RESTORATION OF CIRCADIAN BEHAVIOR BY ANTERIOR HYPOTHALAMIC GRAFTS CONTAINING THE SUPRACHIASMATIC NUCLEUS - GRAFT HOST INTERCONNECTIONS/

Destruction of the hypothalamic suprachiasmatic nucleus (SCN) disrupts circadian behavior. Transplanting SCN tissue from fetal donors into S CN-lesioned recipients can restore circadian behavior to the arhythmic hosts. In the transplantation model employing fetal hamster donors an d SCN-lesioned hamsters as hosts, the period of the restored circadian behavior is hamster-typical. However, when fetal rat anterior hypotha lamic tissue containing the SCN is implanted into SCN-lesioned rats, t he period of the restored circadian rhythm is only rarely typical of t hat of the intact rat. The use of an anterior hypothalamic heterograft model provides new approaches to donor specificity of restored circad ian behavior and with the aid of species-specific markers, provides a means for assessing connectivity between the graft and the host. Using an antibody that stains rat and mouse neuronal tissue but not hamster neurons, it has been demonstrated that rat and mouse anterior hypotha lamic heterografts containing the SCN send numerous processes into the host (hamster) neuropil surrounding the graft, consistent with graft efferents reported in other hypothalamic transplantation models in whi ch graft and host tissue can be differentiated (i.e., Brattleboro rat and hypogonadal mouse). Moreover, SCN neurons within anterior hypothal amic grafts send an appropriately restricted set of efferent projectio ns to the host brain which may participate in the functional recovery of circadian locomotor activity.