show Abstracthide AbstractRats were sacrificed at various development stages at both mid-day and mid-night. Pineal glands were removed and the transcriptomes were interrogated using RNA-Seq to determine developmental changes in gene expression with special emphasis on the acquisition of day-night differences in gene expression levels. It is known from previous studies that in the rat pineal gland several hundred genes exhibit at least a two-fold greater expression at night than during the day; and more than a hundred have a more than two-fold higher expression during the day.