Combined Nicotinic and Muscarinic Cholinergic and Serotonergic Blockade Selectively Impair Acquisition of Spatial Navigation. In: Hanin I, Yoshida M, Fisher A, editors. Alzheimer’s and Parkinson’s Diseases. Boston: Springer US; 1995. pp. 359-69. [DOI: 10.1007/978-1-4757-9145-7_54]

The role of the dorsal raphe-serotonergic system and cholinergic receptors in the modulation of working memory

The present study investigated the role of the dorsal raphe-serotonergic system and its interaction with muscarinic or nicotinic receptors in the modulation of working memory and motor activity by assessing the effects of serotonin lesion with pCA and cholinergic receptor blockade on the performance of rats in a working memory (delayed non-matching to position, DNMTP) task. The pCA lesion did not impair the choice accuracy or motor activity of rats in the DNMTP-task. The lower dose of scopolamine (0.075 mg/kg) impaired percent correct responses already at the shortest delay which is not indicative of a working memory impairment per se. Scopolamine also disrupted motor activity markedly. The effects of scopolamine 0.075 mg/kg on the choice accuracy were aggravated by pCA treatment. Furthermore, the effects of N-methylscopolamine (0.150 mg/kg) were comparable with scopolamine. The higher dose of mecamylamine (3.0 mg/kg) also interfered with motor activity and it decreased the choice accuracy. The performance disruption induced by mecamylamine was not as severe as that seen with scopolamine. Mecamylamine did not reveal any interaction with the serotonergic lesion. Hexamethonium slightly decreased the percent correct responses, while not interfering with motor activity of rats. The present results suggest that: (i) lesion of serotonergic fibers with pCA does not significantly impair the choice accuracy or interfere with motor activity of rats; (ii) the blockade of cholinergic receptors does not impair working memory per se, but disrupts motor activity, and (iii) pCA lesion of serotonergic fibers aggravates the non-mnemonic choice accuracy impairment induced by central muscarinic blockade, while not interacting with the cholinolytics in modulation of motor activity.

Combined treatment with a 5HT1A receptor agonist and a muscarinic acetylcholine receptor antagonist disrupts water maze navigation behavior

The present study was designed to investigate the effects of combined treatment with a serotonin (5-HT)1A receptor agonist, 8-hydroxy-2-(dipropylamino)-tetralin (8-OH-DPAT), and a muscarinic acetylcholine receptor antagonist, scopolamine, on water maze (WM) navigation. Treatment with either 8-OH-DPAT or scopolamine before daily behavioral training disrupted spatial navigation at medium doses and cue navigation at high doses. Pretraining treatment with a combination of subthreshold doses of 8-OH-DPAT and scopolamine impaired WM spatial and cue navigation, but did not impair the WM performance if the drugs were injected post-training. In trained rats, combined injections of subthreshold doses of 8-OH-DPAT and scopolamine given pretraining did not impair the rats' ability to find the platform in a familiar or in a novel position. The combination of 8-OH-DPAT and scopolamine also disrupted WM navigation in rats with central 5-HT depletion. A combination of a peripheral muscarinic acetylcholine receptor antagonist and 8-OH-DPAT had no effect on WM navigation. These data suggest that combined treatment with drugs blocking muscarinic acetylcholine receptors and activating 5-HT1A receptors greatly impairs WM learning/performance, but does not impair spatial memory per se.