[Show abstract][Hide abstract] ABSTRACT: Nicotine is one of the world's most addictive substances and the primary reason that humans inhale tobacco smoke. The pharmacological effects of nicotine can be investigated in planarians, aquatic flatworms that possess an integrated neural network including cephalic ganglia that some consider the earliest 'brain' and spinal cord. Here, we tested the hypothesis that nicotine exposure elicits mammalian-like behaviors in planarians.
Planarian motility and stereotypy (C-shape hyperkinesias) were quantified following acute nicotine exposure. During repeated nicotine exposure, we investigated the presence of withdrawal, tolerance, behavioral sensitization, and environmental place conditioning.
Acute nicotine exposure increased stereotypical activity and elicited biphasic effects on motility. A low concentration (0.01 mM) increased motility whereas higher concentrations (0.3-10mM) elicited the opposite effect. Planarians exposed to nicotine (0.03 mM) for 60 min and then tested in water displayed reduced motility that was not observed during exposure to water, acute nicotine, or continuous nicotine. Nicotine-treated planarians withdrawn from the drug for 3 days before being challenged with nicotine displayed behavioral sensitization at low concentrations (0.1, 0.3mM) but tolerance at higher concentrations (1, 3mM). Planarians conditioned with nicotine in the ambient light (non-preferred environment) displayed a reduction in their natural preference for a dark environment.
The present results suggest nicotine elicits mammalian-like effects in planarians, including decreased motility and increased stereotypy following acute administration and abstinence-induced withdrawal, behavioral sensitization, tolerance, and place conditioning during repeated exposure.
Drug and alcohol dependence 04/2011; 118(2-3):274-9. DOI:10.1016/j.drugalcdep.2011.04.001 · 3.42 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The mechanism of anticonvulsant action of topiramate includes inhibition of glutamate-activated ion channels. The evidence is most convincing for direct inhibitory action at the ionotropic AMPA (alpha-Amino-3-hydroxy-5-methylisoxazole-4-propionic acid) and kainate ((2S,3S,4S)-3-(Carboxymethyl)-4-prop-1-en-2-ylpyrrolidine-2-carboxylic acid) glutamate receptor subtypes. Less direct connection has been made to the NMDA (N-Methyl-d-aspartate) subtype. In the present study, we demonstrate that NMDA and AMPA produce concentration-dependent seizure-like activity in planarians, a type of flatworm which possesses mammalian-like neurotransmitters. In contrast, planarians exposed to the inhibitory amino acid, glycine, did not display pSLA. For combination experiments, topiramate significantly reduced planarian seizure-like activity (pSLA) produced by NMDA or AMPA. Additionally, NMDA-induced pSLA was antagonized by either an NMDA receptor antagonist (MK-801) or AMPA receptor antagonist (DNQX), thus suggesting that NMDA-induced pSLA was mediated by NMDA and non-NMDA receptors. The present results provide pharmacologic evidence of a functional inhibitory action of topiramate on glutamate receptor activity in invertebrates and provide a sensitive, quantifiable end-point for studying anti-seizure pharmacology.