Morphological and Biochemical Changes in Rat Synaptosome Fractions During Neonatal Development

Abstract

A biochemical and quantitative morphologic study of presynaptic endings during postnatal development was carried out in subcellular fractions from cerebral cortex of 1, 4, 8, 12, and 18 day old and adult rats . Crude mitochondrial fractions were subfractionated in Ficoll gradients and all resulting fractions were examined in the electron microscope . Presynaptic terminals and other intact processes were counted . Protein content and enzyme activities were assayed in the fractions and in total brain homogenate . In the first and fourth day of life, most of the presynaptic terminals were found in two "light" fractions, between supernatant and 7 .5% o Ficoll, where they accounted, respectively, for 6 and 22% of all the processes . Progressively with age, more presynaptic terminals were found in the traditional "synaptosomal" fractions between 7 .5 and 13% Ficoll . In that region of the gradient, 40, 54, 75, and 89 % of the processes were presynaptic endings at 8, 12, and 18 postnatal days and in the adult animal, respectively . A similar shift from the lighter to the heavier fractions was observed in the distribution of choline acetyltransferase and acetylcholinesterase between days 8 and 12 . The rate of increase of the specific activity of these two enzymes paralleled that of the percentage of the presynaptic endings after day 8 . This study indicates that subcellular fractions can be used to study formation and maturation of synapses during postnatal development .

Developmental Changes in Brain TRH and in Plasma and Pituitary TSH and Prolactin Levels in the Rat

“…A function of neurotransmitter has been proposed for TRH on the basis of its wide distribution throughout the brain (1, 2), its localization in nerve endings (22), and its effects on behavior (23). During the first month of life, there is an active myelin formation, a marked growth of axons and dendrites from neurons (24), a progression of synaptic contacts (25) and a large increase of various enzyme activities in the brain (26). The physiological influence of TRH on the brain may be of importance during this period of time.…”

Synaptic Parameters in Developing Rat Cerebral Cortex: Comparison of Anaesthetized and Unanaesthetized States

“…It has recently been shown that synaptic curvature varies with age, young material (up to 15 days post-natally) exhibiting a greater range of curved synapses than older material [17], Other parameters, such as vesicle num bers per terminal, increase with age [19], while the length of the post-synaptic thicken ing fluctuates, as does the mean axial ratio of the pre-synaptic terminal [3,17].…”

Skeletal Muscle Calcium Metabolism and Contractile Force in Vitamin D-deficient Chicks

“…To estimiiate the rate of relaxation of triceps surae after cessatioin of electrical stimiiulation of posterior tibial nerve, the timiie required for tension to fall from the deflectioni point at the end of the tetanic plateau to one-halfthe plateau tension value (T1,2 relaxation time) (6) (14). Osmium tetroxide was used instead of Dalton's fixative.…”