Neuronal and neurovascular integration following transplantation of the fetal hypothalamus into the third cerebral ventricle of adult brattleboro rats. Neurological transplants: I

This investigation has confronted some very basic questions of neurobiology and specifically deals with the neurovascular and neuroanatomical interactions that occur between graft and host following neural transplantation. Host Long-Evans rats with chronic autosomal diabetes insipidus (DI) received stereotaxic implants of normal 17 day post-coitus fetal hypothalamic fragments from the rostral (anterior) hypothalamus of normal Long-Evans pups. Following stereotaxic surgery DI hosts were killed 60 or 90 days later and their brain prepared for correlative microangiography-immunocytochemistry coupled with transmission electron microscopy. Explants were rapidly invaded by host vessels from several routes. 1. (1) Vessels appeared to arise from portal capillaries in the underlying median eminence and 2. (2) from adjacent vessels from the paraventricular nucleus and surrounding endocrine hypothalamus and 3. (3) possibly from intrinsic vessels of the graft. The former remained fenestrated and established bonafide neurovascular zones in the ventral regions and in actively growing explants. Small clusters of arginine vasopressin-positive fibers and neurophysin positive neurons were noted throughout the parenchyma of explants. Despite the presence of neurosecretory neurons and neurovascular (neurohemal) zones, none of the host rats exhibited a physiological return to normal parameters of water balance. However the active growth and development of explants in the third cerebral ventricle of DI host rats coupled with emergence of neurovascular zones lends support to a potential model for analyzing the development of anatomical substrates for the central delivery of neuropeptide hormones.