Imprinting behavior is one form of learning and memory in precocial birds. With the aim of elucidating of the neural basis for visual imprinting, we focused on visual information processing.A lesion in the visual wulst, which is similar functionally to the mammalian visual cortex, caused anterograde amnesia in visual imprinting behavior. Since the color of an object was one of the important cues for imprinting, we investigated color information processing in the visual wulst. Intrinsic optical signals from the visual wulst were detected in the early posthatch period and the peak regions of responses to red, green, and blue were spatially organized from the caudal to the nasal regions in dark-reared chicks. This spatial representation of color recognition showed plastic changes, and the response pattern along the antero-posterior axis of the visual wulst altered according to the color the chick was imprinted to.These results indicate that the thalamofugal pathway is critical for learning the imprinting stimulus and that the visual wulst shows learning-related plasticity and may relay processed visual information to indicate the color of the imprint stimulus to the memory storage region, e.g., the intermediate medial mesopallium.
Abstract With the aim of elucidating the neural mechanisms of early learning, we studied the role of brain‐derived neurotrophic factor (BDNF) in visual imprinting in birds. The telencephalic neural circuit connecting the visual Wulst and intermediate medial mesopallium is critical for imprinting, and the core region of the hyperpallium densocellulare (HDCo), situated at the center of this circuit, has a key role in regulating the activity of the circuit. We found that the number of BDNF mRNA ‐positive cells in the HDCo was elevated during the critical period, particularly at its onset, on the day of hatching (P0). After imprinting training on P1, BDNF mRNA ‐positive cells in the HDCo increased in number, and tyrosine phosphorylation of TrkB was observed. BDNF infusion into the HDCo at P1 induced imprinting, even with a weak training protocol that does not normally induce imprinting. In contrast, K252a, an antagonist of Trk, inhibited imprinting. Injection of BDNF at P7, after the critical period, did not elicit imprinting. These results suggest that BDNF promotes the induction of imprinting through TrkB exclusively during the critical period.
A temperature monitoring method to promote safety with regard to tissue heating induced by RF irradiation during MRI procedures, especially carbon-13 magnetic resonance spectroscopy ((13)C-MRS), is proposed. The method is based on the temperature dependence of the water proton chemical shift (-0.01 ppm/ degrees C) combined with phase mapping. Using this method, temperature changes were measured in rats (n = 4) employing practical (1)H-decoupled (13)C-MRS pulse sequences for 1D projections (TR = 1000 ms, acquisition time = 15 ms, matrix = 256, spatial resolution = 0.2 mm) and 2D images (TR = 1500 ms, acquisition time = 840 ms, matrix = 128x32, spatial resolution = 0.8x1.5 mm). Measurement error was 0.18 degrees C (SD) for 1D acquisition and 0.39 degrees C (SD) for 2D acquisition, demonstrating the feasibility of this temperature mapping method. Further studies should be conducted in human subjects to monitor patient safety and to optimize the pulse sequences employed. Magn Reson Med 43:796-803, 2000.
l-[4-13C]Glutamine was synthesized from sodium [2-13C]acetate in 12 steps and 18% overall yield. A Wittig reaction of (R)-benzyl 4-formyl-2,2-dimethyloxazolidine-3-carboxylate and ethyl 2-(triphenylphosphoranylidene)[2-13C]acetate prepared from d-serine and sodium [2-13C]acetate, respectively, gave (4S)-4-(2-ethoxycarbonyl[2-13C]vinyl)-2,2-dimethyloxazolidine-3-carboxylic acid α,β-isopropylidene group, oxidation of the resulting hydroxyl group to a carboxyl group and transamidation of the ester moiety gave l-N-Cbz-[4-13C]glutamine (Cbz = benzyloxycarbonyl). Finally, removal of the Cbz group gave l-[4-13C]glutamine. l-[4-13C]Glutamine can be prepared in fewer steps and higher yield by this method compared with previously reported methods.
