Showing papers on "Developmental plasticity published in 1986"

The role of growth factors in neuronal development and plasticity.

Abstract: The role of growth factors in the development of the nervous system, as well as in injury-induced plasticity, is of great interest. A neuronal growth factor is any substance that influences the growth of neurons, but two general classes of factors exist: diffusible substances and substrate-bound factors. Growth factors may affect neuronal survival as well as the extent and rate of neurite outgrowth in vitro. Although progress is slowly being made in the identification and characterization of putative growth factors, nerve growth factor (NGF) is the only identified molecule that clearly influences neuronal growth in vivo. Furthermore, although there are many examples of neuronal plasticity following injury, the role of growth factors in such rearrangements remains to be established. However, one model of collateral sprouting of axons from the peripheral nervous system (PNS) into the central nervous system (CNS) appears to involve the action of a growth factor with properties similar to NGF. The identification of specific molecules that affect neuronal growth should lead to an understanding of the etiology of degenerative neurological diseases such as Alzheimer's disease and, hopefully, to rational therapeutic approaches.

14 – Sex Differences in Developmental Plasticity of Behavior and the Brain

Abstract: Publisher Summary This chapter reviews the literature on sex differences in behavioral vulnerability and discusses possible mechanisms for this phenomenon, including differences in neural responses to the environment. Considerable evidence indicates that among humans, males are more vulnerable than females during development. Males have a higher incidence of autism, dyslexia, stuttering, childhood seizures, cerebral palsy, and hyperactivity. Males are less likely to cope successfully with major stressors during childhood, such as separation from the primary caretaker, parental illness or discord, or absence of the father. Thus, males appear to be more vulnerable and variable sex during development, while females appear to be more buffered against extremes. At present, the causes for male variability are not known. The developmental surge in androgens represents the major difference between the sexes during development and is probably involved at least indirectly. While human sex differences are an interaction of biological and cultural influences, the sex differences in animals are usually viewed as relatively pure manifestations of biological factors. However, Moore and Morelli have found more maternal licking of the anogenital regions of male than of female rat pups. This differential treatment of male and female offspring may be considered an analog to sex differences in parental expectations in humans.

Plasticity in morphogenetic expression in plant.

Abstract: This article discusses the plasticity of morphogenetic programmes in plants. It outlines the numerous ways in which the flowering programme can be accelerated or modified into partial flower formation and describes the differentiation of naked ovules on anthers in intact plants. The generation of embryos and flowers from cultured cells is then described and some of the properties of hypohaploids outlined. It is concluded that in vitro culture provides a useful facility for manipulating plant development and that the interaction between the nucleus and the cytoplasm may exemplify and explain the process of developmental plasticity.

Modeling and simulation II: specificity models for visual cortex development

Abstract: : Observations of developmental plasticity in the visual cortex of cats have inspired a number of theoretical models. These models attempt to mimic the development of response specificity. We review the assumptions upon which one can build models of the visual cortex. The anatomical layout usually consists of excitatory afferents from the lateral geniculate nucleus with intracortical inhibition among a population of cells. The degrees of convergence of the afference and divergence of the inhibition are some of the more important considerations which distinguish different models. Synaptic modifications rules lie at the heart of these theories. Modification is usually of the Hebbiam type with synaptic strengths changing as some function of the product of pre-and postsynaptic activity. A successful model not only alters synapses to generate specificity in single units, but simultaneously produces a cortical network which is stable and which mimics the behavior of experimental population.

The Role of Hormone-Stimulated cAMP Metabolism in Visual Cortical Plasticity

Abstract: Our interest has been to understand the biochemical basis of the developmental plasticity of vision. We have chosen to study the visual cortex of cats, because it is one of the systems that is most thoroughly characterized electrophysiologically and behaviorally. The critical period (CP), during which visual experience permanently molds many aspects of visual function (Hubel & Wiesel, 1970), spans the first through the fourth month in cats and about the 4.5th month through the third year in humans (Banks et. al., 1975). The receptive field properties which are susceptible to changes include acuity, orientation tuning, directional tuning and ocular dominance (cf. review by Movshon & Van Sluyters, 1981). For cats, the receptive field properties are most modifiable by visual deprivation at the onset of the CP, which is around the end of the first postnatal month (Hubel & Wiesel, 1970). Under normal rearing conditions, this sensitivity subsequently declines towards a minimal level at around the fourth month. In contrast, results of recent experiments suggest that the decline in visual cortical plasticity beyond the first month can be prevented for as long as neuronal activity is suppressed by dark rearing (Cynader & Mitchell, 1980; Mower et al, 1981). Further, once triggered for the onset of the CP by light, plasticity declines with a predetermined time course, irrespective of the subsequent visual environment (Mower et al, 1983). Thus, the dark rearing procedure offers a useful paradigm in which the progression of events associated with the decline of plasticity during the CP can be temporally separated from the progression of the other events that are associated with the general growth of the animal.

Developmental Aspects of Oligodendrocyte Structure and Function

Abstract: An understanding of the development and function of oligodendrocytes is a central issue in assessing the contribution of these cells to the pathology of multiple sclerosis. In particular, repair processes, especially those which relate to neuron-glia and possibly also to astrocyte- oligodendrocyte interactions, have to be considered in terms of developmental plasticity. In addition, the characterization of oligodendrocyte-specific cell surface antigens is expected to elucidate the possible antigenic targets of immune mechanisms leading to the elimination of oligodendrocytes in the disease. We have started to characterize cell surface markers recognized by monoclonal antibodies to define developmental stage- and subclass-specific oligodendrocyte populations and probe for their relation to oligodendrocyte differentiation and interactions with other neural cell types. Furthermore, we have investigated the membrane properties of cultured oligodendrocytes using electrophysiological methods and have compared these to the other macroglial population, the astrocyte.