G. Krinke

Pyridoxine megavitaminosis: an analysis of the early changes induced with massive doses of vitamin B6 in rat primary sensory neurons.

The early effects of high toxic doses of vitamin B6 (pyridoxine) on the peripheral sensory neurons were studied in laboratory rats. The animals were treated with 600 mg/kg of pyridoxine hydrochloride by intraperitoneal injection twice daily. Thereafter they were killed by perfusion-fixation at periods ranging from one to 14 days and the tissues were examined by light and electron microscopy. The primary change consisted of the formation of swollen membranous profiles in both the axon hillock and the initial axonal segment of the large dorsal root cytons. This change occurred within 24 hours of exposure, and was followed by an axonal reaction of the nerve cell bodies and by secondary degeneration of their processes. These findings identify the probable target site for pyridoxine toxicity, and establish a simple animal model for studying not only sensory denervation, but also the axonal reaction and secondary degeneration.

Spinal radiculoneuropathy in aging rats: Demyelination secondary to neuronal dwindling?

SummaryTemporal development of radicular demyelination was studied in male albino rats examined sequentially throughout the lifespan of the animals. The rats were perfusion-fixed with paraformaldehyde and glutaraldehyde and areas of their nervous system including the lumbar spinal roots, the spinal cord, and the peripheral sciatic nerve, were embedded in epoxy resin and submitted to microscopic examination in semithin and ultrathin sections. In addition, a vital fat stain, teasing of single nerve fibers, and estimates of axon diamter and fiber number were obtained. Degenerative changes occurred earlier in the distal portions of nerve fibers than in the spinal roots. The radicular lesion consisted of swelling of myelin and demyelination possibly secondary to shrinkage of axons, resulting in focal accumulation of lipid debris within the spinal roots of old rats. Although the causation of senile neuronal atrophy affecting rat peripheral neurons is not fully obvious, this condition may be exacerbated by such factors as pressure on the nerves and hypoactivity.

Pyridoxine neuropathy: Correlation of functional tests and neuropathology in beagle dogs treated with large doses of vitamin B6

Neurologic examination, electrophysiologic testing and microscopic post-mortem examination was used to study the neuropathy induced in the beagle dog by administration of excessive amounts of vitamin B6.Two female dogs received repeated daily oral doses of 3 g. The treatment was ceased when the dogs developed severe general morbidity, including uncoordinated gait and abnormal neurologic symptoms. The symptoms were most severe during and early after cessation of treatment, and in general they regressed during the subsequent 3 months of treatment-free observation. Sensory central and peripheral maximum nerve conduction velocity started to decrease after a considerable delay; the decrease progressed until late after termination of treatment and failed to fully regress. Morphologic lesions were confined to large, first order sensory neurons.The neurologic examination thus revealed the early changes, while electrodiagnostics and microscopic neuropathology were indicators of more advanced stages of toxic neuropathy and disclosed selective lesions in individuals whose gait appeared to be unremarkable.

Clioquinol and 2,5-hexanedione induce different types of distal axonopathy in the dog.

SummaryThe central distal axonopathy induced in dogs by the administration of high doses of clioquinol is contrasted with the central-peripheral distal axonopathy precipitated by intoxication with 2,5-hexanedione. Mature, pure-bred Beagle dogs received a daily oral dose of 400 mg/kg of clioquinol for up to 7 months, or 1 ml per animal (approximately corresponding to 110 mg/kg) of 2,5-hexanedione for up to 5 months. Intoxicated and control animals were killed and perfused at monthly intervals, so that the spatial-temporal development of the lesion could be followed and correlated with clinical symptoms. During the treatment, dogs intoxicated with 2,5-hexanedione developed symptoms of peripheral neuropathy consisting of flaccid weakness, muscle atrophy, hind-limb foot-drop and areflexia. By contrast, the dogs surviving clioquinol intoxication exhibited a stiff-legged gait, hyperreflexia but no muscle atrophy.Light and electron microscope examination of central and peripheral nervous tissue from dogs intoxicated with 2,5-hexanedione revealed giant axonal swelling and distal axonal degeneration. By contrast, dogs receiving clioquinol showed a distal axonal degeneration confined to the optic tract and the long spinal cord tracts, without any visible involvement of peripheral nerves.

Differential susceptibility of peripheral nerves of the hen to triorthocresyl phosphate and to trauma

The nerve fibres of largest diameter and of greatest length are considered to be the most vulnerable to triorthocresyl phosphate (TOCP). In this study, the differential vulnerability of the particular sciatic nerve branches was determined in the course of TOCP neuropathy and of Wallerian degeneration. The branch innervating the lateral gastrocnemius muscle, made up predominantly of large-diameter fibres, proved most susceptible to TOCP. By contrast, after proximal sciatic-nerve transection, degeneration commenced in the lateral nerve of the third digit, containing long nerve fibres of small diameter.

Differential vulnerability of 3 rapidly conducting somato-sensory pathways in the dog with vitamin B6 neuropathy

In anesthetized dogs with chronically implanted cortical electrodes somatic sensory-evoked potentials (SEPs) were produced by electrical stimulation at neural, muscular or cutaneous sites of the contralateral hind leg. Stimulation of the tibial nerve at the calcaneus or of the short flexor muscles of the hind paw caused SEPs having characteristics following activation of rapidly conducting afferents from muscle spindles. Stimulation of the glabrous skin of the central pad resulted in SEPs arriving after a more protracted latency evidently related to activation of afferents from Merkel cells, Krause and Pacinian corpuscles known to be located at these sites. Stimulation of the hairy skin from the dorsal surface of the hindpaw produced a further type of SEP presumably resulting from activation of afferents from receptors of tylotrich hair follicles.Vitamin B6-induced neuropathy involves the selective degeneration of the largest neurons in the spinal ganglia and of associated long peripheral and central neurites performing rapid impulse transmission. In the course of vitamin B6 neuropathy the relatively slow impulse transmission following stimulation of the central pad was more severely impaired than the faster one after activation of afferents from muscle spindles or receptors from hair follicles. This allows us to conclude that in the dog afferents from the glabrous skin of the central pad conduct centrally via the dorsal columns, susceptible to vitamin B6 intoxication, while muscle and hair receptor afferents ascend in the dorsal spinocerebellar and spinocervical tract, respectively, which are vitamin B6 resistant.

Primary tumours of the thymus in the rat.

The features of 192 primary thymic tumours occurring in the rat are described. Of these neoplasms, 170 were classified as benign thymomas, one as a benign fibrous histiocytoma, 20 as various types of malignant thymoma, 3 lympho-epithelioma-like carcinomas, one mixed small cell undifferentiated-squamous cell carcinoma, one sarcoma-like carcinoma, 4 undifferentiated carcinomas, 11 squamous cell carcinomas and the one remaining tumour as a carcinoid. A mouse, anti-epithelial, monoclonal antibody, lu-5, was used to confirm the epithelial nature of the malignant thymomas, and neuron-specific enolase to confirm the diagnosis of carcinoid. The tumours showed many features in common with those reported in man.

A comparison of endomyocardial disease in the rat with endomyocardial fibrosis in man

The features of 39 cases of spontaneous endomyocardial disease occurring in the rat heart are discussed and the condition is compared with endomyocardial fibrosis occurring in man. Rat endomyocardial disease is an age-related change characterized by subendocardial proliferation of spindle cells that may progress to a lesion histologically similar to fibrosarcoma. Human endomyocardial fibrosis, on the other hand, is not age-related and shows essentially fibrohyaline changes of low cellularity preceded by the occurrence of acid mucopolysaccharides in the subendocardial region; no evidence of malignant change has ever been reported.

Electroretinography in rats

Basic mechanisms of the rat ERG were reinvestigated with contemporary methods of recording and photic stimulation via an optic fiber system connected with a contact lens. Flash stimulation and background illuminance were performed with photometrically defined light stimuli. ERGs recorded in darkness, from dark adapted rats, were similar with those observed in earlier work in which light flashes of much longer duration had been used. Flash stimulation carried out under stepwise increased background illuminance gave new information on the characteristics of oscillatory potentials of the ERG. In general the present observations agreed with the notion that the rods of the rat retina are as sensitive as in man, whereas the cones are functionally less efficient with respect to light sensitivity and temporal resolution. Differences in function of the cones from rat to man have to be kept in mind when using the rat ERG as a model for risk assessment in safety studies.

The assessment of peripheral neurotoxicity in dogs: comparative studies with acrylamide and clioquinol

Monomeric acrylamide was given to beagles in daily oral doses of 15 mg/kg for 22 days and at 5 mg/kg for 60 days. The animals of the high dose group developed neurological signs consistent with peripheral neuropathy. Electrophysiological measurements on the saphenous nerve revealed abnormal nervous function at the end of the treatment period. Conduction velocity was affected to the greatest extent, followed by absolute refractory period and chronaxy. At 30 days upon cessation of treatment conduction velocity and chronaxy were restored to normal but absolute refractory period remained pathological. At that time the first morphological changes of peripheral nerves were detected. Administration of the 5-mg/kg dose resulted in some disability of gait, lengthening of the absolute refractory period and, in half of the animals, in discrete morphological changes. By contrast, after the oral administration of clioquinol up to 200 mg-kg per day for a one-year period there were no signs of functional nor structural alterations of the nervous system. The beagle dog is considered to be a species well suited to reveal neurotoxicity.