Presynaptic Serotonergic Markers in Community-Acquired Cases of Alzheimer's Disease: Correlations with Depression and Neuroleptic Medication

Abstract: Presynaptic serotonergic markers, serotonin uptake sites, and concentrations of serotonin and 5-hydroxyindoleacetic acid were studied in the frontal and temporal cortex of 20 community-acquired cases of Alzheimer's disease and 16 controls matched for age, sex, postmortem delay, and storage. Clinical assessments, including behavioural symptoms, of the Alzheimer patients were made at 4-month intervals during life. There was a significant reduction in the number of serotonin uptake sites in Alzheimer cases in temporal but not frontal cortex. There was no significant alteration in the concentrations of serotonin or 5-hydroxyindoleacetic acid in either region. Alzheimer patients who had persistent depressive symptoms during life had significantly fewer serotonin uptake sites in both cortical areas compared with Alzheimer patients without these symptoms. In addition, Alzheimer patients who were receiving chronic neuroleptic medication had significantly lower concentrations of serotonin in frontal cortex and 5-hydroxyindoleacetic acid in temporal cortex than those patients not receiving such treatment. These data suggest previous studies that reported uniform serotonergic dysfunction may have been subject to unintentional selection of behaviourally disturbed Alzheimer cases or those receiving chronic neuroleptic medication. This study also provides a basis for the treatment of behaviourally disturbed Alzheimer patients with serotonomimetics.     

Binding of the Novel Serotonin Agonist 8-Hydroxy-2-(Di-n-Propylamino) Tetralin in Normal and Alzheimer Brain

Binding of [3H]8-hydroxy-2-(di-n-propylamino) tetralin, a putative ligand for the 5-hydroxytryptamine (5-HT, serotonin) 1A recognition site, was measured in neocortex from postmortem human brain. The substance was found to bind to a saturable site with a KD value and pharmacological profile similar to that of rat. Binding to membranes from normal human temporal cortex was found to significantly correlate (inversely) with age. A significant reduction in binding, reflecting decreased density of recognition sites, was observed in the frontal cortex of patients with Alzheimer's disease (48% loss). This region in the dement brains showed unaltered presynaptic 5-HT function (5-HT and 5-hydroxyindoleacetic acid content) whereas 5-HT concentration was reduced in the temporal cortex.     

Attenuation and recovery of evoked overflow of striatal serotonin in rats treated with neurotoxic doses of methamphetamine

Repeated administration of methamphetamine to animals can lead to long-lasting decreases in striatal monoamine content. In the present study, the effects of neurotoxic doses of methamphetamine on basal and evoked overflow of striatal serotonin and of its primary metabolite 5-hydroxyindoleacetic acid were examined in awake rats using in vivo microdialysis. Male Fischer-344 rats were administered methamphetamine (5 mg/kg, s.c.) or saline four times in 1 day at 2-h intervals. Microdialysis studies were carried out 1 week, 1 month, and 6 months later. At 1 week posttreatment there were significant decreases in potassium- and amphetamine-evoked overflow of serotonin in the striatum of the methamphetamine-treated animals. Basal extracellular levels of 5-hydroxyindoleacetic acid but not of serotonin were also decreased. Evoked overflow of serotonin recovered by 1 month, and extracellular levels of 5-hydroxyindoleacetic acid had recovered by 6 months. Tissue levels of serotonin and 5-hydroxyindoleacetic acid were decreased at 1 week posttreatment but back to control levels by 1 month after treatment. These results indicate that presynaptic serotonergic functioning is attenuated in the striatum of rats treated 1 week earlier with neurotoxic doses of methamphetamine. However, in the model used, the changes are transient, and recovery can occur within 1-6 months posttreatment.     

Serotonergic control of prolactin release in male rats.

To further clarify the relationship between the central serotonergic system and the control of prolactin secretion, we studied the effect of dorsal raphe' lesions, electrical stimulation of the midbrain raphe' nucleus and treatment with parachlorophenylalanine (PCPA) on prolactin secretion. Radio frequency destruction of serotonergic cell bodies in the midbrain dorsal raphe' nucleus or PCPA decreased forebrain serotonin (5HT) and 5-hydroxyindoleacetic acid (5HIAA) concentration and prolactin secretion. Electrical stimulation of the raphe' increased forebrain serotonin turnover and prolactin secretion. These observations indicate that serotonergic neurons located in the raphe' nuclei may be involved in regulating prolactin secretion in male rats.     

Dopaminergic and Serotonergic Neurotransmission Systems Are Differentially Involved in Auditory Cortex Learning: A Long-Term Microdialysis Study of Metabolites

Abstract: Auditory cortex has been shown to be a site of widespread neuronal learning processes even in the context of simple auditory conditioning behavior. In view of their presumed role in determining behavioral and motivational relevance of incoming information we investigated whether the dopaminergic and serotonergic systems are involved in auditory cortex learning. Using a chronic brain microdialysis technique over 4 days, samples from auditory cortex were obtained before, during, and after daily footshock avoidance training simultaneously from trained gerbils and passive control animals or pseudotrained animals. Because of detection limits of dopamine and serotonin in auditory cortex, the response profiles of extracellular homovanillic acid as the metabolite of the dopaminergic system and of 5-hydroxyindoleacetic acid as the metabolite of the serotonergic system were determined from consecutive dialysis samples each day. The response of the dopaminergic system appeared to reflect the initial formation of the behaviorally relevant association exclusively during the first training day, whereas the serotonergic response appeared to correlate with the stress level of animals.     

In vivo Microdialysis of 5-Hydroxyindoleacetic Acid and Glutamic Acid in the Hamster Suprachiasmatic Nuclei

SYNOPSIS. The technique of in vivo brain microdialysis rapidlyis becoming a popular tool for research on the neurochemicalbasis of physiological and behavioral functions. The presentstudy describes the application of microdialysis to investigatethe endogenous release of 5-hydroxyindoleacetic acid (5-HIAA)and glutamic acid in the suprachiasmatic nuclei (SCN) of hamsters.There were apparent circadian patterns of release of both ofthese neurosecretions, with peak levels occurring during thedark phase. Pharmacological manipulations of serotonin releaseand reuptake, using tetrodotoxin and citalopram, respectively,provided evidence that the nocturnal increase in 5-HIAA reflectsan increase in serotonergic synaptic activity, rather than intraneuronalmetabolism of unreleased serotonin. These results illustratethe usefulness of the microdialysis technique for studies onthe neurochemistry of central pacemaker function.     

Changes in brain serotonin metabolism and [3H]-serotonin receptor binding during recall of conditioned passive avoidance in rats

The content of serotonin and its metabolite 5-hydroxyindoleacetic acid, monoamine oxidase activity, and [3H]-serotonin radioligand receptor binding were examined in the prefrontal cortex, striatum, amygdala, hippocampus and periaqueductal gray matter at different time after one-trial passive avoidance training of rats. Changes in the serotonergic activity were observed only in rats, which showed retrieval of conditioned passive avoidance response. No serotonergic changes were found immediately and one day after training. Also, there were no changes in trained rats without retrieval of conditioned passive avoidance response or rats with experimental amnesia. The pattern of the involvement of brain structures in the retrieval process was also revealed. [3H]-serotonin binding was decreased in the amygdala, periaqueductal gray matter and striatum, whereas it did not change in the prefrontal cortex and hippocampus. At the same time, the serotonin content in these structures did not differ from that of intact rats. Deamination of serotonin by monoamine oxidase and active transport of 5-hydroxyindoleacetic acid from nerve terminals were increased in the amygdala and periaqueductal gray matter, whereas in the striatum serotonin catabolism was decreased. The obtained differences in serotonin catabo- lism suggest that the decrease in receptor binding of serotonin in these brain structures is provided by different synaptic processes: presynaptic changes in the striatum and postsynaptic receptor changes in the amygdala and periaqueductal gray matter. It is concluded that the decrease in the serotonergic activity in the amygdala and periaqueductal gray matter represents one of the mechanisms activating the emotiogenic system mediating the memory trace retrieval in inhibitory avoidance learning.     

Evidence for Differing Origins of the Serotonergic Innervation of Major Cerebral Arteries and Small Pial Vessels in the Rat

We have studied the nature and origin of the serotonergic innervation of two distinct anatomical cerebrovascular compartments, namely, small pial vessels and major cerebral arteries, in the rat. To this end, the levels of serotonin [5-hydroxytryptamine (5-HT)] and 5-hydroxyindoleacetic acid (5-HIAA) were measured by HPLC in both cerebrovascular compartments after either bilateral sympathectomy or destruction of the ascending serotonergic pathways, which originate from the raphe nuclei. We first showed that the small pial vessel samples were not contaminated by underlying cortical tissues through the use of an immunohistochemical approach that revealed the glia limitans, the most superficial cortical layer. Superior cervical ganglionectomy caused a marked decrease in noradrenaline concentrations in major cerebral arteries (-77%), although the reduction was less pronounced (-34%) in small pial vessels. Sympathectomy decreased by 33% 5-HT concentrations in the major cerebral arteries but was without effect on 5-HT levels in the small pial vessels. Destruction of the ascending serotonergic pathways (via local administration of 5,7-dihydroxytryptamine into the ventral tegmental area) produced a dramatic fall in 5-HT and 5-HIAA concentrations in both vascular compartments. To establish the authenticity of the serotonergic innervation, the synthesis of 5-HT [as assessed by measuring the accumulation of 5-hydroxytryptophan (5-HTP) after decarboxylase inhibition] was measured in the two vascular beds under control conditions and after destruction of the ascending serotonergic pathways. The rate of accumulation of 5-HTP was higher in the small pial vessels than in major cerebral arteries, an observation that indicates an important de novo synthesis of 5-HT in small pial vessels.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dietary tryptophan does not alter the function of brain serotonin neurons

The hypothesis that alterations in dietary tryptophan modify the functional activity of brain serotonin-containing neurons was tested by recording the electrophysiological activity of single serotonergic cells in awake, behaving cats after meal ingestion of diets containing varying proportions of tryptophan and the neutral amino acids that compete with tryptophan for uptake into the brain. The data revealed that while the various diets produced significant changes in brain serotonin and its major metabolite, 5-hydroxyindoleacetic acid, there was no change in the activity of serotonin-containing dorsal raphe cells following meal ingestion. Furthermore, a pulse injection of tritiated labeled tryptophan following the various diets produced no significant change in the release of tritiated serotonin into the lateral ventricles, while tritiated 5-hydroxyindoleacetic acid was significantly increased. These data suggest that dietary tryptophan does not alter the functional activity of central serotonergic neurons, in contrast with current popular beliefs that such dietary manipulations alter brain function.     

Effects of short- and long-term neuroleptic treatment on brain serotonin synthesis and turnover: focus on the serotonin hypothesis of schizophrenia

Short-term (90 min) administration of haloperidol (2 mg/kg), or chlorpromazine (10 mg/kg) increased the activity of tryptophan hydroxylase as well as the levels of 5-hydroxytryptamine (serotonin) and 5-hydroxyindoleacetic acid in mid-brain of rats. The chronic neuroleptic treatment (21 days) produced more pronounced changes in all parameters related to serotonin synthesis and turnover. The activity of tryptophan hydroxylase in mid-brain was further augmented; the levels of 5-hydroxytryptamine and 5-hydroxyindole-acetic acid were significantly elevated not only in mid-brain, but also in several other discrete regions examined. These data suggest that neuroleptics enhance the synthesis and utilization of brain serotonin. The role of brain serotonergic neurons in the pathophysiology of schizophrenia is further considered.     

A simple, sensitive and reliable assay for serotonin and 5-HIAA in brain tissue using liquid chromatography with electrochemical detection

An extremely sensitive and simple method for simultaneously measuring both serotonin and 5-hydroxyindoleacetic acid (5-HIAA) has been developed using liquid chromatography (LC) and electrochemical detection. Assay conditions are described which resolve and measure as little as 22 picograms of serotonin and its deaminated metabolite in deproteinated brain samples.     

Determination of 5-hydroxytryptophan, 5-hydroxytryptamine, and 5-hydroxyindoleacetic acid in 20 rat brain nuclei using liquid chromatography with electrochemical detection

High-performance liquid chromatography with electrochemical detection is utilized for the simultaneous determination of serotonin, its precursor 5-hydroxytryptophan, and its major metabolite 5-hydroxyindoleacetic acid in nervous tissue samples. Tissue preparation required only homogenization in acidic solution and centrifugation prior to application to the chromatograph. Detection limits in the low picogram range were obtained for those indoles separated. This assay was used in combination with a micropunch dissection technique of 20 discrete rat brain nuclei to measure serotonin, its precursor, and major metabolite. The specificity of the assay was checked with pharmacological experiments aimed to increase or decrease serotonin levels. Pargyline, a monoamine oxidase inhibitor, led to a marked increase in serotonin and a decrease of 5-hydroxyindoleacetic acid while p-chlorophenylalanine, by blocking the conversion of tryptophan to 5-hydroxytryptophan, selectively depleted 5-hydroxytryptophan, serotonin, and 5-hydroxyindoleacetic acid.     

Effects of an acute dose of ethanol on dopaminergic and serotonergic systems from rat cerebral cortex and striatum

Intraperitoneal injection 10 min before sacrifice of 1.5 g ethanol/kg weight produced an increase in rat striatal levels of homovanillic acid (HVA) (p < 0.05) but did not affect the striatal concentrations of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA). A similar ethanol treatment led to decreases in 5-HT (p < 0.05) and 5-HIAA (p < 0.05) from cerebral cortex (prefrontal and anterior cingulate areas). The results point to several ethanol-linked alterations in central serotonergic and dopaminergic systems.     

A comparative study of serotonin metabolism in helminths and their hosts]

Studies have been made on the content of the main metabolite of serotonin, namely 5-hydroxyindoleacetic acid in parasitic worms from various classes. It was shown that 5-hydroxyindoleacetic acid level is lower than that of serotonin, which is taken as an indication of low catabolism of serotonin in worms. This tendency was observed in helminths from different taxonomic, ecological and age groups invading media with both low and high levels of serotonin metabolism.     

Changes in brain serotonergic activity during hierarchic behavior in Arctic charr (Salvelinus alpinus L.) are socially induced

Summary The experiment was performed in two phases. During the first phase (phase 1) the dominance hierarchy was determined in 4 groups of Arctic charr (Salvelinus alpinus L.), each group consisting of 4 fish. Phase 2 was started by rearranging phase 1 fish into 4 new groups. Group 1 consisted of previously dominant fish and groups 2, 3 and 4 of fish that previously held rank 2, 3 and 4, respectively. After phase 2 telencephalon and brain stem were analyzed with regard to their contents of serotonin (5-hydroxytryptamine, 5-HT) and 5-hydroxyindoleacetic acid (5-HIAA), the principle metabolite of 5-HT. No correlation was found between the social rank (measured as dominance index) during phase 1 and the brain serotonergic activity (measured as the ratio 5-HIAA/5-HT) determined after phase 2. However, most important, the 5-HIAA/5-HT ratio was significantly correlated with the last experienced social rank, i.e. that acquired during phase 2. These results shows that the difference in brain serotonergic activity between dominant and subordinate fish develops through social interactions. Further, we found that previous subordinate experience inhibited aggressive behavior, an effect which, in the light of available information on stress and 5-HT, could be related to the increase in brain serotonergic activity. We hypothesize that stress induces an increased serotonergic activity which in turn inhibits the neuronal circuitry which mediates aggressive behavior.Abbreviations 5-HT serotonin (5-hydroxytryptamine) - 5-HIAA 5-hydroxyindoleacetic acid     

Simultaneous Determination of Serotonin, 5-Hydroxyindoleacetic Acid, 3,4-Dihydroxyphenylacetic Acid and Homovanillic Acid by High Performance Liquid Chromatography with Electrochemical Detection

A rapid and highly sensitive procedure for simultaneous determination of serotonin, 5-hydroxyindoleacetic acid, 3,4-dihydroxyphenylacetic acid and homovanillic acid is described. After precipitation of proteins with perchloric acid the samples are applied directly to a high performance liquid chromatograph, with electrochemical detection. As little as 20 pg of serotonin, 5-hydroxyindoleacetic acid, and 3,4-dihydroxyphenylacetic acid and 200 pg of homovanillic acid can be detected. One chromatographic run requires less than 10 min.     

Monoamine neurotransmitters and their metabolites in brain regions in alzheimer's disease: A postmortem study

1. Concentrations of the neurotransmitter amines noradrenaline (NA), dopamine (DA), and 5-hydroxytryptamine (5-HT) and the acid metabolites homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) were determined in four regions of postmortem brains of demented patients with or without Alzheimer's disease (AD). 2. NA was deficient in the temporal cortex (BA 21) of AD, but not of non-AD, patients. 3. Caudate, in particular, had an impaired dopaminergic system in AD patients, with low HVA levels. 4. In all regions investigated [amygdala, caudate, putamen, temporal cortex (BA 21)] 5-HT was significantly depleted in AD patients, and 5-HIAA was also depleted in amygdala and caudate. 5. These results indicate that neurotransmitter systems other than cholinergic systems are also widely affected in AD and suggest that these deficits may also play an important role in determining the symptomatology of AD.     

Changes in the serotonin system of the brains of rats genetically predisposed to catalepsy

Some changes in the brain serotonergic system were found in rats bred for predisposition to catalepsy, and in those bred for its absence. The genetic predisposition for catalepsy was found to be characterized by an increased tryptophan hydroxylase activity in the striatum, and an increased serotonin content in the midbrain. No changes in 5-hydroxyindoleacetic acid level were found. A selection for predisposition to catalepsy turned out to entail a decrease in the sensitivity of postsynaptic serotonin receptors as estimated by the "head twitch" test after 5-hydroxytryptophan administration, while a selection for the absence of catalepsy increased the sensitivity of serotonin receptors.     

Relationship of CSF neurotransmitter metabolite levels to disease severity and disability in multiple sclerosis

Axonal degeneration and brain tissue loss occur during disease progression in multiple sclerosis (MS) and are expected to influence neurotransmitter activities, with consequences on neurologic and psychiatric symptomatology. We searched for relationships of disease duration, disability, and severity of MS patients to CSF levels of the major metabolites of noradrenaline, dopamine, and serotonin, MHPG, methoxyhydroxyphenylglycol (MHPG), homovanillic acid, and 5-hydroxyindoleacetic acid (5-HIAA), respectively, in 39 patients with relapsing–remitting (RR) MS in remission, and 26 patients with progressive (PR) MS. Disability and Disease Severity were assessed by the Expanded Disability Status Scale (EDSS) and the Multiple Sclerosis Severity Score (MSSS). Compared with the levels of 50 control subjects, MHPG levels were not different in either MS group, correlated negatively to duration of illness and number of relapses in the RRMS group, but not to EDSS score or to MSSS. Homovanillic acid levels were significantly lower only in the PRMS group, with a negative correlation to duration of illness, and a strong negative correlation to EDSS score, but not to MSSS. 5-HIAA was significantly lower in both RRMS and PRMS groups. In the RRMS group, 5-HIAA levels were negatively related to EDSS and to MSSS. Multiple regression analyses revealed a significant association of MHPG to duration of illness, and a strong negative association of 5-HIAA to MSSS rather than to EDSS. The strong negative correlation of MSSS to CSF 5-HIAA levels in RRMS group of patients indicates that deficits in central serotonergic activity are related to the rate of disability accumulation in RRMS, and could be linked to the reported reduction of disease activity by serotonergic drugs.