Impact of wave front and coherence optimization in coherent diffractive imaging.

We present single shot nanoscale imaging using a table-top femtosecond soft X-ray laser harmonic source at a wavelength of 32 nm. We show that the phase retrieval process in coherent diffractive imaging critically depends on beam quality. Coherence and image fidelity are measured from single-shot coherent diffraction patterns of isolated nano-patterned slits. Impact of flux, wave front and coherence of the soft X-ray beam on the phase retrieval process and the image quality are discussed. After beam improvements, a final image reconstruction is presented with a spatial resolution of 78 nm (half period) in a single 20 fs laser harmonic shot.

New insights into the relationship of neurogenesis and affect: tickling induces hippocampal cell proliferation in rats emitting appetitive 50-kHz ultrasonic vocalizations.

Adult hippocampal cell proliferation (HCP) has been associated with psychopathology, especially depression. However, it is controversial whether a constitutively low rate of HCP is a trait predisposing an individual to psychopathology or whether HCP varies with the subject's affective state. We made use of a so-far neglected measure of affect, namely ultrasonic vocalizations, to gain new insights into the relationship of HCP and affect. Rats emit distinct types of ultrasonic vocalizations, which serve as situation-dependent affective signals. In appetitive situations, rats produce 50-kHz-calls, whereas 22-kHz-calls occur in aversive situations. We applied a standardized protocol of repeated tickling and assessed tickling-induced ultrasonic vocalizations as an index of the animals affect. Stereological quantifications of 5-bromo-2'-deoxyuridine (BrdU) and proliferating-cells-nuclear-antigen (PCNA) immunolabeled cells were used to estimate the rate of cell proliferation in the subventricular zone and the subgranular zone of the dentate gyrus in the hippocampus. The rate of cell proliferation was compared between the groups of tickled vs. non-tickled rats and between subgroups of tickled rats defined by the effect of tickling on ultrasonic vocalizations. Tickling induced ultrasonic vocalizations in a subject-dependent manner. HCP correlated positively with appetitive 50-kHz-calls, but negatively with aversive 22-kHz-calls in individual animals, while cell proliferation in the subventricular zone was not associated with the emission of ultrasonic vocalizations. Repeated tickling did not change HCP in all rats, but increased HCP in the subgroup of rats, which experienced this procedure as appetitive, i.e. in rats emitting high numbers of 50-kHz-calls or low numbers of 22-kHz-calls. Together, these data indicate that the effect of tickling on HCP depends on an interaction between a predisposing trait and stimulation-dependent variations of the subject's affective state.

Rat ultrasonic vocalization in aversively motivated situations and the role of individual differences in anxiety-related behavior.

Our previous work has shown that male Wistar rats, although identical in breeder, age and housing conditions, can differ systematically in their anxiety-related behavior as measured in the elevated plus-maze. Since such individual dispositions can affect the responsiveness in other aversively motivated situations, we asked in a 1st experiment whether such rats might also differ in a test of conditioned fear. Based on their levels of spontaneous open arm avoidance in the elevated plus-maze, 20 adult male Wistar rats were divided into those with "high open arm" (HOA) versus "low open arm" (LOA) time. These rats were then tested in a standard fear conditioning paradigm. During the conditioning procedure, they received 6 tone (3 kHz, 20 s) and shock (0.5 mA, 0.5 s) pairings, each followed by a 60 s inter-stimulus interval. Conditioned responses to the tone were tested 24 h thereafter. During both days, freezing behavior and ultrasonic vocalization were measured. Differences in ultrasonic vocalization between HOA and LOA rats were detected during the conditioning day, where vocalization was more likely in LOA rats. Furthermore, LOA rats emitted calls with higher frequency components than HOA rats. On the subsequent day of testing, the number of animals vocalizing, and the rate of vocalization was decreased, and call differences between groups were no longer detectable. In freezing, differences between HOA and LOA rats were observed on the conditioning day, where LOA rats showed more freezing behavior during the tone/shock intervals. Also, on the test day, they showed more freezing behavior during the tone intervals compared to HOA rats. These results indicate that acute and conditioned responses of rats in a conventional fear conditioning paradigm can depend on individual dispositions of anxiety-related behavior as measured with the elevated plus-maze. In a 2nd experiment, we asked whether exposure to an elevated plus-maze would lead to ultrasonic vocalization, which we tested in rats which had been handled or non-handled prior to testing. Most importantly, we found that none of the animals displayed any vocalization in the plus-maze, neither during a 1st nor a repeated test 1 day later. These data are discussed with respect to the presumed role of ultrasonic vocalization in aversively motivated situations, and the mechanisms, which may account for the behavioral differences between HOA and LOA rats in such tests.