Development of a Vitamin A Deficient (VAD) Songbird

Abstract

Vitamin A deficiency (VAD) is a global health problem with effects on brain function through altered retinoic acid signaling. However, the specific effect of VAD on speech and vocal‐motor learning has not been studied. Songbirds possess a cortical brain circuit for vocal learning that relies on retinoic acid signaling during the critical period of vocal learning. To study VAD in a vocal learner we developed a special diet from white rice and sunflower seed, two grains that are naturally low in vitamin A and carotenoids, with other essential vitamins and minerals added back. This diet was fed to zebra finch family groups during chick rearing to evaluate the ability of parents to feed the diet to their chicks and the effects of a VAD diet on serum and brain retinol, chick growth and development. We found that adult birds readily consumed the rice/sunflower seed diet and fed it to their nestlings. Adults that consumed the diet maintained the same caloric intakes compared to when fed a regular seed diet and although these birds showed some decline in body mass, it remained within a normal range. Surprisingly, we detected a 28% decline in serum retinol at three weeks on the VAD diet in adult finches, a response that makes songbirds a highly useful model to study VAD. Juveniles that were fed the diet by the adults beginning at hatch also were able to consume and thrive. Compared to controls, chicks on the VAD diet showed no effects on growth rate between 10‐65 days, but the chick survival rate was 63% lower than that of controls with no chicks surviving beyond 65 days old. Chicks that were on the VAD diet did not exhibit sub‐song behavior between 35‐50 days (72 total hours of monitoring), whereas chicks that were on a seed diet or a rice/sunflower seed control diet (with retinol added back) showed song development. We also note that VAD affected eye shape and appearance, consistent with what is found during VAD in non‐avian models. Serum retinol of chicks on the VAD diet showed a 57% decline compared to controls. Further development of this model will require titration of the VAD to moderate levels that allow for song development and high chick survival. This study lays the groundwork for the use of modified diets in the songbird model to examine how VAD or other micronutrients may modulate neural development in the vocal circuit of a vocal learner, as well as open the door for the use of the model in high‐fat diet nutrition experiments and lipid transport studies.