Diurnal rhythms in neurotransmitter receptor binding and choline acetyltransferase activity: different patterns in two rat lines of Wistar origin.

Diurnal cycles for 8 ligand receptor pairs and choline acetyltransferase (ChAT) activity in 3 brain regions differed markedly in two rat lines, both of Wistar origin. Statistically significant differences between diurnal cycles in the two rat lines were found in the following parameters: 24 h means in 6 of 11 measurements, magnitude of cycle amplitudes, and phase position in 6 of 11 measurements, up to complete reversal of the acrophases in the case of ChAT activity in hippocampus. The importance of these findings--such major differences in two closely related rat lines--is obvious in any attempt to compare receptor-binding studies per se between laboratories using the same strain but not line, in studies of receptor rhythm characteristics, and in particular, for analysing the effects of brain-reactive drugs. While there are some reports on strain-dependency of cyclic functions, we are not aware that line-dependency has previously been described.