Jordi Cuadras

Morphometric and ultrastructural changes with ageing in mouse peripheral nerve.

Qualitative and quantitative information is reported on the morphological changes that occur in nerve fibres and nonneuronal cells of peripheral nerve during the lifetime of the mouse. Tibial nerves of mice aged 6–33 mo were studied. With ageing, collagen accumulates in the perineurium and lipid droplets in the perineurial cells. Macrophages and mast cells increase in number, and onion bulbs and collagen pockets are frequently present. Schwann cells associated with myelinated fibres (MF) slightly decrease in number in parallel with an increase of the internodal length from 6 to 12 mo, but increase in older nerves when demyelination and remyelination are common. The unmyelinated axon to myelinated fibre (UA/MF) ratio was about 2 until 12 mo, decreasing to 1.6 by 27 mo. In older mice, the loss of nerve fibres involves UA (50% loss of 27–33 mo cf. 6 mo) more markedly than MF (35%). In aged nerves wide incisures and infolded or outfolded myelin loops are frequent, resulting in an increased irregularity in the morphology of fibres along the internodes. In the mouse there is an adult time period, 12–20 mo, during which several features of degeneration progressively appear, and an ageing period from 20 mo upwards when the nerve suffers a general disorganisation and marked fibre loss.

Ensheathing glia transplants promote dorsal root regeneration and spinal reflex restitution after multiple lumbar rhizotomy

Previously, we have shown that transplants of olfactory bulb ensheathing cells promoted regeneration of transected dorsal roots into the spinal cord. In this study, we assessed the ability of regenerating axons to make functional connections in the cord. Dorsal roots L3 to L6 were sectioned close to their entrance into the spinal cord and reapposed after injecting a suspension of ensheathing cells into each dorsal root entry zone (Group G). Afferent regeneration into the cord and recovery of spinal reflexes were compared with animals that received no injection (Group S) or culture medium without cells (Group C). Electrophysiological tests, to measure nerve conduction and spinal reflexes (H response and withdrawal reflex) evoked by stimulation of afferents of the sciatic nerve, were performed. At 14 days after surgery, H response was found in only 1 of 7 rats of Group G, and withdrawal reflexes were absent from all animals. At 60 days, the H response reappeared in 7 of 10 rats of Group G, and 1 of 5 of each of Groups C and S. The withdrawal reflex recovered in 4 of 10 rats of Group G, but in none of Groups C and S. Immunohistochemical labeling for CALCITONIN GENE– RELATED PEPTIDE (CGRP) in rats of Group G showed immunoreactive fibers entering the dorsal horn from sectioned roots, although at lower density than in the contralateral side. In conclusion, transplanted ensheathing cells promoted central regeneration and functional reconnection of regenerating sensory afferents. Ann Neurol 1999;45:207–215

Histologic assessment of sciatic nerve regeneration following resection and graft or tube repair in the mouse.

The present study determines the number and morphology of myelinated fibers that regenerate after resection of the mouse sciatic nerve. In different groups of mice, a resection of 4 or 6 mm of the sciatic nerve was left unrepaired, repaired with silicone or collagen guides or by an autologous nerve graft of the same or smaller calibre. Regeneration was examined, under light microscopy, 3 months after operation and quantified by morphometric analysis of light micrographs of cross-sectional nerve fibers. The results show that, without repair, few nerve fibers reach the distal nerve stump, while tubulization or autografts allowed better regeneration. Tube repair allowed a comparable degree of regeneration to that of an autograft with 4 mm gaps, but lower with 6 mm gaps. Regeneration was limited with a gap of 6 mm in silicone tubes, but was successful in half the mice with collagen tubes. The size and myelination of regenerated fibers were below normal values in all experimental groups, although they were closer to normal with sciatic autografts than after smaller grafts and tubulization. There were no signs of secondary degeneration in the nerve regenerates within silicone and collagen tubes.

Granule containing cells in the crayfish third abdominal ganglion

1. Four of the 850 neuron cell bodies of the crayfish third abdominal ganglion contain large dense secretory granules. 2. The processes of these cells form a neurohemal organ in the dorsal perineurium/neurilemma in the ganglion. 3. None of the immunocytochemically identified peptides accounts for the observed distribution of granules.

Secretory organelles in the crayfish nervous system

Abstract 1. 1. Eleven categories of secretory organelles are present in the central nervous system of crayfish: oval clear vesicles, five classes of round clear vesicles, vesicles with a small spot, three classes of dense cored vesicles, and large granules. 2. 2. Clear vesicles are associated to synaptic active zones or electrotonic junctions. Small spot vesicles seem specific of lateral giant axons. Dense cored vesicles are ubiquitous. 3. 3. Small clear vesicles release their content at synaptic active zones. Dense cored vesicles are associated to non-synaptic release. But exocytotic release from large clear and small spot vesicles has not been observed.

Neurons in the third abdominal ganglion of the early postnatal crayfish: a quantitative and ultrastructural study.

Ultrastructural data on the third abdominal ganglion of the crayfish was heretofore only available for adult individuals. The fine structure of neurons in the adult that are involved in the escape response has been described in detail, but no similar data existed for the postnatal individual. An increase in the number of neurons in the third abdominal ganglion during postnatal stages had been reported, which suggested that several changes in the features of neurons may occur. Here we describe the general anatomy and ultrastructure of the early postnatal third abdominal ganglion, with emphasis on neurons, and we compare their characteristics to those of the adult. Abdominal ganglia of 56 crayfish of 0, 8, 10, 18, 25, 50, 110, and 150 postnatal days were processed under cacodylate buffered aldehyde fixatives, osmicated, embedded in plastic, sectioned, and examined by light and electron microscopy. The anatomy of postnatal ganglia is homologous to the anatomy of the adult ganglia except that the perineurium is not developed in postnatals. The area of neurons within the postnatal ganglion shows no stratification, but neurons are grouped in nuclei according to their size. Neurons constitute a homogeneous population in different stages of maturity, as revealed particularly by the ultrastructure of the nucleolus. Postnatal development is evident in the perineurium, which may provide structural support to the ganglion.

Relationships between cell size and nuclear morphology in crayfish neurons

The morphology and ultrastructure of cell nuclei in neurons of the third abdominal ganglion of crayfish were studied from alternating series of ultrathin and semithin sections. The ganglion contains approximately 850 neurons with sizes between 10 and 200 microm. Cell nuclei show a great variability. Their size, the chromatin distribution, the number of nuclear pores, the degree of nucleolar segregation and the size of nucleolus vary in close relationships with the cell size.