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Biomedical subjects

A C Johnson

Publications and source records attributed to A C Johnson.

124 records · Page 7Linked to original sources
PubMedDate not supplied

Long-term effects of toluene inhalation on rat behavior.

The effect of inhalation exposure to toluene (3700 mg/m3, 1000 ppm, 21 h/day, 5 days/week, during 4 weeks) on male Sprague-Dawley rats was tested. A wide range of test situations was used, including an operant test with baseline performance and extinction, motor coordination, and exploratory activity. All tests were made 11 to 35 days after the end of the exposure. The results indicate that toluene exposure causes a long-lasting impairment on the extinction process and reduction in the variability of the baseline response in the operant behavior situation. Toluene also had an effect on the water regulation.

Administration, Inhalation↗
PubMedDate not supplied

Assessing herbicide concentrations in the saturated and unsaturated zone of a Chalk aquifer in southern England.

The behavior of the herbicides isoproturon (IPU) and chlortoluron (CTU) in ground water and shallow unsaturated zone sediments were evaluated at a site situated on the Chalk in southern England. Concentrations of IPU in ground water samples varied from < 0.05 to 0.23 microgram/L over a five-year period of monitoring, and were found to correlate with application of the pesticide. Concentrations of pesticides in ground water samples collected during periods of rising water table were significantly higher than pumped samples and suggest that rapidly infiltrating recharge water contains higher herbicide concentrations than the native ground water. Significant variations in herbicide concentrations were observed over a three-month period in ground water samples collected by an automated system, with concentrations of IPU ranging from 0.1 to 0.5 microgram/L, and concentrations of a recent application of CTU ranging from 0.2 to 0.8 microgram/L. Different extraction methods were used to assess pore water concentrations of herbicides in the unsaturated zone, and samples were analyzed by standard HPLC analysis and immunoassay (ELISA) methods. These data indicated highly variable concentrations of herbicide ranging from 4 to 200 g/ha for HPLC and 0.01 to 0.04 g/ha for ELISA, but indicate a general pattern of decreasing concentrations with depth. The results of this study indicate that transport of IPU and CTU through the unsaturated zone to shallow ground water occurs and that this transport increases immediately following herbicide application. Measured concentrations of herbicides are generally lower than specified by the European Union Drinking Water Directive, but are observed to spike above this limit. These results imply that, while delivery of pesticides to ground water can occur as a result of normal agricultural practices, the impact on potable supplies is likely to be negligible due to the potential for degradation during the relatively long travel time through the unsaturated zone and high degree of dilution that occurs within the aquifer. As a result of the wide variation in concentrations detected by different techniques, it is suggested that for future site investigations more than one sampling strategy be employed to characterize the occurrence of pesticide residues and elucidate the transport mechanisms.

Calcium Carbonate↗
PubMedDate not supplied

Effect of interaction between noise and toluene on auditory function in the rat.

Rats were exposed to toluene (1000 ppm, 16 h/d, 5 d/w, 2 w), or noise (100 dB Leq, 10 h/d, 7 d/w, 4 w) or toluene followed by noise. Auditory function was tested by brainstem audiometry using a 1/3 octave filtered sine wave stimulus at the frequencies 1.6, 3.15, 6.3, 12.5 and 20.0 kHz. A high-frequency auditory impairment was observed after exposure to toluene alone and noise alone. A slight recovery was recorded 1 and 6 months after the toluene exposure. Toluene followed by noise resulted in a higher threshold at all frequencies. A slight recovery was recorded 6 months post-exposure. The threshold shift exceeded the summated loss caused by toluene alone and by noise alone, particularly at 3.15 and 6.3 kHz. The latencies varied only slightly. The results indicate that the major cause of the auditory impairment was cochlear damage and that only minor injury was caused to the auditory pathways.

Animals↗
PubMedDate not supplied

Sequence of exposure to noise and toluene can determine loss of auditory sensitivity in the rat.

Rats were exposed to noise (100 dB Leq, 10 h/d, 7 d/w, 4 w), or to toluene (1,000 ppm, 16 h/d, 7 d/w, 2 w), or to noise followed by toluene. Auditory sensitivity was tested before exposure, and 1 to 4 weeks after exposure, by brainstem audiometry using a 1/3-octave filtered sine wave stimulus at the frequencies 1.6, 3.15, 6.3, 12.5 and 20.0 kHz. Some auditory impairment was observed after all exposures. The sensitivity loss after exposure to noise followed by toluene was greater than that recorded after exposure to noise alone or toluene alone, but did not exceed the summated loss caused by noise alone and toluene alone at any frequency. This result contrasts with the earlier reported effect of the same exposures in the reversed order. It is concluded that the exposure sequence can determine the extent of auditory impairment.

Animals↗
PubMedDate not supplied

Combined fat- and water-suppressed MR imaging of orbital tumors.

BACKGROUND AND PURPOSE: The use of a high-resolution T2-weighted MR sequence, which suppresses signal from both fat and water, has been shown to be highly effective for depicting areas of inflammatory damage within the optic nerve. The ability of this sequence to show neoplastic and inflammatory orbital lesions, which may mimic neuritis, is unknown. This study was designed to examine the characteristics of such a sequence for the investigation of orbital mass lesions. METHODS: Twenty-eight patients with known or suspected mass lesions of the orbit and six healthy volunteers were recruited for study. Imaging was performed with a 1.5-T MR unit. Participants were examined by selective partial inversion recovery (SPIR) sequences with T2-weighted fast spin-echo acquisition, selective partial inversion recovery/fluid attenuated inversion recovery (SPIR/FLAIR) sequences with fast spin-echo acquisition, short tau inversion recovery (STIR) sequences with fast spin-echo acquisition, and SPIR sequences with contrast-enhanced T1-weighted fast spin-echo acquisition. Two neuroradiologists, using a randomised, blinded method, scored images for lesion presence and extent. Lesion extent was defined as the number of images with visible abnormality, and was compared with the standard of reference established at a later date by consensus review of all imaging sequences. The ability of the sequences to show the presence and extent of pathologic lesions was compared. RESULTS: The SPIR/FLAIR sequence showed both the presence and extent of orbital masses significantly better than did either STIR or T2-weighted SPIR sequences (P<.01 and P<.001, respectively). Contrast-enhanced T1-weighted SPIR images ranked better than SPIR/FLAIR images, although the difference failed to reach statistical significance. In the orbital apex, the SPIR/FLAIR technique was superior to all other techniques used. This reflected its ability to distinguish enhancing, pathologic lesions from enhancing, normal anatomy. CONCLUSION: SPIR/FLAIR is an appropriate screening technique for orbital masses and offers significant advantages over currently used fat-suppressed sequences for the investigation of orbital disease.

Adolescent↗
PubMedDate not supplied

Combined neurosurgical-orthopedic approach to the correction of radiculopathy and instability in spondylolysis and spondylolisthesis.

The authors give a brief review of the pathologic anatomy, the incidence and distribution, the probable etiologic factors in the development of spondylolysis and spondylisthesis, and a description of the clinical syndrome of this abnormality. It is pointed out that there are two distinct parts to the clinical syndrome: back pain due to instability of the isthmic defect and/or radiculopathy due to direct compression of the lumbar nerve root in its course immediately beneath the osteocartilaginous deformity which is the primary pathologic feature of this disorder. It is suggested that the variable benefits of the several operative procedures advocated for this disorder are largely related to fortuitous removal of some of the osteocartilaginous deformity and/or stabilization of the isthmic defects. Other writers have advocated fusion as a necessary part of any operative intervention for the treatment of spondylolysis. The authors here agree with this viewpoint and in addition, feel that complete and precise removal of the isthmic deformity is an equally imperative part of such surgery. While the principles of isthmic decompression combined with fusion are not innovative, the operative technique described here is innovative, simple, and precise, and has been followed by a high rate of excellent results.

Humans↗