Differences In Spine Density Research Articles

Olfactory learning-induced increase in spine density along the apical dendrites of CA1 hippocampal neurons.

We have previously shown that rule learning of an olfactory discrimination task is accompanied by increased spine density along the apical dendrites of piriform cortex pyramidal neurons. The purpose of the present study was to examine whether such olfactory learning task, in which the hippocampus is actively involved, induces morphological modifications in CA1 pyramidal neurons as well. Rats were trained to discriminate positive cues in pairs of odors for a water reward. Morphological modifications were studied in Golgi-impregnated neurons with light microscopy, 1 and 3 days after training completion. Spine densities were measured on the proximal region of apical dendrites and on basal dendrites after rule learning. Three days after training completion, the mean spine density on apical dendrites in neurons from trained rats was significantly higher by 20.5% than in neurons from pseudo-trained and naive animals, which did not differ from each other. By contrast, there was no significant difference in spine density of basal dendrites among the three groups. As length and diameter of spiny dendritic segments did not change after learning, the learning-related increase in spine density in neurons from trained rats may reflect a net increase in the number of excitatory synapses in the hippocampus following olfactory rule learning.

Sex Differences and Opposite Effects of Stress on Dendritic Spine Density in the Male Versus Female Hippocampus

Dendritic spines are postsynaptic sites of excitatory input in the mammalian nervous system. Despite much information about their structure, their functional significance remains unknown. It has been reported that females in proestrus, when estrogen levels are elevated, have a greater density of apical dendritic spines on pyramidal neurons in area CA1 of the hippocampus than females in other stages of estrous (Woolley et al., 1990). Here we replicate these findings and in addition, show that females in proestrus have a greater density of spines in area CA1 of the hippocampus than males. Moreover, this sex difference in spine density is affected in opposite directions by stressful experience. In response to one acute stressful event of intermittent tailshocks, spine density was enhanced in the male hippocampus but reduced in the female hippocampus. The decrease in the female was observed for those that were stressed during diestrus 2 and perfused 24 hr later during proestrus. The opposing effects of stress were not evident immediately after the stressor but rather occurred within 24 hr and were evident on apical and to a lesser extent on basal dendrites of pyramidal cells in area CA1. Neither sex nor stress affected spine density on pyramidal neurons in somatosensory cortex. Sex differences in hippocampal spine density correlated with sex hormones, estradiol and testosterone, whereas stress effects on spine density were not directly associated with differences in the stress hormones, glucocorticoids. In summary, males and females have different levels of dendritic spine density in the hippocampus under unstressed conditions, and their neuronal anatomy can respond in opposite directions to the same stressful event.

Regional sex differences in spine density along the apical shaft of visual cortex pyramids during postnatal development

Dendritic spines from the apical shaft of layer V pyramids were counted on Golgi-stained sections of the monocular subfield of the primary visual cortex of 10-, 20-, 40- and 60-day-old male and female rats. Dendritic segments located in layer IV and at 100–300 μm from the soma had a significantly higher spine content in 10-day-old females when compared to males. This sex difference was extended to outer dendritic segments with increasing age, and became restricted to dendritic segments of outer layers (II–III) located at 400–550 μm from the perikaryon in 40-day-old rats. Sex differences in spine content finally disappear by day 60. These results show the existence of specific laminar and temporal sex differences in the development of dendritic spines in the apical shaft of visual cortex pyramids.

Granule cell dendritic spine density in the rat hippocampus varies with spine shape and location

The number of granule cell dendritic spines per micrometer of dendritic length in the dorsal and ventral leaves of the dentate gyrus was quantified using light microscopic-Golgi preparations of normal adult rats. Spines were counted in terms of 3 categories of spine form for the 3 afferent termination zones of the molecular layer and corrected for shading errors. Total spine density averaged 1.6 spines/micron of dendritic length in the dorsal leaf and 1.3 spines/micron of dendritic length in the ventral leaf. Statistically significant differences in spine density existed among the 3 shape categories. Variations in spine density occurred by shape category among the afferent termination zones.

Age-related changes in the subiculum of Macaca mulatta: Synaptic density

Dendritic spines and synapses were quantitated in the subiculum of 12 Macaca mulatta from 7 to 29 years of age. Dendritic spines were analyzed in six dendritic foci of pyramidal neurons impregnated by the Golgi-Cox method. The dendritic foci examined were the apical shaft, apical oblique, apical tuft, apical terminal, basal terminal, and basal dendrites. Electron microscopic observations were made on synapses stained with ethanolic phosphotungstic acid. There was no difference in spine density between a group of young (7 to 12 years of age) and middle-aged (18 to 21 years) animals. The mean spine density was 1.09/μm for the young and 1.15/μm for the middle-aged animals. In contrast, the spine density of the old animals was 0.87/μm, which was significantly lower than the spine density found in the young and middle-aged animals. A loss of dendritic spines in the old animals occurred equally in all six dendritic foci. A decline in synaptic density in the aged animals were further evidenced by an ultrastructural analysis. The synaptic density of the old animals was 8.3 × 10 8/mm 3, significantly lower than 9.5 × 10 8/mm 3 and 10.2 × 10 8/mm 3 found in the young and middle-aged animals, respectively. This study on synaptic density demonstrated the decline in synaptic number as a function of age in M. mulatta.

Brainstem immaturity in sudden infant death syndrome: A quantitative rapid Golgi study of dendritic spines in 95 infants

Quantitative analysis of reticular dendritic spines was performed on rapid Golgi impregnated neurons in 7 brainstem areas from 61 sudden infant death syndrome (SIDS) and 34 control infants. Throughout the first postnatal year, mean spine density in SIDS was significantly greater than the mean density in controls ( P < 0.0001). There were significantly higher values of spine density in SIDS compared to controls ( P < 0.0001) in both term and preterm infants. Within the SIDS brainstem itself, the density of dendritic spines was significantly different ( P < 0.05) between two medullary regions and between reticular and non-reticular formation areas. Among these brainstem areas in controls, there was no significant difference. Our findings indicate an immature developmental pattern of increased dendritic spine density in the SIDS brainstem which may be responsible for abnormal central respiratory and arousal control. These significant quantitative differences in spine density are considered in the present study to represent an anatomical substrate of brainstem immaturity in the multifactorial pathogenesis of SIDS.

Morphometric analysis of granule cell dendrites in the mouse dentate gyrus.

We devised a computer program to analyze the dendritic geometry of dentate granule cells as seen in rapid Golgi impregnations from the mouse. Three dimensional coordinates were recorded by using a computer-assisted microscope. Geometric parameters are of two general types: (1) LINEAR parameters include the number of dendritic segments per branch order and their individual and aggregate lengths. (2) ANGULAR parameters define the spatial relationships of branch points and segment terminals with each other and with the axis of symmetry derived for all the dendrites. We find that values for linear parameters are highly variable and more susceptible to artifacts. Values for most angular parameters are more highly constrained and are presumably the best descriptors of the class-characteristic conical shape of granule cell dendrites. Additional features which are necessary to describe granule cell dendrites fully are: (1) Branching frequency is highest proximal to the cell soma, (2) deviant segments are kept "on course" to ensure axial symmetry, and (3) terminal segments end at the plane of the cortical surface. A critical analysis of the various parameters suggests the hypothesis that the characteristic and uniform geometry of granule cell dendrites is controlled largely by factors residing in the molecular layer where growth and differentiation are sustained. An additional finding of potential interest is that there are two subpopulations of granule cells with a twofold difference in spine density.