PubMed Health⌕ Search

Biomedical subjects

Y Geinisman

Publications and source records attributed to Y Geinisman.

36 records · Page 2Linked to original sources
PubMed1988

Remodeling of synaptic architecture during hippocampal "kindling".

The "kindling" phenomenon is associated with long-lasting facilitation of synaptic transmission. A possible mechanism of such facilitation could involve changes in the number of synaptic contacts. However, previous attempts to demonstrate a synaptic morphological alteration that could account for the long-term effects of kindling had failed, possibly due to the unavailability, at the time, of unbiased methods for synapse quantitation. Using the unbiased stereological disector technique, we estimated the number of synapses per neuron in the middle molecular layer of the hippocampal dentate gyrus in rats kindled by electrical stimulation of the medial perforant path with implanted electrodes. Unkindled but stimulated (coulombic control) and unstimulated but implanted rats served as controls. Animals were coded and killed 4 weeks after reaching the kindling criterion of five generalized seizures. The most important results were obtained when axospinous synapses with continuous or discontinuous postsynaptic densities ("nonperforated" or "perforated" synapses) were differentially analyzed. Kindling resulted in a selective loss of nonperforated synaptic contacts in contrast to preservation of perforated ones. Furthermore, the ratio of perforated to nonperforated synapses was increased by 45% or 40% in kindled rats relative to unstimulated or coulombic controls, respectively. These findings suggest that synaptic efficacy may depend on a balance of the two synaptic types; selective elimination of nonperforated synapses may augment the potency of remaining synaptic contacts, a process reminiscent of synaptic remodeling during development.

Algorithms↗
PubMed1987

Axospinous synapses with segmented postsynaptic densities: a morphologically distinct synaptic subtype contributing to the number of profiles of 'perforated' synapses visualized in random sections.

Axospinous synapses were examined in the molecular layer of the rat dentate gyrus. Serial section analysis of synapses, which exhibited a discontinuity of the postsynaptic density (PSD) in at least one consecutive section, was performed. Reconstruction of each discontinuous PSD was made in a plane perpendicular to that of serial sections. The results obtained confirm earlier observations that profiles of 'perforated' synapses visualized in random sections of osmicated material are produced by sectioning of synapses with perforated and horseshoe-shaped PSDs. Additionally, it has been found that two other synaptic subtypes, namely synapses with notched and segmented PSD, contribute to the number of profiles of 'perforated' synapses. Synaptic contacts with notched PSD are characterized by an indentation of an otherwise continuous PSD, relatively small dimensions and simple shape. They appear to be unrelated to the category of synapses with discontinuous PSD. Synaptic contacts with segmented PSD are distinguished by the presence of 2-5 discrete PSD segments at the interface between a presynaptic axon terminal and a postsynaptic dendritic spine. Some PSD segments exhibit 1-3 perforations, while others are horseshoe-shaped. It is postulated that the segmented PSD may evolve through the stages of perforated and horseshoe-shaped PSD to form a specialized synaptic contact of an unusually high efficacy. Every PSD segment is a component of a separate synaptic complex, each one comparable to that of a small, simple-shaped synapse. A concerted activation of several synaptic complexes belonging to a single synaptic junction may provide a mechanism for an amplification of synaptic transmission.

Aging↗
PubMed1987

Synapses on dendritic shafts exhibit a perforated postsynaptic density.

Synapses on dendritic shafts were examined in electron micrographs of serial sections obtained from the molecular layer of the rat dentate gyrus. Some of these synapses have been found to exhibit profiles of a discontinuous postsynaptic density (PSD). PSD reconstructions from serial sections were performed in a plane perpendicular to that of the sections. The results obtained indicate that profiles of discontinuous PSDs observed in random sections of dendritic shaft synapses are generated by sectioning of PSD plates that contain 1-3 holes or perforations. Earlier serial section studies of osmicated material have demonstrated that a proportion of axospinous synapses also exhibit a perforated PSD. It appears, therefore, that the presence of PSD perforations is a general phenomenon shared by subpopulations of different types of synapses, both those involving dendritic shafts and those involving dendritic spines.

Aging↗
PubMed1986

Aged rats need a preserved complement of perforated axospinous synapses per hippocampal neuron to maintain good spatial memory.

Spatial working memory, which crucially depends on the structural integrity of the hippocampal formation and its afferent connections, is impaired in the most, but not all, of aged rats. This study was designed to verify whether aged animals that do not exhibit the spatial memory deficit are the ones in which the hippocampal synaptic connectivity remains preserved with advancing chronological age. Young adult rats with good spatial memory, aged rats with impaired spatial memory and equally aged rats with intact spatial memory were compared. The number of synapses per neuron was estimated in the hippocampal dentate gyrus. The most important results were obtained when axospinous synapses were divided into perforated and non-perforated ones according to the appearance of their postsynaptic density. A significant decrease in the number of perforated synapses was found in memory-impaired aged rats as compared to either young adults or aged animals without memory deficits. The number of non-perforated synapses per neuron was diminished in memory-deficient aged rats relative to young adults, but not to memory-intact aged rats. However, it was only the loss of perforated synapses which correlated with the degree of spatial memory impairment. Thus, aged rats need a preserved complement of hippocampal perforated synapses to maintain good spatial memory.

Aging↗
PubMed1986

Loss of perforated synapses in the dentate gyrus: morphological substrate of memory deficit in aged rats.

Most, but not all, aged rats exhibit a profound deficit in spatial memory when tested in a radial maze--a task known to depend on the integrity of the hippocampal formation. In this study, animals were divided into three groups based on their spatial memory capacity: young adult rats with good memory, aged rats with impaired memory, and aged rats with good memory. Memory-impaired aged animals showed a loss of perforated axospinous synapses in the dentate gyrus of the hippocampal formation in comparison with either young adults or aged rats with good memory. This finding suggests that the loss of perforated axospinous synapses in the hippocampal formation underlies the age-related deficit in spatial memory.

Aging↗
PubMed1984

Anatomical evidence for convergence of olfactory, gustatory, and visceral afferent pathways in mouse cerebral cortex.

Flavor perception requires the neural integration of olfactory, gustatory and, possibly, visceral afferent information. Presently, it is not known where, or how this integration takes place in the brain. Neuroanatomical data presented here suggest that pathways subserving these sensory modalities converge in mouse insular cortex after surprisingly few synaptic relays. Orthograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) was used to label main olfactory bulb (MOB) efferents. A projection into layer I of insular cortex was present in every case. Bulb transections were made to provoke anterograde degeneration and EM analysis confirmed that the olfactory projection to insular cortex was a terminal pathway. WGA-HRP injections in the MOB-recipient zone of insular cortex resulted in ortho and retrograde labeling of ascending and descending gustatory-visceral afferent pathways. It is concluded that in the mouse, there is a remarkably direct convergence of olfactory and gustatory-visceral sensory pathways in insular cortex. Together with the descending connections from insular cortex to the amygdala and to brainstem autonomic structures, it is possible that the cortical integration of olfactory and gustatory-visceral information could modulate mechanisms involved in food selection and autonomic reactions relating to the chemical senses. Basic mechanisms subserving flavor perception might be usefully modelled in mouse insular cortex.

Afferent Pathways↗
PubMed1983

Flat, whole-mount nerve preparations: a useful tool for studying the process of regenerating axon outgrowth.

A method, which is based on the use of flat, whole-mount nerve preparations, has been developed for studying the process of regenerating axon outgrowth, employing the rat sciatic nerve as a model. At various intervals after a nerve crush, animals are perfused with aldehyde fixatives, the nerve dissected out, and its epineurium removed. Next the nerve is flattened between two glass slides, removed and reacted (floating), then whole-mounted on a micro slide and cover-slipped. Regenerating axons have been labeled by means of the horseradish peroxidase tracing technique, a histochemical technique for acetylcholinesterase, or an indirect immunocytochemical technique utilizing antibodies against tubulin. With all these techniques, individual outgrowing axons and their bundles can be clearly visualized. Regenerating axons labeled by horseradish peroxidase are readily traced along their entire undulating courses from the distal margin of the crush zone to axonal tips, which mark the leading edge of several waves of outgrowing axons. It appears that such flat, whole-amount nerve preparations can be useful for obtaining: (1) accurate estimates of the rate of regenerating axon elongation, (2) values characterizing the duration of the initial delay of axonal outgrowth, and (3) information concerning the nature of axonal subpopulations that elongate at different rates.

Acetylcholinesterase↗
PubMed1979

Loss of axosomatic synapses in the dentate gyrus of aged rats.

Axosomatic synapses involving granule cells of the dentate gyrus were studied by means of quantitative electron microscopic analysis in young adult (3-month-old) and aged (25-month-old) rats. The number of axosomatic synapses per unit length of neuronal soma membrane was found to be significantly lower (by 15%) in aged animals than in young adults. This decrease in synaptic numbers is not associated with age-related changes in the size of neuronal soma profiles or in the length of their plasma membranes. The ratio between the total length of synaptic appositions and the membrane length of a neuronal soma profile was diminished by 22% in aged rats, whereas the mean length of synaptic apposition was 10% less in these animals than in young adults. These data, taken together, suggest that an absolute loss of axosomatic synapses occurs with advanced age. It appears, therefore, than not only the loss of axodendritic synapses, described previously, but also the loss of axosomatic synapses, found here, contributes to the process of age-related partial deafferentation of neurons in the rat dentate gyrus.

Afferent Pathways↗
PubMed1979

Interganglionic axonal transport of neural peptides within the nervous system of Aplysia.

Neurons of the circumesophageal ganglia of Aplysia synthesize 1--2000 dalton peptides and subject them to axonal transport in large quantities in the pleuro-visceral connective and pedal nerves. Most of the protein transported in the connective nerves accumulates in the abdominal ganglion, although some passes out its peripheral nerves. Autoradiography revealed no evidence for terminations of the transporting axons in possible neurohemal areas of this ganglion. It is suggested that these data reflect the existence of a pathway mediating the "directed delivery" of neural peptides in this nervous system.

Animals↗
PubMed1978

Dendritic atrophy in the dentate gyrus of the senescent rat.

Quantitative electron microscopic analysis of the supragranular zone of the dentate gyrus molecular layer has shown that the number, volume fraction and surface area of dendritic shaft profiles are significantly decreased in senescent rats, relative to young adults. These modifications of dendritic morphology, which are not associated with age-related changes in dimensions of the molecular layer or in numbers of granule cells, may result from a decrease in the number and/or length of dendrites. In either case, the decreases in the number, volume fraction and surface area of dendritic shaft profiles found in the dentate gyrus of senescent rats signify an age-related atrophy of dendrites. Comparison of changes in the number and volume fraction of dendritic shaft profiles has demonstrated that age-related dendritic atrophy involves predominantly dendritic branches.

Aging↗
PubMed1978

Hypertrophy of astroglial processes in the dentate gyrus of the senescent rat.

Quantitative electron microscopic analysis of the supragranular zone of the dentate gyrus molecular layer has shown that the number and volume fraction of profiles of astroglial processes are significantly increased in senescent rat relative to young adults. These ultrastructural modifications, which are not associated with significant age-related changes in the number of astrocytes or in the width of the molecular layer, may result from a formation of new astroglial processes and/or elongation of existing ones. In either case, the increase in the number and volume fraction of astroglial process profiles is an indicator of age-related astroglial hypertrophy. Hypertrophy of astroglial procecesses, which seems to develop with advanced age as a response to partial deafferentation of neurons, may compensate for a decrease in the dendritic volume fraction, thereby preventing changes in the dimensions of the dentate gyrus molecular layer in senescence.

Aging↗
PubMed1976

Loss of synapses in the dentate gyrus of the senescent rat.

Synapses were counted in electron micrographs of the middle third of the molecular layer of the dentate gyrus of Fischer 344 rats, 3 months and 25 months of age. A 27% decrease in the number of synapses was found in senescent animals compared with young adults. This loss of synapses could not be correlated with changes in synaptic size. tissue volume or number of postsynaptic granule cells.

Aging↗
PubMedDate not supplied

Diminished axonal transport of glycoproteins in the senescent rat brain.

At various time intervals (10, 15, 20, 25, 30 min) after injection of 3H-fucose into the medial septal nucleus of young adult (3 months old) and senescent (25 months old) Fischer-344 rats, the specific activities of trichloroacetic acid-phosphotungstic acid (TCA-PTA) soluble and insoluble fractions were determined in the medial area of the septum and in three successive rostro-caudal sections of the hippocampal formation containing mainly the dentate gyrus, but also its hilus with fields CA4 and CA3c of the hippocampus. The rate of 3H-fucose incorporation into glycoproteins of the septum did not differ in young adult and senescent rats. Part of the TCA-PTA soluble and insoluble radioactive material was transported through the septo-hippocampal pathway to the dentate gyrus. This transport was inhibited by the injection of colchicine into the septum prior to 3H-fucose injection and was completely blocked by electrolytic lesion of the medial septal nucleus. The arrival time and the amount of the TCA-PTA soluble radioactive material transported to the dentate gyrus did not differ in young adult and senescent rats. However, the TCA-PTA insoluble labelled glycoprotein was transported to the dentate gyrus in a significantly smaller amount and during a longer period of time in the senescent animals. This age-related change may reflect a reduction in amount and/or in rate of axonal transport of glycoproteins in the septo-hippocampal pathway of senescent rats.

Aging↗
PubMedDate not supplied

Age-dependent alterations in hippocampal synaptic plasticity: relation to memory disorders.

In this paper, we review the evidence indicating that the common disturbance in recent memory associated with aging is a consequence of functional and structural impairment in the hippocampal formation. In the Fischer 344 rat, an experimental model of the human age-related memory disorder was developed. The majority of aged rats of this strain show impaired performance in the 8-arm radial maze in a manner typical of young rats with bilateral hippocampal lesions. Aged animals also exhibit rapid decay of LTP and slower kindling of the perforant path-dentate synapse. Furthermore, quantitative morphometric analysis of the hippocampal synaptic architecture revealed that aged, memory-impaired rats had a specific loss of perforated axospinous synapses in the middle third of the dentate gyrus molecular layer; the extent of loss was directly related to the degree of memory dysfunction. Most important was the fact that the electrophysiological and morphological abnormalities did not appear in equally old animals with good memory.

Aging↗