Ultrastructure of developing substantia nigra in humans

Abstract

Electron microscopy of the maturing neurons and developing and maturing synapses in the substantia nigra of 14 human embryos/foetuses of 8-24 weeks of gestation are reported. At 8 weeks, cells were immature with very little cytoplasm and cellular organelles. Contact sites of processes appeared more electron dense than the other areas. At 12 weeks, many of the cells had acquired more cytoplasm and cellular organelles and could be identified as neurons. Asymmetric synapses with clear, round synaptic vesicles also were identifiable at this age. Such synapses, first to appear in the developing substantia nigra, are reported to be formed by recurrent collateral nigro-striatal fibres. Substance P fibres from the striatum also are contributing to this type of synapse. At 15-16 weeks, not only was the number of such synapses increased, but many appeared morphologically mature. Symmetric synapses having clear round vesicles along with a few dense core vesicles also appeared at this stage, suggesting striatal input. By 24 weeks of gestation, most of the neurons had cytological features comparable to that of the mature neurons. There was an increase in the total number of synapses and the individual variety from 15 to 24 weeks of gestation. The present study indicates that synaptogenesis starts at 8 weeks and continues beyond 24 weeks of gestation.

A Histological and an Immunohistochemical Study on the Effects of Iron Overdose on the Basal Ganglia of the Adult Albino Rat

“…The cytoplasm contained distinct aggregates of short RER cisternae with many free polyribosomes between them and scattered mitochondria. The present results were in agreement with other studies [32,37] . Asymmetrical synapses with many synaptic vesicles and mitochondria were observed by electron examination of the SNc in this study.…”

Effect of Neuroinflammation on Synaptic Organization and Function in the Developing Brain: Implications for Neurodevelopmental and Neurodegenerative Disorders

“…Postnatally, the number of synapses first continue to grow and later begin to decline until reaching stability in infancy or adulthood, depending on the brain region (Huttenlocher and de Courten, 1987; Huttenlocher and Dabholkar, 1997). It was demonstrated that in the human substantia nigra, synapses start to form by week 12 of gestation and become mature by week 15–16 (Sailaja and Gopinath, 1996). The synapse density reaches its peak in human auditory cortex by 3 months of age while in prefrontal cortex this occurs by 3.5 years of age.…”

Differences in Neuronal Numbers, Morphology and Developmental Apoptosis in Mice Nigra Provide Evidence of Ontogenic Origin of Vulnerability to Parkinson’s Disease

“…Cytomorphological and molecular features of maturation of the nigral DA neurons are seeded during ontogenesis [21,22]. The total number of DA neurons at adulthood may thus be nalised during the postnatal period.…”

“…Preserved motor behavior and compensated/unaffected striatal local eld potentials in PD reminiscent conditions in CD-1 and the crossbreds complement the cytomolecular observations [18]. These features indicate that admixing imparts resilience.Cytomorphological and molecular features of maturation of the nigral DA neurons are seeded during ontogenesis [21,22]. The total number of DA neurons at adulthood may thus be nalised during the postnatal period.…”