J. A. Kiernan

HYPOTHESES CONCERNED WITH AXONAL REGENERATION IN THE MAMMALIAN NERVOUS SYSTEM

11 . Pertinent experimental data . . . . . . . . . . . . 157 (I) Regeneration in the peripheral nervous system . . . . . . . . 158 (2) Axonal regeneration in the C.N.S. . . . . . . . . . . 158 (a) Wounds of the brain and spinal cord . . . . . . . . . 158 . I59 (3) Neurosecretory axons . . . . . . . . . . . . 160 (4) Monoaminergic fibres . . . . . . . . . . . . 161 ( 5 ) Regeneration through spinal roots . . . . . . . . . . 161 (6) Primary olfactory neurones . . . . . . . . . . . 161 (7) Regeneration of axons into non-neural tissues transplanted into the brain . . . 162 (a) Skin . . . . . . . . . . . . . . . 162 (b) Striated muscle . . . . . . . . . . . . . 162 (c) Smoothmuscle . . . . . . . . . . . . . 162 (d) Other tissues . . . . . . . . . . . . . 163

Acceleration of peripheral nervous regeneration in the rat by exogenous triiodothyronine.

Abstract It has been shown, by a histological method of assessment, that exogenous triiodothyronine in doses from 5.0–500 ng per 100 g body weight significantly increases the rate of elongation of axons distal to a crush lesion of the sciatic nerve of the rat. The magnitude of the effect increases with dosage of the hormone, and the mean distance regenerated in 11 days is more than trebled in rats receiving the highest dosage tested. It appears likely that this effect is mediated through an increased rate of neuronal protein synthesis, but the present results do not exclude the possibility that axonal elongation is accelerated by other mechanisms. Further investigations of the mode of action of triiodothyronine, and of the functional specificity of the more rapidly regenerated axons, are required before any possible clinical application of the findings can be entertained.

Endoneurial Vascular Permeability in Degenerating and Regenerating Peripheral Nerves

SummaryThe endoneurial blood vessels of rodents are normally impermeable to proteins but they become permeable when the axons in the nerve have been severed. In this investigation, the increased permeability is examined in relation to the occurrence or absence of axonal regeneration.The sciatic and hypoglossal nerves of rats were either ligated and transected so that axons would not regenerate, or crushed and then allowed to regenerate. Changes in vascular permeability to fluorescently labelled albumin were examined in the endoneurium distal to the sites of both types of injury at postoperative intervals of 1–21 days. When axonal regeneration was prevented, the endoneurial vessels remained impermeable to the protein tracer until the 6th day. They then became permeable throughout the distal stump and remained so for the remainder of the experimental period. When axons regenerated, there was a considerably more intense exudation of the tracer in the distal segment of the nerve. The zone of greatly increased endoneurial vascular permeability advanced along the nerve at the same rate as that of the most rapidly regenerating axons, as observed in silver-stained sections.It is suggested that in the absence of regenerating axons, vascular permeability may be initiated by products of Wallerian degeneration. The greater permeability in regenerating nerves may be induced by vasoactive substances secreted by growth-cones. The results support a hypothesis in which it is maintained that the presence of plasma proteins around growth-cones is necessary for the occurrence of axonal regeneration. The further increase in permeability caused by the most rapidly elongating axons may assist the regenerative process by making larger quantities of plasma proteins available to other growing axons.

Enhancement of axonal regeneration in the brain of the rat by corticotrophin and triiodothyronine

Abstract Rats with simple incised wounds of the telencephalon were treated for either 7 or 50 days with either sunthetic corticotrophin (ACTH) or triiodothyronine (T3). Control animals received no treatment. Regenerating axons, which entered and sometimes crossed the lesions, were detected histologically in rats treated with both hormones. The effects of both ACTH and T3 were mediated during the first 7 days after placement of the lesion. We suggest that ACTH, in suitable dosage, acts by allowing the formation of a suitable type of loose connective tissue in the lesion, while T3 increases the rate of synthesis of axoplasmic structural protein.

Specific, selective, and complete staining of neurons of the myenteric plexus, using Cuprolinic blue

Wholemounts consisting of both muscular layers of the rats intestine have been stained with Cuprolinic blue and magnesium chloride. The procedure, which is specific for RNA, gives selective coloration of the somata of the neurons of the myenteric plexus. The neuronal nucleoli and Nissl substance are the only blue structures in such preparations. For descriptive and quantitative work, Cuprolinic blue is more selective than other cationic dyes, and it colors more neurons than can be shown by staining for mitochondrial NADH diaphorase. The absence of background color enables neurons to be identified more confidently and counted more quickly than is possible with other techniques, in which nuclei or mitochondria in smooth muscle and neuroglial cells are also stained. Numbers of myenteric neurons determined using the new method are higher than those obtained by other means.

The fine structure of the infundibular process of the hedgehog

SummaryThe fine structure of the infundibular process of the hedgehog has been studied, using material fixed in osmium tetroxide and embedded in Vestopal W. The process resembles in general structure that of other mammals, but also shows features not previously described in other species.The nerve fibres contain a number of inclusions, namely: small vesicles, 300–500 Å in diameter; larger vesicles, up to 2000 Å in diameter, which contain a variable amount of osmiophilic material; hexagonal crystal-like bodies, approximately 1250 × 3000 Å in size, lying within a striated membranous sheath; and aggregate bodies made up of small electron dense granules, possibly derived from mitochondria.In addition complex multilamellate bodies occur in some nerve fibres, which apparently give rise to membranous vesicles. Pituicytes, of varying appearance, are often intimately related to the nerve fibres.The findings suggest that synthesis of material may occur in the distal part of the fibres of the hypothalamo-hypophysial tract.

Clinicopathological features of primary lateral sclerosis are different from amyotrophic lateral sclerosis

Primary lateral sclerosis (PLS) bears close resemblance to cases of amyotrophic lateral sclerosis (ALS) presenting with spasticity, but histopathological studies have shown significant difference between the two conditions. When the lower motor neurons in cases of ALS and PLS are compared with the equivalent cells of control subjects, morphometric studies indicate significantly decreased size and increased convexity (rounding) of the cell bodies only in ALS. In both disorders there is loss or shrinkage of the largest cortical motor neurons (Betz cells) in the primary motor cortex, though this change is not conspicuous in all cases of ALS. Morphometry reveals in both diseases a general reduction in the sizes of pyramidal cells in the precentral gyrus, indicating that smaller neurons are involved. The cortical motor neurons shrink more in PLS than in ALS. It is concluded that there is clear difference between ALS and PLS. In PLS, quantitative histopathological data show that the neuronal degeneration is confined to long descending pathways, notably the corticospinal system, with no concomitant involvement of lower motor neurons. In ALS, lower motor neuron degeneration occurs in all cases, whereas involvement of the motor cortex is variable.

Localization of ?-d-glucosyl and ?-d-mannosyl groups of mucosubstances with concanavalin A and horseradish peroxidase

SummaryConcanavalin A is a lectin which is known to bind specifically to α-d-glucosyl and α-d-mannosyl groups in the mucosubstances of mammalian tissues. The lectin molecule is bivalent; after its attachment to mucosubstances present in a histological specimen it can also bind horseradish peroxidase, a mannose-containing glycoprotein. The attached peroxidase may then be visualized by virtue of its histochemically demonstrable enzymatic activity. Other investigators have utilized this principle in the electron microscopic localization of cell-surface carbohydrates.A histochemical technique for light microscopy is described here, along with three control procedures which establish the specificity of the method. The technique is somewhat more fensitive than earlier ones in which fluorescent-labelled concanavalin A was used, and has the additional advantages that all the required reagents are commercially available and that sacilities for fluorescence microscopy are not needed.

Accelerated recovery from peripheral nerve injury in experimental hyperthyroidism.

Abstract The right sciatic nerve was crushed in the thigh in 48 rats, and an indwelling stimulating electrode was implanted at the site of injury. Four groups of rats received respectively, no treatment, triiodothryonine (T3), 1.0 μg/kg daily from day 15 to 21, T3 from day 1 to 7 and T3 from day 1 to 40. Daily testing for recovery of movement at the ankle joint showed that administration of T3 throughout the postoperative period increased the rate of functional recovery by a factor of 50%. The rats were killed after 40 days and a quantitative histological study revealed no differences in the proportions of innervated motor endplates in the tibialis anterior muscle amongst the four experimental groups. It was concluded that reinnervation of this muscle was completed after 40 days, irrespective of hormonal treatment. In specimens of skin from the calf, the proportions of innervated hair follicles were significantly higher in rats treated for the first 7 days and for all 40 days with T3 than in the untreated rats and in those receiving T3 from day 15 to 21. It is possible, therefore, that sensory neurons are more sensitive than motor neurons to T3 administered in the first postoperative week.

Layered structure of saccular aneurysms assessed by collagen birefringence

Cerebral aneurysms are composed principally of collagen, a birefringent protein which is responsible for withstanding the forces of blood pressure. The known correlation between collagen birefringence and its mechanics provides the basis for using polarizing microscopy to evaluate the strength of collagen, layer by layer across the aneurysmal wall. In order to obtain better quantitative measurements, several birefringent enhancement stains were investigated. We concluded that sirius red F3B, at a concentration of 0.05% in saturated picric acid, is an excellent stain to enable measurement of both birefringence and directional organization on the same tissue sections. Six aneurysms from autopsy, fixed at 120 mmHg, and one surgical specimen were cut at 4 microns to provide sets of tangential sections. The polarizing optics emphasizes the multi-layered structure of the aneurysmal wall with the mean fiber alignments distinguishing one layer from another. Birefringence measurements showed that the outer third of the wall had mainly higher strength collagen, although not as high as nearby artery adventitia. The inner layers of the aneurysms had intermediate values, similar to the artery media and subendothelium. Our results are consistent with a model of aneurysmal enlargement that requires the reorganization of higher strength outer fibers while new collagen is added to the inner layers.