Studies on field potentials and on single cells in the inferior olivary complex of the rat.

Field and unitary action potentials have been recorded in the inferior olivary complex of pentobarbital anaesthetized rats. Spontaneous and antidromically evoked unitary potentials, and antidromically evoked field potentials all showed the same biphasic profile. Repetitive antidromic stimulation resulted in attenuation of the field potential with stimulation frequencies as low as 10 Hz. The latency of juxtafastigially evoked spikes was variable, and decreased with increasing stimulus strengths. Electrophoretically applied glycine, gamma-aminobutyric acid, noradrenaline, dopamine and 5-hydroxytyptamine all reduced the amplitude of the antidromic potential, but sometimes caused a transient increase preceding this decrease. Orthodromically (femoral nerve) evoked potentials were different in form and could assume one of two distinct profiles. The effects of electrophoretically applied DL-homocysteate (DLH) and the putative transmitters listed above on the form of such field potentials are described. DLH, ACh and 5-HT were tested on single olivary neurones, which had spontaneous firing rates of less than 2 Hz. These compounds had only slight effects on firing rates although marked changes were seen in action potential configuration. Spontaneous synchronous discharges of groups of olivary neurones are described. This and other findings confirm that olivary units have a tendency to both rhythmical and synchronous firing.