Compared with fish of a slow-growing strain, fast-growing rainbow trout exhibited significantly smaller white fibre diameters, throughout development from hatching to 24 cm body length, although possessing similar total number of fibres. In contrast, in red muscle, no differences were observed in fibre diameter between the two strains, but the fast growing fish showed a significantly higher number of red fibres. The differences in growth rate between the two strains were related to the mean white fibre diameter and were found to be matched by proportional adjustments in recruitment of new fibres to the growing muscle. Thus, the largest and fastestgrowing strain showed evidence of sustained higher recruitment of muscle fibres that endowed this strain with the potential to maintain rapid somatic growth for longer and accomplish greater muscle growth. 1999 The Fisheries Society of the British Isles

Stereology offers a number of tools for the analysis of sections in microscopy (which usually provide only twodimensional information) for the purpose of estimating geometric quantities, such as volume, surface area, length or number of particles (cells or other structures). The use of these tools enables recovery of the threedimensional information that is inherent in biological tissues. This review uses the liver as a paradigm for summarizing the most commonly used state-of-the-art methods for quantitation in design-based stereology. Because it is often relevant to distinguish hyperplasia and hypertrophy in liver responses, we also focus on potential pitfalls in the sampling and processing of liver specimens for stereological purposes, and assess the existing methods for volume and number estimation. With respect to volume, we considered whole liver volume (V), volume density (V V ) and so-called local volumes, including the number-weighted volume ( v N ) and the volume-weighted volume ( v v ). For number, we considered the total number (N) and the numerical density (N V ). If correctly applied, current stereological methods guarantee that no bias is introduced in the estimates, which will be therefore accurate; additionally, methods can be tuned for obtaining precise quantitative estimates that can reveal subtle changes in the volume or number of selected hepatic cells. These methods have already detailed the effects of some substances and specific diets on the liver, and should be routinely included in the toolbox of liver research.

The strategy here presented provides a reliable method for accessing the N of HEP (distinguishing MnHEP from BnHEP) in situations in which these parameters are relevant, namely for evaluating the magnitude of an hyperplastic liver response from its very early onset.

SummaryTo better evaluate the activation and proliferative response of hepatic stellate cells (HSC) in hepatic fibrosis, it is essential to have sound quantitative data in non-pathological conditions. Our aim was to obtain the first precise and unbiased estimate of the total number of HSC in the adult rat, by combining the optical fractionator, in a smooth sampling design, with immunocytochemistry against glial fibrillary acidic protein.Moreover, we wanted to verify whether there was sufficiently relevant specimen inhomogeneity that could jeopardize the high expected estimate precision when using the smooth fractionator design for HSC. Finally, we wanted to address the question of what sampling scheme would be advisable a priori for future studies. Microscopical observations and quantitative data provided no evidence for inhomogeneity of tissue distribution of HSC. Under this scenario, we implemented a baseline sampling strategy estimating the number ( N ) of HSC as 207E 06 (CV = 0.17). The coefficient of error [CE( N )] was 0.04, as calculated by two formerly proposed approaches. The biological difference among animals contributed ≅ 95% to the observed variability, whereas methodological variance comprised the remaining 5%. We then carried out a half reduction of sampling effort, at the level of both sections and fields. In either occasion, the CE( N ) values were low ( ≅ 0.05) and the biological variance continued to be far more important than methodological variance. We concluded that our baseline sampling (counting 650 -1000 cells/rat) would be appropriate to assess the lobular distribution and the N of HSC. However, if the latter is the only parameter to be estimated, around half of our baseline sampling (counting 250-600 cells/rat) would still generate precise estimates [CE( N ) < 0.1], being in this case more efficient to reduce the number of sections than to reduce the sampled fields.

Background: A quantitative study was undertaken for the first time on the normal liver of male and female 2-year-old brown trout, Salmo trutta.Methods: Liver was fixed by controlled perfusion. Organ-level morphometry provided weight and volume. A two-stage stereological approach was performed at light and electron microscopy levels. Systematic sampling and point-counting morphometry were used for estimating the relative volumes of the structural compartments. Total absolute volumes of these components were obtained by multiplying each volume density by the volume of its reference space.Results: Liver volume was 3,423.6 mm 3 for males and 3,657.4 mm 3 for females. Parenchyma accounted for 95% of hepatic volume. Veins and bile ducts occupied, respectively, 76% and 17% of the stroma, whereas arteries, connective tissue, and melanomacrophages together composed only 6%. Hepatocytes occupied 88% of the parenchyma. Nonhepatocytic cells (endothelium, biliary epithelial cells, Ito cells, and macrophages) composed 4% of the parenchyma, the capillary lumen 6%, and other spaces (Disse space, canaliculi, and lumina of preductules and ductules) composed 2%. Significant sexual differences were found: (1) Females showed a greater parenchymal volume density (0.85% vs. 0.35%) and absolute volume (29.5 mm 2 vs. 11.7 mm 3 ) of Ito cells; (2) macrophages of females also presented a greater parenchymal volume density (0.94% vs. 0.46%), but not absolute volume.Conclusions: The need to analyze both relative and absolute stereological data was stressed. Similarities and differences were detected between brown trout and other species (fishes and mammals); the findings suggest that, despite architectural differences, some quantitative parameters of liver microanatomy were retained during phylogeny. Factors mediating sexual differences in Ito cells and macrophages were discussed and the need for further studies was highlighted. Anat.