Biochemical evidence for simultaneous activation of multiple locus coeruleus efferents

To test the hypothesis that all locus coeruleus projections are simultaneously activated when the locus coeruleus cells fire, the norepinephrine metabolite 3-methoxy-4-hydroxyphenethyleneglycol was assayed in four regions of the central nervous system innervated by the locus coeruleus after three treatments designed to increase locus coeruleus firing in rats. Electrical stimulation of the locus coeruleus, intraperitoneal piperoxan treatment, and electric footschock all significantly increased MHPG levels in rat cerebral cortex, cerebellum, hippocampus, and spinal cord. The magnitude of MHPG increase was greater after locus coeruleus stimulation than after footshock or piperoxan. No significant differences between increases in the above brain regions were found within each treatment group.     

大鼠PTSD后蓝斑核 β-catenin的表达下降伴随细胞凋亡

目的 探讨创伤后应激障碍( PTSD) 大鼠蓝斑神经元β-catenin(β-连环蛋白)的表达变化.方法 采用国际认定的SPS方法刺激建立大鼠PTSD模型,取成年健康雄性Wistar 大鼠100 只,随机分为连续单一刺激( single prolonged stress,SPS) 模型1 d、4 d、7 d、14 d 组和对照组,应用免疫组化、免疫印迹方法检测PTSD 大鼠蓝斑神经元β-catenin的表达变化;透射电镜观察PTSD大鼠蓝斑神经元的超微结构变化.结果 经SPS 刺激后大鼠蓝斑神经元细胞内β-catenin于1d开始逐渐减少,14d表达最少;蓝斑神经元出现细胞凋亡改变.结论 蓝斑神经元细胞凋亡可能是导致PTSD 患者蓝斑功能失调的重要原因之一.     

大鼠蓝斑核对迷走-迷走抑胃反射的加强作用

本文研究了蓝斑核对迷走-迷走抑胃反射的影响。实验结果表明,单独刺激迷走神经中枢端抑制胃电和胃运动,胃电慢波的振幅和胃内压分别下降到对照值的60.9％和45.7％,与对照值相比有明显的统计学意义(P<0.05)。刺激迷走神经中枢端的同时,以弱刺激刺激蓝斑核时,胃电慢渡的振幅和胃内压分别下降到对照值的42.1％和34.1％,与单独刺激迷走神经的效果相比较有非常显著的差异(P<0.01)。本文结果提示:蓝斑核的兴奋加强迷走-迷走抑胃反射。     

Locus coeruleus fibre growth in oculo induced by trigeminotomy

Locus coeruleus from fetal donors was homologously grafted to the anterior eye chambers of adult rats whose eyes were sympathetically denervated. After intraocular maturation, outgrowth of noradrenaline-containing fibres from the locus coeruleus neurons on the host iris was studied by Falck--Hillarp fluorescence histochemistry.In control animals locus coeruleus grafts produce a halo of noradrenaline-containing nerve fibres around the graft, covering approximately one third of the surface of the host iris. Sensory denervation of host eyes carrying maturated locus coeruleus grafts was produced by intracranial lesions of the trigeminal nerve. Such lesions induced a rapid growth response in the grafted locus coeruleus neurons, leading within three weeks to complete innervation of the host iris. It was concluded that removal of non-sympathetic, non-parasympathetic nerve fibres on the host iris elicits a strong fibre-growth response in the grafted locus coeruleus.     

BMPs, FGF8 and Wnts regulate the differentiation of locus coeruleus noradrenergic neuronal precursors

In the present study, we investigated the involvement of rhombomere 1 patterning proteins in the regulation of the major noradrenergic centre of the brain, the locus coeruleus. Primary cultures of rat embryonic day 13.5 locus coeruleus were treated with fibroblast growth factor-8, noggin and members of the bone morphogenetic and Wnt protein families. We show that bone morphogenetic proteins 2, 5 and 7 increase and noggin decreases the number of tyrosine hydroxylase-positive locus coeruleus neurons. Interestingly, from all Wnts expressed in the first rhombomere by embryonic day 12.5 in the mice, we only found expression of wnt5a mRNA in the vicinity of the locus coeruleus. In agreement with this finding, from all Wnts studied in vitro, only Wnt5a increased the number of tyrosine hydroxylase-positive neurons in locus coeruleus cultures. Finally, we also found that fibroblast growth factor-8 increased the number of tyrosine hydroxylase-positive cells in locus coeruleus cultures. Neither of the identified factors affected the survival of tyrosine hydroxylase-positive locus coeruleus noradrenergic neurons or the proliferation of their progenitors or neurogenesis. Instead, our results suggest that these patterning signals of rhombomere 1 may work to promote the differentiation of noradrenergic progenitors at later stages of development.     

A selective 5-HT1 agonist,RU 24969, increases locus coeruleus catechol metabolic and neuronal activity

Locus coeruleus activity was monitored by either in vivo electrochemistry, post-mortem HPLC, or single unit activity, after systemic administration of RU 24969, a potent serotonin-1 agonist. Whatever the methodology, activation of the locus coeruleus appeared after RU 24969 injection. Catechol oxidation current, assessed by in vivo differential pulse voltammetry and single unit activity in the locus coeruleus showed simultaneous increases after RU 24969. The increase in catechol oxidation current after RU 24969 was dose dependent (ED₅₀ = 1.4 mg kg⁻¹ of i.p. RU 24969). This increased activity was also observed on microdissected locus coeruleus as shown by the increased levels of dopamine and 3,4-dihydroxyphenylacetic acid measured with high performance liquid chromatography. Furthermore, RU 24969 treatment decreased 5-hydroxyindolacetic acid/serotonin ratio in the same microdissected locus coeruleus. This increased locus coeruleus catechol metabolic activity was suppressed by making lesions in the serotonergic systems with 5,7-dihydroxytryptamine. By contrast, neither 8-OHDPAT nor methysergide produced significant changes in the catechol oxidation current recorded in the locus coeruleus.     

Afferent pathway from locus coeruleus to the nucleus solitarius

After the destruction of the nucleus tractas solitarii, just caudally to the writing pen by means of a stereotaxic instrument, the system of afferent fibres to the nucleus in question was investigated by the methods of Nauta and Fink--Heimer. The fibre terminals were revealed near locus coeruleus. Investigation of the locus coeruleus by Golgi method demonstrated that it usually has neurons of reticular type and transitional ones which resemble by their form the neurons specific for sensory formations. It is possible to conclude that locus coeruleus posesses connections of visceral origin which may play a part in the afferent influence of locus coeruleus on the brain cortex.     

Agonist Binding to α2-Adrenoceptors Is Elevated in the Locus Coeruleus from Victims of Suicide

Abstract: The binding of an agonist, p-[¹²⁵I]iodoclonidine, and an antagonist, [³H]yohimbine, to α₂-adrenoceptors was measured autoradiographically in the locus coeruleus from 10 pairs of antidepressant-free victims of suicide and age-matched controls. Agonist binding to α₂-adrenoceptors was significantly greater in the locus coeruleus from victims of suicide compared with control subjects. In contrast, antagonist binding to α₂-adrenoceptors in the locus coeruleus did not differ significantly between control and suicide subjects. HPLC analysis of norepinephrine in tissue sections of the locus coeruleus did not reveal any differences between control subjects and suicide victims, suggesting that differences in agonist binding are not a result of differences in retention of the endogenous agonist norepinephrine in tissue sections. The increase in agonist binding to α₂-adrenoceptors in the locus coeruleus of victims of suicide links an altered expression of the high-affinity state of autoinhibitory α₂-adrenoceptors with suicide.     

蓝斑对迷走─心血管反射的影响

实验用家兔３６只,采用低频（５－８Ｈｚ）和高频（５０－１００Ｈｚ）电流刺激颈部迷走神经中枢端（ＶＡＳ）,建立迷走－减压和迷走－升压反射,两种频率电刺激均导致肾交感神经传出活动（ＲＳＡ）减少。以迷走－血压反射和迷走－交感反射为指标,连续电流刺激蓝斑（ＬＣ）或ＬＣ微量注射谷氨酸钠均抑制迷走－血压反射和迷走－交感反射。而连续电流刺激ＬＣ或ＬＣ微量注射谷氨酸钠本身均引起平均动脉血压升高和ＲＳＡ增加。本文对新近提出的对ＬＣ整体功能认识的理论,结合本文的结果进行了讨论     

Effect of an analog of vasopressin on the fixation of temporary connections in the intact rat and after destruction of the locus coeruleus

Subcutaneous injection to intact rats and rats with destroyed locus coeruleus of 10 mcg of triglycide-glycinamide-lysinevasopressin (TGDGA-LVP) immediately after elaboration of labyrinth defensive conditioned reflex improves consolidation of temporary connections and raises its resistance to extinction. Improved consolidation of temporary connection is retained in animals with destroyed locus coeruleus for a shorter time than in intact animals. At the same time according to some characteristics, TGDGA-LVP has a more expressed influence of positive character on animals with destroyed locus coeruleus than on intact rats.     

蓝斑对迷走—心血管反射的影响

实验用家兔３６只,采用低频和高频电流刺激颈部迷走神经中枢端,建立迷走－减压和迷走－升压反射,两种频率电刺激均导致肾交感神经传出活动减少。以迷走－血压反射和迷走－交感反射为指标,连续电流刺激蓝斑或ＬＣ微量注射谷氨酸钠均抑制迷走－血压反射和迷走－交感反射。     

Monoaminergic interaction in the central nervous system: a morphological analysis in the locus coeruleus of the rat.

The locus coeruleus of the rat is richly innervated by many aminergic neurons varying in amine content and in site of origin. There are adrenergic and noradrenergic neurons originating in the medulla oblongata, dopaminergic from the hypothalamus, serotonergic from the mesencephalon and also intrinsic noradrenergic neurons in the locus coeruleus complex. Of these, adrenergic and dopaminergic inputs appear relatively specific and powerful.     

TYROSINE HYDROXYLASE ACTIVITY IN NORADRENERGIC NEURONS OF THE LOCUS COERULEUS AFTER RESERPINE ADMINISTRATION: SEQUENTIAL INCREASE IN CELL BODIES AND NERVE TERMINALS

The effect of a single systemic injection of reserpine on tyrosine hydroxylase activity in the locus coeruleus, cerebellum, hypothalamus, and hippocampus was examined. Increases in enzyme activity were seen in all four brain areas; the time-course of the changes, however, was different in each case. In the locus coeruleus the maximum change in enzyme activity was seen 3 days after drug administration; in the cerebellum, 7-11 days; in the hypothalamus, 8-11 days; and in the hippocampus, 21 days. Since tyrosine hydroxylase in the cerebellum and hippocampus is present in terminals of neurons whose cell bodies are located in the locus coeruleus, the delayed increase in enzyme activity in cerebellum and hippocampus probably depends upon the slow rate of transport of TH molecules in these neurons.     

Generators of synchronous activity of the locus coeruleus during development

The locus coeruleus is thought to play an important role in the development of the central nervous system through a coordinated release of noradrenaline. The influence of the locus coeruleus on its diverse targets is strongly synchronized by the existence of electrical and chemical coupling between neurones, afferent supply of the nucleus from restricted sources and diffuse innervation of target areas. Extensive coupling between neonatal locus coeruleus neurones produces rhythmic synchronized electrical activity and distributes afferent synaptic activity throughout the entire nucleus. The strength of electrical coupling declines with age but appears to persist to a limited extent in the adult.     

Atrial natriuretic peptide in the locus coeruleus and its possible role in the regulation of arterial blood pressure, fluid and electrolyte homeostasis.

Atrial natriuretic factor (ANP) is present in neuronal cells of the locus coeruleus and its vicinity in the pontine tegmentum and moderate amount of ANP is detectable in this area by radioimmunoassay. The ANP (both peripheral and brain-born) is known as a neuropeptide which may influence the body salt and water homeostasis and blood pressure by targeting both central and peripheral regulatory mechanisms. Whether this pontine ANP cell group is involved in any of these regulatory mechanisms, the effect of various types of hypertension and experimental alterations in the salt and water balance on ANP levels was measured by radioimmunoassay in the locus coeruleus of rats. Adrenalectomy, as well as aldosterone and dexamethasone treatments failed to alter ANP levels in the locus coeruleus. Reduced ANP levels were measured in spontaneously hypertensive (both young and adult) rats, and in diabetes insipidus (Brattleboro) rats with vasopressin replacement. In contrast to these situations, elevated ANP levels were found in rats with DOCA-salt or 1-kidney-1-clip hypertension. These data suggest a link between ANP levels in the locus coeruleus and fluid volume homeostasis. Whether this link is causal and connected with the major activity of locus coeruleus neurons (noradrenergic influence on brain regulatory activities) needs further informations.     

Selective reduction by serotonin, of neuronal excitation in the locus coeruleus evoked by glutamate

In the rat, iontophoretically applied serotonin substantially attenuated the excitation of locus coeruleus neurons evoked by iontophoretic glutamate but not that elicited by acetylcholine. These results occurred independently of serotonin's variable effects on spontaneous discharge, and indicate a neuromodulatory role of serotonin in locus coeruleus.     

Topography of catecholamine-containing neurons of the locus coeruleus in the cat

Topography of catecholamine-containing (CA) neurons of the cat locus coeruleus was studied using a combination of the catecholamine histofluorescence method and rapid embedding of the brain tissue into the paraffin wax. The distribution of CA neurons was examined at frontal and sagittal sections of the brain stem. Unlike that shown previously the quantity of CA neurons in the rostral pole of the locus coeruleus was somewhat higher while at the frontal level of P--2.0-P--4.0 the significant number of CA cells of the locus coeruleus was localized more ventromedially.     

Genetic inactivation of Kcnj16 identifies Kir5.1 as an important determinant of neuronal PCO2/pH sensitivity

The molecular identity of ion channels which confer PCO(2)/pH sensitivity in the brain is unclear. Heteromeric Kir4.1/Kir5.1 channels are highly sensitive to inhibition by intracellular pH and are widely expressed in several brainstem nuclei involved in cardiorespiratory control, including the locus coeruleus. This has therefore led to a proposed role for these channels in neuronal CO(2) chemosensitivity. To examine this, we generated mutant mice lacking the Kir5.1 (Kcnj16) gene. We show that although locus coeruleus neurons from Kcnj16((+/+)) mice rapidly respond to cytoplasmic alkalinization and acidification, those from Kcnj16((-/-)) mice display a dramatically reduced and delayed response. These results identify Kir5.1 as an important determinant of PCO(2)/pH sensitivity in locus coeruleus neurons and suggest that Kir5.1 may be involved in the response to hypercapnic acidosis.     

Elevated Tyrosine Hydroxylase in the Locus Coeruleus of Suicide Victims

Abstract: The amounts of tyrosine hydroxylase protein in locus coeruleus from nine pairs of antidepressant-free suicide victims and age-matched, sudden-death control cases were determined by quantitative blot immunolabeling of cryostat-cut sections from the caudal portion of the nucleus. In each of the nine age-matched pairs, the concentration of tyrosine hydroxylase was greater in the sample from the suicide victim, with values ranging from 108 to 172% of the matched control value (\-x = 136%). By contrast, there were no differences in the concentrations of neuron-specific enolase protein in the same set of samples. Similarly, the number of neuromelanin-containing cells, counted in sections of locus coeruleus adjacent to those taken for blot immunolabeling analyses, did not differ between the two groups. These data indicate that locus coeruleus neurons from suicide victims contain higher than normal concentrations of tyrosine hydroxylase, thus raising the possibility that the expression of tyrosine hydroxylase in locus coeruleus may be relevant in the pathophysiology of suicide.