Temporal organization of feeding in Syrian hamsters with a genetically altered circadian period.

The variation in spontaneous meal patterning was studied in three genotypes (tau +/+, tau +/- and tau -/-) of the Syrian hamster with an altered circadian period. Feeding activity was monitored continuously in 13 individuals from each genotype in constant dim light conditions. All three genotypes had on average six feeding episodes during the circadian cycle (about 20h in homozygous tau mutants and 22h in heterozygotes compared with 24h in wild-type hamsters). Thus, homozygous tau mutant hamsters had significantly more feeding episodes per 24h than wild types, and heterozygotes were intermediate. The average duration of feeding bouts (FBs) was indistinguishable (around 30 minutes) among the three genotypes, whereas the intermeal (IM) intervals were significantly shorter for homozygote tau mutant hamsters (99 minutes), intermediate for heterozygotes (116 minutes), and the longest for wild-type hamsters (148 minutes). Thus, the meal-to-meal duration was on average 25% shorter in homozygous tau mutants (16% in heterozygous) than in wild-type hamsters. The reduction of the circadian period has a pronounced effect on short-term feeding rhythms and meal frequency in hamsters carrying the tau mutation.