Showing papers on "Developmental plasticity published in 1998"

Local GABA Circuit Control of Experience-Dependent Plasticity in Developing Visual Cortex

Abstract: Sensory experience in early life shapes the mammalian brain. An impairment in the activity-dependent refinement of functional connections within developing visual cortex was identified here in a mouse model. Gene-targeted disruption of one isoform of glutamic acid decarboxylase prevented the competitive loss of responsiveness to an eye briefly deprived of vision, without affecting cooperative mechanisms of synapse modification in vitro. Selective, use-dependent enhancement of fast intracortical inhibitory transmission with benzodiazepines restored plasticity in vivo, rescuing the genetic defect. Specific networks of inhibitory interneurons intrinsic to visual cortex may detect perturbations in sensory input to drive experience-dependent plasticity during development.

Brain plasticity and behavior.

Abstract: Brain plasticity refers to the brain's ability to change structure and function. Experience is a major stimulant of brain plasticity in animal species as diverse as insects and humans. It is now clear that experience produces multiple, dissociable changes in the brain including increases in dendritic length, increases (or decreases) in spine density, synapse formation, increased glial activity, and altered metabolic activity. These anatomical changes are correlated with behavioral differences between subjects with and without the changes. Experience-dependent changes in neurons are affected by various factors including aging, gonadal hormones, trophic factors, stress, and brain pathology. We discuss the important role that changes in dendritic arborization play in brain plasticity and behavior, and we consider these changes in the context of changing intrinsic circuitry of the cortex in processes such as learning.

Adaptive plasticity in amphibian metamorphosis: response of scaphiopus hammondiitadpoles to habitat desiccation

Abstract: Amphibians exhibit extreme plasticity in the timing of metamorphosis, and several species have been shown to respond to water availability, accelerating metamorphosis when their ponds dry. In this study we analyzed the plasticity of the developmental response to water volume reduction in the western spadefoot toad, Scaphiopus hammondii. Also, we attempted to identify the environmental cue(s) that may signal a desiccating larval habitat. We spawned adults in the laboratory and raised tadpoles in aquaria in a controlled environmental chamber. Water levels of aquaria were gradually reduced by removing water at the rate of 0.5–1 L/d; water in control aquaria was similarly disturbed but not removed. Tadpoles subjected to water volume reduction showed significant acceleration of metamorphosis. The developmental acceleration depended on the rate of reduction of the water level; i.e., tadpoles exhibited a continuum of response. This developmental response did not result from thermal differences between treatments...

Experience-dependent plasticity of adult rat S1 cortex requires local NMDA receptor activation

Abstract: The effect of blocking NMDA glutamate receptors in adult rat cortex on experience-dependent synaptic plasticity of barrel cortex neurons was studied by infusing D-AP5 with an osmotic minipump over barrel cortex for 5 d of novel sensory experience. In acute pilot studies, 500 microM D-AP5 was shown to specifically suppress NMDA receptor (NMDAR)-dependent responses of single cells in cortical layers I-IV. To induce plasticity, all whiskers except D2 and D1 were cut close to the face 1 d after pump insertion. The animals were housed with 2 cage mates before recording 4 d later. This pairing of two whiskers for several days in awake animals generates highly significant biases in responses from D2 layer IV (barrel) cells to the intact D1 whisker as opposed to the cut D3 whisker. D-AP5 completely prevented the D1/D3 surround whisker bias from occurring in the D2 barrel cells (p > 0.6 for D1 > D3, Wilcoxon). Fast-spike and slow-spike barrel cells were affected equally, suggesting parity for inhibitory and excitatory cell plasticity. D-AP5 only partially suppressed the D1/D3 bias in supragranular layers (layers II-III) in the same penetrations (p D3). In control animals, the inactive L-AP5 isomer allowed the bias to develop normally toward the intact surround whisker (p D3) for cells in all layers. We conclude that experience-dependent synaptic plasticity of mature barrel cortex is cortically dependent and that modification of local cortical NMDARs is necessary for its expression.

Homeostasis or synaptic plasticity

Abstract: Learning and memory are dependent on synaptic plasticity, through long-lasting changes in synaptic strengths. The two well-characterized forms of plasticity are long-term potentiation (LTP) and long-term depression (LTD). But one group has now discovered a completely different form of plasticity. Whereas LTP and LTD modulate the strength of synapses in a synapse-specific manner, the new form represents a more general regulation of the total synaptic strength of a neuron. And because it is bidirectional, it could have interesting computational properties.

How much brain does a mind need? Scientific, clinical, and educational implications of ecological plasticity.

Abstract: Plasticity is defined as the brain's capacity to modify its structure or function as a reaction to learning and to brain damage. The term has a variety of meanings: sometimes only microanatomic changes are regarded as neuroplastic1, but some authors use plasticity in its broadest sense to mean the capacity of an organism to adapt, as opposed to being a static, fixed structure2. Although Lashley4 can be seen as one of the research pioneers of plasticity as far back as 1944, neurobiological understanding is fairly recent. The number of plasticity studies is rising exponentially: from seven studies between 1966 and 1974, to 1139 between 1995 and 1997. Mechanisms of plasticity include: an increase in synaptic connections, axon sprouting and thickening, neurochemical moditications, construction of new functional pathways4-8, and neuroprotein synthesis9. These phenomena also occur in normal brain development associated with learning9. However, plasticity need not necessarily imply an anatomical change, as in functional compensation10, 11. In this case an impaired function is compensated for by another system, for example, orientation by a blind man through compensatory auditory attention. Functional repair is a term reserved to indicate restoration of functional neural connections after injury. In this article, the tern plasticity is used in its broadest sense.

Developmental plasticity of respiratory behavior in Lymnaea.

Abstract: The authors investigated the contribution of experience to development and maintenance of pulmonary respiration in Lymnaea stagnalis. Respiration in L. stagnalis is bimodal via both the skin and the lung. Rearing snails from eggs to adulthood while preventing lung respiration (differentially reared snails) showed that L. stagnalis can develop and survive without pulmonary respiration. These snails were able to open and close their pneumostome when given the opportunity as adults. However, quantitative aspects of their respiratory behavior were significantly altered. Prevention of pulmonary respiration in adult, normally reared snails also induced behavioral changes. Comparison of these changes with those in differentially reared snails revealed specific developmental effects, which were reversible. Thus, this is a suitable model system for studying questions related to behavioral plasticity.

Activity-dependent Functional and Developmental Plasticity of Drosophila Neurons

Abstract: Publisher Summary This chapter focuses on the study of the in situ physiological and developmental effects of mutations at the neuronal and circuit levels that essentially underlie behavioral plasticity. It provides the recent developments about neural plasticity at the cellular level in Drosophila. The chapter essentially considers in vivo and in vitro preparations that provide insights into cellular processes of neural plasticity. Reflex circuits, plasticity in identified presynaptic arbors, and developmental and functional plasticity in neuronal cultures are presented in this chapter. As the neurogenetic study of neural plasticity unfolds, the results thus obtained indicate that the effects of mutations on neural plasticity are far from uniform at different locations in the nervous system. With complications of the timing of developmental events, such as critical periods of sensitivity to mutational perturbations and the different cell types involved in the assembly of the functioning nervous system, it becomes important to discern the specific components at the different levels of organization that are relevant to a particular form of neural plasticity, observed in neuronal networks and behavioural expression.

Short-term plasticity in adult somatosensory cortex

Abstract: Publisher Summary The majority of studies demonstrating a functional plasticity in the adult brain have been of the somatosensory system. This chapter focuses on short-term plasticity in adult somatosensory cortex. Studies showing short-term plasticity support the general concept that plasticity may result from the unmasking of normally unexpressed inputs to a cortical locus. Despite the clear demonstration of such unmasking, an explanation for the way this occurs is not immediately apparent. The basis of the problem is that a peripheral denervation of a small body part leads to expansion of the receptive field of some cortical neurons onto adjacent body areas but does not directly affect the input from these areas. The areas around a normal receptive field can contribute inhibitory inputs and these have the potential to mask weaker excitatory inputs. Studies on neuronal plasticity have emphasized excitatory synaptic plasticity and much effort has been aimed at elucidating the changes in efficacy of glutamatergic synapses.

Plasticity and growth factors in injury response

Abstract: The central nervous system (CNS) possesses a well-known capacity for circuitry rearrangement, or “plasticity,” which is maintained throughout life. Two well-studied categories of CNS plasticity are the circuitry rearrangement which occurs in response to injury and that which occurs in response to normal environmental stimuli. In an injury response, such as that which follows partial denervation of the hippocampus by unilateral removal of the entorhinal cortex, undamaged fibers in the denervated zone sprout and form new connections to replace lost synapses. In addition, rearrangement of circuitry also takes place in nondenervated zones which are functionally associated with the denervated circuitry. These observations indicate that the CNS is capable of major remodeling of neuronal circuitry, both in response to an injury as well as in the absence of a direct insult. Importantly, such plasticity reactions after injury appear to mediate recovery of lost function in hippocampal-dependent learning. Plasticity can also occur in response to relatively subtle stimuli, such as are found in an enriched environment or with exercise. Even tightly structured repetitive exercise, such as wheel-running by rats, drives plasticity responses in brain regions such as the hippocampus, cortex, and cerebellum. Plasticity in response to injury and environmentally driven plasticity share similar molecular features, such as activation of growth factors, suggesting that some molecular events and mechanisms driving circuitry remodeling are common to all forms of plasticity. In this review, these two categories of CNS plasticity are discussed, using in vivo models to illustrate remodeling occurring after damage, as well as environmentally driven plasticity. MRDD Research Reviews 1998; 4:223–230 © 1998 Wiley-Liss, Inc.

Neuroplasticity and psychiatry

Abstract: Objective: There is increasing concern that the course of psychiatric disorders may be affected by parameters such as the duration and intensity of symptoms of initial episodes of illness. As this indicates that abnormal function produces long-term changes within the brain, a review of the neuroscience literature regarding neuroplasticity is warranted.Method: This article is a selective review, focusing in particular on results obtained from physiological experiments assessing plasticity within the mammalian neocortex. The possible relevance of results to psychiatry is discussed.Results: While the most dramatic examples of neuroplasticity occur during a critical period of neural development, neuroplasticity can also occur in adult neocortex. Neuroplasticity appears to be activity-dependent: synaptic pathways that are intensively used may become strengthened, and conversely, there may be depression of transmission in infrequently used pathways.Conclusions: Results from neurophysiological experiments lend s...

Olfactory development in invertebrates. On the scent of central developmental issues.

Abstract: Invertebrate olfactory systems offer many advantages for cellular and molecular studies of development and for functional studies of developmental plasticity. For example, nematodes have chemical senses that can be studied using genetic approaches. Arthropods, which include insects and crustacea, have the advantages that certain neurons can be reliably identified from one individual to another, and that olfactory receptor neurons are located on peripheral appendages and thus can be manipulated independently of their brain targets even very early in development. Among the insects, olfactory learning can be displayed and used as a basis for studying olfactory plasticity in bees; genes are especially tractable in flies; individual growth cones can be visualized in the grasshopper embryo; and receptor neurons and glomeruli of known olfactory specificity and behavioral significance can be followed during early development in moths. In addition, many insect nervous systems are amenable to organ culture and dissociated-cell culture, opening the door to experimental studies of cellular interactions that can not be performed in situ. Recent research in the moth Manduca sexta attempts to identify the nature of the interactions between olfactory sensory axons, olfactory neurons of the brain, and glial cells in the creation of the array of glomeruli that underlie olfaction in the adult. Results indicate that timing of the ingrowth of olfactory receptor axons is critical for normal glomerulus development, that a subset of axons expresses a fasciclin II-like molecule that may play a role in guidance of their growth, and that glial cells must surround developing glomeruli in order to stabilize the 'protoglomerular' template made by receptor axon terminals. Moreover, glial cells are dye-coupled to each other early in glomerulus development and gradually become uncoupled. Electrical activity in neurons is not necessary for glomerulus formation; and some intercellular interactions, perhaps involving soluble factors, appear to involve tyrosine phosphorylation. In sum, a detailed picture is emerging of the cellular interactions that lead to the formation of glomeruli.

Developmental neurobiology: New concepts in learning, memory, and neuronal development

Abstract: Increasing research efforts and rapidly expanding knowledge in the neuroscientific foundations of learning, memory, and developmental disabilities have provided insights into the normal development and plasticity of neuronal circuits. Likewise, the neurobiologic and molecular genetic substrates of developmental disabilities and mental retardation syndromes are unfolding and leading to potential manipulations of these disorders in children with developmental disabilities. This review highlights the mechanisms of synaptic plasticity, long-term potentiation, and molecular mechanisms of memory. Some mental retardation syndromes due to abnormal genetic regulation are mentioned. MRDD Research Reviews 1998;4:20–25. © 1998 Wiley-Liss, Inc.