Morphogenesis and cytodifferentiation are distinct processes in tooth development. Cell proliferation predominates in morphogenesis; differentiation involves changes in form and gene expression. The cytoskeleton is essential for both processes, being regulated by Rho GTPases. The aim of this study was to verify the expression, distribution, and role of Rho GTPases in ameloblasts and odontoblasts during tooth development in correlation with actin and tubulin arrangements and amelogenin and dentin sialophosphoprotein (DSPP) expression. RhoA, Rac1, and Cdc42 were strongly expressed during morphogenesis; during cytodifferentiation, RhoA was present in ameloblasts and odontoblasts, Rac1 and its effector Pak3 were observed in ameloblasts; and Cdc42 was present in all cells of the tooth germ and mesenchyme. The expression of RhoA mRNA and its effectors RockI and RockII, Rac1 and Pak3, as analyzed by real-time polymerase chain reaction, increased after ameloblast and odontoblast differentiation, according to the mRNA expression of amelogenin and DSPP. The inhibition of all Rho GTPases by Clostridium difficile toxin A completely abolished amelogenin and DSPP expression in tooth germs cultured in anterior eye chamber, whereas the specific inhibition of the Rocks showed only a partial effect. Thus, both GTPases are important during tooth morphogenesis. During cytodifferentiation, Rho proteins are essential for the complete differentiation of ameloblasts and odontoblasts by regulating the expression of amelogenin and DSPP. RhoA and its effector RockI contribute to this role. A specific function for Rac1 in ameloblasts remains to be elucidated; its punctate distribution indicates its possible role in exocytosis/endocytosis.

Several variables can be manipulated to compose high-intensity interval exercise (HIIE) protocols, and these different combinations may evoke different psychological responses (affect, enjoyment, mood, and perceived exertion). This study investigated psychological responses during four HIIE protocols. Following anthropometric measurements and two maximal exercise tests, 23 physically inactive adults (11 males [ Mage = 25.6, SD =  4.8 years; Mbody mass = 68.5, SD =  12.2 kg; Mheight = 1.72, SD =  0.08 m] and 12 females [ Mage = 25.0, SD = 3.5 years; Mbody mass = 57.2, SD =  8.7 kg; Mheight = 1.59, SD = 0.06 m]) performed four different types of HIIE on different days: (a) Long-interval HIIE (HIIEL—10 × 60 seconds:60 seconds), (b) Short-interval HIIE (HIIES—2 blocks of 10 × 30 seconds:30 seconds with 120 seconds between blocks), (c) Repeated Sprint Training (19 × 6 seconds all out:40 seconds), and (d) Sprint Interval Training (4 × 30 seconds all-out efforts: 240 seconds). We used a final session to assess participants’ HIIE preference. We recorded participant reports of affect, mood, and perceived exertion throughout protocols, and we recorded enjoyment after exercise session. Perceived exertion significantly increased across all HIIE protocols ( p <  .001), with higher values in the first quartile during Sprint Interval Training versus HIIEL ( p =  .033). Affective response presented higher values pre-exercise and at the first quartile compared with all other moments ( p <  .001). Tension ( p <  .001) and depression ( p =  .013) decreased from pre- to post-exercise in all experimental conditions. At pre-exercise, female participants were tenser than males ( p =  .018), though males presented higher pre-exercise vigor scores than females ( p =  .023). Vigor increased over time for females ( p =  .022). Enjoyment did not vary between sexes or protocols. Participants expressed a higher preference for Repeated Sprint Training. HIIE protocols promoted positive psychological responses for physically inactive young adults, and exercise designs may modulate psychological responses.

In spite of the clear-cut temporal features exhibited by most species, temporal characteristics have merited little attention from evolutionists. However, it is logical to assume that since the environment oscillates cyclically, organisms that adapt to it must also oscillate; that is, cyclic factors have a clear evolutionary role. This article discusses evidence that the timing system is genetically determined; the role of environmental cues such as zeitgebers and masking factors; the temporal basis of mating; and masking as a disorganizing factor.

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