The effects of N,N-diethyl-4-methyl-3-oxo-4-aza-5 alpha-androstane-17 beta-carboxamide, a 5 alpha-reductase inhibitor and antiandrogen, on the development of baldness in the stumptail macaque.

We used a primate model of male-pattern baldness to test the efficacy of a topically applied 5 alpha-reductase inhibitor and antiandrogen (4-MA) in the prevention of baldness. Six periadolescent stumptail macaques were given daily topical applications of either 4-MA in dimethylsulfoxide or dimethylsulfoxide alone for 27 months. The three control monkeys developed varying degrees of baldness, while the three 4-MA-treated monkeys retained their juvenile pattern of hair growth. The percentage of actively growing hair follicles in the frontal scalp did not change in the 4-MA-treated group [46 +/- 6 (+/- SE) vs. 48 +/- 4], while a significant decrease occurred in the control group (63 +/- 6 vs. 25 +/- 12; P less than 0.025). Skin 5 alpha-reductase activity was reduced in the scalp of the 4-MA-treated monkeys. We conclude that topical 4-MA can prevent the development of baldness in the stumptail macaque, a primate model of androgen-dependent baldness.

Enterotropic mouse hepatitis virus infection in nude mice.

The cause of emaciation and diarrhea in athymic nude mice was found to be hyperplastic typhlocolitis resulting from infection with enterotropic mouse hepatitis virus (MHV). The disease was reproduced in experimentally-inoculated nude mice using intestinal homogenates from affected mice and cell culture-derived virus. Material derived from an experimental mouse was passed into neonatal Swiss mice and caused acute typhlocolitis. Virus failed to grow in NCTC-1469 cells and 17Cl-1 cells, which are normally permissive for MHV, but grew to low titer in a mouse rectal carcinoma cell line, CMT 93. These results show that an enterotropic strain of MHV can cause chronic enteric disease in athymic nude mice. The pattern of infection differs markedly from the more common MHV wasting syndrome in nude mice caused by non-enteric strains of MHV.

Biological and behavioural assessments of young rhesus monkeys after intrauterine exposure to high phenylalanine concentrations.

Nineteen pregnant Macaca mulatta were fed a special diet throughout the gestational period in an attempt to render them hyperphenylalaninaemic. Group C (control group) received a regular diet, group Lo was given a 'low' phenylalanine diet, group Me a 'median' phenylalanine diet, and group Hi a 'high' phenylalanine diet. Nearly all monkeys had an uncomplicated pregnancy and an uneventful delivery. Biological measurements were obtained shortly after the birth of the infants and behavioural assessments were done when the offspring were between 6 and 18 months of age. The results of the biological and behavioural evaluations revealed that there was no statistically significant difference among the respective study groups. We concluded that a combination of factors inherent in an imperfect animal model may account for the negative results of this study.

Eye movements of monkeys during discrimination learning: role of visual scanning.

Four experiments were conducted on stumptailed monkeys (Macaca arctoides) to determine whether the high levels of visual scanning (shifts in fixation from one discriminative stimulus to the other) seen during discrimination learning play a necessary role in this learning. In Experiments 1 and 2, the monkeys were given a series of two-choice, dot-pattern discrimination reversal problems. Normal visual scanning before a choice response was allowed during all but the reversal trials of half of the problems. On these latter trials, the discriminative stimuli were replaced by an uninformative stimulus after the animals made more than one visual fixation on each discriminative stimulus. Thus, on these trials, the animals were limited, in terms of the information received, to the empirically determined minimum number of scans necessary to maintain high levels of performance on such problems. In both experiments, which differed primarily in the number and type of uninformative stimuli used, the rate of reversal learning was markedly retarded by the experimental condition, with the effect persisting over a long series of problems. The magnitude of the effect was unrelated to the similarity of the uninformative stimulus to the discriminative stimuli. In Experiment 3, the monkeys were given a series of discrimination problems without reversals, during half of which the experimental condition was in effect. The results were similar to those of the first two experiments. Experiment 4 was similar to the preceding experiment except that, under the experimental condition, each trial began with the uninformative stimuli, which were replaced by the discriminative stimuli when visual scanning occurred. The uninformative stimuli had no clear-cut effect on discrimination learning in this experiment. These experiments indicate that the information provided by above-minimum levels of scanning is not necessary for discrimination learning per se, but it dose appear necessary for efficient discrimination learning.

Eye movements of monkeys during learning-set formation.

Eye movements of stump-tailed monkeys were measured during learning of a long series of two-choice pattern discrimination problems. The amount of scanning per trial (shifts in visual fixation from one pattern to the other) and the duration of individual fixations on the patterns increased during the course of learning-set formation and (except for the amount of scanning by some animals) remained high during the prolonged training following learning-set formation. Some of the changes in eye movements were different from those seen during the learning of single discrimination problems, a difference that possibly reflects cognitive processes specific to the learning-set task.