Increase In Number Of Spines Research Articles

RGS14414-Mediated Activation of the 14-3-3ζ in Rodent Perirhinal Cortex Induces Dendritic Arborization, an Increase in Spine Number, Long-Lasting Memory Enhancement, and the Prevention of Memory Deficits.

The remedy of memory deficits has been inadequate, as all potential candidates studied thus far have shown limited to no effects and a search for an effective strategy is ongoing. Here, we show that an expression of RGS14414 in rat perirhinal cortex (PRh) produced long-lasting object recognition memory (ORM) enhancement and that this effect was mediated through the upregulation of 14-3-3ζ, which caused a boost in BDNF protein levels and increase in pyramidal neuron dendritic arborization and dendritic spine number. A knockdown of the 14-3-3ζ gene in rat or the deletion of the BDNF gene in mice caused complete loss in ORM enhancement and increase in BDNF protein levels and neuronal plasticity, indicating that 14-3-3ζ-BDNF pathway-mediated structural plasticity is an essential step in RGS14414-induced memory enhancement. We further observed that RGS14414 treatment was able to prevent deficits in recognition, spatial, and temporal memory, which are types of memory that are particularly affected in patients with memory dysfunctions, in rodent models of aging and Alzheimer's disease. These results suggest that 14-3-3ζ-BDNF pathway might play an important role in the maintenance of the synaptic structures in PRh that support memory functions and that RGS14414-mediated activation of this pathway could serve as a remedy to treat memory deficits.

Corticosterone after acute stress prevents the delayed effects on the amygdala.

Even a single 2-hour episode of immobilization stress is known to trigger anxiety-like behavior and increase spine-density in the basolateral amygdala (BLA) of rats 10 days later. This delayed build-up of morphological and behavioral effects offers a stress-free time window of intervention after acute stress, which we used to test a protective role for glucocorticoids against stress. We observed that post-stress corticosterone, given 1 day after acute stress in drinking water, reversed enhanced anxiety-like behavior 10 days later. Quantification of spine-density on Golgi-stained BLA principal neurons showed that the same intervention also prevented the increase in spine numbers in the amygdala, at the same delayed time-point. Further, stress elevated serum corticosterone levels in rats that received vehicle in the drinking water. However, when stress was followed 24 h later by corticosterone in the drinking water, the surge in corticosterone was prevented. Together, these observations suggest that corticosterone, delivered through drinking water even 24 h after acute stress, is capable of reversing the delayed enhancing effects on BLA synaptic connectivity and anxiety-like behavior. Strikingly, although the immobilization-induced surge in corticosterone by itself has delayed detrimental effects on amygdalar structure and function, there exists a window of opportunity even after stress to mitigate its impact with a second surge of exogenously administered corticosterone. This provides a framework in the amygdala for analyzing how the initial physiological and endocrine processes triggered by traumatic stress eventually give rise to debilitating emotional symptoms, as well as the protective effects of glucocorticoids against their development.

The increase in the number of spines on the gonadotropin-releasing hormone neuron across pubertal development in rats.

The onset of puberty is initiated by an increase in the release of the gonadotropin-releasing hormone (GnRH) from GnRH neurons in the hypothalamus. However, the precise mechanism that leads to the activation of GnRH neurons at puberty remains controversial. Spines are small protrusions on the surface of dendrites that normally receive excitatory inputs. In this study, we analyzed the number and morphology of spines on GnRH neurons to investigate changes in synaptic inputs across puberty in rats. For morphological estimation, we measured the diameter of the head (DH) of each spine and classified them into small-type (DH < 0.65μm), large-type (DH > 0.65μm) and giant-type (DH > 0.9μm). The greatest number of spines was observed at the proximal dendrite within 50μm of the soma. At the soma and proximal dendrite, the number of spines was greater in adults than in juveniles in both male and female individuals. Classification of spines revealed that the increase in spine number was due to increases in large- and giant-type spines. To furtherexplore the relationship between spines on GnRH neurons and pubertal development, we next analyzed adult rats neonatally exposed to estradiol benzoate, in which puberty onset and reproductive functionsare disrupted. We found a decrease in the number of all types of spines. These results suggest that GnRH neurons become to receive more and greater excitatory inputs on the soma and proximal dendrites as a result of the changes that occur at puberty and that alteration to spines plays a pivotal role in normal pubertal development.

Long-term incubation with mifepristone (MLTI) increases the spine density in developing Purkinje cells: new insights into progesterone receptor mechanisms.

Cerebellar Purkinje cells (PC) physiologically reveal an age-dependent expression of progesterone with high endogenous concentrations during the neonatal period. Even if progesterone has been previously shown to induce spinogenesis, dendritogenesis and synaptogenesis in immature PC, data about the effects of progesterone on mature PC are missing, even though they could be of significant therapeutic interest. The current study demonstrates for the first time a progesterone effect, depending on the developmental age of PC. Comparable with the physiological course of the progesterone concentration, experimental treatment with progesterone for 24h achieves the highest effects on the dendritic tree during the early neonate, inducing an highly significant increase in dendritic length, spine number and spine area, while spine density in mature PC could not be further stimulated by progesterone incubation. Observed progesterone effects are certainly mediated by classical progesterone receptors, as spine area and number were comparable to controls when progesterone incubation was combined with mifepristone (incubation for 24h), an antagonist of progesterone receptors A and B (PR-A/PR-B). In contrast, an increase in the spine number and area of both immature and mature PC was detected when slice cultures were incubated with mifepristone for more than 72h (mifepristone long-time incubation, MLTI). By including time-lapse microscopy, electron microscopic techniques, PCR, western blot, and MALDI IMS receptor analysis, as well as specific antagonists like trilostane and AG 205, we were able to detect the underlying mechanism of this diverging mifepristone effect. Thus, our results provide new insights into the function and signaling mechanisms of the recently described progesterone receptor membrane component 1 (PGRMC1) in PC. It is highly suitable that progesterone does not just induce effects by the well-known genomic mechanisms of the classical progesterone receptors but also acts through PGRMC1 mediated non-genomic mechanisms. Thus, our results provide first proofs for a previously discussed progesterone-dependent induction of neurosteroidogenesis in PC by interaction with PGRMC1. But while genomic progesterone effects mediated through classical PR-A and PR-B seem to be restricted to the neonatal period of PC, PGRMC1 also transmits signals by non-genomic mechanisms like regulation of the neurosteroidogenesis in mature PC. Thus, PGRMC1 might be an interesting target for future clinical studies and therapeutic interventions.

Age-related spatial learning impairment is unrelated to spinophilin immunoreactive spine number and protein levels in rat hippocampus

Age-related impairments in hippocampus-dependent learning and memory tasks are not associated with a loss of hippocampal neurons, but may be related to alterations in synaptic integrity. Here we used stereological techniques to estimate spine number in hippocampal subfields using immunostaining for the spine-associated protein, spinophilin, as a marker. Quantification of the immunoreactive profiles was performed using the optical disector/fractionator technique. Aging was associated with a modest increase in spine number in the molecular layer of the dentate gyrus and CA1 stratum lacunosum-moleculare. By comparison, spinophilin protein levels in the hippocampus, measured by Western blot analysis, failed to differ as a function of age. Neither the morphological nor the protein level data were correlated with spatial learning ability across individual aged rats. The results extend current evidence on synaptic integrity in the aged brain, indicating that a substantial loss of dendritic spines and spinophilin protein in the hippocampus are unlikely to contribute to age-related impairment in spatial learning.

Transient spine density increases in the mid-molecular layer of hippocampal dentate gyrus accompany consolidation of a spatial learning task in the rodent

In previous studies, we observed a transient increase in dendritic spine frequency in the molecular layer of the dentate gyrus at 6 h following passive avoidance training [O’Malley A., O’Connell C. and Regan C. M. (1998) Neuroscience 87, 607–613]. To determine if a similar change is associated with spatial forms of learning, we have estimated time-dependent modulations of spine number in the dentate gyrus of the adult rat following water maze training. All animals exhibited significant reductions in the latency to locate the platform over the five training sessions of the single trial (median and interquartile ranges of 60, 8 versus 8, 3 s for trials 1 and 5, respectively) and this improved performance was retained just prior to killing at the 6 h post-training time. The unbiased dissector stereological procedure was used to estimate spine number in serial pairs of ultrathin coronal sections obtained at a point 3.3 mm caudal of Bregma. This analysis revealed a significant learning-associated increase in spine number at the 6 h post-training time (1.32±0.18 spines/μm 3) as it was not observed in paired controls exposed to the water maze for a similar swim-time (0.66±0.11 spines/μm 3). The increase was transient as spine number returned to control levels at the 72 h post-training time. These spine frequency changes are proposed to reflect increased synapse turnover rate and concomitant change in connectivity pattern in the processing of information for long-term storage.

Slices Have More Synapses than Perfusion-Fixed Hippocampus from both Young and Mature Rats

Hippocampal slices have long been used to investigate properties of synaptic transmission and plasticity. Here, for the first time, synapses in slices have been compared quantitatively with synapses occurring in perfusion-fixed hippocampus, which is presumed to represent the natural in vivo state. Relative to perfusion-fixed hippocampus, a remarkable 40-50% increase in spine number occurs in adult hippocampal slices, and a 90% increase occurs in slices from postnatal day 21 rats. Serial EM shows that all of the dendritic spines have normal synapses with presynaptic and postsynaptic elements; however, not all spine types are affected uniformly. Stubby and mushroom spines increase in the adult slices, and thin, mushroom, and branched spines increase in the immature slices. More axonal boutons with multiple synapses occur in the slices, suggesting that the new synapses form on preexisting axonal boutons. The increase in spine and synapse number is evident within a couple of hours after preparing the slices. Once the initial spine induction has occurred, no further change occurs for up to 13 hr in vitro, the longest time investigated. Thus, the spine increase is occurring during a period when there is little or no synaptic activity during the first hour, and the subsequent stabilization in spine synapse numbers is occurring after synaptic activity returns in the slice. These findings suggest that spines form in response to the loss of synaptic activity when slices are removed from the rest of the brain and during the subsequent 1 hr recovery period.

TrkB Signaling Modulates Spine Density and Morphology Independent of Dendrite Structure in Cultured Neonatal Purkinje Cells

Neurotrophins cooperate with neural activity to modulate CNS neuronal survival and dendritic differentiation. In a previous study, we demonstrated that a critical balance of neurotrophin and neural activity is required for Purkinje cell survival in cocultures of purified granule and Purkinje cells (Morrison and Mason, 1998). Here we investigate whether TrkB signaling regulates dendrite and spine development of Purkinje cells. BDNF treatment of purified Purkinje cells cultured alone did not elicit formation of mature dendrites or spines. In cocultures of granule and Purkinje cells, however, continuous treatment with BDNF over a 2 week postnatal culture period increased the density of Purkinje cell dendritic spines relative to controls without causing a shift in the proportions of headed and filopodia-like spines. The increase in spine number was blocked by adding TrkB-IgG to the medium together with BDNF. Although BDNF alone did not consistently modify the morphology of dendritic spines, treatment with TrkB-IgG alone yielded spines with longer necks than those in control cultures. None of these treatments altered Purkinje cell dendritic complexity. These analyses reveal a role for TrkB signaling in modulating spine development, consistent with recently reported effects of neurotrophins on synaptic function. Moreover, spine development can be uncoupled from dendrite outgrowth in this reductionist system of purified presynaptic and postsynaptic neurons.

Transient, learning-induced ultrastructural change in spatially-clustered dentate granule cells of the adult rat hippocampus

In semithin, Toluidine Blue-stained plastic coronal sections, we have observed hyperchromatic granule cells in the dorsal crest of the adult rat dentate gyrus following passive avoidance learning. These exhibited a time-dependent, twenty- to thirty-fold increase in their frequency at the 5–7 h post-training time. The hyperchromatic cells formed a rostral-caudal ribbon, 250 μm in diameter and 60 μm in depth, in sections obtained from −2.6 to −4.5 mm with respect to bregma. This was not observed in passive animals or yoked controls. Ultrastructural analysis revealed their cytoplasm and dendrites to be enriched in ribosomes and microtubules, respectively. Dendrites associated with the hyperchromatic cells exhibited a two-fold increase in spine number as compared to those of normochromatic cells in the same region of the dorsal mid-molecular layer. These changes are suggested to be associated with modulation of L1 and neural cell adhesion molecule-mediated neuroplastic change within this discrete post-training period of memory consolidation.

The postnatal development of layer VI pyramidal neurons in the cat's striate cortex, as visualized by intracellular Lucifer yellow injections in aldehyde-fixed tissue

The postnatal development of layer VI pyramidal neurons in the cat's striate cortex has been studied by means of intracellular injections of Lucifer yellow in aldehyde-fixed tissue (LYF technique). It is shown that the LYF technique gives results qualitatively and quantitatively similar to results obtained with other techniques (Golgi, marker-injections in viable tissue). Quantitative analysis demonstrated significant increases in soma diameter, number and length of basal dendrites, length of second order apical dendrites and, in particular, in number of spines/unit dendritic length, during the first postnatal month. Maturation of the basal dendritic tree and increase in number of spines continue in the second postnatal month. At later postnatal times soma diameter and number of spines decrease by about 20%. Dendritic varicosities are most frequent during the first postnatal week, and decrease in number steadily from thereon. The late maturation of layer VI pyramidal neurons suggests that these cells might be affected by early peripheral lesions and/or sensory deprivation to which the striate cortex of the cat has been shown to be most susceptible around the end of the first postnatal month.

A quantitative investigation of spine and dendrite development of neurons in visual cortex (area 17) of Macaca nemestrina monkeys.

In a previous Golgi study (Lund et al., '77) which examined the development of the macaque monkey striate cortex (area 17) it was observed that the dendrites of neurons within the visual cortex show a marked increase in the number of spines on their surface during the first eight weeks of postnatal life. The qualitative observation was also made that all neurons then showed a marked decrease in spine numbers by the time the animal was adult. Since these spines are known to be sites of synaptic contact, changes in their numbers may reflect changes in synapse populations on these neurons. This study examines quantitatively spine frequency and total dendritic development of Golgi impregnated neurons in monkeys ranging in age from 145 days gestation to adult. Four cell types were studied: spiny stellate neurons from laminae IVCalpha and IVCbeta and pyramidal neurons with soma in either lamina IIIB or upper lamina VI. After consideration of possible sources of variation in spine numbers several conclusions are made: (1) Dendritic spine development appears to be a tightly controlled process both in terms of actual numbers of spines on a neuron at any one age and in the rate of change of spine frequency. (2) The neurons populations examined all show a gradual increase in spine numbers up to eight weeks of age. (3) At least two different trends are found in spine population maturation after the eight week point: (A)-the spine population may remain constant at the eight week level for same period of time or (B)-there may be a rapid decline in spine numbers following the eight week peak. (4) There is a suggestion that those neurons associated with direct input, or early stages in the relays, from the parvocellular geniculate laminae show trend B, while those associated with magnocellular input, or later order combined relays within the cortex, show trend A. (5) Different parts of a single pyramidal neuron dendrite may show either trend A or trend B, depending on the lamina location of the dendritic segment considered. (6) All neurons show spine population decreases between nine months of age and adult (5-7 years) suggesting continuing long term maturational changes.