Biochemical and anatomical analysis of cholinergic, noradrenergic and serotonergic innervation of fetal neocortical transplants placed in excitotoxin-induced neocortical lesions of adult rats

Abstract

Fetal neocortical block transplants were implanted into the excitotoxically ablated sensorimotor cortex of adult rats in order to examine the density of innervation and distribution of presumptive host derived afferent fibers within these transplants. Cholinergic fiber innervation was examined at 3 months post grafting by measuring acetylcholinesterase (AChE) and choline acetyl-transferase (ChAT) enzyme activities within the grafts and within the corresponding host cortex by radiochemical enzyme assays as well as by AChE histochemistry for the visualization of AChE positive fibers. Noradrenergic and serotonergic inputs were examined by high performance liquid chromatography (HPLC) measurements of noradrenaline (NA) and serotonin (5-hydroxytryp-tamine, 5-HT) concentrations as well as by tyrosine hydroxylase (TH) and 5-HT immunocytochemistry for the visualization of monoaminergic fiber distribution. Our results demonstrated that the grafts contained significantly lower levels of neurotransmitter markers when compared to normal unablated cortex. The anatomical analysis showed an unequal fiber distribution within the transplants. Areas adjacent to the host tissue revealed a relatively dense fiber innervation when compared to the density observed within the more central parts of the transplants, and the anatomical data therefore supported the biochemical data in suggesting an overall lower cholinergic and monoaminergic innervation of fetal neocortical transplants placed into the lesioned adult cortex when compared to normal cortex.