The effects of amino acids and antagonists on the isolated hemisected spinal cord of the immature rat.

1 Records of ventral and dorsal root polarity of the isolated hemisected spinal cord of the 3-9 day old rat showed that respective dose-dependent depolarizations of motoneurones (VR responses) and primary afferent terminals (DR responses) were produced by both acidic and neutral amino acids in the presence of procaine (1 mM) or tetrodotoxin (0.1 micron). 2 Of the four neutral amino acids, gamma-aminobutyrate (GABA), glycine, taurine, and beta-alanine, GABA was the most effective in producing DR responses and glycine the most effective in producing VR responses. Only taurine depressed the electrical activity recorded from ventral roots. 3 The DR responses produced by GABA, beta-alanine and taurine were all antagonized by bicuculline (5 micron) and picrotoxin (5 micron). Bicuculline was more selective than picrotoxin in antagonizing VR responses produced by GABA. 4 Strychnine (1 micron) antagonized VR responses produced by glycine beta-alanine and taurine without affecting responses produced by GABA. DR responses to the neutral amino acids were unaffected by strychnine.