The role of the neurochemical mechanisms of the medial raphe nucleus in anxiety states formed by various aversive actions

The experimental studies on rats with microinjections of a number of monoamines and amino acids into median raphe nuclei showed functional importance of neither dofamine nor glutamat but of 5-HT or 5-HT- and GABA-ergic mechanisms of median raphe nuclei formation in anxiety states formed by aversive actions of diverse biological importance.     

PTSD促进大鼠中缝背核细胞色素c表达

目的研究创伤后应激障碍(PTSD)大鼠中缝背核神经元细胞色素C(Cyt-c)的表达变化。方法应用无连续单一刺激(SPS)方法建立PTSD大鼠模型,随机分为SPS刺激后1d、4d、7d和对照组,应用酶组织化学法和RT-PCR方法观察中缝背核神经元Cyt-c的表达变化。结果光镜酶细胞化学法和RT-PCR法显示中缝背核神经元Cyt-c染色阳性细胞于SPS刺激后1d明显高于对照组,4d逐渐增高,并于7d达到高峰。电镜下显示Cyt-c阳性反应产物主要分布在中缝背核神经元线粒体膜,SPS刺激后可见Cyt-c释放到胞浆中。结论 SPS刺激引起Cyt-c在PTSD大鼠中缝背核神经元呈过表达。     

The median raphe nucleus participates in the depressive-like behavior induced by MCH: Differences with the dorsal raphe nucleus

An emerging body of evidence involves the hypothalamic neuropeptide melanin-concentrating hormone (MCH) in the regulation of emotional states. We have reported a pro-depressive effect induced by MCH after its microinjection into the dorsal raphe nucleus (DR) evaluated in the forced swimming test (FST) in rats. Here we extended this study to the median raphe nucleus (MnR). Firstly, the presence of MCH-containing fibers in the rat MnR was analyzed by means of immunohistochemistry. Secondly, the behavioral effect induced by the microinjection of MCH into the MnR was assessed using the FST. Morphological results showed a large density of MCHergic fibers within the MnR. Behavioral results indicated that 100 ng of MCH (but not 50 ng) significantly increased the immobility time and decreased the swimming time, demonstrating a depressive-like effect. In contrast, climbing behavior was not significantly affected. Present findings revealed that the MnR neurons participate in the MCHergic control of affective-related behavioral responses. However, the behavioral patterns induced by MCH in the MnR and DR were different. This could be explained by anatomical and physiological differences between both nuclei.     

Synaptic relations of neurotensinergic neurons in the dorsal raphe nucleus

The ultrastructure and synaptic relations of neurotensinergic neurons in the rat dorsal raphe nucleus (DRN) were examined. The neurotensin-like immunoreactive (NT-LI) neurons in the DRN were fusiform or spherical. The NT-LI perikarya could only be detected in colchicine-treated animals whereas the immunoreactive axon terminals could only be found in the anirnals not treated with colchicine. Although many NT-LI dendrites received synapses from nonimmunoreactive axon terminals, the NT-LI perikarya received few synapses. NT-LI axon terminals also made synapses on nonimmunoreactive dendrites. Occasionally, synapses were found between the NT-LI axon terminals and NT-LI dendrites in the cases in which the animals were not treated with colchicine.     

Regulation of nucleus accumbens dopamine release by the dorsal raphe nucleus in the rat

The effects of microinfusingl-glutamate, serotonin (5-HT), (±)-8-hydroxy-2-(di-N-propylamino) tetralin (8-OH DPAT; a 5-HT_1A agonist), and muscimol (a GABA_A agonist) into the dorsal raphe nucleus on the extracellular levels of 5-HT, dopamine (DA) and their metabolites in the nucleus accumbens were studied in unanesthetized, freely moving, adult male Wistar rats, using the technique of microdialysis coupled with small-bore HPLC. Administration of 0.75 gl-glutamate produced a 25–50% increase (P<0.05) in the extracellular levels of both 5-HT and DA. On the other hand, infusion of 8-OH DPAT and, to a lesser extent, 5-HT produced a significant (P<0.05) decrease in the extracellular levels of both 5-HT and DA. Muscimol (0.25 or 0.50 g) had little effect on the extracellular concentrations of 5-HT or DA following its administration. In general, the extracellular levels of the major metabolites of 5-HT and DA in the nucleus accumbens were not altered by microinfusion of any of the agents. The data indicate that (a) the 5-HT neurons projecting to the nucleus accumbens from the dorsal raphe nucleus can be activated by excitatory amino acid receptors and inhibited by stimulation of 5-HT_1A autoreceptors, and (b) the dorsal raphe nucleus 5-HT neuronal system may regulate the ventral tegmental area DA projection to the nucleus accumbens.Special issue dedicated to Dr. Morris H. Aprison     

Study of monoamino- and amino acidergic mechanisms of the rat caudate nucleus in antiaversive effects of tranquilizers in various anxiety models

Administration of anxio-sedative drugs into the rat caudate nucleus revealed that antiaversive effects of chlordiazepide, phemibut, and indoter only occur under dominating fear motivation, whereas antiaversive effects of campirone and campironine occur under the influence of negative or stressful zoo-social actions and are realised via the GABA- and serotoninergic type of synaptic switching in the dorsal part of the caudate nucleus.     

Electron microscopic examination of the orexin immunoreactivity in the dorsal raphe nucleus

The ultrastructure and the synaptic relationships of the orexin-A-like immunoreactive fibers in the dorsal raphe nucleus were examined with an immunoelectron microscopic method. At the electron microscopic level, most of the immunoreactive fibers, a varicosity appearance at the light microscopic level, were found as axon terminals. The large dense-cored vesicles contained in the immunoreactive axon terminals were the most intensely immunostained organellae. These axon terminals were often found to make synapses. While the axo-dendritic synapses were usually asymmetric in appearance, the axo-somatic synapses were symmetric. Orexin-A-like immunoreactive processes with no synaptic vesicles were also found. These processes often received asymmetric synapses. With less frequency, the synapses were found between the orexin-like immunoreactive processes. The results suggest that the orexin peptides are stored in the large dense-cored vesicles; the orexin-containing fibers may have influences on the physiological activities of the dorsal raphe nucleus through direct synaptic relationships.     

中缝背核微量注射L-N-硝基精氨酸甲酯抑制大鼠乙状结肠痛

用Fos免疫组织化学、烟酰胺腺嘌呤二核苷酸磷酸黄递酶(nicotinamide adenine dinucleotide phosphate—di—aphorase,NADPH-d)组织化学及微量注射技术,观察大鼠乙状结肠注射甲醛(5％)诱发的大鼠乙状结肠炎性痛过程中中缝背核一氧化氮合酶(nitric oxide synthase,NOS)神经元的变化,同时观察中缝背核微量注射L-N-硝基精氨酸甲酯(LNAME)对乙状结肠痛的调控作用。结果表明,(1)乙状结肠注射甲醛后,大鼠出现明显的内脏痛反应,中缝背核NOS神经元表达明显增多,中缝背核内出现大量Fos蛋白,在整个中缝背核内均有分布,并且出现Fos／NOS双标神经元,约占中缝背核NOS神经元总数的8％,与生理盐水对照组相比差异有显著性;(2)中缝背核注射L-NAME后,可以明显减少乙状结肠炎性痛大鼠的疼痛学评分及脊髓相应节段Fos蛋白。上述结果提示,中缝背核NOS神经元参与调控大鼠乙状结肠痛,NO在中缝背核促进内脏伤害性信息的传递。     

Estradiol acts in the medial preoptic area, arcuate nucleus, and dorsal raphe nucleus to reduce food intake in ovariectomized rats

Estradiol (E2) exerts an inhibitory effect on food intake in a variety of species. While compelling evidence indicates that central, rather than peripheral, estrogen receptors (ERs) mediate this effect, the exact brain regions involved have yet to be conclusively identified. In order to identify brain regions that are sufficient for E2's anorectic effect, food intake was monitored for 48 h following acute, unilateral, microinfusions of vehicle and two doses (0.25 and 2.5 μg) of a water-soluble form of E2 in multiple brain regions within the hypothalamus and midbrain of ovariectomized rats. Dose-related decreases in 24-h food intake were observed following E2 administration in the medial preoptic area (MPOA), arcuate nucleus (ARC), and dorsal raphe nucleus (DRN). Within the former two brain areas, the larger dose of E2 also decreased 4-h food intake. Food intake was not influenced, however, by similar E2 administration in the paraventricular nucleus, lateral hypothalamus, or ventromedial nucleus. These data suggest that E2-responsive neurons within the MPOA, ARC, and DRN participate in the estrogenic control of food intake and provide specific brain areas for future investigations of the cellular mechanism underlying estradiol's anorexigenic effect.     

The effect of electrostimulation of the locus coeruleus, the medial parabrachial nucleus and the dorsal raphe nucleus on the paired activity of the respiratory center in rats

Using the electromyographic method in acute experiments on anaesthetized with urethanum rats the different influence of locus coeruleus, nucleus medialis parabrachialis and nuclei raphae on respiratory centre activity has been established. The effect of the locus coeruleus depended on parameters of stimulation and on the character of the tested structures between each other and the bilateral regions of the respiratory centre.     

Analysis of analgesia induced by the generator of excitation in the dorsal raphe nucleus

In experiments on white rats the generator of excitation was created in the dorsal raphe nucleus by microinjection of tetanus toxin. After formation of the excitation generator electrical activity in this nucleus was changed as the following: the first negative component (N1) was strongly increased, general EP configuration changed and the spontaneous paroxysmal activity became more frequent. The time of the generator formation correlated with the appearance of intense and prolonged analgesia. Naloxone did not reverse the effects of analgesia described.     

The orexinergic synaptic innervation of serotonin- and orexin 1-receptor-containing neurons in the dorsal raphe nucleus

Orexin/hypocretin has been well demonstrated to excite the serotonergic neurons in the dorsal raphe nucleus (DRN). We studied the morphological relationships between orexin-containing axon terminals and serotonin- as well as orexin-receptor-containing neurons in the dorsal raphe nucleus. Using immunohistochemical techniques at the light microscopic level, orexin A (OXA)-like immunoreactive neuronal fibers in the DRN were found to make close contact with serotonergic neurons, while some of the serotonergic neurons also expressed the orexin 1 receptor (OX1R). At the electron microscopic level, double-immunostaining experiments showed that the orexin A-like immunoreactive fibers were present mostly as axon terminals that made synapses on the serotonin- and orexin 1-receptor-containing neurons. While only axodendritic synapses between orexin A-containing axon terminals and serotonergic neurons were detected, the synapses made by orexin A-containing axon terminals on the orexin 1-receptor-containing neurons were both axodendritic and axosomatic. The present study suggests that excitation effect of orexin A on dorsal raphe serotonergic neurons is via synaptic communication through orexin 1 receptor.     

Neurochemical mechanisms of dorsal pallidum in antiadverse effects of anxiolytics of different models of anxiety

Microinjections of glutamine acid, serotonine and campiron into globus pallidus reveal antiadverse properties of ratsin in the test with avoiding "threatening situation" but not with "illuminated site" under the conditions of rats' free choice between light and dark sites. Dopamine, apomorphine, GABA, chlordiazepoxide, phenibut and indoter injected locally into this formation of basal ganglia do not affect the mechanisms of the involuntary movement, but counteract the conditions of anxiety in both models of behaviour. These results show different functional role of monoamino- and aminoacidergic systems of dorsal pallidum in operative regulation of behaviour with changing of aversive stimulus modality. Preliminary intraperitoneal injection of functional antagonists of investigated synoptotropic followed by microinjection of monoamines and amino acids into globus pallidus reveal selective involvement of neuromediator systems of dorsal pallidum into antiadverse anxiosedative and anxioselective actions.     

Antinociceptive role of oxytocin in the nucleus raphe magnus of rats, an involvement of mu-opioid receptor

Recent studies showed that oxytocin plays an important role in nociceptive modulation in the central nervous system. The present study was undertaken to investigate the role of oxytocin in antinociception in the nucleus raphe magnus (NRM) of rats and the possible interaction between oxytocin and the opioid systems. Intra-NRM injection of oxytocin induced dose-dependent increases in hindpaw withdrawal latencies (HWLs) to noxious thermal and mechanical stimulation in rats. The antinociceptive effect of oxytocin was significantly attenuated by subsequent intra-NRM injection of the oxytocin antagonist 1-deamino-2-D-Tyr-(Oet)-4-Thr-8-Orn-oxytocin. Intra-NRM injection of naloxone dose-dependently antagonized the increased HWLs induced by preceding intra-NRM injection of oxytocin, indicating an involvement of opioid receptors in oxytocin-induced antinociception in the NRM of rats. Furthermore, the antinociceptive effect of oxytocin was dose-dependently attenuated by subsequent intra-NRM injection of the mu-opioid antagonist beta-funaltrexamine (beta-FNA), but not by the kappa-opioid antagonist nor-binaltorphimine (nor-BNI) or the delta-opioid antagonist naltrindole. The results demonstrated that oxytocin plays an antinociceptive role in the NRM of rats through activating the oxytocin receptor. Moreover, mu-opioid receptors, not kappa and delta receptors, are involved in the oxytocin-induced antinociception in the NRM of rats.     

Ghrelin postsynaptically depolarizes dorsal raphe neurons in rats in vitro

Ghrelin promotes growth hormone (GH) secretion and feeding. Recent studies further showed that ghrelin displayed a defending effect against the depressive-like symptoms and affected sleep in animals and humans. Serotonergic system is considered to be implicated in feeding, depression and other mood disorders, and sleep. The dorsal raphe nucleus (DRN) utilizes serotonin (5-HT) as its major neurotransmitter and expresses GH secretagogue receptors (GHS-Rs). Therefore, the present study was carried out to examine the electrophysiological effect of ghrelin on rat DRN neurons in vitro and determine the ionic mechanism involved. Whole-cell recording revealed that ghrelin depolarized DRN neurons dose-dependently in tetrodotoxin-containing artificial cerebrospinal fluid (TTX ACSF). Pretreatment with [d-Lys³]-GHRP-6, a selective antagonist for GHS-Rs, antagonized the ghrelin-induced depolarization. The depolarization was significantly reduced in a low-Na⁺ TTX ACSF and in a high-K⁺ TTX ACSF and was abolished in the combination of both ACSFs, suggesting that the ghrelin-induced depolarization is mediated by a dual ionic mechanism including an increase in nonselective cationic conductance and a decrease in K⁺ conductance. The experiments on the reversal potential also supported an involvement of the dual ionic mechanism in the ghrelin-induced depolarization. On the basis of their electrophysiological and pharmacological properties, approximately 80% of DRN neurons were classified as putative 5-HT-containing neurons and ghrelin depolarized 75% of them. These results suggest that DRN neurons, especially 5-HT-containing neurons, might be involved in the neural mechanisms through which ghrelin participates in the development and/or regulation of feeding behavior, sleep-wake states and depressive-like symptoms.     

Spontaneous unit activity of neurons within the dorsal raphe nucleus of the neonatal rat

Extracellular recordings were made of spontaneously active neurons in the dorsal raphe nucleus (DRN) of neonatal rats. The firing pattern and rate of these neurons were similar to those characterized for 5-HT-containing cells in the DRN of adult rats. Neonatal DRN cells were also inhibiteby small systematic doses of LSD, as previously described for 5-HT-containing DRN neurons in adult rats. These results indicate that DRN neurons in neonatal rats are physiologically active and display many characteristics similar to mature 5-HT-containing DRN neurons.