Stereological age-related changes in neurons of the rat dorsal lateral geniculate nucleus.

Quantitative methods were used to compare the changes taking place in the volume of the dorsal lateral geniculate nucleus (dLGN) and corresponding neurons of young, adult and old rats. The study was carried out on male albino rats aged 3, 18, 24 and 28 months. In order to estimate the volume of the dLGN, neuronal volume density, numerical density and total number of neurons, we used serial sections stained according to the Klüver-Barrera technique and stereological methods. We found that dorsal lateral geniculate nucleus volume increases between 3 and 28 months, with a larger increase between 24 and 28 months. Neuronal volume density and numerical density of neurons are greater at 3 months and undergo a significant decrease between 24 and 28 months. Finally, the total number of neurons is shown to be smaller in adult and old animals than in younger ones, even though no significant variations are found between 18 and 28 months. Furthermore, this study confirms the need to analyze the total number of neurons and not just neuronal density if we want to correctly evaluate some of the microscopic changes occurring during senescence.

Relation between RNA content and ageing in neurons of the dorsal lateral geniculate nucleus.

We carried out a study to establish ribonucleic acid (RNA) content in the nucleus and cytoplasm of single neuronal cells from the dorsal lateral geniculate nucleus (dLGN) of 3-30 month-old rats. Mean RNA content was calculated as the product of RNA concentration and nuclear or cytoplasmic surface. The analysis of neuronal nuclei revealed no significant differences in RNA concentration, nuclear area, and RNA content from 3-18 months. However, a significant decrease in RNA concentration (18.73%) was found from the 18th-24th month, although no changes were observed in nuclear area and RNA content. The oldest rats, 24-30 months old, presented a significant increase in nuclear area and RNA content. As regards to the neuronal cytoplasm, no significant differences were found in any of the parameters at the ages from 3-18 months and 18-24 months. In contrast, a significant increase in RNA concentration (26.26%), cytoplasm area (18%), and RNA content (52%) takes place from the 24th-30th month. The increase in RNA content could be related to neuronal hypertrophy.

Quantitative morphological changes in neurons from the dorsal lateral geniculate nucleus of young and old rats.

BACKGROUND: We studied the morphological changes occurring in neurons from the dorsal lateral geniculate nucleus (dLGN) during aging by analysing the size and shape of cell bodies and nuclei. METHODS: Male albino Wistar rats, aged 3, 18, 24, and 30 months, were used. After appropriate tissue preparation and following the usual histological procedure, the profiles of 1,920 neuronal bodies and nuclei were drawn using a camera lucida. Data was later recorded and processed with a semiautomatic image analyser. RESULTS AND CONCLUSIONS: We observed that dLGN neurons do not change in size from the age of 3-24 months. Between 24 and 30 months, the soma and nucleus of the cell undergo hypertrophy, 32.8% and 35.6%, respectively, when compared to those from 3-month-old animals (P < 0.01). Furthermore, we found a high correlation between cell body size/nucleus size, which does not disappear with age. The r values (correlation coefficient) were 0.7998, 0.8662, 0.8433 and 0.7304, and R2 (determination coefficient) was equal to 0.6397, 0.7504, 0.7112, and 0.5335. These latter values show that in 63.97%, 75.04%, 71.12%, and 53.35% of cases, respectively, modifications in somata size were accompanied by similar changes in nucleus size, and vice-versa. The study of the shape of the soma and nucleus of the cell revealed that both structures have a rounded-oval configuration that does not change in a significant way from adulthood to old age.

The effect of ageing on RNA content in neurons from the thalamic reticular nucleus visual sector.

In this paper we investigate nucleic acid content in neurons from the dorsocaudal region of the thalamic reticular nucleus in ageing Wistar rats. Nucleic acid per surface unit was analysed by calculating mean extinction using cytophotometric methods. Once the mean extinction and nuclear and cytoplasmic areas were known, nucleic acid total content was calculated. There was an increase in nucleic acid total content and in nuclear and cytoplasmic areas from the age of 3 months onwards. We interpreted these findings as a compensatory response, by 'neuronal hypertrophy', to the deterioration process occurring in the ageing rats. Between the 24th and 30th month, i.e. old age, nucleic acid per surface unit and total content in the cytoplasm exhibited a considerable decrease.

Quantitative histochemical study of cytochrome oxidase in the dLGN of aging rats.

We carried out a quantitative histochemical study of the enzyme cytochrome oxidase (CO) in neurons of the dorsal lateral geniculate nucleus (dLGN) of male Wistar rats aged 3, 18, 24 and 28 months. The results show that the activity of cytochrome oxidase decreases significantly between 24 and 28 months. We also checked whether a correlation existed between neuronal size and enzymatic activity. Low correlation coefficients were obtained which were between 0.4139 at 3 months 0.2092 at 28 months. Nevertheless, we observed a certain relationship between both parameters, and therefore we classified the neurons as light, moderate and dark according to their optical density, which correlates with enzyme cytochrome oxidase activity, and as small, medium and large depending on their size. We found that light neurons were scarcely represented in the dLGN. At the age of 3 months, the most frequent neurons were moderate, medium-size ones, and dark, small ones. The population of moderate neurons increased with age, reaching 74.5% at the 28th month, 52.2% of which corresponded to medium-size neurons. In the same group dark neurons decreased, falling to a total of 15.3% made up of medium and large-size ones. These results could be interpreted as reflecting a decrease in the bioenergetic competence of the neurons of this nucleus in old age.

The effect of ageing on neurones in the visual sector of the thalamic reticular nucleus.

This paper studies the quantitative morphological changes occurring during ageing in neurones of the dorsocaudal or visual sector of the thalamic reticular nucleus. Male Wistar rats aged 3, 6, 18, 24 and 30 months were used in this study which applied morphometric methods. We have observed an increase in the size of neurones from this sector between the 3rd and 24th month and a decrease between the 24th and 30th month. In all the ages studied the majority of neurones are fusiform.

Evolution of neuronal density in the ageing thalamic reticular nucleus.

In this paper we present an analysis of the visual sector of the Thalamic Reticular Nucleus (TRN) from 3, 6, 18, 24 and 30 month old Wistar rats using stereological methods. The volume density (Vv), the number of neurones per surface unit (Na) and the neurone numerical density (Nv) showed a progressive decrease between the 3rd and the 24th months as the animals aged, whereas a significant increase was observed between the 24th and the 30th month, the period at which these rodents have fully entered old age.

Cytochrome oxidase activity in the lateral geniculate nucleus of postnatal rats.

We have studied the cytochrome oxidase activity and its pattern of distribution in the dorsal lateral geniculate nucleus of the rat during postnatal development. Between the 1st and the 8th postnatal days, the geniculate nucleus is seen to have a homogeneous enzymatic pattern with high neuronal density and moderately reactive neuropil. On the 15th postnatal day, different levels of neuronal enzymatic activity are found, and adult morphology is attained as of the 21st. The densitometric study has revealed that moderate and lightly reactive neurons are predominant between the 1st and the 8th postnatal days, whereas dark neurons are more numerous and optical density maximum on the 15th postnatal day. No variation in the enzymatic pattern was observed between the 21st and the 42nd days.

Histochemical study of RNA content of neurones in the dorsal lateral geniculate nucleus during postnatal development.

Nuclear and cytoplasmic dLGN neurons were investigated by cytophotometric measurements of RNA. This study has been carried out in rats from birth to adulthood. In order to quantify the RNA content a cytophotometer was used. Extinction mean values were obtained which indicated RNA concentrations per surface unit. The nuclear and cytoplasmic surface were calculated simultaneously and from the product of the mean extinction and the surface the RNA total content was calculated. Our results have suggested that the changes are age-related. From day 1 to day 21 the neuronal size and RNA content increase; this may somehow be involved with the differentiation process. Around post-natal day 21 neuronal maturation may begin, reaching its optimal phase around day 42, on which the RNA concentration per surface unit, surface neuronal content and RNA total content are stable.

Histoenzymatic study of the neurons in the visual sector of the thalamic reticular nucleus in the adult rat.

The different types of neurons within the visual sector of the rat's thalamic reticular nucleus were studied, both in terms of their morphology and their histochemical activity. Neurons were classified according to their dendritic arrangement into bitufted and multipolar. On the basis of the somal shape, bitufted neurons were further subdivided into two types, triangular and fusiform, and multipolar neurons into stellate and ovoid. Bitufted neurons have moderate succinic dehydrogenase (SDH) activity, while multipolar neurons usually have high SDH activity. Finally, the location of neurons in the visual sector of the thalamic reticular nucleus was described.

Quantitative study of the dorsal lateral geniculate nucleus of the rat during the postnatal development.

The chronology of dLGN development was studied in the rat from birth to 90 days postnatal (dpn). Our results indicate the faster dLGN growth occurs from 1 dpn to 21 dpn. The neuronal number and density was calculated. No significant neuronal loss was detected in the period investigated but the present study shows evidence of an important decrease (of 75%) in the neuronal density between 7 dpn and 21 dpn. Immediately the study of neuronal sizes and shapes was undertaken. Approximately at 14 dpn the deep neurons get a size significantly bigger than the marginal neurons. Finally, the different neuronal sizes were used for determining the successive phases of the neuronal development.