A morphometric ultrastructural study of the nucleus of cerebellar granule cells.

A quantitative approach to the nuclear ultrastructure of cerebellar granule cells is described here. The study was made using conventional electron microscopy from cerebellar cortices of adult rats by means of a semiautomatic image analyzer. The basic observation is that the nuclei of mature granule cells constitute a homogeneous population in terms of morphometric and stereologic data; in fact, the volume density of condensed chromatin within the nuclei remains practically constant in all nuclear sections. These results seem to indicate the existence of a cell-specific nuclear morphometric phenotype which might be considered as an effective criterion for the typification of this cellular lineage.

Cytochemical characteristics of the axon membrane at nodes of Ranvier in resting, tetrodotoxin-blocked, and electrically stimulated peripheral nerves of the rat.

To test whether intraaxonal ferric ion-ferrocyanide staining at nodes of Ranvier is influenced by functional state of the nodal membrane, the tibial nerves of Sprague-Dawley rats were subjected to one of the following experimental procedures prior to fixation and staining: General anesthesia to induce nerves at rest, tetrodotoxin blocking of nerve activity, and high-frequency (100 Hz) electrical stimulation. In all cases most but not all nodes were stained. No statistically significant differences were found either in the percentage of total stained nodes or in the percentage of stained nodes from large- and small-diameter fibers among the three conditions tested. An explanation is offered to account for the apparent discrepancy between these results and those from other studies involving related cytochemical markers of the nodal apparatus.

Hereditary motor and sensory neuropathy type II. Clinicopathological study of a family.

A family with hereditary motor and sensory neuropathy (HMSN) type II is described in which 10 affected and 17 unaffected members in three generations were examined. The peak age of onset was in the second decade. In the youngest generation, the proportion of affected to unaffected individuals at risk significantly differed from the expected 50%. There was slight slowing of conduction velocities in 36% of nerves; however, only 3 out of 10 affected members had entirely normal conduction studies. The amplitude of the sensory potentials of median and peroneal nerves was almost uniformly reduced. In all affected patients electromyography of anterior tibial muscles showed signs of neurogenic involvement. Histological study of two sural nerves and a sciatic nerve and its branches revealed loss of myelinated fibres with a proximal-to-distal gradient in this fibre loss, clusters of small regenerating fibres, and atrophic axons. Postmortem study of the proband showed loss of anterior horn and dorsal root ganglion neurons in the lumbar and sacral segments and degeneration of the fasciculus gracilis. Morphometric evaluation of L5 ventral and dorsal roots revealed a normal number of myelinated fibres, diameter histograms being shifted to the left because of a significant loss of large myelinated fibres and regeneration. These anatomical findings are consistent with the hypothesis that HMSN type II represents a primary neuronopathy affecting motor and sensory neurons.

Laminated cytoplasmic bodies in Schwann cells and phagocytes: an ultrastructural and cytochemical study in the normal and lead-damaged peripheral nervous system of the rat.

We studied the distribution and cytochemical characteristics of laminated bodies (LBs) in the peripheral nervous system of normal and lead-intoxicated rats. In normal rats, LBs were exclusively present in myelin-forming Schwann cells (SCs). Nerves from lead-intoxicated animals showed extensive demyelination and remyelination. In these nerves we found an increase of LBs in the SC cytoplasm, and also within phagocytes involved in myelin removal, but not in remyelinating SCs. Cytochemical studies revealed that LBs were positive for acid phosphatase, thus demonstrating the lysosomal nature of such inclusions. Taken together, these data suggest that LBs are autophagolysosomes derived from myelin catabolism, which may be enhanced in the lead-induced demyelinating neuropathy of the rat. The possible mechanisms underlying this phenomenon and their pathological relevance are discussed.

Demyelination-induced plasticity in the axon membrane: an ultrastructural cytochemical study of lead neuropathy in the rat.

We examined the distribution of ferric ion-ferrocyanide stain (a marker for excitable regions of myelinated fibers) in the lead-induced demyelinating neuropathy of the rat. By electron microscopy, we found that paranodal degeneration resulted in spreading of the reaction product from nodal to internodal axolemma. During repair, nodal-like stained areas formed at the contact zones between preremyelinating Schwann cells. These data suggest that the location and extent of excitable axonal regions are influenced by axoglial relationships. Additionally, some fibers displayed staining at paranodal axolemma adjacent to demyelinated segments, suggesting it might be an alternative site for impulse generation in demyelinated fibers.