Prenatal and perinatal development of the somatostatin-immunoreactive neurons in the human prefrontal cortex

The earliest somatostatin-immunoreactive (SS-Ir) perikarya of the human fetal frontal cortex appear in the transient subplate zone at 22 weeks of gestation. Around 32 weeks of gestation there is an increase in the number of SS-Ir neurons at the interface between the subplate zone and the cortical plate. The newborn-cortex shows decline in the overall number of SS-Ir neurons parallel to the appearance of SS-Ir neurons in the superficial layers. In conclusion, the subplate neurons are the source of the earliest peptidergic activity in the cortex. Furthermore, the distribution and density of peptidergic neurons undergo significant reorganization during the perinatal development.