Long-term post-synaptic consequences of methamphetamine on preprotachykinin mRNA expression Kamisha L. Johnson-Davis, Glen R. Hanson and Kristen A. Keefe Department of Pharmacology and Toxicology, University of Utah, Salt Lake City, Utah, USA Abstract Exposure to repeated high doses of methamphetamine pro- duces long-term toxicity to central monoamine systems and alters striatonigral pathway function 3 weeks after exposure. To determine whether these changes in the striatonigral pathway persist for longer we examined neuropeptide mRNA expression in the striatum and cytochrome oxidase activity in the output nuclei of the basal ganglia after treatment with multiple high doses of methamphetamine. Rats exposed to multiple high doses of methamphetamine had significant depletion in dopamine and serotonin content, decreases in tyrosine hydroxylase immunoreactivity, and decreases in preprotachykinin mRNA expression, 6 and 12 weeks after methamphetamine treatment. Preprotachykinin mRNA expression was significantly reduced by 20% in the middle striatum and 32% in the caudal striatum, 6 weeks after treatment. Twelve weeks after treatment, preprotachykinin mRNA expression continued to be significantly reduced by 20% in the middle striatum and 14% in the caudal striatum. Cytochrome oxidase histochemical staining in the ento- peduncular nucleus and substantia nigra pars reticulata was not significantly different from that in controls at either time- point. These data suggest that neurotoxic regimens of meth- amphetamine induce changes in striatonigral neurons that persist for up to 3 months, although there is some recovery. Keywords: in situ hybridization, neurotoxicity, striatum, stri- atonigral, preprotachykinin. J. Neurochem. (2002) 82, 1472–1479. Methamphetamine (METH) is an addictive (Johanson et al. 1976) psychomotor stimulant that is widely abused (Johnston et al. 2001). Studies on rats have shown that METH alters the extracellular concentrations of monoamines in the brain, especially in the region of the basal ganglia (Bradberry and Roth 1989; Galloway 1990). Exposure to multiple high doses of METH results in neurotoxic damage to monoamine neurons, leading to long-lasting depletion of dopamine (DA) in the striatum, substantia nigra and neocortex, and serotonin (5-HT) in the frontal cortex, striatum and amygdala (Ricaurte et al. 1980). METH also causes persistent decreases in tyrosine hydroxylase (TH) and tryptophan hydroxylase activity in these brain regions (Kogan et al. 1976; Hotchkiss et al. 1979; Hotchkiss and Gibb 1980). In addition, this neurotoxic regimen of METH has been shown to alter peptide systems (Chapman et al. 2001). Previous work from our laboratory, as well as that of others, has shown changes in indices of striatonigral efferent neuron function 3 weeks after exposure to a neurotoxic regimen of METH or 6-hydroxydopamine (6-OHDA). Such data illustrate that a partial depletion of DA by 6-OHDA or a partial depletion of both DA and 5-HT by METH decreases preprotachykinin (PPT), but not preproenkephalin, mRNA expression 3 weeks after treatment (Nisenbaum et al. 1996; Chapman et al. 2001). Furthermore, the study by Chapman et al. showed that cytochrome oxidase (CO) histochemical staining in the terminal fields of striatonigral neurons, the entopeduncular nucleus (EPN), and substantia nigra pars reticulata (SNpr), was increased after this METH treatment, suggesting disinhibition and increased activity of these basal ganglia output neurons. Thus, the disruption of monoamine systems induced by METH exposure appears to be associated Received May 3, 2002; revised manuscript received June 12, 2002; accepted June 13, 2002. Address correspondence and reprint requests to Kristen A. Keefe, PhD, Department of Pharmacology and Toxicology, University of Utah, 30 South 2000 East, Room 201, Salt Lake City, UT 84112, USA. E-mail: K.Keefe@m.cc.utah.edu Abbreviations used: CO, cytochrome oxidase; CPU, caudate putamen; DA, dopamine; DAB, 3-3¢-diaminobenzidine; EPN, entopeduncular nucleus; GP, globus pallidus; 5-HT, serotonin; IR, immunoreactivity; METH, methamphetamine; 6-OHDA, 6-hydroxydopamine; PBS, phos- phate-buffered saline; PPT, preprotachykinin; SNpc, substantia nigra pars compacta; SNpr, substantia nigra pars reticulata; SSC, saline sodium citrate; STN, subthalamic nucleus; TH, tyrosine hydroxylase; VTA, ventral tegmental area. Journal of Neurochemistry , 2002, 82, 1472–1479 1472 Ó 2002 International Society for Neurochemistry, Journal of Neurochemistry , 82, 1472–1479