Differential long-term effect of AF64A on [H]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 μl/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]ACh 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.