AN IMMUNOHISTOCHEMICAL STUDY OF NEUROTRANSMITTER PROFILES IN DEVELOPING HUMAN VISUAL-CORTEX

The temporal pattern of development and distribution of gamma aminobut yric acid, serotonin, substance P and neuropeptide Y immunoreactive pr ofiles was studied in the human visual cortex from 16 to 26 weeks of g estation, using an immunohistochemical technique. The immunoreactive p rofiles showed an increase in number and a change in their morphology and distribution pattern over the time period studied. A large number of neurons, fibers and terminals were stained with GABA antibody at 17 -18 weeks and were distributed throughout the five zones of the develo ping visual cortex. GABA neurons were non-pyramidal and bipolar in for m at 17-18 weeks while at 18-19 and 20-21 weeks the cells of subplate and intermediate zones were multipolar. Substance P and serotonin immu nopositive fibers were present mainly in the intermediate zone at 16 a nd 17-18 weeks, where they were oriented in a horizontal manner. At su bsequent ages they invaded the other zones also. Substance P positive neurons could be visualized only at 26 weeks of gestation in the inter mediate, subventricular and ventricular zones; no cell bodies, however , stained with serotonin antibody. Neuropeptide Y immunoreactive cells and fibers were first seen in the intermediate zone but later were fo und to be distributed in other zones too. The observations indicate th at the intermediate zone of the visual cortex in which the transmitter s and peptides appear earlier assumes importance in the normal develop ment as also noted in other mammals.