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L W Means

Publications and source records attributed to L W Means.

At least 37 records · Page 2Linked to original sources
PubMed1991

Working memory and the aged rat: deficient two-choice win-stay water-escape acquisition and retention.

Twelve aged (22 months), 12 adult (12 months) and 12 young (3 months) male Fisher 344 rats were compared on acquisition of a two-choice win-stay (spatial delayed matching-to-sample) water-escape working memory task. The 7 aged, 10 adult and 10 young animals that attained criterion were then compared on performance of the task when the retention interval (RI) was 5, 15, 30, 60 and 120 min. They were also compared on retention after being forced to perform an unsolvable water-escape task in a second maze during the first 5 minutes of a 30-minute RI. The aged animals had longer escape latencies, and required more trials and made more errors in attaining a criterion of 9 correct choices over 10 test trials than did the adult and young animals, who did not differ from one another. Also, comparisons of the animals that attained the acquisition criterion revealed that the aged animals had longer escape latencies and made more errors across all RIs and during trials including an interpolated distraction task than did the adult and young animals. The aged animals failed to perform above chance level on tests at any of the RIs or following the distraction task, while the young animals performed above chance level on tests at all intervals and following distraction. The adult animals failed to perform above chance on tests with the 120-minute RI or following distraction. The aged rats were clearly deficient on acquisition and retention of a two-choice water-escape working memory task.

Aging↗
PubMed1991

The effects of number of trials per day, retention interval, gender and time of day on acquisition of a two-choice, win-stay water-escape working memory task in the rat.

A 2 x 2 x 2 factorial study was conducted to examine the effects of gender, trials/day (TPD), and retention interval (RI) on acquisition of a two-choice win-stay water-escape task in 4-month-old Sprague-Dawley rats. Variations of this task have previously been shown to be sensitive to changes in working memory that occur with age (Means and Kennard, 1991) or to follow treatment with an anxiolytic (Bass et al., 1989) or with cognitive enhancers (Comer and Moore, in press) in males or to estrogen in ovariectomized females (O'Neal et al., 1990). Both training with 1 TPD and with a 5-min RI, time between an information "run" and a test "run", reduced errors during acquisition as compared to giving 3 TPD and a 1-min RI (P less than 0.05 in all cases). Males made fewer errors than did females (P less than 0.05). The three effects were additive: males trained with 1 TPD and a 5-min RI performed best and females trained with 3 TPD and a 1-min RI performed worst. Also, rats given 1 TPD made fewer acquisition errors when trained 2 h before the lights were turned off than when trained during the middle of the light portion of the light/dark cycle (P less than 0.05). Finally, when given 3 TPD, the rats, especially the females, performed significantly worse on their third trial (P less than 0.05). It was concluded that two-choice win-stay water-escape is a very sensitive assay of working memory with much potential for neurobehavioral research.

Animals↗
PubMed1990

Four-choice win-stay water escape acquisition by rats.

Rats were capable of acquiring a four-choice win-stay water-escape task. While preventing access to the incorrect choice sections on information runs affected the first choices made on test runs, it did not affect rate of acquisition.

Animals↗
PubMed1989

Overcoming unlearned response biases: delayed escape following errors facilitates acquisition of win-stay and win-shift working memory water-escape tasks in rats.

Previous research has demonstrated that perseveration in escape situations is an unlearned response bias of rats and mice which is difficult to overcome. In Experiment I, Sprague-Dawley rats were trained to a criterion of nine correct choices in 10 consecutive trials in a win-stay working memory water-escape task wherein an escape platform was hidden in one of two compartments. Subjects were given a forced choice on an Information Trial followed by a free choice on a Test Trial 5 min later. Subjects who were given a 30-s forced swim in the incorrect section following errors on the Test Trial showed faster acquisition and less use of response perseveration than control subjects. In Experiment II, the delayed escape procedure was used to compare acquisition of win-stay and win-shift strategies. Contrary to previous research both groups learned the tasks, although the win-stay group showed better performance. It is concluded that unlearned response biases of perseverating and returning to previous escape sites can be overcome if experimental conditions are appropriately arranged.

Animals↗
PubMed1988

Rats that acquire a THC discrimination more rapidly are more sensitive to THC and faster in reaching operant criteria.

Male Sprague-Dawley rats were trained to discriminate delta-9-tetrahydrocannabinol (THC) from saline in a two-lever operant task using successive training criteria. Untreated animals were first shaped to barpress for a milk reward with one lever available. As each animal reached criterion the second lever was installed, the first lever was removed, and the animal was treated with 3.0 mg/kg THC 30 min prior to barpress training. When criterion on the second lever was reached the rats were trained to discriminate THC from vehicle injections with both levers available. Following acquisition of the discrimination, test doses of THC at 0.00, 0.375, 0.75, 1.5 and 3.0 mg/kg revealed that the half of the 24 rats who reached criterion (STC) more rapidly exhibited significantly greater sensitivity to THC at the 0.75 mg/kg test dose than did the 12 slow-learner rats; the former group generated an ED50 of 0.77 mg/kg, whereas the ED50 for the later group was 1.63 mg/kg. The fast learners acquired both the initial barpress response and the discrimination more rapidly than did slow-learners. Results suggest that some animals are inherently more sensitive to THC and faster in meeting learning criteria.

Animals↗
PubMed1984

The effect of olfactory bulb lesions on agonistic, locomotory and social behavior in mice housed in aggregate.

Eleven Dublin ICR mice sustaining nearly complete bilateral aspiration lesions of the olfactory bulbs were compared to 16 sham-operated mice on the frequency of agonistic, locomotory, social, and maintenance behaviors. The animals were housed in aggregate with two cages of bulbectomized mice and two cages of shams. A time sampling technique was used to quantify the frequency of the various behaviors three times per week during one preoperative and four postoperative weeks. During the first two postoperative weeks the bulbectomized mice were observed to make frequent single bites of the head incision and tail of mice passing directly in front of them, with the bites resulting in mild to severe lesions. Following surgery, the bulbectomized mice also showed a temporary increase in locomotory responses and permanent suppression of social responses.

Aggression↗
PubMed1982

Sex, handedness and asymmetry of hand and foot length.

Measurements of the length of the hands of 156 4-9 yr old children revealed a significant association among sex, handedness and direction of asymmetry of hand-length. Right-handed males have longer right than left hands while non-right-handed males have longer left than right hands (P less than 0.005). Females have a significant association also (P less than 0.005), with the direction of asymmetry the reverse of that found in males. No significant associations were found among the classification variables for foot-length measured at ages 4-9 or at birth.

Child↗
PubMed1982

Effects of alcohol consumption during pregnancy on subsequent maternal behaviour in rats.

Nine Holtzman rats were maintained from days 5-18 of pregnancy on a liquid diet of which ethanol constituted 35% of the calories while nine rats were pair-fed an isocaloric diet that had maltose-dextrin substituted for the ethanol. Beginning on day 19 of gestation and continuing for five days the dams in both groups were given a choice among lab chow, water, and their respective liquid diets. During the five days of choice, alcohol consumption dropped to approximately 20% of pre-choice levels. The dams and pups showed no behavioural withdrawal symptoms. While the alcohol-treated litters showed greater variability in litter size and more pup deaths during nursing, the maternal behaviour of the alcohol dams was essentially normal, with only their pup protectiveness being rated lower than that of the control dams.

Alcohol Drinking↗
PubMed1980

Failure of piracetam to facilitate acquisition or retention in younger or older rats.

The performance of Long-Evans hooded rats of two age groups (450 and 75 days) was observed in open field activity, one-way active avoidance, and passive avoidance conditioning. One-half of the subjects in each group were administered 100 mg/kg of piracetam two hours prior to all testing trials. Younger rats required fewer acquisition trials to reach active avoidance criterion and made more active avoidances on 7-day retention tests than did older rats. Thus, younger rats performed better on both acquisition and retention of active and passive avoidance conditioning. Piracetam did not produce significant behavioral changes in any of the groups on any of the tasks. Neither age nor piracetam was shown to affect activity.

Age Factors↗
PubMed1975

Effects of dorsomedial thalamic lesions on spatial discrimination reversal in the rat.

Eight rats with lesions of the dorsomedial thalamus and 10 rats with sham operations were compared on acquisition and subsequent reversals of a spatial discrimination. The rats with thalamic damage showed greater perseveration to the incorrect choices (p less than 0.002) and made fewer reversals (p less than 0.05) and more errors (p less than 0.02) during the 100 reversal trials following initial acquisition than did the sham-operated animals. The two groups did not differ on the original acquisition.

Animals↗