Transplantation of basal forebrain cells of foetal rats into the subarachnoid space: improvement of disturbance of passive avoidance memory due to injury of nucleus basalis magnocellularis.

Basal forebrain cells of foetal rats were transplanted into the subarachnoid space of adult rats harbouring a kainic acid-induced unilateral lesion in the nucleus basalis magnocellularis. Passive avoidance response tests were performed eight weeks after the transplantation, and the results were compared with those of lesioned but non-transplanted rats and of non-lesioned control rats. Although acquisition impairments did not improve, retention impairments were significantly ameliorated in the transplanted rats. Histologically, transplanted foetal neurons survived and grew very well over the cortical surface, and exhibited facilitated neuritic elongation on acetylcholinesterase staining. Choline acetyl-transferase-immunoreactive neurons were found along the needle track as well as in the subarachnoid graft tissues. The results seem to indicate that not the re-innervation from the graft to the host cortex but the diffusional supply of neurotransmitters and/or their synthetic enzymes and neurotrophic factors were responsible for improvement of memory deficits. The subarachnoid space proved to be an adequate place for growth of transplanted neuronal and glial cells for reasons of ample supply of oxygen and nutrition and of low tissue pressure.