Postnatal development of GABA- and glycine-mediated inhibition of feline retinal ganglion cells in the area centralis.

Intraretinal iontophoresis in the optically intact eye of adult cats (18-22 weeks of age) and kittens (7-9 weeks of age) under pentobarbitone anaesthesia was performed. Studies were concentrated on retinal ganglion cells of the sustained (X) type in the area centralis under photopic conditions. In both the adult and kitten, gamma-aminobutyric acid (GABA) and muscimol inhibited the visually induced excitation, and bicuculline blocked the visually induced inhibition of on-cells. On the other hand, glycine inhibited the excitation and strychnine blocked the inhibition of off-cells. However, a greater current of GABA (muscimol) and glycine was required to produce total inhibition in kitten's on- and off-cells respectively when compared with the adult's. Furthermore, a smaller current of bicuculline and strychnine was needed to abolish the visually induced inhibition of kitten on- and off-cells respectively when compared with the adult's. In the adult, GABA and glycine did not affect the responses of off- and on-cells respectively, but in the kitten GABA inhibited off-cells and glycine inhibited on-cells to some extent. In neither the adult nor the kitten did bicuculline have any effect upon off-cells or strychnine any effect upon on-cells. Thus, the sustained on- and off-cells in the kitten area centralis exhibit: a reduced selectivity to inhibitory transmitters; a reduced sensitivity to exogenously applied inhibitory transmitter agonists; but a greater sensitivity to inhibitory transmitter antagonists, in comparison with the sustained on- and off-cells in the adult area centralis. The observed differences between the kitten and adult cat in transmitter actions on retinal ganglion cells appear to be analogous to those found in the postnatal development of functional synapses at the neuromuscular junction and sympathetic ganglia.