5,7-Dihydroxitryptamine toxicity to serotonergic neurons in serum free raphe cultures

Inhibition of microtubule detyrosination by parthenolide facilitates functional CNS axon regeneration

Injured axons in the central nervous system (CNS) usually fail to regenerate, causing permanent disabilities. However, the knockdown of Pten knockout or treatment of neurons with hyper-IL-6 (hIL-6) transforms neurons into a regenerative state, allowing them to regenerate axons in the injured optic nerve and spinal cord. Transneuronal delivery of hIL-6 to the injured brain stem neurons enables functional recovery after severe spinal cord injury. Here we demonstrate that the beneficial hIL-6 and Pten knockout effects on axon growth are limited by the induction of tubulin detyrosination in axonal growth cones. Hence, cotreatment with parthenolide, a compound blocking microtubule detyrosination, synergistically accelerates neurite growth of cultured murine CNS neurons and primary RGCs isolated from adult human eyes. Systemic application of the prodrug dimethylamino-parthenolide (DMAPT) facilitates axon regeneration in the injured optic nerve and spinal cord. Moreover, combinatorial treatment further improves hIL-6-induced axon regeneration and locomotor recovery after severe SCI. Thus, DMAPT facilitates functional CNS regeneration and reduces the limiting effects of pro-regenerative treatments, making it a promising drug candidate for treating CNS injuries.

Transneuronal delivery of hyper-interleukin-6 enables functional recovery after severe spinal cord injury in mice

Spinal cord injury (SCI) often causes severe and permanent disabilities due to the regenerative failure of severed axons. Here we report significant locomotor recovery of both hindlimbs after a complete spinal cord crush. This is achieved by the unilateral transduction of cortical motoneurons with an AAV expressing hyper-IL-6 (hIL-6), a potent designer cytokine stimulating JAK/STAT3 signaling and axon regeneration. We find collaterals of these AAV-transduced motoneurons projecting to serotonergic neurons in both sides of the raphe nuclei. Hence, the transduction of cortical neurons facilitates the axonal transport and release of hIL-6 at innervated neurons in the brain stem. Therefore, this transneuronal delivery of hIL-6 promotes the regeneration of corticospinal and raphespinal fibers after injury, with the latter being essential for hIL-6-induced functional recovery. Thus, transneuronal delivery enables regenerative stimulation of neurons in the deep brain stem that are otherwise challenging to access, yet highly relevant for functional recovery after SCI.

Vesicular monoamine transporter 2 and the acute and long-term response to 3,4-(±)-methylenedioxymethamphetamine

3,4-(±)-Methylenedioxymethamphetamine (MDMA, Ecstasy) is a ring-substituted amphetamine derivative with potent psychostimulant properties. The neuropharmacological effects of MDMA are biphasic in nature, initially causing synaptic monoamine release, primarily of serotonin (5-HT). Conversely, the long-term effects of MDMA manifest as prolonged depletions in 5-HT, and reductions in 5-HT reuptake transporter (SERT), indicative of serotonergic neurotoxicity. MDMA-induced 5-HT efflux relies upon disruption of vesicular monoamine storage, which increases cytosolic 5-HT concentrations available for release via a carrier-mediated mechanism. The vesicular monoamine transporter 2 (VMAT2) is responsible for packaging monoamine neurotransmitters into cytosolic vesicles. Thus, VMAT2 is a molecular target for a number of psychostimulant drugs, including methamphetamine and MDMA. We investigated the effects of depressed VMAT2 activity on the adverse responses to MDMA, via reversible inhibition of the VMAT2 protein with Ro4-1284. A single dose of MDMA (20 mg/kg, subcutaneous) induced significant hyperthermia in rats. Ro4-1284 (10 mg/kg, intraperitoneal) pretreatment prevented the thermogenic effects of MDMA, instead causing a transient decrease in body temperature. MDMA-treated rats exhibited marked increases in horizontal velocity and rearing behavior. In the presence of Ro4-1284, MDMA-mediated horizontal hyperlocomotion was delayed and attenuated, whereas rearing activity was abolished. Finally, Ro4-1284 prevented deficits in 5-HT content in rat cortex and striatum, and reduced depletions in striatal SERT staining, 7 days after MDMA administration. In summary, acute inhibition of VMAT2 by Ro4-1284 protected against MDMA-mediated hyperthermia, hyperactivity, and serotonergic neurotoxicity. The data suggest the involvement of VMAT2 in the thermoregulatory, behavioral, and neurotoxic effects of MDMA.

Toxicity of amphetamines: an update

Amphetamines represent a class of psychotropic compounds, widely abused for their stimulant, euphoric, anorectic, and, in some cases, emphathogenic, entactogenic, and hallucinogenic properties. These compounds derive from the β-phenylethylamine core structure and are kinetically and dynamically characterized by easily crossing the blood-brain barrier, to resist brain biotransformation and to release monoamine neurotransmitters from nerve endings. Although amphetamines are widely acknowledged as synthetic drugs, of which amphetamine, methamphetamine, and 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) are well-known examples, humans have used natural amphetamines for several millenniums, through the consumption of amphetamines produced in plants, namely cathinone (khat), obtained from the plant Catha edulis and ephedrine, obtained from various plants in the genus Ephedra. More recently, a wave of new amphetamines has emerged in the market, mainly constituted of cathinone derivatives, including mephedrone, methylone, methedrone, and buthylone, among others. Although intoxications by amphetamines continue to be common causes of emergency department and hospital admissions, it is frequent to find the sophism that amphetamine derivatives, namely those appearing more recently, are relatively safe. However, human intoxications by these drugs are increasingly being reported, with similar patterns compared to those previously seen with classical amphetamines. That is not surprising, considering the similar structures and mechanisms of action among the different amphetamines, conferring similar toxicokinetic and toxicological profiles to these compounds. The aim of the present review is to give an insight into the pharmacokinetics, general mechanisms of biological and toxicological actions, and the main target organs for the toxicity of amphetamines. Although there is still scarce knowledge from novel amphetamines to draw mechanistic insights, the long-studied classical amphetamines-amphetamine itself, as well as methamphetamine and MDMA, provide plenty of data that may be useful to predict toxicological outcome to improvident abusers and are for that reason the main focus of this review.

Serotonergic lesions of the dorsal hippocampus differentially modulate locomotor hyperactivity induced by drugs of abuse in rats: implications for schizophrenia

RATIONALE

Psychotomimetic drug-induced locomotor hyperactivity is a widely used animal model of psychotic states, such as in schizophrenia. We previously found that serotonergic lesions of the dorsal, but not ventral, hippocampus in rats result in enhanced phencyclidine-induced locomotor hyperactivity.

OBJECTIVES

The objective of this study was to investigate the effect of serotonin depletion in the dorsal and ventral hippocampus on hyperlocomotion induced by ketamine, cocaine, 3,4-methylenedioxymethampethamine (MDMA), methamphetamine, and D: -amphetamine.

MATERIALS AND METHODS

Male Sprague-Dawley rats were bilaterally microinjected with vehicle or the serotonergic neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT), into the dorsal or ventral hippocampus using a stereotaxic approach. Separate cohorts of rats were used for each drug of abuse; each rat received saline and a low, medium, and high dose of the drug in a random-sequence, repeated-measures protocol. Locomotor hyperactivity following treatment was measured using automated photocell cages.

RESULTS

Similar to phencyclidine, 5,7-DHT-induced lesions of the dorsal hippocampus enhanced ketamine-induced hyperlocomotion at all doses. They also reduced methamphetamine-induced hyperlocomotion at the high dose only and caused a minor, biphasic modulation of responses to cocaine. Locomotor responses to D: -amphetamine and MDMA were unchanged by lesions of the dorsal hippocampus. Serotonergic lesions of the ventral hippocampus did not significantly alter locomotor hyperactivity induced by any of the drugs investigated.

CONCLUSIONS

These findings further implicate a role for serotonin in the dorsal hippocampus in modulating the behavioral effects of dissociative anesthetics, such as ketamine, with more subtle effects on psychostimulant drugs of abuse. The dorsal hippocampus may be a site of serotonergic dysfunction in aspects of schizophrenia.