Numerical estimates of GABA immunoreactive neurons in the human lateral geniculate nucleus in the prenatal period.

Quantitative analysis has been performed on Nissl stained and gamma-aminobutyric acid (GABA) immunoreactive neurons in the lateral geniculate nucleus (LGN) of human fetuses ranging from 8 to 37 weeks of gestation. Total cell density in the LGN increases from 8 to 12 weeks of gestation with a subsequent decline continuously up to 37 weeks. No GABA immunoreactive neurons are visualized in the LGN of 8 and 12 weeks fetuses. At 15-16 weeks of gestation 1% of neurons are immunostained. A peak rise is seen to occur at 17 weeks when 16% cells are GABA immunopositive. However, at 19 weeks there is an equally sharp decline in the percentage of GABA neurons to 4%. Subsequently, with the continued reduction in overall numerical density the percentage of GABA neurons remains relatively constant but rises again to 5% at 26 weeks. On making quantitative estimations of numerical density and percentage of GABA neurons separately for the prospective magno- and parvocellular regions in the early age periods from 15-16 to 21 weeks as well as at 22-23 weeks, when magnocellular laminae begin to segregate, and at 26 weeks when distinct laminae are present, it is observed that the magnocellular regions have a higher density and percentage of GABA neurons at all the gestational ages in comparison to the parvocellular region. With increasing gestational age, non-GABA neurons gradually increase in size with marked growth of magnocellular neurons at 26 weeks. The GABA neurons, on the other hand, have an almost constant size up to 19 weeks and start growing from 21 weeks onwards. The GABA neurons tend to be larger in the magno- than in parvocellular regions at all gestational ages studied.