Search

Possible mechanisms of unilateral ischemic insults in CA1 region of hippocampus and anterior dorsal nuclei of thalamus after bilateral occlusion of common carotid arteries in rats with different types of behavior are discussed.

Permanent bilateral occlusion of common carotid arteries in rats with different behaviour types led to non-uniform structural alterations in the hippocampus. In the majority of animals, morphological changes were diffuse (i.e. having no clear localisation in a definite region of the brain structure) and symmetrical (i.e. having no evident prevalence in one of the brain hemispheres). In 6.6% of survived animals, apart from diffuse structural changes, local and asymmetrical sites of lesions occurred in the hippocampus and mostly in the dorso-lateral thalamic nuclei of the right brain hemisphere. These local zones of strongly pronounced pathology corresponded to ischemic insults which were described earlier by other authors under transient cerebral ischemia. It is supposed that the occurrence of unilateral ischemic insults in a definite region of hippocampus and thalamus after bilateral occlusion of common carotid arteries is due to individual features of the anatomy of the vascular brain system which are found more frequently in rats with passive type of behaviour and in rats of the middle group than in rats with active type of behaviour.

The structure of vestibular nuclei cells was studied in the brain of Macaca mulatta on return from the 14-d flight on satellite BION-11 and in 2 days of recovery. The monkey suddenly deceased on day 2 since landing because of aspiration asphyxia on completion of biopsy of muscle and bone tissues. Basic shifts in neural cells of the vestibular nuclei were focal tigrolysis and formation of larger clodlets by remains of tigroid. The most pronounced changes occurred to cells in the medial, upper and descending vestibular nuclei. Deiter's lateral vestibular nucleus was least changed. The conclusion has been made that loss of reactivity by vestibular nuclei in microgravity is linked not only with the effects of exterofactors (otolith and labyrinthine receptors) but also with the structural-functional deficiency of cells of vestibular nuclei.

1. Black widow spider venom (BWSV), or crustacean-specific toxin purified from it (named latrocrustatoxin, LCT) were lethal for the crayfish. 2. Distortions in the EMG and motor activity pattern after LCT injection indicated venom effects on the crayfish nervous system. 3. In the isolated ventral nerve cord, transient activation of the "silent" interneurons and motoneurons occurred after BWSV or LCT application. 4. In the isolated nerve-muscle preparation, LCT application elicited an intense transmitter release resulting in the complete blockade of neuromuscular transmission. 5. Electron microscopic study of the nervous and muscle tissue in venom treated crayfish demonstrated certain destructive changes in the nervous cells especially in the nerve terminals. 6. The results suggest that the LCT acts as a presynaptic neurotoxin in the central and peripheral nervous system of the crayfish.

Structural alterations in the brain after stress were studied in rats with different behavior type in open field and forced swimming tests. The most typical brain reaction to acute stress was a combination of reactive (hypertrophy and fission of mitochondria, hyperplasia of rough reticulum) and destructive (disintegration of mitochondria and rough reticulum) alterations which were different in rats with various behavior types. Thus, in rats with the active type of behavior showing the greatest resistance to stress (see report 1) the reactive processes were more manifest, while the the rats with the passive type of behavior showing lower resistance to stress developed destructive processes. Rats of the middle group with the least resistance to stress differed from the other two groups by vague structural alterations, i.e. by the lack of evident predominance of any definite process. It is assumed that individual differences in the resistance to acute stress are associated with individual differences in the manifestation of reactive alterations in the brain which can be regarded as a structural component of the urgent adaptation to stress.

In rats with different behaviour types in tests of "open field" and "forced swimming", influence of intraperitoneal administration of P-substance (PC) neuropeptide to survival and structural-metabolic changes in brain after double-sided ligating of carotid arteries. It was established that PC exerts different influence on stability to circulating cerebral hypoxia according to behaviour types: it increases stability in rats with passive behaviour type, decrease stability in rats with active behaviour type and does not influence on rats with middle behaviour type. Results shows the necessity of individual approach to peptide use with the view to increase stabilization to cerebral ischemia.

The effect of a synthetic polypeptic hormone angiotensin-II on the structure of the brain ventricular system was studied in rats. A single injection of angiotensin-II, firm "Ciba", was given to rats in a dose of 0.05 mg/kg of body weight on the 1, 3, 7, 14 and 21st days. The brain was extirpated 15 min after the last injection, fixed in formalin and embedded in celloidin. Intact animals served as controls. A single injection of angiotensin-II was found to be accompanied by a slight dilatation of the brain lateral ventricles. Seven injections resulted in further accumulation of the fluid in the ventricles, and the first symptoms of the corpus callosum atrophy appeared. After the 21st injection of angiotensin-II a typical picture of hydrocephalus demonstrating further accumulation of the fluid in the brain ventricles was seen. The atrophic changes were especially pronounced in the corpus callosum, in white and grey substances of the frontal lobes of the cerebral hemispheres. Besides the atrophic changes, angiotensin-II-induced hydrocephalus resulted in subependymic edema, exfoliation of ependymal cells--the features characteristic for other types of hydrocephalus. Thus, injections of the synthetic hormone angiotensin-II can facilitate in producing an experimental atraumatic hydrocephalus. By means of angiotensin-II a desirable degree of hydrocephalus can be obtained by changing the dose of the preparation.

Changes in ultrastructure of neurones and glial cells of rat auditory cortex were studied after exposure to white noise for 21 days. Appearance of light neurones with peripheral chromatolysis and the increased number of lysosomes, pigment granules and vacuoles were recorded both in the neurones and glial cells. It is concluded that exposure to white noise in chronic experiments is the pathogenic factor which causes destruction in the neurons and glial cells of the auditory cortex.

Ultrastructural transformations of axo-somatic and axo-dendritic synapses of the rabbit sensorimotor cortex were studied during: 1) polarization of the cortical surface with a DC anode and 2) the setting up of a polarization motor dominant. A comparison between the structural characteristics of the examined region of the cerebral cortex of the two groups of animals revealed transformations in the synaptic apparatus, which may be regarded as a result of the formation of a temporary connection: an increase in the number of axo-dendritic synapses with considerably thickened postsynaptic membranes; an increase in the number of axonic terminals with a concentration of synaptic vesicles and mitochondria content. The indicated changes were more pronounced in the deep layers of the sensorimotor cortex.

Structure of capillaries, pericapillary glia and neurons of the sensomotor cerebral cortex was studied in rats after intraperitoneal injections of angiotensin-II (0.05 mg/kg of the body weight) administered once for 1, 3, 7, 14 and 21 days. The animals were decapitated 5 and 15 min after a single injection, and at repeated injections--15 min after the last one. The repeated injections of angiotensin-II were stated to produce a stable edematous syndrome in the brain of the animals. Pericapillary (astrocytic) glial edema was associated with neural cells edema. The more angiotensin-II was injected, the greater was dilatation of astrocytic processes adjoining the capillaries. In some edematous neurons it was cytoplasmic matrix that swelled, in others--liquid was accumulated in the cytoplasmic network cavities. Membrane bodies appeared in the capillary endothelial cells and in neurons made also a peculiar feature. It could be possible that functional shifts in the CNS observed after repeated injections of angiotensin-II were resulted from deficiency of the cerebral circulation and some structural changes in neural and glial elements.

The rat acoustic cortex has been studied at light optic and ultrastructural levels under the white noise stimulation. After the noise stimulation for 7 days, micropunctate hemorrhages, proliferation and hypertrophy in cells of microglia and astrocytic glia are noted. After the noise stimulation for 21 days, the neuroglial reaction becomes less pronounced, there are no hemorrhages, a great amount of neurons with peripheral and total chromatolysis appear. In other neurons, as well as in all types of neuroglia the number of primary lysosomes increases, their structure changes. In lysosomes lipofuscin and lipid drops are accumulating, many of lysosomes turning into multivesicular bodies. The destructive changes observed in the neurons and neuroglia underlie prolonged disturbances in the higher neural activity after the noise stimulation is stopped.

The structure and ultrastructure of the sensomotor cortex in pubertal rats were studied 7, 14 and 21 days after acoustic stress. Focal peripheral chromatolysis and pigment accumulation by lysosomes were found in neurons after 14 and 21 days of exposure to noise. The number of lysosomes in which pigment was accumulated, and multivesicular bodies appeared, increased in the glial cells. The cavities of granular reticulum widened because of the accumulation by them of muddy secretion. These phenomena indicate the diffusive character of structural changes in the cortex of the large hemispheres under acoustic stress. It has been noted that young animals exposed to noise manifest changes characteristic of the process of aging.

Ultrastructure of the rat sensomotor and acoustic cortex has been studied at a separate and joined effect of noise and alcoholic intoxication during 7 and 35 days. Certain changes in vessels, neural and glial cells specific for separate effect of noise and alcohol have been revealed. Combined application of noise and alcohol results in a more profound disorders in the cerebral vessels, with predominance of changes specific for alcoholic intoxication. Simultaneous decrease of the ultrastructural changes, peculiar for the separate effect of noise is explained as a decreasing functional loading on the cortical cells resulted from blocking synapses with alcohol.

Electron microscopic study and quantitative analysis of the visual cortex synapses in 14, 30 and 60-day-old rats were performed after bilateral enucleation of newly-forn rats. A great amount of synapses of other functional systems was shown to be functioning in the area striata in addition to the synapses formed by specific visual afferents. Alterations in the synapses of the area striata of blind rats are developing gradually, achieving the greatest pronouncement in 60-day-old rats. These changes develop according to the type of atrophic process in connection with dysfunction. The atrophic alterations of the synapses were found both in axo-somatic and axo-dendritic synapses on the dendrite trunks and on the thorns. The alterations of synapses being concentrated in layer IV. The quantitative ratio of different kinds of atrophied synapses in the cross-section of the visual cortex was different suggesting the following conclusion about the distribution of the visual afferents. In layers I and III the visual afferents formed mostly axon-thorn contacts and less amount of axo-somatic and axo-dendritic synapses on the dendrite trunks. In layer IV they mainly formed axo-somatic and axo-thorn synapses and less amount of axo-dendritic ones on the dendrite trunks. In layers V and VI they mainly contact with the dendrite trunks and with the nervous cell bodies and more rarely with thorns.

Synapses of the sensorimotor cortex were studied during summation reflex in chronic experiments on rabbits. Structural changes in presynaptic and postsynaptic components of axodendritic synapses were revealed which are considered as an increase in the functional activity of the synaptic apparatus. The most pronounced response was observed in the postsynaptic matrix, which consisted in a considerable thickening of postsynaptic membranes in a number of axodendritic synapses. It is assumed that the postsynaptic membrane of axodendritic synapses is one of the earliest links structurally fixing the traces of the obtained information.

The action of the synthetic polypeptide hormone angiotensin-II (A-II) on the ultrastructure of capillaries and perivascular glia of the cerebral cortex was studied in experiments on adult male rats. Intraperitoneal injections of the hormone are accompanied by swelling of the growing fibers and bodies of the precapillary glia (astrocytes), and by a strong narrowing of the capillary lumen. The endothelium of these vessels swells and layer inclusions appear in the cytoplasm of endothelial cells. The process is characterized by the growth of changes and reaches the maximum day 21 after the drug injections are started. The revealed changes in the pericapillary glia and capillary structure indicate microcirculatory disturbances in the cerebral cortex that may lead to trophic and functional abnormalities of the central nervous system.

Nuclear ultrastructure of neurons and glial cells of the rat sensomotor cortex was studied under chronic alcoholic intoxication. During 24 h the animals drank up about 10 ml of 20 degrees alcohol. In the course of prolonged alcoholic intoxication there occurred processes leading to deformation of the nuclei of neurons and glial cells and to the deficiency of nuclear and cytoplasmic substances. These changes are regarded as an atrophic process responsible for the corrugation of the nucleus and diminution of the cell size.

Ultrastructural changes in the synapses of sensorimotor cortex caused by short and protracted stimulations of mid-brain reticular formation with single electric pulses were studied in rabbits. The observed submicroscopic shift in synaptic apparatus is regarded as a process of enhancing the activity of the sensorimotor synaptic apparatus with involvement of new interneuronal connections. Structural-functional changes in the synaptic apparatus occured at all levels of the sensorimotor cortex, with the predominance of this process at the upper level (layers I-IV); this is probably due to the greater representation of non-specific afferent endings in the upper cortical layers.

The character of functional connections between the midbrain reticular formation (RF) and the neocortex was studied in rabbits. Unit activity was recorded in sensorimotor cortex by extracellular microelectrode during RF stimulation. Short-latency neuronal reactions were found presumably identified as monosynaptic responses. Results of the studies of anterograde degeneration of myelinic fibers and axonal terminals after electrocoagulation of the RF carried out with the help of electronic microscope allowed to suppose that there were few (less than 0.5 per cent) monosynaptic connections between the RF and the sensorimotor cortex. The main forms of direct connections between these structures were axo-dendritic (situated at the dendritic trunk) and axosomatic synapses at the neurones of the sensorimotor cortex.