Brainstem serotonin neurons selectively gate retinal information flow to thalamus.

Retinal ganglion cell (RGC) types relay parallel streams of visual feature information. We hypothesized that neuromodulators might efficiently control which visual information streams reach the cortex by selectively gating transmission from specific RGC axons in the thalamus. Using fiber photometry recordings, we found that optogenetic stimulation of serotonergic axons in primary visual thalamus of awake mice suppressed ongoing and visually evoked calcium activity and glutamate release from RGC boutons. Two-photon calcium imaging revealed that serotonin axon stimulation suppressed RGC boutons that responded strongly to global changes in luminance more than those responding only to local visual stimuli, while the converse was true for suppression induced by increases in arousal. Converging evidence suggests that differential expression of the 5-HT1B receptor on RGC presynaptic terminals, but not differential density of nearby serotonin axons, may contribute to the selective serotonergic gating of specific visual information streams before they can activate thalamocortical neurons.

Improvement Effects of Myelophil on Symptoms of Chronic Fatigue Syndrome in a Reserpine-Induced Mouse Model.

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is associated with various symptoms, such as depression, pain, and fatigue. To date, the pathological mechanisms and therapeutics remain uncertain. The purpose of this study was to investigate the effect of myelophil (MYP), composed of Astragali Radix and Salviaemiltiorrhizae Radix, on depression, pain, and fatigue behaviors and its underlying mechanisms. Reserpine (2 mg/kg for 10 days, intraperitoneally) induced depression, pain, and fatigue behaviors in mice. MYP treatment (100 mg/kg for 10 days, intragastrically) significantly improved depression behaviors, mechanical and thermal hypersensitivity, and fatigue behavior. MYP treatment regulated the expression of c-Fos, 5-HT1A/B receptors, and transforming growth factor ß (TGF-ß) in the brain, especially in the motor cortex, hippocampus, and nucleus of the solitary tract. MYP treatment decreased ionized calcium binding adapter molecule 1 (Iba1) expression in the hippocampus and increased tyrosine hydroxylase (TH) expression and the levels of dopamine and serotonin in the striatum. MYP treatment altered inflammatory and anti-oxidative-related mRNA expression in the spleen and liver. In conclusion, MYP was effective in recovering major symptoms of ME/CFS and was associated with the regulation of dopaminergic and serotonergic pathways and TGF-ß expression in the brain, as well as anti-inflammatory and anti-oxidant mechanisms in internal organs.

Early life stress induced by maternal separation during lactation alters the eating behavior and serotonin system in middle-aged rat female offspring.

Stressful events occurring during early life have been related to behavioral and neurochemical disturbances. Maternal separation during the first two weeks of life is a traumatic event that strongly affects the feeding behavior and serotonergic system of the progeny in adulthood. As this system modulates the feeding behavior, the present study aimed at investigating the effects of maternal separation-induced stress on both the feeding behavior and serotonergic system of the middle-aged female rats by manipulating this system using fluoxetine, a selective serotonin transporter inhibitor. Lactating Wistar rats were separated from their litters from postnatal day 2 (PND 2) to PND 14 for 3 h in the dark phase of the circadian cycle. The maternally separated (MS) and control (C) groups were distinguished from each other based on the incidence or absence of maternal separation (early life stress). All the analyses were done on the female offspring from one-year of age. Maternal separation anticipated the satiety point in these females. This anticipation was linked to lower food intake, meal duration and meal size. These results mirrored the effects of fluoxetine in the control animals. Furthermore, maternal separation was associated with 5ht1b serotonin receptor hyperexpression in the hypothalamus. These findings demonstrate that maternal separation has long-lasting effects on the eating behavior and serotonergic system and that this system could be responsible for mediating these behavioral outcomes.

Early weaning leads to disruption of homeostatic and hedonic eating behaviors and modulates serotonin (5HT) and dopamine (DA) systems in male adult rats.

Early weaning is associated with disruption of eating behavior. However, little is known about the mechanisms behind it. 5HT and DA systems are key regulators of homeostatic and hedonic eating behaviors, respectively. Thus, this study aims to evaluate the effects of early weaning on feeding behavior and 5HT and DA systems. For this, rats were submitted to regular (PND30) or early weaning (PND15) and between PND250 and PND300 were evaluated food intake of standard diet in response to 4 h food deprivation, during the 24 h period and per phase of the circadian cycle, in addition to the palatable food intake. Additionally, body mass and mRNA expression of 5HT1B, 5HT2C, SERT, DRD1 and DRD2 were evaluated in the hypothalamus and brainstem. The results demonstrate that early weaning promoted an increase in standard food intake in response to a 4 h food deprivation in the 24 h period and in the dark phase of the circadian cycle, in addition to an increased palatable food intake. No differences in body mass between regular or early weaning were observed. In the hypothalamus, increased mRNA expression of SERT and DRD1 was observed, but decreased 5HT1B mRNA expression. In the brainstem, the expression of 5HT1B, SERT, 5HT2C, DRD1 and DRD2 was increased in early weaned rats. In a nutshell, the stress promoted by early weaning has programmed the animals to be hyperphagic and to increase their palatable food intake, which was associated with modulation of 5HT and DA systems.

Alkaloids from the rhizomes of Ligusticum striatum exert antimigraine effects through regulating 5-HT1B receptor and c-Jun.

ETHNOPHARMACOLOGICAL RELEVANCE: Migraine is a prevalent, complex, painful, and disabling neurovascular disorder that places an enormous social and economic burden on patients. Rhizome Chuanxiong (RCX), the dried rhizomes of Ligusticum striatum DC., has been widely used in the clinic for the treatment of migraine for centuries in China. Total alkaloids (TAs) are considered to be important effective ingredients of L. striatum, especially for cardiovascular and cerebrovascular diseases. However, there has been no study published, to date, reporting the antimigraine effects of TAs from RCX (RCXTAs). AIM OF THE STUDY: The present study was designed to evaluate the antimigraine effects of RCXTAs and explore the underlying mechanisms in an experimental migraine rat model. MATERIALS AND METHODS: RCXTAs were prepared in accordance with our previous optimized preparation process. A nitroglycerin-induced migraine model in rats and a reserpine-induced migraine model in mice were established to investigate the effects of RCXTAs on monoamine neurotransmitters in brain tissue, including 5-hydroxytryptamine (5-HT) and its metabolite (5-HIAA). Migraine rats or mice were divided into six groups as follows: control; model; zolmitriptan (1.67 mg/kg); and low-, medium-, and high-dose RCXTAs (12.5, 25, and 50 mg/kg, respectively). The levels of 5-HT and 5-HIAA in the brains of rats and mice were determined by using the enzyme-linked immunosorbent assay method. Pathological changes in the brains of migraine rats were examined by immunohistochemistry. The protein expression of 5-HT1B receptor, c-Fos, and c-Jun in the periaqueductal gray (PAG) of migraine rats was measured by Western blot. RESULTS: After preventive administration of RCXTAs to the nitroglycerin-induced migraine rats, the levels of 5-HT and 5-HIAA in the brain tissue were generally upregulated in all three RCXTA dose groups, a finding that was similar to that observed in the control group. Additionally, the 5-HT and 5-HIAA levels were significantly increased in the medium- and high-dose RCXTA groups when compared with the model group (p < 0.01). Therapeutical administration of RCXTAs to reserpine-induced migraine mice also inhibited the reduction of 5-HT and 5-HIAA in the brain (p < 0.01). Both immunohistochemistry and Western blot tests showed that RCXTAs pretreatment has significantly upregulated 5-HT1B receptor expression and downregulated c-Jun expression in the nitroglycerin-induced migraine rats. CONCLUSIONS: RCXTAs exerted significant preventive and therapeutic effects on migraine via increasing the levels of 5-HT and 5-HIAA. Upregulation of the expression of monoamine neurotransmitter 5-HT1B receptor and downregulation of the expression of c-Jun were the possible mechanisms.

N-acetylcysteine blocks serotonin 1B agonist-induced OCD-related behavior in mice.

Glutamate-modulating agents are of increasing interest in obsessive-compulsive disorder (OCD). Current pharmacotherapies for OCD target the serotonin and dopamine systems, and are limited in efficacy. N-acetylcysteine (NAC) is an over-the-counter amino acid supplement that inhibits glutamate neurotransmission and has been shown in preliminary studies to reduce symptoms in OCD and related compulsive disorders. Despite growing interest in NAC as a novel psychiatric medication, no studies currently exist examining the effects of NAC in animal models of compulsive disorders. Here, we investigate NAC in a well-validated mouse model of OCD that is predictive of treatment efficacy as well as the time course for therapeutic onset of OCD medications. NAC (60 mg/kg/day or 120 mg/kg/day) was administered via the drinking water of mice for 3 weeks prior to behavioral testing. Mice were tested in the delayed alternation task (DAT) and open field test following acute serotonin 1B receptor (5-HT1B) agonist challenge to induce OCD-related behavior. We found that both doses of NAC blocked 5-HT1B agonist-induced deficits on the DAT. In a separate study, we administered NAC (60 mg/kg/day) for 1 week or 3 weeks in the drinking water of mice prior to examining OCD-related behavior. We found that blockade of 5-HT1B agonist-induced OCD-like behavior is present at 3 weeks, but not 1 week, of NAC treatment. Together, our findings suggest that NAC is a novel OCD treatment with potential utility as monotherapy and therapeutic effects that emerge on a time-course similar to established medications. (PsycINFO Database Record

Modulation of hippocampal neuronal activity by So-ochim-tang-gamibang in mice subjected to chronic restraint stress.

BACKGROUND: So-ochim-tang-gamibang (SOCG) is a decoction formula which has been used to improve mental activity in traditional Korean medicine. The present study was performed to evaluate whether the treatment of SOCG was involved in activating hippocampal neurons in mice which were subjected to chronic restraint stress (CRS). METHODS: Mice were subjected to CRS for 2 weeks to induce depressive-like behaviors. SOCG was orally administered for the same period. mRNA expression in the hippocampus was analyzed by RT-PCR. Levels of serotonin receptor 5-HT1AR in the hippocampus were determined by western blotting and by immunofluorescence staining in coronal brain sections. Cultured neurons were prepared from the dorsal root ganglia (DRG) in mice to examine the effects of CRS and SOCG treatment on neurite outgrowth. Depressive-like behaviors of experimental animals were measured by open field test (OFT) and forced swimming test (FST). RESULTS: mRNA levels of serotonin 1A and 1B receptors (5-HT1AR and 5-HT1BR) were decreased in the hippocampus of CRS animals and increased by SOCG treatment. Signals of 5-HT1AR protein in CA3 pyramidal cells were decreased by CRS but elevated back to levels in control animals after SOCG treatment. Phospho-Erk1/2 protein in CA3 cells showed similar pattern of changes as in 5-HT1AR, suggesting coordinated regulation after SOCG treatment in CRS animals. Axonal growth-associated protein GAP-43 levels were also decreased by CRS and then increased by SOCG treatment. In vivo administration of SOCG improved neurite outgrowth of primary DRG neurons from CRS animals and also increased 5-HT1AR protein signals. Behavioral tests of open field and forced swimming showed that immobility time periods were significantly decreased by SOCG treatment. CONCLUSIONS: Our data suggest that SOCG treatment may increase synaptic responsiveness to serotonergic neuronal inputs by upregulating 5-HT1AR in the hippocampal neurons.

THE RESTORATION OF HYPOTHALAMIC SIGNALING SYSTEMS AS ONE OF THE CAUSES TO IMPROVE THE METABOLIC PARAMETERS IN BROMOCRYPTINE-TREATED RATS WITH NEONATAL MODEL OF DIABETES MELLITUS.

One of the approaches to correct type 2 diabetes mellitus (T2DM) and its complications is the use of drug bromocryptine mesylate (BCM), a selective agonist of type 2 dopamine receptors (DA2R). At the same time, the efficiency and the mechanisms of action of BCM in treatment of severe forms of T2DM are not currently understood. The objective was to study the effect of four-week treatment of male rats with neonatal T2DM model using BCM (300 mg/kg/day) on their metabolic parameters and activity of the adenylyl cyclase signaling system (ACSS) in the hypothalamus. The BCM treatment restored glucose tolerance and its utilization by exogenous insulin, and normalized lipid metabolism by lowering the levels of triglycerides and atherogenic cholesterol increased in T2DM. In the hypothalamus of BCM-treated diabetic rats, the regulation of ACSS by agonists of type 4 melanocortin receptor (MC4R), DA2R and 1B-subtype serotonin receptor, and the expression of Mc4r gene encoding MC4R were restored. Meanwhile, the BCM treatment had no effect on plasma insulin level and insulin production by pancreatic b-cells. The obtained data indicate the significant prospects of BCM to treat severe forms of experimental T2DM, and show that the therapeutic potential of this drug includes its ability to restore the hypothalamic signaling systems sensitive to monoamines and peptide of the melanocortin family, which are responsible for the control of energy metabolism and insulin sensitivity.

Hypothalamus proteomics from mouse models with obesity and anorexia reveals therapeutic targets of appetite regulation.

OBJECTIVE: This study examined the proteomic profile of the hypothalamus in mice exposed to a high-fat diet (HFD) or with the anorexia of acute illness. This comparison could provide insight on the effects of these two opposite states of energy balance on appetite regulation. METHODS: Four to six-week-old male C56BL/6J mice were fed a normal (control 1 group; n=7) or a HFD (HFD group; n=10) for 8 weeks. The control 2 (n=7) and lipopolysaccharide (LPS) groups (n=10) were fed a normal diet for 8 weeks before receiving an injection of saline and LPS, respectively. Hypothalamic regions were analysed using a quantitative proteomics method based on a combination of techniques including iTRAQ stable isotope labeling, orthogonal two-dimensional liquid chromatography hyphenated with nanospray ionization and high-resolution mass spectrometry. Key proteins were validated with quantitative PCR. RESULTS: Quantitative proteomics of the hypothalamous regions profiled a total of 9249 protein groups (q<0.05). Of these, 7718 protein groups were profiled with a minimum of two unique peptides for each. Hierachical clustering of the differentiated proteome revealed distinct proteomic signatures for the hypothalamus under the HFD and LPS nutritional conditions. Literature research with in silico bioinformatics interpretation of the differentiated proteome identified key biological relevant proteins and implicated pathways. Furthermore, the study identified potential pharmacologic targets. In the LPS groups, the anorexigen pro-opiomelanocortin was downregulated. In mice with obesity, nuclear factor-κB, glycine receptor subunit alpha-4 (GlyR) and neuropeptide Y levels were elevated, whereas serotonin receptor 1B levels decreased. CONCLUSIONS: High-precision quantitative proteomics revealed that under acute systemic inflammation in the hypothalamus as a response to LPS, homeostatic mechanisms mediating loss of appetite take effect. Conversely, under chronic inflammation in the hypothalamus as a response to HFD, mechanisms mediating a sustained 'perpetual cycle' of appetite enhancement were observed. The GlyR protein may constitute a novel treatment target for the reduction of central orexigenic signals in obesity.

OCD is associated with an altered association between sensorimotor gating and cortical and subcortical 5-HT1b receptor binding.

Obsessive-compulsive disorder (OCD) is characterized by impaired sensorimotor gating, as measured using prepulse inhibition (PPI). This effect may be related to abnormalities in the serotonin (5-HT) system. 5-HT1B agonists can impair PPI, produce OCD-like behaviors in animals, and exacerbate OCD symptoms in humans. We measured 5-HT1B receptor availability using (11)C-P943 positron emission tomography (PET) in unmedicated, non-depressed OCD patients (n=12) and matched healthy controls (HC; n=12). Usable PPI data were obtained from 20 of these subjects (10 from each group). There were no significant main effects of OCD diagnosis on 5-HT1B receptor availability ((11)C-P943 BPND); however, the relationship between PPI and (11)C-P943 BPND differed dramatically and significantly between groups. 5-HT1B receptor availability in the basal ganglia and thalamus correlated positively with PPI in controls; these correlations were lost or even reversed in the OCD group. In cortical regions there were no significant correlations with PPI in controls, but widespread positive correlations in OCD patients. Positive correlations between 5-HT1B receptor availability and PPI were consistent across diagnostic groups only in two structures, the orbitofrontal cortex and the amygdala. Differential associations of 5-HT1B receptor availability with PPI in patients suggest functionally important alterations in the serotonergic regulation of cortical/subcortical balance in OCD.

Differential Allelic Expression of HTR1B in Suicide Victims: Genetic and Epigenetic Effect of the Cis-Acting Variants.

OBJECTIVES: In the present study, we tested the allelic imbalance of the C861G single nucleotide polymorphism (SNP) of HTR1B in the frontal cortex of suicide victims. METHODS: The study was conducted using 3 sets of samples. First, C861G allele-specific mRNA levels in the frontal cortex were compared between suicide (n = 13) and nonsuicide controls (n = 13) from the Stanley Medical Research postmortem brain collection. Second, we tested common variants in the HTR1B promoter for linkage disequilibrium (LD) with the C861G variant in an unrelated sample of suicide attempters (SA; n = 38) and non-SA (NSA; n = 42). Finally, we performed a family-based association study of the C861G and promoter variants in 162 nuclear families using suicidal behavior severity scores as phenotype. RESULTS: We observed no alterations in the C/G expression ratio in suicide victims compared to nonsuicide controls (p = 0.370). When comparing the LD between the C861G and cis-acting SNPs, we did not find any differences in SA and NSA. There was no association between preferential transmission of cis-acting SNPs and suicidal behavior severity scores in both maternal and paternal meiosis. CONCLUSIONS: We found several promoter variants in LD that may potentially influence the allelic imbalance in the C861G variant. However, no evidence of allelic imbalance nor parent-of-origin effects of the C861G variant was observed in suicidal behavior. Further research is required to assess this marker in larger cohorts.

[The Impact of Electroacupuncture Intervention on Expression of 5-HTR 1 B/2 C Genes in Mice under Radiation Stimulation from Mobile Phone].

OBJECTIVE: To observe the effect of electroacupuncture (EA) stimulation of "Yifen" (TE 17), "Shenshu" (BL 23) on the expression of 5-hydroxytryptamine receptor 1 B (5-HTR 1 B) mRNA and 5-hydroxytryptamine receptor 2 C (5-HTR 2 C) mRNA in the cochlear nucleus tissue in mice experiencing radiation from mobile phone, so as to explore its mechanisms underlying improvement of tinnitus. METHODS: Thirty Kunming mice were randomly divided into control group (n = 6) and modeling group (n = 24). The tinnitus model was established by giving the mice with mobile phone-radiation for 1 h in the morning and 1 h in the afternoon, continuously for 40 days. EA stimulation was applied to "Yifeng" (TE 17) group (n = 6) and "Shenshu" (BL 23) group (n = 6) for 20 min, once a day for 7 days. The expression of 5-THR 1 B/2 C mRNA in the cochlear nucleus was assayed by fluorescence quantitative polymerase chain reaction (real time-PCR). RESULTS: The expression level of 5-HTR 1 B was significantly lower in the model group than in the control group (P < 0.05), while that of 5-HTR 2 C mRNA significantly increased (P < 0.01). TE 17 group received a significant acupoint intervention effect (P < 0.01). Compared with TE 17 group, BL 23 group received a weaker effect (P < 0.05). CONCLUSION: EA of TE 17 can up-regulate expression level of 5-HTR 1 B and down-regulate expression level of 5-HTR 2 C in the cochlear nucleus in mice experiencing mobile-phone radiation.

Experience-Dependent, Layer-Specific Development of Divergent Thalamocortical Connectivity.

The main input to primary sensory cortex is via thalamocortical (TC) axons that form the greatest number of synapses in layer 4, but also synapse onto neurons in layer 6. The development of the TC input to layer 4 has been widely studied, but less is known about the development of the layer 6 input. Here, we show that, in neonates, the input to layer 6 is as strong as that to layer 4. Throughout the first postnatal week, there is an experience-dependent strengthening specific to layer 4, which correlates with the ability of synapses in layer 4, but not in layer 6, to undergo long-term potentiation (LTP). This strengthening consists of an increase in axon branching and the divergence of connectivity in layer 4 without a change in the strength of individual connections. We propose that experience-driven LTP stabilizes transient TC synapses in layer 4 to increase strength and divergence specifically in layer 4 over layer 6.

The effects of Acorus tatarinowii Schott on 5-HT concentrations, TPH2 and 5-HT1B expression in the dorsal raphe of exercised rats.

ETHNOPHARMACOLOGICAL RELEVANCE: Acorus tatarinowii Schott (Shi Chang Pu) belongs to the family of Acoraceae. The plant is used as an important herb for prolonging life many years in traditional Chinese medicine. It is an ancient herbal tonic nutriment and can be used as anti-fatigue medicine. However, the effects of Acorus tatarinowii Schott on the endurance exercise in relation to central nervous system have not yet been clarified. In this study, the effects of Acorus tatarinowii Schott on treadmill running endurance, 5-HT concentrations, TPH2, 5-HT1B expression in the dorsal raphe of exercised rats were investigated. MATERIALS AND METHODS: Sixty adult male Sprague-Dawley rats were randomly divided into six groups: the normal group, the exercise group, the exercise and the rhizomes of Acorus tatarinowii Schott (ATS)(1mg/kg)-treated group, the exercise and ATS (10mg/kg)-treated group, the exercise and ATS (100mg/kg)-treated group, the exercise and caffeine (10mg/kg)-treated group. The effects of Acorus tatarinowii Schott on endurance exercise were determined by the time to exhaustion during treadmill exercise. The detection of 5-HT concentrations in the dorsal raphe was performed by HPLC analysis. The levels of TPH2, 5-HT1A and 5-HT1B expression were measured by western blot analysis and real-time PCR. RESULTS: We found Acorus tatarinowii Schott could prolong the time to exhaustion in treadmill exercise and suppress the exercise-induced increase of 5-HT synthesis, TPH2 mRNA and protein expression and prevent the exercise-induced decrease of 5-HT1B mRNA and protein expression in the dorsal raphe. Acorus tatarinowii Schott was as effective as caffeine in prolonging the exhaustion time in treadmill running and in decreasing the exercise-induced increase of 5-HT synthesis and TPH2 mRNA and protein expression and in preventing the exercise-induced decrease of 5-HT1B mRNA and protein expression in the dorsal raphe. CONCLUSIONS: The results indicated that the effects of Acorus tatarinowii Schott in inhibiting the exercise-induced synthesis of 5-HT and TPH2 expression and in preventing the exercise-induced decrease of 5-HT1B expression in the dorsal raphe might be the anti-fatigue mechanism of Acorus tatarinowii Schott.

Early MEK1/2 inhibition after global cerebral ischemia in rats reduces brain damage and improves outcome by preventing delayed vasoconstrictor receptor upregulation.

BACKGROUND: Global cerebral ischemia following cardiac arrest is associated with increased cerebral vasoconstriction and decreased cerebral blood flow, contributing to delayed neuronal cell death and neurological detriments in affected patients. We hypothesize that upregulation of contractile ETB and 5-HT1B receptors, previously demonstrated in cerebral arteries after experimental global ischemia, are a key mechanism behind insufficient perfusion of the post-ischemic brain, proposing blockade of this receptor upregulation as a novel target for prevention of cerebral hypoperfusion and delayed neuronal cell death after global cerebral ischemia. The aim was to characterize the time-course of receptor upregulation and associated neuronal damage after global ischemia and investigate whether treatment with the MEK1/2 inhibitor U0126 can prevent cerebrovascular receptor upregulation and thereby improve functional outcome after global cerebral ischemia. Incomplete global cerebral ischemia was induced in Wistar rats and the time-course of enhanced contractile responses and the effect of U0126 in cerebral arteries were studied by wire myography and the neuronal cell death by TUNEL. The expression of ETB and 5-HT1B receptors was determined by immunofluorescence. RESULTS: Enhanced vasoconstriction peaked in fore- and midbrain arteries 3 days after ischemia. Neuronal cell death appeared initially in the hippocampus 3 days after ischemia and gradually increased until 7 days post-ischemia. Treatment with U0126 normalised cerebrovascular ETB and 5-HT1B receptor expression and contractile function, reduced hippocampal cell death and improved survival rate compared to vehicle treated animals. CONCLUSIONS: Excessive cerebrovascular expression of contractile ETB and 5-HT1B receptors is a delayed response to global cerebral ischemia peaking 3 days after the insult, which likely contributes to the development of delayed neuronal damage. The enhanced cerebrovascular contractility can be prevented by treatment with the MEK1/2 inhibitor U0126, diminishes neuronal damage and improves survival rate, suggesting MEK1/2 inhibition as a novel strategy for early treatment of neurological consequences following global cerebral ischemia.

Serotonin (5-HT) activation of immortalized hypothalamic neuronal cells through the 5-HT1B serotonin receptor.

Serotonin [or 5-hydroxytryptamine or (5-HT)] has been implicated as a key modulator in energy homeostasis and a primary focus in the treatment of obesity. There is growing evidence that 5-HT, acting through the 5-HT 1B receptor (5-HT(1B)R) in the paraventricular nucleus of the hypothalamus (PVN), is important to this regulation. However, there is some contention as to whether 5-HT(1B)R action occurs directly on PVN neurons or indirectly via inhibitory inputs into the PVN. To address these questions, we used a novel clonal, hypothalamic neuronal cell model, adult mouse hypothalamic-2/30 (mHypoA-2/30), expressing a PVN-specific marker, single-minded homolog 1, as well as a complement of PVN neuropeptides, including TRH, vasopressin, ghrelin, nucleobindin-2, and galanin. Adult mouse hypothalamic-2/30 neurons were also found to express the 5-HT(1B)R and 5-HT 6 receptor, but not 2C, all previously linked to feeding regulation. Direct serotonergic stimulation (100 nm to 10 µm) of these neurons resulted in dose-dependent cFos activation. 5-HT (10 µm) suppressed forskolin-induced cAMP levels and induced a rise in intracellular Ca(2+) through ER Ca(2+) release, effects that were mimicked by the 5-HT(1B)R agonists, CGS12066B and CP93129, and that were attenuated in the presence of the 5-HT(1B)R-specific inhibitors, GR55562 and isamoltane hemifumarate. Modest transcriptional changes in ghrelin and nucleobindin-2 were also observed in response to 100 nm and 10 µm 5-HT, respectively. These findings support the model wherein 5-HT action through the 1B receptor subtype occurs directly on PVN neurons, leading to potential modification of neuronal transcriptional and secretory machinery.

Effects of selective serotonin antagonism on central neurotransmission.

Aggression and cannibalism in laying hens can differ in intensity and degree due to many factors, including genetics. Previous behavioral analysis of 2 strains of White Leghorns, DeKalb XL (DXL) and HGPS (a group-selected line for high group productivity and survivability), revealed high and low aggressive phenotypes, respectively. However, the exact genetic mechanisms mediating aggressiveness are currently unknown. Analysis of serotonin (5-HT) mediation of aggression in subordinate hens of these strains revealed increases in aggression in DXL hens following antagonism of the 5-HT1A receptor and in HGPS hens following antagonism of the 5-HT1B receptor. Here, we investigate the different neurotransmitter response in the hypothalamus and raphe nucleus mediating these aggressive responses to receptor antagonism. Elevated aggressive response to 5-HT1B antagonism by HGPS hens was also accompanied by a decrease in raphe nucleus dopamine (DA) and an increase in DA turnover. Increased aggressiveness in DXL hens did not coincide with a reduction in raphe nucleus 5-HT or turnover (as indicated by 5-hydroxyindoleacetic acid levels) following 5-HT1A antagonism. A reduction in 5-hydroxyindoleacetic acid (but not 5-HT) was seen in HGPS hens treated with 5-HT1A antagonist; however, these hens exhibited no change in aggressive behaviors. Our data show evidence of different heritable mechanisms of neurotransmitter regulation of aggressive response, specifically heritable differences in the interaction between 5-HT and catecholamines in regulating aggression.

Essential role for orbitofrontal serotonin 1B receptors in obsessive-compulsive disorder-like behavior and serotonin reuptake inhibitor response in mice.

BACKGROUND: Perseveration and sensorimotor gating deficits are core features of obsessive-compulsive disorder (OCD). Serotonin 1B receptor (5-HT1BR) agonists exacerbate OCD symptoms in patients and induce perseveration and sensorimotor gating deficits in mice. Serotonin reuptake inhibitors (SRIs), but not noradrenaline reuptake inhibitors (NRIs), reduce OCD symptoms following 4 to 8 weeks of treatment. Using mice, we compared the effects of chronic SRI versus NRI treatment on 5-HT1BR-induced OCD-like behavior and 5-HT1BR sensitivity in orbitofrontal-subcortical OCD circuits. Furthermore, we localized the 5-HT1BR population that mediates OCD-like behavior. METHODS: Mice chronically received the SRI clomipramine or the NRI desipramine and were examined for 5-HT1BR-induced OCD-like behavior or 5-HT1BR binding and G-protein coupling in caudate putamen, nucleus accumbens, and orbitofrontal cortex. Separate mice were tested for OCD- or depression-like behavior following 4, 14, 21, 28, or 56 days of SRI treatment. Finally, OCD-like behavior was assessed following intra-orbitofrontal 5-HT1BR agonist infusion or intra-orbitofrontal 5-HT1BR antagonist infusion coupled with systemic 5-HT1BR agonist treatment. RESULTS: Effective, but not ineffective, OCD treatments reduced OCD-like behavior in mice with a time course that parallels the delayed therapeutic onset in OCD patients and downregulated 5-HT1BR expression in the orbitofrontal cortex. Intra-orbitofrontal 5-HT1BR agonist infusion induced OCD-like behavior, and intra-orbitofrontal 5-HT1BR antagonist infusion blocked OCD-like effects of systemic 5-HT1BR agonist treatment. CONCLUSIONS: These results indicate that orbitofrontal 5-HT1BRs are necessary and sufficient to induce OCD-like behavior in mice and that SRI pharmacotherapy reduces OCD-like behavior by desensitizing orbitofrontal 5-HT1BRs. Our findings suggest an essential role for orbitofrontal 5-HT1BRs in OCD pathophysiology and treatment.

Decreased plasma ghrelin contributes to anorexia following novelty stress.

We hypothesized that anorexia induced by novelty stress caused by exposure to a novel environment may be due to activation of corticotropin-releasing factor (CRF) and subsequently mediated by decreasing peripheral ghrelin concentration via serotonin (5-HT) and melanocortin-4 receptors (MC4R). Each mouse was transferred from group-housed cages to individual cages to establish the novelty stress. We observed the effect of changes in feeding behavior in a novel environment using the method of transferring group-housed mice to individual cages. We investigated the effect of an intracerebroventricular injection of antagonists/agonists of CRF1/2 receptors (CRF1/2Rs), 5-HT(1B)/(2C) receptors (5-HT(1B)/(2C)R), and MC4R to clarify the role of each receptor on the decrease in food intake. Plasma ghrelin levels were also measured. The novelty stress caused a reduction in food intake that was abolished by administering a CRF1R antagonist. Three hours after the novelty stress, appetite reduction was associated with reduced levels of neuropeptide Y/agouti-related peptide mRNA, increased levels of proopiomelanocortin mRNA in the hypothalamus, and a decrease in plasma ghrelin level. Administering a CRF1R antagonist, a 5-HT(1B)/(2C)R antagonist, an MC4R antagonist, exogenous ghrelin, and an enhancer of ghrelin secretion, rikkunshito, resolved the reduction in food intake 3 h after the novelty stress by enhancing circulating ghrelin concentrations. We showed that anorexia during a novelty stress is a process in which CRF1R is activated at the early stage of appetite loss and is subsequently activated by a 5-HT(1B)/(2C)R and MC4R stimulus, leading to decreased peripheral ghrelin concentrations.

The relevance of preclinical research models for the development of antimigraine drugs: focus on 5-HT(1B/1D) and CGRP receptors.

Migraine is a complex neurovascular syndrome, causing a unilateral pulsating headache with accompanying symptoms. The past four decades have contributed immensely to our present understanding of migraine pathophysiology and have led to the introduction of specific antimigraine therapies, much to the relief of migraineurs. Pathophysiological factors culminating into migraine headaches have not yet been completely deciphered and, thus, pose an additional challenge for preclinical research in the absence of any direct experimental marker. Migraine provocation experiments in humans use a head-score to evaluate migraine, as articulated by the volunteer, which cannot be applied to laboratory animals. Therefore, basic research focuses on different symptoms and putative mechanisms, one at a time or in combination, to validate the hypotheses. Studies in several species, utilizing different preclinical approaches, have significantly contributed to the two antimigraine principles in therapeutics, namely: 5-HT(1B/1D) receptor agonists (known as triptans) and CGRP receptor antagonists (known as gepants). This review will analyze the preclinical experimental models currently known for the development of these therapeutic principles, which are mainly based on the vascular and/or neurogenic theories of migraine pathogenesis. These include models based on the involvement of cranial vasodilatation and/or the trigeminovascular system in migraine. Clearly, the preclinical strategies should involve both approaches, while incorporating the newer ideas/techniques in order to get better insights into migraine pathophysiology.