Growth of the functional components of the rat skull and its alteration by nutritional effects. A multivariate analysis.

Weanling male Holtzman rats were subjected to each of the following nutritional treatments: malnutrition-recuperation; undernutrition; and undernutrition-recuperation. The rats were sacrificed when they were 49 days old, and dimensions of each one of the neurocranial, respiratory, and masticatory components were measured. Each component was compared with its counterpart in control rats (21, 28, 35, 42, and 49 day-old) by means of Mahalanobis D2 distances. The same functional components of 49 day-old control skulls were compared with their counterparts in younger control skulls. The means of the chosen cranial dimensions were compared by Tukey tests. Two periods of craniofacial development were identified. In the first, both facial components showed a similar growth that was greater than the neurocranial growth. In the second period, the growth of the masticatory component was greater than that of the respiratory component, which in turn, was greater than that of the neurocranial component. Nutritional deficiencies delayed the growth of the masticatory component more than that of the neurocranial component, which, in turn, was delayed more than that of the respiratory one. About 7% of the dimensions measured were insensitive to both growth and nutrition; 31% were insensitive to nutrition; and 62% were modified by nutrition. Craniofacial development in the rat seems to be a process more complex than what has been generally accepted. A nutritional stress may alter the relative growth between the facial functional components to a greater extent than that between the major functional components; viz. the neurocranium and the splanchnocranium. The cranial dimensions studied were classified according to their sensitivity to growth and/or nutrition into invariable, nutritionally stable, and nutritionally unstable traits.