3,4-Methylenedioxymethamphetamine induces differential regulation of tryptophan hydroxylase 2 protein and mRNA levels in the rat dorsal raphe nucleus

Abstract

Previous investigations with 3,4-methylenedioxymethamphetamine (MDMA) have suggested that administration of this drug results in a degeneration of 5-HT nerve terminals and subsequent alterations in 5-HT neurotransmission. However, only limited investigations have examined the effects of MDMA on the dorsal raphe nucleus. The present study was designed to assess the effect of MDMA on the rate-limiting enzyme in 5-HT biosynthesis, tryptophan hydroxylase (TPH), by measuring TPH2 protein and mRNA levels in rat dorsal raphe (DR) nucleus. Rats were administered MDMA (20 mg/kg, s.c.) or saline twice daily for 4 days and killed 14 days later. Tissue sections of the DR were processed for quantitative immunoautoradiography and in situ hybridization histochemistry for measurements of the levels of TPH2-immunoreactivity (IR) and TPH2 mRNA. To assess 5-HT axon terminal integrity after MDMA treatment, the density of 5-HT transporter (SERT) binding sites was measured by quantitative autoradiography using [125I]RTI-55 ((-)-2beta-carbomethoxy-3 beta-(4-iodophenyl) tropane) ((125)I-RTI-55) as a ligand. TPH2-IR levels were significantly decreased by 45% in the mid DR and by 40% in the caudal DR in the MDMA-treated rats compared with saline-injected rats. In contrast, TPH2 mRNA levels were significantly increased by 24% in the mid DR and by 12% in the caudal DR. MDMA treatment significantly decreased (125)I-RTI-55 labeled SERT binding sites in the striatum, nucleus accumbens and cingulate cortex demonstrating a loss of 5-HT terminals. The increase in TPH2 mRNA levels in both the mid DR and caudal DR of MDMA-treated rats may reflect a compensatory mechanism in the injured 5-HT neurons to increase TPH2 protein synthesis. Taken together, our results suggest that a serious defect occurs in the biosynthesis of TPH2 in the DR following MDMA administration.

Ultrastructural characterization of tryptophan hydroxylase 2-specific cortical serotonergic fibers and dorsal raphe neuronal cell bodies after MDMA treatment in rat

“…In our study, the comparative analysis of light and electron microscopic results suggests that the light microscopic characteristic of Tph2 immunostaining in the frontal cortex 3 days after the treatment (reduced fiber density and swollen fragmented axonal profiles) may simultaneously reflect to the previously described reduction of the Tph enzyme expression (Bonkale and Austin 2008) and to the decreased axonal transport caused by the collapsed microtubular system. The fragmented-like morphology of serotonergic axons at light microscopic level, which is described by several previous studies, may reflect to the reduced axonal flow rather than the physical fragmentation of fibers.…”

Recovery and aging of serotonergic fibers after single and intermittent MDMA treatment in dark agouti rat

“…activity and protein level of Tph show a long-term decrease after MDMA treatment (Stone et al, 1987;Bonkale and Austin, 2008). Tph immunohistochemistry is an early and sensitive method of demonstrating vulnerability caused by MDMA, reflecting the morphology of serotonergic axons as well as the actual level of Tph protein (Adori et al, 2006;Xie et al, 2006;Kovacs et al, 2007).…”

Animal models as tools to study the pathophysiology of depression

“…43 Changes in TPH2 gene and/or protein expression in the brain have been reported in various mood disorders and have been validated in animal models. [44][45][46] TPH2 variants have also been extensively reported to be associated with major depression. [47][48][49] However, whether these changes might reflect alterations in possible modulatory effects of other neurotransmitter systems on 5-HT systems is still largely unknown.…”