The aim of the present study was to discover how intergenerational undernutrition affects the growth of major and minor functional cranial components in two generations of rats. Control animals constituted the parental generation (P). The undernourished generations (F1 and F2) were fed 75% of the control diet. Animals were X-rayed every 10 days from 20 to 100 days of age. The length, width and height of the major (neurocranium and splanchnocranium) and minor (anterior-neural, middle-neural, posterior-neural, otic, respiratory, masticatory and alveolar) cranial components were measured on each radiograph. Volumetric indices were calculated to estimate size variations of these components. Data were processed using the Kruskal-Wallis and Kolmogorov-Smirnov tests for two samples. Impairment in splanchnocranial and neurocranial growth was found, the latter being more affected than the former in F1. Comparison between F2 and F1 animals showed cumulative effects of undernutrition in both major and minor components (anterior-neural, respiratory, masticatory and alveolar in males, and middle-neural and respiratory in females). Such differential effects on minor components may reflect a residual mechanical strain resulting from the linkage between components. This phenomenon was clearly observed in the neurocranium and could be understood as an adaptive response to the demands of the associated functional matrices.
The cumulative effect of undernutrition on successive generations was tested. The cranial growth of three generations of undernourished rats (F1, F2, F3) was compared to that of the parental generation (P), in order to (1) measure the extent to which the growth of each facial and neurocranial functional component was retarded when animals were undernourished and (2) determine whether any cumulative effect between generations can be found. The P generation was fed ad libitum, and the undernourished generations were fed 50% (F1) and 75% (F2 and F3) of the parental diet. Nine radiographs were taken from the age of 20–100 days. The length, width and height of the neurocranial and facial components were measured on each radiograph. Neurocranial (VNI), facial (VFI), and neurofacial (NFI) indices were calculated. Data were processed by the Kruskal-Wallis and Kolmogorov-Smirnov tests. An impairment in neurocranial and facial growth was found, the latter being more affected than the former in F1. At variance, the neurocranium was more affected than the face in F2 and F3, resulting in variations of the shape of the skull. A cumulative effect of moderate transgenerational undernutrition was evident and points to the need for further analysis on this topic.
A functional skeletal criterion, as an extension of the van der Klaauw's cranial theory, was adopted in the present study. The null hypothesis tested was: "The major skeletal components of the platyrrhine body grow linearly, regardless of their functional dependence to different demands." The acceptance of the hypothesis will imply that all Saimiri skeletal growth may be satisfactorily explained by independent variables in a single equation. The rejection will suggest that such skeletal growth patterns have to be explained by variables in several different equations, and perhaps these equations may vary with the effect of sex and undernutrition. Control and undernourished squirrel monkeys were radiographed monthly for 2 years; they were also measured; and their volumetric and morphometric neurocranial, facial, and pelvic indices were calculated. The curves that best described each of the 24-point sequences were obtained. Three main growth patterns were observed: 1) Simple linear (femur length for all groups, and pelvic index for control and undernourished females), for which the simple regression equation explained more than 95% of the variation; 2) Complex linear (pelvic index for control and undernourished males, and neurocranial and facial indices for all of the groups), for which more than 95% of the variation was explained by one of the four four-function type equations; and 3) Noncorrelated with age (neurofacial index for undernourished males, and pelviofemoral index for control females and undernourished males and females), which showed nonsignificant correlations with respect to age. The food intake and the oscillations of the environmental temperature might help to explain the undulating growth trajectory observed in the complex linear components.
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