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E J Markus

Publications and source records attributed to E J Markus.

6 recordsLinked to original sources
PubMed1989

Synaptic structural plasticity: role of synaptic shape.

Recent research has indicated that synaptic curvature is an important and potentially critical plastic feature of the synapse. Alterations in synaptic shape are related to synaptic function, being found both during maturation and in adulthood following neuronal activation. In this paper we review the evidence supporting synaptic shape as a plastic feature of synaptic structure. We also propose several mechanisms which might underlie these changes in shape. Finally, we suggest the possible functional role of alterations in synaptic curvature, including its potential in altering synaptic transmission efficacy.

Aging↗
PubMed1989

Synaptic structural plasticity following repetitive activation in the rat hippocampus.

The morphological effects of repetitive neuronal activation following systemic kainic acid administration were examined in hippocampal CA1 stratum radiatum synapses. Sporadic activation of CA3 and CA1 neurons began approximately 15-25 min after kainic acid administration, which was followed at 1-2 h by repetitive ictal firing until the completion of the experiments at 4 hr. Synaptic density in the CA1 region increased following stimulation, reaching significance at the earliest time period examined, approximately 5-15 min postactivation. There was an initial increase and then a decline in frown (and then flat)-shaped synaptic subtypes, with an ultimate increase in smile-shaped synapses. This pattern is consistent with either a change in synapses from frown to smile shaped or a selective gain/loss of synaptic subtypes. There was also an increase in the size of smile-shaped synapses, but a decrease in the size of frown synapses. By 4 h there was a decline in most indices of synaptic morphology, suggesting that the stimulation had become cytotoxic. These results indicate that the number and morphology of synapses and synaptic subtypes can be modified with relatively short periods of repeated use and suggest their potential role in activity-dependent phenomenon such as information storage and epilepsy.

Animals↗
PubMed1987

Neocortical synaptogenesis, aging, and behavior: lifespan development in the motor-sensory system of the rat.

Little evidence presently exists on the development and aging of synaptic contacts and their relationship to behavior, particularly in nonvisual brain areas. To investigate this interrelationship, rats at a series of developmental ages [postnatal day 1 (P1) to P90] were initially examined on a battery of motor tasks. The battery, ranging from simple reflexive tests to tests of complex locomotor capacities, consisted of tactile-induced forelimb placing, chin-induced placing, body righting, climbing an inclined plane, traversing a narrow beam, and keeping up with a revolving wheel. Following completion of the behavioral testing, the animals, together with an additional group of aged (28- to 29-month-old) rats, were killed and their motor-sensory cortex was removed, stained with osmium tetroxide or ethanol phosphotungstic acid (EPTA), and examined under electron microscopy for density of synaptic contacts. Simple motor abilities such as tactile-induced placing was present by the end of the first postnatal week, with locomotor performance reaching a mature level by the end of the third postnatal week, and intermediate task abilities maturing within this range. Paralleling the development of complex locomotor skills was a sharp increase in synaptic density in the molecular layer of the motor-sensory cortex, commencing in the second postnatal week and peaking at P30. After P30 there was a sharp decline in synaptic density as well as a decline in performance on some motor tasks, although these two functions seemed to be occurring independently. There was a continued, but less dramatic synaptic loss evident in the aged rats.

Aging↗
PubMed1987

Synaptic structural changes during development and aging.

Although a great deal is known about the development of synaptic number, comparatively little is known about the effects of development, and particularly aging, on the structure of the synapse. The present study examined synaptic structure in the molecular layer of the motor-sensory neocortex during early development (postnatal days (P) 1, 3, 5, 7, 10, 15, 20, 30), adulthood (P60, 90), and old age (28 months). Tissue was stained with osmium tetroxide (osmium) or ethanol phosphotungstic acid and the following synaptic characteristics were quantified: (1) presynaptic element length, area, thickness, maximal projection height and smoothness, and number and size of vesicles adjacent to the presynaptic element; (2) postsynaptic element length, area, and thickness; and (3) cleft width. There is an early developmental increase in synaptic element length, followed by an increase in thickness into adulthood. During development the height and width of the presynaptic dense projections increase, after which they remain stable. While the number of adjacent synaptic vesicles increases throughout the lifespan, there is a parallel decrease in their size. During the period of rapid synaptogenesis in this brain region there are no decreases in any of the synaptic structural parameters examined, indicating that newly generated synapses are either formed the same size as the existing mature synapses, or are extremely plastic and grow very rapidly. Unlike age-associated changes in synaptic number, no changes were found in synaptic structure during aging.

Aging↗