Latent inhibition (LI) is the attenuation in the acquisition of Pavlovian conditioning to a conditioned stimulus (CS) due to prior extensive exposure to that CS. It is assumed that LI is an animal model of attention in that animals learn to ignore the preexposed CS. The present series of experiments investigated the effects of selective serotonergic (5-HT) ligands known to increase 5-HT neurotransmission on LI using a conditioned emotional response (CER) procedure. In experiment 1, rats preexposed (PE) to 40 presentations of a tone CS acquired CER suppression more slowly than vehicle-treated nonpreexposed (NPE) animals, suggesting LI was obtained. Administration of 10 mg/kg fluoxetine (i.p.) did not influence CER acquisition in PE animals, suggesting that LI was not affected by fluoxetine. However, it was assumed that 40 CS presentations exerted a powerful LI effect, which might mask any effect of fluoxetine. Consequently, we assessed the effects of 5-HT ligands on LI following 10, rather than 40, CS preexposures. Under these conditions, both acute fluoxetine (experiment 2), and chronic (14 day) fluoxetine (experiment 3) administration, were found to augment LI. Experiment 4 suggested that acute administration of the 5-HT2 agonist DOI (2.5 mg/kg) also enhances LI. Experiment 5 revealed that 1 mg/kg 8-OH-DPAT did not influence LI, suggesting that postsynaptic 5-HT1a receptors are not involved in LI. These results suggest that enhancement of 5-HT neurotransmission enhance LI and that this effect is mediated, in part, through the 5-HT2 receptor subtype. The results are discussed within the context of the switching model of LI, which suggests that the effects of 5-HT are mediated through the modulation of the mesolimbic dopamine pathway.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.23401 |
| Date | January 1995 |
| Creators | Jakob, Andrea F. (Andrea Frances) |
| Contributors | Rochford, Joseph (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Master of Science (Department of Psychiatry.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001481367, proquestno: MM12207, Theses scanned by UMI/ProQuest. |
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