Effect of 5‐hydroxytryptamine on [3H]‐acetylcholine release from guinea‐pig striatal slices

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Abstract
1 The effect of 5-hydroxytryptamine (5-HT) on spontaneous and electrically-evoked tritium efflux was studied in guinea-pig caudate nucleus slices preloaded with [3H]-choline. 2 5-HT, 10–300 μmol1−1, temporarily increased the spontaneous tritium efflux (as well as the endogenous acetylcholine (ACh) release) and, after 15 min perfusion, inhibited it. The facilitatory effect of 5-HT on spontaneous efflux was increased while the inhibitory effect did not occur in slices taken from dopamine-depleted guinea-pigs. 3 The increase in spontaneous tritium efflux by 5-HT was blocked by methiothepin, methysergide (pA2 8.7) and by the selective 5-HT2 antagonist, ritanserin (pA2 6.7). 4 The inhibition of spontaneous tritium efflux by 5-HT was prevented by methysergide and methiothepin but not by ritanserin and (−)-propranolol. 5 5-HT, 100 μmol1−1, inhibited the electrically-evoked tritium efflux and this effect was unchanged in dopamine-depleted slices. 6 The inhibition of electrically-evoked tritium efflux by 5-HT was blocked by methiothepin and methysergide but not by (−)-propranolol or ritanserin. 7 These results suggest that 5-HT may exert a rapid and transient (excitatory) and a more prolonged (inhibitory) control over striatal cholinergic neurones.

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