Differential dopamine-induced prolactin mRNA levels in various prolactin-secreting cell (sub)populations.

We have examined the effects of dopamine on prolactin gene expression using quantitative in-situ hybridization histochemistry in different pituitary cell (sub)populations separated according to their density on a discontinuous Percoll gradient. Administration of dopamine resulted in a drastic reduction in hybridization of 35S-labelled DNA probe complementary to prolactin mRNA in total pituitary cells and in lactotrophs with low density. In contrast, dopamine significantly stimulated mRNA accumulation in prolactin-secreting cells with high density compared with other cell layers. The combined use of Percoll gradient and quantitative in-situ hybridization is a valuable and sensitive method with which to examine prolactin-secreting cell response to a given stimulation. Prolactin-secreting cells with high and low density clearly show functional heterogeneity in their response to dopamine.

Altered adrenocortical response under the influence of experimentally increased serum very long chain fatty acids in rats.

C 26:0/C 22:0 ratio can be experimentally increased in serum of normal rats by oral administration of hexacosanoic acid (C 26:0) or of thioridazine, an inhibitor of peroxisomal beta-oxidation. This causes a decreased corticosterone response as well as decreased mobilization of cholesterol esters in zona fasciculata interna cells following ACTH administration. Zona fasciculata interna cells and their nuclei are enlarged and contain more Feulgen DNA in thioridazine-fed rats. The similarity of adrenocortical response to inhibition of peroxisomal beta-oxidation and to C 26:0 administration points to raised VLCFA as the common factor which is also operative in many peroxisomal diseases accompanied by adrenocortical function defects.

Automated analysis of muscle fibre images.

A technique for studying the distribution and size of different fibre types in muscles is proposed for automated analysis of individual fibres in optical density images from ATPase-stained muscle sections. After delineation, fibres may be classified into different histological types (1, 2A, 2B and 2C) using the measurement of their mean optical density (mOD). The densitometric measurements were obtained from three serial histological slides stained under different conditions. The delineation procedure is performed on one of the images: the resulting mask is fitted to the other images using a linear coordinate transform. Along with densitometric measurements, the lesser diameter of the fibres is computed. Both in processing and in analysis, extensive use was made of mathematical morphology tools. All software was implemented on a VICOM digital image processor, extended with a VISIOMORPH morphoprocessor board.

Automated cytometry of muscle fibre sections: size and spatial distribution of the four fibre types in young and adult rats.

An automated cytometry program was applied to the extensor digitorum longus muscle of young and adult rats. Lesser diameter and spatial distribution of about 4000 fibres were measured in digital images from ATPase-stained muscle sections. All fibre types grow thicker with age, but the coefficient of variation of the diameter is age-independent. At both ages, 2B fibres have the largest mean diameter and are most frequent. 2A fibres in young rats present a diameter smaller or equal to type 1 but then show a faster increase in size; their relative number increases from 20 to 28%. Consequently type 2A displays the most important change with age. The spatial distribution of fibres is mathematically expressed; most images show a random distribution of type 1 and type 2 fibres. Taking into account the variation of fibre size of each type, the number of fibres which should be measured in order to reach a specified precision was calculated.

Experimental inhibition of peroxisomal beta-oxidation in rats: influence on brain myelination.

Oral administration of thioridazine, an inhibitor of peroxisomal beta-oxidation, to normal rats from weaning till day 60 causes a small increase of the very long chain fatty acid C26 in brain lipids. Myelination in the brain is decreased. In the genu of the corpus callosum the ratio of non-myelinated/myelinated axons is increased. In the commissura anterior the myelin sheaths of the axons are significantly thinner in treated than in control animals. Undernourishment caused by the drug is minimal in this experiment. Area and total DNA of glial nuclei are unaltered in both the genu and the commissura anterior of treated rats. The distribution of chromatin (texture), however, shows small differences in the corpus callosum.