摘要:

Alterations in visual cortical excitability due to tetanization of MRF, SC or PUL were assessed in terms of the amplitude of the cortical response to single, and to paired lateral geniculate (LGB) shocks at varying temporal intervals (the recovery cycle). Tetanization of any one of these subcortical structures could potentiate both the single evoked response and the recovery cycle. In addition, all three structures produced maximal effects on later components of the shock response, and reacted similarly to changes in tetanization intensity, LGB shock intensity and level of Nembutal anesthesia. MRF tetanization generally produced the greatest potentiation effect at lowest voltages, with SC and PUL requiring progressively higher voltages to produce an effect. In the case of PUL smaller effects on both the recovery cycle and single cortical responses were obtained. While there were no significant differences in the magnitude of recovery cycle potentiation following MRF and SC activation, the time course of single evoked response facilitation was different after stimulation of these two structures. Comparing single response potentiation to that of the recovery cycle, it was found that for all structures there were consistent differences in the time course of these two effects. Higher tetanizing intensities were also generally necessary to achieve maximal potentiation of the recovery cycle, and enhancement of the single evoked response could occur without concominant changes in the recovery cycle.

ISSN:0020-7454    

DOI:10.3109/00207457309149444

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

Historically, injury of the mammalian spinal cord resulted in abortive regeneration. Recent findings have shown regeneration of the spinal cord occurs by limited regrowth of severed nerve fibers and massive regrowth of axonal sprouts of normal axons. The foregoing study investigates the regenerative capacity of the spinal cord in 14 Rhesus monkeys(Macaca mulatto)following left hemisection at vertebral segment T2. In addition to three normals, animals were utilized 7, 14, 21 days and 1, 2, 3, and 4 months posthemisection. Tissue was prepared for Golgi impregnation, Protargol-cresyl violet-eosin staining, and electron microscopy. The motor horn rostral to the site of lesion was investigated. Dendrites of motor horn cells adjacent to and facing the lesion developed varicosities which formed at the terminal end of the dendrite by day 7 and progressed to include the entire dendrite by day 14–30 posthemisection. Motor horn cell dendrites (0–5 mm from lesion) were varicose and many possessed only two short, varicose, dendrites by 1 month posthemisection. Varicosities generally formed only on tertiary and secondary dendrites, 5–9 mm rostral to the lesion; however, dendrites facing degenerating tracts often were completely varicose. Neurite fascicles (predominantly axons), often free of neuroglial cell processes, were observed in the enlarged extracellular spaces. Axons, mainly from the neurite fascicles, made several types of synaptic recombinations with reactive neurons. The most frequent type of synaptic complex had a cup-shaped bouton with a central large extracellular space between pre- and postsynaptic membrane. The peripheral portion of the bouton made synaptic complexes with small, equal, pre- and postsynaptic membrane specializations and a 250-300Åsynaptic cleft. The postsynaptic neuron usually possessed a thickened membrane or a subsurface cistern with thickened membranes associated with the enlarged subsynaptic space. In addition, somatic and dendritic synapses were observed with cisterns or extensive Nissl bodies adjacent to the postsynaptic membrane. Synaptic complexes with normal organelles and synaptic clefts were also observed in different states of maturation. The central nervous system of the monkey undergoes regenerative changes involving both dendritic modification and synapse formation. The regenerating nerve fibers synapse on neurons proximal to the site of lesion and do not enter the cicatrix. The specificity of the regenerating nerve fibers for neurons and neuronal membrane is discussed.

ISSN:0020-7454    

DOI:10.3109/00207457309149445

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

We shall define associative recall as follows:‘Associative recall is an operation in which a memorized item is recalled by an arbitrary, sufficiently large known part of it’. In our models for associative recall, memory traces are superimposed on certain engram elements in distributed form.In most models, memorized signals are reconstructed during recall. Reconstructivity places severe demands on physical systems, e.g., neural networks. In this model the reconstruction of items can be made virtually.

ISSN:0020-7454    

DOI:10.3109/00207457309149446

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

The paper criticizes present procedures for analysis of protein synthesis, particularly with the tracer methods. Major points concern not labeling, but the interpretation of the results.

ISSN:0020-7454    

DOI:10.3109/00207457309149447

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

A mathematical model for the neuron is introduced for convenient modelling of neural macrostates. The state and dynamics of the neuron are characterized by the level of transmitter substance acting on its input. The model is continuous in time rendering the use of differential equations possible. The model is best applicable to neuron pools to describe their activity as a single totality.

ISSN:0020-7454    

DOI:10.3109/00207457309149448

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

The few ultrastructural reports on the fine structure of autonomic ganglia in pre- and postnatal animals and humans have clarified a certain age without paying attention to the dynamic aspects of ganglionic development or prenatal development alone. Hamori and Dyachkova presented a detailed description of the developmental differentiation of synapses in autonomic ganglia, but they were concerned with the special calyciform synapse characteristic of the ciliary ganglia of birds and reptiles. The purpose of the present study was to clarify how the synapses to different ganglionic cells differentiate during the postnatal period in the paracervical ganglion of the rat uterus.

ISSN:0020-7454    

DOI:10.3109/00207457309149449

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

The human fetal adrenal medulla evidently contains a pool of primitive sympathetic elements, which possess the capacity for differentiation to both catecholamine storing medullary cells and neurons. Furthermore, these cells are organized into large, rounded, tightly packed avascular cell islands which were easily found and/or isolated.The purpose of the present study was to follow the development of primitive sympathetic cells in human fetal adrenal medulla to find the origin of the adrenal neurons.

ISSN:0020-7454    

DOI:10.3109/00207457309149450

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

The authors wished to test the extent to which TSH, ACTH or both, are secreted by pituitary cells during the stress of acute exposure to cold. Differences in secretion were found between rat and rabbit.

ISSN:0020-7454    

DOI:10.3109/00207457309149451

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

ISSN:0020-7454    

DOI:10.3109/00207457309149452

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor