Acute interactive pharmacologic effects of inhaled toluene and dichloromethane on rat brain electrophysiology

Antisense imaging of gene expression in the brain in vivo

Antisense radiopharmaceuticals could be used to image gene expression in the brain in vivo, should these polar molecules be made transportable through the blood-brain barrier. The present studies describe an antisense imaging agent comprised of an iodinated peptide nucleic acid (PNA) conjugated to a monoclonal antibody to the rat transferrin receptor by using avidin-biotin technology. The PNA was a 16-mer antisense to the sequence around the methionine initiation codon of the luciferase mRNA. C6 rat glioma cells were permanently transfected with a luciferase expression plasmid, and C6 experimental brain tumors were developed in adult rats. The expression of the luciferase transgene in the tumors in vivo was confirmed by measurement of luciferase enzyme activity in the tumor extract. The [(125)I]PNA conjugate was injected intravenously in anesthetized animals with brain tumors and killed 2 h later for frozen sectioning of brain and film autoradiography. No image of the luciferase gene expression was obtained after the administration of either the unconjugated antiluciferase PNA or a PNA conjugate that was antisense to the mRNA of a viral transcript. In contrast, tumors were imaged in all rats administered the [(125)I]PNA that was antisense to the luciferase sequence and was conjugated to the targeting antibody. In conclusion, these studies demonstrate gene expression in the brain in vivo can be imaged with antisense radiopharmaceuticals that are conjugated to a brain drug-targeting system.

Effects of toluene inhalation on detection of auditory signals in rats

Inhalation of organic solvents can affect vigilance and reaction time in humans. An animal model of vigilance was designed to assess the effects of toluene on these processes. Adult male Long-Evans rats were trained to detect auditory signals (20-msec increases in the intensity of white noise). Two to 4 s after each signal (or blank period), two retractable levers were inserted into the test chamber. A press on one lever after a signal and on the other lever after a blank resulted in the delivery of food. Signal detection analysis showed that sensitivity (Sensitivity Index, SI) and response bias (Responsivity Index, RI) increased with signal intensity, indicating that loud signals were more detectable than soft signals and that the animals' criterion for responding "signal" increased with signal intensity. Response latency for correct choices was faster for signal trials than for blank trials. Toluene vapor was added to the airstream of these chambers at concentrations of 0, 1000, 1500, or 2000 ppm, either 10 or 30 min before testing and for the duration of each 1-h test. In air, SI increased across the duration of the test; this within-session improvement was reversed by toluene. RI did not change in air; it was decreased by toluene at the beginning of each exposure session, returned to the control level during exposure to 1000 and 1500 ppm toluene and exceeded air control after 40 min exposure to 2000 ppm toluene. Latency increased monotonically across toluene concentrations and time on test. Neither signal intensity nor the duration of toluene exposure before testing altered these effects of toluene. SI, RI, and latency baselines were recovered after toluene exposure indicating that no persistent effects of toluene were detectable. This conclusion was supported by data from other rats showing that toluene exposure (2000 ppm for 2 h/day for 4 consecutive days) did not affect auditory thresholds, as determined by reflex modification of an acoustic startle response using a 16 kHz tone as a prepulse stimulus, 7 or 17 days after exposure to toluene. Finally, rats tested immediately or 20 min after exposure to 0, 1000, 1500, or 2000 ppm toluene were not affected by the vapor, indicating that the impairment observed during toluene inhalation did not persist beyond the period of exposure.

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.

Effects of toluene, styrene, trichloroethylene, and trichloroethane on the vestibulo-and opto-oculo motor system in rats

The acute effects of inhalation of four solvents on the central vestibular system of rats were analyzed by recording eye movements upon different stimuli. The dose-response relationship was investigated. Optokinetic stimulation was obtained by placing the animals in front of a surrounding visual pattern, moving at different velocities. The slow-phase eye velocity (SPV) of nystagmus was calculated and divided by the stimulus velocity, giving the gain. All the solvents caused a decrease of the gain. Vestibular stimulation was performed on a turntable by an angular acceleration/deceleration in darkness. The SPV and the duration of the post-stimulatory nystagmus were calculated. The shape of the SPV dose-response curves differed among the four solvents. Toluene, styrene, and trichloroethylene prolonged the duration of nystagmus while trichloroethane did not. A conflicting vestibular and optokinetic stimulation was performed by an angular acceleration/deceleration with a surrounding visual pattern moving with the turntable. All solvents decreased the ability to cancel nystagmus, elicited by vestibular stimulation in conflict with a visual input. Quick movements of the eyes, saccades, were elicited by tactile stimulation. Toluene, styrene, and trichloroethylene changed the generation of the saccades while trichloroethane did not. Most of the findings indicate a common site of action in the central vestibular system, viz, the cerebellar-vestibular circuit. However, within this domain, there are evident differences in the effects among the solvents. This findings, together with previous results obtained in other experimental models of the central nervous system (CNS), suggest that different solvents should be considered as individual compounds.(ABSTRACT TRUNCATED AT 250 WORDS)

Combined effects of solvents on the rat's auditory system: styrene and trichloroethylene

Because exposures to toxic agents typically involve more than one substance, it is necessary to know if combined exposures pose different risks than those to single agents. Many solvents have been implicated in central nervous disorders and some of them are known to produce hearing loss, probably mediated by damage to cochlear hair cells. Hearing loss was studied by recording the brainstem auditory evoked response (BAER) in male Long Evans rats exposed 8 h/day for 5 days to mixtures of styrene (STY) and trichloroethylene (TCE). Dose groups included air or solvent pairs (STY/TCE) in the following concentrations (ppm): (0:3000), (250:2250), (500:1500), (750:750) and (1000:0). Decreased BAER amplitude, indicative of hearing loss, was correlated with blood levels of total solvent. The effects were as predicted by a linear dose-addition model, indicating neither synergistic nor antagonistic interactions at the concentrations studied.

Hearing: the effects of chemicals

Recent studies of human beings exposed to environmental chemicals, as well as experimental animal studies, have identified a number of chemical agents that are commercial products, chemical intermediaries, waste products, or contaminants that are potentially ototoxic. The classes of compounds discussed in this review include organic solvents, asphyxiant gases, and heavy metals that are present in the environment as industrial pollutants or byproducts. Both human and animal investigations are summarized in discussing the actions of these ototoxic compounds. The suggested gaps in our knowledge are highlighted to help direct future research.