Retinal regeneration in the adult newt, Notophthalmus viridescens: Appearance of neurotransmitter synthesis and the electroretinogram

The removal or destruction of retina in the adult newt, Notophthalmus viridescens, leads to the formation of a new functional retina by metaplasia of the pigment epithelium. In order to understand the physiological and biochemical changes that occur during regeneration, we have examined the time-course of appearance and maturation of the electroretinogram (ERG) and correlated it with the synthesis of the neurotransmitters, acetylcholine (ACh) and γ-aminobutyric acid (GABA). In addition, we have also determined the pattern of DNA, RNA, and protein synthesis in the regenerating retina. Our experimental results show that: (1) the major peaks of DNA, RNA, and protein synthesis occur at different times during regeneration and that the synthesis of RNA precedes that of DNA which is followed by the protein; (2) synthesis and accumulation of ACh and GABA is lost by the fifth day following ocular devascularization and it reappears by day 23-24. ACh and GABA syntheses continue to increase until they attain plateau around day 35; (3) the appearance of choline acetyltransferase and glutamate decarboxylase activities parallel ACh and GABA synthesis; and (4) transmitter synthesis precedes development of the ERG. The first light evoked response is seen around day 29 by which time the transmitter synthesis is well advanced.