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

Abstract

The ultrastructure of synapses from the molecular layer of parietal cortex was examined in male rats aged between 7 and 75 days. Two groups were compared, one group consisting of rats anaesthetized with 50 mg/kg pentobarbitone and the other consisting of those killed by stunning across the back of the neck. Various synaptic parameters were analyzed. In the anaesthetized material, the sectioned area of the pre-synaptic terminals decreases between 7 and 75 days, as does the number of terminals containing intraterminal profiles other than synaptic vesicles. Mean synaptic vesicle number per terminal increases, while the remaining parameters fluctuate over the developmental period. Comparing these data with those from the unanaesthetized material, the only parameters showing similar trends are the pre-synaptic terminal area, the mean vesicle number per terminal, and the length of the post-synaptic thickening. The remaining parameters are comparable up to 15 or 21 days post-natally, after which they diverge. The percentage of terminals containing intraterminal profiles, the terminal perimeter and the mean vesicle density in the unanaesthetized terminals all show increased values. The form factor indicates these terminals are more ellipsoidal by 75 days, while the mean synaptic curvature is more positive by 75 days. It is concluded that the synaptic organization of the early terminals differs from that of the older ones, and this may be related to different mechanisms of transmitter storage and release.

Ultrastructural Investigation into the Influence of Ethanol on Synaptic Maturation in Rat Neocortex

“…4). This is in ac cordance with other developmental studies [9]The number of synaptic vesicles per pre synaptic terminal increased from day 7 to 76 in the three groups ( fig. 5).…”

“…Since this parameter has proved an extremely reliable indicator of terminal maturity [12,20,25], the present results indicate the absence of a developmental lag following ethanol admin istration. The constancy of the length of the postsynaptic thickening is again typical of the synaptogenic literature [3,9,20] and under lines the normality of the developmental pro cess in this study. One difference to emerge in this study concerns synaptic curvature, which shows no developmental trend, in con trast to the increased proportion of flat and positive junctions with development in other studies [9,12,23].…”

“…The constancy of the length of the postsynaptic thickening is again typical of the synaptogenic literature [3,9,20] and under lines the normality of the developmental pro cess in this study. One difference to emerge in this study concerns synaptic curvature, which shows no developmental trend, in con trast to the increased proportion of flat and positive junctions with development in other studies [9,12,23]. The area of the postsynap tic thickening increases with age in the three groups.…”

“…This has previously been reported by Dyson and Jones [12], although there is a discrep ancy between published data on the develop mental trend of this parameter [9,20], proba bly resulting from different criteria used to delineate terminal boundaries. Terminal perimeter values increase with age.…”

“…Such parameters have proved of value in monitoring synaptic trends in a variety of ex perimental situations, including the effects on the developing brain of malnutrition [11,23], phenylacetate [25], stimulation [ 14], and anaesthesia [9,22]. They have also been employed to follow the response of neural tis sue to K+ and veratridine stimulation and Mg2+ inhibition [15,17], to ovariectomy [24], and to differential rearing [31].…”