Changes of synaptic density in the primary visual cortex of the macaque monkey from fetal to adult stage

Abstract

The kinetics of synaptogenesis in the primary visual cortex (Brodmann's area 17) were analyzed by electron microscopy in 33 rhesus monkeys, ranging in age from the 50th embryonic day (E50) to 20 years. A series of overlapping electron micrographs (vertical probes) were examined at each age on sections of the upper bank of the calcarine fissure. Synaptic contacts were first observed in the E50 specimen in the subplate and marginal zone (prospective layer I). In the cortical plate itself, synapses appear between E65 and E89 starting in the prospective layer VI. By E112, after all cortical neurons have assumed their laminar positions, synapses situated predominantly on dendritic shafts were present at a low density throughout the full thickness of the cortical plate. Thereafter, synapses accumulate more rapidly on dendritic spines and by E144 an equal number of contacts are found on both spines and shafts. The density of synapses continues to increase exponentially in all layers and reaches the mean maximum density of about 90 synapses per 100 microns 3 of neuropil by the third postnatal month. During the next 2 postnatal years the density of synaptic contacts decreases only slightly to a mean of 80/100 microns 3 of neuropil. Around the time of puberty, however, synaptic density decreases more rapidly to reach the adult level of about 40-50/100 microns 3 of neuropil. The 40% decrease in the density of synaptic contacts occurring between 2.7 and 5 years represents a loss of about 5000 synapses per second in the primary visual cortex of the two hemispheres, due primarily to the loss of asymmetric synapses situated on dendritic spines. The transient phase of high density of synaptic contacts located on dendrospines is shorter in thalamo-recipient layer IV than in either supra- or intragranular layers and is completed within the first postnatal year. It ends earlier in sublayer IVC than in layers IVAB and II-III, for example, reflecting biochemical and functional maturation of the different visual subsystems.

Synaptophysin and postsynaptic density protein 95 in the human prefrontal cortex from mid-gestation into early adulthood

“…The pattern of immunoreactivity on Western blots demonstrated by the synaptic marker synaptophysin in human PFC generally agrees with previous studies of developmental changes in synaptic density in the primate cerebral cortex (Huttenlocher 1979;Rakic et al 1986;Zecevic et al 1989;Bourgeois and Rakic 1993). The present data suggests robust synaptogenesis during early childhood, with synaptic density reaching a peak in late childhood, followed by the onset of synaptic elimination (a.k.a.…”

“…Because spines typically receive only one asymmetric synapse (DeFelipe and Farinas 1992;Harris and Kater 1994), the number of spines is a good approximation of the total number of excitatory synapses on a dendrite. The developmental regulation of synaptic density occurs primarily via pruning of the excitatory axospinous synapses (Bourgeois and Rakic 1993). Accordingly, it is the synapses onto spines that have been shown to be selectively eliminated after birth (Zecevic et al 1989).…”

Brain state regulation during normal development: Intrinsic activity fluctuations in simultaneous EEG–fMRI

“…State independent, general mechanisms are also implicated by the fact that global EEG power decrease parallels maturational trajectories in sleep (Buchmann et al, 2011) and awake resting state (Whitford et al, 2007). Gray matter decrease reflects synaptic pruning (Bourgeois and Rakic, 1993;Huttenlocher, 1979), which presumably eliminates redundant connections and may be disrupted in adolescent psychiatric diseases (Paus et al, 2008). Physiologically, synaptic density may affect EEG power, as synaptic density reflects the connectivity and size of neuron populations from which EEG power partly derives (Boord et al, 2007;Feinberg and Campbell, 2010).…”

Evaluation of headache intensity in migrainous patients with visual handicap through the tactile analogical scale (TAS)

“…It is known that the re-organization of the occipital cortex is interrupted at about 14 years old 30 . The age group coincides with the puberty and is associated with a reduction of supernumerary synapses inside the visual cortex 31,32 . Another associative via that occurs between the somatosensory cortex (touch) and visual cortex is through crossmodal mechanism.…”