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PubMed1989

Extension of displacement limits in multiple-exposure sequences of apparent motion.

In order to examine the processes by which motion signals are combined over time, we presented subjects with random dot kinematograms which could vary in terms of the number of frames in the sequence and the duration between the onset of each stationary frame. Performance (as measured by the greatest displacement at which subjects could discriminate opposite directions of movement) improved with increasing number of displacements up to around 5 displacements, whilst manipulations of the frame duration had no affect upon this figure. Thus the results cannot be described in terms of a limited integration time. By creating sequences in which no dots underwent more than a single displacement we show that the improvement is not specific to individual dot paths. We suggest that these results could be accounted for in terms of a co-operative network in which mutual facilitation can propagate between detectors tuned to a common direction of motion.

Humans↗
PubMed1981

Multiple exposures to ethanol facilitate intravenous self-administration of ethanol by rats.

In Experiment 1, male hooded rats (N=11) were implanted with jugular cannulas, and housed in sound attenuated operant chambers 24hr/day. The rats were exposed to periodic cycles of forced ethanol infusions (30% v/v, 9-16 g/kg/day over 4-6 days for each cycle). Following each cycle, forced infusions were discontinued, but the rats were allowed access to lever for self-administration of ethanol on a fixed ration 1 schedule (FR1). Each lever press infused 0.2 ml of ethanol (20% v/v). The rats were maintained on self-administration for at least 24 hr. If a rat did not develop self-administration behavior (SAB) within 24 hr, the next forced cycle fo ethanol exposure was initiated. Eight of the 11 rats developed SAB after a mean of 5.25 cycles of exposure to ethanol, and were then tested for a mean of 15 days on self-administration under FR1, FR2, and FR3 schedules of reinforcement. All rats were tested on FR1 and days of self-administered a mean of 10.43 g ethanol/kg/day over a mean of 10.75 days. Four rats were subsequently tested on FR2 and FR3 and increased lever presses in order to maintain daily ethanol intake comparable to FR1. Following self-administration testing, the rats were placed on withdrawal and exhibited mild to severe withdrawal symptoms, suggesting that SAB maintained physical dependence. In Experiment 2, rats (N=6/group) were allowed to self-infuse either saline or ethanol (20% v/v). These rats had no prior exposure to either saline or ethanol, and forced infusion were never administered. The rats remained in their operant chambers for 21 days under FR1 contingencies. Each lever press led to a 0.2 ml infusion. None of the rats developed SAB, but the saline controls made more lever presses than the ethanol rats (p less than 0.01). These results suggest that the ethanol parameters yielding SAB in Experiment 1 are aversive to ethanol naive rats.

Animals↗
PubMed1994

Cytocidal effect of high energy shock wave on tumour cells enhanced with larger dose and multiple exposures.

Cultured LLC-WRC256 (Walker rat carcinoma) cells were exposed to different doses of high energy shock waves (HESW). The immediate viabilities were 98% in the control cells, and 74%, 53% and 18% following 400, 800, and 1500 HESW treatment, respectively. Surviving cells in the 400 and 800-treated HESW demonstrated delayed upward growth rate curves, and the 1500 HESW-treated a downward curve. Agar clonogenic efficiencies for surviving cells were 36% (control), 20% (400 HESW), 15% (800 HESW) and 3% (1500 HESW). LLC-WRC256 tumours in Wistar rats were treated once every other day with 1500 HESW on a total of three occasions. Tumours treated with HESW grew more slowly (4.9 cm3) than those in the control (13.5 cm3). HESW fragmented cells and destroyed cell membranes and intracellular organelles. A histological examination of tumours treated with HESW demonstrated local haemorrhage with necrosis in the HESW focus area. Damage to the surrounding skin and soft tissue was slight and transient. These findings suggest that the growth of tumour cells can be suppressed in vitro and in vivo by treatment with HESW.

Animals↗
PubMed2004

Single and multiple exposure tolerance study of polystyrene sulfonate gel: a phase I safety and colposcopy study.

OBJECTIVES: To evaluate symptoms and signs of genital irritation, vaginal leakage and acceptability of polystyrene sulfonate (PSS), which is being studied as a vaginal contraceptive and microbicide. METHODS: Forty-nine women applied 2.5 mL of either 5% PSS, 10% PSS, PSS vehicle, or Conceptrol (a marketed spermicidal product containing 4% nonoxynol-9) for 6 consecutive days. RESULTS: All women completed the study except one in the Conceptrol group who experienced vaginal symptoms after her first use and was discontinued. After both the first use and after all uses, irritation was seen among more women in the Conceptrol group than in the PSS groups, reaching statistical significance with regard to any evidence of irritation, signs of irritation and product-related irritation. There were no adverse events that were serious, unexpected and related to product use in any group. The 5% concentration of PSS may be preferable in terms of leakage and acceptability. CONCLUSION: The results suggest that PSS has a safety profile comparable to that of the marketed nonoxynol-9 product, Conceptrol, and appears to be associated with less genital irritation.

Adolescent↗
PubMed1978

Activity of glutamate and malate dehydrogenases in liver and kidneys of rats subjected to multiple exposures of mercuric chloride and sodium selenite.

Rats were subjected for 2 weeks to separate and combined exposures to mercuric chloride and sodium selenite at doses of 0.5 mg Hg/kg and 0.5 mg Se/kg. The content of mercury, selenium and protein as well as the activities of glutamate dehydrogenase (GLDH) and malate dehydrogenase (MDH) were determined in homogenates, mitochondria and intramitochondrial structures of the exposed animals. It was found that both separate and combined exposures of rats to mercuric chloride and sodium selenite inhibited GLDH activity and did not affect MDH activity in the examined organs. Mercury-selenium interaction brought about a decrease in the content of mercury in the intramitochondrial structures of kidneys and an increased accumulation of both elements in the outer and inner membranes of liver mitochondria. The biochemical mechanism of mercury-selenium interaction is discussed.

Animals↗
PubMed2001

Single and multiple exposure tolerance study of cellulose sulfate gel: a Phase I safety and colposcopy study.

Vaginally applied gels offer a promising approach for preventing unwanted pregnancies and sexually transmitted infections. Cellulose sulfate (CS) is a non-cytotoxic antifertility agent that also exhibits in vitro antimicrobial activity against sexually transmitted pathogens, including HIV. This was a randomized, double-blinded, Phase I study of 2.5 mL and 5.0 mL doses of 6% CS gel. A single vaginal application of the gel followed by five consecutive daily doses was assessed for genital irritation, safety, vaginal leakage, and product acceptability compared to two controls, Conceptrol, which is a marketed contraceptive gel containing nonoxynol-9, and K-Y jelly. The results suggest that the safety of 6% CS was comparable to that of Conceptrol and K-Y jelly, and it may be associated with less genital irritation. The 2.5 mL dose of CS may be preferable according to the participants' reports of leakage. All the products had similar acceptability profiles.

Administration, Intravaginal↗
PubMed1984

Comparison of photographic (multiple-exposure photography) and conventional evaluation of ejaculates for fertility prognosis.

Semen obtained from 191 men visiting our infertility clinic was studied by MEP and conventional methods. With MEP, sperm count, percentage of motility, sperm velocity, straight line approach, and speed constancy were determined. Two years afterward 49 of the men appeared to have fertilized their partners. Between the fertile and infertile men, no differences in motility values determined by MEP could be detected. The only differences observed existed in sperm count and duration of infertility.

Humans↗
PubMed1975

Controlled prospective study of the effect on liver function of multiple exposures to halothane.

Patients who had received halothane within a periof of one year and who required another anaesthetic were allocated at random to be given halothane or a control anaesthetic, the control being fiben using halothane-free apparatus. There were 76 patients entries in each group. Serum-glutamic-oxaloacetic-transaminase (S.G.O.T.) levels were measured before the anaesthetics and serially postoperatively for two to three weeks. The S.G.O.T. levels in the halothane group were significantly higher than in the controls. High levels were confined to patients who had had less than four previous halothane anaesthetics, increases above normal in the remainder and in the controls being rate. 1 patient in the halothane group had an S.G.O.T. of 440 I.U. per litre and hepatocellular necrosis on liver biopsy. 2 patients in the halothane group whose S.G.O.T.s rose to more than twice normal showed a similar reaction to re-exposure to halothane, although they had not shown a reaction to an intervening control anaesthetic.

Aged↗
PubMed2003

Multiple exposure to activity anorexia in rats: effects on eating, weight loss, and wheel running.

Animals were given five cycles of an activity anorexia (AA) procedure in order to determine the effect of additional experience on eating, running, and weight loss. Female Sprague-Dawley rats were given a 1h meal and allowed access to a running wheel for the remainder of each day. Upon reaching 75% of free-feeding body weight, each animal was denied wheel access and given ad libitum food until it regained the lost weight. Then, food was again restricted and wheel access provided. Sedentary control animals were placed on the restricted feeding schedule for the median number of days experimental animals required to reach weight loss criterion. Experimental animals showed adaptation by increasing food consumption and decreasing the rate of weight loss despite an increase in running across cycles. Additionally, the distribution of running shifted gradually so that during the later cycles, much of the running occurred in the hours just before feeding. The results support the hypothesis that running interferes with adaptation to the restricted feeding schedule and also that the marked increase in anticipatory behavior during the later cycles is primarily responsible for the maintenance of AA.

Journal Article↗
PubMedDate not supplied

Changes in the hormonal concentrations of pregnant rats and their fetuses following multiple exposures to a stressor during the third trimester.

Human and animal studies indicate that stress during pregnancy can exert long-term effects on the development of the offspring, effects that appear to be mediated in part by the hypothalamic-pituitary-adrenal (HPA) axis. In this experiment changes in levels of a variety of HPA and other hormones in both pregnant rats and their fetuses were investigated. Trunk blood was collected from pregnant females and fetuses following repeated 45-min presentations of restraint, bright lights, and heat during the third trimester. In addition, testes were harvested from the male fetuses. Hormone concentrations were determined by radioimmunoassay. Pregnant females had elevated titers of plasma corticosterone, aldosterone, and ACTH for approximately 15 min following termination of the stressor. No differences were found for beta-endorphin or prolactin. Fetuses showed a pattern of changes in plasma corticosterone and aldosterone that was similar to that of pregnant females, but no effect was observed for fetal ACTH titers. These results are consistent with a role of the HPA axis in the effects of gestational stress. Testicular levels of CRF on gestational day 21 were lower in fetuses of stressed females than in those of nonstressed females. The reduced levels of testicular CRF suggest that CRF may be involved in the altered pattern of sexual differentiation of males stressed during gestation.

Adrenal Glands↗
PubMed2005

Neuropathological studies of rats following multiple exposure to tri-ortho-tolyl phosphate, chlorpyrifos and stress.

Adult male Long-Evans rats were exposed to 2 neurotoxic organophosphates in a setting of chronic stress, over a 63-day period. The organophosphates were tri-ortho-tolyl phosphate (TOTP) administered in 14 gavage doses of 75, 150 or 300 mg/kg, and chlorpyrifos, given in two 60 mg/kg subcutaneous exposures. Corticosterone was added to the drinking water at 400 microg/ml, to model aspects of chronic stress. These compounds/dosages were administered individually and in combination, with appropriate controls, giving rise to 16 experimental groups. The major neuropathologic change was the presence of axonal degeneration progressing to myelinated fiber degeneration, mainly in distal regions of selected fiber tracts and peripheral nerve, seen in animals sacrificed on experimental day 63. The cervical spinal cord and medullary levels of the sensory gracile fasciculus were most prominently affected. This axonopathy/fiber degeneration was TOTP dose-related at the 300 and 150 mg/kg levels. There was association of this lesion with inhibition of the enzyme neurotoxic esterase in hippocampal tissue from TOTP-treated rats. Such an association categorizes this disease process as organophosphate ester-induced delayed neuropathy. Neither chlorpyrifos nor corticosterone appeared to contribute to the neuropathic events or the enzyme inhibition. A cohort of rats was maintained on the corticosterone dosing, but without additional exposure to TOTP or chlorpyrifos, for an additional 27 days. When these rats were examined on day 90, the nerve fiber degeneration had progressed in all experimental groups administered the 300 mg/kg dose of TOTP (lower doses were not studied at the 90-day interval), although hippocampal neurotoxic esterase had returned to control values.

Animals↗
PubMed1985

Lung injury in guinea pigs caused by multiple exposures to submicron zinc oxide mixed with sulfur dioxide in a humidified furnace.

Sulfur dioxide, water vapor, and ultrafine particles rich in oxides of zinc and other surface-deposited trace elements are important products of coal combustion. In order to study the toxicity of zinc oxide generated under conditions simulating combustion, guinea pigs were exposed in a nose-only apparatus for 3 h on 6 consecutive days to 6 mg/m3 of submicron zinc oxide particles (count median diameter of 0.05 micron, sigma g 2.0), which were generated in a humid furnace and mixed with 1 ppm sulfur dioxide. The exposures caused increases in lung weight and [3H] thymidine labeling index of terminal bronchiolar cell nuclei and inflammation of the proximal portion of the alveolar duct. The lung weights and labeling index had returned to normal and inflammatory changes had nearly resolved by 72 h after the last exposure. Total lung capacity, vital capacity, functional residual volume, alveolar volume, and diffusing capacity for carbon monoxide were decreased following exposure and had not returned to normal by 72 h after the last exposure. Large airways were not affected by the repeated exposures, as indicated by normal morphology of trachea and bronchi, unchanged secretory cell concentration, and unaltered epithelial permeability to horseradish peroxidase. These results are essentially identical to changes we reported in guinea pigs exposed to zinc oxide alone, suggesting that surface-deposited sulfur compounds, which are important determinants of the response to a single exposure to these ultrafine particles, become less important as exposure progresses.

Animals↗