Potassium-dependent prolonged field bursts in the dentate gyrus: effects of extracellular calcium and amino acid receptor antagonists.

The dentate gyrus in rat hippocampal slices produces spontaneous, prolonged bursts of population spikes (i.e. prolonged field bursts) when [Ca2+]0 is lowered (0-0.5 mM) and [K+]0 is concurrently elevated (9-11 mM). In this investigation we examined whether the dentate gyrus could also generate spontaneous field bursts in relatively "normal" (i.e. nominal 1.3 mM) or only moderately decreased [Ca2+]0 (i.e. nominal 0.9 mM). In 1.3 mM [Ca2+]0, no prolonged field bursts occurred spontaneously in the dentate gyrus when [K+]0 was raised as high as 12 mM. Prolonged field bursts were generated, however, when [K+]0 was further increased to 13-15 mM. Similar bursts could be generated at [K+]0 within the "physiological ceiling level" observed in vivo during seizure activity (i.e. 11-12 mM) if: (i) the bath [Ca2+] was reduced to 0.9 mM; or (ii) the GABA type A-receptor antagonist bicuculline was added in the presence of "normal" (1.3 mM) [Ca2+]0. Adding both the N-methyl-D-aspartate and non-N-methyl-D-aspartate receptor antagonists, (+/-)-2-amino-5-phosphonopentanoic acid (50-100 microM) and 6,7-dinitroquinoxaline-2,3-dione (50-100 microM), respectively, did not block the occurrence of the field bursts. The bursts generated in 1.3 mM [Ca2+]0, 12 mM [K+]0, bicuculline, (+/-)-2-amino-5-phosphonopentanoic acid and 6,7-dinitroquinoxaline-2,3-dione could, however, be reversibly depressed or blocked if [Ca2+]0a was raised to 2.0 mM.(ABSTRACT TRUNCATED AT 250 WORDS)