Antonio Ruiz-Marcos

The metric analysis of three-dimensional dendritic tree patterns: a methodological review

Metric analysis methods used to study neuronal arborizations are reviewed and discussed. The analysis methods considered are those examining the spatial orientation and density of the whole dendritic field of a neuron, the metrics of dendritic segments and the bifurcation angles. General variables indicating the size of the soma and the dendritic field are indicated. In addition, the instrumentation used for providing 3-dimensional data for metric analyses and the shrinkage of Golgi-stained neurons are discussed.

The temporal evolution of the distribution of dendritic spines in the visual cortex of normal and dark raised mice

SummaryA set of equations which define the distribution of spines along the apical dendrites have been developed. They are satisfied by the distribution of spines and its evolution with the age in the apicals of the layer V pyramidal cells of the visual cortex in normal and dark raised mice. The principal equation describes the distribution of the spines with three coefficients IF, B and K whose values have a functional relation with the age T of the animal. This relation has been defined by three additional equations whose coefficients were calculated. The equations have been used to predict the distribution of dendritic spines corresponding to age-groups of mice not previously studied and to find out the age of mice from the data of their known spine distribution resolving the inverse equations of IF (T) and B(T).

Reversible morphological alterations of cortical neurons in juvenile and adult hypothyroidism in the rat

We have studied: (i) whether or not hypothyroidism induced experimentally in the adult rat affects the number and distribution of spines along the apical shaft of pyramidal cells from the visual cortex; and (ii) whether treatment with thyroid hormone would reverse such changes. Two experiments were performed. Experiment A involved the study of rats which were thyroidectomized (T) at 40 or at 120 days of age, killed at 120 and 220 days of age, respectively, data being compared to those of adequate sex and age-paired controls. Experiment B involved rats which were T at 40 days of age; they were subdivided into two groups, one of which was left untreated and the other received 0.2 microgram of thyroxine/100 g body weight/day for 25 days. Both groups were killed at 90 days of age. We found that: (i) T at 40 and at 120 days of age resulted in a decrease of the number of spines and a derangement of their distribution along the shaft, the observed changes being qualitatively comparable to those previously described for rats T at 10 days of age; and (ii) preliminary results from experiment B indicate that the observed changes in neuronal morphology might be reversible. It is suggested that age-independent and reversible alterations of learning capacity and electrocortical activity of hypothyroid rats might have age-independent and reversible morphological correlates at the level of the cortex.

Thyroxine treatment and recovery of hypothyroidism-induced pyramidal cell damage.

We have previously shown that changes occur in pyramids of area 17 of the rat visual cortex both after thyroidectomy (T) at 10 and at 40 days of age. To assess the effects of thyroxine treatment, instituted at different ages after T, two series of experiments were performed. A : rats were T at 10 days of age and either left untreated, or injected once daily with 1.5 micrograms thyroxine (T4)/100 g body weight. Treatment was started at 12, 15, 20, 30 or 40 days of age. Groups of untreated and T4-treated T rats and of age-paired intact controls were killed at different ages, ranging from 40 to 80 days. B : rats were T at 40 days of age, a group being treated with the same T4 dose starting 30 days after T. These animals, solvent-treated T rats and intact age-paired controls were killed at 90 days of age. The number and distribution of spines along the shaft of Golgi-stained pyramidal cells of the visual cortex were measured and fitted by a mathematical model developed previously. Body weights, pituitary growth hormone contents, plasma thyrotropic hormone, thyroxine and triiodothyronine levels were measured to assess the degree of hypothyroidism. It was found that treatment with T4 of rats T at 10 days of age prevented the alterations of pyramidal cells, provided treatment was started by 12 days of age and euthyroidism was maintained. In rats T at 40 days of age, treatment with T4 had an ameliorating effect despite a delay in onset of treatment of 30 days after T. Whatever the mechanisms which are involved, the present results stress once more the importance of very early treatment of hypothyroid newborns, if permanent cortical brain damage is to be prevented.

Dynamic architecture of the visual cortex

Abstract Several aspects of the organization of the visual cortex in the mouse have been examined in Golgi preparations. Special attention has been devoted to the afferent systems innervating the basal dendrites of pyramidal cells of layers III and V. A computer analysis using matrix algebra of the projected dendritic field of the basal and apical-collateral dendrites of pyramidal cells of layers III and V of the visual cortex has been carried out. The data were obtained from Golgi preparations from three age groups of normal and neonatally enucleated mice. Statistical comparisons of the dendritic fields showed, in enucleated mice, the existence of decreased dendrite density in an area of the dendritic field below the cell body, bounded by two lines forming an angle of 90° with vertex in the cell body and bisector perpendicular to the surface of the brain. The dendrite diminution is more pronounced in younger enucleated subjects. It is also more intense in pyramidal cells of layer III. The possible dependence of these differences on different innervations of basal dendrites has been discussed.

Dendritic spines in the visual cortex of the mouse: Introduction to a mathematical model

SummaryThe spines of apical dendrites of the layer V pyramidal cells of the area striata in the mouse represent a sequence of post-synaptic structures receiving a variety of contacts from terminal fibers derived fundamentally from short axon cells and superficial pyramidal cells. The study of Golgi preparations of mice 180 days old shows the existence of the most complicated terminal structures over portions of apical dendrites at the levels of layers III and IV. Observations on young mice reveals the terminations of the specific afferent fibers on the dendrites of short axon cells. A mathematical model which defines the distribution of spines along the apical dendrites is introduced. The principal equation of the model has been adjusted from the data processing of microscope countings through a series of programs written for an IBM 7070. The equation defines satisfactorily the different distributions of dendritic spines in mice 10–180 days old raised in normal conditions and in complete darkness. The equation defines also the distribution of dendritic spines in the visual cortex of mice enucleated at birth on one side, and the distribution along the apical dendrites of various cortical areas of the hamster, cat and man. The number of dendritic spines increases with the age of the subject and their distribution varies significantly according to the values of the parameters of the model.

Effect of neonatal and adult-onset hypothyroidism on pyramidal cells of the rat auditory cortex

Abstract Hearing dysfunctions of varying type and intensity are often found in endemic cretinism or associated with hypothyroidism, either congenital or acquired, and both in humans and experimental animals. We have studied the possible effect of thyroidectomy ( T ) of neonatal and adult rats on the morphology of pyramidal cells of the auditory cortex, the number and distribution of spines along their shaft being measured as parameters. The changes were compared to those found previously in the pyramids of the visual cortex of the same animals30–34. Both the number of apical shaft spines and their distribution change with age in pyramids of the auditory cortex, as studied between 10 and 220 days after birth, but the changes were not identical to those in the visual cortex. Results suggest a slower age-related evolution of the pyramidal cells of the auditory, as compared to the visual, cortex. T at 10 days of age resulted in a decreased number of apical shaft spines, the spine distribution curves also being affected. Treatment of these rats with 1.5 μg T 4/100 g body weight/day did not prevent these changes, even if started at 12 and 15 days of age. On the contrary, clear amelioration of visual cortex pyramidal cells was observed in the same animals. The number and distribution of spines along the shaft of the pyramidal cells of the auditory cortex was also affected by T of rats at 40 and 120 days of age, though longer exposure to hypothyroidism appears to be needed than to observe similar changes in neurons of the visual cortex. Present data therefore show a causal relationship between hypothyroidism and alterations of pyramidal cells of the auditory cortex. Some of the results also suggest that during the neonatal period hypothyroidism may induce changes in auditory cortex pyramids which are either more sensitive to a minor degree of hypothyroidism, or have a shorter ‘critical period’ during which treatment may reverse damage, than other cerebral or cerebellar neurons and structures.

Developmental sex differences and effect of ovariectomy on the number of cortical pyramidal cell dendritic spines

Dendritic spines in the apical shafts of layer V pyramidal neurons were quantitatively assessed in Golgi preparations of visual cortex from male and female rats, 10-60 postnatal days old. The number of dendritic spines increased in both sexes from days 10 to 20. However, we found that 10-day-old females had a significantly greater number of dendritic spines than males of the same age. The absolute difference further increased with increasing age, reaching a maximum at 20 days. Then, the number of dendritic spines progressively decreased in females between days 20 and 60, showing a certain tendency to increase in males during the same period. As a result of this different developmental trend, the number of spines was similar in 60-day-old male and female rats. Ovariectomy of females, at day 30, prevented the decrease in the number of dendritic spines. These results indicate that spine development in the rat visual cortex is dependent on sex, suggesting a possible influence of sex steroids on pyramidal cell maturation.

Rapid effects of adult-onset hypothyroidism on dendritic spines of pyramidal cells of the rat cerebral cortex.

SummaryWe have previously shown (Ruiz-Marcos et al. 1980, 1982) that thyroidectomy (T) performed in rats at 40 days of age, well past the neonatal period of development, results by 80–90 days of age in a decrease of the number of spines along the shaft of pyramidal neurons with the cell body in layer V in the visual area of the cerebral cortex. We have here studied how soon after the operation an effect on spine number and distribution may be observed. We have found that the response of these neurons to T is very rapid: a decrease in the number of spines/shaft between T and age-paired controls (C) rats is statistically significant by the earliest period of observation, namely 5 days after T. These results may be related to those of Dembri et al. (1983) showing that T performed in adult rats decreases the activity of Type I RNA polymerase by 5 days after the operation. It is possible that T impairs the synthesis of some compound(s) necessary for the formation and maintenance of spines. The present results suggest that spine number is not a fixed structure of the apical shaft once brain development is over, but is in a state of continuous formation and degradation. We have further observed that the effect of T performed at 40 days of age is more pronounced in the distal part of the shaft than on the rest, a result similar to that found after neonatal T (Ruiz-Marcos et al. 1982). However, contrary to findings after early hypothyroidism, T at 40 days of age does not distort the distribution of spines along the shaft.

Geometrical and topological characteristics in the dendritic development of cortical pyramidal and non-pyramidal neurons.

Publisher Summary This chapter deals with regression or reduction in the size of dendritic fields in some cell types during normal development, while the general developmental characteristics of cortical neurons are also discussed. Developmental characteristics are illustrated using data from layer II/III pyramidal neurons, layer IV multipolar non-pyramidal neurons, small layer V pyramidal neurons and large layer V pyramidal neurons in rat visual cortex. These neurons show some different developmental characteristics. The data available concerning cortical dendrite development describe that, irrespective of birth date or an earlier start of dendritic maturation, the phase of rapid dendritic growth ends around the same age for all types of cortical pyramidal and non-pyramidal neurons. In general, the mode of branching appears to be the same for all the types of cortical neurons examined at the various ages studied, i.e. mainly random branching at the terminal segments. However, the branching probability per dendritic unit of length is lower in non-pyramidal neurons, resulting in fewer bifurcations per dendrite. The results indicate the occurrence of some regression in the basal dendrites of pyramidal cell types during normal development and puberty. The major part of dendritic development appears to follow an intrinsic ‘program’ which can be modified, however, by environmental influences without altering the mode of branching.