Prenatal development of gabaergic, glycinergic, and dopaminergic neurons in the rabbit retina

The main findings from our studies on the emergence and maturation of neurotransmitter systems in the rabbit retina are that, during normal development: (1) the commitments for certain neurons to become GABAergic, glycinergic, or dopaminergic are made prenatally; the maturation of these neurons, however, occurs postnatally; (2) specific accumulations of exogenously supplied transmitters by presumed retinal neurons were first observed autoradiographically around embryonic day 22 (E22) for gamma-aminobutyric acid (GABA), E25 for glycine, and E27 for dopamine, suggesting that putative GABAergic, glycinergic, and dopaminergic neurons are determined phenotypically at least by these days; (3) based upon the three transmitter-specific properties--uptake, synthesis, and release--the uptake property is generally the first to emerge, while the appearance of the other properties follows a precise and distinct temporal pattern for each of the transmitters studied; (4) for GABAergic and glycinergic systems, the emergence of K+-stimulated, Ca2+-dependent release mechanisms occurs many days after the first appearance of the uptake properties; in contrast, the mechanisms for dopamine uptake and release emerge at about the same time; and (5) by our criteria, putative GABAergic and glycinergic amacrine cells are mature between postnatal day 10 (P10) and P12, around the time when the eyes first open and direction-selective ganglion cells can first be recorded; however, the dopaminergic neurons probably are not mature until about P24.