Startle tests

Newborn children from mothers who ate oontaminated fish were more likely to exhibit hypoactive reflexes, more motor immaturity, poorer lability of states, and greater amount of startle. Testing at 4 years of age found that prenatal exposure was associated with poorer performance on the Verbal and the Memory scales of the McCarthy Scales of Children s Abilities, as well as less efficient visual discrimination processing and more errors in short-term memory scanning. Evaluation of the children at 11 years of age showed that prenatal exposure was significantly associated with lower full-scale and verbal IQ scores and poorer reading word comprehension. 

Neuromuscular and sensory effects were evaluated in Long Evans rats exposed to 500 ppm (6 hours a day for 5 or 12 weeks) using an acoustic startle test (Clerici and Fechter 1991). Neuromuscular integrity was shown to be compromised based on auditory startle reflex amplitude animals showed a 70% recovery 4 weeks postexposure. No clinical signs of neurotoxicity or changes in hearing function or acoustic tone thresholds were noted. Use of a single exposure concentration precluded assessment of dose response. 

The a-tocopherol, P-carotene (ATBC) Cancer Prevention study was a randomised-controlled trial that tested the effects of daily doses of either 50 mg (50 lU) vitamin E (all-racemic a-tocopherol acetate), or 20 mg of P-carotene, or both with that of a placebo, in a population of more than 29,000 male smokers for 5-8 years. No reduction in lung cancer or major coronary events was observed with any of the treatments. What was more startling was the unexpected increases in risk of death from lung cancer and ischemic heart disease with P-carotene supplementation (ATBC Cancer Prevention Study Group, 1994). Increases in the risk of both lung cancer and cardiovascular disease mortality were also observed in the P-carotene and Retinol Efficacy Trial (CARET), which tested the effects of combined treatment with 30 mg/d P-carotene and retinyl pahnitate (25,000 lU/d) in 18,000 men and women with a history of cigarette smoking or occupational exposure to asbestos (Hennekens et al, 1996). 

Rat, Rattus sp. 6.7 mg/kg body weight (BW) Single intraperitoneal (ip) injection caused deficits in auditory startle habituation tests 1... 

Using tactile startle, bufotenin, a hallucinogen that does not cross the blood-brain barrier readily, also produced biphasic dose-response effects when given intraventricularly (76). After systemic administration, however, low doses of indole hallucinogens have not been reported to increase tactile startle (73). Thus LSD (20-80 Mg/kg), DMT (0.25-1.0 mg/kg), and psilocin (2.5-5.0 mg/kg) did not increase tactile startle. A slightly higher dose of LSD (100 Mg/kg) did increase startle toward the end of the test session, perhaps because of blocking habituation (see below). 

In contrast to the rather weak effects produced by these indole hallucinogens, another indole hallucinogen, 5-MeODMT, produces a marked increase in acoustic startle (44). In this case, the excitatory effect is monotonically related to the dose over a range from 0.03 to 8 mg/kg. In fact, 5-MeODMT is one of the most efficacious drugs we have found in increasing acoustic startle. Thus far, the effects of 5-MeODMT on tactile startle have not been tested. 

Another test paradigm for detecting treatment effects on brain functioning in Fj offspring measures auditory startle habituation. In this test, the animal is placed in a chamber with a floor that detects movement. The animal is exposed to a sequence of 50 to 60 auditory stimuli, each at 110 to 120 decibels for 20 to50 sec and separated by 5 to 20 sec. The gradual diminution of the animal s movement response is indicative of normal habituation. 

In another study (Lock et al. 1984), peak response time, based on the startle reflex assay, was increased in rats after intermediate inhalation of diesel fuel aerosol, but at higher exposure levels than those used in the Kainz study. These studies conflict with the negative neurotoxicity findings of a second intermediate-duration study in which diesel fuel aerosol was tested in rats at even higher concentrations (Dalbey et al. 1987). Thus, MRLs cannot be derived from these data. 

Referred to as a conditioned fear paradigm, the fear potentiated startle response was first described by Brown et al. (1951). In the original test, an acoustic stimulus is presented in the presence of a conditioned stimulus that has previously been paired with an aversive, unconditioned stimulus. The amplitude of the acoustic startle response is thought to indicate the degree of conditioned anxiety, which can be reduced by anxiolytic drugs (Davis et al. 1993 Hijzen et al. 1995). 

Some media outlets trumpeted the 1996 book Our Stolen Future,5 a compilation of mostly unverified observations and speculations, and a paper published in Science that presented startling results purportedly showing that tiny concentrations of some chemicals behaved as endocrine disruptors. Congress rushed legislation that requires billions of dollars to be spent to test chemicals that were regarded as safe except for the alleged estrogenic effects.5... 

Limited data indicate that orally (gavage) administered PBBs can produce neurological effects in rats. FireMaster FF-1 at 10 mg/kg/day (3 days/week) for 8 weeks did not alter the performance of rats in tests of operant behavior, but decreased motor activity, grip strength, and startle responsiveness observed in rats following administration of 10 mg/kg/day for 6 months or 30 mg/kg/day for 4 weeks (Tilson and Cabe... 

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