Amphetamine and pseudoephedrine cross-tolerance measured by c-Fos protein expression in brains of chronically treated rats
1 Neuro-Behavioral Biology Center, Institute of Science and Technology for, Research and Development, Mahidol University, Salaya, Nakornpathom, 73170, Thailand
2 Faculty of Lifelong Learning, Birkbeck, University of London, Malet Street, London, WC1E 7HX, UK
3 UCL Ear Institute, University College London, 332 gray's Inn Road, London, WC1X 8EE, UK
4 Center for Neuroscience and Department of Pharmacology, Faculty of Science, Mahidol University, Rama 6 Road, Bangkok, 10400, Thailand
BMC Neuroscience 2008, 9:99 doi:10.1186/1471-2202-9-99Published: 6 October 2008
Pseudoephedrine is a drug commonly prescribed as a nasal decongestant and bronchodilator and is also freely available in cold remedies and medications. The structural and pharmacological similarity of pseudoephedrine to amphetamine has led to evaluation of its psychomotor stimulant properties within the central nervous system. Previous investigations have shown that the acute responses to pseudoephedrine were similar to those of amphetamine and other psychostimulants.
This study examined the effect of chronic administration of pseudoephedrine in rat nucleus accumbens and striatum and identified three further similarities to amphetamine. (i) Chronic exposure to pseudoephedrine reduced the c-Fos response to acute pseudoephedrine treatment suggesting that pseudoephedrine induced tolerance in the animals. (ii) In animals chronically treated with amphetamine or pseudoephedrine the acute c-Fos response to pseudoephedrine and amphetamine was reduced respectively as compared to naïve animals indicating cross-tolerance for the two drugs. (iii)The known involvement of the dopamine system in the response to amphetamine and pseudoephedrine was further confirmed in this study by demonstrating that pseudoephedrine similarly to amphetamine, but with lower potency, inhibited [3H]dopamine uptake in synaptosomal preparations.
This work has demonstrated further similarities of the effect of pseudoephedrine to those of amphetamine in brain areas known to be associated with drug addiction. The most significant result presented here is the cross tolerance effect of amphetamine and psudoephedrine. This suggests that both drugs induce similar mechanisms of action in the brain. Further studies are required to establish whether despite its considerable lower potency, pseudoephedrine could pose health and addiction risks in humans similar to that of known psychostimulants.