Differential long-term effect of AF64A on [3H]ACh synthesis and release in rat hippocampal synaptosomes.

The activities of various presynaptic cholinergic parameters were determined in hippocampal synaptosomes of rats 29 weeks after intracerebroventricular injection of ethylcholine aziridinium (AF64A) (3 nmol/2 microliters/side) or vehicle (saline). Synaptosomes were preloaded with 3H]choline (3H]Ch), treated with diisopropyl fluorophosphate to inhibit cholinesterase activity and then were assayed for their content of 3H]Ch and 3H]acetylcholine (3H]ACh) and for their ability to synthesize and release 3H]ACh. In synaptosomes from AF64A-treated rats compared with synaptosomes from vehicle-treated rats we observed that: (i) specific uptake of 3H]Ch was reduced to 60% of control; (ii) residing 3H]ACh levels were 43% of control while residing 3H]Ch levels were 72% of control; (iii) basal and K(+)-induced 3H]ACh release were 77% and 73% of control, respectively; (iv) high K(+)-induced synthesis of 3H]ACh was only 9% of control; (v) but, choline acetyltransferase activity remained relatively high, being 80% of control. These results suggest that AF64A-induced cholinergic hypofunction is expressed by both loss of some cholinergic neurons and impairment in the functioning of the spared neurons.