Anna Y. Klintsova

Synaptic regulation of protein synthesis and the fragile X protein.

Protein synthesis occurs in neuronal dendrites, often near synapses. Polyribosomal aggregates often appear in dendritic spines, particularly during development. Polyribosomal aggregates in spines increase during experience-dependent synaptogenesis, e.g., in rats in a complex environment. Some protein synthesis appears to be regulated directly by synaptic activity. We use “synaptoneurosomes,” a preparation highly enriched in pinched-off, resealed presynaptic processes attached to resealed postsynaptic processes that retain normal functions of neurotransmitter release, receptor activation, and various postsynaptic responses including signaling pathways and protein synthesis. We have found that, when synaptoneurosomes are stimulated with glutamate or group I metabotropic glutamate receptor agonists such as dihydroxyphenylglycine, mRNA is rapidly taken up into polyribosomal aggregates, and labeled methionine is incorporated into protein. One of the proteins synthesized is FMRP, the protein that is reduced or absent in fragile X mental retardation syndrome. FMRP has three RNA-binding domains and reportedly binds to a significant number of mRNAs. We have found that dihydroxyphenylglycine-activated protein synthesis in synaptoneurosomes is dramatically reduced in a knockout mouse model of fragile X syndrome, which cannot produce full-length FMRP, suggesting that FMRP is involved in or required for this process. Studies of autopsy samples from patients with fragile X syndrome have indicated that dendritic spines may fail to assume a normal mature size and shape and that there are more spines per unit dendrite length in the patient samples. Similar findings on spine size and shape have come from studies of the knockout mouse. Study of the development of the somatosensory cortical region containing the barrel-like cell arrangements that process whisker information suggests that normal dendritic regression is impaired in the knockout mouse. This finding suggests that FMRP may be required for the normal processes of maturation and elimination to occur in cerebral cortical development.

Synaptic plasticity in cortical systems

Recent studies indicate that synapse addition and/or loss is associated with different types of learning. Other factors influencing synaptogenesis and synapse loss include neurotrophins, hormones, and the induction of long-term potentiation. An emerging view of synaptic plasticity suggests that local neurotrophin action and synaptically associated protein synthesis may promote synaptic remodelling and changes in receptor expression or activation.

Induction of Multiple Synapses by Experience in the Visual Cortex of Adult Rats

This study examined experience effects upon the formation of multiple synaptic contacts among individual dendritic and axonal elements. Axonal boutons and dendritic spines forming contacts with more than one process were assessed within layer IV of the visual cortex in adult rats following 60 days of housing in standard laboratory cages (IC) or in complex environments (EC). Multiple synaptic boutons (MSBs) that formed synaptic contacts with both a dendritic spine and a dendritic shaft were found to be markedly increased in number per neuron in EC rats in comparison to those in IC rats. In contrast, single-synaptic contacts were not increased, indicating that the formation of new single-synaptic boutons is, at most, merely sufficient to replace boutons that may have been recruited into the population of MSBs. This apparent tendency to reutilize presynaptic processes may indicate a constraint upon the formation of neural circuitry and a fundamental form of plastic synaptic change.

The effects of exercise on adolescent hippocampal neurogenesis in a rat model of binge alcohol exposure during the brain growth spurt.

Exposure to alcohol during the brain growth spurt results in impaired cognition and learning in adulthood. This impairment is accompanied by permanent structural changes in the hippocampal formation. Exercise improves performance on hippocampal-dependent learning and memory tasks and increases adult neurogenesis in the rat hippocampal dentate gyrus. The present study examined the effects of wheel running during adolescence on dentate gyrus cell proliferation and neurogenesis after postnatal binge-like alcohol exposure. On postnatal days (PD) 4-9, pups were either intubated with alcohol in a binge-like manner, sham intubated, or reared normally. On PD30-42, all animals were randomly assigned to two adolescent conditions: wheel running or inactive control. Animals were injected with BrdU every day between PD32 and PD42 and perfused on PD42 or PD72. In inactive control animals at both PD42 and PD72, cell proliferation and neurogenesis did not differ between postnatal treatment groups. Wheel running significantly increased the number of BrdU-labeled cells on PD42 in all three postnatal treatments. On PD72, only the normal controls showed significant increases in survival of newly generated cells resulting from the wheel running. These results indicate that adolescent wheel running can induce comparable increases in cell proliferation and neurogenesis in alcohol-exposed and control rats, but the long-term survival of those newly generated cells is impaired relative normal controls. Exercise may provide a means to stimulate neurogenesis, with implications for amelioration of hippocampal-dependent learning impairments associated with alcohol exposure. However, benefits requiring long-lasting survival of the newly generated cells will depend on identifying ways to promote survival.

Postnatal binge-like alcohol exposure decreases dendritic complexity while increasing the density of mature spines in mPFC Layer II/III pyramidal neurons.

Prenatal exposure to alcohol in humans can result in a wide range of deficits collectively referred to as fetal alcohol spectrum disorders. Of these deficits, cognitive impairments are among the most debilitating and long‐lasting. Specifically, cognitive impairments in executive functioning suggest damage to the prefrontal cortex (PFC). Several external stimuli, such as morphine, chronic stress, and maternal stress have been found to alter the dendritic structure of cells within the PFC. In this study, three groups of rat pups were used: intubated with alcohol (5.25 g/kg/day; AE), sham intubated (SI), or suckle controls (SC) on PD 4–9. On PD 26–30 rats were anesthetized, perfused with saline and brains were processed for Golgi‐Cox staining. Basilar dendritic complexity, spine density, and spine phenotypes were evaluated for Layer II/III neurons in the medial PFC. Results indicate that AE rats have an altered basilar dendritic complexity due to a significant decrease in both length and number of intersections in proximity to the neuronal soma. Furthermore, spine density patterns of basilar dendrites remain unchanged while the density of mature vs. immature spines significantly changes. These effects were not seen in the apical dendrites, indicating alcohols influence on different neuronal parts in a single cell. In addition, these results suggest that the innervations of the soma and basilar dendrites by thalamic projections may play a role. Thus, our data demonstrates that postnatal exposure to alcohol produces changes in the neuronal organization of rat adolescent PFC that may affect the performance on prefrontal‐dependant behavioral tasks. Synapse 64:127–135, 2010.

Stability of synaptic plasticity in the adult rat visual cortex induced by complex environment exposure.

Studies have demonstrated the effects of complex environment (EC) housing on brain plasticity both during postnatal development and in adulthood, but it is not clear how long these plastic changes persist nor what happens when environmental exposure is discontinued. Here we examined layer IV in the visual cortex of adult male rats for the: (1) effects of EC housing on synaptic plasticity, and (2) persistence of the synaptic changes after withdrawal from the complex environment. Fifty-eight adult male Long Evans rats were assigned to either: EC, socially paired housing (SC), or individual housing (IC). These rats remained in their assigned environment for 30 days. After 30 days, all rats in SC and some animals from the EC and IC groups were removed and perfused. The remaining animals in EC were then assigned to either remain in EC (ECEC) or be subsequently housed in IC (ECIC) for another 30 days. Similarly, rats in the IC group either remained in IC (ICIC) or were subsequently housed in EC (ICEC) for another 30 days. Electron microscopy results showed that all rats exposed to EC had significantly more synapses/neuron compared to SC, IC, and ICIC animals. Longer exposure to EC (ECEC) did not result in statistically more synapses per neuron; however, decreased neuron volume was seen. EC-induced synaptic changes persisted for an additional 30 days after withdrawal from EC (ECIC) confirming that EC-induced plastic changes occur in the brain regardless of age and indicating that once changes occur they tend to persist.

Postnatal binge-like alcohol exposure reduces spine density without affecting dendritic morphology in rat mPFC.

Among the deficits associated with fetal alcohol syndrome (FAS), cognitive impairments are the most debilitating and permanent. These impairments, including deficits in goal‐directed behavior, attention, temporal planning, and other executive functions, could result from damage to the prefrontal cortex (PFC), an area that has not been studied sufficiently in the context of FAS. Neuronal connectivity in this area, as measured by distribution of dendritic spines and the complexity of dendritic tree structure, can be influenced by exogenous variables other than alcohol, and the neuronal connectivity in other brain regions can be affected by alcohol exposure. The goal of this study was to determine whether binge‐like alcohol exposure on postnatal days (PD) 4–9 affects dendritic spine density and other dendritic tree parameters in mPFC that could possibly underlie functional damage. Rats were intubated with alcohol [5.25 g/kg/day; alcohol exposed (AE)], sham intubated (SI), or remained with the mother (SC, suckle control) on PD 4–9. Animals were sacrificed between PD 26 and PD 30 and brains were processed for Golgi‐Cox staining. Apical dendrite complexity and spine density were evaluated for layer III neurons in the mPFC using NeuroLucida software (MicroBrightField, Inc.). Spine density was significantly decreased in AE animals relative to SI and SC controls, but no differences in dendritic complexity were found across experimental groups. Our findings demonstrate that neonatal alcohol exposure has a persistent effect on the spine density in mPFC that can explain functional deficits in this cortical area. Synapse 62:566–573, 2008.

Therapeutic motor training ameliorates cerebellar effects of postnatal binge alcohol

We have used training on complex motor tasks to ameliorate effect of neonatal alcohol exposure. On postnatal days 4-9, alcohol-exposed (AE) rats were given 4.5 g/kg/day of alcohol by artificial rearing; gastrostomy control (GC) rats were given an isocaloric mixture of maltose/dextrin; suckling control (SC) rats were suckled normally. At 6 months of age, animals from the three groups underwent either rehabilitation training on a series of complex motor tasks, motor conditioning on a flat runway, or an inactive home cage condition. Subsequently, animals were either tested on three tests of balance and coordination, or were used for cerebellar morphology. After rehabilitation, but not after motor conditioning, male and female AE rats exhibited significant improvement in independent tests of motor skills. Using unbiased stereological morphological techniques, rehabilitated SC and AE animals were found to exhibit significantly more parallel fiber synapses per Purkinje cell in the paramedian lobule.

Biological Effects of Long-Duration, High-Field (4 T) MRI on Growth and Development in the Mouse

The effects of long‐duration, high‐field magnetic resonance imaging (MRI) on fetal growth and postnatal development in mice were studied. Seven experimental groups of pregnant ICR mice were exposed for 9 hours on day 9 and/or day 12 post coitus (pc) to magnetic fields (4 T static, 5 T/sec switched gradient, and 0.2 W/kg radiofrequency at 170 MHz) associated with MRI conditions. Two experimental groups (sham and exposure groups) were exposed to a combination of ultrasound (day 9 pc, 3.25 MHz, focused) and MRI‐associated fields (day 12 pc). No statistically significant changes in fetal growth were observed in the animals exposed to only MRI or ultrasound fields. However, in the combined ultrasound and MRI‐exposed group, the fetal weight and crown‐rump length were reduced compared with the sham and cage controls. These results suggest that MRI and ultrasound exposure well in excess of current clinical conditions can exert biological effects if applied at sensitive stages of fetal development. J. Magn. Reson. Imaging 2000;12:140–149.

Brain damage, behavior, rehabilitation, recovery, and brain plasticity

This paper focuses on roles of behavior, both in response to debilitation and in response to therapeutic intervention, in brain and behavioral recovery from brain damage. Recent evidence suggests that the brain damaged animals behavior may often play a greater role in the recovery process than has been evident in previous work. In many cases, what may initially appear to be “spontaneous” brain adaptations to damage may be mediated by behavioral attempts to compensate for the effects of damage. This is seen in changes in the use of forelimbs following unilateral damage of the adult rat sensorimotor forelimb cortex, which have been shown to be essential to the dendritic growth and synaptogenesis that occurs in the contralateral hemisphere. In other cases, behavioral training can allocate new tissue to the functions targeted by training. In the case of global damage resulting from neonatal alchohol exposure, a therapeutic motor training intervention that “forces” the subjects involvement appears more effective than previous interventions that merely allowed the subjects to passively engage in activity. Properties of the brain damage also affect the recovery process (e.g., sensitizing both damaged and undamaged brain regions to the effects of behavioral compensation). While this paper emphasizes plastic mechanisms associated with active learning, we also review the evidence that mere physical exercise may stimulate protective mechanisms that contribute to both recovery from damage and successful aging. Exercise may protect the brain by regulating trophic and angiogenic processes across the life span, and, because of this, excercise may deserve greater attention in integrated treatment approaches in Parkinsons disease. MRDD Research Reviews 1998;4:231–237, 1998.