Showing papers on "Developmental plasticity published in 1993"

Postsynaptic control of plasticity in developing somatosensory cortex

Abstract: THE rearrangement of synaptic connections during normal and deprived development is thought to be controlled by correlations in afferent impulse activity1. A favoured model is based on postsynaptic detection of synchronously active afferents; synapses are stabilized when pre- and postsynaptic activity is correlated and weakened or eliminated when their activity is uncorrelated2,3. Most evidence for this model comes from demonstrations that correlated afferent input is necessary for the segregation of eye-dominant inputs in the developing vertebrate visual system1,4,5 and that critical period plasticity of ocular dominance columns in cat visual cortex is disrupted by blockade of postsynaptic transmission6–8. We tested whether the developmental plasticity of somatosensory columns, known as 'barrels', in rodent primary somatosensory cortex (S1)9–13 is similar to that of ocular dominance columns. We report here that the selective disruption of postsynaptic activation in rat S1 by application of a glutamate receptor antagonist inhibits rearrangements in the somatotopic patterning of thalamocorticalafferents induced by manipulations of the sensory periphery during the critical period. These findings show that postsynaptic activation has a prominent role in critical period plasticity in S1 cortex.

Developmental plasticity, genetic variation, and the evolution of andromonoecy in solanum hirtum (solanaceae)

Abstract: Studies of andromonoecious species have shown that sex expression (proportions of hermaphrodite and staminate flowers) is quite variable. It is not known, however, whether this variation is due to variation among individuals for genetically fixed patterns of allocation to staminate and hermaphrodite flowers (population level variation) and/or to developmental plasticity of individuals in a heterogeneous environment (organismal level variation). Distinguishing between these two levels of variation is important for understanding the evolution of andromonoecy. This study investigates levels of variation in sex expression in the andromonoecious Solanum hirtum. Sex expression in this species is shown to be plastic among individuals of the same genotype (organismal level variation) and determined, in part, by the resource status of the individual. Among the genotypes examined there is also genetic variation for developmental plasticity. Thus, developmental plasticity can

Developmental plasticity in cerebellar tactile maps: Fractured maps retain a fractured organization

Abstract: Plasticity following deafferentation has been repeatedly demonstrated in topographic sensory maps in the mammalian brain. In this paper we investigated the developmental plasticity of the fractured somatotopic map found in the tactile regions of the rat cerebellum. At various stages of postnatal development between postnatal days 1 and 30, we cauterized the infraorbital branch of the trigeminal nerve, which innervates the upper lip, furry buccal pad, and vibrissae that are represented within cerebellar folium crus IIa. The organization of the crus IIa map was then examined 2 to 3 months after denervation. We found that tactile receptive fields had reorganized throughout the denervated area but maintained a fractured somatotopy. Comparison of the reorganization in different animals showed that the denervated upper lip region was consistently and predominantly replaced by representation of the upper incisors. Analysis of evoked field potentials revealed an alteration, in denervated animals, of the response of the granule cell layer to brief tactile stimulation. This response in normal animals consists of two components at different latencies. Animals lesioned later in development were less likely to have the short latency component. This result suggests a difference in the developmental sensitivity of different cerebellum-related pathways to nerve lesions.

Neuronal plasticity and function

Abstract: Neuronal plasticity is a key issue in neuroscience. It is defined as the capability of the neuron to adapt to a changing internal or external environment, to previous experience or to trauma. It appears that during all phases of the individual life span in the nervous system, changes take place that relate to development, degeneration, and regeneration. Growth cones are a focus of neuronal plasticity, and current views emphasize the importance of local intracellular [Ca2+] to the control of their function. Hence, outgrowth of neurites from neurons in culture may be manipulated by drugs that affect intracellular Ca2+ homeostasis. In the adult nervous system, much research deals with synaptic plasticity, especially with the activity-dependent changes seen after long-term potentation of hippocampal synapses. As in the growth cone, such changes involve Ca(2+)-dependent pre- and postsynaptic processes, among which is the activation of protein kinase C. During aging, Ca2+ homeostasis may be slightly disturbed over a long period of time that could result in loss of function seen after a short, toxic high level of intracellular [Ca2+]. In this respect, the beneficial effects of chronic treatment with the L-channel Ca(2+)-blocker nimodipine on sensorimotor function of aged rats is discussed.

Glial cell functions and activity-dependent plasticity of the mammalian visual cortex.

Abstract: The presence of highly ordered connectivities is one basic characteristic of the central nervous systems and is believed to be a prerequisite for its proper function. The elaboration of precise, topographic projections has been shown to include two subsequent steps: (1) The formation of exuberant projections with limited topographic accuracy, and (2) the activity-dependent refinement of the appropriate connectivities by synapse elimination and synapse stabilization. Although most current theories on the mechanisms underlying activity-dependent developmental plasticity focus on adaptive changes of the efficacy of synaptic transmission, the present overview deals with possible mechanisms underlying morphologic adaptations in the developing central nervous system. Especially the contribution of glial cells in the activity-dependent selection of neuronal projections in the thalamocortical visual system of higher mammals is elaborated and a unifying hypothesis on the involvement of nonneuronal cells in neuronal plasticity is formulated on the basis of the current knowledge on glial physiology and specific experimental data.

Calcium and neuronal plasticity

Abstract: The proposed involvement of free intracellular calcium concentration ([Ca]i) in neuronal plasticity is examined. While it is generally believed that a rise of [Ca]i is necessary for the triggering of long-term modification of synaptic connections, there are many unresolved issues related to this dogma; it is not entirely clear what is the source of the elevated calcium, how much of a calcium rise is sufficient to produce the synaptic potentiation, where and for how long, and what are the relevant chemical consequences of the transient rise of [Ca]i. It is generally believed that the dendritic spine is the locus of synaptic modification, yet little evidence exists to support this view. High resolution calcium imaging studies may contribute to the clarification of some key issues in the field of neuronal plasticity.