Loss of dendritic spines in aging cerebral cortex

Abstract

Previous work has shown that the dendritic spines of pyramidal neurons of the cerebral cortex are sensitive to a wide variety of environmental and surgical manipulations. The present study shows that the normal aging process also affects these spines. The spines were studied with the light microscope in Golgi preparations from rats ranging in age from 3 to 29.5 months. Visible spines were counted on either 25 or 53 mu segments of the basal dendrites, apical dendrites, oblique branches, and terminal tufts of layer V pyramidal cells in area 17. A progressive loss of spines occurred at each of these loci. The smallest observed spine loss (24%) occurred on the dendrites of the terminal tuft, and the largest (40%) on the oblique branches. Age-related spine loss appears to affect all animals, and for animals of any one age the overall loss is similar. However, the cell-to-cell variability within an individual animal is pronounced, some cells with high spine densities being present at every age examined. As a general rule, there is a positive relationship between visible spine density along the apical dendrite as it traverses layer IV and the thickness of the dendrite. With advancing age, the relatively thick dendrites decrease in number so that the thinner dendrites make up an increasingly larger proportion of the total apical dendrite population. Questions that remain for the future include the genesis of the spine loss, its relation to other aging changes, and its functional significance for the neuron.

The Effect of Epidural Compression on Cerebral Cortex: A Rat Model

“…Long-term potentiation and enriched environment can increase dendritic spine densities (Globus et al, 1973). On the other hand, reduction of dendritic spines can result from aging (Feldman and Dowd, 1975), injuries such as deafferentation (Rutledge et al, 1972) and hypoxia (Kim, 1975;Pokorny and Trojan, 1983), and pathological conditions such as dementia (Ferrer et al, 1990), temporal lobe epilepsy (Olney et al, 1983;Paul and Scheibel, 1986), and mental retardation states (Marin-Padilla, 1972, 1974, 1976. In addition, earlier morphological study on the epitumorous human cerebral cortex have documented the loss of dendritic spines on neurons near the tumor mass (Spacek, 1987).…”

Metabolic Maturation of the Brain: A Study of Local Cerebral Glucose Utilization in the Developing Cat

“…Golgi studies in the visual cortex of a number of species have also shown that shortly after birth there is a period characterized by excessive den dritic spines (Fifkova, 1970;Feldman and Dowd, 1975;Boothe and Lund, 1976;Ruiz-Marcos and Valverde, 1976). Following this, there is significant loss of dendritic spines and synapses.…”

The Effects of Decompression and Exogenous NGF on Compressed Cerebral Cortex

“…First, loss of basal forebrain cholinergic neurons, often associated with dementia or aging, is usually accompanied by loss of dendritic spines on cortical neurons (Feldman and Dowd, 1975;Ferrer et al, 1990). Second, activation of cholinergic pathways enhances the formation of long-term potentiation, which is often associated with an increase of dendritic spine density (Globus et al, 1973).…”

“…It is known that dendritic spines are dynamic structures that can change form and density according to their environment (Horner, 1993); long-term potentiation and enriched environment increase dendritic spine densities (Globus et al, 1973), while aging (Feldman and Dowd, 1975) and pathological conditions such as dementia (Ferrer et al, 1990), temporal lobe epilepsy (Paul and Scheibel, 1986), and mental retardation states (Marin-Padilla, 1972) decrease them. The lack of recovery of dendritic spine density suggests that exposing the cortex to a few days of physical compression alone could lock the cortex into an altered functional status even after clinical manipulation removes CHEN ET AL.…”