Activity-related rise in extracellular potassium concentration in the brain
of 1-3-day-old chicks.
Sykova E, Jendelova P, Svoboda J, Sedman G, Ng KT
Institute of Physiological Regulations, Czechoslovak Academy of Sciences,
Prague.
The concentration of K+ [( K+]) was measured in the cerebrospinal fluid
(CSF) and in the extracellular fluid [( K+]e) in the medial forebrain of
two-day-old chicks by means of K(+)-sensitive microelectrodes (K-ISM).
The K-ISM potential in the CSF was compared with that in artificial CSF
with 3, 4 or 6 mmol/l of [K+]. The [K+] found in CSF was 3.79 +/- 0.57
(n = 8), in the hyperstriatum accessorium (HA) 3.70 +/- 0.32 (n = 13) and
in the neostriatum (N) 3.51 +/- 0.32 (n = 13; mmol/l; mean +/- SEM). Trains
of local electrical stimuli (10-100 Hz, 30 sec) applied to the surface
of the forebrain increased [K+]e in both HA and N by 11-13 mmol/l. Increases
in [K+]e in the ectostriatum (E) of 5-6 mmol/l was found in response to
electrical stimulation (30-100 Hz, 5-10 sec) of the contralateral optic
nerve, and of about 2 mmol/l by applying pressure to the bulb. In chicks
adapted to the dark, stimulation of the contralateral eye or both eyes
with bright light flashes (1-2 Hz) or with continuous light resulted in
an increase in [K+]e of 0.5-1.0 mmol/l. Smaller increases in [K+]e of 0.15-1.25
mmol/l were found in HV and N after the application of a small quantity
(0.1 ml) of the chemical taste aversant methylanthranilate (MeA) or the
electrical stimulation of the beak by two needle electrodes inserted into
the palatum or into the tongue. After application of MeA the increase in
[K+]e began 3-4 min after application and persisted for 20 min.