Effect of p-Chloroamphetamine on 5-HT 1A and 5-HT 7 Serotonin Receptor Expression in Rat Brain Ana Garcı ´a-Osta, Diana Frechilla, and Joaquı ´n Del Rı ´o Department of Pharmacology, University of Navarra Medical School, Pamplona, Spain Abstract: The aim of this study was to investigate if p-chloroamphetamine (PCA), which is neurotoxic to se- rotonin (5-HT) nerve terminals, was able to induce, like 3,4-methylenedioxymethamphetamine, a region-specific regulation of 5-HT 1A receptor mRNA expression. The effect of PCA on the expression of 5-HT 7 receptors, which share some pharmacological properties with 5-HT 1A receptors, was comparatively studied. PCA (2  5 mg/kg) produced a lasting depletion of 5-HT content in the rat frontal cortex and hippocampus. In the hip- pocampus, the maximal 5-HT depletion was found on day 21 (-70%), whereas in the cortex, the highest 5-HT depletion was found on day 14 (-73%), with a partial but significant recovery on day 21. At the latter time point, 5-HT 1A receptor mRNA expression was increased by 80% in the cortex and decreased by 50% in the hip- pocampus. The 5-HT 1A receptor mRNA expression was also enhanced after exposure to PCA of rat cortical but not of hippocampal primary cultures. In regard to 5-HT 7 receptor mRNA expression, the most remarkable change after PCA was the great increase (+200%) in the brain- stem. Binding studies to 5-HT 1A receptors matched the changes in receptor mRNA expression. Gel shift assays revealed enhanced nuclear protein binding to the B sequence with use of cortical but not hippocampal ex- tracts of PCA-treated rats. Overall, the data show region- specific changes in 5-HT receptor-type expression that may not be entirely dependent on the neurotoxic effect of PCA on 5-HT terminals. Key Words: p-Chloroamphet- amine—5-Hydroxytryptamine—5-Hydroxytryptamine 1A receptors—5-Hydroxytryptamine 7 receptors—Nuclear factor B. J. Neurochem. 74, 1790 –1797 (2000). The halogenated amphetamine derivative p-chloroam- phetamine (PCA) is neurotoxic to the serotonergic sys- tem. The neurotoxic effect involves an initial release of serotonin (5-hydroxytryptamine; 5-HT) from presynaptic nerve terminals, which results in a persistent depletion in 5-HT content (Steranka and Sanders-Bush, 1978). There is a subsequent degeneration of 5-HT axon terminals in different forebrain areas along with the corresponding decrease in the density of the [ 3 H]paroxetine-labeled 5-HT transporter, whereas 5-HT cell bodies in the raphe nuclei remain spared (Sekerke et al., 1973; Mamounas and Molliver, 1988; Murray et al., 1996; Sprague et al., 1996). The release of 5-HT from endogenous stores appears to be a prerequisite for the neurotoxicity induced by PCA. Combined treatment with p-chlorophenylala- nine (PCPA), an irreversible inhibitor of tryptophan hy- droxylase, and reserpine, which produces a virtually complete 5-HT depletion, protects against the neurotox- icity induced by PCA (Berger et al., 1992). PCA is metabolized to reactive intermediates (Miller et al., 1986) that give rise on further metabolism to free radi- cals that may produce tissue damage (Colado et al., 1997). In a previous study, we found that repeated ad- ministration of another serotonergic neurotoxin, 3,4- methylenedioxymethamphetamine (MDMA), increased 5-HT 1A receptor density and 5-HT 1A receptor gene tran- scription in the frontal cortex, suggesting an increased receptor synthesis, perhaps in an attempt to compensate for the loss of 5-HT nerve terminals (Aguirre et al., 1997). It is known, however, that the serotonergic neu- rotoxin 5,7-dihydroxytryptamine (5,7-DHT) may pro- duce an extensive lesion of the serotonergic system with- out changing postsynaptic 5-HT 1A receptor density in the cerebral cortex (Hensler et al., 1991; Miquel et al., 1992; Compan et al., 1998). Some differences have been sug- gested between the mechanism of the neurotoxicity in- duced by PCA and MDMA (Sprague et al., 1996; see also Discussion). Consequently, it appeared of interest to investigate whether the increased number of cortical 5-HT 1A receptors was a specific effect of MDMA or was also shared by the serotonergic neurotoxin PCA. In the hippocampus, MDMA attenuates 5-HT 1A receptor gene transcription notably through an effect on corticosterone Received July 2, 1999; revised manuscript received November 26, 1999; accepted December 4, 1999. Address correspondence and reprint requests to Dr. J. Del Rı ´o at Department of Pharmacology, University of Navarra Medical School, c/Irunlarrea, 1, 31008-Pamplona, Spain. E-mail: jdelrio@unav.es Abbreviations used: DA, dopamine; 5,7-DHT, 5,7-dihy- droxytryptamine; DRN, dorsal raphe nucleus; EMSA, electrophoretic mo- bility shift assay; 5-HT, 5-hydroxytryptamine (serotonin); MAO, mono- amine oxidase; MDMA, 3,4-methylenedioxymethamphetamine; NF-B, nuclear factor B; OD, optical density; 8-OH-DPAT, 8-hydroxy-2-(di-n- propylamino)tetralin; PCA, p-chloroamphetamine; PCPA, p-chlorophenyl- alanine; SDS, sodium dodecyl sulfate; SSC, saline/sodium citrate. 1790 Journal of Neurochemistry Lippincott Williams & Wilkins, Inc., Philadelphia © 2000 International Society for Neurochemistry