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Schoenfeld, Thomas A.; Hamilton, Leonard W.; Gandelman, Ronald
doi: 10.1002/dev.420070303pmid: 4838168
Septal lesions were inflicted in young rats either during or after the maturation of inhibitory responding. When tested as juveniles (Day 25) or as adults, septal‐operates were significantly different from controls on 2‐way active avoidance and habituation responding, regardless of the age at which the lesion was produced. These data are in contrast with others showing that damage to subcortical structures can result in sparing of certain behavioral functions. The difference between functional sparing and functional disruption may be due to different patterns of brain projection pathways established after early lesions are produced. Neurochemical supersensitivity may also be a differentiating factor.
doi: 10.1002/dev.420070304pmid: 4838169
Although gross brain properties averaged over many individuals are highly unlikely to exhibit possible special growth periods, the hypothetical spurts in brain growth can be recovered to some extent from averaged data by computing multiyear weight increments. And, since brain weight correlates very well with skull circumference, similar spurts may be found in that parameter. A review of the literature shows that, indeed, characteristic spurts in brain and skull occur, roughly, at ages 6‐8, 10‐12, 14‐17, and possibly 2‐4 yr. The spurts are, as expected, especially clear in data from longitudinal studies, although spurts are detectable in the data from every study thus far found in the literature.
doi: 10.1002/dev.420070305pmid: 4599087
Spurts in the mental age of humans are shown to be recoverable from data giving the average mental age as a function of chronological age. Data from 13 independent studies are shown to give a highly consistent spectrum of ages at which spurts are found; these are 2‐4, 6‐8, 10‐12, and 14‐16, with an especially clear low rate of growth at 12‐14 yr. These ages correlate very well with those found for spurts in brain and skull sizes so that an obvious working hypothesis is that mutations for increased brain weight were selected for by virtue of the greater mental ability thus afforded to humans.
Hutchings, Donald E.; Gaston, John
doi: 10.1002/dev.420070306pmid: 4838170
Pregnant rats were administered a teratogenic dose of vitamin A excess on Days 17 and 18 of gestation. Intubation controls received the vehicle alone and nontreated mothers were left undisturbed. All groups were fostered to other nontreated mothers at birth. During adulthood, offspring were lever‐trained to obtain a water reward on an intermittent reinforcement schedule and on an S+, S− auditory discrimination. Unlike animals treated with vitamin A excess on Days 14 and 15 of gestation, these animals revealed no retardation in growth and development nor in brain size. Throughout the VI‐40 sessions and the S+ trials of discrimination training, the vitamin A animals had consistently slower rates of response compared to the controls. However, they did not evidence any impaired learning ability; like the nontreated, they extinguished S− responding, acquired long S− latencies, and maintained short S+ latencies. Possibly, the treatment may have produced a subtle motor deficit affecting fine motor coordination.
Bell, Robert W.; Nitschke, Werner; Bell, Nancy J.; Zachman, Thomas A.
doi: 10.1002/dev.420070307pmid: 4838171
Following a 2‐min exposure to 5–6°c, neonatal rats emit ultrasounds for about 5 min, resulting in effective maternal care. Five minutes of 5–6°C, causes prolonged ultrasonic vocalizations and correlated agitation in the mothers. The nonlinear effects of variable intensities of neonatal stimulation appear to related to these differences in maternal behavior.
Turkewitz, Gerald; Gilbert, Michel; Birch, Herbert G.
doi: 10.1002/dev.420070308pmid: 4838172
Twelve kittens with vibrissae clipped on the 1st day of life were compared to matched controls for the development of a preferential behavior in a visual cliff situation in an effort to examine the developmental relationship between sense systems. The kittens with reduced tactile input (vibrissae‐clipped) were found to discriminate between the “shallow” and “Sdeep” sides of the visual cliff at younger ages and with greater consistency than controls. The results for which there are alternative explanations available support the hypothesis that reduction of input in one modality reduces competition between sense systems, thereby resulting in the precocial use of another sense system.
doi: 10.1002/dev.420070309pmid: 4855512
Inbred (A/J and C57BL/6J) and hybrid mice were given access to low‐ or normal‐protein diets (4 or 26% casein) at 5 weeks of age and housed 1, 2, or 5 mice per cage. For all groups body weights of mice fed normal‐protein diets were greater for group‐caged than for isolated mice, and body weights of mice fed low‐protein diets were less for group‐caged than for isolated mice. At 15 and 16 weeks of age, mice fed low‐protein diets engaged in more exploratory behavior and were less emotional than mice fed normal‐protein diets. Mice that were group caged engaged in less exploration and were more motional than isolated mice. In addition to the major effects of caging and diet on behavior, mode of inheritance was significantly modified.
doi: 10.1002/dev.420070310pmid: 4857839
Young female laboratory mice reared in the presence of an adult male mouse or male bedding containing a pheromone reach sexual maturity earlier than control females. A pheromone produced by grouped female mice leads to long, irregular estrous cycles or anestrus. The present study demonstrated that a female‐produced pheromone delays sexual maturation when females are grouped and that free social interaction and tactile contact among the grouped females are necessary for the production of this inhibitory pheromone. Both young and adult females caged in groups produced the inhibitory pheromone. This study provided additional support for the hypothesis that in female mice morphological and sexual development are under separate control mechanisms. Two pheromones may be active in reproductive processes of female mice: one exhibiting inhibitory effects and the other acceleratory effects.
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