Central Somatostatin Inhibits Cholecystokinin-lnduced Oxytocin Secretion in Conscious Rats

Recent studies have demonstrated the presence of fibres immunoreactive for somatostatin-28 (SS-28), which originate in the brainstem and selectively innervate the magnocellular oxytocin (OT) cells of the supraoptic nucleus. The potential physiological relevance of this pathway was investigated in the present study by measuring plasma OT levels in response to intraperitoneal administration of cholecystokinin in conscious male rats pretreated with intracerebroventricular injections of either SS-28 or artificial cerebrospinal fluid. Cholecystokinin treatment produced the expected marked rise in plasma OT levels in control rats pretreated intracerebroventricularly with artificial cerebrospinal fluid. However, this response was markedly blunted by prior intracerebroventricular administration of SS-28, even though SS-28 itself had no effect on basal plasma OT levels, nor did it impair OT release in response to hypertonic saline injection. These results demonstrate that centrally injected SS-28 can selectively block cholecystokinin-stimulated release of OT in rats, and support an inhibitory role for this peptide in brainstem-mediated neurohypophysial hormone secretion. Central SS-28 administration also elicited up to 3-fold increases in the amount of food ingested in 1 h by previously sated rats. These observations suggest the possibility that endogenous SS-28 may be involved in stimulating food intake in rats, and establish the basis for future studies to clarify the role of this neuropeptide in controlling ingestive behaviours.     

Somatostatin type 2 receptor expression in the rat hippocampus following cerebral ischemia.

We examined how transient cerebral ischemia affects the mRNA expression, and the immunoreactive distribution, of the somatostatin type 2 (sst2) receptor in the adult rat hippocampus. Following reperfusion, sst2 mRNA levels increased significantly in the CA1 region by 3 h, and were also increased in the CA3 and CA4/hilus subfields at 6 and 12 h. At 24 h, however, sst2 receptor mRNA levels returned to baseline throughout the hippocampus. At the protein level, we found the regional immunoreactivity of the sst2a receptor was maintained, or slightly elevated, throughout the hippocampus at 6 h, but not different from control at 24 h. These results suggest that sst2 receptors maintain their normal distribution and prevalence in the post-ischemic hippocampus before the deterioration of the vulnerable CA1 neurons. Thus, they represent attractive targets for neuroprotective interventions.     

Somatostatin receptor type 2 undergoes plastic changes in the human epileptic dentate gyrus

Temporal lobe epilepsy (TLE) is characterized by hippocampal sclerosis together with profound losses and phenotypic changes of different classes of interneurons, including those expressing somatostatin (SRIF). To understand the functional significance of the plasticity of SRIF transmission in TLE, unraveling the status of SRIF receptors is, however, a prerequisite. To address this issue, we characterized expression and distribution of the major SRIF receptor, the sst2 subtype, in hippocampal tissue resected in patients with TLE using complementary neuroanatomic approaches. In patients with hippocampal sclerosis, the number of cells expressing sst2 receptor mRNA as well as sst2 receptor-binding sites and immunoreactivity decreased significantly in the CA1-3, reflecting neuronal loss. By contrast, in the dentate gyrus, sst2 receptor mRNA expression was strongly increased in the granule cell layer, and sst2 receptor-binding sites and immunoreactivity was preserved in the inner but decreased significantly in the outer molecular layer. In this latter region, pronounced changes in SRIF terminal fields were observed. Decreased receptor density in the distal dendrites of granule cells is likely to reflect downregulation of sst2 receptors in response to physiopathologic release of SRIF. Because sst2 receptors have anticonvulsant and antiepileptogenic properties, this phenomenon may contribute to the etiology of TLE seizures.     

慢性癫痫大鼠脑组织生长抑素mRNA及其表达产物的研究

目的　为探讨生长抑素 (SOM)在癫痫发病中的作用。方法　应用原位杂交组织化学方法研究慢性癫痫大鼠海马回、齿状回、大脑皮质 SOM m RNA表达的变化 ,并用放射免疫法检测了海马、大脑皮质内基因表达产物的变化。结果　慢性癫痫大鼠海马回、齿状回、大脑皮质 SOM m RNA胞体数量、胞体截面积均明显高于对照组 ,胞体灰度值均明显低于对照组。与此同时 ,海马及大脑皮质内 SOM含量亦明显增高。结论　慢性癫痫发病过程中编码 SOM的基因被活化 ,同时伴随着其表达产物的增加 ,SOM与癫痫的发病密切相关。     

局灶性脑缺血再灌注大鼠皮质中谷氨酸相互作用蛋白和谷氨酸受体2的表达

目的 研究脑缺血再灌注模型半暗带皮质中谷氨酸相互作用蛋白(glutamate receptor interacting protein,GRIP)表达的变化及其与谷氨酸受体2(glutamate receptor 2,GluR2)的关系.方法 36只SD雄性大鼠随机分为缺血再灌注1、6、12、24、72 h组和假手术组...     

Distinct Agonist-Mediated Endocytosis of Cloned Rat Somatostatin Receptor Subtypes Expressed in Insulinoma Cells

Endocytosis of somatostatin receptors could regulate cellular responses to the two natural peptides, somatostatin-14 and somatostatin-28, and to synthetic ligands used in the clinical diagnosis and symptomatic therapy of neuroendocrine tumours. The five cloned SSTRs with or without epitope tags at their carboxyl-termini were expressed in rat insulinoma 1046-38 cells. Application of the two natural peptides or octreotide, at 37 °C but not at 4 °C, to cells transfected with somatostatin receptor subtype 2 or 3 cDNA resulted in a significant decrease of cell surface binding-sites for ¹²⁵I-Tyr¹¹-somatostatin-14. In contrast, cells transfected with subtype 5 cDNA only responded to stimulation with octreotide or somatostatin-28. Cells transfected with subtype 1 cDNA responded to somatostatin-14 and 28, while cells expressing subtype 4 cDNA showed no response. Confocal microscopy revealed that 6 min after stimulation with somatostatin-14 at 37 °C, tagged somatostatin receptor subtypes 1, 2 and 3 were internalized into vesicles. Internalization was not observed at 4 °C in the presence of 0.4 M sucrose and 80 &mgr;M phenylarsine oxide and hence proceeded via endocytosis through clathrin-coated pits and vesicles. After 20 min the internalized receptors appeared in perinuclear vesicles and after 120 min they reappeared at the plasma membrane. This recycling was not sensitive to cycloheximide and, hence, not dependent on de novo protein synthesis. Recovery of cell surface receptors was, however, inhibited by brefeldin A, monensin and bafilomycin A1, indicating that receptor recycling proceeded through vesicular traffic of acidified compartments. The data are consistent with the assumption that the observed agonist and subtype specific internalization of somatostatin receptors in a neuroendocrine cell line may be important for tumour diagnosis and therapy and, thus, suggest a manifold control in cellular signalling.     

Role of PGE2 EP1 Receptor in Intracerebral Hemorrhage-Induced Brain Injury

Prostaglandin E₂ (PGE₂) has been described to exert beneficial and detrimental effects in various neurologic disorders. These conflicting roles of PGE₂ could be attributed to its diverse receptor subtypes, EP1–EP4. At present, the precise role of EP1 in intracerebral hemorrhage (ICH) is unknown. Therefore, to elucidate its possible role in ICH, intrastriatal injection of collagenase was given in randomized groups of adult male wildtype (WT) and EP1 receptor knockout (EP1^?/?) C57BL/6 mice. Functional outcomes including neurologic deficits, rotarod performance, open field activity, and adhesive removal performance were evaluated at 24, 48, and 72 h post-ICH. Lesion volume, cell survival and death, were assessed using Cresyl Violet, and Fluoro-Jade staining, respectively. Microglial activation and phagocytosis were estimated using Iba1 immunoreactivity and fluorescently-labeled microspheres. Following 72 h post-ICH, EP1^?/? mice showed deteriorated outcomes compared to the WT control mice. These outcomes were demonstrated by elevated neurological deficits, exacerbated lesion volume, and significantly worsened sensorimotor functions. Fluoro-Jade staining showed significantly increased numbers of degenerating neurons and reduced neuronal survival in EP1^?/? compared to WT mice. To assess in vivo phagocytosis, the number of microspheres phagocytosed by Iba1-positive cells was 145.4 ± 15.4 % greater in WT compared to EP1^?/? mice. These data demonstrate that EP1 deletion exacerbates neuro-behavioral impairments following ICH, potentially by slowing down/impairing microglial phagocytosis. A better understanding of this EP1 mechanism could lead to improved intervention strategies for hemorrhagic stroke.     

Measurements of Somatostatin and Neuropeptide Y in the Visual Cortex of Monocularly Deprived Rats

The levels of somatostatin and neuropeptide Y were measured with radioimmunoassay bilaterally in visual cortical areas 17, 18, and 18a of rats which had received monocular enucleation at birth. Neuropeptide levels were consistently three- to fourfold higher for neuropeptide Y than for somatostatin. Monocular enucleation did not change somatostatin levels within areas 17 or 18 of either hemisphere but significantly increased somatostatin levels in contralateral area 18a when compared to contralateral areas 17 or 18 3 months after enucleation. The concentrations of neuropeptide Y are significantly greater in areas 17 and 18a than those in area 18, however, neonatal enucleation had no significant effect on neuropeotide Y levels within any visual cortical area of either hemisphere. Visual cortical areas 17, 18, and 18a show differences in the relative concentrations of neoropeptide Y compared to somatostatin. Furthermore, these two peptides respond distinctively to neonatal enucleation. Enuclestion had no effect on the concentration of either peptide in samples of frontal cortex. Immunohistochemical analysis showed that area 17 contains far fewer somatostatin neurons than areas 18 or 18a, in marked contrast to the uniform levels of somatostatin measured in all visual cortical areas by radioimmunoassay. Immunohistochemically identified neuropeptide Y-immunoreactive neurons are evenly distributed between areas 17, 18, and 18a and represent about half of the number of somatostatin-immunoreactive cells. While neuropeptide Y levels are significantly different between these visual cortical areas, the numbers of immunoreactive neurons are similar. Thus, relatively few neuropeptide Y cells are accompanied by neuropeptide Y concentrations that are four- to fivefold higher than those for somatostatin, the more abundant cell type. In view of the high degree of colocalization of neuropeptide Y and somatostatin in cortical nonpyramidal neurons, these observations imply differences in the biosynthetic and degradation/release mechanisms in these neurons.     

金纳多对血管性痴呆大鼠认知功能及生长抑素表达的影响

目的研究金纳多对血管性痴呆(vascular dementia,VD)大鼠认知功能及生长抑素(SS)表达的影响。方法采用结扎双侧颈总动脉方法制备慢性前脑缺血动物模型。将100只老龄大鼠随机分为假手术组、模型组和金纳多组。应用水迷宫及免疫组化方法对各组大鼠学习记忆及SS表达进行观察。结果模型组与假手术组学习记忆能力差异有统计学意义(P<0.05);与模型组比较,金纳多治疗30 d后大鼠学习记忆能力明显改善(P<0.05),SS阳性神经元表达增加(P<0.05)。结论金纳多可增加SS阳性神经元表达,改善VD大鼠学习记忆能力。     

The Effect of Intracerebroventricular Administration of Somatostatin on Prolactin and TSH Release in Rats

Abstract: We investigated the effect of intracerebroventrciular (icv) administration of somatostatin (SRIF) on prolactin (PRL) and thyroid-stimulating hormone (TSH) release in freely moving rats chronically cannulated with en atrial catheter. The plasma PRL levels were significantly elevated following the icv administration of 0.5 ug SRIF. No further increase in PRL following the icv administration of SRIF were found in the rats in the course of repeated intravenous of injection of 5.0 mg/kg sulpiride, a specific D2 receptor antagonist. On the other hand, the injection of 5.0 /ig SRIF resulted in no significant change in the plasma TSH levels. These results suggest that the effect of SRIF on PRL release was exerted through brain D2 receptors.     

Effects of Somatostatin on the Growth Hormone-Releasing Factor-Induced Growth Hormone Secretion in Rats with Electrical and Chemical Inhibitions of Endogenous Growth Hormone-Releasing Factor and Somatostatin

The episodic pattern of growth hormone (GH) secretion of the male rat was simulated in rats exhibiting impaired GH-releasing factor (GRF) and Somatostatin (SRIF) secretion, by administering various combinations of human GRF-(1–44)NH₂ (hGRF) and SRIF. Electrical lesions of the arcuate nucleus resulted in a marked decrease in the amplitude of GH secretory bursts, while the administration of cysteamine (200 mg/kg) did not change the GH secretory profile in rats with arcuate nucleus lesions. Immunohistochemical examinations revealed a marked decrease of GRF and SRIF immunoreactivity in the median eminence of the cysteamine-treated rats with arcuate nucleus lesions. The intravenous injection of 5 μg of hGRF every 3 h caused equivalent surges of GH in the cysteamine-treated rats with arcuate nucleus lesions. The additional infusion of 4 μg/h of SRIF during the trough periods of GH secretion did not affect the amplitude of the GH surges. Hourly injection of 5 μg of hGRF caused transient desensitization to hGRF. Interestingly, the additional infusion of 4 μg/h of SRIF every 3 h enhanced the amplitude of the GH bursts induced by the fourth and the seventh hGRF injections. However, the more frequent injection of 5 μg of hGRF every 30 min caused constant desensitization to hGRF with time, and the additional infusion of 4 μg/h of SRIF every 3 h did not change the attenuated responses to hGRF. These results indicated that the simultaneous administration of hourly GRF and continuous SRIF with brief pauses was most effective for producing high GH peaks. This simulation model suggests that SRIF may play an important role not only in the production of GH troughs, but also in the maintenance of GH surges with distinct peaks in the male rat.     

A Novel Second-Generation EP2 Receptor Antagonist Reduces Neuroinflammation and Gliosis After Status Epilepticus in Rats

Prostaglandin-E₂ (PGE₂), an important mediator of inflammation, achieves its functions via four different G protein–coupled receptors (EP1, EP2, EP3, and EP4). We previously demonstrated that the EP2 receptor plays a proinflammatory and neurodegenerative role after status epilepticus (SE). We recently developed TG8-260 as a second-generation highly potent and selective EP2 antagonist. Here, we investigate whether TG8-260 is anti-inflammatory and combats neuropathology caused by pilocarpine-induced SE in rats. Adult male Sprague–Dawley rats were injected subcutaneously with pilocarpine (380–400 mg/kg) to induce SE. Following 60 min of SE, the rats were administered three doses of TG8-260 or vehicle and were allowed to recover. Neurodegeneration, neuroinflammation, gliosis, and blood–brain barrier (BBB) integrity were examined 4 days after SE. The results confirmed that pilocarpine-induced SE results in hippocampal neurodegeneration and a robust inflammatory response that persists days after SE. Furthermore, inhibition of the EP2 receptor by TG8-260 administered beginning 2 h after SE significantly reduced hippocampal neuroinflammation and gliosis but, in distinction to the earlier generation EP2 antagonist, did not mitigate neuronal injury or BBB breakdown. Thus, attenuation of neuroinflammation and gliosis is a common feature of EP2 inhibition following SE.Supplementary InformationThe online version contains supplementary material available at 10.1007/s13311-020-00969-5.Key Words: Pilocarpine, PGE₂, EP2, COX-2, TG8-260, hippocampus, neurodegeneration, inflammation, status epilepticus, gliosis, BBB.     

The Role of Serotonin Receptor Subtypes in the Behavioural Effects of Neuroleptic Drugs. A Paw Test Study in Rats

The present study was designed to evaluate the roles of serotonin 5-HT_1A and 5-HT₂ receptors in the effects of neuroleptic drugs in the paw test. This behavioural test has been shown to model both the antipsychotic efficacy as well as the extrapyramidal side-effect liability of neuroleptic drugs. Whereas the 5-HT_1A receptor agonist 8-hydroxy-2-(di- n -propylamino)tetralin (8-OHDPAT) reduced the effects of the classical neuroleptic haloperidol, it increased the effects of the atypical neuroleptic clozapine. The 5-HT₂ receptor antagonist ketanserin as well as the 5-HT_1C/5-HT₂ receptor antagonist ritanserin, on the other hand reduced the effects of haloperidol, whereas the 5-HT_1C/5-HT₂ receptor agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOl) reduced the effects of clozapine. The most important finding, however, was that the behavioural effects of different (putative) neuroleptics (fluphenazine, SCH-39166, remoxipride, prothipendyl, thioridazine and risperidone) were differentially influenced by both 8-OHDPAT and DOl, suggesting that there are important differences between the neuronal mechanisms underlying the behavioural effects of these neuroleptic drugs, even within the subclasses of classical and atypical neuroleptics.     

Cloning,Expression, Pharmacology and Tissue Distribution of the Mouse Somatostatin Receptor Subtype 5

The gene encoding the mouse somatostatin receptor subtype 5 has been isolated from a genomic library and the mRNA start point mapped to position ?95 relative to the translational start codon. The promoter region is devoid of TATA and CAAT boxes but contains putative binding sites for AP-1, AP-2 and SP1 and response elements for glucocorticoids (GRE) and phorbol esters (TRE). The encoded receptor protein with a predicted molecular weight of 42.5 kDa is comprised of 385 amino acids and thus contains 22 and 21 amino acids more than rat and human counterparts. The extra amino acids are caused by another translational initiation codon located further upstream. In the region of overlap the mouse somatostatin receptor subtype 5 displays 96.7% sequence identity to the rat and 81.7% to the human homologue. Application of somatostatin-14 and ?28 to human embryonic kidney cells expressing the recombinant receptor resulted in the inhibition of forskolin-stimulated adenylyl cyclase with comparable EC₅₀ values. Consistent with the observed sequence relationship, the mouse somatostatin receptor subtype 5 displays a pharmacological profile that resembles the rat homologue more closely than the human counterpart. mRNA for the mouse somatostatin type 5 receptor has been detected in pituitary, kidney, spleen and ovary and, to a lesser extent, in brain, stomach, intestine and thymus but was not observed in heart, pancreas and liver.     

杏仁核毁损对甲基苯丙胺大鼠脑内5-HT2A受体的影响

目的探讨杏仁核毁损对甲基苯丙胺（MAP）大鼠脑内5-HT2A受体表达的影响。方法24只SD大鼠分为对照组、模型组、假手术组和手术组，每组各6只；采用腹腔注射MAP制备精神分裂症模型，立体定向毁损杏仁核，采用Sams-Dodd法评定各组动物刻板行为的变化，以PCR技术测定脑组织中5-HT2A受体mRNA的表达。结果杏仁核毁损可明显降低MAP大鼠刻板行为评分（P〈0．05）。各组大鼠额叶、颞叶皮质和中脑均有5-HT2A受体mNRA（61lbp）的阳性表达，且均以额叶皮质表达最为强烈；模型组及假手术组大鼠中脑5-HT2A受体mRNA受体表达的水平明显低于对照组和手术组（P〈0．05）。结论杏仁核毁损可改善MAP大鼠的刻板行为，这可能是通过中脑5-HT2A受体mRNA表达的增高而起作用。     

慢性癫癎大鼠脑组织生长抑素mRNA表达变化及糖皮质激素的作用

为探讨生长抑素在癫（疒间）发病中的作用及糖皮质激素对慢性癫（疒间）大鼠脑组织生长抑素mRNA(SOMmRNA)表达的影响.应用原位杂交组织化学方法研究了3组大鼠海马回、齿状回SOMmRNA表达变化,并用显微图像分析仪进行检测分析.结果表明,慢性癫(疒间)大鼠海马回、齿状回SOMmRNA胞体数量、胞体截面积均明显高于对照组,胞体灰度值均明显低于对照,应用地塞米松(Dex)后上述改变不明显.提示:SOM基因的活化参与了癫(疒间)的发病,Dex的抗(疒间)作用与其抑制SOM基因的活化有关.     

Transient Receptor Potential Melastatin 2 Expression is Increased Following Experimental Traumatic Brain Injury in Rats

Traumatic brain injury (TBI) elicits a sequence of complex biochemical changes including oxidative stress, oedema, inflammation and excitotoxicity. These factors contribute to the high morbidity and mortality following TBI, although their underlying molecular mechanisms remain poorly understood. Transient receptor potential melastatin 2 (TRPM2) is a non-selective cation channel, highly expressed in the brain and immune cells. Recent studies have implicated TRPM2 channels in processes involving oxidative stress, inflammation and cell death. However, no studies have investigated the role of TRPM2 in TBI pathophysiology. In the present study, we have characterised TRPM2 mRNA and protein expression following experimental TBI. Adult male Sprague Dawley rats were injured using the impact-acceleration model of diffuse TBI with survival times between 5 and 5 days. Real-time RT-PCR (including reference gene validation studies) and semi-quantitative immunohistochemistry were used to quantify TRPM2 mRNA and protein levels, respectively, following TBI. Significant increases in TRPM2 mRNA and protein expression were observed in the cerebral cortex and hippocampus of injured animals, suggesting that TRPM2 may contribute to TBI injury processes such as oxidative stress, inflammation and neuronal death. Further characterisation of how TRPM2 may contribute to TBI pathophysiology is warranted.     

Cortical 5HT<Subscript>2A</Subscript> Receptor Function under Hypoxia in Neonatal Rats: Role of Glucose,Oxygen, and Epinephrine Resuscitation

Neonatal hypoxia induces brain injury through alterations in neurotransmitters and its receptors. Molecular processes regulating serotonergic receptors play an important role in the control of respiration under hypoxia. The present study evaluates the serotonergic regulation of neonatal hypoxia and its resuscitation methods. Receptor binding assays and gene expression studies were done to evaluate the changes in 5HT_2A receptors and its transporter in the cerebral cortex of hypoxic neonatal rats and hypoxic rats resuscitated with glucose, oxygen, and epinephrine. Hypoxic stress increased total 5HT and 5HT_2A receptor number along with an upregulation of 5HT_2A receptor and 5HT transporter gene in the cortex. The enhanced cortical 5HT_2A receptors may act as a modulator of ventilatory response to hypoxia. These alterations were reversed to near control by glucose supplementation. Glucose supplementation helped in managing the serotonergic functional alterations. Hypoxia-induced adenosine triphosphate depletion causes a reduction in blood glucose levels which can be encountered by glucose administration, and oxygenation helps in overcoming the anaerobic condition. The adverse effect of immediate oxygenation and epinephrine supplementation was also reported. This has immense clinical significance in establishing a proper resuscitation for the management of neonatal hypoxia.