A demonstration that 5-hydroxytryptamine administered peripherally can affect sexual behavior in male rats

In the male rat, subcutaneous injections for 7 days of 20 mg/Kg B.W./day of 5-hydroxytryptamine creatinin sulphate (5-HT), caused remarkable i$\text{n}$hibitory effects on sexual behavior.The mount and intromission latencies were incre$\text{a}$sed in rats treated with 5-HT, whereas ejacul$\text{a}$tion latency in the few rats treated with 5-HT that it achieved, was similar to that obtained in control rats.The mount and intromission frequencies were decreased in the rats treated with 5-HT.The mean inter-intromission interval (MII) and post-ejaculatory interval were prolonged in rats treated with 5-HT.These data provide evidence for the role of peripheral 5-HT in regulating sexual behavior of - male rats.     

The role of 5-HT1B receptors in the regulation of serotonin cell firing and release in the rat brain

The release of 5-HT in terminal areas of the rodent brain is regulated by 5-HT1B receptors. Here we examined the role of 5-HT1B receptors in the control of 5-HT output and firing in the dorsal raphe nucleus (DR), median raphe nucleus (MnR) and forebrain of the rat in vivo. The local perfusion (30-300 microM) of the selective 5-HT1B receptor agonist CP-93,129 to freely moving rats decreased 5-HT release in the DR and more markedly in the MnR. Likewise, 300 microM CP-93,129 reduced 5-HT output in substantia nigra pars reticulata, ventral pallidum, lateral habenula and the suprachiasmatic nucleus. The effect of CP-93,129 was prevented by SB-224289, but not by WAY-100635, selective 5-HT1B and 5-HT1A receptor antagonists, respectively. SB-224289 did not alter dialysate 5-HT in any raphe nuclei. The intravenous administration of the brain-penetrant selective 5-HT1B receptor agonist CP-94,253 (0.5-2.0 mg/kg) to anesthetized rats decreased dialysate 5-HT in dorsal hippocampus and globus pallidus, increased it in MnR and left it unaltered in the DR and medial prefrontal cortex. SB-224289, at a dose known to block 5-HT1B autoreceptor-mediated effects (5 mg/kg), did not prevent the effect of CP-94,253 on MnR 5-HT. The intravenous administration of CP-94,253 (0.05-1.6 mg/kg) to anesthetized rats increased the firing rate of MnR, but not DR-5-HT neurons. The local perfusion of CP-94,253 in the MnR showed a biphasic effect, with 5-HT reductions at 0.3-3 microM and increase at 300 microM. These results suggest that 5-HT cell firing and release in midbrain raphe nuclei (particularly in the MnR) are under control of 5-HT1B receptors. The activation of 5-HT1B autoreceptors (possibly located on 5-HT nerve endings and/or varicosities within DR and MnR) reduces 5-HT release. The effects of higher concentrations of 5-HT1B receptor agonists seem more compatible with the activation of 5-HT1B heteroreceptors on inhibitory neurons.     

综述与专论：甘丙肽对抑郁症状的调控作用及其机制的研究进展

甘丙肽(galanin, GAL)作为治疗抑郁症的可能靶点被关注已久,但目前仍未有广泛应用的GAL类抗抑郁药物。GAL可与3种G蛋白偶联受体(GalR1～3)结合,GalR1和GalR3介导促进抑郁的作用,GalR2介导抗抑郁的作用。GAL的N端有生物活性的片段GAL (1-15),通过其受体GalR1-GalR2异聚体(heteromer),介导比GAL更强的调节抑郁效应。GAL (1-15)还可以通过GalR1-GalR2异聚体与5-羟色胺1A受体(5-HT1AR)相互作用形成GalR1-GalR2-5-HT1AR异聚体的方式,加强5-HT1AR激动剂的抗抑郁效果。此外,GAL及其受体还与去甲肾上腺素、神经肽Y、脑源性神经营养因子、多巴胺等递质或因子交互作用调节抑郁。本文梳理GAL及其受体对抑郁的调节作用及其可能机制,并对以GAL及其受体为靶点开发的药物应用于临床治疗抑郁症的可能性进行探讨。     

甘丙肽对抑郁症状的调控作用及其机制的研究进展

甘丙肽(galanin, GAL)作为治疗抑郁症的可能靶点被关注已久,但目前仍未有广泛应用的GAL类抗抑郁药物。GAL可与3种G蛋白偶联受体(GalR1~3)结合,GalR1和GalR3介导促进抑郁的作用,GalR2介导抗抑郁的作用。GAL的N端有生物活性的片段GAL (1-15),通过其受体GalR1-GalR2异聚体(heteromer),介导比GAL更强的调节抑郁效应。GAL (1-15)还可以通过GalR1-GalR2异聚体与5-羟色胺1A受体(5-HT1AR)相互作用形成GalR1-GalR2-5-HT1AR异聚体的方式,加强5-HT1AR激动剂的抗抑郁效果。此外,GAL及其受体还与去甲肾上腺素、神经肽Y、脑源性神经营养因子、多巴胺等递质或因子交互作用调节抑郁。本文梳理GAL及其受体对抑郁的调节作用及其可能机制,并对以GAL及其受体为靶点开发的药物应用于临床治疗抑郁症的可能性进行探讨。     

Brain 5-HT synthesis in the Flinders Sensitive Line rat model of depression: an autoradiographic study

Alterations of serotonin (5-HT) levels and serotonergic transmission have been associated with depression. 5-HT synthesis is an important factor of serotonergic neurotransmission that may also be altered in depression. Many studies of the relationships between brain serotonergic functions and affective disorders have been performed in different animal models. In this study, brain regional 5-HT synthesis was examined using the alpha-[(14)C]methyl-L-tryptophan (alpha-MTrp) autoradiographic method in a genetic rat model of depression, Flinders Sensitive Line (FSL) rats, and was compared to both the Flinders Resistant Line (FRL) rats and the control Sprague-Dawley (SD) rats. The plasma concentration of free tryptophan in the FSL rats was not significantly different (p > 0.05; ANOVA and post-hoc Bonferroni correction) when compared to that of the FRL and SD rats. The FSL rats had significantly lower 5-HT synthesis (one sample two-tailed t-test on the ratio) than both the FRL and SD rats (the mean ratios were 0.78 +/- 0.12 and 0.73 +/- 0.15, respectively). Overall, the 5-HT synthesis in the FRL rats was not significantly different (p > 0.05) from that in the SD rats (one sample two-tailed t-test on the ratio and the mean ratio was 0.93 +/- 0.13). Studies of individual brain structures, such as the raphe nuclei and their many terminal areas, including the nucleus accumbens, cingulate and frontal cortex, hippocampus, amygdala, and thalamus revealed significant reductions (typically 25-50%) in 5-HT synthesis in the FSL rats compared to the non-depressive FRL and SD rats. These results suggest that significantly reduced 5-HT synthesis in the raphe nuclei and limbic areas in FSL rats may contribute to their depressive features.     

Effects of neonatal maternal separation on neurochemical and sensory response to colonic distension in a rat model of irritable bowel syndrome

Early life stress has been implicated as a risk factor for irritable bowel syndrome (IBS). We studied the effect of neonatal maternal separation on the visceromotor response and the expression of c-fos, 5-HT, and its receptors/transporters along the brain-gut axis in an animal model of IBS. Male neonatal Sprague-Dawley rats were randomly assigned to a 3-h daily maternal separation (MS) or nonhandling (NH) on postnatal days 2-21. Colorectal balloon distention (CRD) was performed for assessment of abdominal withdrawal reflex as a surrogate marker of visceral pain. Tissues from dorsal raphe nucleus in midbrain, lumbar-sacral cord, and distal colon were harvested for semiquantitative analysis of c-fos and 5-HT. The expression of 5-HT expression, 5-HT3 receptors, and 5-HT transporter were analyzed by RT-PCR. Pain threshold was significantly lower in MS than NH rats. The abdominal withdrawal reflex score in response to CRD in MS rats was significantly higher with distension pressures of 40, 60, and 80 mmHg. In MS rats, the number of c-fos-like immunoreactive nuclei at dorsal horn of lumbar-sacral spinal cord increased significantly after CRD. 5-HT content in the spinal cord of MS rats was significant higher. In the colon, both 5-HT-positive cell number and 5-HT content were comparable between MS and NH groups before CRD. Post-CRD only MS rats had significant increase in 5-HT content. Protein and mRNA expression levels of 5-HT3 receptors and 5-HT transporter were similar in MS and NH rats. Neonatal maternal separation stress predisposes rats to exaggerated neurochemical responses and visceral hyperalgesia in colon mimicking IBS.     

Additive effects of apomorphine and clonidine on serotonin neurons in the dorsal raphe

Effects of apomorphine (APO) and clonidine (CLON) on the mesostriatal and mesolimbic serotonergic systems were examined in the present study. Both drugs selectively elevated serotonin (5-HT) concentrations in the dorsal raphe and the striatum without significantly altering 5-HT measures in the median raphe and the hippocampus. Apomorphine also increased tryptophan and 5-hydroxyindoleacetic acid (5-HIAA) levels in the dorsal raphe and 5-HIAA level in the striatum. Clonidine did not markedly alter tryptophan and 5-HIAA measures, while it decreased 5-HT turnover rate in both region, as indicated by the ratio of 5-HIAA/5-HT levels. Co-administration of APO and CLON, at doses of each drug exerted maximum effects on 5-HT alone, produced an additive effect on 5-HT in the dorsal raphe, while their effects on 5-HT and 5-HIAA in the striatum were counteracting each other. Effects of APO on 5-HT and 5-HIAA were attributed to the elevation of 5-HT precursor tryptophan, while effects of CLON on 5-HT and 5-HIAA were due to a decreased rate of 5-HT turnover. Therefore, the present results support the hypothesis that the additive effects of APO and CLON on dorsal raphe 5-HT are mediated through different receptors and neuropharmacological mechanisms.     

Some contrasting effects of surgical and “chemical” castration on the behavior of male cynomolgus monkeys (Macaca fascicularis)

In nonhuman primates, surgical castration reduces plasma testosterone levels and male sexual behavior, and testosterone replacement restores them. Chemical castration with compounds that lower plasma testosterone levels is used clinically in the treatment of certain forms of cancer and to reduce aberrant sexual behavior in male sex offenders. In the United States, medroxyprogesterone acetate (MPA) is the drug most used to help reduce serious sexual behavioral problems in men. We were therefore interested in comparing the behavioral effects of MPA treatment (40 mg once a week) in 4 intact male cynomolgus monkeys (4 pairs, 120 tests) with data from an earlier study in our laboratory on 4 males observed before and after surgical castration (16 pairs, 192 tests). Both MPA treatment and surgical castration reduced plasma testosterone to very low levels and decreased ejaculatory activity, but MPA treatment additionally affected measures of male sexual motivation (decreased numbers of male mounting attempts and increased mounting attempt latencies) which were not primarily affected by surgical astration. However, surgical castration decreased intromission ability (percentage of intromitted thrusts per test) and male yawning behavior more rapidly than did MPA treatment. This suggested a hypothesis that different mechanisms could be involved in the behavioral effects—namely, that surgical castration may act primarily via testosterone-dependent peripheral mechanisms, while chemical castration with MPA does so primarily via central mechanisms regulating sexual motivation.     

In Vivo Brain Dialysis Study of the Somatodendritic Release of Serotonin in the Raphe Nuclei of the Rat: Effects of 8-Hydroxy-2-(Di-n-Propylamino)tetralin

Abstract: The characteristics of the serotonin (5-HT) output in the dorsal and median raphe nuclei of the rat were studied using in vivo microdialysis. The basal output of 5-HT increased after KC1 was added to the perfusion fluid. In contrast, neither the omission of calcium ions nor the addition of 0.5 nM tetrodotoxin affected dialysate 5-HT or 5-hy-droxyindoleacetic acid (5-H1AA). Reserpine did not decrease the output of 5-HT and 5-HIAA 24 h later and p-chloroamphetamine increased 5-HT in both vehicle- and reserpine-treated rats severalfold. 8-Hydroxy-2-(di-n-pro-pylamino)tetralin (8-OH-DPAT), at 1 or 10 μM, perfused into the raphe did not change the outputs of 5-HT or 5-HIAA. Higher doses (0.1, Land 10 mM) increased extracellular 5-HT in the raphe, probably via an inhibition of uptake. In animals bearing two probes (raphe nuclei and ventral hippocampus), only the 10 vaM dose of 8-OH-DPAT perfused into the raphe decreased the hippocampal output of 5-HT and 5-HIAA. The systemic injection of 0.1 mg/kg 8-OH-DPAT decreased dialysate 5-HT and 5-HIAA in the raphe and hippocampus. These results suggest that extracellular 5-HT in raphe nuclei originates from a cytoplasmic pool and is not dependent on either nerve impulse of 5-HT neurons or local activation of 5-HT_1A receptors.     

Differential Effect of NMDA on Extracellular Serotonin in Rat Midbrain Raphe and Forebrain Sites

Abstract: The contribution of NMDA receptors to regulation of serotonin (5-HT) release was assessed by in vivo microdialysis in freely behaving rats. During infusion of NMDA (30, 100, and 300 µ M ) into the dorsal raphe nucleus (DRN), 5-HT was increased by ∼25, 100, and 280%, respectively. Competitive and noncompetitive NMDA-receptor antagonists blocked this effect on DRN 5-HT. Infusion of NMDA (300 µ M ) into the DRN also produced an 80% increase in extracellular 5-HT in the nucleus accumbens. During infusion of NMDA (100 and 300 µ M ) into the median raphe nucleus (MRN), 5-HT was increased by ∼15 and 80%, respectively. NMDA-receptor antagonists blocked this effect on MRN 5-HT. Infusion of NMDA into the MRN also produced a significant increase in hippocampal 5-HT. In contrast, infusion of NMDA into the nucleus accumbens, frontal cortex, or hippocampus produced small decreases in 5-HT in these forebrain sites. Taken together, these results suggest that NMDA receptors in the midbrain raphe, but not the forebrain, can have an excitatory influence on 5-HT neurons and, thus, produce increased 5-HT release in the forebrain. Furthermore, in comparison with the MRN, DRN 5-HT neurons were more sensitive to the excitatory effect of NMDA.     

Acute administration of fluoxetine normalizes rapid eye movement sleep abnormality, but not depressive behaviors in olfactory bulbectomized rats

In humans, depression is associated with altered rapid eye movement (REM) sleep. However, the exact nature of the relationship between depressive behaviors and sleep abnormalities is debated. In this study, bilateral olfactory bulbectomy (OBX) was carried out to create a model of depression in rats. The sleep-wake profiles were assayed using a cutting-edge sleep bioassay system, and depressive behaviors were evaluated by open field and forced swimming tests. The monoamine content and monoamine metabolite levels in the brain were determined by a HPLC-electrochemical detection system. OBX rats exhibited a significant increase in REM sleep, especially between 15:00 and 18:00 hours during the light period. Acute treatment with fluoxetine (10 mg/kg, i.p.) immediately abolished the OBX-induced increase in REM sleep, but hyperactivity in the open field test and the time spent immobile in the forced swimming test remained unchanged. Neurochemistry studies revealed that acute administration of fluoxetine increased serotonin (5-HT) levels in the hippocampus, thalamus, and midbrain and decreased levels of the 5-HT metabolite 5-hydroxyindoleacetic acid (5-HIAA). The ratio of 5-HIAA to 5-HT decreased in almost all regions of the brain. These results indicate that acute administration of fluoxetine can reduce the increase in REM sleep but does not change the depressive behaviors in OBX rats, suggesting that there was no causality between REM sleep abnormalities and depressive behaviors in OBX rats.     

The Distribution of Serotonergic Nerves in Microencephalic Rats Treated Prenatally with Methylazoxymethanol

Prenatal exposure of pregnant rats to methylazoxymethanol acetate (MAM) induces microencephaly in the offspring. In the present study of these microencephalic rats (MAM rats) we used quantitative autoradiography to investigate [³H] paroxetine binding sites, which are a selective marker of serotonin (5-HT) transporters (5-HTT). The binding in the accumbens, cortex, hippocampus, and dorsolateral thalamus was significantly increased in MAM rats, compared to the control rats, while there was a significant decrease in the dorsal raphe nucleus of the MAM rats. The levels of 5-HTT mRNA in the dorsal raphe nuclei were analyzed by in situ hybridization, which revealed a significant decrease in 5-HTT mRNA-positive neurons in the MAM rats compared to the control rats. The results imply serotonergic hyperinnervation in the cerebral hemispheres of MAM rats, while a target-dependent secondary degeneration of 5-HT neurons might be induced in the dorsal raphe nuclei of MAM rats.     

Conversion of testosterone to estradiol may not be necessary for the expression of mating behavior in male Syrian hamsters (Mesocricetus auratus)

Male sexual behavior is mediated in part by androgens, but in several species, mating is also influenced by estradiol formed locally in the brain by the aromatization of testosterone. The role of testosterone aromatization in the copulatory behavior of male Syrian hamsters is unclear because prior studies are equivocal. Therefore, the present study tested whether blocking the conversion of testosterone to estradiol would inhibit male hamster sexual behavior. Chronic systemic administration of the nonsteroidal aromatase inhibitor Fadrozole (2.0 mg/kg/day) for 5 or 8 weeks did not significantly increase mount latency or reduce mount frequency, intromission frequency, ejaculation frequency, or anogenital investigation relative to levels shown by surgical controls. However, Fadrozole effectively inhibited aromatase activity, as evidenced by the suppression of estrogen-dependent progesterone receptor immunoreactivity in the male hamster brain. The JZB39 anti-progesterone receptor antibody labeled significantly more neurons in brains of sham-treated hamsters than in brains of Fadrozole-treated hamsters. These data suggest that aromatization of testosterone to estradiol is not necessary for normal mating behavior in Syrian hamsters.     

Dynamic changes of brain serotonergic and dopaminergic activities during development of anxious depression: experimental study

Chronic psychoemotional stress of social defeats produces development of experimental anxious depression in male mice similar to this disorder in humans. 5-HT and 5-HIAA levels, TPH and MAO A activities, 5-HT1A-receptors in different brain areas were investigated at different stages of development of experimental disorder. It has been shown that initial stage (3 days of social stress) is accompanied by increase of 5-HT level in some brain areas. Decreased 5-HIAA levels in the hippocampus, amygdala and nucleus accumbens were discovered at the stage of forming depression (10 days of social stress). Pharmacological desensitisation and decreased number of 5-HT1A-receptors were shown in frontal cortex and amygdala. At the stage of pronounced depression (20 days of stress), there were no differences in 5-HT and 5-HIAA levels in all brain areas (excluding hypothalamus) of depressive animals. However increased number of 5-HT1A-receptors and decreased affinity in amygdala and decreased TPH and MAOA activities in hippocampus were found in depressive mice. Hypofunction of serotonergic system is suggested at the stage of pronounced depression state in animals. Similar processes had place in brain dopaminergic systems. It is concluded that dynamic changes of brain monoaminergic activities accompany the development of anxious depression in animals. Various parameters of monoaminergic systems are differently changed depending on brain area, mediator system and stage of disorder.     

Effects of clozapine on the efflux of serotonin and dopamine in the rat brain: the role of 5-HT1A receptors

In vivo microdialysis in conscious rats was used to examine the effect of clozapine on serotonin (5-hydroxytryptamine, 5-HT) efflux in the prefrontal cortex and dorsal raphe nucleus and dopamine efflux in the prefrontal cortex. Both systemic and local administration of clozapine (systemic, 10 or 20 mg/kg, i.p.; local, 100 microM) increased 5-HT efflux in the dorsal raphe. However, in the prefrontal cortex, dialysate 5-HT increased when clozapine (100 microM) was administered through the probe, while no effect was observed when it was administered systemically. By pretreatment with the selective 5-HT1A receptor antagonist p-MPPI (3 mg/kg, i.p.), systemic treatment of clozapine (10 mg/kg, i.p.) significantly increased 5-HT efflux in the prefrontal cortex. This result suggests that the ability of clozapine to enhance the extracellular concentrations of 5-HT in the dorsal raphe attenuates this drug's effect in the frontal cortex, probably through the stimulation of 5-HT1A somatodendritic autoreceptors in the dorsal raphe. We also found that pretreatment with p-MPPI (3 mg/kg, i.p.) attenuated by 45% the rise in cortical dopamine levels induced by clozapine (10 mg/kg, i.p.). These findings imply that the reduction in serotonergic input from the dorsal raphe nucleus induced by clozapine could lead to an increase in dopamine release in the prefrontal cortex.     

Reversal of ageing changes in the thymus of rats by chemical or surgical castration

Summary Differences in the thymus of young and old male CSE Wistar rats were examined by use of routine histological stains on paraffin-embedded sections. There was a highly significant loss of thymic weight and disruption of architecture with age. Both surgical castration and chemical castration induced by a luteinizing hormone-releasing hormone analogue (Goserelin) caused a significant increase in thymic weight and the reappearance of a well-defined cortex and medulla in ageing rats. Cell surface antigens were detected on cryosections after incubation with a range of monoclonal antibodies. The Pan T cell marker (detected with antibody W3/13) showed fewer positive cells in ageing rats, and an increase after chemical castration. The smaller glands of old rats had fewer positive T cells with CD4 (MRC OX35) and CD8 (MRC OX8) antigens, and more after chemical castration in both young and ageing rats, but the greatest changes were seen in the intensity of Class II major histocompatibility complex (MRC OX6) immunoreactivity. In both young and ageing chemically-castrated rats, the numbers of cells and the intensity of immunoreactivity were greatly increased in the medulla.