The extrasynaptic effect of gamma-aminobutyric acid and pentobarbital and the influence of temperature on the response of parallel fibres of the frog cerebellum in vitro.

The authors studied the effect of two biologically active substances (gamma-aminobutyric acid-GABA, pentobarbital-PB) and a physical factor (temperature-T) on the direct response of parallel fibres of the isolated frog cerebellum to electrical stimulation in vitro. The extrasynaptic action of GABA and PB during superfusion (10(-6), 10(-5), 10(-4) and 10(-3) mol.l-1) significantly reduced the amplitude of the response of parallel fibres. Superfusion with picrotoxin (10(-6) mol.l-1) only partly blocked the effect of GABA (10(-3) mol.l-1), although it abolished the effect of PB (10(-3) mol.l-1). Cooling the cerebellum from the control temperature (T = 16 degrees C) to T = 13 and 10 degrees C significantly augmented the amplitude of the responses, while raising it to 19 and 22 degrees C significantly reduced their amplitude. At T = 13 degrees C, depression of direct responses was significant only in superfusion with GABA (10(-6) and 10(-3) mol.l-1) and not in superfusion with PB (10(-6) and 10(3-) mol.l-1). The results with picrotoxin (PTX) applications, indicated that the extrasynaptic action of GABA and PB took effect by partly different mechanisms. That would account for the difference in the effect of GABA and PB in conjunction with the physical factor.