Depolarizing responses to glycine, β‐alanine and muscimol in isolated optic nerve and cuneate nucleus

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Abstract
1 Concentration-dependent depolarizations were evoked by glycine and β-alanine 5 × 10−4-10−2m and by the γ-aminobutyric acid (GABA) analogue, muscimol 10−6-10−4m. 2 The maximal response to glycine was several-fold higher than that to muscimol on optic nerve but the reverse was found on the dorsal funiculus fibres in the cuneate nucleus, β-Alanine evoked a similar maximal response to glycine on optic nerve but a considerably higher maximum than glycine in the cuneate nucleus. 3 Strychnine was 19.5 times more potent as a glycine antagonist (pA2 = 6.58) than as a muscimol antagonist. Bicuculline was 156 times more potent as a muscimol antagonist than as a glycine antagonist. Other antagonists of muscimol, i.e. tubocurarine, Picrotoxin and leptazol, and potentiators of muscimol, i.e. pentobarbitone and flurazepam, had little or no effect on responses to glycine. 4 Responses to β-alanine had pharmacological properties compatible with a mixed action on both GABA and glycine receptors. 5 The rat isolated optic nerve appears to be a useful preparation for studying the pharmacology of the neuronal glycine receptor plus chloride ionophore complex.