Increase In Synaptic Density Research Articles

Effects of partial truncal vagotomy on intragastric pressure responses to vagal stimulation and gastric distension in ferrets.

Changes in intragastric pressure after dorsal truncal vagotomy, investigated by stimulation of the surviving vagal branches and by step inflation of the stomach, were divided into an early phase lasting five days, and a late phase continuing for at least three months. During the early phase the amplitude of vagal evoked contraction was diminished but the resting pressure and the response to gastric inflation were increased. After the fifth day vagal evoked contractions doubled in amplitude but the resting pressure and the response to step inflation of the stomach returned to control levels. Ventral vagotomy did not produce any substantial changes. Alterations to gastric and body weight, or to the relation between resting pressure and evoked contraction and relaxation were excluded as causes of the enhanced vagal effectiveness. Sprouting of axons into denervated territory occurred too late to explain the changes, but an increase in synaptic density within the innervated territory has not been ruled out.

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.

Cytodifferentiation and synaptogenesis in the neostriatum of fetal and neonatal rhesus monkeys.

Cytodifferentiation and synaptogenesis in the neostriatum (caudate nucleus and putamen) were analyzed by the Golgi impregnation method and electron microscopy in 14 fetuses and 8 postnatal rhesus monkeys. During the second fetal month the neostriatum consists primarily of simple, mostly bipolar, immature cells and a small number of undefined profiles ending with growth cones. The first morphologically defined synapses appear in the putamen at embryonic day 60 ( E60 ) and in the head of the caudate nucleus at E65 . Synaptic density in both structures is less than one per 1000/micron2 of neuropil at this stage; synapses are characterized by asymmetric junctions between axonal profiles and immature dendritic shafts, accumulation of an intermembrane web and aggregation of round clear vesicles in presynaptic profiles. During the third fetal month neuronal cell bodies and glial cells enlarge, and axonal and dendritic processes in Golgi preparations become more complex. Although the basic morphology of synapses remains unchanged, their density increases to 9/1000 micron2 in the putamen and 3.7/1000 micron2 in the caudate. During the fourth fetal month the four principal cell classes of the neostriatum emerge. Spines on the shafts of dendrites are followed closely by the appearance of axospinous synapses. Synaptic density in the putamen is still significantly higher (10.1/1000 micron2) than in the caudate (5.4/1000 micron2), but by the end of the fifth fetal month ( E150 ) it is the same (80/1000 micron2) in both structures. A dramatic increase in synaptic density to 125/1000 micron2 occurs before term ( E165 ) with the emergence of the first asymmetric synapses as well as symmetric synapses with flat or pleomorphic vesicles that terminate predominately on dendritic shafts. Synaptic density continues to increase after birth, reaching a plateau of approximately 190/1000 micron2 at the end of the first postnatal month. Throughout postnatal development the proportions of symmetric and asymmetric synapses on the smooth dendritic shafts undergo systematic fluctuations which may reflect the ingrowth of various afferents as well as local cytological differentiation including the formation of cellular compartments.

Synaptic development in the human fetus: A morphometric analysis of normal and Down's syndrome neocortex

Postmortem tissue was obtained from six normal and four Down's syndrome brains ranging in age from 12 to 40 weeks postconception. Tissue was processed for electron microscopy using routine osmium and EPTA staining procedures, and to examine synaptic development, photomicrographs were systematically taken throughout the molecular layer of the sensorimotor neocortex. The number of EPTA-stained synapses were consistently greater than the number of osmium-stained synaptic contacts. A progressive increase in synaptic density throughout the range of ages examined was observed for both normal and Down's syndrome tissue. There was also an increase with developmental age in apparent measures of synaptic maturity, e.g., an increased ratio of mature to primitive contacts and asymmetrical to symmetrical contacts. In normal tissue, pre- and postsynaptic membrane lengths were observed to increase with the ages studied, whereas synaptic membrane widths appeared to attain mature values by 29 weeks postconception. Cleft width remained fairly constant to 28 weeks postconception. Although direct statistical comparisons could not be made, in Down's tissue synaptic parameter development was generally less consistent and the parameters appeared to be reduced during the later stages of development studied.

A quantitative ultrastructural study of the effects of phenylacetate on synaptic organization in the developing rat cerebral cortex.

Male rats were injected with either phenylacetate (PA; a phenylalanine metabolite) or saline (control). Osmicated tissue from the parietal cortex was analyzed qualitatively and quantitatively, attention being focused on possible synaptic changes in the molecular layer. PA-treated rats differed from controls in the following ways: a 20% decrease in body weight at 21 days, and a reduction in brain weight at 10 and 21 days; the presence of 'atypical' profiles (possibly derived from axonal growth cones) in the neuropil; a lag in the accretion of synapses per 100 micron2 of tissue, and of vesicles per micron2 of presynaptic terminal; the presence of a 'crossover' in the developmental trend for several synaptic organizational parameters between days 15 and 21; an elevation in synaptic density at day 21; an increased proportion of negatively curved synapses at 21 days; a significant difference in the preponderance of axodendritic synapses over days 7-21. This suggests that the metabolism of some neurons in the PA brain is initially different from normal, with a lag in synaptic development being evident. The increase in synaptic density and the relative preponderance of other synaptic parameters at 21 days signifies that an initial lag in development may alter the developmental scheme. This may be coupled with changes in synaptic efficacy and connectivity.