IV nicotine self-administration in rats using a consummatory operant licking response: sensitivity to serotonergic, glutaminergic and histaminergic drugs.

Tobacco smoking is characterized by repeated self-administration of nicotine by placing the cigarette in the mouth. The repeated hand-to-mouth self-administration is essentially a consummatory act. We recently developed a paradigm in which rats lick one of two spouts to trigger intravenous (IV) delivery of nicotine, which combines a consummatory act with rapid delivery of nicotine to model the act of tobacco smoking. We have found that rats will lick hundreds of times per nicotine infusion. In the current study, using the operant licking nicotine self-administration model with young adult Sprague-Dawley rats (0.03mg/kg/infusion of nicotine), we tested the effect of antagonists of H1 histamine receptors pyrilamine, serotonin (5HT) type 2 receptors ketanserin and N-methyl-d-aspartate (NMDA) glutamate receptors with d-cycloserine as well as an agonist of 5HT2c receptors lorcaserin, in dose ranges that we have found in previous studies to significantly reduce IV nicotine self-administration with the operant lever press operand. The H1 antagonist pyrilamine significantly reduced operant licking for nicotine self-administration. Pyrilamine caused significant reductions in the operant licking paradigm at lower doses (10 and 20mg/kg) than those we previously observed to affect responding in the operant lever press paradigm. In contrast, the 5HT2A and C antagonist ketanserin did not show an effect of reducing nicotine self-administration in the same dose range we had found in a previous study to significantly reduce operant lever press nicotine self-administration. The 5HT2C agonist lorcaserin significantly decreased nicotine self-administration in the licking paradigm at the same dose threshold as with lever press responding. The NMDA glutamate partial agonist d-cycloserine did not produce any change in nicotine self-administration with the licking operand, in contrast to its effect on the classic lever-pressing task. The rat model incorporating consummatory aspects of tobacco addiction can provide distinct and potentially more relevant information concerning possible new avenues of treatment to combat tobacco addiction.
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