Modulation of 5-HT system in mice with a targeted disruption of neuromedin B receptor

To assess the role of neuromedin B receptor (NMB-R) on the modulation of serotonergic (5-HT) system, the function of the 5-HT system was examined in mice lacking the NMB-R gene. Immunohistochemical analysis of brain sections revealed that 5-HT expression level in the dorsal raphe neurons was elevated in NMB-R-deficient mice compared with wild-type mice. Although restraint stress enhanced 5-HT expression in these neurons in wild-type mice, this treatment did not affect 5-HT expression level in NMB-R-deficient mice, indicating the modulation of 5-HT system in the mutant mice. Since 5-HT system is involved in responses to stress and anxiety, we characterized stress response in these mice. The number of c-Fos expressing cells in the paraventricular nucleus of the hypothalamus was higher in NMB-R-deficient mice than in wild-type mice in both basal and stressed conditions. Moreover, the plasma corticosterone level under restraint stress was elevated in NMB-R-deficient mice compared to wild-type mice. In the forced swimming tests, the duration of immobility was longer in mutant mice than in wild-type mice. These data show dysregulated response to stress in NMB-R-deficient mice. However, behavior related to anxiety, assessed by elevated plus-maze and light-dark box, was not affected in NMB-R-deficient mice. NMB-R is known to be expressed in dorsal raphe neurons, and our data suggest that NMB-R has an important role in fine tuning of subsets of 5-HT neurons in this nucleus, and impairment of this system leads to the dysregulated response to stress.     

Dietary restriction changes behaviours in brain-derived neurotrophic factor heterozygous mice: role of serotonergic system

Accumulating evidence has suggested that brain-derived neurotrophic factor (BDNF) plays a role in eating behaviours, and that BDNF-heterozygous (+/-) mice exhibit abnormal behaviours (e.g. obesity, anxiety and aggression). The present study was undertaken to determine whether or not dietary restriction (DR) alters the behaviours in BDNF(+/-) mice, as DR has been shown to exert a number of beneficial effects on the brain. Eight-week-old male wild-type (+/+) and BDNF(+/-) mice were divided into two groups, ad libitum (AL) diet group and DR group, for 16 weeks. After carrying out a behavioural evaluation, we determined the BDNF mRNA levels, as well as mRNA levels for subtypes (5-HT(1A), 5-HT(1B), 5-HT(2A) and 5-HT(2C)) of the 5-HT receptor and 5-HT transporter (5-HTT), protein levels of BDNF and concentrations of 5-HT and 5-HIAA in the hypothalamus, hippocampus and frontal cortex. DR significantly ameliorated behaviours including obesity, anxiety and aggression in BDNF(+/-) mice. The concentrations of 5-HT and 5-HIAA in the frontal cortex, and 5-HT in the hippocampus, of BDNF(+/-) mice were significantly lower than those of wild-type mice. Interestingly, DR significantly increased the levels of 5-HT and 5-HIAA in the frontal cortex of BDNF(+/-) mice. These findings suggest that DR may alter the behaviours in BDNF(+/-) mice, and that the 5-HT system may be implicated in the beneficial effects of DR on these behaviours.     

Acetaminophen differentially enhances social behavior and cortical cannabinoid levels in inbred mice

Supratherapeutic doses of the analgesic acetaminophen (paracetomol) are reported to promote social behavior in Swiss mice. However, we hypothesized that it might not promote sociability in other strains due to cannabinoid CB(1) receptor-mediated inhibition of serotonin (5-HT) transmission in the frontal cortex. We examined the effects of acetaminophen on social and repetitive behaviors in comparison to a cannabinoid agonist, WIN 55,212-2, in two strains of socially-deficient mice, BTBR and 129S1/SvImJ (129S). Acetaminophen (100mg/kg) enhanced social interactions in BTBR, and social novelty preference and marble burying in 129S at serum levels of ≥70 ng/ml. Following acetaminophen injection or sociability testing, anandamide (AEA) increased in BTBR frontal cortex, while behavior testing increased 2-arachidonyl glycerol (2-AG) levels in 129S frontal cortex. In contrast, WIN 55,212-2 (0.1mg/kg) did not enhance sociability. Further, we expected CB(1)-deficient (+/-) mice to be less social than wild-type, but instead found similar sociability. Given strain differences in endocannabinoid response to acetaminophen, we compared cortical CB(1) and 5-HT(1A) receptor density and function relative to sociable C57BL/6 mice. CB(1) receptor saturation binding (Bmax=958±117 fmol/mg protein), and affinity for [(3)H] CP55,940 (K(D)=3±0.8 nM) was similar in frontal cortex among strains. CP55,940-stimulated [(35)S] GTPγS binding in cingulate cortex was 136±12, 156±22, and 75±9% above basal in BTBR, 129S and C57BL/6 mice. The acetaminophen metabolite para-aminophenol (1 μM) failed to stimulate [(35)S] GTPγS binding. Hence, it appears that other indirect actions of acetaminophen, including 5-HT receptor agonism, may underlie its sociability promoting properties outweighing any CB(1) mediated suppression by locally-elevated endocannabinoids in these mice.     

Prebiotic administration normalizes lipopolysaccharide (LPS)-induced anxiety and cortical 5-HT2A receptor and IL1-β levels in male mice

The manipulation of the enteric microbiota with specific prebiotics and probiotics, has been shown to reduce the host’s inflammatory response, alter brain chemistry, and modulate anxiety behaviour in both rodents and humans. However, the neuro-immune and behavioural effects of prebiotics on sickness behaviour have not been explored. Here, adult male CD1 mice were fed with a specific mix of non-digestible galacto-oligosaccharides (Bimuno®, BGOS) for 3 weeks, before receiving a single injection of lipopolysaccharide (LPS), which induces sickness behaviour and anxiety. Locomotor and marble burying activities were assessed 4 h after LPS injection, and after 24 h, anxiety in the light–dark box was assessed. Cytokine expression, and key components of the serotonergic (5-Hydroxytryptamine, 5-HT) and glutamatergic system were evaluated in the frontal cortex to determine the impact of BGOS administration at a molecular level. BGOS-fed mice were less anxious in the light–dark box compared to controls 24 h after the LPS injection. Elevated cortical IL-1β concentrations in control mice 28 h after LPS were not observed in BGOS-fed animals. This significant BGOS × LPS interaction was also observed for 5HT2A receptors, but not for 5HT1A receptors, 5HT, 5HIAA, NMDA receptor subunits, or other cytokines. The intake of BGOS did not influence LPS-mediated reductions in marble burying behaviour, and its effect on locomotor activity was equivocal. Together, our data show that the prebiotic BGOS has an anxiolytic effect, which may be related to the modulation of cortical IL-1β and 5-HT2A receptor expression. Our data suggest a potential role for prebiotics in the treatment of neuropsychiatric disorders where anxiety and neuroinflammation are prominent clinical features.     

Role of bombesin (BN)-like peptides/receptors in emotional behavior by comparison of three strains of BN-like peptide receptor knockout mice.

Bombesin (BN)-like peptides are involved in the regulation of a wide variety of behaviors, such as spontaneous activity and feeding. We assessed the role of BN-like peptides/receptors in emotional and/or anxiety-related behavior using three strains of knockout mice, each deficient in a single BN-like peptide receptor (gastrin-releasing peptide receptor, bombesin receptor subtype-3, or neuromedin B receptor). Two representative behavioral paradigms, the light-dark (L-D) box test and the elevated plus maze test, were chosen for this purpose. In these two tests, the level of anxiety can be measured as the preference for exploring the light box, or the length of time spent in the open arms, respectively. By conventional parameters, the only significant finding was that BRS-3-deficient mice exhibited a longer duration of remaining in the open arms compared to the wild-type cohort (P < 0.01). However, analyses of risk assessment behavior revealed that BRS-3-deficient mice exhibited increased 'stretched attend posture' behavior (P < 0.01, compared to wild-type mice in both the L-D box and elevated plus maze tests) while NMB-R-deficient mice exhibited decreased behavior (P < 0.05, compared to wild-type mice in both tests). These results suggest that BN-like peptides/receptors may play a role in modulating emotion including some forms of anxiety (e.g., risk assessment behavior). Further, we found that the type of emotional behavior to which each of the peptide/receptor pathways contributes can be clearly specified.     

Agomelatine reverses the decrease in hippocampal cell survival induced by chronic mild stress

The antidepressant agomelatine is a MT(1)/MT(2) receptor agonist and 5-HT(2C) antagonist. Its antidepressant activity is proposed to result from the synergy between these sets of receptors. Agomelatine-induced changes in the brain have been reported under basal conditions. Yet, little is known about its effects in the brain exposed to chronic stress as a risk factor for major depressive disorder. Recently, we described agomelatine-induced changes on neuronal activity and adult neurogenesis in the hippocampus of rats subjected to chronic footshock stress. In order to better characterize the actions of agomelatine in the stress-compromised brain, here we investigated its effects on hippocampal neurogenesis in the chronic mild stress (CMS) model. Adult male rats were subjected to various mild stressors for 5 weeks, and treated with agomelatine during the last 3 weeks of the stress period. The sucrose preference test was performed weekly to measure anhedonia, and the marble burying test was carried out at the end of the experiment to assess anxiety-like behavior. In our model, the CMS paradigm did not change sucrose preference; however, it increased marble burying behavior, indicating enhanced anxiety. Interestingly, this stress model differentially affected distinct stages of the neurogenesis process. Whereas CMS did not influence the rate of hippocampal cell proliferation, it significantly decreased the newborn cell survival and doublecortin expression in the dentate gyrus. Importantly, treatment with agomelatine completely normalized stress-affected cell survival and partly reversed reduced doublecortin expression. Taken together, these data show that agomelatine has beneficial effects on hippocampal neurogenesis in the CMS paradigm.     

Hyperserotonaemia and reduced brain serotonin levels in NaS1 sulphate transporter null mice

Sulphate (SO4) is conjugated to numerous endogenous compounds, including serotonin (5-HT). The NaS1 sulphate transporter is primarily expressed in the kidney, where it maintains blood SO4 concentrations. Previously, we generated NaS1 null (Nas1) mice, which have hyposulphataemia and decreased anxiety and locomotor activity. In this study, we investigated 5-HT and 5-hydroxyindole acetic acid (5-HIAA) concentrations, and 5-HT receptor mRNA levels. Nas1 mice exhibited a doubling in blood 5-HT concentration, but a 12% reduction in brain levels of 5-HT and 5-hydroxyindole acetic acid. Brain 5-HT1A and 5-HT1B receptor mRNA levels were increased by 50%, compared with wild-type mice. Our data indicate that decreased circulating SO4 concentrations modulate 5-HT neurotransmitter and receptor levels, in a manner consistent with the behavioural phenotypes of Nas1 mice.     

Commensal microbiota modulate murine behaviors in a strictly contamination‐free environment confirmed by culture‐based methods

Background

There is increasing evidence suggesting the existence of an interaction between commensal microbiota, the gut and the brain. The aim of this study was to examine the influence of commensal microbiota on the host behaviors in a contamination‐free environment, which was verified by culture‐based methods.

Methods

Open‐field and marble‐burying tests were used to analyze anxiety‐like behaviors and locomotor activity in gnotobiotic BALB/c mice with a common genetic background in a sterile isolator. The monoamine levels in several regions of the brain were measured in germfree (GF) mice and commensal fecal microbiota‐associated mice (EX‐GF).

Key Results

A 24‐h exposure to the environment outside the sterile isolators rendered GF mice less anxious than those not contaminated, while there was no change in the locomotion. EX‐GF mice, the gnotobiotic mice with normal specific pathogen‐free microbiota, were less anxious and active than GF mice using open‐field and marble‐burying tests. The norepinephrine, dopamine, and serotonin turnover rates were higher in the EX‐GF mice than in the GF mice in most regions of the brain, suggesting that monoaminergic neurotransmission might increase in the EX‐GF mice comparing the GF mice. Monoassociation with Brautia coccoides reduced the anxiety level, but it did not affect the locomotor activity. In contrast, colonization with Bifidobacterium infantis decreased the locomotor activity, while having little effect on the anxiety level.

Conclusions & Inferences

These results strongly support the current view that gut microorganisms modulate brain development and behavior.     

Differential expression of 5-HT(2A) and 5-HT(2C) receptor mRNAs in mice prone, or resistant, to chronic high-fat diet-induced obesity

The present study examined the levels of 5-HT(2A) and 5-HT(2C) (2A and 2C receptors of 5-hydroxytryptamine; serotonin) receptor messenger RNA (mRNA) expressions in the brain of chronic high-fat diet-induced obese (DIO) and obese-resistant (DR) mice. Thirty-one mice were used in this study. Twenty-four mice were fed with a high-fat diet (HF: 40% of calories from fat) for 4 weeks and then classified as the DIO (n = 8) or DR (n = 8) mice according to the highest and lowest body weight (BW) gainers. Seven mice were placed on a low-fat diet (LF: 10% of calories from fat) and were used as controls. After 20 weeks of feeding, the visceral fat accumulation was 620 +/- 42 mg in the DIO group versus 198 +/- 89 mg in the DR and 84 +/- 18 mg in the LF groups. Using quantitative in situ hybridization techniques, levels of 2A and 2C serotonin (5-HT) receptor mRNAs were measured in multiple brain sections of mice from the three groups. Most regions did not differ between groups but, importantly, the DIO mice had a significantly higher level of 5-HT(2A) receptor mRNA expression in the olfactory nucleus (Olf) compared to the DR and LF mice (+30% and +37%, respectively). The levels of Olf 5-HT(2A) receptor mRNA expression were related to body fat mass. The level of 5-HT(2C) mRNA receptor expression in the ventromedial hypothalamic (VMH) nucleus was 40% higher in the DIO mice than in the LF mice. Furthermore, the 5-HT(2C) receptor mRNA expression in the posterodorsal part of the medial amygdaloid (MePD) nucleus was 25% higher in the DIO mice than in the DR mice. The level of VMH 5-HT(2C) receptor mRNA expression was correlated with body fat mass. In conclusion, this study has demonstrated differentially regulated levels of the 5-HT(2A) and 5-HT(2C) receptor mRNA expressions in the specific brain regions of the DIO and DR mice. It provides neural anatomical bases that the 5-HT(2C) receptors positively influence satiety center (VMH) while the 5-HT(2A) receptor regulates olfactory sensory effects. The findings also assist us to understand the role of these receptors in mice susceptible or resistant to diet-induced obesity.     

Lack of cyclin D2 impairing adult brain neurogenesis alters hippocampal-dependent behavioral tasks without reducing learning ability

The exact function of the adult brain neurogenesis remains elusive, although it has been suggested to play a role in learning and memory processes. In our studies, we employed cyclin D2 gene knockout (cD2 KO) mice showing impaired neurogenesis as well as decreased hippocampal size. However, irrespectively of the genetic background of cD2 KO mice, this phenotype resulted in neither deficits in the hippocampal-dependent learning ability nor the memory formation. In the present study, cD2 KO mice and control littermates were subjected to hippocampal-dependent behavioral tests with little or no learning component. The knockout mice showed significant impairment in such species-typical behaviors as nest construction, digging, and marble burying. They were building none or poorer nests, digging less robustly, and burying fewer marbles than control mice. Such impairments were previously described, e.g., in animals with hippocampal lesions. Moreover, cD2 KO animals were also more active in the open field and automated motility chamber as well as showed increased explorative behavior in IntelliCage. Both increased motility and explorative behaviors were previously observed in hippocampally lesioned animals. Finally, cD2 KO mice showed normal sucrose preference, however starting from the second exposure to the sweetened solution, while control animals displayed a strong preference immediately. Presented results suggest that either morphological abnormalities of the hippocampal formation or adult brain neurogenesis impairment (or both) alter hippocampal-dependent behaviors of mutant mice without influencing learning abilities. These results may also suggest that adult brain neurogenesis is involved in species-typical behaviors.     

Gabrb3 gene deficient mice exhibit increased risk assessment behavior, hypotonia and expansion of the plexus of locus coeruleus dendrites

Gabrb3 gene deficient (gabrb3(-/-)) mice, control littermates (gabrb3(+/+)) and their progenitor strains C57Bl/6J and 129/SvJ were assessed for changes in the morphology of the main noradrenergic nuclei, the locus coeruleus (LC) and LC-associated behaviors including anxiety and muscle tone. While the area defined by the cell bodies of the LC was found not to differ between gabrb3(-/-) mice and controls, the pericoerulear dendritic zone of the LC was found to be significantly enlarged in gabrb3(-/-) mice. Relative to controls, gabrb3(-/-) mice were also found to be hypotonic, as was indicated by poor performance on the wire hanging task. Gabrb3(-/-) mice also exhibited a significant increase in stretch-attend posturing, a form of risk assessment behavior associated with anxiety. However, in the plus maze, a commonly used behavioral test for assessing anxiety, no significant difference was observed between gabrb3(-/-) and control mice. Lastly, relative to controls, gabrb3(-/-) mice exhibited significantly less marble burying behavior, a method commonly used to assess obsessive-compulsive behavior. However, the poor marble burying performance of the gabrb3(-/-) mice could be associated with the hypotonic condition exhibited by these mice. In conclusion, the results of this study indicate that the gabrb3 gene contributes to LC noradrenergic dendrite development with the disruption of this gene in mice resulting in an enlarged plexus of LC dendrites with a concurrent reduction in muscle tone and marble burying behavior, an increase in risk assessment behavior but no change in the plus maze parameters that are commonly used for assessing anxiety.     

Neurotransmitter Receptors in Adult Tottering (tg/tg) Mice

Neurotransmitter receptor binding was analyzed in adult tottering (tg/tg) and control wild-type mice. Saturation studies were performed to analyze the density of muscarinic cholinergic receptors in whole brain, cortical, and hippocampal homogenates of 8-9-week-old animals. Scatchard plot analysis was also performed to determine the density and affinity of alpha-adrenergic and beta-adrenergic receptors. No significant difference in Bmax or Kd values was identified between adult tottering and control mice in any of the tissue preparations. The amount of radioligand binding to 5-hydroxytryptamine 1A (5-HT1A), non-5-HT1A, 5-HT2, dopamine D2, and benzodiazepine receptors was also identical in tottering and control mice. These findings suggest that the epilepsy expressed by adult tottering mice does not result from alterations in the density or affinity of the neurotransmitter receptors studied.     

Serotonin 5-HT7 Receptor Blockade Reverses Behavioral Abnormalities in PACAP-Deficient Mice and Receptor Activation Promotes Neurite Extension in Primary Embryonic Hippocampal Neurons

The serotonin 5-HT(7) receptor has been linked to various psychiatric disorders, including schizophrenia, anxiety and depression, and is antagonized by antipsychotics such as risperidone, clozapine and lurasidone. In this study, we examined whether inhibiting the 5-HT(7) receptor could reverse behavioral abnormalities in mice lacking pituitary adenylate cyclase-activating polypeptide (PACAP), an experimental mouse model for psychiatric disorders such as schizophrenia. The selective 5-HT(7) antagonist SB-269970 effectively suppressed abnormal jumping behavior in PACAP-deficient mice. SB-269970 tended to alleviate the higher immobility in the forced swim test in PACAP-deficient mice, although SB-269970 reduced the immobility also in wild-type mice. In addition, we found that mutant mice had impaired performance in the Y-maze test, which was reversed by SB-269970. In the mutant mouse brain, 5-HT(7) protein expression did not differ from wild-type mice. In primary embryonic hippocampal neurons, the 5-HT(7) agonist AS19 increased neurite length and number. Furthermore, SB-269970 significantly inhibited the increase in neurite extension mediated by the 5-HT(1A/7) agonist 8-OH-DPAT. These results indicate that 5-HT(7) receptor blockade ameliorates psychomotor and cognitive deficits in PACAP-deficient mice, providing additional evidence that the 5-HT(7) receptor is a rational target for the treatment of psychiatric disorders.     

Evidence for topographically organized endogenous 5-HT-1A receptor-dependent feedback inhibition of the ascending serotonin system

Raphe and extra-raphe 5-HT-1A receptors contribute to feedback inhibition of serotonin (5-HT) neurons; however, the endogenous function of 5-HT-1A receptor-dependent feedback inhibition remains poorly understood. Here, the possibility that 5-HT-1A-mediated feedback inhibition of the raphe nuclei is topographically organized was examined. This was done by testing the effect of systemic blockade of 5-HT-1A receptors on Fos expression in 5-HT neurons in the dorsal raphe (DR) and median raphe (MR). The premise was that appearance of Fos after 5-HT-1A receptor blockade would implicate endogenous inhibition via 5-HT-1A-dependent processes. 5-HT-1A receptor antagonist administration (WAY-100635) in rats returned to their home cage significantly increased the number of Fos-containing 5-HT cells in the lateral wings and the ventral caudal part of the DR as compared to vehicle-injected controls, suggesting that tonic activity of brain 5-HT-1A receptors impacts on these regions. In rats receiving vehicle injections, swim, a behavior known to influence 5-HT neurotransmission, increased the number of Fos-containing 5-HT cells only in the caudal third of DR. Administration of WAY-100635 preceding a swim did not change the amount of Fos in the caudal DR, but increased the number of Fos-containing 5-HT cells in the rostral DR, lateral wings of the DR, and MR. These results confirm, using an imaging approach, that 5-HT-1A receptor-dependent feedback inhibition depends on behavioral state (return to home cage vs. swim). Moreover, they reveal that the effect of 5-HT-1A receptor blockade in each case is subregionally organized.     

Molecular cloning and characterization of receptors for the mammalian bombesin-like peptides

The bombesin-like peptides comprise a large family of peptides common to both amphibians and mammals that function as growth factors, neurotransmitters, and paracrine hormones. GRP, the mammalian homolog of bombesin and its receptor, as well as NMB, the mammalian homolog of ranatensin, are expressed in human neoplasms and, in particular, in small cell lung carcinomas (SCLC). To better characterize the physiological roles of bombesin-like peptides, our laboratory has cloned the receptors for GRP in murines, rats, and humans. The 3T3 GRP receptor was isolated and characterized using the two-electrode-voltage-clamp analysis and acquorinemission methods in xenopus oocytes expression system. The rat and human GRP and NMB receptors were cloned by hybridization at low stringency, using the mouse cDNA receptor probe. Sequence analysis of the receptors showed 384 and 390 amino acids for GRP and NMB receptors, respectively. The homology between the two receptors is 60% and between species in the same receptor, 90%. The receptors belong to the 7-membrane spanning domains superfamily. The specific GRP-R antagonist blocked the response to bombesin in oocytes injected with GRP-R, but failed to do so in oocytes injected with NMB-R. The two receptors differ in their distribution of tissue expression. RNA blot and RNase protection analysis showed the same size of mRNA without alteration in the receptors. RT + PCR analysis performed on genomic DNA revealed similarity between normal and cell DNAs, suggesting no major gene deletion or rearrangement. Southern blot analysis indicated the absence of gene amplification. Sequence analysis of the exonic segments of the receptor genes displayed identical amino acids to the respective cDNAs. None of the genes had classic TATAA box. Somatic cell hybrids localized the GRP-R on the X-chromosome and the NMB-R on chromosome 6. The same sequence of normal genes and cDNAs of GRP and NMB receptors, together with the gene characterization, demonstrated that SCLC cell lines do not require a structural change in receptor protein or genomic rearrangement.     

Evidence for a postsynaptic action of the serotonergic anxiolytics: Ipsapirone, indorenate and buspirone

In the present experiment we analyzed whether the antianxiety action of the serotonergic 1A agonists buspirone (5 mg/kg), ipsapirone (5 mg/kg), indorenate (5 mg/kg), and 8-OH-DPAT (0.5 mg/kg) were mediated through the stimulation of pre- or postsynaptic serotonergic receptors. The experimental anxiety values were determined with the burying behavior test, where a reduction in the cumulative time of burying behavior was interpreted as a reduction in anxiety. To that purpose we analyzed the putative anxiolytic action of these drugs in animals with lesion of the serotonergic fibers after the intracerebroventricular (ICV) injection of 5,7-dihydroxytyptamine (5,7-DHT, 10 or 150 micrograms/10 microliters). The neurochemical analysis shows that these treatments produce a statistically significant reduction in 5-HT and 5-HIAA levels in various brain areas. The results of the behavioral experiments reveal that buspirone, ipsapirone, and indorenate produced exactly the same reduction in burying behavior in lesioned animals as compared with control rats. The reduction in burying behavior produced by 8-OH-DPAT was effectively prevented by the lesion with 5,7-DHT. These data suggest that the anxiolytic effect of buspirone, ipsapirone, and indorenate is mediated via the stimulation of postsynaptic receptors, while the somatodendritic receptors are involved in the antianxiety effect of 8-OH-DPAT.     

Blockade of the anxiolytic-like action of ipsapirone and buspirone, but not that of 8-OH-DPAT, by adrenalectomy in male rats.

The effect of the 5-HT1A agonists ipsapirone (5 mg/kg), buspirone (5 mg/kg) and 8-OH-DPAT (0.5 mg/kg) on experimental anxiety was examined in sham-operated, adrenalectomized and adrenally demedullated male rats. The animal model of anxiety used was the defensive burying test. At the doses selected, all 5-HT1A compounds produced an anxiolytic-like action by reducing the burying behavior in both sham-operated and demedullated rats. However, in adrenalectomized subjects, while 8-OH-DPAT still reduced burying behavior, ipsapirone and buspirone lost their action. Data suggest that adrenocortical secretions play a role in the anxiolytic-like actions of buspirone and ipsapirone, but not in those of 8-OH-DPAT. Buspirone and ipsapirone also produced a reduction in burying behavior latency in sham-operated animals that was not observed in adrenalectomized or adrenally demedullated rats. These data suggest that adrenaline may be participating in the action of these compounds on the burying behavior latency. Present findings support possible direct relationships between the stimulation of 5-HT1A receptors and adrenal secretions.     

Peptides that fine-tune the serotonin system

The dorsal raphe nucleus (DR) contains serotonin (5-HT) neurons that innervate the cortex and limbic system and through these projections is thought to regulate cognition and behavior. Clinical and pharmacological findings implicate dysfunctions in the DR-5-HT system in affective disorders, including anxiety, depression and suicide. Although the DR is often considered in light of its 5-HT neurons, recent studies underscore the complexity of this nucleus and its heterogeneous nature. Of particular interest, are peptides that are either present within neurons in the DR, innervate DR-5-HT neurons or act upon local circuitry within the DR to indirectly impact on this 5-HT system. These peptides are positioned to fine-tune the activity of selective groups of serotonergic neurons within the DR and thereby 5-HT release in different terminal fields. This review will focus on substance P and corticotropin-releasing factor as two peptides that act independently and interdependently to influence DR-5-HT function. The role of non-serotonergic components of the DR in translating the effect of each of these peptides is discussed. This synthesis refines our views on the regulation of the DR-5-HT system and importantly, gives insight into mechanisms of endogenous control of DR function, the dysregulation of which may contribute to pathophysiology.     

Differential effects of acute morphine, and chronic morphine-withdrawal on obsessive-compulsive behavior: Inhibitory influence of CRF receptor antagonists on chronic morphine-withdrawal

Recent studies have provided convincing evidences for co-morbidity between opioid addiction and obsessive-compulsive disorder (OCD), and the involvement of the corticotrophin-releasing factor (CRF) in the effects of morphine-withdrawal. Some scanty evidences also point towards the role of CRF in OCD and related disorders. But, no evidence indicated the role of CRF in morphine withdrawal associated obsessive-compulsive behavior (OCB). Therefore, the present study investigated the role of CRF in morphine-withdrawal induced OCB in mice. Marble-burying behavior in mice was used to assess OCB as this model has good predictive and face validity. The results revealed that acute morphine dose dependently attenuated the marble burying behavior, whereas withdrawal of chronic morphine was associated with significant rise in marble burying behavior. This indicates the differential effect of acute morphine and chronic morphine-withdrawal on OCB. Further, acute treatment with CRF receptor antagonists like antalarmin (2 and 4μg/mouse, i.c.v.) or astressin-2B (3 and 10nmol/mouse, i.c.v.) dose dependently attenuated the peak morphine-withdrawal induced increase in marble burying behavior. Moreover, concomitant treatment with antalarmin (4μg/mouse, i.c.v.) or astressin-2B (10nmol/mouse, i.c.v.) along with morphine blocked the morphine-withdrawal associated exacerbation of OCB. These results indicate that OCB associated with morphine withdrawal state is partly mediated by the activation of central CRF receptors.     

Modulation by vasoactive intestinal peptide (VIP) of serotonin receptors in membranes from rat hippocampus

The vasoactive intestinal peptide (VIP) has been located in various structures of the rat brain, but few actions of the peptide have been reported as yet. Because VIP might interact with classical neurotransmitter systems in the central nervous system as it does in the periphery, we investigated whether VIP can modulate serotonin (5-HT1) receptors in membrane preparations obtained from brain areas which contain various amounts of VIP and 5-HT receptors. The presence of bacitracin alone, which protects VIP from proteolytic degradation, decreases the affinity of [3H]5-HT binding in almost all of the structures tested. Scatchard analysis indicates that, in the presence of bacitracin, VIP significantly decreases the affinity and increases the number of specific high affinity binding sites for [3H]5-HT in the dorsal hippocampus. VIP induces a dose-dependent increase in the number of 5-HT1 receptors with a maximal response of 60% with 10(-7) M VIP. At the same concentration, neither secretin nor glucagon modifies 5-HT1 receptor density. No effect of VIP is observed in the ventral hippocampus, parietal cortex, whole hypothalamus, and midbrain. This effect of VIP is not observed when bacitracin is omitted, and the presence of calcium ions does not alter the efficacy of the VIP effect. No effect of VIP is obtained on [3H]spiperone binding assayed with 10 microM mianserin to define specific binding. The present data suggest that some of the effects of 5-HT in the hippocampus may be modulated by VIP.