|Cheng, Heng wei|
Submitted to: European Journal of Neuroscience
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/23/2004
Publication Date: 12/5/2004
Citation: Freire, R., Cheng, H. 2004. Experience-dependent changes in the hippocampus of domestic chicks: a model for spatial memory. European Journal of Neuroscience. 20(4):1065-1068. Interpretive Summary: In the modern broiler industry, chickens housed in large groups do not space themselves evenly but instead crowd in particular areas, which may affect chicken health and increase mortality. One contributing factor may be a deficit in spatial skills arising from the absence of essential environmental factors during routine rearing. The present study was to examine whether chick spatial skills can be improved by experimental training at an early age. Compared to control chicks, experience-induced changes in brain morphology reported here suggest that early experience leads to changes in the hippocampus that appear to be related to the development of spatial memory. Enhanced spatial memory in chickens may result in improving their well-being by increasing their distribution and their skills to locate the feeder and water. The method could be adapted by producers to improve broiler chickens well-being and reduce mortality resulting from physical and social stress.
Technical Abstract: In the domestic chicken, providing visual barriers for a brief period early in life has been found to improve spatial memory. In the present study we compared the structure of neurons in the hippocampus and neostriatum in chicks reared with or without visual barriers. From 8 to 16 days of age, chicks were reared in pens either with two wooden screens (Treatment E) or with no screens (Treatment C). At 16 days of age, chicks were anaesthetised, perfused intracardially and brain samples collected and stained using a Golgi-Cox technique. Morphometric analysis revealed that the multipolar projection neurons of Treatment E chicks had longer dendrites (ANOVA, F1,14= 7.4, P<0.05) and had more spines per 20µm of dendrite (SLD; ANOVA, F1,14= 10.6, P<0.01) than those of Treatment C chicks. In contrast, no evidence was found that rearing treatment differentially influences dendrite length or SLD in the neostriatum, suggesting that the above environment-induced changes may be specific to the hippocampus. Multipolar projection neuron dendrites of the right hemisphere were longer (ANOVA, F1,14= 36.4, P<0.0001) and had more spines (ANOVA, F1,14= 8.8, P<0.05) than dendrites of the left hemisphere supporting previous findings that the right hemisphere of chickens is predominantly involved in spatial processing. We conclude that the chicken provides a useful model for the study of developmental plasticity in brain and behaviour, partly because the possibility of rearing chicks in isolation and imprinting them on an artificial object provides a means of accurately manipulating early experience.