Does hypertonic saline have preventive effects against delayed neuronal death in gerbil hippocampus?

Crystalloid vs. hypertonic crystalloid-colloid solutions for induction of mild therapeutic hypothermia after experimental cardiac arrest

PURPOSE

To compare cerebral and hemodynamic consequences of different volumes of cold acetated Ringer's solution or cold hypertonic saline dextran administered in order to achieve mild hypothermia after cardiac arrest (CA) in a pig model of experimental cardiopulmonary resuscitation (CPR).

METHODS

Using an experimental pig model of 12 min CA (followed by 8 min CPR or no resuscitation) we compared four groups of piglets: a control group, a normothermic group and two groups with different solutions administered for induction of hypothermia. The control group of 5 piglets underwent 12 min CA without subsequent CPR, after which the brain of the animals was removed immediately. After restoration of spontaneous circulation (ROSC) the resuscitated piglets were randomized into a normothermic group (NT group=10), and two hypothermic groups that received cold infusions of either 30 mL/kg acetated Ringer's solution (Much fluid group, M, n=10) or 3mL/kg hypertonic saline dextran solution (Less fluid group, L, n=10), respectively, administered during 30 min. Additional external cooling with ice packs was used in hypothermic groups. Sixty or 180min after ROSC the experiment was terminated. Immediately after arrest the brain was removed for histological analyses.

RESULTS

The median time to reach the target core temperature of 34 °C after ROSC was 51.5±7.8 min in L group and 48.8±8.6 min in M group. Less cerebral tissue content of water (p<0.001), sodium (p<0.0001), potassium (p<0.0001) and less central venous pressure (CVP) at 5 and 15 min after ROSC were demonstrated in L group. Increased brain damage was demonstrated over time in NT group (p<0.001). Less neurologic damage and BBB disruptions (albumin leakage) was observed at 180min in M group in comparison with both NT and L groups (p<0.001).

CONCLUSION

No statistical differences were observed between the hypothermic groups in the time to achieve mild hypothermia. Although inclusion of cold hypertonic crystalloid-colloidal solutions in the early resuscitation after ROSC may be more effective than cold crystalloids in reducing brain edema, this study demonstrates that mild hypothermia induced with small volumes of cold hypertonic crystalloid-colloids is less as effective as crystalloid's induced hypothermia in mitigating brain injury after cardiac arrest.

Hypertonicity promotes survival of corticospinal motoneurons via mitogen-activated protein kinase p38 signaling

Extracellular hypertonicity can induce the phosphorylation of mitogen-activated protein kinases (MAPKs). Of these, both extracellular signal-regulated kinases (ERKs) and the stress-activated kinase p38 have been implicated in neuronal cell survival. Resuscitation with hypertonic saline decreases secondary brain injury after trauma, as well as neuronal damage, after ischemia. Since hypertonicity has been shown to support somatic cell survival, we investigated if hypertonicity can also prevent neuronal cell death via MAPK signaling. Death of postnatal rat corticospinal motoneurons (CSMNs) was induced by serum deprivation, and survival in both isotonic and hypertonic media was assessed after 20 h. Addition of NaCl (4-250 mM) to isotonic medium significantly and dose dependently protected CSMN in enriched cultures, increasing cell survival by up to 70% over that in isotonic medium. This response was not restricted to NaCl; addition of KCl, choline chloride, and sucrose had similar effects on cell survival. In addition, hypertonicity supported the survival of pure CSMN populations, albeit with lower potency. In cortical cell suspensions, hypertonic NaCl (20-100 mM) increased basal phosphorylation of p38 and ERK. The activation of both MAPKs, which was induced by 40 mM NaCl, was transient. Cultivation of CSMNs in media containing the specific p38 inhibitor SB203580 abolished the protective effect of hypertonic NaCl, indicating a central role for p38. We therefore conclude that hypertonicity can prevent neuronal cell death via MAPK signaling.

Five percent, 7.5% or 10% hypertonic saline prevents delayed neuronal death in gerbils

PURPOSE

To clarify the appropriate concentration and dose of hypertonic saline solution (HSS) for preventing delayed neuronal death in the hippocampal CA1 subfield after transient forebrain ischemia in gerbils.

METHODS

Thirty gerbils were randomly assigned to five groups: physiological saline solution (PSS) group, ischemia/reperfusion treated with PSS 2 mL x kg(-1); 5% HSS group, treated with 5% HSS 2 mL x kg(-1); 7.5% HSS group, treated with 7.5% HSS 2 mL x kg(-1); 10% HSS group, treated with 10% HSS 2 mL x kg(-1); 20% HSS group, treated with 20% HSS 2 mL x kg(-1). Transient forebrain ischemia was induced by occluding the bilateral common carotid arteries for four minutes. Five days later, histopathological changes in the hippocampal area were examined, and the degenerative ratio of the pyramidal cells were measured according to the following formula: (number of degenerative pyramidal cells/total number of pyramidal cells per 1 mm of hippocampal CA1 subfield) x 100.

RESULTS

In PSS and 20% groups, neuronal cell damage was observed five days after ischemia. In the other three groups, these changes were not observed. The degenerative ratios of pyramidal cells were as follows; PSS group: 91.6 +/- 5.6%, 5% HSS group: 7.2 +/- 1.6%, 7.5% group: 8.3 +/- 1.4%, 10% HSS group: 6.2 +/- 1.1%, 20% HSS group: 85.8 +/- 8.7% (P < 0.05; PSS and 20% HSS vs three other groups).

CONCLUSION

This study demonstrates that 5, 7.5 or 10% HSS 2 mL x kg(-1) may prevent delayed neuronal death in the hippocampal CA1 subfield after cerebral ischemia/reperfusion in gerbils.

Propofol prevents delayed neuronal death following transient forebrain ischemia in gerbils

PURPOSE

This study was conducted to ascertain whether propofol may protect against delayed neuronal death in the hippocampal CA1 subfield in gerbils.

METHODS

Thirty-five gerbils were randomly assigned to five groups: Group I, the control group, a sham operation treated with physiological saline solution (PSS); Group II, ischemia/reperfusion treated with PSS; Group III, ischemia/reperfusion treated with 50 mg x kg(-1) propofol; Group IV, ischemia/reperfusion treated with 100 mg x kg(-1) propofol; Group V ischemia/reperfusion treated with 150 mg x kg(-1) propofol. Transient forebrain ischemia was induced by occluding the bilateral common carotid arteries for four minutes under N2O/O2/halothane anesthesia after administration of propofol or PSS. Five days later, histopathological changes in the hippocampal CA1 subfield were examined using a light microscope and degenerative ratio of the pyramidal cells were measured according to the following formula: (number of degenerative pyramidal cell/total number of pyramidal cells per 1 mm of hippocampal CA1 subfield) x 100.

RESULTS

In group II, the pyramidal cells were atrophic and pycnotic; vacuolation and structural disruption of the radial striated zone was observed. In the other four groups, these changes were not observed. The degenerative ratios of pyramidal cells were as follows; group I: 5.9 +/- 1.9%, group II: 94.6 +/- 2.5% (P < 0.01), group III: 10.7 +/- 1.7%, group IV: 9.7 +/- 1.8%, group V: 9.2 +/- 1.9%.

CONCLUSION

This study suggests that propofol may prevent delayed neuronal death in the hippocampal CA1 subfield after cerebral ischemia/reperfusion in gerbils.

Involvement of the glutamate transporter and the sodium-calcium exchanger in the hypoxia-induced increase in intracellular Ca2+ in rat hippocampal slices

Hippocampal slices prepared from adult rats were loaded with fura-2 and the intracellular free Ca2+ concentration ([Ca2+]i) in the CA1 pyramidal cell layer was measured. Hypoxia (oxygen-glucose deprivation) elicited a gradual increase in [Ca2+]i in normal Krebs solution. At high extracellular sodium concentrations ([Na+]o), the hypoxia-induced response was attenuated. In contrast, hypoxia in low [Na+]o elicited a significantly enhanced response. This exaggerated response to hypoxia at a low [Na+]o was reversed by pre-incubation of the slice at a low [Na+]o prior to the hypoxic insult. The attenuation of the response to hypoxia by high [Na+]o was no longer observed in the presence of antagonist to glutamate transporter. However, antagonist to Na+-Ca2+ exchanger only slightly influenced the effects of high [Na+]o. These observations suggest that disturbance of the transmembrane gradient of Na+ concentrations is an important factor in hypoxia-induced neuronal damage and corroborates the participation of the glutamate transporter in hypoxia-induced neuronal injury. In addition, the excess release of glutamate during hypoxia is due to a reversal of Na+-dependent glutamate transporter rather than an exocytotic process.

Extracellular sodium concentration has diverse effects on the hypoxia-induced increase in intracellular Ca2+ in rat hippocampal slices

The intracellular free Ca2+ concentration ([Ca2+]i) in the CA1 pyramidal cell layer was measured using fura-2-loaded hippocampal slices prepared from adult rats. Hypoxia (oxygen-glucose deprivation) elicited a gradual increase in [Ca2+]i in normal Krebs solution. With a high extracellular sodium concentration ([Na+]o), the hypoxia-induced response was attenuated, its onset-latency was longer and the time constant of its decay phase was shorter than in controls. In contrast, hypoxia in low [Na+]o elicited a significantly enhanced response with a short onset-latency and delayed decay phase. This exaggerated response to hypoxia in low [Na+]o was reversed by pre-incubation of the slice in low [Na+]o prior to the hypoxic insult. Some possible mechanisms and the functional significance of the observed effects of [Na+]o on the hypoxia-induced increase in [Ca2+]i are discussed, with particular emphasis on the putative participation of the glutamate transporter and the sodium-calcium exchanger in hypoxia-induced neuronal injury.