Elevations in plasmatic titers of corticosterone and aldosterone, in the absence of changes in ACTH, testosterone, or glial fibrillary acidic protein, 72 h following D,L-fenfluramine or D-fenfluramine administration to rats

Alterations in body temperature, corticosterone, and behavior following the administration of 5-methoxy-diisopropyltryptamine ('foxy') to adult rats: a new drug of abuse

Many drugs are used or abused in social contexts without understanding the ramifications of their use. In this study, we examined the effects of a newly popular drug, 5-methoxy-diisopropyltryptamine (5-MEO-DIPT; 'foxy' or 'foxy-methoxy'). Two experiments were performed. In the first, 5-MEO-DIPT (0, 10, or 20 mg/kg) was administered to rats four times on a single day and animals were examined 3 days later. The animals that received 5-MEO-DIPT demonstrated hypothermia during the period of drug administration and delayed mild hyperthermic rebound for at least 48 h. Corticosterone levels in plasma were elevated in a dose-dependent manner compared to saline-treated animals with minor changes in 5-HT turnover and no changes in monoamine levels. In experiment 2, rats were examined in behavioral tasks following either 0 or 20 mg/kg of 5-MEO-DIPT. The animals treated with 5-MEO-DIPT showed hypoactivity and an attenuated response to (+)-methamphetamine-induced stimulation (1 mg/kg). In a test of path integration (Cincinnati water maze), 5-MEO-DIPT-treated animals displayed deficits in performance compared to the saline-treated animals. No differences were noted in the ability of the animals to perform in the Morris water maze or on tests of novel object or place recognition. The data demonstrate that 5-MEO-DIPT alters the ability of an animal to perform certain cognitive tasks, while leaving others intact and disrupts the endocrine system. 5-MEO-DIPT may have the potential to induce untoward effects in humans.

Platelet monoamine oxidase B (MAO-B) activity and its relationship to DL-fenfluramine-induced prolactin response in healthy men

Several techniques are used to assess central serotonergic neurotransmission in man, e.g. challenge tests (hormonal and physiological responses to serotonin active drugs), platelet MAO-B activity as well as brain imaging techniques. Little is known about how these tests relate to each other. The aim of the present study was therefore to investigate if platelet MAO-B activity could be related to hormonal and temperature responses to the serotonin active drug DL-fenfluramine in healthy men. Twelve male subjects without any history of psychiatric disorders or drug abuse/dependencies were recruited. Prior to the challenge with 60 mg DL-fenfluramine, which was given orally, blood for determination of platelet MAO-B activity was drawn. Blood samples for determination of serum prolactin and serum cortisol were drawn at baseline and thereafter every hour for the following six hours. In addition, body temperature was measured at the same time-points. Delta-values were calculated as the difference between the baseline values and the highest (prolactin and cortisol) or lowest value (temperature) thereafter. There was a strong positive correlation (r = 0.75, p < 0.02) between platelet MAO-B activity and Delta-prolactin. No correlations were found to Delta-cortisol, Delta-temperature or any of the baseline values. The results support the notion that the peripheral marker platelet MAO-B activity is related to the function of the central serotonergic neurotransmitter system as assessed by the prolactin response to 60 mg DL-fenfluramin.

Metyrapone attenuates the sequential learning deficits but not monoamine depletions following d,l-fenfluramine administration to adult rats

Fenfluramine (FEN) is a substituted amphetamine known for its anorectic effects, without the stimulatory or abuse potential associated with other amphetamine derivatives. FEN is a potent serotonin (5-HT) releaser and reuptake inhibitor and has been shown to cause depletions of 5-HT that can last days and even weeks after administration. Administration of FEN four times on a single day also causes a prolonged increase of corticosterone (CORT) that lasts approximately 72 h following the first FEN dose. This dosing regimen also produces deficits in sequential learning as measured in the Cincinnati water maze (CWM). Adrenalectomy blocks this effect but removes more than CORT. Accordingly, the purpose of this study was to determine whether inhibiting glucocorticoid production, by administration of the 11 beta-hydroxylase inhibitor metyrapone (MET), will similarly attenuate or eliminate the sequential learning deficits seen with FEN exposure. MET (50 mg/kg) injections were administered 90 min prior to and for 3 days after FEN (four doses given at 2-h intervals). Animals pretreated with MET and treated with FEN showed no sequential learning deficits when tested 1 week following FEN administration compared to FEN alone. The depletions of monoamines were similar following FEN administration, regardless of MET treatment. Taken together, this suggests that a potential mechanism for the sequential learning deficits in FEN-treated animals is a result of prolonged increases in CORT output.

Microglial activation is a pharmacologically specific marker for the neurotoxic amphetamines

Neurotoxic amphetamines cause damage to monoamine nerve terminals of the striatum by unknown mechanisms. Microglial activation contributes to the neuronal damage that accompanies injury, disease, and inflammation, but a role for these cells in amphetamine-induced neurotoxicity has received little attention. We show presently that D-methamphetamine, 3,4-methylenedioxymethamphetamine (MDMA), D-amphetamine, and p-chloroamphetamine, each of which has been linked to dopamine (DA) or serotonin nerve terminal damage, result in microglial activation in the striatum. The non-neurotoxic amphetamines l-methamphetamine, fenfluramine, and DOI do not have this effect. All drugs that cause microglial activation also increase expression of glial fibrillary acidic protein (GFAP). At a minimum, microglial activation serves as a pharmacologically specific marker for striatal nerve terminal damage resulting only from those amphetamines that exert neurotoxicity. Because microglia are known to produce many of the reactive species (e.g., nitric oxide, superoxide, cytokines) that mediate the neurotoxicity of the amphetamine-class of drugs, their activation could represent an early and essential event in the neurotoxic cascade associated with high-dose amphetamine intoxication.

Administration of D,L-fenfluramine to rats produces learning deficits in the Cincinnati water maze but not the Morris water maze: relationship to adrenal cortical output

Fenfluramine (FEN) is an amphetamine derivative with anorectic properties similar to amphetamine, but without the stimulatory or abuse potential. Administration of FEN produces an immediate release of serotonin as well as inhibits reuptake; ultimately FEN produces a decrease in serotonin stores in the central nervous system. We have previously shown that the administration of FEN to rats results in increased adrenal cortical hormones under resting conditions, without simultaneous elevations in adrenocorticotropin hormone (ACTH). We hypothesized that the adrenal output would be altered following stress and that the altered adrenal output would affect learning and memory, since the adrenal hormones influence learning and memory capability. In this series of experiments, we administered D,L-FEN (15 mg/kg) four times every 2 h on a single day to rats and investigated the effect on hormonal output following forced swim and the effect on sequential learning in the Cincinnati water maze and spatial learning in the Morris maze beginning 3 days after FEN administration. Animals that received FEN had increased corticosterone and aldosterone titers following forced swim relative to control animals, although no differences in ACTH or testosterone were noted. Animals exposed to FEN had lasting deficits in the Cincinnati water maze but not in the Morris water maze, regardless of testing order. These deficits in the Cincinnati water maze appear to be mediated by the elevation in adrenal output since adrenalectomy abolished the effect of FEN. Corticosterone levels were shown to be elevated during the behavioral testing period in animals exposed to FEN.

Impaired spatial and sequential learning in rats treated neonatally with D-fenfluramine

D-Fenfluramine, a serotonin releaser, was administered to neonatal rats on postnatal days 11-20 (a stage of hippocampal development analogous to third trimester human ontogeny). As adults, the D-fenfluramine-treated offspring exhibited dose-related impairments of sequential and spatial learning and reference memory in the absence of sensorimotor impairments. Procedures to minimize stress and to control for other performance effects prior to testing for spatial learning demonstrated that nonspecific factors did not account for the selective effects of D-fenfluramine on learning and memory. Developmental D-fenfluramine-induced spatial and sequential learning deficits are similar to previous findings with developmental MDMA treatment. By contrast, recent findings with developmental D-methamphetamine treatment showed spatial learning deficits while sparing sequential learning. The spatial learning effects common to all three drugs suggest that they may share a common mechanism of action, however, the effects are not related to long-lasting changes in hippocampal 5-HT levels as no differences were found in adulthood. Whether the cognitive deficits are related to the effects of substituted amphetamines on corticosteroids, other aspects of the 5-HT system, or some unidentified neuronal substrates is not known, but the data demonstrate that these drugs are all capable of inducing long-term adverse effects on learning.