Experimental Electron Microscopic Study Research Articles

On the nature of humic substances

It is argued that the isolation of low-molecular-weight compounds from humic substances does not prove their supramolecular nature, because small molecules can be sorbed on macromolecules by interacting with them due to noncovalent bonds. The relative mobility of molecular segments in humic substances has been proposed to be used as a criterion for the discrimination between the humic substances of supraand macromolecular nature. The macromolecules are characterized by mobility of their segments, whereas supramolecular systems have stiff structure. This difference between macroand supramolecules results in different behaviors of the matrices (gels) formed from them in the processes of segregation. In the macromolecules, the formations of a new phase appearing at the segregation (microphase separation) are of nano size, at least in one dimension. They are incapable of moving within the matrix and form a well-known, limited set of systems. In the supramolecular matrices, the new-phase formations should have higher mobility and ability to move within the matrix with the formation of particles and zones of not only nano, but also micro sizes, as well as a significantly larger set of systems, including fractal configurations. The experimental electron microscopic study of the humic matrices of soil gels shows that the new-phase formations in the matrix of humic substances have not only nano, but also micro sizes and are capable of moving within the matrix, which confirms the supramolecular nature of humic substances. The proposed method has allowed generalizing the supraand macromolecular approaches, because macromolecules can enter into the composition of supramolecular systems. It is no less important that the behavior of HSs can be perceived as the behavior of stiff impenetrable particles that may compose the structures of different types and sizes.

A quantitative map of the circuit of cat primary visual cortex.

We developed a quantitative description of the circuits formed in cat area 17 by estimating the "weight" of the projections between different neuronal types. To achieve this, we made three-dimensional reconstructions of 39 single neurons and thalamic afferents labeled with horseradish peroxidase during intracellular recordings in vivo. These neurons served as representatives of the different types and provided the morphometrical data about the laminar distribution of the dendritic trees and synaptic boutons and the number of synapses formed by a given type of neuron. Extensive searches of the literature provided the estimates of numbers of the different neuronal types and their distribution across the cortical layers. Applying the simplification that synapses between different cell types are made in proportion to the boutons and dendrites that those cell types contribute to the neuropil in a given layer, we were able to estimate the probable source and number of synapses made between neurons in the six layers. The predicted synaptic maps were quantitatively close to the estimates derived from the experimental electron microscopic studies for the case of the main sources of excitatory and inhibitory input to the spiny stellate cells, which form a major target of layer 4 afferents. The map of the whole cortical circuit shows that there are very few "strong" but many "weak" excitatory projections, each of which may involve only a few percentage of the total complement of excitatory synapses of a single neuron.

Vestibulospinal projections in the toad. An experimental electron microscopic study

An experimental electron microscopical study has been made on the mode of termination of the vestibulospinal projections in the toad. Degenerating fibers and boutons were observed in the ventromedial region of the spinal cord in which five types of terminals were identified in normal preparations: S-type, F-type, C-type, NfS-type and NfF-type. The latter two types represent the largest terminals in the spinal gray. In the medial region of the ventral horn they seem to belong to supraspinal fibers. Following electrolytic lesions of the dorsal and ventral nuclei nervi octavi, some of the NfF-type of boutons undergo filamentous degeneration which progresses into the dark type at longer survival periods (7–20 days). In two animals, a few NfS-type of boutons also display filamentous hypertrophy. Problems connected with the filamentous type of degeneration in amphibians and with the identification of bouton types belonging to the vestibulospinal pathway are discussed. Degenerating fibers and boutons are seen at all levels of the spinal cord, ipsilateral and also, in smaller number, contralateral to the lesions. The vestibulospinal fibers terminate predominantly on large and small dendrites, and only occasionally on the somata of large neurons on the ipsilateral side.

Thalamic projections of the superior colliculus in the rhesus monkey, Macaca mulatta. A light and electron microscopic study

The projections of the superior colliculus to the thalamus have been studied in the monkey, Macaca mulatta, with anterograde degeneration techniques. The superior colliculus has been shown to project to the inferior nucleus of the pulvinar in a topographical manner with the lower visual field represented dorsomedially and the upper field ventrolaterally. The peripheral zone is located along the medial border and the fovea at the dorsolateral angle adjacent to the lateral geniculate nucleus. The superior colliculus also sends a dense projection to the ipsilateral intralaminar complex, i.e., to the parafascicular, central lateral and paracentral nuclei, and a lesser projection to the same contralateral nuclei. Degenerating tectal fibers were also found in the lateral geniculate nuclei. Four types of vesicle containing profiles were observed in the inferior pulvinar and paracentral nucleus. The large RL and small RS terminals contain round vesicles of uniform size and form asymmetric contacts mainly with large and small dendrites respectively. The F terminal contains a mixture of small round and flat vesicles. It forms symmetric contacts with dendrites and cell somata. The P profile is very pale and contains a relatively sparse population of vesicles showing a great variation in size. It forms symmetric contacts with medium to large dendrites. It is frequently found postsynaptic to the other types, especially the RL terminal, and is regularly seen as the intermediate element of serial and triadic synaptic arrangements. The experimental electron microscopic study has shown that many fibers from the superior colliculus terminate as RL profiles, undergoing direct dense degeneration, in both the inferior pulvinar and the paracentral nucleus. Others probably end as smaller RS terminals.

The meaning of the Leydig cell in relation to the etiology of cryptorchidism: An experimental electron-microscopic study

In our electron-microscopic studies of testicular biopsies, both normal and cryptorchid, we found a simple atrophy of the Leydig cell in the cryptorchid testis. Based on experiments by Raynaud 1,2 and Jean 3 on pregnant mice, we tried to find the reason for changes in the Leydig cell relating to the etiology of cryptorchidism. We found on electron microscopic study of testes in the offspring of pregnant mice treated with estrogen the same atrophy of the Leydig cell as we see in human cryptorchidism. These changes are not evident when estrogen and HCG are given together. We can conclude from this experiment that lack of gonadotropin stimulation leads to the atrophy of Leydig cells. This atrophy then produces a lack of androgen which could be responsible for cryptorchidism.

Diversity of mossy fibres in the cerebellar cortex in relation to different afferent systems: An experimental electron microscopic study in the cat

The evolution of the terminal degeneration has been compared in two systems of mossy fibres: the spinocerebellar and the pontocerebellar projections. The two systems exhibit both dense and clear types of terminal degeneration. However, there are important differences between the evolutive processes of terminal degeneration in the two systems: (i) the time course of the degenerating process is much faster for spinocerebellar than for pontocerebellar rosettes, and (ii) the glial phagocytic process accompanying the dense type of degeneration is different for the two systems. Spinocerebellar rosettes are generally removed from their glomerular central position by reactive glia, leaving fragments of the presynaptic membrane attached to their postsynaptic partner. This feature is exceptional for pontocerebellar rosettes which, in the course of their glial engulfment, leave free the postsynaptic differentiation of their former target granule cell dendrites. These differences of terminal degenerative processes have been reconciled with optical microscope observations by Brodal and Drablos1 of morphological differences between the rosettes of two different fibre systems.

An experimental electron microscopic study on the striatonigral projection in the cat.

The ultrastructure of the cat's substantia nigra was investigated from 2–21 days following large lesions of the caudate nucleus and the putamen. From 4 days on a large number of degenerating boutons and degenerating unmyelinated fibers are seen in the substantia nigra, in the pars compacta as well as the pars reticulata. Both parts, mainly the latter, receive striatal afferents. The degeneration in the substantia nigra following striatal lesions is of the dark type. Most of the degenerating boutons apparently are of the type I (see Rinvik and Grofova, 1970) and end on all parts of the nigral cell surface, including the dendritic spines. One instance of a degenerating presynaptic bouton in an axo-axonic synapse has been found. Some degenerating boutons also probably belong to the type II bouton, while degenerating boutons of type III were never seen following the striatal lesions. The electron microscopic identification of early axonal degeneration in the central nervous system, is discussed with reference to the paper of Cohen and Pappas (1969). Problems concerning the pars compacta versus the pars reticulata of the substantia nigra are taken up. The possible sources of origin of the different types of boutons in the cat's substantia nigra, is discussed.

Experimental electron microscopic studies on excitatory and inhibitory synapses in the cerebellar cortex of the rat.

Excitatory synapses in the rat cerebellar cortex contain large, spheroid vesicles and inhibitory synapses contain small, ovoid vesicles. Presynaptic terminals can be characterized by the ratio of spheroid: ovoid vesicles (Q-value). Neither the inhibition of acetylcholine synthesis by hemicholinium, nor the inhibition of GABA synthesis by thiosemicarbazide, does induce any significant alterations in the Q values. It is suggested that synaptic vesicles bind mediator substances on their surface membranes.

Experimental electron microscopic study of the sequential stages of in vitro formation of ceroid

The results of this study have indicated that a certain amount of unsaturated fatty acids is necessary to the in vitro formation of ceroid, as evidenced by its absence in the hydrogenated coconut oil mixture. The differences in the pigment found in the cod liver oil and in the butter mixtures probably was related to the different unsaturated fatty acid content of these fats.