Is long-term heavy alcohol consumption toxic for brain serotonergic neurons? Relationship between years of excessive alcohol consumption and serotonergic neurotransmission.

The relationship between years of excessive alcohol consumption and central serotonergic neurotransmission, as assessed by the prolactin (PRL) response to D-fenfluramine, was investigated in 22 male alcohol-dependent subjects. A negative correlation was obtained, that is, the longer duration of excessive alcohol consumption the lower PRL response to D-fenfluramine. It is therefore suggested that long duration of excessive alcohol consumption in alcohol-dependent subjects causes a reduction in central serotonergic neurotransmission, possibly by a toxic effect of alcohol on serotonin neurons. The relationship between depressive and anxiety symptoms during on-going drinking and the PRL response to D-fenfluramine was also investigated. No such correlations were obtained, suggesting that reduction in central serotonergic neurotransmission does not pre-dispose to the development of depressive and anxiety symptoms, at least in relation to on-going drinking in alcohol-dependent subjects.     

A comparison of<Emphasis Type="Italic"> d</Emphasis>,<Emphasis Type="Italic">l</Emphasis>-fenfluramine and citalopram challenges in healthy adults

Dimensional personality characteristics (e.g. impulsivity) and related behaviors and psychiatric disorders are linked to abnormalities of central nervous system (CNS) serotonergic functioning. Although neuroendocrine [e.g. plasma prolactin (PRL)] responses to the serotonin agonist, fenfluramine, have been used widely to index CNS serotonergic responsivity, safety concerns constrain continued use of fenfluramine. Citalopram, which inhibits serotonin reuptake, may serve as an alternative pre-synaptic neuropharmacologic challenge agent, due to its high selectivity and absence of intrinsic activity at serotonin or other receptor families. Twenty-two healthy adults who had been administered a fenfluramine challenge before May 1996 completed a 5-h oral citalopram challenge 3–6 years later. PRL responsivity to citalopram correlated significantly with PRL response to fenfluramine for baseline-corrected maximal and area-under-the-curve (AUC) indices (rs0.49, Ps0.02). The magnitude of the correlations is notable given the length of time between challenges. The results support the use of citalopram as an alternate neuroendocrine challenge to index CNS serotonergic responsivity.     

Retest reliability of prolactin response to dl-fenfluramine challenge in adults.

Neuropharmacologic probes to assess central nervous system (CNS) serotonergic responsivity (e.g., dl-fenfluramine) stimulate serotonergic neurotransmission, thereby causing proportional release of pituitary-derived hormones into the circulation. Individual differences in these hormonal responses are thus thought to reflect dimensional variability in central serotonergic activity, which may, in turn, underlie variation in serotonin-related traits of personality (e.g., impulsivity, behavioral inhibition, harm avoidance). However, the long-term temporal stability of neuropharmacologic indices of CNS serotonergic responsivity has not previously been tested in nonpsychiatric patients. dl-Fenfluramine was administered here to 57 adults, aged 24-60 years, on two occasions 6 months apart, to examine the retest reliability of fenfluramine-induced prolactin [PRL] response to fenfluramine. Baseline PRL concentration (i.e., before administration of fenfluramine) was highly stable over the 6 months (r = 0.88). Variability in serotonergic responsivity, adjusted for baseline PRL concentration, age, sex, and drug concentration during the challenge, was moderately reproducible (r = 0.50 for peak DeltaPRL and 0.57 for PRL "area under the curve," p <.0001). These findings are consistent with speculation that variability in indices of central serotonergic function reflects a temporally stable dimension of individual differences.     

Acute administration of citalopram facilitates memory consolidation in healthy volunteers

OBJECTIVES: Decreasing serotonergic neurotransmission in humans has been found to impair memory consolidation. Such effects may be relevant to the memory deficits seen in major depression and the cognitive actions of antidepressant drugs used to treat them. However, the improvement in cognitive function often found following successful pharmacological treatment in depression may be confounded by symptom improvement. RATIONALE: The present study assessed the effects of an acute challenge with the selective serotonergic re-uptake inhibitor citalopram in healthy (non-depressed) females. METHODS: Immediate and delayed recall/recognition was assessed using the auditory verbal learning test following 10 mg (intravenous) citalopram or placebo in a double-blind between groups design. RESULTS: Immediate recall on the verbal memory test was unaffected by citalopram administration. However, volunteers receiving citalopram showed enhanced long-term memory performance in terms of delayed recall and recognition relative to those receiving placebo. Sustained attention performance was also comparable in the two groups of subjects suggesting that non-specific increases in information processing are not responsible for this effect. CONCLUSIONS: These results indicate that augmentation of serotonergic neurotransmission is associated with increased memory consolidation, which may be relevant to its therapeutic and cognitive actions in acutely depressed patients.     

Central serotonergic activity is related to the aggressive behaviors of Alzheimer's disease.

The clinical correlates of reduced serotonin (5-HT) in Alzheimer's disease (AD) remain unknown. The hypothesis of this study was that altered central serotonergic activity is related to aggression in AD. Twenty-two institutionalized, nondepressed elderly (12 M/10 F, mean age +/- SD: 82.2 +/- 6.4) with probable AD, severe cognitive impairment (MMSE = 4.1 +/- 4.7) and significant behavioral disturbance (Neuropsychiatric Inventory (NPI) score > or = 8) were studied. The prolactin (PRL) response to d,l-fenfluramine (60 mg p.o.) was used as an index of central serotonergic function. The NPI aggression score, NPI irritability score, and Behavioral Pathology in AD aggression score were positively correlated to prolactin concentrations following fenfluramine challenge (r(S) =.61, p =.003; r(S) =.53, p =.012; and r(S) =.47, p =.029 respectively). In addition, aggressive patients showed a greater mean PRL increase (% baseline) (215 +/- 60, n = 11) than nonaggressive subjects (123 +/- 54, n = 11) (p =.01, 2-tailed t-test). The change in PRL concentration depended on level of cognitive impairment (p =.0004) and the gender x aggression interaction (p =.015) with the overall regression model accounting for 74% of the variance (r = 0.86, F = 11.9, p =.0001). Female aggressive subjects with less cognitive impairment had the largest response to fenfluramine challenge. These results suggest a complex link between aggression in AD and central serotonergic dysfunction having interactions with gender and cognitive impairment.     

Serotonergic modulation of striatal D2 dopamine receptor binding in humans measured with positron emission tomography

The modulating effect of serotonergic drugs on the striatal dopamine neurotransmission has remained controversial, and there are no published data on serotonin-dopamine interaction obtained from living human brain. Citalopram is a selective serotonin reuptake inhibitor widely used in the treatment of depression (20–40 mg/day). We measured the effects of acute (20 mg, per os) and chronic (20 mg/day for 14 days) doses of citalopram and placebo intake on [¹¹C]-raclopride binding to striatal D₂-receptors in eight healthy volunteers by using positron emission tomography. Although the effect magnitude was not large, the results indicate that chronic citalopram intake slightly decreases the raclopride binding which may reflect increased dopamine release in the striatum. In addition, after 14 days there was a high correlation between the citalopam plasma levels and the decrease in the [¹¹C]-raclopride binding in both the caudate and the putamen, although statistically significant effect in the raclopride binding potential was more pronounced in the putamen. This report suggests functional interaction of brain dopaminergic and serotonergic systems in vivo in man.     

Effect of fenfluramine on prolactin and thyroid-stimulating-hormone response to thyrotropin-releasing-hormone in obese and normal women

Summary In order to demonstrate the suggested failure of the serotoninergic system in human obesity and to evaluate the role of central serotoninergic activity in prolactin (PRL) and thyroid stimulating hormone (TSH) release in this condition, 13 euthyroid obese and 9 healthy women of normal weight were studied. A TRH test (200 μg i. v.) was performed before and after administration of fenfluramine (FF) 60 mg b. d. for 14 days. In the controls, FF did not modify the expected significant increase in PRL induced by TRH. In obese patients, however, the PRL levels was significantly increased after TRH, but the increase was less than in the controls. After FK the PRL response to TRH was larger than in the pretreatment phase, with values similar to those observed in normal subjects. In neither group FF did change the TSH-stimulating effect of TRH, but the hormonal response in obese patients was greater than in the controls. The restoration of the responsiveness of PRL to TRH after central serotoninergic stimulation confirms the hypothesis that a failure of the serotoninergic system may occur in human obesity. Since FF does not interfere with the secretory pattern of basal and stimulated TSH in normal or obese subjects, the serotoninergic system does not seem to play a major role in the control of TSH secretion.     

Comparison of light treatment with citalopram in winter depression: a longitudinal single case study.

A woman with seasonal affective disorder (SAD) remitted within a week in each of six separate trials of light therapy. She remitted within 2 weeks of initiating citalopram treatment. Light treatment in the morning advanced and improved sleep, whereas citalopram delayed sleep and induced intermittent awakenings. These opposite patterns suggest that sleep deprivation or sleep shifts were not crucial for eliciting therapeutic response. Light and citalopram both selectively reduced intake of sweet carbohydrate parallel with improvement, implicating CNS serotonergic mechanisms in the interaction of mood and food in winter.     

The effect of intravenous L-tryptophan on prolactin and growth hormone and mood in healthy subjects

In order to assess the effects of increased central nervous system serotonergic function in humans on prolactin (PRL), growth hormone (GH) and mood, intravenous L-tryptophan (TRP) was administered to ten healthy subjects. The TRP infusion induced robust increases in PRL in all ten subjects. A significant increase in GH concentration was also observed, although the response was more variable. The subjects reported feeling significantly more high, mellow, and drowsy following the TRP infusion in comparison to placebo. These findings indicate an important role for serotonin in PRL and GH secretion, as well as in mood regulation. The intravenous TRP challenge may be of use in the study of serotonergic function in a variety of neurologic and psychiatric diseases.     

Effects of p-chlorophenylalanine and scopolamine on retention of habits in rats

Rats were trained on a conventional maze test or on a swim-to-platform test. Retention of swim-to-platform performance 7 days later was severely impaired by posttraining treatment with a combination of p-chlorophenylalanine (PCPA) and scopolamine although neither drug alone had any effect. Retention of the maze habit was moderately impaired by scopolamine alone and severely impaired by a combination of scopolamine and PCPA, but was unaffected by PCPA alone. Polygraphic recordings confirmed previous reports that a combination of PCPA and scopolamine can abolish neocortical low voltage fast activity and hippocampal rhythmical slow activity. Combined blockade of central cholinergic and serotonergic neurotransmission in rats may provide a useful animal model of Alzheimer's disease.     

Selective serotonin re-uptake inhibition attenuates evoked glutamate release in the dorsal horn of the anaesthetised rat in vivo.

Augmentation of serotonergic neurotransmission at the level of the dorsal spinal cord is proposed to contribute to the analgesic activity of selective serotonin (5-HT) reuptake inhibitors (SSRIs). In this study we have utilised microdialysis perfusion to determine the effect of two structurally unrelated SSRIs on depolarisation-induced aspartate and glutamate release in the dorsal spinal cord of the anaesthetised rat. Perfusion with artificial extracellular fluid containing 45 mM potassium produced a significant increase in aspartate and glutamate efflux. Sensitivity, at least in part, to antagonism of calcium entry by high extracellular Mg2+ indicated a neuronal origin for a proportion of stimulated release. Reverse dialysis of paroxetine (1-30 microM) reduced the increase in glutamate in a concentration dependent manner, with a significant reduction evident following inclusion in the perfusate of 30 microM. Administration of an equi-potent dose of citalopram (300 micoM) also reduced depolarisation induced glutamate release. Aspartate levels tended to decrease in the presence of paroxetine and citalopram, but this trend did not reach significance. Co-perfusion of paroxetine (30 microM) with the selective 5-HT(1A) receptor antagonist WAY 100635 (100 microM) did not prevent the reduction in depolarisation induced glutamate efflux. These results demonstrate that local administration of SSRIs has an inhibitory influence on evoked release of glutamate in the dorsal horn. This could indicate regulation of excitatory neurotransmission mediated through augmented serotonergic neurotransmission and activation of a serotonergic receptor other than the 1A subtype. Alternatively, direct inhibition with voltage dependent calcium channels, potentially a property intrinsic to molecules with high selectivity for the 5-HT transporter, may underlie this effect.     

Positron emission tomography study of regional brain metabolic responses to a serotonergic challenge in major depressive disorder with and without comorbid lifetime alcohol dependence.

This is the first study contrasting regional glucose metabolic rate (rCMRglu) responses to a serotonergic challenge in major depressive disorder (MDD) with and without comorbid alcohol dependence. In a university hospital, patients with MDD without a history of alcohol dependence (MDD only) and patients with MDD and comorbid alcohol dependence (MDD/ALC) were enrolled in this study. Subjects with comorbid borderline personality disorder were excluded. A bolus injection of approximately 5 mCi of (18)fluorodeoxyglucose was administered 3 h after the administration of placebo or fenfluramine. We found an anterior medial prefrontal cortical area where MDD/ALC subjects had more severe hypofrontality than MDD only patients. This area encompassed the left medial frontal and left and right anterior cingulate gyri. This group difference disappeared after fenfluramine administration. The fact that the observed group difference disappeared after the fenfluramine challenge suggests that serotonergic mechanisms play a role in the observed differences between the groups.     

Prolactin secretion in man: a useful tool to evaluate the activity of drugs on central 5-hydroxytryptaminergic neurones. Studies with fenfluramine.

Acute oral administration of various doses of fenfluramine, a 5-HT releaser, induced a dose-related increase of PRL secretion in nine healthy volunteers. Fenfluramine reached the maximum effect on PRL secretion at 4 h after its administration. This effect was already significant at 2 h and lasted till 8 h. Metergoline, a 5-HT receptor blocker, when administered alone, decreased serum PRL levels in six healthy subjects. The pretreatment with this drug significantly antagonized the PRL-releasing action of fenfluramine (60 mg) suggesting that the effect of fenfluramine on PRL release may be mediated through a 5-HT mechanism in the brain. These findings suggest the possibility that serum PRL levels in humans may represent a useful tool to evaluate, in vivo, the activity of drugs possessing putative 5-hydroxytryptaminergic properties.     

Specific serotonergic reuptake inhibition impairs vigilance performance acutely and after subchronic treatment

Subchronic treatment with the selective serotonergic reuptake inhibitors (SSRIs) fluoxetine, venlafaxine and paroxetine, but not sertraline, were previously shown to specifically impair vigilance performance. The current study was designed to compare the vigilance effects of subchronic treatment with the SSRIs sertraline and citalopram in healthy volunteers, according to a placebo-controlled, double-blind, three-way cross-over design. Twenty-four healthy subjects, aged 30-50 years, of whom 21 completed the study, underwent three treatment periods of 2 weeks in which they received sertraline (50 mg on days 1-8, 100 mg on days 8-15), citalopram (20 mg on days 1-8, 40 mg on days 8-15) and placebo. Treatment periods were separated by 14 days washout periods. Vigilance performance was assessed through a 45-min Mackworth Clock Test at days 1, 8 and 15 of each treatment period. It was found that citalopram impaired vigilance performance acutely after the first 20 mg dose and subchronically after 40 mg daily doses. By contrast, no vigilance impairment was found during sertraline treatment. Sertraline is the only SSRI studied so far with no detrimental effects on vigilance. This may be due to the affinity of sertraline for the dopamine reuptake site. Because citalopram is the most specific SSRI showing this effect, it is concluded that the SSRI-induced decrement of vigilance performance is specifically associated with serotonergic reuptake inhibition.     

Evaluation of Guanfacine as a Potential Medication for Alcohol Use Disorder in Long-Term Drinking Rats: Behavioral and Electrophysiological Findings

One of the main treatment challenges in alcohol use disorder (AUD) is the high rate of craving in combination with decreased cognitive functioning including impaired decision making and impulse control that often lead to relapse. Recent studies show that guanfacine, an α-2-adrenoceptor agonist and FDA-approved ADHD medication, attenuates stress-induced relapse of several drugs of abuse including alcohol. Here we evaluated guanfacine''s effects on voluntary alcohol intake, the alcohol deprivation effect (ADE), alcohol seeking behavior, and cue/priming-induced reinstatement in Wistar rats that had voluntarily consumed alcohol for at least 2 months before treatment. In addition, guanfacine''s ability to regulate glutamatergic neurotransmission was evaluated through electrophysiological recordings in medial prefrontal cortex (mPFC) slices prepared from long-term drinking rats (and alcohol-naive controls) that had received three daily guanfacine (0.6 mg/kg/day) or vehicle injections in vivo. Guanfacine decreased alcohol intake in high, but not low, alcohol-consuming rats and the effects were generally more long lasting than that of the AUD medication naltrexone. Repeated guanfacine treatment induced a long-lasting decrease in alcohol intake, persistent up to five drinking sessions after the last injection. In addition, guanfacine attenuated the ADE as well as alcohol seeking and cue/priming-induced reinstatement of alcohol seeking. Finally, subchronic guanfacine treatment normalized an alcohol-induced dysregulated glutamatergic neurotransmission in the mPFC. These results support previous studies showing that guanfacine has the ability to improve prefrontal connectivity through modulation of the glutamatergic system. Together with the fact that guanfacine appears to be clinically safe, these results merit evaluation of guanfacine''s clinical efficacy in AUD individuals.     

Evaluation of central serotonergic function in affective and related disorders by the fenfluramine challenge test: a critical review

Plasma prolactin levels following oral administration of the serotonin (5-HT) releasing agent, fenfluramine hydrochloride, have been extensively used to evaluate central serotonergic function in affective and related disorders. Cortisol responses to fenfluramine have generally been a less informative measure. In healthy subjects, prolactin release by fenfluramine is dose-dependent, blocked by antagonists of serotonin receptors of the 5-HT-2a/2c type, negatively correlated with age and increased in young females. In major depression, a preponderance of studies have found blunted prolactin responses compared to matched normal controls. Although a significant minority of studies have not found blunting, increased prolactin release has not been observed. The blunted prolactin release is not due to a deficient secretory capacity of pituitary lactotrophs and is congruent with other evidence for reduced central serotonergic function in major depression. Blunting of the prolactin response may be associated with severity of depression and with elevated baseline cortisol levels. Treatment with antidepressant drugs and electroconvulsive therapy has been reported to increase the prolactin response but this has not been replicated in all studies. Blunted prolactin responses to fenfluramine have been fairly consistently associated with impulsive aggression in different personality disorders and with severity of suicide attempts in depressed patients. A number of studies employing the fenfluramine challenge test (FCT) have been conducted in obsessive compulsive disorder but their results have been variable. Prolactin responses to fenfluramine may be enhanced in panic disorder and chronic fatigue syndrome but the number of studies in these conditions is small as is the case for seasonal affective disorder. Since the therapeutic administration of fenfluramine as an appetite suppressant has been suspended because of reports of cardiac complications, further use of this compound as a challenge agent is not anticipated. Future studies are likely to employ agents acting on specific serotonin receptors and should apply methodological insights from the use of the FCT, which are considered in this review. Use of concomitant brain imaging to evaluate the central effects of challenge agents directly is likely to become more prevalent and may supplant neuroendocrine challenge paradigms such as the FCT which have been remarkably heuristic but are limited in scope and methodologically complex.     

Effect of subchronic lithium carbonate treatment on anxiolytic-like effect of citalopram and MKC-242 in conditioned fear stress in the rat

We investigated the effect of citalopram [selective serotonin (5-HT) reuptake inhibitor] and MKC-242 (5-[3-?(2S)-(1, 4-Benzodioxan-2-ylmethyl) amino?propoxy]-1, 3-benzo-dioxol hydrochloride; a selective 5-HT(1A) receptor agonist) on the expression of conditioned freezing, an index of anxiety, following treatment with subchronic lithium carbonate (LiCO(3)). Male Sprague-Dawley rats were used in these experiments. Acute administration of citalopram (subcutaneously, s.c.) reduced freezing significantly at a high dose (30 mg/kg), while showing no effect at lower doses (3 and 10 mg/kg). Acute administration of MKC-242 (s.c.; 0.1-10 mg/kg) dose dependently reduced freezing. Subchronic LiCO(3) treatment (1 week; 0.05% or 0.2% LiCO(3) in diet; p.o.) showed no effect on freezing behavior. Acute treatment with both citalopram (3 and 30 mg/kg) and MKC-242 (1 mg/kg) after subchronic treatment with the higher, but not the lower concentration of LiCO(3) (1 week), reduced freezing markedly and significantly, as compared with either drug alone. These results suggest that subchronic LiCO(3) treatment enhanced the anxiolytic-like effects of these serotonergic drugs by facilitating central 5-HT neurotransmission at clinically therapeutic plasma lithium levels.     

Pharmacogenetic insights to monoaminergic dysfunction in alcohol dependence

Rationale Alcohol dependence is characterized by the development of tolerance, withdrawal symptoms, and craving for alcohol. Chronic alcohol consumption causes neuroadaptive changes in the central dopaminergic and serotonergic system, which are partially reversible after detoxification. The severity and time-course of recovery of these neuroadaptive changes may depend on the genetic constitution of monoamine transporters and receptors and contribute to the relapse risk of alcoholics.Objectives To assess the interaction between the genetic constitution and the in vivo availability of dopamine and serotonin transporters and receptors, chronic alcohol intake, alcohol craving and withdrawal.Methods Review of brain imaging studies that assess the genotype and availability of dopamine and serotonin transporters in detoxified alcoholics and healthy control subjects.Results Chronic alcohol intake induced neuroadaptive reductions in striatal dopamine transporter (DAT) availability, which were reversible during early abstinence. A polymorphism of the DAT gene (SLC6A3) was associated with the in vivo transporter availability and with the severity of alcohol withdrawal. Neurotoxic reductions in 5-HTT protein expression were limited to homozygous carriers of the long allele in the 5-HTT gene (SCL6A4) regulatory region and correlated with negative mood states.Conclusion Genetic constitution interacts with the in vivo availability of central dopamine and serotonin transporters during alcohol detoxification and may affect the severity of alcohol withdrawal and clinical depression.     

Serotonergic Mechanisms Involved in the Exploratory Behaviour of Mice in a Fully Automated Two-Compartment Black and White Test Box

Abstract A fully automated version of the black and white two-compartment box for mice is presented. The anxiolyticlike effects of the benzodiazepines, diazepam and chlordiazepoxide, were confirmed, and the involvement of serotonergic mechanisms was studied in this animal model of anxiety. The partial 5-HT_1A receptor agonists, buspirone and ipsapirone showed anxiolytic-like effects in a limited dose interval. The full agonist hydroxy-2-(di-n-propylamino)tetraline (8-OH-DPAT) was inactive. The non-selective 5-HT₁ receptor agonist, eltoprazine, induced marked increases of exploratory behaviour in the white compartment over a broad range of doses. Also pindolol a mixed 5-HT_1A/1B and β-adrenergic receptor antagonist showed anxiolytic-like effects, whereas another compound with a similar profile (-)-, penbutolol and the β-adrenoceptor antagonist ICI 118,551, was inactive. The 5-HT_2A/2C receptor antagonist, ritanserin, showed anxiogenic-like, and the 5-HT₃ receptor antagonists, zacopride and ondansetron, showed anixiolytic-like effects. An overall increase of serotonergic activity by means of 5-HT uptake inhibition (citalopram), 5-HT release (fenfluramine) or administration of a 5-HT precursor (1–5-HTP) facilitated exploratory activity in the white compartment. Reduction of serotonergic activity by treatment with the 5-HT depletor p-chloro-phenylalanine methyl ester (PCPA) did not change the exploratory behaviour, but attenuated the response to fenfluramine significantly.     

Addictive and nonaddictive smoking as related to responsivity to neurotransmitter systems

In a double-blind crossover design on 36 male smokers, differences in hormone responses to a serotonergic (citalopram) and dopaminergic (bromocriptine) challenge were tested, to compare transmitter responsivities in addicted and pleasure-motivated smokers with respective controls. A general score of smoking addiction, according to DSM IV criteria, was associated with a blunted prolactin decrease to bromocriptine, indicating a possible nicotine-induced desensitization of DA receptors. The single questionnaire-based symptom of tolerance was associated with a blunted cortisol response to citalopram, indicating a particular desensitization of serotonin receptors. Nontolerant but addicted subjects exhibited increased serotonergic responsivity, interpreted as resulting from low serotonin levels associated with lack of impulse control. The questionnaire-based score of pleasure-motivated (='indulgent') smoking was associated with high dopaminergic activity (pronounced prolactin responses), confirming findings obtained in subjects exhibiting reward-related personality factors.