Trophic ecomorphology of Siluriformes (Pisces, Osteichthyes) from a tropical stream.

The present study analysed the relationship between morphology and trophic structure of Siluriformes (Pisces, Osteichthyes) from the Caracu Stream (22º 45' S and 53º 15' W), a tributary of the Paraná River (Brazil). Sampling was carried out at three sites using electrofishing, and two species of Loricariidae and four of Heptapteridae were obtained. A cluster analysis revealed the presence of three trophic guilds (detritivores, insectivores and omnivores). Principal components analysis demonstrated the segregation of two ecomorphotypes: at one extreme there were the detritivores (Loricariidae) with morphological structures that are fundamental in allowing them to fix themselves to substrates characterised by rushing torrents, thus permitting them to graze on the detritus and organic materials encrusted on the substrate; at the other extreme of the gradient there were the insectivores and omnivores (Heptapteridae), with morphological characteristics that promote superior performance in the exploitation of structurally complex habitats with low current velocity, colonised by insects and plants. Canonical discriminant analysis revealed an ecomorphological divergence between insectivores, which have morphological structures that permit them to capture prey in small spaces among rocks, and omnivores, which have a more compressed body and tend to explore food items deposited in marginal backwater zones. Mantel tests showed that trophic structure was significantly related to the body shape of a species, independently of the phylogenetic history, indicating that, in this case, there was an ecomorphotype for each trophic guild. Therefore, the present study demonstrated that the Siluriformes of the Caracu Stream were ecomorphologically structured and that morphology can be applied as an additional tool in predicting the trophic structure of this group.

Physiological loads in the team technical and free routines of synchronized swimmers.

PURPOSE: The purpose of the present study was to examine the physiological loads on synchronized swimmers during team technical and free routines by measuring their blood lactate concentrations and percentage of peak blood lactate concentration. METHODS: Four trained college female synchronized swimmers participated as the subjects. The blood lactate concentration was measured in the first and middle periods and after the team technical and free routines. Peak blood lactate concentration was measured after maximum exertion in 100-m freestyle swimming. RESULTS: Average values and SD of blood lactate concentration and the percentage of peak blood lactate concentration after the team technical and free routines were 4.7 +/- 1.1 mmol x L(-1), 46.2 +/- 11.0% and 4.3 +/- 1.1 mmol x L(-1), 42.8 +/- 11.5%, respectively. The blood lactate concentration and percentage of peak blood lactate concentration after the team technical routine were significantly higher than those in the first period, and the blood lactate concentration after the team free routine was significantly higher than in the middle period. CONCLUSIONS: The blood lactate concentration of synchronized swimmers during the team technical and free routines in the present study tended to increase with the performance time. Thus, the predominant sources of energy may be phosphocreatine stores and aerobic metabolism during these routines, although glycolysis may also play an important role in relation to the energy requirements in the final period.

Decreased expression of t-SNARE, syntaxin 1, and SNAP-25 in pancreatic beta-cells is involved in impaired insulin secretion from diabetic GK rat islets: restoration of decreased t-SNARE proteins improves impaired insulin secretion.

The physiological role of soluble N-ethylmaleimide-sensitive factor attachment protein (SNAP) receptor (SNARE) proteins in insulin exocytosis has been reported in pancreatic beta-cells. To determine whether the beta-cells of GK rats, a nonobese rodent model of type 2 diabetes, exhibit abnormalities in their SNARE proteins, we studied the expression and function of target (t)-SNAREs, syntaxin 1A, and synaptosomal-associated protein of 25 kDa (SNAP-25) in GK rat islets. Although insulin release and insulin content of islets isolated from 12-week-old GK rats were reduced, the proinsulin biosynthetic rate was about twofold higher than that in control rat islets, and no change in the preproinsulin mRNA level was observed. Pulse-chase experiments suggested the increased degradation of insulin in GK rat islets. Immunoblot analysis revealed that protein levels of syntaxin 1A and SNAP-25 in GK rat islets decreased to approximately 60% of the levels in control rat islets. We then examined whether the restoration of the decreased expression of t-SNAREs to the normal level in GK rat islets affected insulin secretion. Restoration was achieved by the overexpression of syntaxin 1A and SNAP-25 via the recombinant adenovirus-mediated gene transduction system, which recovered levels of these proteins to almost control levels. Glucose-stimulated insulin release from AdexlCA syntaxin 1A and Adex1CA SNAP-25-infected GK rat islets increased up to approximately 135 and 200%, respectively, of those from uninfected GK rat islets, although no difference in basal (2.2 mmol/l glucose) insulin release was evident between them. We conclude that decreased expression of t-SNAREs in GK rat islets is in part the defect responsible for impaired insulin secretion.

Physiological characteristics of well-trained synchronized swimmers in relation to performance scores.

The purpose of this study was to examine the relationships between the physiological characteristics of synchronized swimmers and their performance scores. The subjects were 16 trained female synchronized swimmers with a mean age of 17.2 +/- 1.7 years (mean +/- SD). The examined variables were body dimensions (height, width, body mass, circumference of the body and segment length), body composition, isokinetic muscle strength of the elbow and knee during extension and flexion, abdominal muscle endurance, anaerobic power (leg extension power and peak blood lactate concentration), aerobic power (maximum oxygen uptake [VO2max], swimming velocity at the onset of blood lactate accumulation [OBLA-V]), and flexibility (standing trunk flexion, prone trunk extension and distance between the open legs). The performance scores had significant correlations (p < 0.05) with isokinetic muscle strength of the elbow extension and flexion, and the knee extension, abdominal muscle endurance, leg extension power, VO2max x wt(-1), OBLA-V and distance between the open legs. However, no significant correlations were found between the performance scores and anthropometric variables. This study showed that the performance scores of synchronized swimmers correlated significantly with the functional aspects, and that muscle strength, muscle endurance and aerobic capacity seem to be particularly important determinants.

alpha-soluble N-ethylmaleimide-sensitive factor attachment protein is expressed in pancreatic beta cells and functions in insulin but not gamma-aminobutyric acid secretion.

The function of soluble N-ethylmaleimide-sensitive attachment protein-alpha (alpha-SNAP) in exocytosis still remains obscure. This study was conducted to determine the physiological role of alpha-SNAP in the secretion of insulin and gamma-aminobutryric acid (GABA) from pancreatic beta cells. Reverse transcriptase-polymerase chain reaction analysis of total RNA isolated from rat islets disclosed alpha-SNAP, but not beta-SNAP, mRNA expression, and an immunofluorescence study of rat pancreas showed that alpha-SNAP was present predominantly in the cytoplasm of the islets of Langerhans. alpha-SNAP overexpression in rat islets enhanced insulin release relative to the control levels. An in vitro binding study showed that both wild-type alpha-SNAP and C-terminal-deleted alpha-SNAP mutant (1-285) can bind to syntaxin 1A. alpha-SNAP mutant (1-285) was overexpressed to evaluate its activity as dominant-negative effector on insulin release. Overexpression of alpha-SNAP mutant (1-285) in rat islets and MIN6 cells decreased glucose-stimulated insulin release to about 50% of the control levels. Suppression of endogeneous alpha-SNAP in MIN6 cells by treatment with an antisense phosphorothioate oligonucleotide resulted in inhibition of insulin release. In order to examine if alpha-SNAP functions in exocytosis from synaptic-like microvesicles in pancreatic beta cells, the functional role of alpha-SNAP in GABA release from MIN6 cells was studied. The data showed no effect of alpha-SNAP mutant (1-285) overexpression on GABA release. We conclude that 1) alpha-SNAP plays a crucial role in insulin exocytosis via large dense core vesicles, but not GABA released via synaptic-like microvesicles, in pancreatic beta cells; and 2) the interaction of alpha-SNAP and syntaxin 1A may play an important role in the insulin exocytotic process.

Differential controls of small and large motor unit activity in the masseter muscle with incisal stimulation in humans.

The activity of masseter motor units with different spike amplitudes was recorded and reflex responses by force stimulation of an incisor were analyzed in humans. The effects of reflex responses varied depending on the level of prestimulus firing frequency (background activity, BGA). When small amplitude motor units and large amplitude motor units were tested at the same level of BGA, the former tended to exhibit excitatory reflexes and the latter inhibitory ones.

Patterns of jaw reflexes induced by incisal and molar pressure stimulation in relation to background levels of jaw-clenching force in humans.

Patterns of jaw reflexes induced by periodontal stimulation were examined in ten adults. Surface electromyograms (EMGs) from the masseter and anterior temporal muscles were recorded when pressure stimulation was applied to either an incisor or a molar. Reflex responses to periodontal pressure stimulation varied, depending on the background levels of jaw-clenching force that preceded stimulation (background clenching force, BCF). At low BCF, excitatory reflexes were elicited from the jaw-closing muscles and jaw-clenching force. However, the magnitude of excitatory reflexes varied with the location of the stimulated tooth along the dentition. While excitatory reflexes were induced equally in the masseter and temporal muscles during incisal stimulation, stronger excitatory reflexes were induced in the temporal muscle than in the masseter muscle during molar stimulation. At high BCF, inhibitory reflexes in the jaw-closing muscles and jaw-clenching force were elicited in eight subjects (group A) during periodontal stimulation. However, excitatory reflexes in the muscles and force were elicited in the remaining two subjects (group B). In the subjects of group A, stronger inhibitory reflexes were elicited in the temporal muscle than in the masseter muscle, and jaw-clenching force also decreased during both incisal and molar stimulation. In the subjects of group B, the magnitude of excitatory reflexes decreased with increases in BCF.

Excitatory and inhibitory controls of the masseter and temporal muscles elicited from teeth in the rat.

The periodontal mechanism that controls the jaw reflexes was examined in lightly anesthetized rats. Motor-unit activity in the masseter and temporal muscles was recorded electromyographically and pressure stimulation was applied to either an upper incisor or an upper molar. Reflex effects of dental stimulation varied depending on the level of ongoing activity (background activity, BGA) in each motor unit. Incisal or molar stimulation elicited excitatory reflexes in both the masseter and temporal motor units at a low BGA, but inhibitory reflexes in both types of motor unit at a higher BGA. In contrast to these synergistic reflex actions, the reciprocal reflex actions of the two motor units that belonged to the respective muscles occurred when the BGA was intermediate. The results suggest that different patterns of periodontal jaw reflexes may be elicited, depending on the different levels of BGAs. Furthermore, the present reflexes were modified with the site of a stimulated tooth within the dentition. Incisal stimulation produced greater excitation in the masseter motor unit than in the temporal one, and the opposite type of response occurred during molar stimulation. Moreover, smaller-amplitude motor units with a low reflex threshold and larger-amplitude motor units with a higher reflex threshold tended to exhibit excitatory and inhibitory reflexes, respectively.