Movement activity recovers the loss of spines owing to chronic immobilization

In chronically movement-restricted Wistar rats, we described a significant decrease of spines along apical shafts of layer V cortical pyramids. Current study indicates that the liberation at 40 days of rats whose movements had been restricted since 20 days of age produces a gradual recovery of the number of spines, reaching the control values at 80 days of age and that this process occurred faster in the motor than in the sensory cortices. Nevertheless, when R(20) rats were liberated at 80 days, the number of spines had not fully recovered when rats were 120 days old. Spine recovery is a form of cortical experience-dependent plasticity.     

Effect of hypothyroidism on the size of spines of pyramidal neurons of the cerebral cortex

We have previously shown that hypothyroidism produces a decrease in the number of spines counted along the apical shafts of pyramidal neurons of the cortex. Nevertheless, other authors have found that when an animal is subjected to some adverse living conditions the size of the spines decreases, making them invisible to the light microscope. The question arises then of whether the decrease in the number of spines reported by us in hypothyroid animals is real or is due to a shrinking effect. In order to elucidate this question the cross-surface area of dendritic spines of apical shafts belonging to 20- and 60-day-old rats, thyroidectomized at 10 days of age, as well as those of their corresponding controls were measured in different layers of their cortex, studied using conventional electron microscopic techniques. The application of the three-way analysis of variance model to these data has shown us that while the age of the animal produces a definite increase in the size of the spines, hypothyroidism does not produce any change in their size, leading us to the conclusion that the decrease in the number of spines previously reported is due to an actual loss of these elements.     

AGING OF DENDRITES IN THE CEREBRAL CORTEX OF THE MOUSE

Quantitative analysis of the dendritic branchings of pyramidal cells in layers V and III of the visual cortex was performed in aging mice (540 and 720 days) and compared to adult mice (180 days). The number of spines on apical dendrites of the same cells was also counted. Between 180 and 720 days of age, the decrease in dendritic branchings around the perikaryon was dramatic (30–40%) and that in dendritic spines was even more so (about 50%). However, most of the decrease in both dendritic branchings and spines has already occurred at 540 days, and the difference between 540 and 720 days was not statistically significant. This suggests a real loss in cortical connections with aging, taking place prior to the final months of the lifespan of the mouse.     

A comparison of dendritic spine number and type on pyramidal neurons of the visual cortex of old adult rats from social or isolated environments

The present study determined the effect of the housing condition experienced by old adult male rats on the appearance and number of dendritic spines. Specifically, 20-month-old rats were killed following 6 months of living in either a social environment (three to a cage) or living alone. The total number of dendritic spines per unit length was examined along segments of oblique, basal, and apical dendritic branches of pyramidal cells from layers II, III, Va, and Vb of the visual cortex. In addition to determining the total spine number, the spines were differentiated into two topographical categories: those with a lollipop configuration (type L) and those with a nubbin configuration (type N). Our results show that neither the total spine density nor the type L spine density were generally influenced by the two housing conditions. However, the density of type N spines was almost always greater on neurons from rats which had been living alone irrespective of the cortical layer or the dendritic segment counted. Some differences in total spine density and type L spine density were noted when neurons from the same environment but different cortical layers were compared, and these findings are discussed. However, the major focus of this paper was to extend our previous report of a selective increase in type N spines with age. We now show that in addition to increasing with age, type N spine density is also selectively increased by the condition of social deprivation.     

Spine-distribution of pyramidal neurons of the CAl-region of the rat hippocampus following long-term oral alcohol administration]

The distribution of the dendritic spines in the CA1 hippocampal region of adult rats was investigated by means of lightmicroscopical and statistical methods. The rats received daily equal amounts of aethanol for a period of 52 days. The average number of spines for a part of 50 mum along the apical main dendrite raised from 35 to 36.9 spines. The average spines-density for a part of 1 mum length on the apical dendritic branches raised from 0.71 to 0.94 spines. In a similar way the average spines-density on the basal dendritic branches raised from 0.65 to 0.94 spines. According to our results received after a period of aethanol application the total number of dendritic spines of one rat CA1 hippocampal pyramidal neuron was calculated with 4177 visible spines. The value was compared with the normal value of 3029 dendritic spines. The results were discussed by the aid of additional light- and electronmicroscopical findings.     

A Golgi study of the early postnatal development of the visual cortex of the hooded rat

Although neuroanatomical plasticity has been demonstrated in the rat visual cortex, no systematic data on the dendritic development of the area are available. In the present study, the visual cortex of hooded rats at 1, 3, 5, 7, 10 and 15 postnatal days of age (P1-P15) was impregnated with the rapid Golgi method. The cortex was divided into the superficial layers, II-IV, and the middle layer V. At P1, pyramidal neurons had apical shafts and the beginning of the apical terminal arch. Analysis of both basilar and oblique dendritic number showed that pyramidal neurons of the middle layer developed more quickly than those in the superficial layers. The number of lower order basilar dendritic branches reached asymptote over the examined time period, whereas the higher order branches were still increasing in number but at a decelerating rate by P15. Dendrites at all ages exhibited varicosities which were especially prominent on the thin dendritic branches of the earlier ages. Some thin, filamentous processes, termed protospines, were found on dendrites and cell bodies at P1 to P5. They seemed to decrease by P7, when a few mature spines appeared. Spines increased in number on days P10 and P15. A comparison of the data from this study with quantified Golgi studies in adult rats indicates that by P10 and P15 the number of basilar branches is in the range seen in the adult.     

Pregnancies alters spine number in cortical and subcortical limbic brain regions of old rats

Pregnancy is a complex process, involving a number of hormones and trophic factors, many of which are formed in the placenta. Several of these trophic factors have an effect at the neuronal level, such as BDNF. Consequently, recent reports have shown that exposure to these hormones (estrogen and progesterone) and trophic factors such as BDNF exert a neuroprotective effect. Here, we study the effect of the number of pregnancies on dendritic morphology of aged female rats (18 months of age). Rats of the 18‐month‐old Sprague Dawley strain with zero, one, two, and three gestations were evaluated for locomotor activity, and Golgi–Cox stain was performed to evaluate the dendritic morphology parameters, the number of dendritic spines, total dendritic length, and branching order number. Adult nulliparous rats (3 months of age) were used as another control group. Adult nulliparous and aging rats with two pregnancies showed an increase in locomotor activity. Adult nulliparous showed an increase in the dendritic spine number compared to old nulliparous rats in both layers of the PFC, the DG, and NAcc. Old rats with two and three pregnancies also showed an increase in the number of dendritic spines compared to old nulliparous rats in layers 3 and 5 of the PFC and in the CA1. Aging animals with one pregnancy also showed an increase in dendritic length compared to old nulliparous rats in the CA1. Our results clearly suggest that two and three pregnancies increase the dendritic spines number in the PFC and CA1 of aged female rats.     

Loss of sexual dimorphism in rat arcuate nucleus neuronal membranes with reproductive aging

Arcuate neurons of the rat hypothalamus have a sexual dimorphic membrane phenotype: quantitative analysis of freeze-fracture replicas has revealed that a population of intramembrane protein particles (IMP) of small size (less than 10 nm) is enriched in the plasma membrane of perikarya and dendritic shafts of cycling females compared to males, whereas a population of large IMPs (greater than 10 nm) is enriched in the membrane of dendritic shafts of males. This different membrane organization is associated with a sex dimorphic synaptic connectivity. To determine whether sex differences in neuronal membrane are affected by reproductive senescence, IMPs were assessed in freeze-fracture replicas of arcuate neuronal plasma membranes of male and female Sprague-Dawley rats aged 3, 15, and 18 months. Three-month-old cycling females were studied on the morning of estrus. Senescent females were in constant estrus (15 months old) or in constant diestrus (18 months old). Young females had more IMPs with diameters under 10 nm in the inner and outer leaflets of the plasma membrane of the perikarya and dendritic shafts compared to males of the same age. In addition, young males showed an increased number of large (greater than 10 nm) IMPs in the outer membrane leaflet of dendritic shafts. No sex differences were detected in the membrane of dendritic spines. In senescent females the number of small IMPs was decreased in the perikarya and dendritic shafts compared to young females while the number of large particles was increased in the outer leaflet of the membrane of dendritic shafts, reaching values similar to those observed in males. IMP counts were not modified with aging in males and in dendritic spines of females. These results indicate that reproductive aging in female rats is associated with a remodeling of neuronal plasma membranes in arcuate neurons.     

Effect of protein malnutrition on CA3 hippocampal pyramidal cells in rats of three ages

Prenatal and postnatal protein deprivation effect on CA3 hippocamapal pyramidal pyramidal cells were investigated in 30-, and 90- and 220-day old rats Female rats were fed either a 6% or a 25% casein diet 5 wk before conception and the litters were maintained on their respective diet until sacrificed. In 216 rapid Golgi-impregnatd cells, we measured somal size, length and diameter of apical dendrite, number of apical dendrites intersecting 10 concentric rings 38 μm apart, thorny excrescence area and length, head diameter and density of synaptic spines on 50-μm segments of apical dendrite. The present experiments showed that malnutrition produced significant reductions of somal size in animals at 220 days of age. There were significant reductions of apical dendrite diameters in animals of 30 and 90 days, and of density and head diameter of synaptic spines at the three ages studied, and significant decrease of the thorny excrescence area at 220 days of age. At this latter age, dendritic branching was significantly decreased in the last four rings representing the area into which the perforant pathway projects. In 30-day malnourished rats, dendritic branching showed a significant increase in rings 4–6 representing the area in which the Schaffer collaterals synapse. The location of the deficit spines corresponds to the sites where mossy fibers synapse on the apical dendrites of CA3 neurons. Age-related changes normally observed in control rats (e.g., the 30-day-old control group showed the smallest somal size and 220-day-old controls the largest size) failed to occur in the malnourished rats. The deficits in spine density and dendritic branching (in animals of 220 days old) were similar to those found in our previous studies on fascia dentata.     

Development of dendritic spines in the Vth's layer pyramidal neurons of the rat's somatosensory cortex. A qualitative and quantitative study with the Golgi method

Increases in the number of dendritic spines (DS) and modifications in the morphology of spines are observed through the maturation of pyramidal neurons in the somatosensory cortex of the rat. A two-fold increment in the number of spines occurs during days 15 to 30, but a 20% reduction in the overall number of DS is observed between days 30 and 90 to reach the stabilized values in the rat aged 6 months. The representation in a graph of the distribution of spines along the apical dendrite is adjusted to a curve with the maximal score lying at a distance of 200-300 microns from the cellular body. Beyond this region the number of spines decreases following a gentle descending profile. In addition, modifications in the morphology of DS occur through the development. Mushroom-shaped, stubby and short, thin spines in the 30-day-old rat replace spines with long, thin pedicles characteristic of the early developmental stages. Both variability in the density of DS and individual variability with regard to the percentage of the different types of spines on the apical dendrites are observed among neurons in the same animal even in rats 90 days old and in rats aged 6 months.     

Étude,en Golgi-Cox,de la distribution des épines dendritiques du cortex cérébral chez le chaton: Partie 1. Quinze premiers jours post-nataux

In order to study quantitatively the development of dendritic spines of pyramidal neurones, the suprasylvian cortex of kittens (1 to 15 days of age) was fixed and embedded by the Golgi-Cox (Sholl) method. The spines seen at different cortical levels were counted to establish their distribution along apical and basal dendrites. Disposition of spine contacts varied during the first month of post-natal cortical development. Three periods were established in relation to the morphological growth of neurones. The first period (days 1 to 4) was characterized by an irregular distribution of neurones and a reduced number of spines and was not clearly defined. The second period (days 6 to 9), showed better defined layers and differentiation of spines in areas of maximal density. The third period (days 10 to 15) was defined by a remarkable enlargment of cellular processes, neural stratification and spinal distribution comparable to that of adult animals, although with a smaller number of spines. It is concluded that the organization of dendritic spines is closely related to neuronal development, coinciding with the initiation of cortical afferent systems.     

A quantitative study of synaptic patterns in turtle visual cortex

The distribution of different synaptic types has been analyzed quantitatively in the molecular and subcellular layers of turtle ?vislual”? cortex. The density of vesicle-containing-profiles (VCPs) is 122.2/400 square μm in the molecular layer and 61.0/400 square μm in the subcellular layer. In both layers, approximately 85% of VCPs conatin round vesicles (RVCPs), 12%, flat vesicles (FVCPs) and 1%, dense core vesicles (DVCPs). Vacuolar invaginations (VIs) are not uncommon in the molecular layer (3.4%) but are rare in the subcellular layer (0.6%). Synaptic conatacts are formed in the plane of section by three out of ten RVCPs and FVCPs, while only one out of the 146 DVCPs sampled in this study was associated with a membrane differentiation. In the molecualr layer, the percentage distribution of the different subgroups of synaptic types is as follows: round-asymmetrical contacts, 82.5% (77.5% on dendritic spines and 5.0% on dendritic shafts); round-symmetrical contacts, 3.8% (2.3% on spines and 1.5% on shafts);flat-symmetrical contacts, 13.1% (8.8% on shafts and 4.3% on spines; flatasymmetrical contacts 0.6% (0.4% on spines and 0.2% on shafts)). In the subcellular layer, the distribution is quite different: round-asymmetrical contacts. 72.4% (38.6% on shafts and 33.8% on spines); round-symmertical contacts, 12.8% (8.2% on shafts and 4.6% on spines); flat-symmetrical contacts, 13.9% (9.3% on shafts and 4.6% on spines); flat-asymmetrical contacts, 0.9% all on dendritic shafts. The density distribution of VCPs in the molecular layer changes with depth. RVCPs are fewer on the distal third of the apical dendrites, and most numerous in the middle third with a small dercease in number in th proximal third. FVCPs are more homogeneously distributed, perhaps increasing slightly in number towards the proximal parts of the dendritets. RVCPs are most numerous on dendritic spines. These spines are of two types whose relative number varies with depth. Large organelle-filled spines predominate in the upper third while small ?empty”? spines are most numerous in the lower third of the molecular layer.     

The effect of continuous illumination on the development of cortical neurons in the rat: A Golgi study

The effect of continuous illumination on the development of dendritic spines of neurons in the visual cortex of albino rats has been studied. Using the rapid Golgi technique, spine counts were performed on pyramidal cells of layers IV and V in animals 8 to 80 days of age. An increase in spine density was first observed in apical dendrites of the 16-day-old rats reared in continuous illumination. Higher density of spines was found in the entire dendritic field of the cells by Day 20 and persisted thereafter at least until Day 80. This increase appeared prior to the onset of photoreceptor degeneration. These results suggest that visual overstimulation produces spine growth in pyramidal cells of the visual cortex.     

Effects of prenatal ethanol exposure on dendritic spines of layer V pyramidal neurons in the somatosensory cortex of the rat

The number of dendritic spines on consecutive segments from the cell body along the 400-600 micron proximal region of the apical dendrites of layer V pyramidal neurons, impregnated with the rapid Golgi method, in the somatosensory cortex was counted in ethanol-treated rats during gestation (25% ethanol in drinking water representing 30-35% of the total caloric intake) and in age-matched controls at postnatal ages 4, 15, 30 and 90 days. Although the mean values were lower in ethanol-treated rats than in controls during the first fortnight of postnatal life, significantly lower numbers of spines were observed only in the 15-day-old rat (Student's t-test, P less than 0.01-0.001). Spines with long, thin pedicles were characteristically encountered in ethanol-treated and controls aged 4 days; this sort of spine also predominated in ethanol-treated rats aged 15 days, but not in age-matched controls. The decrease in number and the abnormal morphology of spines was no longer present in ethanol-treated rats aged 30 and 90 days. These data suggest that impaired maturation of dendritic spines on cortical pyramidal cells, followed by recovery of the altered parameters at the end of the first postnatal month, occurs in the offspring of ethanol-treated rats during gestation.     

Effect of specific and non-specific stimuli on the visual and motor cortex of the rat

In order to study the possible simultaneous influences of light and darkness, and mobility and restraint on the visual and motor areas of the cortex, we have studied the visual and motor cortex of 4 groups of rats raised under the following conditions: (1) in normal light conditions and large cages; (2) in normal light conditions and cages small enough to restrain the movement of the animals; (3) in total darkness and large cages and (4) in total darkness and small cages. They were kept in these conditions from weaning until they were 90 days old. At this time they were killed and their brains stained following the rapid Golgi procedure. The spines along the apical shaft of the pyramidal neurons of layer V of the visual and motor cortex (a total of 20–25 cells/group) were counted. The results were processed in a PDP 11/40 computer. While darkness produced a decrease in the mean number of dendritic spines of only the visual cortex, restraining the animal produced a significant decrease in the mean number of spines in both cortices, motor and visual. Furthermore, the influence of restraining was found so strong on the visual cortex that it masked the effect of darkness. There was no significant difference between the mean number of spines per shaft of animals held restrained and in light, versus animals held restrained and in darkness. These results indicate that movement itself is very important for the correct development of dendritic spines in the visual cortex.     

Structure of the piriform cortex of the opossum. II. Fine structure of cell bodies and neuropil

The fine structure of cell bodies and neuropil in the piriform cortex of the opossum has been examined. A close similarity in ultrastructure of many features has been demonstrated between this pylogenetically old cortex in a primitive mammal and the neocortex of higher mammals. Cell bodies of pyramidal cells are very similar to those in the neocortex: The nucleus is pale with a smooth surface, the cytoplasm has a modest number of organelles, and the soma receives a small number of exclusively symmetrical synapses. Semilunar cells, which have apical but no basal den-drites, are very similar to pyramidal cells in ultrastructure of their cell bodies. Two populations of neurons with nonpyramidal ultrastructural features have been distinguished: (1) cells in layer III that closely resemble the well-known large multipolar cells in neocortex by virtue of a large number of symmetrical and asymmetrical somatic synapses and long cisterns of rough endoplasmic reticulum (ER); and (2) large cells in layer I with very few somatic synapses, a large number of mitochondria, and short cisterns of rough ER that may correspond to cells with somatic appendages described with the Golgi method. Large numbers of profiles are found in all layers that contain round vesicles and make asymmetrical synapses onto dendritic spines, and occasionally, dendritic shafts. Theseprofileshavedistinctly different morphological features in layer Ia, in which olfactory bulb afferents are concentrated, and in layers Ib, II, and III, which contain terminals of association and commis-sural fibers. A smaller number of profiles containing pleomorphic vesicles make symmetrical contacts onto initial segments, dendritic shafts, cell bodies, and occasionally, dendritic spines. Most dendritic spines in all layers are small to medium in size (0.3–1.2 μm) and presumably originate from pyramidal cells. In layer Ia, however, large, flattened spines are also present which appear to originate from semi-lunar cells. In layer III, and to a lesser extent other layers, large irregular spines are present that may be branched appendages on dendrites of complex appendage cells (Haberly, 1983).     

Effects of intraocular tetrodotoxin on dendritic spines in the developing rat visual cortex: a Golgi analysis

The effect of tetrodotoxin (TTX)-induced monocular impulse blockade on the growth of dendritic spines in the developing rat primary visual cortex was analysed by quantitative Golgi techniques. Between 5 and 21 days postnatal (dpn), rats were injected with TTX every 2 days into the right eye to chronically eliminate optic impulses. Effectiveness of TTX was monitored by loss of the pupillary light reflex. At 21 dpn, the number of spines located on the portion of the apical dendrite within layers III, IV and the superficial region of layer V was reduced by approximately 26%. These decreases were found on the apical dendrites of both large and medium sized pyramidal cells. TTX also reduced the number of spines on the proximal portion of oblique dendrites in layer IV by 16%, yet did not change the number of spines on basilar dendrites. No evidence of transneuronal degeneration was seen following long-term TTX treatment. These data indicate that dendritic spine development in the visual cortex is sensitive to the loss of optic impulses and that the decrease in spine population is principally due to a reduction in spine growth.     

Number and distribution of the apical dendritic spines of the layer V pyramidal cells in man

The number and the distribution of the apical dendritic spines was investigated in the layer V pyramidal cells of the human cerebral cortex. This study was carried out in the motor cortices of an 8-month fetus, a premature infant, and a newborn, 15-, 19- and 45-day-old infants; in the somesthetic cortex of a newborn infant; and in the auditory cortex of a newborn infant. This study has shown: (a) that the number of spines increases with the age, (b) that the spines are distributed along the apical dendrites in a characteristic manner which, graphically represented, consists of a curve with three distinct deflexions, (c) that the spine-distribution along the apical dendrites of the layer V pyramidal cells is similar in all cases studied regardless of their age or their cortical location (motor, somesthetic and auditory cortices), (d) that the distribution of the spines along the apical dendrites appears to depend on the nature of the dendrite, (e) that the sequence of the mean number of spines maintains an exponential relationship with the distance from the cell body for the first and second deflexions of the spine-distribution curves. The significance of the distribution of the spines along the apical dendrites of the layer V pyramidal cells is discussed. A new method is presented and its possible application to the study of the normal development and pathoIogical conditions of the cerebra1 cortex is suggested.     

Intrinsic circuitry: synapses involving the local axon collaterals of corticocortical projection neurons in the mouse primary somatosensory cortex

Pyramidal neurons in the mouse SmI cortex were labeled by the retrograde transport of horseradish peroxidase (HRP) injected into the ipsilateral MsI cortex. Terminals of the local axon collaterals of these neurons (CC terminals) were identified in SmI, and their distribution and synaptic connectivity were examined. To avoid confusion, terminals in SmI cortex labeled by the anterograde transport of HRP injected into MsI were eliminated by lesion-induced degeneration. Lesions of MsI were made 24 hours after the injection of HRP; postlesion survival time was 4 days. Most CC axon terminals occurred in layers III and V where they formed asymmetrical synapses. Of 139 CC synapses in layer III and 104 in layer V, approximately 13% were formed with dendritic shafts. Reconstruction of 19 of these dendrites from serial thin sections showed them to originate from both spiny and nonspiny neurons. Most synapses of CC terminals (about 87%) were onto dendritic spines. In contrast, White and Keller (1987) demonstrated that terminals belonging to the local axon collaterals of corticothalamic (CT) projection cells synapse mainly with dendritic shafts of nonspiny neurons: 92% onto shafts, the remainder onto spines. The distribution of asymmetical synapses onto spines and dendritic shafts was analyzed for neuropil in layers III, IV, and V. Depending on the layer, from 34 to 46% of the asymmetrical synapses in the neuropil were onto dendritic shafts. Results showing that CC and CT terminals form proportions of axodendritic vs. axospinous synapses that differ from each other, and from the neuropil, indicate that local axon collaterals are highly selective with regard to their postsynaptic elements.     

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.