Temporal distribution of mRNA expression levels of various genes in the developing human inferior colliculus

The inferior colliculus (IC) is a major binaural integration center in the auditory pathway. Interestingly, studies on the prenatal development of the human IC are lacking. During development of the nervous system a large repertoire of proteins is involved in transforming simple neuroblast cells into functional elements of the adult neural circuits. The present study reports on the mRNA levels produced by 12 genes involved in pre- [12-29 weeks of gestation (WG)], postnatal [40 postnatal days (PND) as well as 2 and 5 postnatal months (PNM)] developing human IC. The mRNA expression levels of nestin, vimentin, GFAP and DCX during 12-24 WG indicate the stages of neurogenesis, migration and differentiation of the human fetal IC. A decrease in the GAP-43 mRNA levels along with an increase in synaptophysin and PSD-95 mRNA levels during late gestational ages (24-29 WG) suggests the formation of primitive contacts by neurons with their targets and the onset of synapse formation. Expression levels of EGAD mRNA were transient with an increase in the early gestational ages, whereas that of GAD-67 mRNA increased in late gestational ages, indicating the changing role of GABA from a trophic factor to that of a neurotransmitter. High levels of BDNF, NT-3 and MBP mRNA in the late gestational ages reveal that the human IC undergoes neuronal maturation, synaptogenesis and myelination by 29 WG. Therefore, it may be suggested that the morphological maturation of the human IC occurs between 22 and 29 WG and that this period appears to be critical in the shaping of adult-like physiological attributes.