George Battaglia

MDMA-induced neurotoxicity: Parameters of degeneration and recovery of brain serotonin neurons

This study investigates a number of parameters that influence the neurotoxic effects of 3,4-methylenedioxymethamphetamine (MDMA) on serotonin (5-HT) neurons in brain. Both the dose and number of injections of MDMA affect the degree of neurotoxicity on 5-HT axons and terminals as assessed by decreases in the content of 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) and the density of 5-HT uptake sites. Repeated systemic administration of various doses of MDMA (5-20 mg/kg twice daily for 4 consecutive days) results in dose-dependent decreases in 5-HT, 5-HIAA and 5-HT uptake sites. Increasing the number of injections of MDMA resulted in progressively greater reductions in 5-HT and 5-HIAA which occurred prior to decreases in 5-HT uptake sites. In contrast, no significant changes were observed in the density of norepinephrine uptake sites following single or repeated injections of 20 mg/kg MDMA. With respect to neuronal regeneration, following an initial 90% loss of 5-HT uptake sites after treatment with MDMA, the recovery of these sites occurred over a protracted period of time; a marked 25% reduction was seen at 6 months and the concentration of 5-HT uptake sites returned to control levels at 12 months following treatment with MDMA. Pretreatment with the selective 5-HT uptake blocker, citalopram, prior to each injection of MDMA prevented the neurotoxic effects of MDMA on the 5-HT parameters described above suggesting that active uptake of MDMA or a MDMA-related substance into brain 5-HT neurons was involved in the neurotoxic actions of the drug. In addition, the neurodegenerative effects of MDMA on 5-HT neurons exhibited some species specificity as comparable decreases in cerebral cortical 5-HT, 5-HIAA and 5-HT uptake sites were observed in rat and guinea pig while no significant changes in any of these serotonergic parameters were seen in mouse brain.

Pharmacologic profile of MDMA (3,4-methylenedioxymethamphetamine) at various brain recognition sites

We report here an in vitro pharmacologic profile for MDMA (3,4-methylenedioxymethamphetamine) at various brain recognition sites. The rank order of affinities of MDMA at various brain receptors and uptake sites are as follows: 5-HT uptake greater than alpha 2-adrenoceptors = 5-HT2 serotonin = M-1 muscarinic = H-1 histamine greater than norepinephrine uptake = M-2 muscarinic = alpha 1-adrenoceptors = beta-adrenoceptors greater than or equal to dopamine uptake = 5-HT1 serotonin much greater than D-2 dopamine greater than D-1 dopamine. MDMA exhibited negligible affinities (greater than 500 microM) at opioid (mu, delta and kappa), central-type benzodiazepine, and corticotropin-releasing factor receptors, and at choline uptake sites and calcium channels.

Methylphenidate and pemoline do not cause depletion of rat brain monoamine markers similar to that observed with methamphetamine.

Methylphenidate (Ritalin) and pemoline (Cylert) are central nervous system stimulants which are widely prescribed for attention deficit and other psychiatric disorders. Several other related stimulants, including amphetamine and methamphetamine, have been shown to cause long lasting decreases in monoamine markers in rat brain, characteristic of axonal degeneration. To assess the neurotoxic potential of methylphenidate and pemoline, we compared the effects of multiple injections (sc, bid for up to 4 days) of methylphenidate (21 and 50 mg/kg) and pemoline (20 and 70 mg/kg) with methamphetamine (5 and 15 mg/kg) on rat brain norepinephrine, dopamine, and serotonin levels and transport sites. While decreases were observed in all brain monoamine markers measured in rats treated with methamphetamine, no changes were observed in animals treated with methylphenidate as compared to saline-treated controls. Pemoline failed to induce significant changes in the level of monoamine transport sites; however, a wide array of changes were observed in the levels of 5-hydroxyindoleacetic acid, dopamine, and norepinephrine in various brain areas after a 3-day treatment regimen with a high dose (70 mg/kg) of pemoline. The lack of changes in monoamine transport sites following the repeated administration of high doses of methylphenidate and pemoline suggests that these drugs do not affect axonal integrity. However, the pattern of changes observed in the levels of monoamines after pemoline treatment may have relevance to the self-injurious behavior seen in these animals.

Increased corticotropin-releasing factor receptors in rat cerebral cortex following chronic atropine treatment

Rats were treated chronically with atropine (14 days, 20 mg/kg/day, s.c.) and corticotropin-releasing factor (CRF) receptors and CRF-mediated adenylate cyclase activity were measured in discrete brain regions. Chronic atropine treatment produced significant increases in muscarinic cholinergic receptors in the frontoparietal cortex (30% increase) and hippocampus (20% increase). No significant changes in the concentration of [125I]Tyr0-rat CRF binding sites were observed in olfactory bulb, cerebellum, striatum and hippocampus. In contrast, there was a significant and selective increase (35%) in CRF receptors in the frontoparietal cortex of atropine-treated rats. However, no significant corresponding changes in the Vmax or EC50 of CRF-stimulated adenylate cyclase activity accompanied the upregulation of CRF receptors in the cerebral cortex. These results demonstrate that CRF receptors in rat brain are subject to receptor regulation, the upregulation of CRF receptors occurs as a consequence of chronic muscarinic cholinergic receptor blockade, and this interaction between acetylcholine and CRF may be limited to the cerebral cortex.

MDMA Effects in Brain: Pharmacologic Profile and Evidence of Neurotoxicity from Neurochemical and Autoradiographic Studies

3,4-Methylenedioxymethamphetamine (MDMA), a ring-substituted derivative of methamphetamine, has been reported to exhibit both stimulant and psychotomimetic properties [1–3]. MDMA has recently attracted a great deal of attention due to its increasing abuse among certain segments of the population [4, 5] and has been the focus of a number of review articles [6, 7] and symposia [8, 9]. Recent data demonstrating that MDMA is self-administered by both rhesus monkeys [10] and baboons [11] suggest that MDMA may have high abuse potential in man. These reports are particularly disturbing, as we and others have recently demonstrated that MDMA is a potent neurotoxin that appears to cause selective degeneration of brain serotonin neurons [12–16], comparable to that reported for its structural analogue. 3,4-methylenedioxyamphetamine (MDA) [12,17–18].

Corticotropin-Releasing Hormone (CRH) Receptors in Brain

Studies with iodine-125-labeled analogues of CRH have identified, characterized, and localized binding sites for CRH in rat and human brain. In addition, we have demonstrated that CRH stimulates cAMP production in various regions of the rat CNS. The significant regional differences in the stoichiometric relationship between receptor number and receptor-mediated cAMP production suggests that some populations of CRH receptors in brain may be functionally coupled to alternative signal transduction mechanisms. The autoradiographic data demonstrate that the distribution of CRH binding sites in the rat CNS corresponds well with the immunohistochemical distribution of CRH pathways and pharmacological sites of action of CRH in some areas of brain but not in others. The demonstration of an upregulation of CRH receptors following a decrease in CRH-IR in the cerebral cortex in Alzheimers disease indicates a physiological relevance of the receptor site and is consistent with the concept that CRH acts as a neurotransmitter in regulating normal cortical functions. In addition, the data suggest that disease of this peptidergic system may be important in certain clinical manifestations of Alzheimers disease. The effects of chronic atropine treatment to selectively upregulate CRH receptors in the cerebral cortex suggests an interaction between CRH and acetylcholine. These data provide further support for the proposed role of CRH as a neurotransmitter in the CNS. Furthermore, these studies demonstrating the characteristics of CRH receptors and CRH receptor-mediated signal transduction mechanisms in brain provide a means for better understanding the various functions of this neuropeptide under physiological and pathological conditions.