Context dependence of head bobs in gerbils and potential neural contributions

Headbobs are up-down movements of the cranium associated with the use of motion parallax for depth perception. Mongolian gerbils (aka jirds; Meriones unguiculatus) often execute a series of headbobs prior to jumping between surfaces. Gerbils were tested in a jumping stand task and headbobs videotaped under three light levels approximating low daylight, dawn/dusk, and moonlight across a range of distances to target. Headbobs per trial increased linearly with increasing distance to the target platform, whereas headbob frequency (rate of headbobbing pre-jump on the start platform) increased with gap distance up to an intermediate level and then decreased. Overall, gerbils made the most headbobs per trial under the darkest conditions, whereas their headbobbing rate was highest for medium illumination, especially for medium-long gap distances. There was a positive correlation between headbob frequency and volume of the superior colliculus (SC), but no relationship between headbobs and relative size of the temporo-posterior (TP) visual cortex. The results suggest that gerbils employ a specific visuomotor strategy for depth perception differentially under different conditions. We suggest that the deployment of headbobs under specific conditions may be part of an SC-driven vigilant state, of which more rapid sampling of the visual environment using headbobs for depth estimation is one component. Moreover, the findings highlight the importance of considering ecological factors in designing studies of visual behavior and its underpinnings in rodents.

Grading odor similarities in a Go/No-Go task

Recent studies show that some features of odor perception are predicted by olfactory receptor biophysics and olfactory bulb physiology. Those studies used a behavioral assay in which rodents dig in a dish of scented cage bedding after pretraining to associate a buried reward with an odorant. The advantage of the digging task is an intensity measure of similarity (number of seconds spent digging). The method has the disadvantages of odorant contamination and low control over concentration and timing, making it difficult to use in electrophysiology. We describe an operant task that avoids these disadvantages and provides a reliable intensity-based similarity measure. Odorants can be delivered with a standard air dilution olfactometer, and rats learn to lever press to one odorant and avoid pressing to another in a Go/No-Go (CS+/CS-) task with a partial reinforcement protocol. Generalization tests substitute a portion of the unrewarded CS+ trials with test odorants. The number of generalization trials on which a subject responds to a test odorant is the measure of odor similarity intensity. We present validation tests using mixture component recognition, which show high repeatability, little variability across subjects and no decrease in responding across sessions. The results match those obtained with the digging task in four of five mixtures tested. This method allows optimal control over stimulus parameters and is compatible with simultaneous electrophysiological recording.

Detection of mitochondrial electron chain carrier redox status by transhepatic light intensity during rat liver reperfusion

The aim of the study was to investigate mitochondrial electron transfer during rat liver reperfusion after cold storage and hypothermic machine perfusion. Livers from male Brown Norway rats were preserved (UW) for 10h either by cold storage (CS) or by hypothermic oxygenated perfusion extracorporal (HOPE). Transhepatic photometric analysis allowed determination of the redox status of mitochondrial cytochromes during preservation, rewarming and reperfusion. Mitochondrial electron chain carriers were inhibited at different sites with rotenone and cyanide in some experiments. reversed transcriptional polymerase chain reaction (RT-PCR) was performed after reperfusion concerning transcription of TNFalpha, caspase 9, and c-jun kinase (JNK). Increased superoxide anion formation as well as transcription of TNFalpha, caspase 9, and JNK during reperfusion after cold storage (CS) were related with completely reduced cytochromes before and during reperfusion. In contrast, hypothermic oxygenated livers (HOPE) showed oxygenated cytochromes as well as decreased superoxide anion formation and no detectable transcription of TNFalpha, caspase 9, and JNK. A similar low level of superoxide anion formation was found when electron chain transfer of cold stored livers was inhibited during reperfusion with rotenone but not with cyanide. After hypothermic oxygenation (HOPE) inhibition of mitochondrial electron chain with rotenone showed no change in formation of superoxide anion formation whereas inhibition with cyanide showed increased superoxide anion formation. Thus mitochondrial cytochrome redox status is suggested to be related: (i) with the release of reactive oxygen substances as well as (ii) with the expressions of TNFalpha, caspase 9, and JNK during reperfusion and may thus be usable as predictive marker of liver grafts.

Calcium prevents loss of glutathione and reduces oxidative stress upon reperfusion in the perfused liver

BACKGROUND

Addition of 1.5 mM Ca2+ to the preservation solution (UW) during static cold rat liver preservation have been shown to improve liver function upon reperfusion. Effects of adding calcium to the perfusate during liver machine perfusion are yet not described.

METHODS

A recently developed model for rat liver machine perfusion (hypothermic oscillating oxygenated liver perfusion) was used to perfuse rat livers with calcium free modified UW solution (Group 1) or with modified UW + 2 mM CaCl2 (Group 2) for a period of 10 h (4 degrees C). In both experimental groups an acellular reperfusion at 37 degrees C with Ringer solution and 50 microM ferricytochrome c over a period of 90 min was performed. Liver and perfusate samples were taken before and after reperfusion to assess the cellular energy charge, metabolites, parameters of oxidative stress, cellular calcium, bile flow, enzyme release and TNF alpha.

RESULTS

Hypothermic perfusion with oxygenated calcium free modified UW solution resulted in depletion of cellular calcium and glutathione. Upon reperfusion bile function was inhibited in spite of a sufficiently reloaded energy charge and low LDH release. In contrast machine perfusion with modified UW solution +2 mM Ca2+ prevented the loss of both, cellular calcium and glutathione during the preservation period and led to sufficient bile flow and less release of superoxide anions upon reperfusion.

CONCLUSIONS

The loss of cellular calcium and glutathione during oxygenated machine liver perfusion appeared to be reducible by adding 2 mM Ca2+. Furthermore, upon reperfusion, livers with preserved cellular calcium demonstrated significantly lower oxidative stress and an improved liver function.

Reduced oxidative stress during acellular reperfusion of the rat liver after hypothermic oscillating perfusion

BACKGROUND

ATP resynthesis during reperfusion after liver preservation has been shown to be well correlated with the function of transplanted grafts. Nevertheless, the advantages of a cellular energy charge loading during the preservation period are yet not fully understood. This study evaluates the effects of different nucleotide levels at the end of preservation on metabolic changes and oxidative stress during reperfusion.

METHODS

Two experimental groups were chosen reflecting different energy charge states after preservation: static cold storage for 10 hr and hypothermic oxygenated oscillating perfusion for 10 hr. In both experimental groups, normothermic ex vivo acellular reperfusion over 40 min was performed. A third group consisted of nonpreserved livers similarly reperfused for 40 min. Superoxide formation was detected by the superoxide dismutase inhibitable reduction of ferricytochrome c added to the normothermic perfusate.

RESULTS

Superoxide formation and lipid peroxidation malondialdehyde were significantly lower during reperfusion after the energy charge loading before reperfusion by the hypothermic oscillating perfusion technique. However, oxygen radical formation, liver cell injury (lactate dehydrogenase [LDH] release), and TNFalpha release were significantly higher in energy charge-depleted groups (nonpreserved and cold stored livers).

CONCLUSIONS

Hypothermic oscillating oxygenated perfusion led to the elevated energy charge during preservation and led to reduced oxygen radical formation as well as less lipid peroxidation during reperfusion, in contrast to cold stored livers and nonpreserved livers. This suggests a correlation between the energy charge before reperfusion and oxygen radical formation as well as liver injury at reperfusion.

Hypothermic oscillating liver perfusion stimulates ATP synthesis prior to transplantation

BACKGROUND

ATP and glycogen depletion often have been demonstrated during cold storage of the liver prior to transplantation. Suppression of events that lead to metabolic depression and to lipid peroxidation could contribute to improvement of liver preservation. A new method of liver preservation for transplantation is therefore suggested, an oscillating oxygenated hypothermic liver perfusion.

METHODS

Biochemical analysis of liver tissue samples and perfusate after 10 h of perfusion by the presented oscillating perfusion model were compared with results after continuous liver perfusion for 10 h as well as with data derived from cold-stored livers over a period of 10 h. Particular reference was made to nucleotide metabolites, glycogen content, lipid peroxidation, glutathione content, glycolytic metabolites, and enzyme release before and after preservation.

RESULTS

Glycogen depletion occurred to the same degree in hypothermic storage and machine perfusion (oscillating as well as continuous perfusion), but the energy charge was significantly increased after oxygenated perfusion, whereas cold storage resulted in a significant energy charge depletion. In addition, perfusion by an oscillating technique yielded superior energy charge loading compared to the continuous perfusion technique and diminished the other hand lipid peroxidation.

CONCLUSIONS

Hypothermic oscillating oxygenated perfusion could be important for the improvement of the quality of energy-depleted organs prior to transplantation.