CIRCADIAN-RHYTHMS DIFFER BETWEEN SELECTED MOUSE LINES - A MODEL TO STUDY THE ROLE OF VASOPRESSIN NEURONS IN THE SUPRACHIASMATIC NUCLEI

Mice selected for differences in nest-building behavior differ in the number of arginine-vasopressin (AVP)-immunoreactive neurons in the sup rachiasmatic nuclei (SCN). Although previous efforts to link AVP-immun oreactive neurons in the SCN to clock function have failed, we show th at differences in several circadian parameters are associated with dif ferences in the number of AVP-immunoreactive neurons between the selec ted lines. Although an alternative interpretation is discussed, we hyp othesize that these neurons may relay timing information from the circ adian pacemaker in the SCN for wheel-running activity. In addition, ph ase-response curves (PRCs) to 15-min light pulses in constant darkness also differ between the selected lines. However, these differences ar e not associated with the number of the AVP-immunoreactive neurons in the SCN, but are associated with the level of nest-building behavior. Compared to the Brattleboro rat, in which homozygous rats are deficien t for AVP in the entire brain, our system, exhibiting a wide range of variability, has more specific utility for studying the role of the ou tput pathways of the SCN in circadian rhythm control.