PubMed Health⌕ Search

Biomedical subjects

D P Ivanov

Publications and source records attributed to D P Ivanov.

At least 19 recordsLinked to original sources
PubMed1989

The fine structure of the inferior colliculus in the cat. I. Neuronal perikarya in the central nucleus.

The fine structure of the neurons in the ventrolateral and the dorsomedial parts of the central nucleus of the inferior colliculus has been studied. 318 neurons, followed in serial ultrathin sections were examined. On the basis of the cell size, four major types of neuronal perikarya were identified: large (greater than 22 microns), medium-large (18-22 microns), medium-small (12-18 microns), and small (less than 12 microns). According to the shape of the perikarya, the ultrastructural features of their organelles, the occurrence and number of axosomatic synaptic contacts, the main neuronal types were subdivided in more discrete varieties. The large neurons have three varieties (oval, irregular, and fusiform). The nucleocytoplasmic ratio of these cells is usually above 1:1.8. They possess voluminous cytoplasm, that is rich in organelles. The granular endoplasmic reticulum is organized in NISSL bodies. Extremely numerous axosomatic synapses are present. These neurons represent the large stellate and disc-shaped projection (efferent) neurons, described in GOLGI studies. The medium-large neurons have two varieties. The nucleocytoplasmic ratio is 1:1.6-1:1.3. They possess a lesser amount of cytoplasm. Only the first variety possess discrete NISSL bodies. These cells are moderately afferented. The medium-small neurons display distinct differences in the number and pattern of cell organelles, and might be splitted in four varieties. The nucleocytoplasmic ratio is 1:1.4-1:1.1. Some of the medium-small neurons (especially--the first and the second variety) are probably projection cells, whilst others (especially--the third variety) might be interneurons. The small neurons display relatively large nucleus, small amount of cytoplasm (nucleocytoplasmic ratio approx. 1:1.2), general paucity of organelles, and extremely few axosomatic synapses. The both varieties of the small neurons, in all probability, represent local circuit neurons. From the total number of 318 neurons, 250 cells were followed in long rows of serial sections, that allowed distinct discrimination. From the latter, 18.4% were classified as large, 27.2%-medium-large, 44.4%-medium-small, and 10.0%-small neurons. The remaining 68 perikarya do not offer reliable electron microscopic criteria that could allow an unequivocal identification. The description of the cell somata in the central nucleus of the inferior colliculus, and its synaptic organization (to be published) will provide a basis for future studies on the connectivity, synaptic events, and neurotransmitter interactions in the relay nuclei of the auditory system.

Animals↗
PubMed1988

Reciprocal connections between the claustrum and the auditory cortical fields in the cat. An experimental study using light- and electron microscopic anterograde degeneration methods, and the horseradish peroxidase retrograde axonal transport.

The reciprocal connections between the claustrum and the auditory cortical fields AI, AII and Ep were investigated by means of Nauta and Fink-Heimer selective silver impregnation procedures, electron microscopic identification of degenerated axons and synaptic boutons, and with the Mesulam horseradish peroxidase retrograde tracing technique. The course and termination of degenerating corticoclaustral axons were investigated following circumscript lesions of the AI, AII and Ep areas in 19 cats. The greatest amount of degeneration debris was observed following destruction of the AII area. The central third of the claustrum (stereotaxic level A13-A15) is filled with degenerating terminals (d. t.), with greatest concentration in the lateral wedge of the nucleus, and along its inferolateral border. Rostrally and caudally the density of degeneration diminishes but scattered d. t. were observed up to the rostral pole, and a moderate number - up to the caudal pole of the claustrum. Slightly lesser amount of d. t. was observed following Ep destruction. The caudal portion of the claustrum is filled with d. t. In the central third the degeneration field occupies mainly the ventrolateral zone of the nucleus. The rostral pole of the claustrum is free of degeneration. The projection from the AI field is considerably more moderate, and is diffusely organized. A substantial number of d. t. is encountered only in the lateral parts of the central claustral third. The crossed corticoclaustral connections mirror the ipsilateral ones but are far more modest. The AII area projects mainly to the central claustral third, the Ep area--to the caudal third. The projection of the AI area to the contralateral claustrum is very weak. The electron microscopic examination of the claustrum following auditory cortex destruction in 9 cats revealed an appreciable number of degenerating synaptic boutons. They undergo dark and more rarely light degenerative changes. The cortical terminals are classified in two types: "small round" (SR), comprising approximately 70 to 75% of the corticoclaustral boutons, and "large round" (LR)-25-30%, resp. The SR boutons measure 0.6-1.2 micron, contain tightly packed round synaptic vesicles (380-420 A), and form asymmetrical axodendritic contacts. The LR boutons measure 1-2.5 microns, contain round vesicles (400-500 A) and form asymmetrical axodendritic and (far more rarely) axosomatic contacts. The claustrocortical connection was investigated in 13 cats with selective injections of 30% HRP in the three subdivisions of the auditory cortex.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1987

A note on the synapses between vesicle containing profiles in the pontine nuclei of the cat.

In the cat synapses between vesicle containing profiles were observed in ventral and dorsolateral pontine nuclei. The presynaptic elements consisted of two types of axon terminals: axon terminals characterized by a population of small (38-40 nm) round synaptic vesicles (SSV) and axon terminals containing pleomorphic synaptic vesicles (PSV). The postsynaptic pale elements (PP) had pleomorphic vesicles and some features attributed to dendrites. In the dorsolateral pontine nucleus most of PP profiles took part in serial synapses, usually as an intermediate component, they were rarely observed in triads. On the basis of their electron microscopical appearance and synaptic relations they might be considered to represent a dendritic part of putative interneurons.

Animals↗
PubMed1985

Retinal innervation of the inferior colliculus in adult cats: electron microscopic observations.

A moderate number of degenerating synaptic boutons (DSB) in the pericentral nucleus of the inferior colliculus (IC) were identified electron microscopically following contralateral eye enucleation in adult cats. Most of the DSB measure 0.6-1 micron and a lower percent are larger (1-2.5 micron). Both types contain a slightly polymorph population of clear vesicles, mainly round and oval, and a very few are elongated. The DSB are involved in asymmetric axodendritic contacts. The present report provides evidence for a crossed retinofugal monosynaptic excitatory tract innervating the IC pericentral nucleus, a possible audio-visual integrative subcortical center.

Animals↗
PubMed1982

Electron microscopic evidence for the existence of a corticonigral tract in the cat.

Young adult cats were subjected to unilateral ablation of the frontal and prefrontal cerebral cortex and were allowed to survive for 4 to 5 days. Routine electron microscopic technique was employed to examine orthograde degenerative changes in the ipsilateral and contralateral substantia nigra (Ni). A moderate number of degenerating synaptic boutons (d. s. b.) were observed in the ipsilateral Ni-pars comacta, and only very few d.s.b. were observed in the ipsilateral Ni-pars reticulata. The d. s. b. exhibited features attributed to the dark degeneration type, and might be referred to two main categories; "small-round-vesicle bouton" and "large-round-vesicle bouton" (Hajdu et al., 1973; Hassler et al. 1975). The d. s. b. performed asymmetrical synapses with dendrites of varying size, much more rarely -- with the neuronal perikarya, and extremely rarely -- with initial axonal segments. No degeneration was observed in the contralateral Ni.

Animals↗
PubMed1981

Modified Nauta and Fink-Heimer procedures with special reference to the demonstration of monoaminergic pathways in the central nervous system.

Modifications of the selective silver impregnation methods of Nauta and Fink-Heimer are described. Both procedures were tested in wide variety of species: from reptiles to carnivores, as well as in human autoptic cases. The modified Nauta procedure is recommended as a method of choice for tracing axonal trajectories due to an improved impregnation selectivity of the degenerating axoplasm. Its use for the demonstration of monoaminergic (NA, DA, 5-HT) pathways, however, remains limited. The modified Fink-Heimer procedure demonstrates successfully the degeneration of axons, and especially--the thin preterminal arborizations, as well as the terminal boutons in many fiber systems studied, including the nigrostriatal, raphe-nigral, and coerulocortical tracts. Both methods provide an additional cytoarchitectonic orientation due to a counterstain of nerve cell bodies with cresylechtviolett.

Animals↗
PubMed1980

Pallidosubthalamic projection in the cat. Electron microscopic study.

The degenerative changes within the cat's subthalamic nucleus (Sth) following lesions of the external pallidum were studied by electron microscopy. Four to five days following pallidal lesions a great number of terminals undergoing degenerative changes were encountered in the ipsilateral Sth. The contralateral Sth was free of degeneration. The degenerating terminals show predominantly the light degenerative type, less frequently the dark degenerative pattern, and occasionally exhibit signs of filamentous hyperplasia. The degenerated boutons usually insert on perikarya of the large Sth neurons, on proximal dendrites, and more rarely contact dendritic spines. They were observed neither to perform synaptic contacts with the perikarya of the small Sth neurons nor with other vesicle-containing profiles. On the basis of the ultrastructural aspect of the degenerating terminals, they were identified as F1 terminals, discriminated in a previous study (Romansky et al., 1978). The normal appearance, the synaptic relationships, and the degenerative features of the F1 terminials in the Sth closely resemble the entopeduncular terminals in the thalamus described by Rinvik and Grofová (1974a), and Grofová and Rinvik (1974). The possible contribution of the interrupted passing fibers to the observed degeneration is discussed. The present findings corroborate the relevant morphological, physiological, neurochemical, and neuropharmacological data in the literature.

Animals↗
PubMed1980

Vesicle containing dendrites in the subthalamic nucleus of the cat.

During the ultrastructural investigation of the cat's subthalamic nucleus (STN), profiles exhibiting features attributed to dendrites and simultaneously containing synaptic vesicles, were encountered. Most of them take part in synaptic triads, usually as an intermediate component. On the basis of their electron microscopical appearance, and synaptic relationships, they might be discriminated, as a distinct ultrastructural entity. Although not conspicuous in number, they might have their own contribution to the synaptic events taking place in the STN.

Animals↗