Early motor experiences have been shown to be important for the development of motor skills in humans and animals. However, little is known about the role of motor experience in motor system development. In this study, we address the question of whether early motor experience is important in shaping the development of the corticospinal (CS) tract. We prevented limb use by the intramuscular injection of botulinum toxin A into selected forelimb muscles to produce muscle paralysis during the period of development of CS connection specificity, which is between postnatal weeks 3 and 7. CS terminations were examined using an anterograde tracer. Preventing normal forelimb use during CS axon development produced defective development of CS terminations at week 8 and in maturity. There were reductions in the topographic distribution of axon terminals, in terminal and preterminal branching, and in varicosity density. This suggests that limb use is needed to refine CS terminals into topographically specific clusters of dense terminal branches and varicosities. To determine correlated effects on motor behavior, cats were tested in a prehension task, to reach and grasp a piece of food from a narrow food well, when the neuromuscular blockade dissipated (by week 10) and in maturity (week 16). Preventing normal limb use also produced a prehension deficit later in development and in maturity, in which there was a loss of the supination component of grasping. This component of prehension in the cat depends on CS projections from the paw representation of rostral motor cortex to the cervical enlargement. Our findings show that motor experiences are necessary for normal development of CS terminations and function.
Background Consumption of ultra-processed foods has been linked with higher energy intakes. Food texture is known to influence eating rate (ER) and energy intake to satiation, yet it remains unclear whether food texture influences energy intakes from minimally-processed and ultra-processed meals. Objectives We examined the independent and combined effects of food texture and degree of processing on ad-libitum food intake. We also investigated whether differences in energy intake during lunch influenced post-meal feelings of satiety and later food intake. Design In this crossover study, 50 healthy-weight participants (n = 50 (24 men); 24.4 ± 3.1y; BMI = 21.3 ± 1.9kgm−2) consumed four ad-libitum lunch-meals consisting of “soft- minimally-processed,” “hard-minimally-processed,” “soft-ultra-processed,” and “hard-ultra-processed” components. Meals were matched for total energy served, with some variation in meal energy density ( ±0.20 kcal/g). Ad-libitum food-intake (kcal and g) was measured and ER derived using behavioral coding of videos. Subsequent food intake was self-reported by food-diary. Results There was a main effect of food texture on intake, where “hard-minimally-processed” and “hard-ultra-processed” meals were consumed slower overall, and produced a 21% and 26% reduction in food weight (g) and energy (kcal) consumed respectively. Intakes were higher for “soft-ultra-processed” and “soft-minimally-processed” meals (P < 0.001), after correcting for meal pleasantness. The effect of texture on food weight consumed was not influenced by processing levels (weight-of-food: Texture*Processing-effect, P = 0.376), but the effect of food-texture on energy intake was (energy-consumed: Texture*Processing-effect, P = 0.015). The lowest energy was consumed from “hard-minimally-processed” meal (482.9 kcal; 95%CI: 431.9, 531.0), and the most from “soft-ultra-processed” meal (789.4 kcal; 95%CI: 725.9, 852.8; Δ=↓∼300 kcal). Energy intake was lowest when harder texture was combined with the “minimally-processed” meals. Total energy intake across the day varied directly with energy intakes of the test meals (Δ15%, P < 0.001). Conclusions Findings suggest that food texture-based differences in ER and meal energy density contribute to observed differences in energy intake between minimally-processed and ultra-processed meals.
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