Differential expression of ADAM15 and ADAM17 metalloproteases in the rat brain after severe hypobaric hypoxia and hypoxic preconditioning

The ADAMs (a disintegrin and metalloprotease) are a family of membrane-anchored glycoproteins capable of shedding a multitude of proteins from the cell surface. Although ADAMs are being considered as crucial modulators of physiological and pathophysiological processes, their roles in neuronal death/survival are largely unexplored. In the present study, changes in brain expression of ADAM15 and ADAM17 (TACE) have been quantitatively examined in rats in response to injurious severe hypoxia (SH) and in animals which acquired hypoxic tolerance through preconditioning to mild hypoxia prior SH. SH persistently up-regulated ADAM15 mRNA and protein levels in hippocampus and neocortex but not in thalamus or hypothalamus. This effect was not observed in the preconditioned rats tolerant to SH. In contrast, hippocampal levels of ADAM17 mRNA and neocortical levels of ADAM17 mRNA and protein were largely reduced following SH in non-preconditioned rats. Hypoxic preconditioning prevented down-regulation of the adam17 gene and considerably enhanced ADAM17 protein expression in hippocampus and neocortex in response to SH. The present findings implicate ADAM15 in the processes of neuronal hypoxic injury. On the other hand, these results also provide evidence for a pro-survival neuroprotective role of ADAM17 and its engagement in the process of preconditioning-induced hypoxic tolerance. The analysis of the protein levels of soluble and membrane-bound forms of APP in the neocortex and hippocampus of rats subjected to SH and SH with preconditioning has demonstrated that an increased ADAM17 expression in preconditioned animals 24h after hypoxia corresponded to a higher level of soluble form of APP and a reduction of the membrane bound fraction which reflects the role of ADAM17 in APP shedding.

Preconditioning induces prolonged expression of transcription factors pCREB and NF-kappa B in the neocortex of rats before and following severe hypobaric hypoxia

Preconditioning using mild repetitive hypobaric hypoxia is known to increase a tolerance of brain neurons to severe hypoxia and other injurious exposures. In the present study, the effects of mild hypoxic preconditioning on the expression of transcription factors NF-kappaB and phosphorylated CREB (pCREB) has been studied in the neocortex of rats exposed to severe hypobaric hypoxia. As revealed by quantitative immunocytochemistry, the injurious severe hypobaric hypoxia (180 Torr, 3 h) remarkably reduced the neocortical levels of pCREB and NF-kappaB. The three-trial hypoxic preconditioning (360 Torr, 2 h, 3 days) induced persistent up-regulation of pCREB and NF-kappaB expression in the neocortex of rats 3-24 h following the severe hypoxia. In addition, the preconditioning alone which was not followed by the severe hypoxia, considerably increased neocortical pCREB and NF-kappaB levels. The findings suggest a role for transcription factors cAMP response element-binding protein and NF-kappaB in the neuroprotective mechanisms activated by the hypoxic preconditioning.

Involvement of the hypothalamic-pituitary-adrenal axis in the antidepressant-like effects of mild hypoxic preconditioning in rats

The preconditioning (PC) by using mild intermittent hypobaric hypoxia (PC) increases a resistance of the brain to severe hypoxia/ischemia and various stresses. Recently, potent antidepressant-like effects of PC have been described in animal models of depression. In the present study, the impact of PC on the activity and feedback regulation of the hypothalamic-pituitary-adrenal axis (HPA) impaired in depression has been studied in the model of shock-induced depression in rats. PC completely prevented depressive-like behavior (54% reduction in ambulance, 59% reduction in rearing in the open field, 654% increase of the anxiety level in the elevated plus maze), the HPA hyperactivity and the impairment of HPA feedback regulation that appeared in response to the inescapable footshock. Not affecting basal HPA activity, PC remarkably enhanced the HPA reactivity to stresses and substantially up-regulated the expression of glucocorticoid receptors in the ventral hippocampus following footshock that apparently contributes to the mechanisms responsible for the antidepressant-like action of PC.

Antidepressant-like effects of mild hypoxia preconditioning in the learned helplessness model in rats

The effects of preconditioning using mild repetitive hypobaric hypoxia (360 Torr for 2 h each of 3 days) have been studied in the learned helplessness model of depression in rats. Male Wistar rats displayed persistent depressive symptoms (depressive-like behaviour in open field, increased anxiety levels in elevated plus maze, ahedonia, elevated plasma glucocorticoids and impaired dexamethasone test) following the exposure to unpredictable and inescapable footshock in the learned helplessness paradigm. Antidepressant treatment (ludiomil, 5 mg/kg i.p.) augmented the development of the depressive state. The hypoxic preconditioning had a clear antidepressive action returning the behavioural and hormonal parameters to the control values and was equally effective in terms of our study as the antidepressant. The findings suggest hypoxic preconditioning as an effective tool for the prophylaxis of post-stress affective pathologies in humans.

Mild preconditioning hypoxia modifies nerve growth factor-induced gene A messenger RNA expression in the rat brain induced by severe hypoxia

The effect of preconditioning (PC) on the changes of nerve growth factor-induced gene A (NGFI-A) expression induced by severe hypobaric hypoxia was studied by in situ hybridization. A PC consisted of three trials of mild hypobaric hypoxia (360 Torr, 2 h) spaced at 24 h. The last trial was followed by severe hypoxia (SH; 180 Torr, 3 h) 24 h later. The PC hypoxia prevented the NGFI-A messenger RNA (mRNA) increase in the cortex, neostriatum, piriform cortex, amygdala and hippocampus detected 3 h after SH. The preconditioned SH caused a peak in NGFI-A mRNA expression at the 24 h time-point and thus abolished the dramatic decrease of the mRNA in vulnerable areas seen by 24 and 72 h after SH. The findings suggest a role of brain NGFI-A in the protective effect of hypoxic/ischemic PC.

Nicotinic stimulation of polyphosphoinositide turnover in rat adrenal medulla slices

When rat adrenal medulla slices, treated with atropine (1 X 10(-6) mol X l-1], were stimulated with acetylcholine (1 X 10(-5) mol X l-1), an enhanced 32P incorporation into phosphatidylinositol-bis-phosphate (PIP2) and phosphatidylphosphate (PIP) was observed. On the ather hand, stimulation of myo-[3H] inositol prelabelled slices led to a decline in radioactivity of PIP2, indicating an increased turnover of this phospholipid. A possible affection of monoesterphosphate groups of PIP2 or of both PIP2 and PIP during cholinergic nicotinic stimulation is assumed.