Biomedical subjects

S L Ipiña

Publications and source records attributed to S L Ipiña.

5 recordsLinked to original sources

PubMed2000

A measure of sexual dimorphism in populations which are univariate normal mixtures.

Measures of sexual dimorphism have been used extensively to predict the social organization and ecology of animal and human populations. There is, however, no universally accepted measure of phenotypic differences between the sexes. Most indices of sexual dimorphism fail to incorporate all of the information contained in a random data set. In an attempt to have a better alternative, an index is proposed to measure sexual dimorphism in populations that are distributed according to a probabilistic mixture model with two normal components. The index calculates the overlap between two functions that represent the contribution of each sex in the mixture. In order to assess such an index, sample means, variances and sizes of each sex are needed. As a consequence, the sample information used is greater than that used by other indices that take intrasexual variability into account. By evaluating some examples, our proposed index appears to be a more realistic measure of sexual dimorphism than other measures currently used.

Animals↗

PubMed1987

Pyramidal cortical cell morphology studied by multivariate analysis: effects of neonatal thyroidectomy, ageing and thyroxine-substitution therapy.

The changes produced on the whole dendritic morphology of layer III cortical pyramidal neurons by neonatal hypothyroidism, induced in rats by thyroidectomy at 10 days of age (T), as well as those changes related to ageing, have been studied in rats at 40 and 80 days of age. For these purposes, the dendritic structure of these neurons was defined by a set of 10 variables whose measurements were analyzed using multivariate methods. The effect of tyroxine (T4) substitution therapies applied to T rats between 12-40 and 30-80 days of age has been further investigated with the same mathematical methodology. The results obtained from the analyses performed show that hypothyroidism affects both the apical tuft and the basal dendritic arborization of these neurons. The observed damage was similar: a decrease of the total length of the dendritic segments of the apical tuft and the basal arborization. This change, however, was detected in these two different subregions with a different timing. These results seem to reinforce our findings concerning the selective effect of T on different sites of these neurons. On the other hand, 3 morphological changes have been revealed regarding the development of the pyramidal neuron studied: (1) the total length of the apical tuft dendritic segments increases from 40 to 80 days of age; (2) the total length of the basal dendritic segments decreases from 40 to 80 days of age; and (3) the perimeter of the cell body decreases from 40 to 80 days of age. Finally, the results obtained did not allow us to detect any recovery of the damage induced by T, as a consequence of the T4 substitution therapies applied.

Aging↗

PubMed1987

A multivariate phenetic approach to neuronal nuclei resemblances across species, with examples from three regions of cerebral cortex of a mammal, a bird and a reptile.

In order to test the assumed homology between three examples of cortical cerebral architecture corresponding to three species of mammals, birds and reptiles respectively, a method arising from the quantitative standpoint of the concept of homology has been utilized. For this purpose, data corresponding to randomly selected neurons were analysed by means of multivariate techniques such as principal component, principal co-ordinates and hierarchical cluster analyses since on each neuron a set of nineteen variables, chosen as a definition of its dendritic morphology, was measured. This method has made it possible both to discern the neuron forms which are responsible for the discrimination between the three cortical nuclei studied and to show by setting up a discriminant index, the degree of overall similarity between such nuclei. These two findings provide evidence against both the fibrous connection criterion with which some modern neurobiologists ascertain homologs and the categorical concept of homology.

Animals↗

PubMed1986

Hypothyroidism affects preferentially the dendritic densities on the more superficial region of pyramidal neurons of the rat cerebral cortex.

The effect of neonatal hypothyroidism on the dendritic density of layer III pyramidal neurons of the rat cerebral cortex has been investigated using a special matric algorithm. The results obtained indicate that this disease affects preferentially the dendritic density on the upper region of these cells.

Animals↗

PubMed1986

Dendritic structure alterations induced by hypothyroidism in pyramidal neurons of the rat visual cortex.

In order to study the effect that neonatal hypothyroidism has on the whole morphology of pyramidal neurons of the cerebral cortex, the dendritic structure of these cells was defined by a set of 10 variables divided into two subsets, one composed of 7 variables defining the apical shaft and the other composed of 3 variables concerning the basal arborization. The canonical multivariate analysis applied to the measurements of these variables made on two groups of layer III pyramidal neurons belonging to 80-day-old control and thyroidectomized rats revealed that this disease only affects the development of the apical tuft region of those neurons. This result is in agreement with our previous finding concerning the effect of hypothyroidism on the dendritic densities of layer III pyramidal neurons (Dev. Brain Res., 28 (1986) 259-262).

Analysis of Variance↗