Anxiolytic-like Effects and Quantitative EEG Profile of Palmitone Induces Responses Like Buspirone Rather Than Diazepam as Clinical Drugs.

Anxiety is a mental disorder with a growing worldwide incidence due to the SARS-CoV-2 virus pandemic. Pharmacological therapy includes drugs such as benzodiazepines (BDZs) or azapirones like buspirone (BUSP) or analogs, which unfortunately produce severe adverse effects or no immediate response, respectively. Medicinal plants or their bioactive metabolites are a shared global alternative to treat anxiety. Palmitone is one active compound isolated from Annona species due to its tranquilizing activity. However, its influence on neural activity and possible mechanism of action are unknown. In this study, an electroencephalographic (EEG) spectral power analysis was used to corroborate its depressant activity in comparison with the anxiolytic-like effects of reference drugs such as diazepam (DZP, 1 mg/kg) and BUSP (4 mg/kg) or 8-OH-DPAT (1 mg/kg), alone or in the presence of the GABAA (picrotoxin, PTX, 1 mg/kg) or serotonin 5-HT1A receptor antagonists (WAY100634, WAY, 1 mg/kg). The anxiolytic-like activity was assayed using the behavioral response of mice employing open-field, hole-board, and plus-maze tests. EEG activity was registered in both the frontal and parietal cortex, performing a 10 min baseline and 30 min recording after the treatments. As a result, anxiety-like behavior was significantly decreased in mice administered with palmitone, DZP, BUSP, or 8-OH-DPAT. The effect of palmitone was equivalent to that produced by 5-HT1A receptor agonists but 50% less effective than DZP. The presence of PTX and WAY prevented the anxiolytic-like response of DZP and 8-OH-DPAT, respectively. Whereas only the antagonist of the 5-HT1A receptor (WAY) inhibited the palmitone effects. Palmitone and BUSP exhibited similar changes in the relative power bands after the spectral power analysis. This response was different to the changes induced by DZP. In conclusion, brain electrical activity was associated with the anxiolytic-like effects of palmitone implying a serotoninergic rather than a GABAergic mechanism of action.

Ginsenoside Re Protects against Serotonergic Behaviors Evoked by 2,5-Dimethoxy-4-iodo-amphetamine in Mice via Inhibition of PKCδ-Mediated Mitochondrial Dysfunction.

It has been recognized that serotonin 2A receptor (5-HT2A) agonist 2,5-dimethoxy-4-iodo-amphetamine (DOI) impairs serotonergic homeostasis. However, the mechanism of DOI-induced serotonergic behaviors remains to be explored. Moreover, little is known about therapeutic interventions against serotonin syndrome, although evidence suggests that ginseng might possess modulating effects on the serotonin system. As ginsenoside Re (GRe) is well-known as a novel antioxidant in the nervous system, we investigated whether GRe modulates 5-HT2A receptor agonist DOI-induced serotonin impairments. We proposed that protein kinase Cδ (PKCδ) mediates serotonergic impairments. Treatment with GRe or 5-HT2A receptor antagonist MDL11939 significantly attenuated DOI-induced serotonergic behaviors (i.e., overall serotonergic syndrome behaviors, head twitch response, hyperthermia) by inhibiting mitochondrial translocation of PKCδ, reducing mitochondrial glutathione peroxidase activity, mitochondrial dysfunction, and mitochondrial oxidative stress in wild-type mice. These attenuations were in line with those observed upon PKCδ inhibition (i.e., pharmacologic inhibitor rottlerin or PKCδ knockout mice). Furthermore, GRe was not further implicated in attenuation mediated by PKCδ knockout in mice. Our results suggest that PKCδ is a therapeutic target for GRe against serotonergic behaviors induced by DOI.

Receptor-mediated biological effects of extracts obtained from three Asplenium species.

This study reports the effects of aqueous extracts obtained from three fern species of Bulgarian origin: Asplenium ceterach L., Asplenium scolopendrium L., and Asplenium trichomanes L. on the contractility and bioelectrogenesis of rat gastric smooth muscle tissues. In the concentration range 0.015-0.150 mg/mL the three extracts contracted smooth muscle tissues in a concentration-dependent manner. The contractions caused by A. ceterach L. and A. scolopendrium L. extracts (0.150 mg/mL) were reduced by ketanserin (5 × 10-7 and 5 × 10-6 mol/L), an antagonist of serotonin 5-HT2 receptor. The contraction evoked by A. trichomanes L. (0.150 mg/mL) was significantly reduced by 1 × 10-6 mol/L atropine, an antagonist of muscarinic receptors, and turned into relaxation against the background of 3 × 10-7 mol/L galantamine. After combined pretreatment with galantamine and l-arginine (5 × 10-4 mol/L), this relaxation become more pronounced. The study demonstrates that constituents of A. ceterach L. and A. scolopendrium L. extracts act as agonists of 5-HT2 receptors and cause contraction by activating serotonergic signaling system. A. trichomanes L.-induced reaction is an additive result of two opposite-in-character effects. The dominant contraction is initiated by inhibition of acetylcholinesterase activity. The relaxation develops with pre-inhibited acetylcholinesterase, it is significantly potentiated by l-arginine, and therefore associated with nitrergic signaling pathway.

Contribution of serotonin receptor subtypes to hallucinogenic activity of 25I-NBOMe and to its effect on neurotransmission.

BACKGROUND: 4-Iodo-2,5-dimethoxy-N-(2-methoxybenzyl)phenethylamine (25I-NBOMe) is a potent serotonin (5-HT) receptor agonist with hallucinogenic properties. The aim of our research was to examine the role of the 5-HT2A, 5-HT2C and 5-HT1A serotonin receptor subtypes in 25I-NBOMe hallucinogenic activity and its effect on dopamine (DA), 5-HT and glutamate release in the rat frontal cortex. METHODS: Hallucinogenic activity was investigated using the wet dog shake (WDS) test. The release of DA, 5-HT and glutamate in the rat frontal cortex was studied using a microdialysis in freely moving rats. Neurotransmitter levels were analyzed by HPLC with electrochemical detection. The selective antagonists of the 5-HT2A, 5-HT2C and 5-HT1A serotonin receptor subtypes: M100907, SB242084 and WAY100635, respectively were applied through a microdialysis probe. RESULTS: The WDS response to 25I-NBOMe (1 and 3 mg/kg) was significantly reduced by local administration of M100907 and SB242084 (100 nM). The 25I-NBOMe-induced increase in glutamate, DA and 5-HT release was inhibited by M100907 and SB242084. WAY100635 had no effect on 25I-NBOMe-induced WDS and glutamate release, while it decreased DA and 5-HT release from cortical neuronal terminals. CONCLUSION: The obtained results suggest that 5-HT2A and 5-HT2C receptors play a role in 25I-NBOMe-induced hallucinogenic activity and in glutamate, DA and 5-HT release in the rat frontal cortex as their respective antagonists attenuated the effect of this hallucinogen. The disinhibition of GABA cells by the 5-HT1A receptor antagonist seems to underlie the mechanism of decreased DA and 5-HT release from neuronal terminals in the frontal cortex.

Effect of serotonin modulation on dystrophin-deficient zebrafish.

Duchenne muscular dystrophy (DMD) is a progressive muscle-wasting disease caused by mutation of the dystrophin gene. Pharmacological therapies that function independently of dystrophin and complement strategies aimed at dystrophin restoration could significantly improve patient outcomes. Previous observations have suggested that serotonin pathway modulation ameliorates dystrophic pathology, and re-application of serotonin modulators already used clinically would potentially hasten availability to DMD patients. In our study, we used dystrophin-deficient sapje and sapje-like zebrafish models of DMD for rapid and easy screening of several classes of serotonin pathway modulators as potential therapeutics. None of the candidate drugs tested significantly decreased the percentage of zebrafish exhibiting the dystrophic muscle phenotype in the short-term birefringence assay or lengthened the lifespan in the long-term survival assay. Although we did not identify an effective drug, we believe our data is of value to the DMD research community for future studies, and there is evidence that suggests serotonin modulation may still be a viable treatment strategy with further investigation. Given the widespread clinical use of selective serotonin reuptake inhibitors, tricyclic antidepressants and reversible inhibitors of monoamine oxidase, their reapplication to DMD is an attractive strategy in the field's pursuit to identify pharmacological therapies to complement dystrophin restoration strategies.

Role of 5-HT1A Receptor in the Anxiolytic-Relaxant Effects of Bergamot Essential Oil in Rodent.

The essential oil obtained by the fresh fruit of Citrus bergamia Risso et Poiteau is used worldwide in aromatherapy to reduce pain, facilitate sleep induction, and/or minimize the effects of stress-induced anxiety. Preclinical pharmacological data demonstrate that bergamot essential oil (BEO) modulates specific neurotransmissions and shows an anxiolytic-relaxant effect not superimposable to that of the benzodiazepine diazepam, suggesting that neurotransmissions, other than GABAergic, could be involved. Several studies on essential oils indicate a role for serotonergic (5-HT) neurotransmission in anxiety. Interestingly, among serotonergic receptors, the 5-HT1A subtype seems to play a key role in the control of anxiety. Here, we report that modulation of the 5-HT1A receptor by selective agonist ((±)8-OH-DPAT) or antagonist (WAY-100635) may influence some of the anxiolytic-relaxant effects of BEO in Open Field and Elevated Plus Maze tests.

Systemic serotonin inhibits brown adipose tissue sympathetic nerve activity via a GABA input to the dorsomedial hypothalamus, not via 5HT1A receptor activation in raphe pallidus.

AIM: Serotonin (5-hydroxytryptamine, 5-HT), an important neurotransmitter and hormone, modulates many physiological functions including body temperature. We investigated neural mechanisms involved in the inhibition of brown adipose tissue (BAT) sympathetic nerve activity (SNA) and BAT thermogenesis evoked by 5-HT. METHODS: Electrophysiological recordings, intravenous (iv) injections and nanoinjections in the brains of anaesthetized rats. RESULTS: Cooling-evoked increases in BAT SNA were inhibited by the intra-rostral raphé pallidus (rRPa) and the iv administration of the 5-HT1A receptor agonist, 8-OH-DPAT or 5-HT. The intra-rRPa 5-HT, the intra-rRPa and the iv 8-OH-DPAT, but not the iv 5-HT-induced inhibition of BAT SNA were prevented by nanoinjection of a 5-HT1A receptor antagonist in the rRPa. The increase in BAT SNA evoked by nanoinjection of NMDA in the rRPa was not inhibited by iv 5-HT, indicating that iv 5-HT does not inhibit BAT SNA by acting in the rRPa or in the sympathetic pathway distal to the rRPa. In contrast, under a warm condition, blockade of 5HT1A receptors in the rRPa increased BAT SNA and BAT thermogenesis, suggesting that endogenous 5-HT in the rRPa contributes to the suppression of BAT SNA and BAT thermogenesis. The increases in BAT SNA and BAT thermogenesis evoked by nanoinjection of NMDA in the dorsomedial hypothalamus (DMH) were inhibited by iv 5-HT, but those following bicuculline nanoinjection in the DMH were not inhibited. CONCLUSIONS: The systemic 5-HT-induced inhibition of BAT SNA requires a GABAergic inhibition of BAT sympathoexcitatory neurones in the DMH. In addition, during warming, 5-HT released endogenously in rRPa inhibits BAT SNA.

Shuangxia decoction alleviates p-chlorophenylalanine induced insomnia through the modification of serotonergic and immune system.

As a Traditional Chinese Medicine (TCM), Shuangxia Decoction (SXD) has been used to treat insomnia in oriental countries for more than thousands of years and it presents remarkable clinical effects. However, its active pharmacological fraction and the mechanism of sedative-hypnotic effects have not been explored. In this paper, we investigated active pharmacological fraction and revealed the detailed mechanisms underlying the sedative-hypnotic effects of SXD. It showed that SXD water extract compared to ethanol extract possessed better sedative effects on locomotion activity in normal mice and increased sleep duration in subhypnotic dose of sodium pentobarbital-treated mice. SXD alleviated p-chlorophenylalanine (PCPA) -induced insomnia by increasing the content of 5-HT in cortex [F (4, 55) = 12.67], decreasing the content of dopamine (DA) and norepinephrine (NE). Furthermore, SXD enhanced the expression of 5-HT1A and 5-HT2A receptors in hypothalamic and reduced serum levels of IL-1,TNF-α [F (5, 36) = 15.58]. In conclusion, these results indicated that SXD produced beneficial sedative and hypnotic bioactivities mediated by regulating the serotonergic and immune system.

Effects of 5-HT1 and 5-HT 2 Receptor Agonists on Electromagnetic Field-Induced Analgesia in Rats.

Much evidence demonstrates the antinociceptive effect of magnetic fields (MFs). However, the analgesic action mechanism of the electromagnetic field (EMF) is not exactly understood. The aim of the present study was to investigate the effects of 5-HT1 and 5-HT2 receptor agonists (serotonin HCl and 2,5-dimethoxy-4-iodoamphetamine [DOI] hydrochloride) on EMF-induced analgesia. In total, 66 adult male Wistar albino rats with an average body mass of 225 ± 13 g were used in this study. The animals were subjected to repeated exposures of alternating 50 Hz and 5 mT EMF for 2 h a day for 15 days. Prior to analgesia tests, serotonin HCl (5-HT1 agonist) 4 mg/kg, WAY 100635 (5-HT1 antagonist) 0.04 mg/kg, DOI hydrochloride (5-HT2 receptor agonist) 4 mg/kg, and SB 204741 (5-HT2 antagonist) 0.5 mg/kg doses were injected into rats. For statistical analysis of the data, analysis of variance was used and multiple comparisons were determined by Tukey's test. Administration of serotonin HCl MF (5 mT)-exposed rats produced a significant increase in percent maximal possible effect (% MPE) as compared with EMF group (P < 0.05). On the contrary, injection of WAY 100635 to MF-exposed rats produced a significant decrease in analgesic activity (P < 0.05). Similarly, the administration of DOI hydrochloride significantly increased % MPE values as compared with the EMF group while SB 204741 reduced it (P < 0.05). In conclusion, our results suggested that serotonin 5-HT1 and 5-HT2 receptors play an important role in EMF-induced analgesia; however, further research studies are necessary to understand the mechanism. Bioelectromagnetics. 2019;40:319-330. © 2019 Bioelectromagnetics Society.

5-HT1A receptor-mediated activation of neuroendocrine responses and multiple protein kinase pathways in the peripubertal rat hypothalamus.

Increasing evidence suggests that multiple factors can produce effects on the immature brain that are distinct and more long-lasting than those produced in adults. The hypothalamic paraventricular nucleus (PVN) is a region integral to the hypothalamic-pituitary-adrenal axis and is affected by anxiety, depression, and drugs used to treat these disorders, yet receptor signaling mechanisms operative in hypothalamus prior to maturation remain to be elucidated. In peripubertal male rats, systemic injection of the selective serotonin 1A (5-HT1A) receptor agonist (+)8-OH-DPAT (0.2 mg/kg) markedly elevated plasma levels of oxytocin and adrenocorticotropic hormone (ACTH) at 5 and 15 min post-injection. The 5-HT1A receptor selectivity was demonstrated by the ability of the 5-HT1A receptor selective antagonist WAY100635 to completely block both oxytocin and ACTH responses at 5 min, with some recovery of the ACTH response at 15 min. At 15 min post-injection, (+)8-OH-DPAT also increased levels of phosphorylated extracellular signal-regulated kinase (pERK) and phosphorylated protein kinase B (pAkt) in the PVN. As previously observed in adults, (+)8-OH-DPAT reduced levels of pERK in hippocampus. WAY100635 also completely blocked (+)8-OH-DPAT-mediated elevations in hypothalamic pERK and pAkt and the reductions in hippocampal pERK, demonstrating 5-HT1A receptor selectivity of both kinase responses. This study provides the first demonstration of functional 5-HT1A receptor-mediated ERK and Akt signaling pathways in the immature hypothalamus, activated by a dose of (+)8-OH-DPAT that concomitantly stimulates neuroendocrine responses. This information is fundamental to identifying potential signaling pathways targeted by biased agonists in the development of safe and effective treatment strategies in children and adolescents.

Estradiol suppresses ingestive response evoked by activation of 5-HT1A receptors in the lateral hypothalamus of ovariectomized rats.

The present study investigated the effects of estradiol (E2) on ingestive behavior after activation of 5-HT1A receptors in the lateral hypothalamus (LH) of female rats habituated to eat a wet mash diet. Ovariectomized rats treated with corn oil (OVX) or estradiol cypionate (OVX+E) received local injections into the LH of vehicle or an agonist of 5-HT1A receptors, 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT; at a dose of 6 nmol). To determine the involvement of these receptors in food intake, some animals were pretreated with N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexane carboxamide maleate (WAY-100635, a 5-HT1A receptor full antagonist, at a dose of 0.37 nmol), followed by the injection of the agonist 8-OH-DPAT or its vehicle. The results showed that the injection of 8-OH-DPAT into the LH of OVX rats significantly increased food intake, and the duration and frequency of this behavior. The pretreatment with E2 suppressed the hyperphagic response induced by 8-OH-DPAT in OVX animals. The inhibition of 5-HT1A receptors after pretreatment with WAY-100635 blocked the hyperphagic effects evoked by 8-OH-DPAT in OVX. These results indicate that the activity of LH 5-HT1A receptors could be affected by blood E2 levels.

Mining the Potential of Label-Free Biosensors for In Vitro Antipsychotic Drug Screening.

The pharmaceutical industry is facing enormous challenges due to high drug attribution rates. For the past decades, novel methods have been developed for safety and efficacy testing, as well as for improving early development stages. In vitro screening methods for drug-receptor binding are considered to be good alternatives for decreasing costs in the identification of drug candidates. However, these methods require lengthy and troublesome labeling steps. Biosensors hold great promise due to the fact that label-free detection schemes can be designed in an easy and low-cost manner. In this paper, for the first time in the literature, we aimed to compare the potential of label-free optical and impedimetric electrochemical biosensors for the screening of antipsychotic drugs (APDs) based on their binding properties to dopamine receptors. Particularly, we have chosen a currently-used atypical antipsychotic drug (Buspirone) for investigating its dopamine D3 receptor (D3R) binding properties using an impedimetric biosensor and a nanoplasmonic biosensor. Both biosensors have been specifically functionalized and characterized for achieving a highly-sensitive and reliable analysis of drug-D3R binding. Our biosensor strategies allow for comparing different affinities against the D3R, which facilitates the identification of strong or weak dopamine antagonists via in vitro assays. This work demonstrates the unique potential of label-free biosensors for the implementation of cost-efficient and simpler analytical tools for the screening of antipsychotic drugs.

Ex vivo study of human visceral nociceptors.

OBJECTIVE: The development of effective visceral analgesics free of deleterious gut-specific side effects is a priority. We aimed to develop a reproducible methodology to study visceral nociception in human tissue that could aid future target identification and drug evaluation. DESIGN: Electrophysiological (single unit) responses of visceral afferents to mechanical (von Frey hair (VFH) and stretch) and chemical (bradykinin and ATP) stimuli were examined. Thus, serosal afferents (putative nociceptors) were used to investigate the effect of tegaserod, and transient receptor potential channel, vanilloid 4 (TRPV4) modulation on mechanical responses. RESULTS: Two distinct afferent fibre populations, serosal (n=23) and muscular (n=21), were distinguished based on their differences in sensitivity to VFH probing and tissue stretch. Serosal units displayed sensitivity to key algesic mediators, bradykinin (6/14 units tested) and ATP (4/10), consistent with a role as polymodal nociceptors, while muscular afferents are largely insensitive to bradykinin (0/11) and ATP (1/10). Serosal nociceptor mechanosensitivity was attenuated by tegaserod (-20.8±6.9%, n=6, p<0.05), a treatment for IBS, or application of HC067047 (-34.9±10.0%, n=7, p<0.05), a TRPV4 antagonist, highlighting the utility of the preparation to examine the mechanistic action of existing drugs or novel analgesics. Repeated application of bradykinin or ATP produced consistent afferent responses following desensitisation to the first application, demonstrating their utility as test stimuli to evaluate analgesic activity. CONCLUSIONS: Functionally distinct subpopulations of human visceral afferents can be demonstrated and could provide a platform technology to further study nociception in human tissue.

A hypothalamo-midbrain-medullary pathway involved in the inhibition of the respiratory chemoreflex response induced by potassium cyanide in rodents.

Recent studies have demonstrated that a mild stimulation of the dorsomedian nucleus of the hypothalamus (DMH), a defense area, induces the inhibition of the carotid chemoreflex tachypnea. DMH activation reduces the cardiac chemoreflex response via the dorsolateral part of the periaqueductal grey matter (dlPAG) and serotonin receptors (5-HT3 subtype) in the nucleus tractus solitarius (NTS). The objectives of this study were to assess whether dlPAG and subsequent NTS 5-HT3 receptors are involved in chemoreflex tachypnea inhibition during mild activation of the DMH. For this purpose, peripheral chemoreflex was activated with potassium cyanide (KCN, 40 µg/rat, i.v.) during electrical and chemical minimal supra-threshold (mild) stimulation of the dlPAG or DMH. In both situations, changes in respiratory frequency (RF) following KCN administration were reduced. Moreover, pharmacological blockade of the dlPAG prevented DMH-induced KCN tachypnea inhibition. Activation of NTS 5-HT3 receptors also reduced chemoreflex tachypnea in a dose-dependent manner. In addition, blockade of NTS 5-HT3 receptors with granisetron (2.5 but not 1.25 mM), or the use of mice lacking the 5-HT3a receptor (5-HT3a KO), prevented dlPAG-induced KCN reductions in RF. A respiratory hypothalamo-midbrain-medullary pathway (HMM) therefore plays a crucial role in the inhibition of the hyperventilatory response to carotid chemoreflex.

The serotonin hallucinogen 5-MeO-DMT alters cortico-thalamic activity in freely moving mice: Regionally-selective involvement of 5-HT1A and 5-HT2A receptors.

5-MeO-DMT is a natural hallucinogen acting as serotonin 5-HT1A/5-HT2A receptor agonist. Its ability to evoke hallucinations could be used to study the neurobiology of psychotic symptoms and to identify new treatment targets. Moreover, recent studies revealed the therapeutic potential of serotonin hallucinogens in treating mood and anxiety disorders. Our previous results in anesthetized animals show that 5-MeO-DMT alters cortical activity via 5-HT1A and 5-HT2A receptors. Here, we examined 5-MeO-DMT effects on oscillatory activity in prefrontal (PFC) and visual (V1) cortices, and in mediodorsal thalamus (MD) of freely-moving wild-type (WT) and 5-HT2A-R knockout (KO2A) mice. We performed local field potential multi-recordings evaluating the power at different frequency bands and coherence between areas. We also examined the prevention of 5-MeO-DMT effects by the 5-HT1A-R antagonist WAY-100635. 5-MeO-DMT affected oscillatory activity more in cortical than in thalamic areas. More marked effects were observed in delta power in V1 of KO2A mice. 5-MeO-DMT increased beta band coherence between all examined areas. In KO2A mice, WAY100635 prevented most of 5-MeO-DMT effects on oscillatory activity. The present results indicate that hallucinatory activity of 5-MeO-DMT is likely mediated by simultaneous alteration of prefrontal and visual activities. The prevention of these effects by WAY-100635 in KO2A mice supports the potential usefulness of 5-HT1A receptor antagonists to treat visual hallucinations. 5-MeO-DMT effects on PFC theta activity and cortico-thalamic coherence may be related to its antidepressant activity. This article is part of the Special Issue entitled 'Psychedelics: New Doors, Altered Perceptions'.

The brain-penetrant 5-HT7 receptor agonist LP-211 reduces the sensory and affective components of neuropathic pain.

Neuropathic pain is a debilitating pathological condition of high clinical relevance. Changes in neuronal excitability in the anterior cingulate cortex (ACC) play a central role in the negative emotional and affective aspects of chronic pain. We evaluated the effects of LP-211, a new serotonin-receptor-type-7 (5-HT7R) agonist that crosses the blood-brain barrier, on ACC neurons in a mouse model of neuropathic pain. LP-211 reduced synaptic integration in layer 5 pyramidal neurons, which was enhanced in neuropathic pain due to a dysfunction of dendritic hyperpolarization-activated-and-cyclic-nucleotide-regulated (HCN) channels. Acute injection of LP-211 had an analgesic effect, increasing the mechanical withdrawal threshold in neuropathic animals, which was partially mediated by an action in the ACC. Additionally, the acute application of LP-211 blocked the switch in the place escape/avoidance behavior induced by noxious stimuli. Thus systemic treatment with a 5-HT7R agonist leads to modulation of the ACC, which dampens sensory and affective aspects of chronic pain.

Isobolographic analysis of the cutaneous antinociceptive interaction between bupivacaine co-injected with serotonin in rats.

BACKGROUND: The aim of this experiment was to investigate a long-lasting local anesthetic bupivacaine combined with serotonin at inducing cutaneous antinociception. METHODS: The skin antinociception, characterized by an inhibition of the cutaneous trunci muscle reflex (CTMR) following the pinprick on the dorsal skin of rats, was evaluated. The cutaneous antinociceptive effects of bupivacaine alone, serotonin alone, or bupivacaine co-injected with serotonin in a dose-dependent fashion were constructed, while the drug-drug interactions were evaluated by isobologram. RESULTS: Subcutaneous serotonin, as well as the local anesthetic bupivacaine provoked dose-related cutaneous antinociception. On an equipotent basis (50% effective dose [ED50]), the relative potency was bupivacaine (0.43 [0.37-0.50] µmol)>serotonin (1.27 [1.15-1.40] µmol) (p<0.01). At the equi-anesthetic doses (ED75, ED50 and ED25), the duration of bupivacaine was similar to that of serotonin at producing cutaneous antinociceptive effects. Co-administration of bupivacaine and serotonin displayed a synergistic antinociception. CONCLUSIONS: The preclinical data demonstrated that serotonin is less potent in eliciting cutaneous antinociceptive effects but has the similar duration of action, compared with bupivacaine. We also found a more significant depth of the sensory block with bupivacaine+serotonin than bupivacaine alone.

Genistein modulation of seizure: involvement of estrogen and serotonin receptors.

Genistein, a major source of phytoestrogen exposure for humans and animals, has been shown to mediate neuroprotection in Alzheimer's disease and status epilepticus. In the present study, we investigated the effect of genistein on pentylenetetrazole-induced seizures in ovariectomized mice and the possible involvement of estrogenic and serotonergic pathways in the probable effects of genistein. Intraperitoneal (i.p.) administration of genistein (10 mg/kg) significantly increased the seizure threshold 30 min prior to induction of seizures 14 days after ovariectomy surgery. Administration of fulvestrant (1 mg/kg, i.p.), an estrogen receptor antagonist, completely reversed the anticonvulsant effect of genistein (10 mg/kg) in ovariectomized mice. Administration of the antagonist of serotonin receptor (5-HT3), tropisetron (10 mg/kg, i.p.), eliminated the anticonvulsant effect of genistein, whereas co-administration of m-chlorophenylbiguanide (5-HT3 receptor agonist; 1 mg/kg) and a non-effective dose of genistein (5 mg/kg) increased the seizure threshold. To conclude, it seems that estrogenic/serotonergic systems might be involved in the anticonvulsant properties of genistein.

Activation of 5-HT1A receptors in the rat dorsomedial hypothalamus inhibits stress-induced activation of the hypothalamic-pituitary-adrenal axis.

Acute activation of the hypothalamic-pituitary-adrenal (HPA) axis, leading to the release of corticosteroid hormones into the circulation, is an adaptive response to perceived threats. Persistent activation of the HPA axis can lead to impaired physiological or behavioral function with maladaptive consequences. Thus, efficient control and termination of stress responses is essential for well-being. However, inhibitory control mechanisms governing the HPA axis are poorly understood. Previous studies suggest that serotonergic systems, acting within the medial hypothalamus, play an important role in inhibitory control of stress-induced HPA axis activity. To test this hypothesis, we surgically implanted chronic jugular cannulae in adult male rats and conducted bilateral microinjection of vehicle or the 5-HT1A receptor agonist, 8-hydroxy-2-(di-n-propylamino) tetralin hydrobromide (8-OH-DPAT; 8 nmol, 0.2 µL, 0.1 µL/min, per side) into the dorsomedial hypothalamus (DMH) immediately prior to a 40 min period of restraint stress. Repeated blood sampling was conducted using an automated blood sampling system and plasma corticosterone concentrations were determined using enzyme-linked immunosorbent assay. Bilateral intra-DMH microinjections of 8-OH-DPAT suppressed stress-induced increases in plasma corticosterone within 10 min of the onset of handling prior to restraint and, as measured by area-under-the-curve analysis of plasma corticosterone concentrations, during the 40 min period of restraint. These data support an inhibitory role for serotonergic systems, acting within the DMH, on stress-induced activation of the HPA axis. Lay summary: Inhibitory control of the hypothalamic-pituitary-adrenal (HPA) stress hormone response is important for well-being. One neurochemical implicated in inhibitory control of the HPA axis is serotonin. In this study we show that activation of serotonin receptors, specifically inhibitory 5-HT1A receptors in the dorsomedial hypothalamus, is sufficient to inhibit stress-induced HPA axis activity in rats.

Activity of etv5a and etv5b genes in the hypothalamus of fasted zebrafish is influenced by serotonin.

Serotonin has been implicated in the inhibition of food intake in vertebrates. However, the mechanisms through which serotonin acts has yet to be elucidated. Recently, ETV5 (ets variant gene 5) has been associated with obesity and food intake control mechanisms in mammals. We have analyzed a putative physiological function of the two etv5 paralogous genes (etv5a and etv5b) in neuronal food intake control in adult zebrafish that have been exposed to different nutritional conditions. A feeding assay was established and fluoxetine, a selective serotonin re-uptake inhibitor (SSRI), was applied. Gene expression changes in the hypothalamus were determined using real-time PCR. Fasting induced an up-regulation of etv5a and etv5b in the hypothalamus, whereas increased serotonin levels in the fasted fish counteracted the increase in expression. To investigate potential mechanisms the expression of further food intake control genes was determined. The results show that an increase of serotonin in fasting fish causes a reduction in the activity of genes stimulating food intake. This is in line with a previously demonstrated anorexigenic function of serotonin. Our results suggest that obesity-associated ETV5 has a food intake stimulating function and that this function is modulated through serotonin.