5-HT1A receptors within the intermediate lateral septum modulate stress vulnerability in male mice

Chronic stress is a major risk factor for psychiatric disorders. However, certain individuals may be at higher risk due to greater stress susceptibility. Elucidating the neurobiology of stress resilience and susceptibility may facilitate the development of novel strategies to prevent and treat stress-related disorders such as depression. Mounting evidence suggests that the serotonin (5-HT) system is a major regulator of stress sensitivity. In this study, we assessed the functions of 5-HT1A and 5-HT2A receptors within the lateral septum (LS) in regulating stress vulnerability. Among a group of male mice exposed to chronic social defeat stress (CSDS), 47.2% were classified as stress-susceptible, and these mice employed more passive coping strategies during the defeat and exhibited more severe anxiety- and depression-like behaviors during the following behavioral tests. These stress-susceptible mice also exhibited elevated neuronal activity in the LS as evidenced by greater c-Fos expression, greater activity of 5-HT neurons in both the dorsal and median raphe nucleus, and downregulated expression of the 5-HT1A receptor in the intermediate LS (LSi). Finally, we found the stress-induced social withdrawal symptoms could be rapidly relieved by LSi administration of 8-OH-DPAT, a 5-HT1A receptor agonist. These results indicate that 5-HT1A receptors within the LSi play an important role in stress vulnerability in mice. Therefore, modulation of stress vulnerable via 5-HT1A receptor activation in the LSi is a potential strategy to treat stress-related psychiatric disorders.

Impact of Serotonergic 5HT1A and 5HT2A Receptor Activation on the Respiratory Response to Hypercapnia in a Rat Model of Parkinson's Disease

In Parkinson's disease (PD), along with typical motor dysfunction, abnormal breathing is present; the cause of which is not well understood. The study aimed to analyze the effects of stimulation of the serotonergic system with 5-HT1A and 5-HT2A agonists in a model of PD induced by injection of 6-hydroxydopamine (6-OHDA). To model PD, bilateral injection of 6-OHDA into both striata was performed in male Wistar rats. Respiratory disturbances in response to 7% hypercapnia (CO2 in O2) in the plethysmographic chamber before and after stimulation of the serotonergic system and the incidence of apnea were studied in awake rats 5 weeks after 6-OHDA or vehicle injection. Administration of 6-OHDA reduced the concentration of serotonin (5-HT), dopamine (DA) and norepinephrine (NA) in the striatum and the level of 5-HT in the brainstem of treated rats, which have been associated with decreased basal ventilation, impaired respiratory response to 7% CO2 and increased incidence of apnea compared to Sham-operated rats. Intraperitoneal (i.p.) injection of the 5-HT1AR agonist 8-OH-DPAT and 5-HT2AR agonist NBOH-2C-CN increased breathing during normocapnia and hypercapnia in both groups of rats. However, it restored reactivity to hypercapnia in 6-OHDA group to the level present in Sham rats. Another 5-HT2AR agonist TCB-2 was only effective in increasing normocapnic ventilation in 6-OHDA rats. Both the serotonergic agonists 8-OH-DPAT and NBOH-2C-CN had stronger stimulatory effects on respiration in PD rats, compensating for deficits in basal ventilation and hypercapnic respiration. We conclude that serotonergic stimulation may have a positive effect on respiratory impairments that occur in PD.

Establishing an OCD Model in BALB/c Mice Using RU24969: A Molecular and Behavioural Study of Optimal Dose Selection

Obsessive-compulsive disorder (OCD) is a disabling disease characterized by distressing obsessions and repetitive compulsions. The etiology of OCD is poorly known, and mouse modeling allows to clarify the genetic and neurochemical basis of this disorder and to investigate potential treatments. This study evaluates the impact of the 5-HT1B agonist RU24969 on the induction of OCD-like behaviours in female BALB/c mice (n = 30), distributed across five groups receiving varying doses of RU24969. Behavioural assessments, including marble test, tail suspension test, sucrose preference test, forced swim test, and nestlet shredding test, were conducted. Gene expression and protein quantitation of Gabra1 and serotonin transporter in mouse brain were also performed. Marble-burying behaviour increased significantly at high doses of RU24969 (15-20 mg/kg). The forced swimming test consistently showed elevated values at the same high concentrations, compared to the control. Altered reward-seeking behaviour was indicated by the sucrose preference test, notably at 15 and 20 mg/kg doses of RU24969. Nestlet shredding results did not show statistical significance among the tested animal groups. Gene expression analysis revealed reduced Gabra1 expression with increasing doses of RU, while serotonin transporter was not related to varying doses of RU24969. Western blotting corroborated these trends. The results underscore complex interactions between the serotonin system, GABAergic signaling, and OCD-relevant behaviours and suggest the use of intraperitoneal injection of 15 mg/kg of RU24969 to induce OCD-like behaviour in BALB/c mouse models.

5-HT1F agonists

5-Hydroxytryptamine (HT)/serotonin receptor agonism has been a long-recognized property of triptan medications, and more recently, the study and development of medications with selective binding to the 1F receptor subtype have been explored. While the exact mechanism contributing to decreased symptoms of an acute migraine attack remains unclear, selective 5-HT1F agonists have demonstrated clinical efficacy with lasmiditan as the only approved medication from this class to date. Lasmiditan lacks vasoconstrictive properties, giving it utility in specific patient populations in whom triptans should be avoided. Availability, central nervous system (CNS) side effects, and 8-hour driving restriction may affect its clinical use.

Beneficial effect of 5-HT1b/1d agonist on Parkinson's disease by modulating glutamate and reducing deposition of α-synuclein

The given investigation examined the neuroprotection role of 5-HT1b/1d agonist in reserpine induced Parkinson's disease (PD) in male Wistar rats. PD was induced in rats by reserpine at 5 mg/kg ip for 3 days and thereafter the rats were provided with the following treatments for 4 days, zolmitriptan (ZLM) group (30 mg/kg ip); STD group (levodopa + carbidopa, 200 + 5 mg/kg ip); ZLM + GA group (zolmitriptan, 30 mg/kg ip and glutamic acid, 1.5 mg/kg); ZLM + DX group (zolmitriptan, 30 mg/kg ip and dextromethorphan, 20 mg/kg ip). All the groups were then assessed for cognitive and motor functions at the end of the protocol. Moreover, oxidative stress parameters and histopathological changes were observed in rats of all treatment groups. Deposition of α-synuclein in the brain tissue was observed by silver staining. Data of this investigation revealed that motor and cognitive functions were improved in the ZLM-treated group compared with the negative control group, which was observed to be reversed in ZLM + GA group. Treatment with ZLM ameliorated oxidative stress and histopathological changes in the brain tissue of PD rats. Further, ZLM reduced the deposition of α-synuclein in PD rats, which reversed in ZLM + GA-treated group. This study concludes by stating that 5-HT1b/1d agonist can prevent neurodegeneration and reduce oxidative stress in PD rats. The probable underlying mechanism of such an effect of 5-HT1b/1d agonist could be by regulating the deposition of α-synuclein and reducing the expression of NMDA receptor.

Opposing effects of 5-HT1A receptor agonist buspirone on supraspinal abdominal pain transmission in normal and visceral hypersensitive rats

The serotonergic 5-HT1A receptors are implicated in the central mechanisms of visceral pain, but their role in these processes is controversial. Considering existing evidences for organic inflammation-triggered neuroplastic changes in the brain serotonergic circuitry, the ambiguous contribution of 5-HT1A receptors to supraspinal control of visceral pain in normal and post-inflammatory conditions can be assumed. In this study performed on male Wistar rats, we used microelectrode recording of the caudal ventrolateral medulla (CVLM) neuron responses to colorectal distension (CRD) and electromyography recording of CRD-evoked visceromotor reactions (VMRs) to evaluate post-colitis changes in the effects of 5-HT1A agonist buspirone on supraspinal visceral nociceptive transmission. In rats recovered from trinitrobenzene sulfonic acid colitis, the CRD-induced CVLM neuronal excitation and VMRs were increased compared with those in healthy animals, revealing post-inflammatory intestinal hypersensitivity. Intravenous buspirone (2 and 4 mg/kg) under urethane anesthesia dose-dependently suppressed CVLM excitatory neuron responses to noxious CRD in healthy rats, but caused dose-independent increase in the already enhanced nociceptive activation of CVLM neurons in post-colitis animals, losing also its normally occurring faciliatory effect on CRD-evoked inhibitory medullary neurotransmission and suppressive action on hemodynamic reactions to CRD. In line with this, subcutaneous injection of buspirone (2 mg/kg) in conscious rats, which attenuated CRD-induced VMRs in controls, further increased VMRs in hypersensitive animals. The data obtained indicate a shift from anti- to pronociceptive contribution of 5-HT1A-dependent mechanisms to supraspinal transmission of visceral nociception in intestinal hypersensitivity conditions, arguing for the disutility of buspirone and possibly other 5-HT1A agonists for relieving post-inflammatory abdominal pain.

The Serotonin 1A (5-HT1A) Receptor as a Pharmacological Target in Depression

Clinical depression is a common, debilitating and heterogenous disorder. Existing treatments for depression are inadequate for a significant minority of patients and new approaches are urgently needed. A wealth of evidence implicates the serotonin 1A (5-HT1A) receptor in the pathophysiology of depression. Stimulation of the 5-HT1A receptor is an existing therapeutic target for treating depression and anxiety, using drugs such as buspirone and tandospirone. However, activation of 5-HT1A raphe autoreceptors has also been suggested to be responsible for the delay in the therapeutic action of conventional antidepressants such as selective serotonin reuptake inhibitors (SSRIs). This narrative review provides a brief overview of the 5-HT1A receptor, the evidence implicating it in depression and in the effects of conventional antidepressant treatment. We highlight that pre- and post-synaptic 5-HT1A receptors may have divergent roles in the pathophysiology and treatment of depression. To date, developing this understanding to progress therapeutic discovery has been limited, partly due to a paucity of specific pharmacological probes suitable for use in humans. The development of 5-HT1A 'biased agonism', using compounds such as NLX-101, offers the opportunity to further elucidate the roles of pre- and post-synaptic 5-HT1A receptors. We describe how experimental medicine approaches can be helpful in profiling the effects of 5-HT1A receptor modulation on the different clinical domains of depression, and outline some potential neurocognitive models that could be used to test the effects of 5-HT1A biased agonists.

FPT, a 2-Aminotetralin, Is a Potent Serotonin 5-HT1A, 5-HT1B, and 5-HT1D Receptor Agonist That Modulates Cortical Electroencephalogram Activity in Adult Fmr1 Knockout Mice

There are no approved medicines for fragile X syndrome (FXS), a monogenic, neurodevelopmental disorder. Electroencephalogram (EEG) studies show alterations in resting-state cortical EEG spectra, such as increased gamma-band power, in patients with FXS that are also observed in Fmr1 knockout models of FXS, offering putative biomarkers for drug discovery. Genes encoding serotonin receptors (5-HTRs), including 5-HT1A, 5-HT1B, and 5-HT1DRs, are differentially expressed in FXS, providing a rationale for investigating them as pharmacotherapeutic targets. Previously we reported pharmacological activity and preclinical neurotherapeutic effects in Fmr1 knockout mice of an orally active 2-aminotetralin, (S)-5-(2'-fluorophenyl)-N,N-dimethyl-1,2,3,4-tetrahydronaphthalen-2-amine (FPT). FPT is a potent (low nM), high-efficacy partial agonist at 5-HT1ARs and a potent, low-efficacy partial agonist at 5-HT7Rs. Here we report new observations that FPT also has potent and efficacious agonist activity at human 5-HT1B and 5-HT1DRs. FPT's Ki values at 5-HT1B and 5-HT1DRs were <5 nM, but it had nil activity (>10 μM Ki) at 5-HT1FRs. We tested the effects of FPT (5.6 mg/kg, subcutaneous) on EEG recorded above the somatosensory and auditory cortices in freely moving, adult Fmr1 knockout and control mice. Consistent with previous reports, we observed significantly increased relative gamma power in untreated or vehicle-treated male and female Fmr1 knockout mice from recordings above the left somatosensory cortex (LSSC). In addition, we observed sex effects on EEG power. FPT did not eliminate the genotype difference in relative gamma power from the LSSC. FPT, however, robustly decreased relative alpha power in the LSSC and auditory cortex, with more pronounced effects in Fmr1 KO mice. Similarly, FPT decreased relative alpha power in the right SSC but only in Fmr1 knockout mice. FPT also increased relative delta power, with more pronounced effects in Fmr1 KO mice and caused small but significant increases in relative beta power. Distinct impacts of FPT on cortical EEG were like effects caused by certain FDA-approved psychotropic medications (including baclofen, allopregnanolone, and clozapine). These results advance the understanding of FPT's pharmacological and neurophysiological effects.

Buspirone, a 5-HT1A agonist attenuates social isolation-induced behavior deficits in rats: a comparative study with fluoxetine

Social isolation is a potent stressor in both humans and animals that results in increased anger-like emotion, (anger in humans), aggression and suicidal ideation in humans [suicidal trait-related behavior in rats (STRB)]. The study's purpose was to compare the effects of buspirone (BUS) and fluoxetine (Flx) on social isolation-induced behavior deficits in rats. The male Wistar rats were randomized into six groups and caged individually for 14 days except for the non stress control (nSC) group. They were then divided into the following groups, stress control (SC), Flx (30), BUS (10), BUS (20) and BUS (40) and treated from day 14 to day 28. On the last day of treatment behavior parameters were recorded. Serum cortisol, blood pressure (BP) measurement, magnetic resonance imaging (MRI) of the rat's brain and brain-derived neurotrophic factor (BDNF) expression were performed. SC group showed a significant increase in anger-like emotion, aggression, irritability score, learned helplessness, increased cortisol level and reduced BDNF. These behavioral deficits were attenuated by BUS and Flx, Both were found to be equally beneficial in preventing anger-like emotions and aggression. Flx, which has been found to promote suicidal thoughts in people, did not reduce irritability in rats, showing that it did not affect it. BUS significantly improved all behavioral traits also reduced cortisol levels, significantly increased BDNF and normalized BP. Neuroimaging studies in SC brains showed a reduction in amygdala size compared to nSC, BUS treatment mitigated this reduction. Buspirone is effective in preventing social isolation induced behavioural-deficits.

The selective 5-HT 1A receptor agonist, NLX-112, overcomes tetrabenazine-induced catalepsy and depression-like behavior in the rat

Tetrabenazine, a preferential inhibitor of the vesicular monoamine transporter type 2, depletes the brain monoamines dopamine, serotonin and norepinephrine. Tetrabenazine and deutetrabenazine (Austedo ®) are used to treat chorea associated with Huntington's disease. However, both compounds are known to aggravate Parkinsonism and depression observed in Huntington's disease patients. NLX-112 (a.k.a. befiradol/F13640) is a highly selective, potent and efficacious serotonin 5-HT 1A agonist. In animal models, it has robust efficacy in combating other iatrogenic motor disorders such as L-DOPA-induced dyskinesia and has marked antidepressant-like activity in rodent tests. In the present study, we investigated, in rats, the efficacy of NLX-112 to counteract tetrabenazine-induced catalepsy (a model of Parkinsonism) and tetrabenazine-induced potentiation of immobility in the forced swim test (FST, a model to detect antidepressant-like activity). The prototypical 5-HT 1A agonist, (±)8-OH-DPAT, and the 5-HT 1A partial agonist/dopamine D2 receptor blocker, buspirone, were used as comparators. Both NLX-112 and (±)8-OH-DPAT (0.16-2.5 mg/kg p.o. or s.c., respectively) abolished catalepsy induced by tetrabenazine (2 mg/kg i.p.). In comparison, buspirone (0.63-5.0 mg/kg p.o.) was ineffective and even tended to potentiate tetrabenazine-induced catalepsy at 0.63 mg/kg. In the FST, NLX-112 and (±)8-OH-DPAT (0.63 mg/kg) strongly reduced immobility when administered alone but also significantly opposed potentiation of immobility induced by tetrabenazine (1.5 mg/kg i.p.). Buspirone (0.63 and 2.5 mg/kg p.o.) had no effect by itself or against tetrabenazine. These results strongly suggest that selective and highly efficacious 5-HT 1A agonists, such as NLX-112, may be useful in combating tetrabenazine-induced Parkinsonism and/or depression in Huntington's disease patients.

The selective 5-HT1A receptor agonist NLX-112 displays anxiolytic-like activity in mice

Anxiety is amongst the commonest neuropsychiatric disorders, and there is a large body of evidence to suggest that abnormalities in serotonergic function are involved in its pathogenesis. Several studies have implicated 5-HT1A receptor activation in mitigating anxiety disorders, so this study investigated the acute effects of a highly selective, potent and efficacious 5-HT1A receptor full agonist, NLX-112 (a.k.a. befiradol, F13640), in middle-aged C57bl/6 J male mice. Video tracking was used to measure several parameters including time spent in the open and closed arms of an elevated plus maze (EPM), distance travelled and thigmotaxis in an open field test (OFT). At 0.1 to 1.0 mg/kg s.c., NLX-112 markedly decreased thigmotaxis and increased exploratory behaviour in the OFT and EPM assays. Hence, at 0.3 mg/kg, NLX-112 augmented locomotor activity in the centre of an open field arena by 164% and increased the time spent in the open arms of the EPM by 119% of control. These results indicate that anxiety-like behaviours in mice are significantly diminished with low doses of NLX-112. NLX-112 may therefore possess anxiolytic properties which complement its known activity in models of movement disorders.

Activation of 5-HT 1b/d receptor restores the cognitive function by reducing glutamate release, deposition of β-amyloid and TLR-4 pathway in the brain of scopolamine-induced dementia in rat

OBJECTIVES

This study evaluates the effect of 5-HT 1b/d agonist on cognitive function in scopolamine (SPN)-induced dementia in the rat.

METHODS

Dementia was induced by administration of SPN 2 mg/kg/day, intraperitoneally, for a duration of 21 days. The effect of zolmitriptan (ZMT) 30 mg/kg, intraperitoneally, was observed on cognitive function, and the parameters of oxidative stress like malondialdehyde (MDA) level, nitric oxide (NO), superoxide dismutase (SOD) and glutathione peroxidase (GPX) were estimated at the end. Histopathology study of brain tissue was performed for the determination of β-amyloid peptide, and qRT-PCR was used to determine the mRNA expression of Toll-like receptor 4 (TLR-4), IL-17 and β-amyloid.

KEY FINDINGS

Data of the study suggested that treatment with ZMT alone and in combination with DMP (dextromethorphan) significantly (P < 0.01) decreases the escape latency in conditioned avoidance response (CAR) and transfer latency in elevated plus maze (EPM) as compared with negative control group. Moreover, the result of Morris water maze (MWM) shows an increase in retention time and a decrease in escape latency in ZMT alone and in combination with DMP-treated group of SPN-induced dementia than in the negative control group. There was a significant decrease in MDA and NO and increase in SOD and GPX in the brain tissues of ZMT and ZMT + DMP-treated group than negative control group. Histopathology study also suggested that the concentration of Aβ peptide decreases in the brain tissues in ZMT and ZMT + DMP-treated group than the negative control group. Moreover, ZMT treatment ameliorates the altered mRNA expression of TLR-4 and IL-17 in the brain tissue of SPN-induced dementia rat.

CONCLUSIONS

In conclusion, ZMT restores the cognitive functions and impaired memory in SPN-induced dementia in the rat by decreasing oxidative stress and Aβ peptide in the brain tissue of rat.

Discriminative stimulus properties of the 5-HT1A receptor biased agonists NLX-101 and F13714, in rats trained to discriminate 8-OH-DPAT from saline

NLX-101 and F13714 are selective, full efficacy, biased agonists of the serotonin (5-HT1A) receptor. NLX-101 preferentially activates cortical postsynaptic 5-HT1A receptors, whereas F13714 preferentially activates raphe nuclei presynaptic 5-HT1A receptors. We compared NLX-101 and F13714 for their efficacy and potency to substitute for the discriminative cue produced by the prototypical, nonbiased 5-HT1A receptor agonist 8-OH-DPAT (racemate). Male and female Sprague-Dawley rats were trained to discriminate 8-OH-DPAT (0.1 mg/kg i.p., 20 min pretreatment) from saline using a classical two-lever drug-discrimination procedure. 8-OH-DPAT (0.01 and 0.05 mg/kg i.p.) dose-dependently substituted for the training dose, with about 50% responding on the 8-OH-DPAT-associated lever at 0.05 mg/kg. F13714 fully and very potently substituted for the training dose of 8-OH-DPAT from 0.018 mg/kg i.p., whereas NLX-101 only achieved full substitution at 0.5 mg/kg i.p., a dose which is known to also activate presynaptic 5-HT1A receptors. The 5-HT1A receptor partial agonist, buspirone, partially substituted (~80%) at 1 and 2 mg/kg i.p., doses which also decreased response rates. F13714 decreased response rates at 0.05 mg/kg. The selective 5-HT1A receptor antagonist WAY-100 635 (1 mg/kg s.c., 40 min pretreatment) elicited almost no responding on the 8-OH-DPAT-associated lever by itself, but blocked the discriminative stimulus effects produced by administration (20 min pretreatment) of 8-OH-DPAT (0.1 mg/kg), F13714 (0.025 mg/kg), NLX-101 (0.5 mg/kg) or buspirone (1 mg/kg). These data suggest that the discriminative cue produced by 0.1 mg/kg i.p. 8-OH-DPAT results from activation of presynaptic 5-HT1A receptors. They also further demonstrate the distinct profiles in behavioral models of 5-HT1A receptor-biased agonists.

The 5-HT1A receptor as a serotonergic target for neuroprotection in cerebral ischemia

Cerebral ischemia due to stroke or cardiac arrest greatly affects daily functioning and the quality of life of patients and has a high socioeconomic impact due to the surge in their prevalence. Advances in the identification of an effective pharmacotherapy to promote neuroprotection and recovery after a cerebral ischemic insult are, however, limited. The serotonin 1A (5-HT_1A) receptor has been implicated in the regulation of several brain functions, including mood, emotions, memory, and neuroplasticity, all of which are deleteriously affected by cerebral ischemia. This review focuses on the specific roles and mechanisms of 5-HT_1A receptors in neuroprotection in experimental models of cerebral ischemia. We present experimental evidence that 5-HT_1A receptor agonists can prevent neuronal damage and promote functional recovery induced by focal and transient global ischemia in rodents. However, indiscriminate activation of pre-and postsynaptic by non-biased 5-HT_1A receptor agonists may be a limiting factor in the anti-ischemic clinical efficacy of these compounds since 5-HT_1A receptors in different brain regions can mediate diverging or even contradictory responses. Current insights are presented into the 'biased' 5-HT_1A post-synaptic heteroreceptor agonist NLX-101 (also known as F15599), a compound that preferentially and potently stimulates postsynaptic cortical pyramidal neurons without inhibiting firing of serotoninergic neurons, as a potential strategy providing neuroprotection in cerebral ischemic conditions.

Role of serotonin in regulation of pancreatic and mesenteric arterial function in diabetic mice

The aim of this study was to investigate the reaction of pancreatic and mesenteric artery to 5-hydroxytryptamine (5-HT, serotonin) and the mechanism of nitric oxide in diabetes. Diabetic mice were induced by streptozotocin through intraperitoneal injection. The vascular tension of the pancreatic, mesenteric and brain basilar arteries in diabetic and control mice were measured by myograph in the applications of angiotensin II, 5-HT, 5-HT_2A receptor agonist 2,5-dimethoxy-4-iodoamphetamine hydrochloride (DOI), 5-HT_1B/1D receptor agonist sumatriptan, 5-HT_2B receptor agonist BW723C86, 5-HT_1D receptor antagonist Palonosetron and 5-HT₂ receptor antagonist Sarpogrelate. The effect of 5-HT on arteries pretreated with L-NAME and sodium nitroprusside (SNP) on arteries pretreated with norepinephrine were measured. The mRNA expressions of eNOS, 5-HT_1B, 5-HT_1D, 5-HT_2A and 5-HT_2B in pancreatic and mesenteric arteries were measured by Real-time PCR. The concentration of 5-HT in plasma and eNOS in pancreatic and mesenteric arteries were tested. Our results showed that the tension of pancreatic and mesenteric arteries in diabetic mice impaired to 5-HT, but not Ang II, and to DOI and sumatriptan, but normalized by incubation with L-NAME. Pancreatic and mesenteric arteries showed no differences to SNP after pretreated with NE between diabetic and control mice. The mRNA of eNOS and 5-HT receptors in pancreatic and mesenteric artery showed no difference between control and diabetic mice. We conclude that the effect of 5-HT on the tension of pancreatic and mesenteric arteries decrease in diabetic mice. It may due to the decreased activity of 5-HT receptors and the activation of eNOS, which causes nitric oxide to release more and makes the tension of vessels decreased.

Activation of 5-HT1A and 5-HT7 receptors enhanced a positively reinforced long-term memory

Memory is one of the most important capabilities of our mind since it determines our individuality. Memory formation involves different stages: acquisition, consolidation and retrieval. There are many studies about early stages, however little is known about memory retrieval. Retrieval is the use of learned information and represents a big problem in patients with memory deficits where the main issue is that they can learn but cannot remember. Previous findings have demonstrated that 5-hydroxytryptamine (5-HT) is a neurotransmitter involved in memory process. Hence, here we are exploring the role of 5-HT in memory retrieval by using its metabolic precursor l-tryptophan and several ligands at 5-HT1A and 5-HT7 receptors. Experimental protocol consisted of evaluating conditioned responses (%CR) after one week of interruption following autoshaping sessions for memory formation; a decrease of %CR was interpreted as memory decay. Systemic administration of: (1) l-tryptophan (50 and 100 mg/kg), (2) 5-HT1A receptor agonist 8-OH-DPAT (0.031 and 0.062 mg/kg), (3) the selective antagonist 5-HT1A receptor WAY 100635 (0.3 and 0.6 mg/kg), (4) the 5-HT7 receptor agonist, LP 211, in a dose-dependent manner (1, 2.5, 5.0 and 10.0 mg/kg) enhanced memory retrieval. Further, the 5-HT7 receptor antagonist, SB 269970 (10.0 mg/kg), had no effect. Finally, SB 269970 (10.0 mg/kg) significantly blocked memory retrieval enhancement produced by 10.0 mg/kg LP 211, but not that induced by 2.5 mg/kg LP 211.These results, taken together, suggest that activation of 5-HT1A and 5-HT7 receptors enhanced memory retrieval and these receptors may be therapeutic targets to improve long-term memory retrieval.

Uncaria rhynchophylla ameliorates unpredictable chronic mild stress-induced depression in mice via activating 5-HT1A receptor: Insights from transcriptomics

BACKGROUND

Depression is a pervasive or persistent mental disorder that causes mood, cognitive and memory deficits. Uncaria rhynchophylla has been widely used to treat central nervous system diseases for a long history, although its efficacy and potential mechanism are still uncertain.

PURPOSE

The present study aimed to investigate anti-depression effect and potential mechanism of U. rhynchophylla extract (URE).

STUDY DESIGN AND METHODS

A mouse depression model was established using unpredictable chronic mild stress (UCMS). Effects of URE on depression-like behaviours, neurotransmitters, and neuroendocrine hormones were investigated in UCMS-induced mice. The potential target of URE was analyzed by transcriptomics and bioinformatics methods and validated by RT-PCR and Western blot. The agonistic effect on 5-HT1A receptor was assayed by dual-luciferase reporter system.

RESULTS

URE ameliorated depression-like behaviours, and modulated levels of neurotransmitters and neuroendocrine hormones, including 5-hydroxytryptamine (5-HT), 5-hydroxyindole acetic acid (5-HIAA), dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), corticosterone (CORT), corticotropin-releasing hormone (CRH), and adrenocorticotropic hormone (ACTH), in UCMS-induced mice. Transcriptomics and bioinformatics results indicated that URE could regulate glutamatergic, cholinergic, serotonergic, and GABAergic systems, especially neuroactive ligand-receptor and cAMP signaling pathways, revealing that Htr1a encoding 5-HT1A receptor was a potential target of URE. The expression levels of downstream proteins of 5-HT1A signaling pathway 5-HT1A, CREB, BDNF, and PKA were increased in UCMS-induced mice after URE administration, and URE also displayed an agonistic effect against 5-HT1A receptor with an EC50 value of 17.42 μg/ml.

CONCLUSION

U. rhynchophylla ameliorated depression-like behaviours in UCMS-induced mice through activating 5-HT1A receptor.

Marble Burying in NMRI Male Mice Is Preferentially Sensitive to Pre- Versus Postsynaptic 5-HT1A Receptor Biased Agonists

Obsessive compulsive disorder (OCD) is a psychiatric disorder characterized by excessive and repetitive thoughts and gestures, mainly treated pharmacologically with selective serotonin reuptake inhibitors (SSRIs). The marble burying test in mice is commonly used to model OCD and has been shown to be sensitive to SSRIs, which decrease burying behavior. The activity of SSRIs in this model is mediated through activation of 5-hydroxytryptamine (5-HT) 1A receptors, but the respective implication of pre- versus postsynaptic 5-HT1A receptors has not been elucidated. Here, we investigated marble burying behavior by male NMRI mice following acute administration of 3 biased agonists, which preferentially activate presynaptic 5-HT1A receptors (F13714) or postsynaptic receptors (NLX-101) or which exhibit balanced activation of both pre- and postsynaptic 5-HT1A receptors (NLX-112). When administered at the dose of 2.5 mg/kg i.p., all 3 biased agonists completely or nearly completely abolished marble burying behavior. However, they varied in their potency with minimal effective doses of 0.16, 0.63, and 2.5 mg/kg i.p., for F13714, NLX-112, and NLX-101, respectively. The selective 5-HT1A receptor antagonist, WAY100,635 was inactive up to 2.5 mg/kg. These results suggest that marble burying behavior in male NMRI mice is preferentially sensitive to activation of pre- versus postsynaptic 5-HT1A receptors. Moreover, they suggest that targeting 5-HT1A receptors with biased agonists could provide an innovative therapeutic approach to combat OCD.

Key role of the 5-HT1A receptor addressing protein Yif1B in serotonin neurotransmission and SSRI treatment

BACKGROUND

Altered function of serotonin receptor 1A (5-HT1AR) has been consistently implicated in anxiety, major depressive disorder and resistance to antidepressants. Mechanisms by which the function of 5-HT1AR (expressed as an autoreceptor in serotonergic raphe neurons and as a heteroreceptor in serotonin [5-HT] projection areas) is altered include regulation of its expression, but 5-HT1AR trafficking may also be involved.

METHODS

We investigated the consequences of the lack of Yif1B (the 5-HT1AR trafficking protein) on 5-HT neurotransmission in mice, and whether Yif1B expression might be affected under conditions known to alter 5-HT neurotransmission, such as anxious or depressive states or following treatment with fluoxetine (a selective serotonin reuptake inhibitor) in humans, monkeys and mice.

RESULTS

Compared with wild-type mice, Yif1B-knockout mice showed a significant decrease in the forebrain density of 5-HT projection fibres and a hypofunctionality of 5-HT1A autoreceptors expressed on raphe 5-HT neurons. In addition, social interaction was less in Yif1B-knockout mice, which did not respond to the antidepressant-like effect of acute fluoxetine injection. In wild-type mice, social defeat was associated with downregulated Yif1B mRNA in the prefrontal cortex, and chronic fluoxetine treatment increased Yif1B expression. The expression of Yif1B was also downregulated in the postmortem prefrontal cortex of people with major depressive disorder and upregulated after chronic treatment with a selective serotonin reuptake inhibitor in monkeys.

LIMITATIONS

We found sex differences in Yif1B expression in humans and monkeys, but not in mice under the tested conditions.

CONCLUSION

These data support the concept that Yif1B plays a critical role in 5-HT1AR functioning and brain 5-HT homeostasis. The opposite changes in its expression observed in anxious or depressive states and after therapeutic fluoxetine treatment suggest that Yif1B might be involved in vulnerability to anxiety and depression, and fluoxetine efficacy.

Targeting the 5-HT1B/1D and 5-HT1F receptors for acute migraine treatment

Migraine is a common and highly disabling headache disorder associated with a substantial socioeconomic burden. Migraine treatments can be categorized as preventive treatment, aimed at reducing the frequency and severity of migraine attacks, and acute therapy, intended to abort attacks. Traditionally, acute treatment can be classified as specific (ergot derivatives and triptans) or nonspecific (analgesics and nonsteroidal anti-inflammatory drugs). Triptans, a class of 5-HT1B/1D receptor agonists with some affinity for the 5-HT1F receptor subtype, have been proven to be efficacious for acute treatment of moderate to severe migraine and have been deemed the gold standard. The availability of triptans in non-oral formulations, such as subcutaneous (SC) and intranasal forms, can be beneficial for patients who suffer from prominent nausea or vomiting, have a suboptimal response to oral agents, and/or seek a more rapid onset of treatment effects. However, triptans are contraindicated in patients with preexisting cardiovascular and/or cerebrovascular diseases due to their 5-HT1B-mediated vasoconstrictive action. For this reason, studies have focused on the development of ditans, a group of antimigraine drugs targeting 5-HT1D and 5-HT1F receptors. Unfortunately, 5-HT1D receptor agonists have been shown to be ineffective in the acute treatment of migraine. Several ditans targeting the 5-HT1F receptor have been developed and have shown no vasoconstrictive effect in preclinical studies, but only two of them, lasmiditan and LY334370, have been tested in clinical trials for migraine, and only lasmiditan has reached to Phase III clinical trials. These Phase III trials have demonstrated the efficacy and safety of lasmiditan, a selective 5-HT1F receptor agonist, in acute migraine treatment. Lasmiditan might offer an alternative migraine therapy without cardiovascular risks. This review will summarize the development of agents targeting the 5-HT1B/1D and 5-HT1F receptors and the clinical evidence supporting the use of these agents for acute migraine treatment.

The selective 5-HT1A receptor agonist, NLX-112, exerts anti-dyskinetic and anti-parkinsonian-like effects in MPTP-treated marmosets

l-DOPA is the gold-standard pharmacotherapy for treatment of Parkinson's disease (PD) but can lead to the appearance of troubling dyskinesia which are attributable to 'false neurotransmitter' release of dopamine by serotonergic neurons. Reducing the activity of these neurons diminishes l-DOPA-induced dyskinesia (LID), but there are currently no clinically approved selective, high efficacy 5-HT1A receptor agonists. Here we describe the effects of NLX-112, a highly selective and efficacious 5-HT1A receptor agonist, on LID in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated marmosets, a non-human primate model of PD. NLX-112 exhibited modest plasma half-life (~2h) and marked plasma protein binding (96%). When administered to parkinsonian marmosets with l-DOPA (7 mg/kg p.o.), NLX-112 (0.025, 0.1 and 0.4 mg/kg p.o.) reduced LID scores at early time-points after administration, whilst only minimally interfering with the l-DOPA-induced reversal of motor disability. In contrast, the prototypical 5-HT1A receptor agonist, (+)8-OH-DPAT (0.6 and 2 mg/kg p. o.), reduced LID but also abolished l-DOPA's anti-disability activity. Administered by itself, NLX-112 (0.1, 0.2 mg/kg p.o.) produced very little dyskinesia or locomotor activity, but reduced motor disability scores by about half the extent elicited by l-DOPA, suggesting that it may have motor facilitation effects of its own. Both NLX-112 and (+)8-OH-DPAT induced unusual and dose-limiting behaviors in marmoset that resembled 'serotonin behavioral syndrome' observed previously in rat. Overall, the present study showed that NLX-112 has anti-LID activity at the doses tested as well as reducing motor disability. The data suggest that additional investigation of NLX-112 is desirable to explore its potential as a treatment for PD and PD-LID.

Identification and quantification of the quality markers and anti-migraine active components in Chuanxiong Rhizoma and Cyperi Rhizoma herbal pair based on chemometric analysis between chemical constituents and pharmacological effects

ETHNOPHARMACOLOGICAL RELEVANCE

Chuanxiong Rhizoma and Cyperi Rhizoma (CRCR), an ancient and classic herbal pair, has been used in herbal medicines for treating migraine, but its effective components are not clear.

AIM OF THE STUDY

The present study aimed to identify and quantify the quality markers and anti-migraine active components in CRCR based on chemometric analysis between chemical constituents and pharmacological effects.

MATERIALS AND METHODS

The HPLC fingerprints of eight batches of CRCR samples were obtained, and their characteristic common peaks were identified by HPLC-ESI-Q-TOF-MS/MS. The therapeutic effects of eight batches of CRCR samples on nitroglycerin-induced migraine rats were evaluated by migraine-related neurotransmitters and neuropeptides. Similarity analysis, hierarchical cluster analysis and principal component analysis were applied to screen the quality markers. Artificial neural network and partial least squares regression models were used to screen the anti-migraine compounds by correlating the chemical constituents in HPLC fingerprints and pharmacological indicators.

RESULTS

Eighteen characteristic common peaks were found in the HPLC fingerprints, including eleven known compounds and seven unknown compounds. Ferulic acid (FA), senkyunolide I (SI), senkyunolide A (SA), 3-n-butylphthalide (NBP), Z-ligustilide (LIG), Z-3-butylidenephthalide (BDPH), nookatone (NKT), levistilide A (LA), α-cyperone (CYP) and other five unknown compounds (P1, P2, P7, P8 and P9) were identified as quality markers. SA, NBP, LIG, NKT, CYP and other three unknown compounds (P1, P4 and P9) can be considered as anti-migraine prototype compounds. The quality markers and anti-migraine active components were further quantified in CRCR extract, rat serum and cerebral cortex by UPLC-MS/MS, which gives a clue to track the dynamic changes of the contents of the main constituents.

CONCLUSIONS

Our study explored the anti-migraine material basis, and could lay a foundation for the improvement of the quality control of CRCR in practice.

Dual inhibitory action of trazodone on dorsal raphe serotonergic neurons through 5-HT1A receptor partial agonism and α1-adrenoceptor antagonism

Trazodone is an antidepressant drug with considerable affinity for 5-HT_1A receptors and α₁-adrenoceptors for which the drug is competitive agonist and antagonist, respectively. In this study, we used cell-attached or whole-cell patch-clamp recordings to characterize the effects of trazodone at somatodendritic 5-HT_1A receptors (5-HT_1AARs) and α₁-adrenoceptors of serotonergic neurons in rodent dorsal raphe slices. To reveal the effects of trazodone at α₁-adrenoceptors, the baseline firing of 5-HT neurons was facilitated by applying the selective α₁-adrenoceptor agonist phenylephrine at various concentrations. In the absence of phenylephrine, trazodone (1–10 μM) concentration-dependently silenced neurons through activation of 5-HT_1AARs. The effect was fully antagonized by the selective 5-HT_1A receptor antagonist Way-100635. With 5-HT_1A receptors blocked by Way-100635, trazodone (1–10 μM) concentration-dependently inhibited neuron firing facilitated by 1 μM phenylephrine. Parallel rightward shift of dose-response curves for trazodone recorded in higher phenylephrine concentrations (10–100 μM) indicated competitive antagonism at α₁-adrenoceptors. Both effects of trazodone were also observed in slices from Tph2^-/- mice that lack synthesis of brain serotonin, showing that the activation of 5-HT_1AARs was not mediated by endogenous serotonin. In whole-cell recordings, trazodone activated 5-HT_1AAR-coupled G protein-activated inwardly-rectifying (GIRK) channel conductance with weak partial agonist efficacy (~35%) compared to that of the full agonist 5-CT. Collectively our data show that trazodone, at concentrations relevant to its clinical effects, exerts weak partial agonism at 5-HT_1AARs and disfacilitation of firing through α₁-adrenoceptor antagonism. These two actions converge in inhibiting dorsal raphe serotonergic neuron activity, albeit with varying contribution depending on the intensity of α₁-adrenoceptor stimulation.

Cannabinoid CB1 receptors mediate the anxiolytic effects induced by systemic alprazolam and intra-periaqueductal gray 5-HT1A receptor activation

The endocannabinoid system has been implicated in the modulation of behaviors related to anxiety and panic disorders. Accordingly, facilitation of CB₁ receptor signaling reduces the consequences of aversive stimuli in animal models. However, the role of the CB₁ receptor in the effects of anxiolytic drugs has remained unclear. Here, we tested the hypothesis that the anxiolytic and panicolytic responses to systemic alprazolam injection and local 5-HT_1A receptor activation in the dorsolateral periaqueductal gray (dlPAG) depend on CB₁ receptor activation. Systemic injection of alprazolam (4 mg/kg) induced an anxiolytic-like effect in the elevated T maze (ETM) model of panic and anxiety, which was prevented by the CB₁ antagonist AM251 (0.3 mg/kg). Likewise, intra-dlPAG injection of the 5-HT_1A receptor agonist 8-OH-DPAT (3.2 nmol/0.2 u L) also reduced anxiety-like behavior, a response prevented by intra-dlPAG injection of AM251 (100 pmol/0.2 µL). 8-OH-DPAT (8 nmol/0.2 µL) also presented a panicolytic-like activity in the escape reaction induced by chemical stimulation of the dlPAG, which was not prevented by AM251 (100 pmol/0.2 µL). These results suggest that CB₁ receptor signaling is involved in the effects of anxiolytic drugs, with potential implications for developing new treatments for anxiety disorders.

Dissecting the roles of β-arrestin2 and GSK-3 signaling in 5-HT1BR-mediated perseverative behavior and prepulse inhibition deficits in mice

Serotonin-1B receptors (5-HT1BRs) modulate perseverative behaviors and prepulse inhibition (PPI) in humans and mice. These inhibitory G-protein-coupled receptors signal through a canonical G-protein-coupled pathway that is modulated by GSK-3β, and a noncanonical pathway mediated by the adaptor protein β-arrestin2 (Arrb2). Given the development of biased ligands that differentially affect canonical versus noncanonical signaling, we examined which signaling pathway mediates 5-HT1BR agonist-induced locomotor perseveration and PPI deficits, behavioral phenotypes observed in both obsessive-compulsive disorder (OCD) and autism spectrum disorder (ASD). To assess the role of canonical 5-HT1BR signaling, mice received acute pretreatment with a GSK-3 inhibitor (SB216763 or AR-A014418) and acute treatment with the 5-HT1A/1B receptor agonist RU24969 prior to assessing perseverative locomotor behavior in the open field, and PPI. To determine the role of noncanonical 5-HT1BR signaling, Arrb2 wild-type (WT), heterozygous (HT), and knockout (KO) mice received acute RU24969 treatment prior to behavioral testing. GSK-3 inhibition increased locomotor perseveration overall, and also failed to influence the RU24969-induced perseverative locomotor pattern in the open field. Yet, GSK-3 inhibition modestly reduced RU24969-induced PPI deficits. On the other hand, Arrb2 HT and KO mice showed reduced locomotion and no changes in perseveration overall, in addition to modest reductions in RU24969-induced locomotion and PPI deficits. In conclusion, our data do not support use of either GSK-3 inhibitors or β-arrestin2 inhibition in treatment of perseverative behaviors.

Depletion of apomorphine induced behavioral sensitization in rats treated with escitalopram

Apomorphine is a classical psychostimulant and used throughout the world as prescribed medicine. Despite of their therapeutic effects, use of psychostimulants is restricted because some psychosis and impulse control disorders are the consequence of their long term use. Studies suggest that serotonin (5-Hydroxytryptamine; 5-HT) has a critical role in psychosis and drug abuse. Center of the present article is to assess the impacts of serotonin in the easing of misuse potential; the sensitization prompted by recommended psychostimulant apomorphine. We researched that whether Escitalopram can weaken apomorphine instigated behavioral sensitization. Rats treated with Escitalopram (10 mg/kg) daily for 7 days followed by apomorphine injections (1mg/kg) for next 7 days. Apomorphine increased motor activity after single injection and repeated injections produced a progressive sensitization of motor activity. Whereas, in rats pretreated with Escitalopram apomorphine induced behavioral sensitization did not occur. In this article, from the results of this study it is concluded that apomorphine induced behavioral sensitization was smaller in rats pretreated with SSRIs. It might be due to the desensitization of somatodendritic 5-HT-1A receptors.

Report: Attenuation of apomorphine induced behavioral sensitization in rats pre-treated with tryptophan

Psychostimulants substances, some of which are abused by humans, are generally believed to produce sensitization effects when they are repeatedly administered to animals. Apomorphine, a non-narcotic derivative of morphine, having agonistic property for dopamine in order to produce psycho stimulant-like effects. Meanwhile, chronic administration leads to behavioral sensitization. Therefore, present study destine to produce desensitization in animals by the repeated administration of tryptophan (100 mg/kg), thereafter treated with apomorphine (1.0 mg/kg) to observe the intensity of sensitization in rats pre-treated with tryptophan. Apomorphine on acute administration known to increase motor activity whereas repeated treatment of apomorphine initiates the sensitization of motor behavior. It is expected that the intensity of apomorphine induced sensitization would be affected in tryptophan-treated rats. Present study provide the clear-cut evidence that chronic treatment of apomorphine arouses the motor behavior of animals in both novel and anxiolytic model over the saline treated animals, whereas hypo locomotive behavior was seen in animals pre-treated with tryptophan, provides the evidence that preliminary treatment of tryptophan perturbs the apomorphine induced sensitization in animals. The discoveries present an inventive methodology for amplifying the remedial utilization of apomorphine and traditional psychostimulants.

Cerebral serotonin release correlates with [11C]AZ10419369 PET measures of 5-HT1B receptor binding in the pig brain

Positron emission tomography (PET) can, when used with appropriate radioligands, non-invasively capture temporal and spatial information about acute changes in brain neurotransmitter systems. We here evaluate the 5-HT1B receptor partial agonist PET radioligand, [11C]AZ10419369, for its sensitivity to detect changes in endogenous cerebral serotonin levels, as induced by different pharmacological challenges. To enable a direct translation of PET imaging data to changes in brain serotonin levels, we compared the [11C]AZ10419369 PET signal in the pig brain to simultaneous measurements of extracellular serotonin levels with microdialysis after various acute interventions (saline, escitalopram, fenfluramine). The interventions increased the cerebral extracellular serotonin levels to two to six times baseline, with fenfluramine being the most potent pharmacological enhancer of serotonin release. The interventions induced a varying degree of decline in [11C]AZ10419369 binding in the brain, consistent with the occupancy competition model. The observed correlation between changes in the extracellular serotonin level in the pig brain and the 5-HT1B receptor occupancy indicates that [11C]AZ10419369 binding is sensitive to changes in endogenous serotonin levels to a degree equivalent to that reported of [11C]raclopride to dopamine, a much used approach to detect in vivo change in cerebral dopamine.

Discovery of DSP-1053, a novel benzylpiperidine derivative with potent serotonin transporter inhibitory activity and partial 5-HT1A receptor agonistic activity

We have previously shown that SMP-304, a serotonin uptake inhibitor with weak 5-HT_1A partial agonistic activity, may act under high serotonin levels as a 5-HT_1A antagonist that improves the onset of paroxetine in the rat swimming test. However, SMP-304 is mostly metabolized by CYP2D6, indicating limited efficacy among individuals and increased side effects. To reduce CYP2D6 metabolic contribution and enhance SERT/5-HT_1A binding affinity, we carried out a series of substitutions at the bromine atom in the left part of the benzene ring of SMP-304 and replaced the right part of SMP-304 with a chroman-4-one. This optimization work led to the identification of the antidepressant candidate DSP-1053 as a potent SERT inhibitor with partial 5-HT_1A receptor agonistic activity. DSP-1053 showed low CYP2D6 metabolic contribution and a robust increase in serotonin levels in the rat frontal cortex.

Identification of dual mechanisms mediating 5-hydroxytryptamine receptor 1F-induced mitochondrial biogenesis

Our laboratory recently made the novel observation that 5-hydroxytryptamine 1F (5-HT1F) receptor activation induces mitochondrial biogenesis (MB), the production of new, functional mitochondria, in vitro and in vivo. We sought to determine the mechanism linking the 5-HT1F receptor to MB in renal proximal tubule cells. Using LY344864 , a selective 5-HT1F receptor agonist, we determined that the 5-HT1F receptor is coupled to Gαi/o and induces MB through Gβγ-dependent activation of Akt, endothelial nitric oxide synthase (eNOS), cyclic guanosine-monophosphate (cGMP), protein kinase G (PKG), and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α). We also report that the 5-HT1F receptor signals through a second, Gβγ-dependent pathway that is linked by Akt phosphorylation of Raf. In contrast to the activated Akt pathway, Raf phosphorylation reduced extracellular signal regulated kinases (ERK1/2) and foxhead box O3a (FOXO3a) phosphorylation, suppressing an inhibitory MB pathway. These results demonstrate that the 5-HT1F receptor regulates MB through Gβγ-dependent dual mechanisms that activate a stimulatory MB pathway, Akt/eNOS/cGMP/PKG/PGC-1α, while simultaneously repressing an inhibitory MB pathway, Raf/MEK/ERK/FOXO3a. Novel mechanisms of MB provide the foundation for new chemicals that induce MB to treat acute and chronic organ injuries.

The 5-HT1B serotonin receptor regulates methylphenidate-induced gene expression in the striatum: Differential effects on immediate-early genes

Drug combinations that include a psychostimulant such as methylphenidate (Ritalin) and a selective serotonin reuptake inhibitor such as fluoxetine are indicated in several medical conditions. Co-exposure to these drugs also occurs with "cognitive enhancer" use by individuals treated with selective serotonin reuptake inhibitors. Methylphenidate, a dopamine reuptake inhibitor, by itself produces some addiction-related gene regulation in the striatum. We have demonstrated that co-administration of selective serotonin reuptake inhibitors potentiates these methylphenidate-induced molecular effects, thus producing a more "cocaine-like" profile. There is evidence that the 5-HT1B serotonin receptor subtype mediates some of the cocaine-induced gene regulation. We thus investigated whether the 5-HT1B receptor also modifies methylphenidate-induced gene regulation, by assessing effects of a selective 5-HT1B receptor agonist (CP94253) on immediate-early gene markers ( Zif268, c- Fos, Homer1a) in adolescent male rats. Gene expression was measured by in situ hybridization histochemistry. Our results show that CP94253 (3, 10 mg/kg) produced a dose-dependent potentiation of methylphenidate (5 mg/kg)-induced expression of Zif268 and c- Fos. This potentiation was widespread in the striatum and was maximal in lateral (sensorimotor) sectors, thus mimicking the effects seen after cocaine alone, or co-administration of fluoxetine. However, in contrast to fluoxetine, this 5-HT1B agonist did not influence methylphenidate-induced expression of Homer1a. CP94253 also potentiated methylphenidate-induced locomotor activity. These findings indicate that stimulation of the 5-HT1B receptor can enhance methylphenidate (dopamine)-induced gene regulation. This receptor may thus participate in the potentiation induced by fluoxetine (serotonin) and may serve as a pharmacological target to attenuate methylphenidate + selective serotonin reuptake inhibitor-induced "cocaine-like" effects.

Antinociceptive, antiallodynic and antihyperalgesic effects of the 5-HT1A receptor selective agonist, NLX-112 in mouse models of pain

BACKGROUND AND PURPOSE

NLX-112 (a.k.a. befiradol, F13640) is a drug candidate intended for the treatment of l-DOPA-induced dyskinesia. It is a highly selective serotonin 5-HT_1A receptor full agonist which has been previously tested in a variety of models of CNS effects including analgesic activity in rat. Its activity in mouse models of pain has not been previously investigated.

EXPERIMENTAL APPROACH

The activity of NLX-112 was tested in mouse models of acute pain (hot plate), tonic pain (intraplantar formalin test), in the oxaliplatin-induced neuropathic pain model of chemotherapy-induced peripheral neuropathy and in the streptozotocin (STZ)-induced model of painful diabetic neuropathy.

KEY RESULTS

The main findings indicate that (i) NLX-112 was markedly active in the formalin test with potent reduction of paw licking in both phases of the test (minimal effective dose (MED) 0.5 mg/kg i.p. and p.o. in acute phase, and 0.1 mg/kg i.p. and 1 mg/kg p.o. in late phase). The effects of NLX-112 in this test were completely abolished by the selective 5-HT_1A receptor antagonist, WAY100635; (ii) NLX-112 was active in the hot plate test and in the oxaliplatin-induced neuropathic pain model of chemotherapy-induced peripheral neuropathy, but at markedly higher doses (MED 2.5 mg/kg i.p.); (iii) NLX-112 was least active in the STZ-induced model of painful diabetic neuropathy (MED 5 mg/kg i.p.); (iv) NLX-112 did not affect locomotor activity.

CONCLUSIONS AND IMPLICATIONS

NLX-112 may have significant potential for treatment of tonic pain but may be less promising as a candidate for treatment of chemotherapy-induced or diabetic neuropathic pain.

Bioactivity-guided synthesis of gramine derivatives as new MT1 and 5-HT1A receptors agonists

Twenty-four gramine derivatives were synthesized and evaluated on MT₁ and 5-HT_1A receptors in vitro. Among them, seven derivatives (7, 8, 16, 19, 20, 21, and 24) exhibited higher agonisting activities on MT₁ or 5-HT_1A receptors. Compared with gramine, derivatives 7, 8, 16, 19, 20, 21, and 24 displayed 1.6-3.5-fold increase in agonistic rates on 5-HT_1A receptor. Particularly, derivatives 7, 19, and 21 exhibited significant agonistic activities on MT₁ and 5-HT_1A receptors with EC₅₀ values of 0.51, 0.39, 0.50 mΜ and 0.28, 0.46, 0.23 mΜ, respectively. The preliminary structure-activity relationships of gramine derivatives were summarized for further investigation on MT₁ and 5-HT_1A receptors as new potential agonists.

Serotonin 1A agonism decreases affiliative behavior in pair-bonded titi monkeys

Relatively little is known about serotonergic involvement in pair-bonding despite its putative role in regulating social behavior. Here we sought to determine if pharmacological elevation of serotonin 1A (5-HT_1A) receptor activity would lead to changes in social behavior in pair-bonded male titi monkeys (Callicebus cupreus). Adult males in established heterosexual pairs were injected daily with the selective 5-HT_1A agonist 8-OH-DPAT or saline for 15days using a within-subjects design. Social behavior with the female pair-mate was quantified, and plasma concentrations of oxytocin, vasopressin, and cortisol were measured. When treated with saline, subjects showed reduced plasma oxytocin concentrations, while 8-OH-DPAT treatment buffered this decrease. Treatment with 8-OH-DPAT also led to decreased plasma cortisol 15minutes post-injection and decreased social behavior directed toward the pair-mate including approaching, initiating contact, lipsmacking, and grooming. The reduction in affiliative behavior seen with increased activity at 5-HT_1A receptors indicates a substantial role of serotonin activity in the expression of social behavior. In addition, results indicate that the effects of 5-HT_1A agonism on social behavior in adulthood differ between rodents and primates.

Sphingolipids modulate the function of human serotonin1A receptors: Insights from sphingolipid-deficient cells

Sphingolipids are essential components of eukaryotic cell membranes and are known to modulate a variety of cellular functions. It is becoming increasingly clear that membrane lipids play a crucial role in modulating the function of integral membrane proteins such as G protein-coupled receptors (GPCRs). In this work, we utilized LY-B cells, that are sphingolipid-auxotrophic mutants defective in sphingolipid biosynthesis, to monitor the role of cellular sphingolipids in the function of an important neurotransmitter receptor, the serotonin_1A receptor. Serotonin_1A receptors belong to the family of GPCRs and are implicated in behavior, development and cognition. Our results show that specific ligand binding and G-protein coupling of the serotonin_1A receptor exhibit significant enhancement under sphingolipid-depleted conditions, which reversed to control levels upon replenishment of cellular sphingolipids. In view of the reported role of sphingolipids in neuronal metabolism and pathogenesis of several neuropsychiatric disorders, exploring the role of serotonin_1A receptors under conditions of defective sphingolipid metabolism assumes relevance, and could contribute to our overall understanding of such neuropsychiatric disorders. This article is part of a Special Issue entitled: Lipid order/lipid defects and lipid-control of protein activity edited by Dirk Schneider.

Firing characteristics of deep dorsal horn neurons after acute spinal transection during administration of agonists for 5-HT1B/1D and NMDA receptors

Spinal cord injury (SCI) results in a loss of serotonin (5-HT) to the spinal cord and a loss of inhibition to deep dorsal horn (DDH) neurons, which produces an exaggerated excitatory drive to motoneurons. The mechanism of this excitatory drive could involve the DDH neurons triggering long excitatory postsynaptic potentials in motoneurons, which may ultimately drive muscle spasms. Modifying the activity of DDH neurons with drugs such as NMDA or the 5-HT1B/1D receptor agonist zolmitriptan could have a large effect on motoneuron activity and, therefore, on muscle spasms. In this study, we characterize the firing properties of DDH neurons after acute spinal transection in adult mice during administration of zolmitriptan and NMDA, using the in vitro sacral cord preparation and extracellular electrophysiology. DDH neurons can be categorized into three major types with distinct evoked and spontaneous firing characteristics: burst (bursting), simple (single spiking), and tonic (spontaneously tonic firing) neurons. The burst neurons likely contribute to muscle spasm mechanisms because of their bursting behavior. Only the burst neurons show significant changes in their firing characteristics during zolmitriptan and NMDA administration. Zolmitriptan suppresses the burst neurons by reducing their evoked spikes, burst duration, and spontaneous firing rate. Conversely, NMDA facilitates them by enhancing their burst duration and spontaneous firing rate. These results suggest that zolmitriptan may exert its antispastic effect on the burst neurons via activation of 5-HT1B/1D receptors, whereas activation of NMDA receptors may facilitate the burst neurons in contributing to muscle spasm mechanisms following SCI.

[THE DAMAGING EFFECTS AT AN EARLY AGE ALTER PAIN SENSITIVITY IN ADULT FEMALE RATS, CORRECTION WITH BUSPIRONE]

Most studies on the damaging effects of pain and stress impacts in the neonatal period of development on pain sensitivity were performed on individuals of the male sex. In the present study, we investigated the influence of inflammatory pain and/or stress of isolation from the mother in newborn female rats to pain sensitivity when they reached adulthood; an attempt was undertaken to correct identified deviations using 5-HT1A-receptor agonist buspirone. Adult females exposed to early pain displayed increased hypoalgesia in the hot plate test and rats subjected to stress of isolation from the mother showed increased hyperalgesia in the formalin test. The pain and subsequent isolation from the mother did not change pain sensitivity in the adult females. The chronic injection of buspirone from 25 th to 39 th day of life to females subjected to inflammatory pain and isolation from the mother in the neonatal period caused the normalization of pain sensitivity when they reached adulthood. It is found that the prepubertal period is a critical period for the correction of deviations caused by damaging impacts in neonatal rata in the functional activity of the nociceptive system.

Involvement of GABAA receptors in 5-HT1A and σ1 receptor synergism on prefrontal dopaminergic transmission under circulating neurosteroid deficiency

RATIONALE

We previously reported that the fluvoxamine-induced increase in prefrontal dopamine levels is enhanced by adrenalectomy/castration (which results in circulating neurosteroid deficiency), via combined activation of serotonin1A (5-HT1A) and σ1 receptors. However, the mechanistic details of the interaction between 5-HT1A and σ1 receptors are unknown.

OBJECTIVES

Because most neurosteroids have affinity for γ-aminobutyric acid (GABA)A receptors, in the present study, we examined the involvement of GABAA receptors in this process.

RESULTS

Adrenalectomy/castration decreased pentobarbital-induced sleeping time in mice, suggesting that it reduced GABAA receptor function. The GABAA receptor antagonist picrotoxin (1 mg/kg) enhanced the fluvoxamine-induced increase in prefrontal dopamine, but not noradrenaline or serotonin, levels in mice, suggesting that picrotoxin mimicked the effect of adrenalectomy/castration. Picrotoxin also potentiated the increase in prefrontal dopamine levels mediated by co-administration of the 5-HT1A receptor agonist osemozotan and the σ1 receptor agonist (+)-SKF-10,047, while it did not affect the co-administration-induced changes in noradrenaline and serotonin levels. Conversely, the GABAA receptor agonist diazepam (1 mg/kg) blocked the effect of adrenalectomy/castration on the fluvoxamine-induced increase in prefrontal dopamine levels. Co-administration of osemozotan and (+)-SKF-10,047 did not affect the expression of the neuronal activity marker c-Fos in the prefrontal cortex, ventral tegmental area, and nucleus accumbens in control mice, while it increased the c-Fos expression only in the prefrontal cortex and ventral tegmental area in picrotoxin-treated mice.

CONCLUSIONS

These results suggest that the GABAA receptor plays a key role in mediating the synergistic effects of 5-HT1A and σ1 receptor activation on prefrontal dopamine neurotransmission.

In Vitro and In Vivo Characterization of the Alkaloid Nuciferine

Rationale

The sacred lotus (Nelumbo nucifera) contains many phytochemicals and has a history of human use. To determine which compounds may be responsible for reported psychotropic effects, we used in silico predictions of the identified phytochemicals. Nuciferine, an alkaloid component of Nelumbo nucifera and Nymphaea caerulea, had a predicted molecular profile similar to antipsychotic compounds. Our study characterizes nuciferine using in vitro and in vivo pharmacological assays.

Methods

Nuciferine was first characterized in silico using the similarity ensemble approach, and was followed by further characterization and validation using the Psychoactive Drug Screening Program of the National Institute of Mental Health. Nuciferine was then tested in vivo in the head-twitch response, pre-pulse inhibition, hyperlocomotor activity, and drug discrimination paradigms.

Results

Nuciferine shares a receptor profile similar to aripiprazole-like antipsychotic drugs. Nuciferine was an antagonist at 5-HT_2A, 5-HT_2C, and 5-HT_2B, an inverse agonist at 5-HT₇, a partial agonist at D_2, D₅ and 5-HT₆, an agonist at 5-HT_1A and D₄ receptors, and inhibited the dopamine transporter. In rodent models relevant to antipsychotic drug action, nuciferine blocked head-twitch responses and discriminative stimulus effects of a 5-HT_2A agonist, substituted for clozapine discriminative stimulus, enhanced amphetamine induced locomotor activity, inhibited phencyclidine (PCP)-induced locomotor activity, and rescued PCP-induced disruption of prepulse inhibition without induction of catalepsy.

Conclusions

The molecular profile of nuciferine was similar but not identical to that shared with several approved antipsychotic drugs suggesting that nuciferine has atypical antipsychotic-like actions.

Yohimbine is a 5-HT1A agonist in rats in doses exceeding 1 mg/kg

Yohimbine is a prototypical alpha2-adrenergic receptor antagonist. Due to its relatively high selectivity, yohimbine is often used in experiments whose purpose is to examine the role of these receptors. For example, yohimbine has been employed at doses of 1-5 mg/kg to reinstate drug-seeking behavior after extinction or to antagonize general anesthesia, an effects presumably being a consequence of blocking alpha2-adrenergic receptors. In this report we characterized dose-dependent autonomic and behavioral effects of yohimbine and its interaction with an antagonist of 5-HT1A receptors, WAY 100,635. In low doses (0.5-2 mg/kg i.p.) yohimbine induced locomotor activation which was accompanied by a tachycardia and mild hypertension. Increasing the dose to 3-4.5 mg/kg reversed the hypertension and locomotor activation and induced profound hypothermia. The hypothermia as well as the suppression of the locomotion and the hypertension could be reversed by the blockade of 5-HT1A receptors with WAY 100635. Our data confirm that yohimbine possesses 5-HT1A properties, and demonstrated that in doses above 1mg/kg significantly activate these receptors.

Functional Selectivity and Antidepressant Activity of Serotonin 1A Receptor Ligands

Serotonin (5-HT) is a monoamine neurotransmitter that plays an important role in physiological functions. 5-HT has been implicated in sleep, feeding, sexual behavior, temperature regulation, pain, and cognition as well as in pathological states including disorders connected to mood, anxiety, psychosis and pain. 5-HT1A receptors have for a long time been considered as an interesting target for the action of antidepressant drugs. It was postulated that postsynaptic 5-HT1A agonists could form a new class of antidepressant drugs, and mixed 5-HT1A receptor ligands/serotonin transporter (SERT) inhibitors seem to possess an interesting pharmacological profile. It should, however, be noted that 5-HT1A receptors can activate several different biochemical pathways and signal through both G protein-dependent and G protein-independent pathways. The variables that affect the multiplicity of 5-HT1A receptor signaling pathways would thus result from the summation of effects specific to the host cell milieu. Moreover, receptor trafficking appears different at pre- and postsynaptic sites. It should also be noted that the 5-HT1A receptor cooperates with other signal transduction systems (like the 5-HT1B or 5-HT2A/2B/2C receptors, the GABAergic and the glutaminergic systems), which also contribute to its antidepressant and/or anxiolytic activity. Thus identifying brain specific molecular targets for 5-HT1A receptor ligands may result in a better targeting, raising a hope for more effective medicines for various pathologies.

Heterologous Expression in Remodeled C. elegans: A Platform for Monoaminergic Agonist Identification and Anthelmintic Screening

Monoamines, such as 5-HT and tyramine (TA), paralyze both free-living and parasitic nematodes when applied exogenously and serotonergic agonists have been used to clear Haemonchus contortus infections in vivo. Since nematode cell lines are not available and animal screening options are limited, we have developed a screening platform to identify monoamine receptor agonists. Key receptors were expressed heterologously in chimeric, genetically-engineered Caenorhabditis elegans, at sites likely to yield robust phenotypes upon agonist stimulation. This approach potentially preserves the unique pharmacologies of the receptors, while including nematode-specific accessory proteins and the nematode cuticle. Importantly, the sensitivity of monoamine-dependent paralysis could be increased dramatically by hypotonic incubation or the use of bus mutants with increased cuticular permeabilities. We have demonstrated that the monoamine-dependent inhibition of key interneurons, cholinergic motor neurons or body wall muscle inhibited locomotion and caused paralysis. Specifically, 5-HT paralyzed C. elegans 5-HT receptor null animals expressing either nematode, insect or human orthologues of a key Gαo-coupled 5-HT1-like receptor in the cholinergic motor neurons. Importantly, 8-OH-DPAT and PAPP, 5-HT receptor agonists, differentially paralyzed the transgenic animals, with 8-OH-DPAT paralyzing mutant animals expressing the human receptor at concentrations well below those affecting its C. elegans or insect orthologues. Similarly, 5-HT and TA paralyzed C. elegans 5-HT or TA receptor null animals, respectively, expressing either C. elegans or H. contortus 5-HT or TA-gated Cl- channels in either C. elegans cholinergic motor neurons or body wall muscles. Together, these data suggest that this heterologous, ectopic expression screening approach will be useful for the identification of agonists for key monoamine receptors from parasites and could have broad application for the identification of ligands for a host of potential anthelmintic targets.

Proopiomelanocortin but not vasopressin or renin-angiotensin system induces resuscitative effects of central 5-HT1A activation in haemorrhagic shock in rats

The aim of this study was to determine the effectory mechanisms: vasopressin, renin-angiotensin system and proopiomelanocortin-derived peptides (POMC), partaking in the effects of serotonin through central serotonin 1A receptor (5-HT1A) receptors in haemorrhagic shock in rats. The study was conducted on male Wistar rats. All experimental procedures were carried out under full anaesthesia. The principal experiment included a 2 hour observation period in haemorrhagic shock. Drugs used - a selective 5-HT1A agonist 8-OH-DPAT (5 μg/5 μl); V1a receptor antagonist [β-mercapto-β, β-cyclo-pentamethylenepropionyl(1),O-me-Tyr(2),Arg(8)]AVP (10 μg/kg); angiotensin type I receptor antagonist (AT1) ZD7155 (0.5 mg/kg, i.v.); angiotensin-converting-enzyme inhibitor captopril (30 mg/kg, i.v.); melanocortin type 4 (MC4) receptor antagonist HS014 (5 μg, i.c.v.). There was no influence of ZD715, captopril or blocking of the V1a receptors on changes in the heart rate (HR), mean arterial pressure (MAP), peripheral blood flow or resistance caused by the central stimulation of 5-HT1A receptors (P≥0.05). However, selective blocking of central MC4 receptors caused a slight, but significant decrease in HR and MAP (P<0.05). POMC derivatives acting via the central MC4 receptor participate in the resuscitative effects of 8-OH-DPAT. The angiotensin and vasopressin systems do not participate in these actions.

Conformational analysis and geometry optimization of buspirone-A 5-HT1A receptor agonist

Buspirone, a partial 5-HT1A receptor agonist, is a clinically prescribed anxiolytic. In the present study, conformational analysis and geometry optimization of buspirone were done as per Hartree-Fock (HF) calculation method by Argus Lab 4.0.1 software. The minimum potential energy was calculated by geometry convergence function by Argus Lab software. The results indicate that the best conformation of molecule is present at minimum potential energy of-100679.5513 kcal/mol. At this point, buspirone will be more active.

Optogenetic recruitment of dorsal raphe serotonergic neurons acutely decreases mechanosensory responsivity in behaving mice

The inhibition of sensory responsivity is considered a core serotonin function, yet this hypothesis lacks direct support due to methodological obstacles. We adapted an optogenetic approach to induce acute, robust and specific firing of dorsal raphe serotonergic neurons. In vitro, the responsiveness of individual dorsal raphe serotonergic neurons to trains of light pulses varied with frequency and intensity as well as between cells, and the photostimulation protocol was therefore adjusted to maximize their overall output rate. In vivo, the photoactivation of dorsal raphe serotonergic neurons gave rise to a prominent light-evoked field response that displayed some sensitivity to a 5-HT1A agonist, consistent with autoreceptor inhibition of raphe neurons. In behaving mice, the photostimulation of dorsal raphe serotonergic neurons produced a rapid and reversible decrease in the animals' responses to plantar stimulation, providing a new level of evidence that serotonin gates sensory-driven responses.

Mechanism of action of the bimodal antidepressant vilazodone: evidence for serotonin1A-receptor-mediated auto-augmentation of extracellular serotonin output

RATIONALE

The recently approved antidepressant vilazodone, a serotonin (5-HT)1A receptor partial agonist/selective 5-HT reuptake inhibitor offers new possibilities to study the underlying mechanisms of depression pharmacotherapy and of 5-HT augmenting antidepressants.

OBJECTIVE

The role of the 5-HT1A receptor with respect to the regulation of 5-HT output in the mechanism of action of vilazodone.

METHOD

We measured 5-HT levels in two subregions of the rat prefrontal cortex by microdialysis, and 5-hydroxytryptophan (5-HTP) accumulation and tissue 5-HT concentrations ex vivo.

RESULTS

Vilazodone-induced maximal 5-HT levels were similar in the medial and the lateral cortex and were up to sixfold higher than those induced by paroxetine, citalopram, or fluoxetine tested in parallel. Depolarization/autoreceptor-insensitive 5-HT release by vilazodone could be excluded. The citalopram (1 μM, locally infused)-induced increase of 5-HT was further increased by vilazodone (1 mg/kg i.p.), but not by citalopram (10 mg/kg i.p.). Unlike fluoxetine, vilazodone-induced extracellular 5-HT output was not potentiated by cotreatment with the 5-HT1A receptor blocker N-[2-(4-{2-methoxyphenyl}-1-piperazinyl)-ethyl]-N-2-pyridinylcyclohexanecarboxamide (WAY 100635). In contrast to fluoxetine, vilazodone exhibited intrinsic 5-HT1A agonist activity: it reduced, similar to (±)-8-hydroxy-2-(dipropylamino)-tetralin (8-OH-DPAT), 5-HTP accumulation in striatum and n. raphe of reserpinized rats. Hence, vilazodone's agonistic actions must be 5-HT1A receptor-related since endogenous 5-HT is lacking in the reserpine-depleted animal.

CONCLUSIONS

In spite of high intrinsic 5-HT1A activity in reserpinized rats, the net effect of vilazodone at release-regulating 5-HT1A autoreceptors must be inhibitory, leading to markedly increased 5-HT output. Another possibility is that vilazodone rapidly desensitizes autoinhibitory 5-HT1A receptors by an unknown mechanism.

Activation of postsynaptic 5-HT1A receptors improve stress adaptation

RATIONALE

Serotonin-1A (5-HT1A) receptors modulate the stress response and have been implicated in the etiology and treatment of depression and anxiety disorders. A reduction in postsynaptic 5-HT1A receptor function in limbic areas has consistently been observed following exposure to chronic stress.

OBJECTIVES

To investigate the hypothesis that increased activation of 5-HT1A receptors in rats having reduced 5-HT function may improve stress adaptation and the behavioral sequelae commonly associated with chronic stress.

METHODS

One hundred forty-four Sprague-Dawley rats received injections of para-chlorophenylalanine to partially deplete 5-HT then were given daily systemic pretreatment with the 5-HT1A receptor agonist, 8-hydroxy-2- (di-n-propylamino) tetralin (8-OH-DPAT), the antagonist, WAY 100635, or vehicle prior to either restraint stress (6 h/day for 10 daily sessions) or control conditions. Anxiety- and depressive-like behaviors were then assessed using the open field and sucrose preference tests. Protein level of hippocampal glucocorticoid receptors (GR) and mineralocorticoid receptors was detected by immunohistochemistry and brain-derived neurotrophic factor (BDNF) was determined by in situ hybridization.

RESULTS

8-OH-DPAT pretreatment prior to stress exposure attenuated later stress-induced anxiety- and depression-like behaviors and increased GR and BDNF mRNA expression in the hippocampus relative to vehicle- and WAY 100635-pretreated, stressed animals.

CONCLUSION

The stress-related impairments associated with 5-HT deficiency can be improved by 8-OH-DPAT pretreatment prior to stress exposure and are associated with an augmentation of GR-like immunoreactivity and BDNF mRNA expression in the hippocampus. It suggested that selective activation of 5-HT1A receptors may be a potential treatment strategy for stress-related disorders such as anxiety and depression.

Serotonergic mechanisms responsible for levodopa-induced dyskinesias in Parkinson's disease patients

Levodopa-induced dyskinesias (LIDs) are the most common and disabling adverse motor effect of therapy in Parkinson's disease (PD) patients. In this study, we investigated serotonergic mechanisms in LIDs development in PD patients using 11C-DASB PET to evaluate serotonin terminal function and 11C-raclopride PET to evaluate dopamine release. PD patients with LIDs showed relative preservation of serotonergic terminals throughout their disease. Identical levodopa doses induced markedly higher striatal synaptic dopamine concentrations in PD patients with LIDs compared with PD patients with stable responses to levodopa. Oral administration of the serotonin receptor type 1A agonist buspirone prior to levodopa reduced levodopa-evoked striatal synaptic dopamine increases and attenuated LIDs. PD patients with LIDs that exhibited greater decreases in synaptic dopamine after buspirone pretreatment had higher levels of serotonergic terminal functional integrity. Buspirone-associated modulation of dopamine levels was greater in PD patients with mild LIDs compared with those with more severe LIDs. These findings indicate that striatal serotonergic terminals contribute to LIDs pathophysiology via aberrant processing of exogenous levodopa and release of dopamine as false neurotransmitter in the denervated striatum of PD patients with LIDs. Our results also support the development of selective serotonin receptor type 1A agonists for use as antidyskinetic agents in PD.

Yokukansan, a traditional Japanese herbal medicine, alleviates the emotional abnormality induced by maladaptation to stress in mice

The aim of the present study was to examine the effect of yokukansan, a traditional Japanese herbal medicine that is composed of Atractylodis lanceae Rhizoma, Poria, Cnidii Rhizoma, Uncariae Uncis cum Ramulus, Angelicae Radix, Bupleuri Radix and Glycyrrhizae Radix, on the emotional abnormality induced by maladaptation to stress in mice. Mice were exposed to repeated restraint stress for 60 or 240 min/day for 14 days. From the 3rd day of stress exposure, mice were given yokukansan orally (p.o.) or the 5-HT1A receptor agonist flesinoxan intraperitoneally (i.p.) immediately after the daily exposure to restraint stress. After the final exposure to restraint stress, the emotionality of mice was evaluated using an automatic hole-board apparatus. A single exposure to restraint stress for 60 min induced a decrease in head-dipping behavior in the hole-board test. This emotional stress response disappeared in mice that had been exposed to repeated restraint stress for 60 min/day for 14 days, which confirmed the development of stress adaptation. In contrast, mice that were exposed to restraint stress for 240 min/day for 14 days did not develop this stress adaptation, and still showed a decrease in head-dipping behavior. The decreased emotionality observed in stress-maladaptive mice was significantly recovered by chronic treatment with yokukansan (1000 mg/kg, p.o.) as well as flesinoxan (0.25 and 0.5 mg/kg, i.p.) immediately after daily exposure to stress. These findings suggest that yokukansan may have a beneficial effect on stress adaptation and alleviate the emotional abnormality under conditions of excessive stress.

On the behavioural specificity of hypophagia induced in male rats by mCPP, naltrexone, and their combination

RATIONALE

Serotonergic (5-hydroxytryptamine, 5-HT) and opioidergic mechanisms are intimately involved in appetite regulation.

OBJECTIVES

In view of recent evidence of positive anorectic interactions between opioid and various non-opioid substrates, our aim was to assess the behavioural specificity of anorectic responses to the opioid receptor antagonist naltrexone, the 5-HT2C/1B receptor agonist mCPP and their combination.

METHODS

Behavioural profiling techniques, including the behavioural satiety sequence (BSS), were used to examine acute drug effects in non-deprived male rats tested with palatable mash. Experiment 1 characterised the dose-response profile of mCPP (0.1-3.0 mg/kg), while experiment 2 assessed the effects of combined treatment with a sub-anorectic dose of mCPP (0.1 mg/kg) and one of two low doses of naltrexone (0.1 and 1.0 mg/kg).

RESULTS

Experiment 1 confirmed the dose-dependent anorectic efficacy of mCPP, with robust effects on intake and feeding-related measures observed at 3.0 mg/kg. However, that dose was also associated with other behavioural alterations including increased grooming, reductions in locomotion and sniffing, and disruption of the BSS. In experiment 2, naltrexone dose-dependently reduced food intake and time spent feeding, effects accompanied by a behaviourally selective acceleration in the BSS. However, the addition of 0.1 mg/kg mCPP did not significantly alter the behavioural changes observed in response to either dose of naltrexone given alone.

CONCLUSIONS

In contrast to recently reported positive anorectic interactions involving low-dose combinations of opioid receptor antagonists or mCPP with cannabinoid CB1 receptor antagonists, present results would not appear to provide any support for potentially clinically relevant anorectic interactions between opioid and 5-HT2C/1B receptor mechanisms.