8 research outputs found
Factors Determining the Restoration of Circadian Behavior by Hypothalamic Transplants
The expression of locomotor activity by
golden hamsters is temporally controlled by
circadian oscillators contained within the
suprachiasmatic nucleus (SCN). A genetic
mutation has been found that alters the
freerunning period of the locomotor activity
rhythm from the wild-type value of ~24 hours to
~20 hours in homozygous mutants. It has been
shown previously that a transplant of fetal
hypothalamic tissue containing the SCN to a
host rendered arrhythmic by a complete lesion
of the SCN restores rhythmicity with the
freerunning period which is normally expressed
by the donor genotype. To investigate the
mechanisms by which the SCN controls the
temporal organization of behavior, we made
partial lesions to the SCN of hosts of one
genotype, and then placed hypothalamic
implants from fetal donors of a different
genotype into the lesion site. By varying the size
of the host's partial SCN lesion and the duration
of time between lesioning and transplantation,
we have attempted to alter the relative amount
of host and donor control over the expression of
locomotor activity. We found that the expression
of donor rhythmicity requires the presence of a
lesion to the host SCN, and that the incidence of
donor expression increased as a function of host
SCN lesion size. Neither the duration of time
between lesioning and transplantation, nor the
location of the transplant within the third
ventricle had independent effects on the incidence of donor rhythm expression; however,
there was a strong suggestion of an effect of
their interaction