The dynamics of changes in hippocampal GABAergic system in rats exposed to early-life hypoxia-induced seizures.

Hypoxia-evoked seizures (H/S) early in life lead to multiple chronic neurological deficits. Here, we present the results of studying GABA release and uptake in hippocampal axon terminals of rats exposed to H/S at 10-12 days of age. We characterized (i) exocytotic release of GABA; (ii) the initial rate of GABA uptake; (iii) the regulation of GABA release by presynaptic GABA(B) receptors. Rats were used for experiments 2, 4 and 8 weeks after H/S. We found that exocytotic [(3)H]GABA release was higher in rats exposed to H/S, and a maximal difference in the release was observed between the control and experimental rats tested 2 weeks after H/S. In contrast, the initial rate of GABA uptake decreased with age, and this tendency was more pronounced in rats exposed to H/S. Using (±)-baclofen and SKF 97541 as agonists of GABA(B) receptor, we revealed that a significant difference in the auto-inhibition of exocytotic [(3)H]GABA release was detected only between the control and experimental adult rats (8 weeks after hypoxia). The inhibitory effect dropped dramatically in the control adults, but only slightly decreased in adult rats exposed to H/S, thus becoming threefold more potent after hypoxic injury. Together, the results show that H/S affects the dynamics of age-dependent changes in the GABAergic system, and that the enhanced GABA(B) receptor-mediated auto-inhibition can be an important factor in weakening the postsynaptic inhibition and in the development of hyperexcitability in rats exposed to H/S.

Perinatal hypoxia induces a long-lasting increase in unstimulated gaba release in rat brain cortex and hippocampus. The protective effect of pyruvate.

Hypoxia and seizures early in life can cause multiple neurological deficits and even chronic epilepsy. Here, we report the data obtained in rats exposed to hypoxia and seizures at age 10-12 postnatal days and taken in experiments 8-9 weeks after hypoxia treatment. A level of the extracellular GABA and the initial velocity of GABA uptake were measured in the brain cortex, hippocampus and thalamus using isolated nerve terminals (synaptosomes). It has been revealed that the extracellular [(3)H]GABA level maintained by cortical and hippocampal synaptosomes in standard conditions (with glucose as an energy substrate) was significantly higher in adult rats exposed to hypoxia/seizures at P10-12 than in the control ones, and, moreover, became unstable with tendency to increase. Pyruvate as a single energy substrate was shown to be a highly effective for lowering and stabilizing the extracellular [(3)H]GABA level. This effect of pyruvate was tightly correlated with increase in GABA uptake and GATs affinity to GABA. Thalamus was insensible to the action of perinatal hypoxia/seizures, and thalamic GATs, in contrast to cortical and hippocampal ones, had a lower affinity to GABA (the apparent Km is 39.2±3.1 µM GABA vs 8.9±1.8 µM GABA in the hippocampus). A selective vulnerability of brain regions to hypoxia is suggested to be attributed to distinct terms of their maturation at the postnatal period. Thus, perinatal hypoxia/seizures evoke a long-lasting increase in the extracellular GABA level that could be attenuated by pyruvate treatment. This effect of pyruvate is likely due to a significant increase in GATs-mediated GABA uptake and modulation of GATs kinetic properties.

Enhanced alignment and orientation of polar molecules by vibrational resonant adiabatic passage.

The authors show that polar molecules can be adiabatically aligned and oriented by laser pulses more efficiently when the laser frequencies are vibrationally resonant. The aligned molecules are found in a superposition of vibrational pendular states, each associated with the alignment of the rotor in one vibrational state. The authors construct the dressed potential associated with this mechanism. Values of detunings and field amplitudes are given to optimize the degree of alignment and orientation for the CO molecule.

Orientation of polar molecules by laser induced adiabatic passage.

We show that two overlapping linearly polarized laser pulses of frequencies omega and its second harmonic 2omega can strongly orient linear polar molecules, by adiabatic passage along dressed states. The resulting robust orientation can be interpreted as a laser-induced localization in the effective double well potential created by the fields, which induces a preliminary molecular alignment. The direction of the orientation can be selected by the relative phase of the fields.

Floquet perturbative analysis for STIRAP beyond the rotating wave approximation.

We present a perturbative analysis of Floquet eigenstates in the context of two delayed laser processes (STIRAP) in three level systems. We show the efficiency of a systematic perturbative development which can be applied as long as no non-linear resonances occur.

The effect of thermal sample pretreatment on the absorption signal in graphite furnace AAS.

The origin of the unusual maxima observed in the decomposition curves for pure solutions of some elements has been investigated theoretically and experimentally. An increase in the atom residence time caused by longitudinal redistribution of the analyte in the tube during the pyrolysis step was found to be responsible. The effect can be observed only if the sample is atomized under gas-flow conditions. To prevent any influence on analytical results, atomization should be done in the gas-stop mode.