Effects of barium on isolated frog spinal cord

Abstract

1. 1. The effects of Ba 2+ were studied in vitro on the isolated frog spinal cord. 2. 2. Ba 2+ (25μM–5mM) caused a concentration-dependent depolarization of ventral (VR) and dorsal (DR) roots. TTX and MgP 2+ substantially reduced the depolarization suggesting that interneuronal effects were involved. 3. 3. Ba 2+ (25–500μM) markedly increased the frequency and duration of spontaneous VR and DR potentials and substantially enhanced the duration (and frequently the amplitude) of VR and DR potentials evoked by DR stimulation. Higher concentrations of Ba 2+ (1–5 mM) reduced both spontaneous and evoked potentials. 4. 4. Bs 2+ (25–500 μ M) enhanced the amount of K. + released by a DR volley and by application of l-glutamate and l-aspartate. The cation reduced VR and DR root depolarizations produced by elevated [K +] 0. 5. 5. VR potentials induced by l-glutamate, l-aspartate, GABA and glycine and DR depolarizations caused by GABA were reduced by Ba 2+. 6. 6. These results show that Ba 2+ has complex actions on reflex transmission, interneuronal activity, the postsynaptie actions of excitatory and inhibitory amino acids and the evoked release of K +.