Working memory deficits following muscarinic blockade combined with depletion of brain somatostatin in rats

In a working memory task with three-panel runway paradigm, cysteamine, a depletor of somatostatin, at 100 or 200 mg/kg i.p. given 24 h before testing, had no effect on the number of errors (attempts to pass through two incorrect panels of the three panel-gates at four choice points). Cysteamine at 100 mg/kg caused a significant reduction in somatostatin-like immunoreactivity in the rat brain, including the hippocampus and cerebral cortex. Working memory errors were significantly increased by scopolamine, a muscarinic receptor antagonist, at 0.32 mg/kg i.p. given 20 min before testing, whereas errors were not affected by the 0.1 mg/kg dose. Combined administration of 100 mg/kg cysteamine and 0.1 mg/kg scopolamine significantly increased the number of working memory errors. However, cysteamine at 100 mg/kg and scopolamine at 0.1 mg/kg had no effect on reference memory errors, whether they were administered alone or in combination. These results suggest that depletion of brain somatostatin aggravates working memory deficits induced by blockade of muscarinic receptors.