To improve our understanding of the role of electromagnetic ion cyclotron (EMIC) waves in radiation belt electron dynamics, we perform a comprehensive analysis of EMIC wave‐induced resonant scattering of outer zone relativistic (>0.5 MeV) electrons and resultant electron loss time scales with respect to EMIC wave band, L shell, and wave normal angle model. The results demonstrate that while H+‐band EMIC waves dominate the scattering losses of ~1–4 MeV outer zone relativistic electrons, it is He+‐band and O+‐band waves that prevail over the pitch angle diffusion of ultrarelativistic electrons at higher energies. Given the wave amplitude, EMIC waves at higher L shells tend to resonantly interact with a larger population of outer zone relativistic electrons and drive their pitch angle scattering more efficiently. Obliquity of EMIC waves can reduce the efficiency of wave‐induced relativistic electron pitch angle scattering. Compared to the frequently adopted parallel or quasi‐parallel model, use of the latitudinally varying wave normal angle model produces the largest decrease in H+‐band EMIC wave scattering rates at pitch angles < ~40° for electrons > ~5 MeV. At a representative nominal amplitude of 1 nT, EMIC wave scattering produces the equilibrium state (i.e., the lowest normal mode under which electrons at the same energy but different pitch angles decay exponentially on the same time scale) of outer belt relativistic electrons within several to tens of minutes and the following exponential decay extending to higher pitch angles on time scales from <1 min to ~1 h. The electron loss cone can be either empty as a result of the weak diffusion or heavily/fully filled due to approaching the strong diffusion limit, while the trapped electron population at high pitch angles close to 90° remains intact because of no resonant scattering. In this manner, EMIC wave scattering has the potential to deepen the anisotropic distribution of outer zone relativistic electrons by reshaping their pitch angle profiles to “top‐hat.” Overall, H+‐band and He+‐band EMIC waves are most efficient in producing the pitch angle scattering loss of relativistic electrons at ~1–2 MeV. In contrast, the presence of O+‐band EMIC waves, while at a smaller occurrence rate, can dominate the scattering loss of 5–10 MeV electrons in the entire region of the outer zone, which should be considered in future modeling of the outer zone relativistic electron dynamics.

Background:In the learned helplessness (LH) paradigm, approximately 35% of rats are resilient to inescapable stress.Methods:The roles of brain-derived neurotrophic factor (BDNF) and dendritic spine density in the brain regions of LH (susceptible) and non-LH rats (resilient) were examined. Western blot analysis and Golgi staining were performed.Results:BDNF levels in the medial prefrontal cortex, CA3, and dentate gyrus (DG) were significantly lower in the LH group than in the control and non-LH groups, whereas BDNF levels in the nucleus accumbens (NAc) in the LH group but not the non-LH group were significantly higher than those in the control group. Furthermore, spine density in the prelimbic cortex, CA3, and DG was significantly lower in the LH group than in the control and non-LH groups, although spine density in the NAc was significantly higher in the LH group than in the control and non-LH groups.Conclusions:The results suggest that regional differences in BDNF levels and spine density in rat brain may contribute to resilience to inescapable stress.

Background:Similar to the N-methyl-D-aspartate receptor antagonist ketamine, the metabotropic glutamate 2/3 receptor antagonist, MGS0039, shows antidepressant effects. However, there are no reports comparing these 2 compounds in the social defeat stress model of depression.Methods:We examined the effects of MGS0039 (1 mg/kg) and ketamine (10 mg/kg) on depression-like behavior in susceptible mice after repeated social defeat stress. Protein levels of brain-derived neurotrophic factor, TrkB, phospho-TrkB, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (GluA1), postsynaptic density protein 95, and dendritic spine density in selected brain regions were measured.Results:In the tail suspension and forced swimming tests, both MGS0039 and ketamine significantly attenuated the increased immobility time observed in susceptible mice, compared with vehicle-treated animals, 1 or 2 days after a single dose of drug. In the sucrose preference test, both compounds significantly improved the reduced preference typically seen in susceptible mice at 3 to 7 days after a single dose of drug. Western-blot analyses showed that similar to ketamine, MGS0039 significantly attenuated the reduced brain-derived neurotrophic factor, phospho-TrkB/TrkB ratio, GluA1 and postsynaptic density protein 95 seen in the prefrontal cortex, dentate gyrus, and CA3 of the hippocampus from susceptible mice, 8 days after a single dose. Again, in a similar manner to ketamine, MGS0039 significantly attenuated the reduction of spine density in the prelimbic regions of the medial prefrontal cortex, dentate gyrus, and CA3 of the hippocampus, but not infralimbic regions of the medial prefrontal cortex and CA1, in susceptible mice 8 days after a single dose. In contrast, neither drug elicited an effect on altered brain-derived neurotrophic factor-TrkB signaling, GluA1, and postsynaptic density protein 95 levels and did not increase spine density observed in the nucleus accumbens of susceptible mice.Conclusions:Similar to ketamine, MGS0039 shows rapid and sustained antidepressant effects in the social defeat stress model. Long-lasting synaptogenesis in the prelimbic regions of medial prefrontal cortex, dentate gyrus, and CA3 might be implicated in this sustained antidepressant effect.

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[1] Using the Dst value corrected for the effects of magnetopause currents (Dst*) and solar wind magnetic field and plasma data from 1 January 1998 to 30 April 2002, during elevated solar conditions, we have statistically examined the relationship of 271 storms (Dst* À30 nT) to 104 magnetic clouds. It is found that most of the magnetic clouds result in geomagnetic storms, but only about 30% of storms are due to magnetic clouds. A storm can be driven by a cloud's various regions or their combinations with dissimilar occurrence percentages. These percentages change as a function of geomagnetic activity levels as well. It is found that the leading field is the most geoeffective region and the sheath region is equally effective at causing magnetic storms during solar maximum (42%) compared to solar minimum (43%) as a percentage of magnetic cloud-induced storms. The occurrence percentage of intense storms caused by clouds is 72%, which is much higher than the $20% occurrence percentage of smaller storms caused by clouds. It is also found that ''unipolar B z '' and ''bipolar B z '' clouds have different geoeffectiveness percentages, depending on the B z orientation. The long-known control of magnetic activity mainly by southward B z is supported by the results of this study. It is also shown that multistep development storms can result not only from both the combinations of sheath and cloud fields but also from different fields within a cloud. A new name, quasi-cloud, is proposed for those cloud-like solar wind structures which show evidence of relatively organized field rotations.

[1] Superposed epoch analyses of 549 storms are performed to make a comparison of solar wind features of geomagnetic storm events at solar minimum (July 1974 to June 1977 July 1984 to June 1987 July 1994 to June 1997 and solar maximum (January 1979 to December 1981 January 1989 to December 1991 July 1999 to June 2002. In this study, geomagnetic storms are defined by the pressure-corrected Dst (Dst*) and classified into moderate storms (À100 nT < Dst* À50 nT) and intense storms (Dst* À100 nT). The average values of interplanetary magnetic field (IMF), solar wind plasma, NOAA/POES hemispheric power, Kp, and Dst* are analyzed and compared among the different storm categories. During the main phase of storms in each category, the average solar wind plasma parameters and IMF components are disturbed and compressed by a relative high-speed plasma stream. It is shown that the peak of the average solar wind density leads the minimum Dst* (the zero epoch time) by 4.3-7.0 hours, which is longer than the peak time difference (0.3-1.0 hour) between the average IMF B s and Dst* min . For intense storms at solar minimum, the average IMF B y is greatly disturbed during both the main phase and the recovery phase. In addition, the average solar wind density is enhanced up to 28 cm À3 , but the average solar wind bulk flow in this storm category is lower than those in all other categories. A significant finding is that the average interplanetary causes of intense storms at solar minimum are found to be against the well-known empirical criteria (B s ! 10 nT or VB s ! 5.0 mV/m for !3 hours), having a long interval of average B s = $10 nT with dual peaks separated by $4.0 hours. The interplanetary and solar origins of storms in the different storm categories are also discussed.

RationaleThe N-methyl-d-aspartate (NMDA) receptor antagonists, including R-ketamine and rapastinel (formerly GLYX-13), show rapid antidepressant effects in animal models of depression.ObjectiveWe compared the rapid and sustained antidepressant effects of R-ketamine and rapastinel in the social defeat stress model.ResultsIn the tail suspension and forced swimming tests, R-ketamine (10 mg/kg, intraperitoneal (i.p.)) or rapastinel (10 mg/kg, i.p.) significantly attenuated the increased immobility time in the susceptible mice, compared with the vehicle-treated group. In the sucrose preference test, both compounds significantly enhanced the reduced preference in susceptible mice 2, 4, or 7 days after a single injection. All mice were sacrificed 8 days after a single injection. Western blot analyses showed that R-ketamine, but not rapastinel, significantly attenuated the reduced brain-derived neurotrophic factor (BDNF)-TrkB signaling, postsynaptic density protein 95 (PSD-95), and GluA1 (a subtype of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor) in the prefrontal cortex, dentate gyrus, and CA3 of the hippocampus in the susceptible mice. In contrast, both compounds had no effect against the increased BDNF-TrkB signaling, PSD-95, and GluA1 seen in the nucleus accumbens of susceptible mice. Moreover, sustained antidepressant effect of R-ketamine (3 mg/kg, intravenous (i.v.)), but not rapastinel (3 mg/kg, i.v.), was detected 7 days after a single dose.ConclusionsThese results highlight R-ketamine as a longer lasting antidepressant compared with rapastinel in social defeat stress model. It is likely that synaptogenesis including BDNF-TrkB signaling in the prefrontal cortex (PFC) and hippocampus may be required for the mechanisms promoting this sustained antidepressant effect.

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