Effects of hypoxia on rat hippocampal neurones in vitro.

Abstract

SUMMARY1. The effects of hypoxia on the rat hippocampal CAI neurones in tissue slices of the rat brain were studied in vitro by intracellular recording.2. In response to superfusion of a hypoxic medium equilibrated with 95 % N2-5 % C02, a majority of the neurones showed a hyperpolarization of5-15 mV in amplitude and 4-12 min in duration. The hyperpolarization was, in turn, followed by a slow depolarization which within 20 min of hypoxic exposure reached a plateau level of about 25 mV above the pre-hypoxic resting potential. Both the initial hyperpolarization and subsequent depolarization were associated with a reduction in membrane resistance. 3. The hyperpolarization reversed in polarity at a membrane potential of -83 mV. There was an almost linear relationship between amplitude of the hyperpolarization and membrane potential. The hyperpolarization was markedly enhanced in potassium-free media and was depressed in high-potassium solutions.4. The hyperpolarization was not significantly affected by low-chloride or lowsodium medium or by solution containing tetraethylammonium (10 mM), 4-aminopyridine (1-5 mM) or caesium (3 mM). Moreover, intracellular injection of ethyleneglycol-bis-(fi-aminoethylether)N,N-tetraacetic acid (EGTA) did not alter the hyperpolarization. On the other hand, barium (0 5 mM)-containing medium reduced the amplitude of the hyperpolarization by 20-40 %.5. Superfusion of ouabain (5-7 puM)-containing medium in normoxic conditions produced hyperpolarizing and depolarizing responses similar to those elicited by hypoxic exposure. The slow depolarization was also mimicked by elevation of the extracellular potassium concentration to 10-20 mm.6. Evoked i.p.s.p.s were abolished within 4 min of hypoxic exposure while evoked e.p.s.p.s were maintained for about 20 min of hypoxic superfusion. Soma spikes of the neurones elicited by a depolarizing pulse were also well preserved. Their threshold was, however, raised, concomitant with a decrease in the peak amplitude.7. When the slice was reoxygenated after 20-40 min of hypoxic exposure, the neurones immediately began to repolarize and showed a transient hyperpolarization of 5-10 mV in amplitude and 1-2 min in duration. The membrane potential, input t To whom all correspondence and reprint requests should be sent.5-2 N. FUJIWARA AND OTHERS resistance and action potential returned to the pre-hypoxic levels after 15-20 min of reoxygenation. The amplitude of the reoxygenation-induced hyperpolarization was not significantly changed when the membrane was hyperpolarized or depolarized. The hyperpolarization was eliminated by potassium-free medium or solution containing ouabain (1 ,tM).8. In a minority of the neurones the slow depolarization was suddenly followed by a rapid depolarization, after which the neurones showed no functional recovery. Such an abrupt and irreversible depolarization appeared when the slow depolarization reached membrane potentials of -30 to -40 mV.9. The results suggest that hypoxia-induced hyperpolarization is due to an increase in voltag...

Adenosine, ‘pertussis-sensitive’ G-proteins, and K+ conductance in central mammalian neurones under energy deprivation

“…For the determination of input resistance, hyperpolarizing current pulses (800 ms, -0.2 hA) were regularly applied via the electrode. the membrane hyperpolarization under these conditions is due to an enhanced K" conductance [5,8,10,14]. In our experiments, however, there was less reduction of' membrane resistance for the same hyperpolarization during adenosine as compared to hypoxia.…”

“…The latter period was accompanied by a transient membrane hyperpolarization. This event can be explained by a reactivation of the Na+/K + pump [5].…”

“…This has been observed during hypoxia [5][6][7]10] as well as during glucose depletion [14]. The controlling substance which links cellular metabolism and K ÷ conductance is still subject of discussion.…”

EEG Suppression and Anoxic Depolarization: Influences on Cerebral Oxygenation during Ischemia

“…In terpretation of these results is complicated since EEG activity may be transiently enhanced prior to suppression (e.g., Hansen, 1978) by early depres sion of inhibitory activity and initial depolarization in anoxic neurons (Fujiwara et al, 1987). However, EEG enhancement does not fully explain our data because the decreases in rates of K + 0 rise, tP02 decline, and cytochrome a,a3 reduction were de fined vs. rates recorded in the lO-s period just prior to EEG isoelectricity at a time when the EEG was already showing marked depression in most ani mals.…”

Optical Imaging of Hippocampal Neurons with a Chloride‐Sensitive Dye: Early Effects of In Vitro Ischemia

“…Slices were placed tials are powerfully suppressed during in vitro ischemia on a net submerged in a beaker containing oxygenated Ring- (Fujiwara et al, 1987;Krnjevic et al, 1991). In addier's buffer (room temperature) and then incubated with the tion, increased neuronal excitability has been demonresuspended dihydro-MEQ (final concentration of -300 strated in area CAl pyramidal cells ofthe hippocampus 1.tM) at room temperature for 0.5 h in Ringer's buffer.…”