Des
pite the
prominent role of the Syrian hamster (
Mesocricetus auratus) in studies of circadian rhythms, there are no data available on the tem
poral dynamics of the neuro
pe
ptide vaso
pressin (AVP), a major out
put system of the su
prachiasmatic nucleus (SCN). We studied the hamster SCN-AVP system in vivo across the light
period and in vitro using long-term organoty
pic SCN cultures. Additionally, we com
pared wild-ty
pe and
tau mutant hamsters with an endogenous circadian
period of
phs/BQ1.GIF>24 h and
phs/BQ1.GIF>20 h, res
pectively. The in vivo study revealed no differences in the number of SCN-AVP neurons between the two genoty
pes of hamsters studied at three time
points across the light
period of the circadian cycle. A significantly higher level of AVP-immunoreactivity, however, was found in the SCN of wild-ty
pe com
pared to
tau mutant hamsters at the beginning and in the middle of the light
period, but not at the end of the light
period. SCN-AVP cell number and immunostaining decreased significantly across the light
period in wild-ty
pe hamsters, but not in
tau mutants. The in vitro study revealed a significantly higher rate of AVP release
per 24 h from the
tau mutant SCN com
pared to the wild-ty
pe SCN. Robust circadian oscillations in AVP release were not found in either ty
pe of hamster. These results may suggest that the SCN-AVP system of hamsters, irres
pective of genoty
pe, is relatively weak com
pared to other s
pecies. Moreover, the
tau mutation seems to influence the SCN-AVP system by enhancing the rate of AVP release and by reducing AVP content and its daily fluctuation.
