Early development of tyrosine hydroxylase-like and substance P-like immunoreactivity in the human fetal retina.

Tyrosine hydroxylase-(TH)-like and Substance-P-(SP)-like immunoreactivity has been tentatively located in the retina of 24-29 week-old fetuses, newborn infants, 2-8-month-old children, and adults. The first TH immunoreactive cells were demonstrated as early as 24 weeks of fetal life, while SP immunoreactivity appeared a little later, between 24 and 29 weeks. Thus the period ranging between 24 and 29 weeks of fetal life is considered to be important in the establishment of transmitter specific characteristics in human retinal neurons.