of pathological changes in fiber tracts within the central nervous system. Although the present experiments were negative, the degenerating axons previously observed by us in silver sections from the pyramid, pons and internal capsule after lesions of the pyramidal tract in the spinal cord, can not be satisfactorily explained as evidence of retrograde, indirect Wallerian, degeneration of corticospinal fibers.

Neuro-histological reactions following tooth extractions

The neuro-histological reactions after tooth extraction were investigated in the extraction alveolus, the mandibular nerve and the trigeminal ganglion. In the ganglion, nerve cell bodies showing signs of retrograde reaction (chromatolysis and nuclear displacement) were seen 12 h after extraction. Maximal number of reacting cells were registered in the first postoperative week. Three weeks after extraction the number of reacting cells were at a normal low level. In the mandibular nerve no signs of axon degeneration could be demonstrated. In the alveolus, initial traumatic axon degeneration was followed by regeneration 2 days after extraction. Within the first postoperative week the alveolus was filled with connective tissue, in which many long thin axons were seen. Cancellous bone then filled the alveolus; the axons were thereby gathered - concentrated - into fascicles in the central part, with a direction towards the limbus. However, this was only passed by very few axons. Four months after extraction signs of axon degeneration were seen, and 2 months later the myelin sheaths also displayed degenerative signs. Ten months after extraction a minor area of connective tissue with a content of few axons and vessels was found at the bottom of the former alveolus. The histological appearance was of a small traumatic neuroma.

Fibers of trigeminal mesencephalic neurons in the maxillary nerve of the rat

Indirect Wallerian degeneration after sectioning the infraorbital nerve, and retrograde axonal transport following injection of horseradish peroxidase (HRP) into the maxillary nerve were studied in rats. These experiments showed the existence of primary trigeminal neurons in the pars caudalis of the ipsilateral trigeminal mesencephalic nucleus and in the supratrigeminal nucleus of Lorente de Nó. Such neurons were interpreted as being responsible for the sensitive innervation of the periodontal membrane.

Further observations on transganglionic degeneration in trigeminal primary sensory neurons

Transganglionic degeneration has been studied with the Fink-Heimer method in the trigeminal sensory nuclei of adult cats and rats following peripheral nerve transections. Degeneration was observed ipsilaterally as well as contralaterally in all cats, surviving 11-30 days after transection of the infraorbital nerve. In the rats the infraorbital or the auriculotemporal nerve was transected. After transection of the former nerve the first signs of transganglionic degeneration were observed after 7 days postoperative survival and even after 130 days there were still a lot of degenerating structures present. Between 7 and 14 days survival there was a small amount of degeneration in substantia gelatinosa. After transection of the auriculotemporal nerve, degeneration was observed only in the most caudal parts of the trigeminal sensory nuclear complex. Opposite to the situation in the cat, there was no contralateral degeneration in the rat. All degeneration areas were somatotopically organized, both in the cat and in the rat. The results are discussed in relation to a previous study of transganglionic degeneration in the trigeminal sensory nuclear complex by the authors and to anatomical and physiological studies of somatotopic organization in the trigeminal sensory nuclei. They clearly show the value of transganglionic degeneration used as a tool for analysis of central projections of primary sensory neurons.

Is the solitary dark neuron a manifestation of postmortem trauma to the brain inadequately fixed by perfusion?

Dark neurons, classified as solitary because of their sparse occurrence, were discerned in the transitional zones between gray and white matter in various species of laboratory animals fixed by perfusion. These neurons, histologically indistinguishable from dark neurons in immersion fixed material, tended to develop when the saline perfusion was delayed or slow, the amount of the Bouin fixative was excessive, or the autopsy was performed shortly after the perfusion. Under these conditions, the white matter manifested a softer consistency and a paler color than the gray matter. These observations suggest that, as the consequence of regional differences in intensity and speed of fixation, distortion during extraction of the brain may activate a stress force in the transitional zones where incompletely fixed neurons become affected and acquire an abnormal affinity for aniline dyes and silver.

Thalamic projections of the dorsomedial prefrontal cortex in the rhesus monkey (Macaca mulatta)

Cortical aspirations were made of the dorsomedial prefrontal sector in the rhesus monkey and the resultant anterograde and retrograde degeneration plotted. Retrograde changes were mapped using both cresyl violet and modified Fink-Heimer techniques. Following large dorsomedial lesions, small numbers of degenerating fibers were traced through the medial part of the magnocellular ventral anterior nucleus (VAmc) and the ventral part of the internal medullary lamina surrounding the anterior nuclei. Degenerating fibers were also traced medially through the inferior thalamic peduncle and rostrodorsally through the basal thalamic region into the mediodorsal nucleus. All pathways converged on areas in the dorsal part of the parvocellular mediodorsal nucleus (MDpc) containing fine-grain dust and argyrophilic neurons, reactions usually associated with retrograde degenerative changes. Sparse fiber degeneration was also noted in the ventral part of the magnocellular mediodorsal nucleus (MDmc). After a longer survival period, slight to moderate cell loss and gliosis were seen in MDpc along with an increase in the number of degenerating fibers passing through the medial part of VAmc. Rostral dorsomedial lesions resulted in small numbers of degenerating fibers in the medial part of VAmc; no degenerating fibers appeared in the basal thalamic region. Fine-grain dust was noted in the dorsal part of MDpc along with sparse preterminal degeneration in the dorsal and ventral parts of MDpc and MDmc respectively. Following caudal dorsomedial lesions, fiber degeneration was traced through the medial part of VAmc and through the inferior thalamic peduncle and basal thalamic regions to areas of degenerating preterminals in the dorsal part of MDpc. Sparse fiber degeneration was also noted in MDmc. No evidence of cell loss and gliosis or increased numbers of degenerated fibers was noted following longer survival periods. Dorsolateral and orbital lesions resulted in large areas of fine-grain dust, argyrophilic neurons, and severe cell loss in MDpc and MDmc respectively. A large combined dorsolateral and orbital lesion made 32 days prior to sacrifice of the animal resulted in coarse fiber degeneration in the medial part of VAmc and in the anterior nuclear capsule. Severe cell loss and fiber degeneration were evident in the entire MD. These results suggest that the rostral dorsomedial prefrontal sector receives projections from MDpc while the caudal sector does not. This projection courses dorsally and rostrally through the ventral part of the capsule surrounding the anterior nuclei and into the medial part of VAmc. The entire dorsomedial sector projects sparsely to both MDpc and MDmc. The projection from the rostral medial surface passes through the medial part of VAmc while that from the caudal surface reaches MD both by the dorsal approach through VAmc and through a ventral approach via the inferior thalamic peduncle and the basal thalamic region.

Neonatal neuronal loss in rat superior cervical ganglia: retrograde effects on developing preganglionic axons and Schwann cells

Beginning prenatally and during the first week after birth, there is normally a loss of axons in rat cervical sympathetic trunk. To test the hypothesis that this spontaneous axonal loss represents a natural process whereby an excessive number of immature preganglionic axons in the cervical sympathetic trunk adapts to the neuronal population in the superior cervical ganglion, the number of nerve cells in the superior cervical ganglion was reduced in newborn rats by administration of nerve growth factor antiserum, 6-hydroxy-dopamine or postganglionic anxotomy. Quantitative ultrastructural studies of these animals at later stages of development revealed that, with each method, the number of preganglionic axons and Schwann cells was reduced to nearly one-third of normal. These findings indicate that the superior cervical ganglion plays an important role in the development of the cervical sympathetic trunk. Removal of ganglionic cells causes a retrograde loss of preganglionic fibres. This process probably represents an exaggeration of the normal mechanism for elimination of redundant axons. Because the changes in axonal numbers are associated with similar reductions in the number of Schwann cells, it can also be concluded that postnatal Schwann cell proliferation is influenced by axonal populations.

Transganglionic degeneration in trigeminal primary sensory neurons

In 16 kittens either the frontal or the inferior alveolar nerve was transected and in 17 adult rats either the supraorbital, the infraorbital or the mental nerve was divided. The postoperative survival periods were kept at 3-28 days for the kittens and 15-26 days for the rats. Sections from the caudal brain stem and the upper part of the cervical cord were impregnated according to the Fink-Heimer method, procedure II. In the kittens degeneration was found after the 8th postoperative day ipsilaterally in both the spinal and main sensory trigeminal nuclei and the spinal trigeminal tract. In the rats degeneration was found in all cases in the same ipsilateral structures as in the kittens. The amount of degeneration was relatively great in the rats, whereas it was very modest in the kittens. A somatotopical pattern was found for the degeneration both within the spinal and the main sensory nuclei. It was in agreement with what has been found in earlier studies, where other techniques have been used. By a comparison with the results of a previous study on the trigeminal nerve in the rat, where partial lesions of the ganglia had been made, it was found that the degeneration in the present study did not cover the whole area receiving primary trigeminal afferents. Possible explanations for this are discussed.

Retrograde cortical aand axonal changes following lesions of the pyramidal tract

Following lesions of the pyramidal tract in hamsters, retrograde changes were studied in the sensorimotor cortex and in the pyramidal tract axons proximal to the lesion, at survival times ranging from 2 weeks to 14 months. Severe cell shrinkage occurred in layer 5 pyramidal neurons as early as 2 weeks, but there was no cell loss among these neurons even with long survival times. Use of the Fink-Heimer method for degenerating axons revealed that the pyramidal tract proximal to the lesion had undergone a retrograde axon degeneration which, in some respects, resembled anterograde degeneration. The retrograde axon degeneration began at the lesion site and advanced slowly rostralwards with time involving increasingly greater numbers of fibers. However, even at the longest survival times the degeneration fell off markedly at pontine levels. The results indicate that this process represents a true retrograde fiber degeneration (as opposed to an indirect Wallerian degeneration) which appears to reach a point of equilibrium such that a partially shrunken pyramidal cell is maintaining a partially degenerated axon.