1A Receptor Density Research Articles

Chronic buspirone treatment normalizes open field behavior in olfactory bulbectomized rats: Assessment with a quantitative autoradiographic evaluation of the 5-HT 1A binding sites

The olfactory bulbectomized (OBX) rat model of depression has been widely used in studies on the behavioral and neurochemical aspects of human depression. The objective of the present investigation was to assess open field (OF) activity and the brain regional 5-HT 1A receptor densities of the sham operated (SHX) and OBX rats treated with saline (SHX-SAL, OBX-SAL), and either 10 mg/(kg day) (SHX-B10, OBX-B10) or 20 mg/(kg day) (SHX-B20, OBX-B20) of buspirone for 14 days, delivered by a subcutaneous osmotic minipump. Adult Sprague–Dawley rats were used for this experiment. The surgery was performed on the first day of the experiment and the rats were randomly assigned to either the SHX or OBX groups. The results of the OF tests were organized in eight groups. Following 14 days of treatment and the final OF tests, the rats were sacrificed and the brains were used for 5-HT 1A receptor autoradiography using [ 3H]8-OH-DPAT. The data showed that the OF activities, 14 days following surgery, in the OBX rats were significantly elevated when compared to the SHX rats. In the OBX rats, only the 14-day treatment with 20 mg/(kg day) of buspirone normalized the elevated OF activity, the same dose shown previously to be needed for the normalization of the regional 5-HT synthesis. A significant reduction in the number of 5-HT 1A receptor sites was found in most brain regions in the OBX rats when compared to the SHX rats. Data also show that the regional density of the 5-HT 1A receptors in OBX-SAL treated rats is lower than that of the SHX-SAL rats. The 14-day treatment with either 10 or 20 mg/(kg day) of buspirone reduced the 5-HT 1A receptors in most brain regions of the SHX rats, without an obvious dose-dependent effect of the buspirone. The comparison between the OBX-B20 and control (SHX-B20) rats suggests that the buspirone treatment resulted in a regional balance in the 5-HT 1A sites. A dose dependent reduction in the density of 5-HT 1A sites was observed in the sham rats, but the buspirone treatment had very little effect on the density of the 5-HT 1A receptors in the OBX rats. From these observations, we conclude that the antidepressant effects of buspirone in the OBX rat model of depression are likely mediated through the fine tuning of the regional imbalance of 5-HT 1A receptors with even increases of about 20% in some limbic regions. The data suggest that the neurochemical effects of antidepressants should be studied in animal models of depression rather than in normal rats.

Marked decrease of LSD-induced stimulus control in serotonin transporter knockout mice

Rationale Based upon extensive studies in the rat, it has been suggested that stimulus control by LSD is mediated by 5-HT 2A receptors, with serotonergic receptors of the 5-HT 1A and 5-HT 2C subtypes playing modulatory roles. In genetically modified mice lacking the serotonin transporter (SERT), 5-HT 2A receptor density is decreased and, at a functional level, the head-twitch response following the administration of DOI, an index of activation of 5-HT 2A receptors, is reduced. Taken together, these studies led us to hypothesize that the efficacy of LSD in establishing stimulus control is diminished or abolished in mice lacking the serotonin transporter. Objective Determine the efficacy of LSD for establishing stimulus control in SERT knockout (KO) mice. Methods SERT KO mice and wildtype (WT) littermates were trained in a visual discrimination on a progressive fixed ratio (FR) water-reinforced task and subsequently trained on a FR10 schedule with LSD (0.17 or 0.30 mg/kg) or vehicle. To control for general deficiencies in drug discrimination, mice were trained with pentobarbital (15 or 30 mg/kg) or vehicle. Results The visual stimulus exerted control in both genotypes. LSD-induced stimulus control in 90% of WT mice but only 31% of SERT KO mice. In contrast, pentobarbital-induced stimulus control in 80% of WT mice and 54% of knockout mice. Conclusions Although SERT KO mice exhibited stimulus control by the non-serotonergic drug, pentobarbital, the efficacy of LSD in these animals was markedly decreased, suggesting that reduced density of 5-HT 1A and/or 5-HT 2A receptors underlies the absence of stimulus control by LSD.

Preparation and biodistribution of 99mTc-tricarbonyl complex with 4-[(2-methoxyphenyl)piperazin-1-yl]-dithioformate as a potential 5-HT 1A receptor imaging agent

The goal of this study is to develop a novel 5-HT 1A receptor imaging agent. 4-[(2-methoxyphenyl)piperazin-1-yl]-dithioformate (MPPDTF) was labeled with 99mTc-tricarbonyl core via dithioformate moiety in high yield (>96% by HPLC). 99mTc(CO) 3–MPPDTF is a neutral and lipophilic complex, which was confirmed by paper electrophoresis and octanol/water partition coefficient ( P=27.0±1.4, n=3), respectively. In vivo biodistribution indicated that this complex had moderate brain uptake (0.53±0.10% ID/g at 5 min and 0.42±0.02% ID/g at 120 min) and good retention (about 80% of the activity was retained in the brain at 120 min post-injection). Regional brain distribution study showed that hippocampus, where the 5-HT 1A receptor density is high, had the highest uptake (0.60±0.02% ID/g at 5 min p.i.) and the cerebellum, where the 5-HT 1A receptor density is low, had the lowest uptake (0.10±0.02% ID/g at 5 min p.i.). After blocking with 8-OH-DPAT, the hippocampus uptake was decreased obviously while the cerebellum uptake was increased slightly. This result indicates that 99mTc(CO) 3–MPPDTF complex has specific binding to 5-HT 1A receptor.

Caffeine protects Alzheimer’s mice against cognitive impairment and reduces brain β-amyloid production

A recent epidemiological study suggested that higher caffeine intake over decades reduces the risk of Alzheimer’s disease (AD). The present study sought to determine any long-term protective effects of dietary caffeine intake in a controlled longitudinal study involving AD transgenic mice. Caffeine (an adenosine receptor antagonist) was added to the drinking water of amyloid precursor protein, Swedish mutation (APPsw) transgenic (Tg) mice between 4 and 9 months of age, with behavioral testing done during the final 6 weeks of treatment. The average daily intake of caffeine per mouse (1.5 mg) was the human equivalent of 500 mg caffeine, the amount typically found in five cups of coffee per day. Across multiple cognitive tasks of spatial learning/reference memory, working memory, and recognition/identification, Tg mice given caffeine performed significantly better than Tg control mice and similar to non-transgenic controls. In both behaviorally-tested and aged Tg mice, long-term caffeine administration resulted in lower hippocampal β-amyloid (Aβ) levels. Expression of both Presenilin 1 (PS1) and β-secretase (BACE) was reduced in caffeine-treated Tg mice, indicating decreased Aβ production as a likely mechanism of caffeine’s cognitive protection. The ability of caffeine to reduce Aβ production was confirmed in SweAPP N2a neuronal cultures, wherein concentration-dependent decreases in both Aβ1–40 and Aβ1–42 were observed. Although adenosine A 1 or A 2A receptor densities in cortex or hippocampus were not affected by caffeine treatment, brain adenosine levels in Tg mice were restored back to normal by dietary caffeine and could be involved in the cognitive protection provided by caffeine. Our data demonstrate that moderate daily intake of caffeine may delay or reduce the risk of AD.

Parallel regulation by olanzapine of the patterns of expression of 5-HT 2A and D 3 receptors in rat central nervous system and blood cells

Patterns of protein expression can be used to identify biomarkers of disease, prognosis or treatment response. Peripheral 5-HT 2A and D 3 receptors have been proposed as protein markers in schizophrenia. We investigated the possible parallel regulation of these candidate biomarkers in central nervous system (CNS) and peripheral blood cells by a comparative study of the effects of antipsychotic treatment on the expression of the receptors in both systems in rats. Acute (24 and 48 h) and subchronic (16 days) treatment of rats with olanzapine induced a significant decrease in 5-HT 2A receptor density both in frontal cortex ( B max = 76.2%, 83.0% and 46.0% of control after 24 h, 48 h and 16 days of treatment, respectively; P < 0.01) and blood platelets ( B max ≈ 55% of control at all times measured; P < 0.01), without any changes in receptor affinity. Furthermore, olanzapine induced redistribution in 5-HT 2A-like immunoreactivity and time-dependent remodelling of synaptic circuits involved in the activity of pyramidal and GABAergic neurons in frontoparietal motor cortex of treated rats, as assessed by immunohistochemical studies. D 3 receptor mRNA levels increased significantly by 52.5% ( P < 0.01) and 21.1% ( P < 0.05) in nucleus accumbens, and by 53.4% ( P < 0.05) and 91.7% ( P < 0.01) in lymphocytes, after acute (24 h and 48 h) treatment with olanzapine, returning to levels similar to control after subchronic treatment (16 days). In conclusion, we observed in rats after olanzapine treatment: (1) parallelism in the regulation of 5-HT 2A receptors in frontal cortex and in blood platelets; (2) parallelism in the regulation of D 3 mRNA levels in nucleus accumbens and lymphocytes. These results endorse the interest in future studies aimed at validating these receptors as candidate biomarkers in schizophrenia.

Cortical Serotonin 5-HT&lt;char aid="99791656" id="sub"&gt;2A&lt;/char&gt; Receptor Binding and Social Communication in Adults With Asperger’s Syndrome: An in Vivo SPECT Study

Objective: The cause of autistic spectrum disorder (i.e., autism and Asperger’s syndrome) is unknown. The serotonergic (5-HT) system may be especially implicated. However, cortical 5-HT 2A receptor density in adults with the disorder has not been examined, to the authors’ knowledge. Method: The authors investigated cortical 5-HT 2A receptor binding in eight adults with Asperger’s syndrome and in 10 healthy comparison subjects with single photon emission computed tomography and the selective 5-HT 2A receptor ligand 123I iodinated 4-amino-N-[1-[3-(4-fluorophenoxy)propyl]-4-methyl-4-piperidinyl]-5-iodo-2-methoxybenzamide ( 123 I-5-I-R91150). Results: People with Asperger’s syndrome had a significant reduction in cortical 5-HT 2A receptor binding in the total, anterior, and posterior cingulate; bilaterally in the frontal and superior temporal lobes; and in the left parietal lobe. Also, reduced receptor binding was significantly related to abnormal social communication. Conclusions: The authors’ findings suggest that adults with Asperger’s syndrome have abnormalities in cortical 5-HT 2A receptor density and that this deficit may underlie some clinical symptoms.

Serotonin 1A and 2A receptor densities, neurochemical and behavioural characteristics in two closely related mice strains after long-term isolation

Knowledge about individual differences in behavioural traits and their neurostructural and neurochemical correlates should improve therapeutic approaches of corresponding psychopathology. The presented investigations are aimed to reveal interrelationships between central nervous serotonergic [5-HT] receptor densities and neurochemical as well as behavioural traits in two mice strains. Male AB-Halle [ABH] and AB-Gatersleben [ABG] mice differing in aggression were investigated after 6 weeks of isolation housing. 5-HT1A and 5-HT2A receptors were analysed in different brain regions by in vitro autoradiography. HPLC determinations of aminergic transmission in the cortex, hippocampus, striatum as well as in the raphe-region and radioimmunoassay determination of serum corticosterone were done before (basal condition) and after behavioural tests (challenge condition). Receptor autoradiography revealed higher 5-HT1A receptor densities, especially in limbic regions, and lower 5-HT2A receptor densities in the basal ganglia of ABH mice. Furthermore, ABH mice characterized as behaviourally more active in the open field and plus maze as well as more reactive and aggressive during the social interaction test showed lower basal 5-hydroxyindolacetic acid [5-HIAA] concentrations in the hippocampus, cortex and raphe-region as well as a different activation pattern in serotonergic, dopaminergic and noradrenergic brain systems after challenge in comparison to ABG mice. Additionally lower corticosterone concentrations were found in ABH mice. Lower basal serotonergic and striatal dopaminergic, but higher basal cortical dopaminergic metabolism in contrast to enhanced challenge-induced central nervous serotonergic and cortical dopaminergic reactivities are discussed to be crucial for an enhanced reactive behavioural trait, which could secondarily result in aggression-related behaviours, where higher 5-HT1A receptor and lower 5-HT2A receptor densities may be essential.

Increased density and synapto-protective effect of adenosine A2A receptors upon sub-chronic restraint stress

Stress initially causes adaptive changes in the brain and can lead to neurodegeneration if continuously present. Noxious brain conditions trigger the release of adenosine that can control brain function and neurodegeneration through inhibitory A1 and facilitatory A2A receptors. We tested the effect of restraint stress on the density of adenosine receptors and their effect on the outcome of stress, focusing in a known affected region, the hippocampus. Sub-chronic restraint stress (6 h/day for 7 days) caused a parallel decrease of the density of A1 receptors (15–20%) and an increase (near 250%) of A2A receptor density in rat hippocampal nerve terminals. This indicates that sub-chronic stress unbalances adenosine receptors, up-regulating A2A and down-regulating A1 receptors. Sub-chronic stress did not cause hippocampal neurodegeneration but decreased the immunoreactivity (immunohistochemistry and Western blot) of a synaptic marker, synaptophysin. The blockade of A2A receptors with 7-(2-phenylethyl)-5-amino-2-(2-furyl)-pyrazolo-[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidine (0.05 mg/kg, daily i.p. injection) attenuated the loss of synaptophysin immunoreactivity observed in the hippocampus of rats subjected to sub-chronic restraint stress. This ability of A2A receptor antagonists to prevent the earliest stress-induced synaptic modifications provides a neurochemical and morphological correlate for the interest of A2A receptor antagonists to attenuate the burden of chronic stress.

Maternal separation alters serotonergic transporter densities and serotonergic 1A receptors in rat brain

Rationale The basic mechanisms underlying the association between early life maternal separation and adulthood psychiatric disorders are largely unknown. One possible candidate is the central serotonergic system, which is also abnormal in psychiatric illnesses. Neuroadaptational changes in serotonergic transporter and serotonergic 1A receptors may underlie links between early life stress and adulthood psychiatric disorders. Objective The aim of this study was to investigate the consequences of a rat model of maternal separation on serotonergic transporter and serotonergic 1A receptor densities and function in adult rat forebrain. Methods Rat pups were separated from dams from postnatal day 2 to postnatal day 14, each day, for zero time, 15 min and 180 min to determine the time-course of effects. A non-handled group was added to control for the effects of handling by an experimenter compared with the animal facility-reared group. Quantitative [ 125I]3β-(4-iodophenyl)tropan-2β-carboxylic acid methyl ester and [ 125I]-mPPI autoradiography was used to determine serotonergic transporter and serotonergic 1A densities, respectively. Adult rats were challenged with saline or serotonergic 1A agonist (+) 8-hydroxy-2-(di- n-propylamino)tetralin, 0.4 mg/kg, s.c.) and plasma adrenocorticotropic hormone and corticosterone were determined. Results serotonergic transporter and serotonergic 1A densities were significantly lower in the non-handled group in the paraventricular, arcuate, dorsomedial and ventromedial nuclei of the hypothalamus. The non-handled group also displayed lower serotonergic transporter and serotonergic 1A densities in the basolateral anterior, basolateral ventral and basomedial amygdaloid nuclei. Serotonergic transporter densities were also decreased in the CA3 area of the hippocampus in the non-handled group. In contrast, the maternal separation 15 min group displayed the highest serotonergic transporter and serotonergic 1A densities in the basomedial nucleus of amygdala, basolateral anterior nucleus of amygdala, basolateral ventral nucleus of amygdala and basomedial nucleus of amygdala amygdaloid nuclei. Conclusions Early life maternal separation and the extent of handling can alter adult brain serotonergic transporter and serotonergic 1A levels and function in the forebrain. Alterations in these serotonergic systems by early rearing conditions might increase vulnerability for behavioral disorders in adulthood.

Desensitization of 5-HT 2A receptor function by chronic administration of selective serotonin reuptake inhibitors

We have previously shown that chronic treatment with selective serotonin reuptake inhibitors (SSRIs), fluvoxamine and paroxetine, attenuated m-chlorophenylpiperazine ( mCPP)-induced hypolocomotion in rats. The effect of these SSRIs on the response to mCPP is thought to be caused by the desensitization of 5-HT 2C receptor function. In the present study, we investigated whether chronic administration of SSRI could reduce another pharmacological response to mCPP in rats, i.e., the induction of the secretion of corticosterone. The mCPP-induced increase in the serum concentration of corticosterone was not blocked by the 5-HT 2C antagonist SB242084, but was blocked by the 5-HT 2A antagonist ketanserin. Chronic treatment with fluvoxamine and paroxetine attenuated the response to mCPP, while these SSRIs had no effects in control rats. These results suggest that the desensitization of 5-HT 2A receptor function occurs in the same way as that of 5-HT 2C receptor function through chronic treatment with either fluvoxamine or paroxetine as a consequence of prolonged exposure to elevated levels of serotonin. The hypersensitivity of 5-HT 2A receptors is observed in depressed patients, and chronic treatment with many antidepressants such as tricyclic antidepressants have been reported to reduce 5-HT 2A receptor density and/or efficacy. The desensitization of 5-HT 2A receptor function might contribute to the therapeutic mechanism of action of these SSRIs, as seen with other classes of antidepressants.

Modification of adenosine A 1 and A 2A receptor density in the hippocampus of streptozotocin-induced diabetic rats

Adenosine A 1 and A 2A receptors are neuromodulatory systems that can control mnemonic behavior, which is modified by diabetes. Since the density of these adenosine receptors can change upon chronic noxious brain conditions, we now tested if the density of A 1 and A 2A receptors was modified in the hippocampus of streptozotocin-induced diabetic rats. The binding density of the selective A 1 receptor antagonist, 3H-DPCPX, was decreased by 36% in total hippocampal membranes 7 days after induction of diabetes and this down-regulation was maintained after 30 and 90 days, which was also confirmed by Western blot analysis of A 1 receptor immunoreactivity. In contrast, the binding density of the selective A 2A receptor antagonist, 3H-SCH 58261, was enhanced by 83% in total hippocampal membranes 7 days after induction of diabetes and this up-regulation persisted after 30 and 90 days. These results show that the balance between inhibitory A 1 and facilitatory A 2A adenosine receptors is modified in the hippocampus of streptozotocin-induced diabetic rats. Thus, the most abundant A 1 receptors are down-regulated and there is an up-regulation of A 2A receptors, suggesting a gain of function of hippocampal A 2A receptors compared to A 1 receptors in diabetes, as has been observed in other chronic noxious brain conditions where A 2A receptor blockade affords robust neuroprotection.

Greater adenosine A 2A receptor densities in cardiac and skeletal muscle in endurance-trained men: a [ 11C]TMSX PET study

We examined the densities of adenosine A 2A receptors in cardiac and skeletal muscles between untrained and endurance-trained subjects using positron emission tomography (PET) and [7- methyl- 11C]-( E)-8-(3,4,5-trimethoxystyryl)-1,3,7-trimethylxanthine ([ 11C]TMSX), a newly developed radioligand for mapping adenosine A 2A receptors. Five untrained and five endurance-trained subjects participated in this study. The density of adenosine A 2A receptors was evaluated as the distribution volume of [ 11C]TMSX in cardiac and triceps brachii muscles in the resting state using PET. The distribution volume of [ 11C]TMSX in the myocardium was significantly greater than in the triceps brachii muscle in both groups. Further, distribution volumes [ 11C]TMSX in the trained subjects were significantly grater than those in untrained subjects (myocardium, 3.6±0.3 vs. 3.1±0.4 ml g −1; triceps brachii muscle, 1.7±0.3 vs. 1.2±0.2 ml g −1, respectively). These results indicate that the densities of adenosine A 2A receptors in the cardiac and skeletal muscles are greater in the endurance-trained men than in the untrained men.

Studies on the chemistry of thienoanellated O, N- and S, N-containing heterocycles. Part 30: Synthesis and pharmacological properties of thieno[2,3- b][1,4]thiazines with potential vasopressin receptor antagonistic activity

A series of new nonpeptide vasopressin antagonists with a 6-ethyl-thieno[2,3- b][1,4]thiazine or 6-benzyl-thieno[2,3- b][1,4]thiazine skeleton and structural modifications of the aryl side chain were synthesized in this study. The effects on guinea pig heart and smooth muscle preparations were investigated. In the presence of AVP the compounds showed an antagonistic effect. The compounds did not change spontaneous rate in right atria and exerted a slight but not significant negative inotropic effect in papillary muscles. The relaxing effect on vascular smooth muscle and terminal ileum was far more pronounced. Generally the relaxing effect on terminal ilea was more potent maybe due to difference in V 1a receptor density. Our results demonstrate that compounds with an ethyl group in position six on the thienothiazine ring ( 14, 16, 18 and 22) exerted the most potent relaxing activity in terminal ilea, whereas compounds with a phenyl ring in position six reduced this effect.

Effects of donepezil, nicotine and haloperidol on the central serotonergic system in mice: Implications for Tourette's syndrome

We have previously reported that acute and chronic donepezil and nicotine administration significantly attenuate DOI-induced head twitch response (HTR) in mice. This behavior, primarily mediated by stimulation of 5-HT 2A receptors, has been proposed to model tic symptoms seen in Tourette's syndrome (TS). Haloperidol, a drug widely used to treat symptoms of TS, has also been reported to reduce DOI-induced head shakes in rodents when administered acutely. These findings suggest an inhibitory interaction of these drugs with 5-HT 2A receptors. To test this hypothesis, we evaluated the effects of chronic donepezil, nicotine and haloperidol on expression levels of 5-HT 2A mRNA and 5-HT 2A receptor density in select brain regions. Initially, we established a dose–response relationship for the acute and chronic haloperidol and DOI-induced HTR. Male ICR mice were treated twice daily with donepezil (0.1 mg/kg), nicotine (0.5 mg/kg), and once daily with haloperidol (0.4 mg/kg) for 14 days and were sacrificed 16–18 h after the last injection. These drug regimens were chosen because of their significant effects on DOI-induced HTR. Donepezil significantly increased 5-HT 2A mRNA level, but not the receptor density in the striatum. In the midbrain, donepezil significantly decreased the receptor density without affecting the 5-HT 2A mRNA level. In the frontal cortex, only haloperidol significantly reduced the 5-HT 2A receptor density. The cortex was the only area where donepezil, nicotine and haloperidol significantly reduced the 5-HT 2A receptor density. The results suggest that the anti-tic properties of donepezil, nicotine and haloperidol in this paradigm might be due to antagonism of cortical 5-HT 2A receptors. Thus, further investigation of involvement of cortical 5-HT 2A receptors in TS as well as evaluation of selective 5-HT 2A receptor antagonists in this disorder is warranted.

Long‐term Effect of Convulsive Behavior on the Density of Adenosine A1 and A2A Receptors in the Rat Cerebral Cortex

Adenosine is a neuromodulator that has been proposed to act as an anticonvulsant mainly via inhibitory A1 receptors, but recent data show that genetic deletion of facilitatory A 2A receptors might also attenuate convulsions. Since both A1 and A 2A receptors are prone to down- and upregulation in different stressful situations, we investigated if convulsive behavior leads to a long-term change in A1 and A 2A receptor density in the rat cerebral cortex. Stage 4-5 convulsions (Racine's scale) were induced in adult Wistar rats either through amygdala stimulation (kindling) or by intraperitoneal injection of kainate (10 mg/ml). Rats were killed after 4 weeks to evaluate adenosine A1 and A 2A receptor density in the cerebral cortex using both Western blot and membrane binding assays. The binding density of the A1 antagonist, 3H-DPCPX, decreased by 40. +/- 4.4% and by 20.7 +/- 0.5% after kindling or kainate injection. Likewise, A1 receptor immunoreactivity in cortical membranes from kindled or kainate-injected rats decreased by 19.1 +/- 3.3% and 12.7 +/- 5.7%, respectively. In contrast, the binding density of the A 2A receptor antagonist 3H-SCH 58261 increased by 293 +/- 34% and by 159 +/- 32% in cortical membranes from kindled or kainate-injected rats, and A 2A receptor immunoreactivity also increased by 151 +/- 12% and 79.6 +/- 7.0%. This indicates that after convulsive behavior there is a long-term decrease of A1 receptors accompanied by an increased density of A 2A receptors, suggesting that A 2A antagonists rather than A1 agonists may be more promising anticonvulsive drugs.

Influence of forced swimming stress on 5-HT 1A receptors and serotonin levels in mouse brain

Several stressful factors are able to modify 5-HT 1A receptors; for example, different schemes of forced swimming-induced stress (FS) produce a variety of changes in synthesis as well as in 5-HT 1A binding in the brain. In addition, it is known that the concentration of 5-HT in the brain is modified as a consequence of acute stressing. The main purpose of this study was to characterize the influence of 15 min of FS on 5-HT levels and on 5-HT 1A receptor density in specific brain areas. Mice stressed 24 h before were sacrificed and their brains processed by means of a quantitative autoradiography technique. The following areas were studied: dorsal raphe nucleus (DRN); median raphe nucleus (MRN); thalamus; hypothalamus; amygdala, and hippocampus. 5-HT and 5-hydroxyindolacetic acid (5-HIAA) concentrations in the brainstem, thalamus–hypothalamus, and hippocampus of stressed (ST) mice were analyzed 24 h after stressing by high performance liquid chromatography (HPLC) with fluorometric detection. All data were compared with corresponding unstressed (UST) controls. A significant decrease in 5-HT 1A receptor density in DRN, MRN, and hippocampus, accompanied by an increase in labeling of 5-HT 1A receptor in thalamus, hypothalamus, and amygdala was observed in ST animals. FS induced a decrease in the 5-HT concentration in the thalamus–hypothalamus, accompanied by an increase in hippocampus areas without affecting 5-HT concentration in the brainstem. Additionally, 5-HIAA/5-HT ratio in the thalamus–hypothalamus area was increased. This study showed that stress alters both 5-HT concentration and 5-HT 1A receptors in a region-specific manner.

Loss of serotonin 5-HT2A receptors in the postmortem temporal cortex correlates with rate of cognitive decline in Alzheimer’s disease

Previous studies have demonstrated reductions of serotonin 5-HT 2A receptors in the neocortex of Alzheimer's disease (AD) patients. However, it is unclear whether such losses play a role in the cognitive decline of AD. To correlate neocortical 5-HT 2A receptor alterations with cognitive decline in AD. Postmortem frontal and temporal cortical 5-HT 2A receptors were measured by [3H]ketanserin binding in aged controls as well as in a cohort of AD patients who had been longitudinally assessed for cognitive decline and behavioral symptoms. 5-HT 2A receptor densities in both regions were reduced in severely demented AD patients compared to age-matched controls. In the temporal cortex, this reduction also correlated with the rate of decline of Mini-Mental State Examination (MMSE) scores. The association between 5-HT 2A receptor loss and cognitive decline was independent of the effects of choline acetyltransferase (ChAT) activity and presence of behavioral symptoms. Our data suggest that loss of neocortical 5-HT 2A receptors may predict for faster cognitive decline in AD, and point to serotomimetics as potentially useful adjuvants to cholinergic replacement therapies.

No effect of MDMA (ecstasy) on cell death and 5-HT 2A receptor density in organotypic rat hippocampal cultures

MDMA (3,4 Methylenedioxy-methamphetamine) binds and blocks the presynaptic serotonin reuptake transporters and postsynaptic serotonin 5-HT 2A receptors, with highest affinity for the first. Whether 5-HT 2A receptor density decreases due to MDMA's direct effect on postsynaptic serotonin receptors is at present not known. This study analyzes whether direct stimulation of the postsynaptic 5-HT 2A receptor by MDMA in organotypic hippocampal cultures results in cell death and downregulation of this receptor. Fifty or 100 μM MDMA was added to 1 week old cultures, made of 11 day old rat pups. Fluorojade and immunostaining for MAP2 and 5-HT 2A to determine neurodegeneration, and changes in receptor density, respectively, resulted in no significant differences. MDMA's neurotoxicity and regulation of post-synaptic 5-HT 2A receptors thus seems to require the presence of intact serotonergic terminals.

Prenatal cocaine exposure potentiates paroxetine-induced desensitization of 5-HT 2A receptor function in adult male rat offspring

This study investigated the ability of prenatal exposure to cocaine to alter serotonin 2A (5-HT 2A) receptor function and paroxetine-induced desensitization of 5-HT 2A receptor function in rat offspring. Following exposure to saline or (−)cocaine (15 mg/kg, s.c., b.i.d.), during gestational days 13–20, adult male offspring were treated with either saline or paroxetine (10 mg/kg/day, i.p. 14 days). Eighteen hours post-treatment, changes in the stimulation of oxytocin, adrenocorticotropic hormone (ACTH) and corticosterone by (−)4-iodo-2,5-dimethoxyphenylisopropylamine (DOI, 0.5 or 2.0 mg/kg, s.c.) and in 5-HT 2A receptor densities were determined. Prenatal cocaine exposure did not alter 5-HT 2A receptor-mediated neuroendocrine responses or 5-HT 2A receptor densities. In contrast, paroxetine treatment reduced cortical 5-HT 2A receptors (18–25%) and desensitized 5-HT 2A receptor-mediated oxytocin responses in both offspring groups. Furthermore, in cocaine offspring, paroxetine produced an inhibition of 5-HT 2A receptor-mediated increase in plasma ACTH levels and a greater attenuation of the oxytocin responses to (−)DOI. Paroxetine-induced reductions in body weight gain (−8.8%) were comparable in both offspring groups. These data, demonstrating that prenatal exposure to cocaine potentiates paroxetine-induced desensitization of 5-HT 2A receptor function, may be clinically relevant with respect to treating mood disorders in adults exposed in utero to cocaine.

Region specific changes in forebrain 5-hydroxytryptamine 1a and 5-hydroxytryptamine 2a receptors in isolation-reared rats: an in vitro autoradiography study

The neurochemical correlates of the behavioural consequences of isolation rearing of rats are complex and involve many neurotransmitters, including the serotonergic system. Impaired functioning of the ascending serotonergic system has been implicated in many neuropsychiatric syndromes, including attention deficit hyperactivity disorder and schizophrenia. In the present investigation serotonergic function was assessed using in vitro receptor autoradiography. The 5-hydroxytryptamine 2A (5-HT 2A) receptor antagonist [ 3H]ketanserin and the 5-HT 1A receptor antagonist, [ 3H]WAY100, 635 were used to compare 5-HT receptor subtype densities in the forebrains of socially and isolation-reared rats. Regions of highest receptor density were observed in the frontal cortex for 5-HT 2A receptors and in the frontal cortex, dorsal hippocampus and lateral septum for 5-HT 1A receptors. In isolation-reared rats, 5-HT 2A receptor binding site densities were significantly increased by between 36 and 67% in the prelimbic, motor and cingulate cortices compared with socially reared controls. By contrast, 5-HT 1A receptor binding site densities were significantly reduced by 22% in the prelimbic cortex, and significantly increased by between 10 and 50% in the motor cortex, somatosensory cortex, dentate gyrus and CA fields of the hippocampus. These data demonstrate that isolation-rearing produces significant effects on forebrain 5-HT 1A and 5-HT 2A receptor densities in the adult rat. It is hypothesised that altered serotonergic function, particularly in the hippocampus and prefrontal cortex, may underlie some of the behavioural abnormalities associated with isolation-rearing.