Direct evidence for axonal outgrowth from cholinergic grafts to cholinergically-deafferented rat cortex

True Blue, a retrograde fluorescent tracer, was used to investigate axonal outgrowth after grafting embryonic forebrain cholinergic tissue into the cholinergically-deafferented rat frontal cortex. Unilateral deafferentation was achieved by injecting alpha-amino-3-OH-4-isoxozole propionic acid (AMPA) into the ipsilateral nucleus basalis magnocellularis. Grafting occurred 3 weeks after the lesion. Eight to 10 weeks later, True Blue was injected bilaterally into the cortex at a superficial site which, on the transplanted side, was located at least 2 mm away from the transplant. Forty-eight h later, retrogradely labelled fluorescent neurones could be seen in the deepest part of the transplants. Some of these neurones were shown to be ChAt-positive, providing evidence of axonal outgrowth from transplanted cholinergic neurones into cholinergically-deafferented frontal cortex.