Synthesis Of Acetylcholine In Slices Research Articles

Effects of Tri-, Di and Monobutyltin on Synaptic Parameters of the Cholinergic System in the Cerebral Cortex of Mice

Triorganotin compounds like tributyltin have been reported to be biodegraded to diorganotin, monoorganotin and then inorganic tin in animals after they have been ingested. Effects of tributyltin, dibutyltin and monobutyltin on various cholinergic parameters that are involved in synaptic transmission in the mouse cerebral cortex were investigated in vitro. Tributyltin and dibutyltin, but not monobutyltin, inhibited the activity of choline acetyltransferase, both the high-affinity and low-affinity uptakes of choline into synaptosomes, and the binding of [3H]quinuclidinyl benzilate to muscarinic acetylcholine receptors. Tributyltin and dibutyltin, but not monobutyltin, had a slightly suppressive effect on the K+-induced release and synthesis of acetylcholine in slices of the cortex. All three butyltins at concentrations from 10 −6 to 10−4 M had no effect on the activity of acetylcholinesterase. The extent of the inhibitory effects on the cholinergic parameters, apart from the activity of acetylcholinesterase, was slightly greater in the case of tributyltin than dibutyltin, in particularly at the highest concentration (10−4 M) tested. Therefore, it is concluded that tributyltin metabolites inhibit various parameters of cholinergic activity with a potency ranking of tributyltin > dibutyltin > monobutyltin.

Cholinergic system of brain tissue in rats poisoned with the organophosphate, 0,0-dimethyl 0-(2,2-dichlorovinyl) phosphate

The cholinergic system of the brain was investigated in rats acutely poisoned with the organophosphate, 0,0-dimethyl 0-(2,2-dichlorovinyl) phosphate (DDVP), (6 mg/kg, sc, with saline as a control). The amounts of three fractions of acetylcholine (ACh)—free (extraterminal), labile-bound (intraterminal/cytoplasmic), and stable-bound (intraterminal/vesicular)—increased in the rats over a period of 5 to 60 min after injection of DDVP, showing peaks which were 2.45, 1.82, and 1.4 times as high as the respective control amounts. No difference was seen in the amount of any fraction of ACh between treated and control rats killed 3 and 24 hr after injection. Acetylcholinesterase (AChE) activity decreased to between 12 and 43% of the control over a period of 5 to 180 min and recovered almost completely within 24 hr after injection. No appreciable changes were seen in either spontaneous or potassium-induced ACh release in brain tissue slices obtained from rats treated with DDVP. ACh synthesis in slices was suppressed significantly 20 min, but not 24 hr, after injection of DDVP. In the brain crude synaptosomal preparation, high-affinity choline uptake, which is generally thought to be a rate-limiting step for ACh synthesis, was suppressed 20 min after DDVP. No appreciable changes were seen in high-affinity choline uptake at 24 hr low-affinity choline uptake, and choline acetyltransferase activity after injection of DDVP. These results suggest that ACh synthesis and high-affinity choline uptake may be in a suppressed state when ACh concentration, especially intraterminal ACh, is increased and AChE activity is decreased in the brain cholinergic system of rats poisoned with DDVP. The increase in the intratermianl ACh may be due to an inhibition of AChE activity at this site and/or a re-uptake of ACh in the synaptic cleft, not to an inhibition of ACh release or an increase in ACh synthesis.

Intracerebroventricular administration of ethylcholine mustard aziridinium ion (AF64A) reduces release of acetylcholine from rat hippocampal slices

Ethylcholine mustard aziridinium ion (AF64A), or vehicle, was infused bilaterally (3 nmol/3 μl per side) into the lateral ventricles of rats. The effect of such treatment on various cholinergic responses was measured in the hippocampus, cortex and striatum. Potassium-stimulated release of acetylcholine from superfused slices of hippocampus was reduced, 7 and 21 days after treatment with AF64A, to 24 and 35% of control, respectively. The activity of choline acetyltransferase in the hippocampus also decreased, to 42% of control, both 7 and 21 days after treatment with AF64A. Similarly, the activity of acetylcholinesterase and the high affinity transport of choline in the hippocampus were reduced, to 40 and 30% of control; and to 33 and 48% of control, respectively, 7 and 21 days after treatment with AF64A. Synthesis of acetylcholine in slices of hippocampus was also decreased after treatment with AF64A (71 and 51% of control, 7 and 21 days post-AF64A respectively). Only the binding of [ 3h]qnb in the hippocampus was unchanged at 7 days after treatment with AF64A, although a small reduction (11%) was noted 21 days after treatment with AF64A. The activity of choline acetyltransferase and acetylcholinesterase, the high-affinity transport of choline and the binding of fhiqnb in cortex and striatum were unaffected by treatment with AF64A under the same experimental conditions. Using a substantially smaler dose than that earlier reported in mice, the earlier finding was thus confirmed, and extended, in rats, of a highly selective effect of AF64A on several components of the cholinergic system. Under the conditions of this study, these effects appeared to be confined to the hippocampus.