Showing papers on "Developmental plasticity published in 1994"

Patterns of form and function in developing hearts: contributions from non-mammalian vertebrates.

Abstract: Although most research on developmental cardiovascular physiology has focused on the bird embryo as a model for emulating developmental processes in mammals, there are increasingly compelling reasons to expand research to a variety of lower vertebrate systems. These reasons include circumventing inherent limitations of the avian embryo and identifying general vertebrate developmental patterns in the cardiovascular system. In this paper, we first review data from hemodynamic studies on amphibians and birds (and what little exists from fish and reptiles), to provide a background against which lower vertebrate development can be examined. We then describe non-mammalian, non-avian paradigms for studying developmental patterns of vertebrate hearts. Developmental spects of cardiovascular performance, especially heart rate, blood pressure and cardiac output and how they change with ontogeny, are described for several amphibians and a few reptiles, identifying, where possible, processes in common with birds and mammals. Finally, we indicate productive areas for future research with lower vertebrate cardiovascular systems, such as establishing "critical windows" for cardiovascular physiology during development, and determining the extent of developmental plasticity at the level of organ system physiology.

The flexible fly: experience-dependent development of complex behaviors in Drosophila melanogaster.

Abstract: We demonstrate that Drosophila melanogaster provides a rich model system for studying behavioral development. Two additions to the many well-known advantages of this species are exploited here. First, as in mammals and higher vertebrates, early experience affects behavioral development of Drosophila. Second, the affected behaviors are complex and yet readily studied in the laboratory. Thus, Drosophila can be used to study the developmental mechanisms by which organisms can optimize their behavioral repertoires to enhance their chances for survival. Evidence that early experience affects female responsiveness to courting males is reviewed; in each case, experience modifies responses to behavioral targets. Our results demonstrate that developmental plasticity allows adjustment of intrinsically determined responses to visual targets so that they can take into account the actual characteristics of the developing animal's environment. Furthermore, plasticity makes it possible to introduce 'cultural' and 'social' elements into courtship and mate choice in insects. This previously unrecognized role for developmental plasticity in insects has broad theoretical and practical implications.

Dynamic synaptic modification threshold: computational model of experience-dependent plasticity in adult rat barrel cortex.

Abstract: Previous electrophysiological experiments have documented the response of neurons in the adult rat somatic sensory ("barrel") cortex to whisker movement after normal experience and after periods of experience with all but two whiskers trimmed close to the face (whisker "pairing"). To better understand how the barrel cortex adapts to changes in the flow of sensory activity, we have developed a computational model of a single representative barrel cell based on the Bienenstock, Cooper, and Munro (BCM) theory of synaptic plasticity. The hallmark of the BCM theory is the dynamic synaptic modification threshold, theta M, which dictates whether a neuron's activity at any given instant will lead to strengthening or weakening of the synapses impinging on it. The threshold theta M is proportional to the neuron's activity averaged over some recent past. Whisker pairing was simulated by setting input activities of the cell to the noise level, except for two inputs that represented untrimmed whiskers. Initially low levels of cell activity, resulting from whisker trimming, led to low values for theta M. As certain synaptic weights potentiated, due to the activity of the paired inputs, the values of theta M increased and after some time their mean reached an asymptotic value. This saturation of theta M led to the depression of some inputs that were originally potentiated. The changes in cell response generated by the model replicated those observed in in vivo experiments. Previously, the BCM theory has explained salient features of developmental experience-dependent plasticity in kitten visual cortex. Our results suggest that the idea of a dynamic synaptic modification threshold, theta M, is general enough to explain plasticity in different species, in different sensory systems, and at different stages of brain maturity.

Neuronal modulation and plasticity in vitro.

Abstract: Publisher Summary This chapter emphasizes on the contribution that in vitro studies that have made in determining the influence of trophic factors and physical environment on neuronal survival and phenotypic plasticity. It also considers the control of neurite extension and growth cone activity in finding pathways and establishing synaptic connections. All possible phases of plasticity, ranging from the regulation of neurite initiation and outgrowth to the formation of synaptic connections, integration of successful circuitry, and the expression of gross phenotype have been carefully monitored in vitro , and continues to be investigated in cultured neurons. The interplay of the physical substratum with trophins and with inhibitory factors, and its pole position in modulating neuronal choices is of paramount importance in understanding the regulation of plasticity in the nervous system. The means by which neurons perceive these cues and mediate a response underlies developmental decisions throughout differentiation, and continues to be fundamental to plasticity in the mature nervous system. In vitro data can also compliment in vivo work in developing neuronal tissues, as illustrated in the chapter by monitoring c-fos expression and its role in embryonic remodeling and programmed cell death.