Effects of trichloroethylene exposure on hearing. An investigation of cochlear microphonics and action potential of the guinea pig

Differential susceptibility of rats and guinea pigs to the ototoxic effects of ethyl benzene

The present study was designed to compare the ototoxic effects of volatile ethyl benzene in guinea pigs and rats. Rats showed deteriorated auditory thresholds in the mid-frequency range, based on electrocochleography, after 550-ppm ethyl benzene (8 h/day, 5 days). Outer hair cell (OHC) loss was found in the corresponding cochlear regions. In contrast, guinea pigs showed no threshold shifts and no OHC loss after exposure to much higher ethyl benzene levels (2500 ppm, 6 h/day, 5 days). Subsequently, a limited study (four rats and four guinea pigs) was performed in an attempt to understand these differences in susceptibility. Ethyl benzene concentration in blood was determined in both species after exposure to 500-ppm ethyl benzene (8 h/day, 3 days). At the end of the first day, blood of the rats contained 23.2+/-0.8-microg/ml ethyl benzene, whereas the concentration in guinea pig blood was 2.8+/-0.1 microg/ml. After 3 days, the concentration in both species decreased with respect to the first day, but the ethyl benzene concentration in rat blood was still 4.3 times higher than that in guinea pig blood. Thus, the difference in susceptibility between the species may be related to the ethyl benzene concentration in blood.

An epidemic in Cuba of optic neuropathy, sensorineural deafness, peripheral sensory neuropathy and dorsolateral myeloneuropathy

An epidemic outbreak of peripheral neuropathy affected Cuba in 1992-93 resulting in 50,862 cases (national cumulative incidence rate (CIR) 461.4 per 100,000). Clinical forms included retrobulbar optic neuropathy, sensory and dysautonomic peripheral neuropathy, dorsolateral myeloneuropathy, sensorineural deafness, dysphonia and dysphagia, spastic paraparesis, and mixed forms. For epidemiological purposes, cases were classified as optic forms (CIR 242.39) or peripheral forms (CIR 219.25). Increased risk was found among smokers (odds ratio (OR) 4.9), those with history of missing meals (OR 4.7) resulting in lower intake of animal protein, fat, and foods that contain B-vitamins, combined drinking and smoking (OR 3.5), weight loss (OR 2.8), excessive sugar consumption (OR 2.7) and heavy drinking (OR 2.3). Optic neuropathy was characterized by decreased vision, bilateral and symmetric central or cecocentral scotomata, and loss of color vision due to selective lesion of the maculopapillary bundles. Peripheral neuropathy was a distal axonopathy lesion affecting predominantly large myelinated axons. Deafness produced selective high frequency (4-8 kHz) hearing loss. Myelopathy lesions combined dorsal column deficits and pyramidal involvement of lower limbs with spastic bladder. Clinical features were those of Strachan syndrome and beriberi. Intensive search for neurotoxic agents, in particular organophosphorus esters, chronic cyanide, and trichloroethylene intoxication, yielded negative results. Treatment of patients with B-group vitamins and folate produced rewarding results. Most patients improved significantly and less than 0.1% of them remained with sequelae; there were no fatal cases. Supplementation of multivitamins to the entire Cuban population resulted in curbing of the epidemic. Overt malnutrition was not present, but a deficit of micronutrients, in particular thiamine, cobalamine, folate and sulfur amino acids appears to have been a primary determinant of this epidemic.

The neuroepidemiology of styrene: a critical review of representative literature

Because exposure to styrene occurs commonly in some industries and styrene is highly lipid soluble, it is reasonable to be concerned about the possibility that styrene is neurotoxic. Styrene, like many other solvents, volatile anesthetics, and drugs, does, at certain concentrations, produce acute changes in consciousness with consequent alterations of feelings, cognition, and psychomotor functioning. Such acute actions do not imply that styrene also would produce reversible or irreversible damage to the nervous system; the evaluation of long-term exposures to styrene also is necessary to draw conclusions about the full range of neural effects that styrene might produce. To that end, several studies of workers exposed to styrene for up to 30 years have been undertaken in factories in many parts of the world. Epidemiologists have suggested that neuropsychological deficits such as slowing of reaction time, loss of color vision, and vestibulooculomotor dysfunction are reliably induced by styrene at levels near or below current exposure standards, which range from 20 to 50 ppm in most of the world. However, the workers so studied always were described as healthy, and the effects noted were considered to be subclinical. A detailed evaluation of much of the neuroepidemiological literature on styrene (38 papers and related literature), however, indicated that the findings were, almost universally, false positive outcomes due to (1) type I statistical error, (2) the action of some factor other than styrene, and (3) misinterpretation of data. Despite the study of workers exposed for many years, no indications of persisting damage to the nervous system were evident from this review. The conclusions of this review of the neuroepidemiology of styrene are consistent with those based on critical reviews of the solvent literature in general, with specific reference to the probable absence of such an entity as the "painter's syndrome" or "chronic toxic encephalopathy". Because the results on styrene neurotoxicity that provide an inclination to lower the current threshold limit values (TLVs) are false positive findings, there is no scientific basis for a reduction in the current TLV.