Researchers at University of Calgary Faculty of Medicine and Alberta Children's Hospital, Canada, have studied synaptophysin immunoreactivity (sIR) in postmortem sections of 162 normal human fetal and neonatal brains of both sexes from 6 to 41 weeks' gestational age. A consistent temporal and spatial pattern of sIR was apparent in the hippocampus and cerebral neocortex. In the hippocampus, sIR first developed in the molecular zone of the dentate gyrus at 12 weeks and successively in CA2, 3, 4, and CA1, until complete at 26 weeks. In frontal neocortex, sIR developed in a laminar pattern starting at 12 weeks, and was complete at 38 weeks. The sIR was preserved for >96 hours postmortem, even in autolytic brain. Synaptophysin is a reliable marker of synaptic vesicle formation in axonal terminals and hippocampal and neocortical maturation or immaturity. [1]

COMMENT. The reader is referred to the excellent colored sections of fetal and term neonate hippocampus and cortex in the original article. The authors add that synaptogenesis is concerned with maintenance of a resting membrane potential and excitability and synthesis of chemical neurotransmitters. The fetal EEG (Anders T et al, 1971) and magnetoencephalography may correlate with brain development, but histological and synaptophysin studies provide the optimal means of determining the temporal and spatial sequence of synaptogenesis in developing brain. sIR correlates with thalamocortical development and EEG maturation in the fetus and neonate. The four dominant patterns of fetal EEG are low voltage irregular 10-25 mcv at 5-10 cps; mixed activity 10-50 mcv at 2.5-10 cps; high voltage slow 50-100 mcv at <5 cps, and trace alternant 20-100/5-25 mcv at 2.5-10/2.5-15 cps. Surface abdominal EEG recordings were unsatisfactory. [2]