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PubMed1996

Gonadal steroids and astroglial plasticity.

1. Recent evidence indicates that astroglia participate in the metabolism of gonadal hormones, in the synthesis of neurosteroids, and in the plastic responses of neurons to gonadal steroids. The role of astroglia on plastic responses of neural tissue to gonadal hormones and neurosteroids is examined in this review. 2. Gonadal steroids and neurosteroids promote astroglia plasticity in several areas of the central nervous system, including the hypothalamus, the striatum, and the hippocampus. 3. Gonadal steroids and neurosteroids modulate astroglia proliferation and the formation of reactive astroglia after brain injury. 4. Astroglia is a source of trophic factors that may mediate effects of gonadal steroids on neural tissue. 5. Astroglia is involved in the promotion of synaptic plastic changes by gonadal hormones. 6. The effect of gonadal hormones on astroglial plasticity is dependent on specific membrane interactions with neurons and on the expression of the embryonic highly polysialylated isoform of the neural cell adhesion molecule on neuronal membranes. 7. In conclusion, coordinated responses of neurons and astroglia appear to be involved in the modulation of neural function and response to injury by gonadal hormones and neurosteroids.

Animals↗
PubMedDate not supplied

Cholinoreceptor neurons of the snail: identification, plasticity, and its regulation by opioids and second messengers.

A review of the author's own data on the cholinoreceptors of identified neurons of the snail and the regulation of their plasticity. The following sections are presented: the identification of the cholinoreceptors; the coupling of the cholinoreceptors with ion channels; the identification of the opioid receptors; the modulation by opioids of the activity of the cholinoreceptors; the plasticity of the cholinoreceptors; the regulation of the plasticity of the cholinoreceptors by opioids; the regulation of the plasticity of the cholinoreceptors by second messengers; the second messengers involved in the regulation of the plasticity of the cholinoreceptors by the opiate kappa agonist, bremazocine.

Animals↗
PubMedDate not supplied

The effects of the dynamic state of the cytoskeleton on neuronal plasticity.

The effects of degrading and stabilizing microtubules and microfilaments on the formation of plastic reactions were studied in isolated nerve cells from the mollusk Lymnaea stagnalis. Degradation of the cytoskeleton affected the performance, retention, and repeated acquisition of plastic reactions. Stabilization of microtubules led to the appearance of a relationship between the dynamics of the development and retention of plastic reactions and the series of stimulation. Stabilization of microfilaments led to transient plastic reaction, along with long-term reactions. These results show that rearrangements of the cytoskeleton have a key role in the processes of neuronal plasticity.

Actin Cytoskeleton↗
PubMed2005

Do plants and animals differ in phenotypic plasticity?

This paper compares the flexibility in the nexus between phenotype and genotype in plants and animals. These taxa although considered to be fundamentally different are found to be surprisingly similar in the mechanisms used to achieve plasticity. Although non-cognitive behaviour occurs in plants, its range is limited, while morphological and developmental plasticity also occur to a considerable extent in animals. Yet both plants and animals are subject to unique constraints and thus need to find unique solutions to functional problems. A true comparison between the plant and animal phenotype would be a comparison between plants and sessile photosynthesizing colonial invertebrates. Such comparisons are lacking. However, they would provide important insights into the adaptive significance of plasticity in these groups. It is also suggested that a comparison of inflexible traits in these groups would provide an understanding of the constraints, as well as the costs and benefits,of a plastic versus non-plastic phenotype in plants and animals.

Adaptation, Physiological↗
PubMed1991

Growth-regulated proteins and neuronal plasticity. A commentary.

Growth-regulated proteins (GRPs) of the neuron are synthesized during outgrowth and regeneration at an increased rate and enriched in nerve growth cones. Therefore, they can be used to some degree as markers of neurite growth. However, these proteins are not unique to the growing neuron, and their properties are not known sufficiently to assign them a functional and/or causal role in the mechanisms of outgrowth. During synaptogenesis, GRPs decrease in abundance, and growth cone functions of motility and organelle assembly are being replaced by junctional contact and transmitter release. However, there is a stage during which growth cone and synaptic properties overlap to some degree. We propose that it is this overlap and its continuation that allow for synaptic plasticity in developing and adult nervous systems. We also propose a hypothesis involving (a) trophic factor(s) that might explain the regulation of synaptic sizes and collateral sprouting. Some GRPs, especially GAP43/B50/pp46/F1, are more prominent in adult brain regions of high plasticity, and they undergo change, such as phosphorylation, during long-term potentiation (LTP). Without precise functional knowledge of GRPs, it is impossible to use changes in such proteins to explain the plasticity mechanism. However, changes in these "growth markers" are likely to be an indication of sprouting activity, which would explain well the various phenomena associated with plasticity and learning in the adult. Thus, plasticity and memory may be viewed as a continuation of the developmental process into adulthood.

Animals↗
PubMed2002

Cytokine modulation of murine stem cell engraftment: the role of adherence to plastic surfaces.

Murine marrow stem cells acquire an engraftment defect when cultured for 48 hours in cytokines, whereas the number of progenitor cells expands. Stem or progenitor cells have been noted to adhere to various surfaces, including plastic. Despite vigorous harvesting by cell scraping, the possibility existed that cytokines might induce selective adhesion of the rare engraftable stem cells to plastic surfaces. We have evaluated whether loss of engraftability by cytokine-treated marrow cells could be due to adhesion to plastic culture vessels. BALB/c marrow cells were cultured in the presence of interleukin 3 (IL-3), IL-6, IL-11, and steel factor for 48 hours in plastic tissue culture flasks from which cells were harvested by standard scraping and washing or after 5 or 10 minutes of additional exposure to trypsin (0.25%), or they were cultured with the same cytokines in nonadherent polytetrafluoroethylene (Teflon) culture bottles. Harvested cultured or fresh-starting male cells were then engrafted into nonirradiated female hosts or were placed in competition with fresh female BALB/c marrow in lethally irradiated female hosts. Defective engraftment was seen in nonmyeloablated or irradiated female hosts 7 to 24 weeks after marrow infusion in all cultured cell groups. These data indicate that cytokine-treated engraftable stem cells do not show significant adherence to plastic surfaces.

Animals↗
PubMed1990

Loss of resistance technique for locating the epidural space: evaluation of glass and plastic syringes.

Location of the epidural space in epidural anaesthesia usually involves the measurement of loss of resistance using glass or plastic syringes. In the present study two varieties of glass syringe and one plastic type were evaluated to determine the resistive forces associated with plunger movement. The mean static (fs) and dynamic (fd) forces for polished glass syringes having a ground plunger only were fs = 0.47 X 10(-3) +/- 0.22 X 10(-3) N and fd = 0.37 X 10(-3) +/- 0.19 X 10(-3) N and for polished glass syringes having a ground barrel and plunger were fs = 0.43 X 10(-3) +/- 0.16 X 10(-3) N and fd = 0.38 X 10(-3) +/- 0.15 X 10(-3) N. Each of these values was significantly lower (P less than 0.5) than those for plastic syringes fs = 2.22 X 10(-3) +/- 0.48 X 10(-3) N and fd = 1.46 X 10(-3) +/- 0.37 X 10(-3) N. It is concluded that glass syringes are favoured over plastic for locating the epidural space because frictional forces developed with glass syringes were significantly lower than with plastic.

Anesthesia, Epidural↗
PubMed2000

[Gene therapy possibilities in plastic surgery].

Advances in gene technologies have meanwhile reached plastic surgery. Important contributions in this field (which are not all included in the paper) come not only from plastic surgeons, but also from neighboring specialities like dermatology, trauma surgery, orthopedics and vascular surgery. The uniting principle for all this work is improving wound healing and reconstructing tissue defects taking into consideration functional and aesthetic aspects. Gene-therapy is gaining further importance in the clinical field of plastic surgery. In this regard, every clinician has to be aware of the fact that progress in experimental and experimental-clinical work will be achieved only with the help of basic science. On the other hand, basic science needs the clinical input to get relevant patient-oriented studies started. Further intensive cooperation between clinicians and basic scientists is therefore mandatory. In plastic surgery, 2 years ago we founded a forum called ECSAPS (European Conference of Scientists and Plastic Surgeons), which takes place in European city every year.

Animals↗
PubMed2004

Chronic treatment with milnacipran reverses the impairment of synaptic plasticity induced by conditioned fear stress.

RATIONALE: Recent studies have focused on neural plasticity at the cellular and molecular levels in the etiology and treatment of stress-related disorders; however, there are no reports concerning modulation of synaptic plasticity in the hippocampus underlying therapeutic effects of antidepressants and/or anxiolytics. OBJECTIVES: To elucidate the functional interaction between the stress-induced alteration of synaptic plasticity and therapeutic effects, we examined the anxiolytic mechanism(s) of milnacipran, focusing on modulation of long-term potentiation (LTP) in the hippocampal CA1 field. METHODS: Rats that received footshock stimulation five times (intensity, 0.5 mA; duration, 2 s; shock interval, 30 s) for 5 days were treated with milnacipran (30 mg kg(-1), p.o.) or vehicle for 14 days. On the 15th day, rats were subjected to conditioned fear stress (CFS) to evaluate freezing behavior. Separate from the behavioral study, electrophysiological approach was performed to evaluate the synaptic efficacy under anesthesia. RESULTS: Exposure to CFS suppressed LTP in the CA1 field. Chronic treatment with milnacipran (30 mg kg(-1), i.p. after 30 mg kg(-1) day(-1), p.o. x14 days), but not acute treatment (30 mg kg(-1), i.p. after vehicle 5 ml kg(-1) day(-1), p.o. x14 days), reduced freezing behavior and reversed the impairment of LTP induced by CFS. CONCLUSION: The present data suggest that a correspondence exists between fear-related behavior and synaptic plasticity in the hippocampus. In other words, anxiolytic mechanism(s) of chronic treatment with milnacipran may be explained by reversal effects on the psychological stress-induced impairment of synaptic plasticity.

Animals↗
PubMed2002

Transcranial magnetic stimulation: new insights into representational cortical plasticity.

In the last decade, transcranial magnetic stimulation (TMS) has been used increasingly as a tool to explore the mechanisms and consequences of cortical plasticity in the intact human cortex. Because the spatial accuracy of the technique is limited, we refer to this as plasticity at a regional level. Currently, TMS is used to explore regional reorganization in three different ways. First, it can map changes in the pattern of connectivity within and between different cortical areas or their spinal projections. Important examples of this approach can be found in the work on motor cortex representations following a variety of interventions such as immobilization, skill acquisition, or stroke. Second, TMS can be used to investigate the behavioural relevance of these changes. By applying TMS in its "virtual lesion" mode, it is possible to interfere with cortical function and ask whether plastic reorganization within a distinct cortical area improves function. Third, TMS can be used to promote changes in cortical function. This is achieved by using repetitive TMS (rTMS) to induce short-term functional reorganization in the human cortex. The magnitude and the direction of rTMS-induced plasticity depend on extrinsic factors (i.e. the variables of stimulation such as intensity, frequency, and total number of stimuli) and intrinsic factors (i.e. the functional state of the cortex targeted by rTMS). Since conditioning effects of rTMS are not limited to the stimulated cortex but give rise to functional changes in interconnected cortical areas, rTMS is a suitable tool to investigate plasticity within a distributed functional network. Indeed, the lasting effects of rTMS offer new possibilities to study dynamic aspects of the pathophysiology of a variety of diseases and may have therapeutic potential in some neuropsychiatric disorders.

Animals↗
PubMed2004

Background sounds contribute to spectrotemporal plasticity in primary auditory cortex.

The mammalian auditory system evolved to extract meaningful information from complex acoustic environments. Spectrotemporal selectivity of auditory neurons provides a potential mechanism to represent natural sounds. Experience-dependent plasticity mechanisms can remodel the spectrotemporal selectivity of neurons in primary auditory cortex (A1). Electrical stimulation of the cholinergic nucleus basalis (NB) enables plasticity in A1 that parallels natural learning and is specific to acoustic features associated with NB activity. In this study, we used NB stimulation to explore how cortical networks reorganize after experience with frequency-modulated (FM) sweeps, and how background stimuli contribute to spectrotemporal plasticity in rat auditory cortex. Pairing an 8-4 kHz FM sweep with NB stimulation 300 times per day for 20 days decreased tone thresholds, frequency selectivity, and response latency of A1 neurons in the region of the tonotopic map activated by the sound. In an attempt to modify neuronal response properties across all of A1 the same NB activation was paired in a second group of rats with five downward FM sweeps, each spanning a different octave. No changes in FM selectivity or receptive field (RF) structure were observed when the neural activation was distributed across the cortical surface. However, the addition of unpaired background sweeps of different rates or direction was sufficient to alter RF characteristics across the tonotopic map in a third group of rats. These results extend earlier observations that cortical neurons can develop stimulus specific plasticity and indicate that background conditions can strongly influence cortical plasticity.

Acoustic Stimulation↗
PubMed2005

Electrophysiological correlates of neural plasticity compensating for ischemia-induced damage in the hippocampus.

Injury to the brain often results in loss of synapses or cell death in the damaged area. Subsequent to the injury, the areas that are not directly affected often exhibit enhanced neuronal plasticity. Although there are many reports of morphological changes resulting from such plasticity, their functional consequences are poorly understood. In this study we examined electrophysiological changes associated with ischemia-induced neurogenesis in the hippocampus, a brain region that is particularly vulnerable but also exceptionally plastic. Transient global ischemia was induced in Sprague-Dawley rats by occlusion of both carotid arteries and a reduction in blood pressure for 12 min. The procedure resulted in delayed cell death in the CA1 field of the hippocampus while the dentate gyrus (DG) was spared. To assess neurogenesis and synaptic changes in parallel we used both hemispheres from each animal. One side was used for immunohistochemistry and the other for in vitro electrophysiological experiments in brain slices. Synaptic field responses and synaptic plasticity (LTP) in perforant path within the DG were reduced by 50% at 10 days after the ischemic injury but recovered at 35 days. Synaptic responses in non-neurogenic CA1 were abolished in parallel with cell death and did not recover. Gamma irradiation applied focally to the head selectively prevented neurogenesis and the synaptic recovery in the DG. These experiments reveal electrophysiological changes associated with reactive neural plasticity in the hippocampus.

Animals↗
PubMed2006

Transcranial magnetic stimulation and the motor learning-associated cortical plasticity.

It has been well established that repetitive motor performance and skill learning alter the functional organization of human corticomotoneuronal system. Over the past decade, transcranial magnetic stimulation (TMS) has helped to demonstrate motor practice and learning-related changes in corticomotoneuronal excitability and representational plasticity. It has also provided some insights into the mechanisms underlying such plasticity. TMS-derived indices show that motor practice, skill acquisition and learning are associated with an increase in cortical excitability and a modulation of intracortical inhibition partly related to the amount of GABA-related inhibition. It has been suggested that these changes in excitability might be related to learning and motor memory formation in the motor cortex. However, it has proved difficult to relate different aspects of TMS-derived representational plasticity with specific behavioral outcomes. A better understanding of the relationship between TMS measurements of practice-related cortical plasticity and underlying mechanisms, in the context of associated changes in behavior, will facilitate the development of techniques and protocols that will allow predictable modulation of cortical plasticity in health and disease.

Animals↗
PubMed2006

Rapid plasticity follows whisker pairing in barrel cortex of the awake rat.

Synaptic plasticity can be induced easily throughout life in the rodent somatic sensory cortex. Trimming all but two whiskers on one side of an adult rat's face, called 'whisker pairing', causes the active (intact) whiskers to develop a stronger drive on cortical cells in their respective barrel columns, while inactive (trimmed) whisker efficacy is down-regulated. To date, this type of activity-dependent plasticity has been induced by trimming all but two whiskers, letting the rats explore their environment from 1 day to 1 month, after which cortical responses were analyzed physiologically under anesthesia. Such studies have enhanced our understanding of cortical plasticity, but the anesthesia complicates the examination of changes that occur in the first few hours after whisker trimming. Here we assayed the short-term changes that occur in alert, active animals over a period of hours after whisker trimming. The magnitude of barrel cortex evoked responses was measured in response to stimulation of the cut and paired whiskers of rats under several conditions: (a) whisking in air (control), (b) active whisking of an object by the rat, and (c) epochs of passive whisker stimulation to identify the onset of whisker pairing plasticity changes in cortex. The main difference between whisking in air without contact and passive whisker stimulation is that the former condition induces an increased response to stimulation of inactive cut whiskers, while the latter condition increases the responses to the stimulated whiskers. The results support the conclusion that whisker pairing plasticity in barrel cortex occurs within 4 h after whisker trimming in an awake, alert animal.

Animals↗
PubMed2004

Phylogenetic, ontogenetic and adult adaptive plasticity of rhythmic neural networks: a common neuromodulatory mechanism?

Neuromodulatory inputs are known to play a major role in the adaptive plasticity of rhythmic neural networks in adult animals. Using the crustacean stomatogastric nervous system, we have investigated the role of modulatory inputs in the development of rhythmic neural networks. We found that the same neuronal population is organised into a single network in the embryo, as opposed to the two networks present in the adult. However, these adult networks pre-exist in the embryo and can be unmasked by specific alterations of the neuromodulatory environment. Similarly, adult networks may switch back to the embryonic phenotype by manipulating neuromodulatory inputs. During development, we found that the early established neuromodulatory population display alteration in expressed neurotransmitter phenotypes, and that although the population of modulatory neurones is established early, with morphology and projection pattern similar to adult ones, their neurotransmitter phenotype may appear gradually. Therefore the abrupt switch from embryonic to adult network expression occurring at metamorphosis may be due to network reconfiguration in response to changes in modulatory input, as found in adult adaptive plasticity. Strikingly, related crustacean species express different motor outputs using the same basic network circuitry, due to species-specific alteration in neuromodulatory substances within homologous projecting neurones. Therefore we propose that alterations within neuromodulatory systems to a given rhythmic neural network displaying the same basic circuitry may account for the generation of different motor outputs throughout development (ontogenetic plasticity), adulthood (adaptive plasticity) and evolution (phylogenetic plasticity).

Animals↗
PubMed2002

Converging evidence for a simplified biophysical model of synaptic plasticity.

Different mechanisms that could form the molecular basis for bi-directional synaptic plasticity have been identified experimentally and corresponding biophysical models can be constructed. However, such models are complex and therefore it is hard to deduce their consequences to compare them to existing abstract models of synaptic plasticity. In this paper we examine two such models: a phenomenological one inspired by the phenomena of AMPA receptor insertion, and a more complex biophysical model based on the phenomena of AMPA receptor phosphorylation. We show that under certain approximations both these models can be mapped on to an equivalent, calcium-dependent, differential equation. Intracellular calcium concentration varies locally in each postsynaptic compartment, thus the plasticity rule we extract is a single-synapse rule. We convert this single synapse plasticity equation to a multi-synapse rule by incorporating a model of the NMDA receptor. Finally we suggest a mathematical embodiment of metaplasticity, which is consistent with observations on NMDA receptor properties and dependence on cellular activity. These results, in combination with some of our previous results, produce converging evidence for the calcium control hypothesis including a dependence of synaptic plasticity on the level of intercellular calcium as well as on the temporal pattern of calcium transients.

Animals↗
PubMed1982

Response plasticity of single neurons in rabbit auditory association cortex during tone-signalled learning.

Single unit activity was monitored in rabbit auditory association cortex (AC) throughout the acquisition of classically conditioned, nictitating-membrane response. The CS was a tone burst at the characteristic frequency of each neuron. Rabbits which were pseudoconditioned or received conditioning trials but did not learn the response served as control groups. Significant alterations in CS-evoked firing rate were termed 'response plasticity'. Neurons in conditioned animals were more than twice as likely to show response plasticity during the 250 ms CS-US interval than neurons in control animals. Such differences were evident both in the early (0-60 ms) and late (60-250 ms) portions of the CS-US interval. Most early changes appeared at 21-40 ms after CS onset. Response plasticity was most commonly manifested as an increase or decrease in CS-evoked firing rate with little change in the response pattern (PST histogram shape). In some neurons, subcomponents of response patterns (early or late portions of the CS-US interval) were observed to change independently of each other. Spontaneous rate and UCS-evoked activity were not modified with learning. Early in training (transition trials), neural activity evoked by the tone CS in conditioned animals was not different from that in controls. Response plasticity was most pronounced after the CR was first learned (trained trials) and stabilized once the Cr was well established (overtrained trials). Recording sites of neurons showing conditioning-related response plasticity were co-extensive with those of cells that did not.

Animals↗
PubMed1994

Neurotransmitter receptor plasticity in aging.

Neurotransmitter receptor plasticity is an important part of the compensatory processes by which the central nervous system adapts to pathological insult, long-term exposure to drugs or neuronal loss with advanced age. Receptor plasticity can be manifest as changes in the number of receptors (i.e., up- or down-regulation), changes in expression of mRNA for discrete receptor proteins, or alterations in receptor coupling to signal transduction systems. Evidence exists for impaired plasticity of neurons in the aged brain, which results in decreased ability to adjust to changes in their environment. However, such data are highly dependent on the neurotransmitter examined, the stimulus for receptor regulation and the animal model chosen for study. For example, senescent rats show an age-related impairment of muscarinic receptor up- or down-regulation after long-term exposure to cholinergic drugs. Thus, young rats exposed to chronic (three weeks) intracerebroventricular infusions of methylatropine or oxotremorine exhibit compensatory changes in the density of muscarinic receptors in frontal cortex and hypothalamus. In contrast, 3H-QNB binding is unaltered in the same brain regions of identically treated senescent rats. Similar observations of impaired muscarinic receptor plasticity in senescent animals have been confirmed by other investigators. Age-related differences in coupling of brain muscarinic receptors to G-proteins and in muscarinic receptor-stimulated phosphoinositide hydrolysis have also been reported. Interestingly, neuropeptides such as neurotensin, cholecystokinin and VIP can potentiate carbachol-stimulated phosphoinositide hydrolysis in frontal cortex of both young and aged rats. This adds another level at which cholinergic neurotransmission may be modulated in senescent animals. Potential age-related differences in the effects of chronic drug treatments or experimental brain lesions on muscarinic receptor coupling to second messenger systems or on expression of mRNA for particular muscarinic receptors are currently unknown. Hence, it is possible that senescent animals may show additional deficiencies in plasticity of muscarinic receptor mediated signal transduction or expression of muscarinic receptors subtypes.

Aging↗