Endogenous responses in brain pH andP_O2in a rodent model of birth asphyxia

Abstract

Aim:To study brain-sparing physiological responses in a rodent model of birth asphyxia which reproduces the asphyxia-defining systemic hypoxia and hypercapnia.Methods: Steady or intermittent asphyxia was induced for 15-45 min in anesthetized 6 and 11 days old rats and neonatal guinea pigs using gases containing 5% or 9% O2 plus 20% CO2 (in N2).Hypoxia and hypercapnia were induced with low O2 and high CO2, respectively. Oxygen partial pressure (PO2) and pH were measured with microsensors within the brain and subcutaneous ("body") tissue. Blood lactate was measured after asphyxia.Results: Brain and body PO2 fell to apparent zero with little recovery during 5% O2 asphyxia and 5% or 9% O2 hypoxia, and increased more than twofold during 20% CO2 hypercapnia. Unlike body PO2, brain PO2 recovered rapidly to control after a transient fall (rat), or was slightly higher than control (guinea pig) during 9% O2 asphyxia. Asphyxia (5% O2) induced a respiratory acidosis paralleled by a progressive metabolic (lact)acidosis that was much smaller within than outside the brain. Hypoxia (5% O2) produced brain-confined alkalosis. Hypercapnia outlasting asphyxia suppressed pH recovery and prolonged the post-asphyxia PO2 overshoot. All pH changes were accompanied by consistent shifts in the blood-brain barrier potential. Conclusion:Regardless of brain maturation stage, hypercapnia can restore brain PO2 and protect the brain against metabolic acidosis despite compromised oxygen availability during asphyxia. This effect extends to recovery phase if normocapnia is restored slowly, and it is absent during hypoxia, demonstrating that exposure to hypoxia does not mimic asphyxia.

ν solution to the strong CP problem

“…with m eff ≡ |m u m d m s |/(|m u m d | + |m u m s | + |m d m s |), F π ∼ 93MeV is the pion decay constant, and the masses of the quarks and the strong CP phase are evaluated at the scale Q ∼ 1 GeV. Using the currently determined values for |m u,d,s |[1], this result becomes consistent with the calculation of Refs [33,34]. by using the QCD sum rules,…”

Multiphonon excitations from dark matter scattering in crystals

“…For DM heavier than 1 MeV, electronic excitations in atoms or semiconductors with energy gaps in the ∼ eV range are well suited, if the DM couples to electrons [2][3][4][5][6][7][8][9]. For light DM with nucleon couplings on the other hand, one must rely on chemical bond breaking [10], nuclear de-excitations [11], crystal defects [12,13] or soft nuclear recoils, where the latter in particular require very low thresholds [14][15][16][17][18][19][20]. For DM lighter than 1 MeV, vibrational modes in crystals [9,[21][22][23], molecular systems [24,25] or superfluid helium [26][27][28][29] naturally have energy spectra in the required 1 -100 meV range.…”

Reviving millicharged dark matter for 21-cm cosmology

“…The viable parameter space for which a fraction of mDM can explain EDGES in our setup can be effectively probed by the rich collider experimental program aimed at searching for millicharged particles at beam dump facilities [39][40][41][42][43]. Moreover, future single-electron-threshold direct detection experiments above ground [47] (either in balloon or satellites), together with ground-based direct detection experiments with energy threshold below the single electron recoil [48][49][50][51][52][53][54][55][56][57][58] serve as a complementary probe at lower mDM charges.…”

“…Alternatively, the experimental threshold of direct detection experiments can be reduced such that they become sensitive to the very slow mDM particles reaching the surface of the Earth. Given the existing proposals for low-threshold experiments below single-electron recoil energy [48][49][50][51][52][53][54][55][56][57][58] and the flourishing ongoing activity in this direction, it would be interesting to study the ability of these experiments to probe the strongly interacting window for mDM.…”

“…[47] for an updated reach of these experiments for mDM). Pushing the reach to higher Q can be achieved by either lowering the threshold of the detectors [48][49][50][51][52][53][54][55][56][57][58] or reducing the atmospheric shielding using balloon-and satelliteborne detectors [47].…”