Using a microelectrode with carbon filaments and the voltammctric technique, changes evoked in the catechol oxidation current (CA.OC) and multiple unit activity (MUA) by microinjection of 3-5 ¿ri 03 mol.I'1 KC1 were studied in the reticular formation (RF) of the medulla oblongata of anaesthetized rats; the effect of KC1 stimulation of the RF and corpus striatum (S) on the CA.OC in these structures was compared. The microinjection of KC1 in the vicinity of the working electrode in the RF caused depression of MUA which began 2-3 s after administration, persisted for up to 6 min after and then diminished, reaching control values within 9 min. The voltammctric signal was first recorded in the 1st min after microinjection, when there was an evident decrease in the CA.OC value (59 % of the control value); this effect reached its maximum 7 min after administration (a mean drop to 23 % of the control), while at the end of the experiment (i.e. after 24 min) CA.OC values had risen to 45-80 % of the control value. The response in the S had a biphasic character, however. Immediately after the microinjection (1st min), the mean CA.OC value rose to 626 % of the control, while in the second phase (3-10 min) it was seen to fall below the control values (means 21-63 % of the control). The differences in the changes evoked by K+ depolarization in the concentration of catecholamines in the RF and S microenvironment are discussed from the aspect of the existence of different pools of the transmitter and
other regional differences. The possibility of a relationship between considered.