Hatched from natural geomagnetic conditions, 1-day-old chicks were stimulated with Methyl Anthranilate (MeA) and labeled as the control group (CG). We found that the line density of dendritic spines (LDds) from the neurons in the memory-related nuclei [Intermediate Medial Hyperstriatum Ventrale (IMHV) and lobus parolfactorius (LPO)] was increased by 38.7%, and the total dendritic lengths (TLds) of individual neurons in IMHV were increased by 37.1 to 45.4%. In addition, the average LDds of individual neurons in imprinted chicks (ICs) were increased by 10.8%, and the neurons that had long dendrites were increased by 50%. In contrast, in the experimental group (EG), where chicks were hatched from hypomagnetic field, the average LDds of each neuron in IMHV and LPO of the native chick (NC) were similar to the NC of CG. After a 12 h exposure to MeA, the LDds from IMHV and LPO of the no-imprinted chick (n-IC) and IC were similar to NC but decreased by 17.4% to the n-IC and IC of CG. Furthermore, the average TLd of single neurons from the memory nuclei in NC, n-IC and IC were significantly decreased by 30.9%. However, the LPOs were not different in n-IC. These results indicate that if the natural geomagnetic environment is disrupted, the development of the dendritic spines from the neurons in the related memory nuclei is unchanged, but the hyperplasia of the dendritic spines in the neurons involved in long-term memory was ablated by MeA. Further, the development and growth of dendrites were significantly reduced.
Key words: Hypomagnetic field space, day-old chicks, memory-related nuclei (Medial Hyperstriatum Ventrale and lobus parolfactorius), neuron morphology.
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