The functional morphology of the intermandibulo-cervical envelope of the American alligator (Alligator mississippiensis)

Alligators appear to swallow prey items that are large relative to their head size. Therefore, the intermandibulo-cervical envelope (i.e., the skin, Fascia superficialis, and constrictor musculature) was expected to be expandable. The three main layers of the intermandibulo-cervical envelope expand and recoil in tandem, but through different mechanisms. In the skin, which consists of hard-cornified scales and soft-cornified interscale skin segments, only the latter are expandable. Therefore, the width and orientation of the interscale skin segments determine the extent and direction of expansion of the skin. Whereas the intermandibular skin region is very expandable and enables the manipulation and crushing of large prey items in the mouth cavity, the gular and cervical skin regions can expand longitudinally, but have very limited circumferential expansibility. Elastic fibers in the dermis and Fascia superficialis provide the resilience needed to return the skin to its resting condition. The trilaminate Fascia superficialis expands by changing the orientation of its helically arranged collagen fibers. The three main skin regions, which are also characterized by particular scale and interscale skin patterns, are in congruence with the three parts of the underlying constrictor musculature. The expansibility of the constrictor muscles is determined by their proportion of muscle length to tendon length, because muscle fibers can lengthen passively, whereas collagenous tendon fibers resist lengthening. The expansibility of the constrictor muscles diminishes from rostral to caudal. Whereas the longitudinal expansibility of the intermandibulo-cervical envelope allows lateral and dorso-ventral movements of the head and neck, the limited circumferential expansibility of the gular and cervical regions constrains the size of prey items that can pass through the throat and matches the narrow isthmus of the thoracic inlet. Hence, the functional-morphological data of the intermandibulo-cervical envelope require a reinterpretation of feeding mechanics and prey choice of alligators

Comparison of diabetic nephropathy between male and female eNOS\u3csup\u3e−/−\u3c/sup\u3e \u3ci\u3edb\u3c/i\u3e/\u3ci\u3edb\u3c/i\u3e mice

Sex is an important biological variable that impacts diverse physiological and pathological processes, including the progression of diabetic nephropathy. Diabetic nephropathy is one of the most common complications of diabetes mellitus and is the leading cause of end-stage renal disease. The endothelial nitric oxide synthase-deficient (eNOS−/−) db/ db mouse is an appropriate and valuable model to study mechanisms in the development of diabetic nephropathy because of the similarities of the features of diabetic kidney disease in this model to those in humans. The aim of the present study was to determine whether there was a sex difference in renal injury in eNOS−/− db/ db mice. Both male and female eNOS−/− db/ db mice showed hyperglycemia, obesity, and renal hypertrophy. However, there was no significant difference in those variables between male and female mice. Furthermore, both male and female diabetic mice showed progressive albuminuria and significantly greater levels of serum creatinine and blood urea nitrogen compared with the same sex of wild-type mice (nondiabetic controls). Although all three variables in female eNOS−/− db/ db mice had a tendency to be greater than those in male eNOS−/− db/ db mice, those sex differences were not statistically significant. Moreover, both male and female eNOS−/− db/ db mice showed significant mesangial expansion, higher glomerular injury scores, profound renal fibrosis, and substantial accumulation of fibronectin and collagen type IV proteins. However, sex differences in those structural changes were not observed. Similarly, survival rates of male and female eNOS−/− db/ db mice were comparable. Taken together, the results from the present study suggest no sex difference in renal structural and functional damage in eNOS−/− db/ db mice