Nicotine and clozapine cross-prime the locus coeruleus noradrenergic system to induce long-lasting potentiation in the rat hippocampus

Authors

  • Ramamoorthy Rajkumar,

    1. Department of Pharmacology, Yong Loo Lin School of Medicine, National University Health System, National University of Singapore, Singapore
    2. Neurobiology and Ageing Programme, Life Sciences Institute, National University of Singapore, Singapore
    3. SINAPSE, Singapore Institute for Neurotechnology, Singapore
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  • Sana Suri,

    1. Department of Pharmacology, Yong Loo Lin School of Medicine, National University Health System, National University of Singapore, Singapore
    2. Neurobiology and Ageing Programme, Life Sciences Institute, National University of Singapore, Singapore
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  • Hong Min Deng,

    1. Department of Pharmacology, Yong Loo Lin School of Medicine, National University Health System, National University of Singapore, Singapore
    2. Neurobiology and Ageing Programme, Life Sciences Institute, National University of Singapore, Singapore
    3. SINAPSE, Singapore Institute for Neurotechnology, Singapore
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  • Gavin Stewart Dawe

    Corresponding author
    1. Neurobiology and Ageing Programme, Life Sciences Institute, National University of Singapore, Singapore
    2. SINAPSE, Singapore Institute for Neurotechnology, Singapore
    • Department of Pharmacology, Yong Loo Lin School of Medicine, National University Health System, National University of Singapore, Singapore
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Correspondence to: Gavin Stewart Dawe, Department of Pharmacology, Yong Loo Lin School of Medicine, National University Health System, National University of Singapore, Centre for Life Sciences (CeLS), #04-04, 28 Medical Drive, Singapore 117456, Singapore. E-mail: gavindawe@nus.edu.sg

ABSTRACT

A priming-challenge schedule of nicotine treatment causes long-lasting potentiation (LLP), a form of synaptic plasticity closely associated with the norepinephrine (NE) neurotransmitter system, at the medial perforant path (MPP)-dentate gyrus (DG) synapse in the rat hippocampus. Previous reports revealed that nicotine activates the locus coeruleus (LC) noradrenergic (NAergic) system and this mechanism may underlie its beta-adrenoceptor sensitive LLP effects. Clozapine, an atypical antipsychotic, is also known to activate the LC. Interactions between nicotine and clozapine are of interest because of the prevalence of smoking in patients with schizophrenia and increasing interest in the use of nicotinic receptor ligands as cognitive enhancers. Rats were subchronically primed with nicotine, clozapine or saline. Twenty-one to twenty-eight days later, the effects of the nicotine, clozapine or saline challenge on the evoked field excitatory postsynaptic potentials (fEPSP) at the MPP-DG monosynaptic pathway were recorded as a measure of LLP. We confirmed the hypothesis that a challenge dose of either nicotine or clozapine induces LLP exclusively in nicotine- and clozapine-primed rats, and not in saline-primed rats, thus indicating a cross-priming effect. Moreover, unilateral suppression of LC using lidocaine abolished the LLP induced by nicotine in clozapine-primed rats. Furthermore, systemic treatment with clonidine (an α2 adrenoceptor agonist that reduces NAergic activity via autoreceptors) prior to the challenge doses blocked the nicotine/clozapine-induced LLP in nicotine- and clozapine-primed rats. These findings may add to understanding of the cognitive enhancing effects of nicotine. © 2013 Wiley Periodicals, Inc.

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