Impact of regional 5-HT depletion on the cognitive enhancing effects of a typical 5-ht(6) receptor antagonist, Ro 04-6790, in the Novel Object Discrimination task

• Published in: Psychopharmacology (Berlin, Germany) Germany), 2009-01, Vol.202 (1-3), p.111-123
• Main Authors: King, M V, Spicer, C H, Sleight, A J, Marsden, C A, Fone, K C F
• Format: Article
• Language: English
• Subjects: 5,7-Dihydroxytryptamine - administration & dosage; 5,7-Dihydroxytryptamine - pharmacology; Analysis of Variance; Animals; Body Weight - drug effects; Brain Chemistry - drug effects; Cognition - drug effects; Discrimination (Psychology) - drug effects; Discrimination Learning - drug effects; Injections, Intraventricular; Male; Psychomotor Performance - drug effects; Psychotropic Drugs - pharmacology; Pyrimidines - pharmacology; Raphe Nuclei - physiology; Rats; Receptors, Serotonin - drug effects; Serotonin - physiology; Serotonin Agents - administration & dosage; Serotonin Agents - pharmacology; Serotonin Antagonists - pharmacology
• ISSN: 1432-2072
• DOI: 10.1007/s00213-008-1334-1

Selective 5-ht(6) receptor antagonists like Ro 04-6790 prolong memory in many rodent preclinical paradigms, possibly by blocking tonic 5-HT-evoked GABA release and allowing disinhibition of cortico-limbic glutamatergic and cholinergic neurones. If this is the case, behavioural responses to Ro 04-6790 should be abolished by depletion of endogenous 5-HT, and selective lesions of dorsal raphé (DR) or median raphé (MR) 5-HT pathways would allow the neuroanatomical substrates underlying the cognitive effects of 5-ht(6) receptor antagonists to be elucidated. This study compared the effect of Ro 04-6790 on novel object discrimination (NOD) before and after sham or 5,7-dihydroxytryptamine (5,7-DHT)-induced lesions produced by injection into the lateral ventricles (LV), DR or MR. NOD tests used a 4 h inter-trial interval (ITI) and Ro 04-6790 (10 mg kg(-1) i.p.) was administered 20 min before the familiarization trial. Brain region-specific 5-HT depletion was assessed by high performance liquid chromatography with electrochemical detection (HPLC-ED). Widespread LV or selective MR, but not DR lesions, abolished the ability of Ro 04-6790 to delay natural forgetting. Successful performance of all lesioned rats in subsequent 'drug-free' NOD tests using a 1 h ITI excluded the possibility of any confounding effects on visual acuity or motivation. The ability of Ro 04-6790 to prolong object recognition memory requires blockade of MR 5-HT function. Because DR lesions did not produce the expected depletion of striatal 5-HT an additional contribution of DR inputs to this region cannot be completely excluded.