Interaction of fenfluramine with d-amphetamine-induced excitatory behaviour and hyperthermia

Dopamine activates NF-κB and primes the NLRP3 inflammasome in primary human macrophages

Induction of innate immune genes in the brain is thought to be a major factor in the development of addiction to substances of abuse. As the major component of the innate immune system in the brain, aberrant activation of myeloid cells such as macrophages and microglia due to substance use may mediate neuroinflammation and contribute to the development of addiction. All addictive drugs modulate the dopaminergic system and our previous studies have identified dopamine as a pro-inflammatory modulator of macrophage function. However, the mechanism that mediates this effect is currently unknown. Inflammatory activation of macrophages and induction of cytokine production is often mediated by the transcription factor NF-κB, and prior studies have shown that dopamine can modulate NF-κB activity in T-cells and other non-immune cell lines. Here we demonstrated that dopamine can activate NF-κB in primary human macrophages, resulting in the induction of its downstream targets including the NLRP3 inflammasome and the inflammatory cytokine IL-1β. These data also indicate that dopamine primes but does not activate the NLRP3 inflammasome in human macrophages. Activation of NF-κB was required for dopamine-mediated increases in IL-1β, as an inhibitor of NF-κB was able to abrogate the effects of dopamine on production of these cytokines. Connecting an increase in extracellular dopamine to NF-κB activation and inflammation suggests specific intracellular targets that could be used to ameliorate the inflammatory impact of dopamine in neuroinflammatory conditions associated with myeloid cell activation such as addiction.

•

Dopamine exposure primes, but does not activate the NLRP3 inflammasome.

•

Inflammasome priming can be mediated, at least partially, by a dopamine-induced increase in the activation and nuclear translocation of NF-κB in primary human macrophages.

•

Dopamine additively increases the impact of cytomegalovirus on NF-κB activation in macrophages.

•

Dopamine priming increases IL-1β release in response to inflammasome activation.

Psychostimulants affect dopamine transmission through both dopamine transporter-dependent and independent mechanisms

The precise mechanisms by which cocaine and amphetamine-like psychostimulants exert their reinforcing effects are not yet fully defined. It is widely believed, however, that these drugs produce their effects by enhancing dopamine neurotransmission in the brain, especially in limbic areas such as the nucleus accumbens, by inducing dopamine transporter-mediated reverse transport and/or blocking dopamine reuptake though the dopamine transporter. Here, we present the evidence that aside from dopamine transporter, non-dopamine transporter-mediated mechanisms also participate in psychostimulant-induced dopamine release and contribute to the behavioral effects of these drugs, such as locomotor activation and reward. Accordingly, psychostimulants could increase norepinephrine release in the prefrontal cortex, the latter then alters the firing pattern of dopamine neurons resulting in changes in action potential-dependent dopamine release. These alterations would further affect the temporal pattern of dopamine release in the nucleus accumbens, thereby modifying information processing in that area. Hence, a synaptic input to a nucleus accumbens neuron may be enhanced or inhibited by dopamine depending on its temporal relationship to dopamine release. Specific temporal patterns of dopamine release may also be required for certain forms of synaptic plasticity in the nucleus accumbens. Together, these effects induced by psychostimulants, mediated through a non-dopamine transporter-mediated mechanism involving norepinephrine and the prefrontal cortex, may also contribute importantly to the reinforcing properties of these drugs.

Administration of fenfluramine at different ambient temperatures produces different core temperature and 5-HT neurotoxicity profiles

This study investigated the effect of two different ambient temperatures on fenfluramine-induced 5-HT neurotoxicity. Fenfluramine (FEN) (12.5 mg/kg x 4; injections made hourly) or saline (SAL) was administered to rats in either a normal laboratory temperature of 24 degrees C or a warm environment of 30 degrees C. Animals were kept at that ambient temperature for 20 h after FEN administration. Ambient temperature was controlled to +/-0.5 degrees C and rat core temperature was continually measured using a non-invasive apparatus. FEN-treated rats at 24 degrees C displayed a core temperature hypothermia with a peak low of 33.8 degrees C, and this core temperature hypothermia lasted for 20 h after FEN administration. Rats treated with FEN at 30 degrees C displayed a significant core temperature hyperthermia for 4 h after the first drug injection compared to SAL-treated groups, with a peak core temperature of 38.6 degrees C. 2 weeks after FEN injections, brain regions were analyzed by HPLC. Both groups of FEN-treated rats showed decreases in 5-HT and 5-HIAA in the hippocampus, frontal cortex, somatosensory cortex, striatum, hypothalamus and septum. However, FEN rats treated at 30 degrees C had significantly greater decreases (26-35%) in 5-HT compared to FEN-treated rats at 24 degrees C in the frontal cortex, hippocampus, striatum and somatosensory cortex and significantly greater decreases (26-50%) in 5-HIAA in the frontal cortex, hippocampus and somatosensory cortex. This study indicates fenfluramine can produce neurotoxicity in rats that display either a core temperature hypothermia or hyperthermia, although hyperthermic rats have greater 5-HT and 5-HIAA depletions than the hypothermic rats.

Fenetylline: new results on pharmacology, metabolism and kinetics

In the fenetylline molecule, theophylline is covalently linked with amphetamine via an alkyl chain. The inclusion of amphetamine and results from early metabolic studies have led to speculation that fenetylline may be merely a prodrug for amphetamine and/or theophylline. Although previous studies are not consistent with this hypothesis, additional studies were conducted to comparatively evaluate the profiles of activity exhibited by fenetylline and its two postulated primary metabolites, (+/-)-amphetamine and theophylline. Investigations were also initiated using newly developed high pressure liquid chromatography (HPLC) techniques to further characterize the metabolic pattern that fenetylline undergoes and to examine the relationship between plasma pharmacokinetics and the pharmacodynamic actions of the drug. Fenetylline inhibits activity associated with amphetamine in certain test systems, an effect similar to that previously observed with fenfluramine. Only small amounts of the amphetamine theoretically available in the fenetylline molecule are released. Pharmacodynamic activity associated with fenetylline administration is more closely tied to plasma levels of the parent compound than to any (+/-)-amphetamine produced.

Effects of d-amphetamine and d-fenfluramine on performance of rats in a food maze

d-Amphetamine and d-fenfluramine caused different patterns of disruption in a learned maze performance reinforced with food. A 0.8 mg/kg dose of amphetamine increased correct and incorrect (errors) alley entrances as well as earned reinforcers consumed. Larger doses (1.6-3.2 mg/kg) decreased correct responses, increased errors, and resulted in earned reinforcers not being consumed. Metergoline pretreatment did not reverse these deficits. d-Fenfluramine (1.5 and 3.0 mg/kg) reduced correct responses dose- relatedly with a slight increase in errors after the larger dose; all earned reinforcers were consumed. Pretreatment with metergoline reversed the deficit in correct responses but not the errors. Combinations of d-amphetamine and d-fenfluramine produced greater deficits than each drug separately, with fewer correct responses and an increase in reinforcers earned but not consumed. Metergoline pretreatment before the combination did not reverse these effects but increased alley entrances scored as errors. The results indicate that the d-fenfluramine but not the d-amphetamine deficit relates to a 5-hydroxytryptamine (5-HT) mechanism. Furthermore, the enhanced effect of the combination appears to relate to drug interactions not dependent upon a 5-HT component.

Changes in body temperature after administration of adrenergic and serotonergic agents and related drugs including antidepressants

This survey, the third in a series, presents extensive tabulations of literature, primarily since 1965, on thermoregulatory effects of adrenergic and serotonergic agonists and their antagonists including ergot alkaloids, amphetamines, tryptamines, monoamine oxidase inhibitors, tricyclic and other antidepressants, a variety of other agents which alter presynaptic aminergic mechanisms including reserpine, 6-hydroxydopamine, p-chlorophenylalanine, alpha-methyltyrosines, cocaine, guanethidine and bretylium. The information listed includes the species used, route of administration and dose of drug, the environmental temperature at which the experiments were performed, the number of tests, the direction and magnitude of body temperature change and remarks on the presence of special conditions, such as age or lesions, or on the influence of other drugs, such as antagonists, on the response to the primary drug.