Abstract
GABA has been believed to be a sole transmitter in spinal presynaptic inhibition. Recently, transmitter switching was reported in the lower central nervous system. That is, transmitter for IPSP was initially GABAergic, and was changed to be glycinergic during early development. This experiment was planned to elucidate the possibility of this transmitter switching in primary afferent depolarization ( PAD ), which is closely related to presynaptic inhibition. In the isolated spinal cord preparation from newborn rats, the dorsal root ( L4 or L5 ) was split into two or three rootlets. Using suction electrodes, one rootlet was stimulated electrically and PAD was recorded from the adjacent rootlet. PAD consisted of fast and slow portions. The slow PAD was usually hidden, and appeared only when bicuculline or ( /and ) strychnine was applied. The fast PAD was glycinergic and GABAergic, and the slow PAD was glutaminergic. In this report, the fast PAD will be discussed. In 0-day-old rat, strychnine had little effect, and additional bicuculline eliminated fast PAD. In 7-day-old rat, strychnine enhanced fast PAD, and additional bicuculline eliminated it. In older rats, strychnine depressed fast PAD to a little extent, and additional bicuculline eliminated it. These results suggested that PAD at birth was dependent predominantly on GABA, and that glycinergic component increased until 7th day. In older age, glycinergic component decreased. It is concluded that a part of transmitter in related to PAD, changed from GABA to glycine, but this change is only transient in the course of development. [Jpn J Physiol 55 Suppl:S145 (2005)]
