Glucose utilization and insulin binding in discrete brain areas of obese rats.

The present study was carried out to determine whether genetically obese Zucker rats present changes in brain glucose utilization and/or insulin binding when compared to their lean counterparts. Glucose utilization in the whole brain, determined by measurement of 2-deoxy(1-3H)glucose-6-phosphate, was significantly lower in obese than in lean Zucker rats. In order to precise the structure involved, we then used quantitative autoradiography methods after either (1-14C) 2-deoxyglucose injection or 125I-insulin incubation. In obese rats, local cerebral glucose utilization (LCGU) was significantly decreased in the external plexiform layer (-37%, p < 0.05), in the lateral hypothalamus (-23%, p < 0.05), and in the basolateral amygdaloid nucleus (-30%, p < 0.05). In contrast, no difference in specific insulin binding was found between the two genotypes in any of the areas studied. These results are consistent with some data showing a decrease of LCGU in hyperinsulinemic rats. All together, these data show perturbations of glucose utilization, particularly in structures linked to the regulation of body weight and food intake in obese Zucker rats.     

Lack of effect of insulin on glucose utilization of the hypothalamus in normotensive and hypertensive rats

Hypertension is frequently associated with insulin resistance and enhanced sympathetic activity supposedly mediated by an effect of the hormone on the hypothalamus. In this study we sought to determine whether insulin modifies the functional activity of the hypothalamus and other brain areas of spontaneously hypertensive (SHR) and normotensive WKY rats. The study was carried out in control and hyperinsulinemic, normoglycemic rats. Insulin plasma levels were increased to 198 +/- 10 (WKY) or 220 +/- 10 microunits/ml (SHR). Brain functional activity was evaluated by the 2-[14C]deoxyglucose method for measuring local rates of glucose utilization. The results show that insulin has no effect on any of the brain areas examined including the hypothalamus, of both WKY and SHR rats. The two strains of rats have comparable cerebral metabolic rates also under basal conditions.     

Hypothalamic obesity: comparison of radio-frequency and electrolytic lesions in weanling rats

Female rats were subjected to radio-frequency or anodal electrolytic lesions of the ventromedial hypothalamus (VMH) when 28 days old. Blood samples for determination of basal plasma insulin and glucose levels were taken on postoperative day 30 (Experiment 1) and on day 10 (Experiment 2). Body weight and daily food intake of rats with either type of lesion did not differ from unoperated animals during the first 10 days, but rats with electrolytic lesions, unlike radio-frequency lesioned animals, displayed excess food intake and weight gain starting in the third postoperative week. Both types of lesions produced stunted linear growth and a higher than normal Lee Obesity Index. Only the rats with electrolytic VMH lesions were significantly hyperinsulinemic on postoperative day 30, with a mean plasma insulin level that was at least double that observed in unoperated or radio-frequency lesioned animals. On day 10, however, the animals with electrolytic lesions had markedly lower plasma insulin and glucose levels compared to the other two groups, which did not differ from one another. There was no apparent difference in the size of the lesions produced by the two techniques, and it is therefore concluded that some of the endocrine dysfunctions resulting from electrolytic VMH lesions are due to metallic ion deposits (stimulating adjacent tissue) rather than to tissue ablation.     

Uncoupling of local blood flow and metabolism in the hippocampal CA3 in kainic acid-induced limbic seizure status

Limbic seizure status was induced by microinjection of kainic acid into a unilateral amygdala in rats. Two hours after kainic acid injection, distant neuronal cell damage was produced, especially in the hippocampal CA3 on the kainic acid-injected side. In order to elucidate the mechanism of this neuronal cell damage, local cerebral glucose utilization and local cerebral blood flow were studied by means of an autoradiographic method using [14C]2-deoxyglucose and [14C]iodoantipyrine during kainic acid-induced limbic seizure status. These studies were performed 2 h after kainic acid microinjection into a unilateral amygdala. Both local cerebral glucose utilization and local cerebral blood flow were remarkably increased in the limbic system, ventrobasal complex of the thalamus, septal nucleus, nucleus accumbens, caudate nucleus, substantia nigra and hypothalamus on the kainic acid-injected side. In the hippocampus, local cerebral glucose utilization increased 2.6 times control in CA1 and 4.1 times in CA3, whereas the rates of increase in local cerebral blood flow were similarly low in CA1 and CA3: 1.2 and 1.4 times control, respectively. The results demonstrated that the degree of uncoupling of local cerebral glucose utilization and local cerebral blood flow were higher in CA3 than in CA1, and also suggested that relative hypoxia occurred in CA3 in this high degree of uncoupling, resulting in pyramidal cell damage in CA3 in kainic acid-induced limbic seizure status.     

胰岛素对糖尿病大鼠海马内神经营养因子-3阳性神经元表达的影响

目的：观察糖尿病大鼠海马中神经营养因子-3(NT-3)的表达变化及胰岛素治疗对其表达的影响。方法：将雄性大鼠随机分为对照组,糖尿病1,3月组,胰岛素治疗1,3月组,STZ 腹腔注射制模,测体重与血糖值并取海马行 HE 和免疫组化 SABC 法染色,计算机图像分析系统测平均光密度值。结果：血糖在糖尿病组比对照组显著升高;胰岛素组与对照组无显著性差异。海马各区 NT-3免疫阳性神经元的数量及阳性强度在糖尿病组有不同程度降低,以 CA1区最明显。胰岛素组则不降低。结论：糖尿病大鼠海马神经元 NT-3表达减弱,胰岛素治疗可使海马神经元 NT-3表达恢复正常。     

银杏叶提取物对1型糖尿病大鼠认知功能及海马神经细胞凋亡的影响

目的： 探讨银杏叶提取物(EGB)对1型糖尿病脑病大鼠海马神经细胞的保护机制。方法: 36只SD雄性大鼠随机分为正常对照组（C组）、糖尿病模型组(DM组)、银杏叶提取物治疗组（EGB组）。用链脲佐菌素（STZ）腹腔注射建立糖尿病动物模型,EGB组腹腔注射银杏叶提取物注射液,其余2组给予同等体积的生理盐水。于12周末通过Morris水迷宫法评价各组大鼠学习记忆能力并测定血清中的血糖和胰岛素浓度;用Image-Pro Plus 6.0图像分析技术检测大鼠海马组织神经细胞密度;Western blotting和免疫组织化学法检测其Bax、Bcl-2和caspase-3蛋白的表达。结果: DM组大鼠血糖浓度(P<0.01)、海马神经细胞中Bax(P<0.01)、caspase-3(P<0.01)蛋白的表达、Bax/ Bcl-2比例 (P<0.01)及Morris水迷宫潜伏期(P<0.01)均高于C组,而胰岛素水平(P<0.01)、海马CA1和CA2区域的神经细胞密度(P<0.05) 及Morris水迷宫搜索策略能力(P<0.01)均低于C组。EGB干预治疗后大鼠胰岛素水平(P<0.05)、海马CA1和CA2区域的神经细胞密度(P<0.05) 及Morris水迷宫搜索策略能力(P<0.01)均高于DM组,而血糖浓度(P<0.01)、海马组织中Bax(P<0.05)、caspase-3(P<0.05)蛋白的表达、Bax/ Bcl-2比例 (P<0.01) 及Morris水迷宫潜伏期(P<0.05)均低于DM组。各实验组大鼠Bcl-2蛋白的表达没有明显变化。结论: 银杏叶提取物提高糖尿病大鼠的空间学习记忆能力,可能通过减少Bax、caspase-3蛋白表达、降低Bax/ Bcl-2比例,从而减少神经细胞的凋亡,提高神经细胞密度而发挥作用。提示通过有效调节神经元凋亡相关基因是EGB治疗糖尿病脑病的的重要作用机制之一。     

清醒大鼠胰岛素钳夹术及其糖代谢变化

为准确地评价在体组织对胰岛素 (Ins)的敏感性及探讨在胰岛素抵抗 (IR)状态下机体糖代谢变化。采用 6 ,6 D2 葡萄糖作为示踪剂 ,建立了自由状态下大鼠正常血糖 -高胰岛素钳夹术 ,并动态观察了其体内糖代谢的动态改变及血浆游离脂肪酸 (FFA)和Ins浓度随时间变化的过程。大鼠在 4 8mU (kg·min)速率Ins输注下 ,血糖稳定在正常水平而肝糖输出被抑制 ,胰岛素介导的机体葡萄糖利用率较基础状态显著增加 ,游离脂肪酸 (FFA)浓度显著下降。本钳夹术平均血糖变异系数为 5 76 %。平均GIR变异系数为 6 2 5 % ,GRd为 9 17%。重复试验GIR与GRd误差范围为 1 2 %和 1 7%。以 6 ,6 D2 葡萄糖作为示踪剂建立的自由状态下的大鼠正常血糖钳夹技术具有准确、可靠 ,无放射污染等优点 ,在外源性胰岛素 -葡萄糖代谢稳定状态下 ,机体对葡萄糖利用显著增加 ,脂肪分解显著减少。     

Insulin sensitivity of the body in experimental hypothalamic obesity

Two-month hyperphagia after injury inflicted to the ventromedial hypothalamus in rats led to the development of marked obesity in an essential increase of the content of immunoreactive insulin, glucagon, and C-peptide in the blood. Increase of excessive body weight was attended by gradual diminution of the organisms sensitivity to exogenous insulin given in a dose of 0.03 U/100 g and maintenance of normal sensitivity to 0.1 U/100 g of exogenous insulin. It is most likely, therefore, that despite the increased function of the pancreatic islets and hyperinsulinemia, glucose tolerance decreased significantly due to diminished sensitivity of the peripheral tissues to insulin.     

Effects of insulin and 2-deoxy-D-glucose on plasma glucose level and lateral hypothalamic eating threshold in the rat

Thresholds for elicited eating through monopolar electrodes in the perifornical region of the lateral hypothalamus and plasma glucose concentration were determined over periods of several hours, while blood glucose levels and cellular glucose utilization were altered by means of forced feeding through hypothalamic stimulation, subcutaneous insulin injections and/or intraperitonneal 2-deoxy-D-glucose injections. Forced feeding resulted in increased thresholds for elicited eating, whereby the plasma glucose concentration in the tail vein was positively correlated to these thresholds. A subsequent, long-lasting, severe insulin-hypoglycemia was not sufficient to normalize such elevated thresholds. However, 2-deoxy-D-glucose in doses of 100–250 mg/kg, after an initial increase, decreased thresholds 90 min after injection. When insulin and 2-deoxy-D-glucose were combined so as to balance the contrary glycemic effects, the insulin effect dominated, resulting in slightly increasing thesholds. The results are discussed in terms of the recently suggested hypothesis that insulin regulates glucose entry into glucosensitive systems of the ventromedial hypothalamus, and thus generates satiety signals rather than hunger.     

Potent hyperglycemic and hyperinsulinemic effects of thyrotropin-releasing hormone microinjected into the rostroventrolateral medulla and abnormal responses in type 2 diabetic rats

We identified ventrolateral medullary nuclei in which thyrotropin-releasing hormone (TRH) regulates glucose metabolism by modulating autonomic activity. Immunolabeling revealed dense prepro-TRH-containing fibers innervating the rostroventrolateral medulla (RVLM) and nucleus ambiguus (Amb), which contain, respectively, pre-sympathetic motor neurons and vagal motor neurons. In anesthetized Wistar rats, microinjection of the stable TRH analog RX77368 (38–150 pmol) into the RVLM dose-dependently and site-specifically induced hyperglycemia and hyperinsulinemia. At 150 pmol, blood glucose reached a peak of 180±18 mg% and insulin increased 4-fold. The strongest hyperglycemic effect was induced when RX77368 was microinjected into C1 area containing adrenalin cells. Spinal cord transection at cervical-7 abolished the hyperglycemia induced by RVLM RX77368, but not the hyperinsulinemic effect. Bilateral vagotomy prevented the rise in insulin, resulting in a prolonged hyperglycemic response. The hyperglycemic and hyperinsulinemic effects of the TRH analog in the RVLM was peptide specific, since angiotensin II or a substance P analog at the same dose had weak or no effects. Microinjection of RX77368 into the Amb stimulated insulin secretion without influencing glucose levels. In conscious type 2 diabetic Goto–Kakizaki (GK) rats, intracisternal injection of RX77368 induced a remarkably amplified hyperglycemic effect with suppressed insulin response compared to Wistar rats. RX77368 microinjected into the RVLM of anesthetized GK rats induced a significantly potentiated hyperglycemic response and an impaired insulin response, compared to Wistar rats. These results indicate that the RVLM is a site at which TRH induces sympathetically-mediated hyperglycemia and vagally-mediated hyperinsulinemia, whereas the Amb is mainly a vagal activating site for TRH. Hyperinsulinemia induced by TRH in the RVLM is not secondary to the hyperglycemic response. The potentiated hyperglycemic and suppressed hyperinsulinemic responses in diabetic GK rats indicate that an unbalanced “sympathetic-over-vagal” activation by TRH in brainstem RVLM contributes to the pathophysiology of impaired glucose homeostasis in type 2 diabetes.     

大鼠下丘脑腹内侧核与海马神经纤维联系研究

目的:探讨大鼠下丘脑腹内侧核与海马的传入、传出神经纤维联系,为摄食和能量代谢等内脏活动的神经调节机制的深入研究提供形态学依据。方法:参考大鼠脑立体定位图谱,借助脑立体定位仪将逆行示踪剂伊文思蓝(EB)分别注入SD大鼠左侧下丘脑腹内侧核(A组,18只)或海马CA2区(B组,18只),大鼠存活3 d后,4%多聚甲醛心脏灌注,冰冻切片,荧光显微镜下观察。结果:A组双侧海马的CA2,CA3处均显示有荧光标记细胞,且对侧荧光强于同侧;B组下丘脑腹内侧核处未见荧光标记细胞。结论:下丘脑腹内侧核与海马有广泛的纤维联系,可接受来自双侧海马CA2,CA3区的神经纤维投射,两者可能在内脏活动调节中发挥重要作用。     

Chronic intrahypothalamic infusions of insulin or insulin antibodies alter body weight and food intake in the rat.

In Experiment 1, one-week infusion of insulin (0.15, 1.5, or 15.0 microU/hr) into the ventromedial hypothalamus (VMH) of rats reduced body weight (BW) and nighttime food intake (FI). While 0.15 microU/h decreased daytime FI, 1.5 microU/h increased daytime FI and 15.0 microU/h left daytime FI unchanged. Total daily FI was decreased by the two highest doses. In Experiment 2, intra-VMH infusion of specific insulin antibodies (1.5 microUeq/h) increased BW and FI, while C-peptide antibodies were ineffective. In Experiment 3a, intracerebroventricular infusions of insulin failed to decrease FI and BW comparably to similar intrahypothalamic infusions. In Experiment 3b, intra-VMH insulin was infused via cannulae that bypassed the cerebral ventricles. The decrease in FI and BW was comparable to that observed when insulin was infused via cannulae that penetrated a ventricle. Histology from animals used in Experiments 1-3 indicates that optimum sites for insulin-induced changes in BW and FI in the hypothalamus lie in an area that includes portions of the paraventricular, arcuate, dorsomedial, and ventromedial nuclei.     

Neuropeptide Y: brain localization and central effects on plasma insulin levels in chicks

A rich network of NPY-like immunoreactive fibers was found in the paraventricular nucleus and the ventromedial region of the hypothalamus juxtapositioned to the third ventricle, including the median eminence. Brain regions, areas or nuclei found densely innervated by NPY-like immunoreactive fibers included the olfactory bulb region, septal area, organum vasculosum of the lamina terminalis, preoptic periventricular nucleus, hypothalamic periventricular nucleus, medial suprachiasmatic nucleus, subseptal (subfornical) organ, ventromedial hypothalamic nucleus, infundibular nucleus and nucleus tractus solitarius. NPY-like containing perikarya were localized within the hippocampus, bed nucleus of the stria terminalis and surrounding the nucleus rotundus and nucleus of the basal optic root. Since the immunocytochemical study showed that NPY was localized in brain structures known to alter food intake and the compound is a member of the pancreatic polypeptide family, a second study was designed to determine if the neuropeptide altered plasma concentrations of insulin, glucagon and glucose following intracerebroventricular administration. It was found that NPY significantly increased plasma concentration of insulin. It is proposed that two reasons why NPY is such a potent orexigenic agent is that the paraventricular nucleus and structures surrounding the third ventricle throughout the ventromedial hypothalamic region show high levels of NPY-like immunoreactivity. Secondly, NPY effects an increase in plasma insulin in the periphery.     

白细胞介素6受体样免疫反应性细胞在大鼠脑内的分布

目的　研究白细胞介素６ 受体（ＩＬ－６Ｒ和ｇｐ１３０）免疫反应性细胞在大鼠脑内的分布。方法　采用ＡＢＣ免疫组织化学方法。结果　ＩＬ－６Ｒ免疫反应性细胞主要分布在下丘脑的视前区、腹内侧核、室旁核和弓状核;在海马,ＩＬ－６Ｒ阳性细胞呈强阳性,密集分布于齿状回颗粒细胞层和ＣＡ１ ～ＣＡ２ 锥体细胞层;在大脑皮层、嗅结节、丘脑腹内侧核、终纹床核等处也有ＩＬ－６Ｒ阳性细胞。ｇｐ１３０ 阳性细胞主要分布于下丘脑的室周核、室旁核的内侧小细胞部、弓状核及视上核,在大脑皮层也有ｇｐ１３０ 阳性大锥体细胞的分布。ｇｐ１３０ 阳性细胞亦见于尾壳核、杏仁核区、终纹床核,在海马结构内的ｇｐ１３０ 阳性细胞较ＩＬ－６Ｒ染色较浅。此外,ＩＬ－６ 两种受体亚单位的免疫反应性细胞也散在分布于小脑皮层、小脑外侧核以及延髓／脑干。结论　在大鼠脑内广泛分布着ＩＬ－６ 两种受体亚单位的免疫反应性细胞,提示ＩＬ－６ 及其受体可能具有重要的神经生物学意义。     

Effects of acute haloperidol treatment on regional catecholamine levels and utilization in rats exposed to toluene

The aim of the present investigation was to evaluate whether the responses of central catecholamine (CA) neurons to CA receptor blockade by haloperidol are altered upon toluene exposure. Male rats were exposed to air or toluene (80 ppm) for 5 and 4 days, 6 h day^-1. CA levels and utilization were determined in discrete regions of the forebrain and hypothalamus as well as in the substantia nigra (SN) and anteromedial frontal cortex (AMFC). Serum levels of corticosterone, thyroid stimulating hormone, luteinizing hormone and prolactin were determined by radioimmunoassay procedures. Toluene exposure led to increased dopamine (DA) utilization in the AMFC and increased CA utilization in the paraventricular hypothalamic nuclei. In air-exposed rats haloperidol (1 mg kg^-1, i.p., 2 h before killing) increased DA utilization in the marginal part of the nucleus caudatus putamen (CAUD). In toluene-exposed rats, haloperidol induced significant depletions of DA stores in the SN and in the medial and central parts of the CAUD. In the posterior nucleus accumbens (ACC) DA utilization was significantly increased. Combined haloperidol and toluene treatment selectively decreased DA levels in the ACC and SN, and significantly increased DA utilization in the CAUD, as compared with the air-exposed control group. Furthermore, after combined treatment, there was a specific increase in noradrenaline (NA) utilization in the SN and in CA utilization in the medial palisade zone of the median eminence. Serum prolactin levels were substantially raised in both the air and toluene groups after the haloperidol treatment. In conclusion, acute haloperidol treatment preferentially reduces DA levels and increases DA and NA utilization in the SN and in discrete tel- and diencephalic areas in rats exposed to toluene.     

Systemic insulin decreases lateral hypothalamic unit activity

In succynilcholine immobilized rats unit activity of lateral hypothalamic neurons decreased after intraperitoneal injections of insulin. Some neurons in a region between lateral and medial hypothalamus and at the ventromedial nucleus increased their activity after insulin injection. Results are interpreted as electrophysiological evidence of an insulin dependent hypothalamic mechanism and its behavioral role is discussed.     

Partial kindling of the ventral hippocampus: identification of changes in limbic physiology which accompany changes in feline aggression and defense.

This study examined the interictal consequences of partial kindling of the ventral perforant path on attack and defensive behavior in the domestic cat. Partial kindling produced a lasting increase in defense response of cats to both rats and conspecific threat howls. In addition, there was a lasting suppression of approach-attack behaviors directed toward rats. The suppression of some components of approach-attack were shown to be independent of the increases in defensive response. The effects of partial kindling of the ventral perforant path on spread of seizure activity into the amygdala, and on the output of the amygdala to both the ventromedial hypothalamus (VMH) and bed nucleus of the stria terminalis (BNST) were also examined. In addition, the effects of repeated hippocampal seizures on recurrent inhibition in the trisynaptic circuit (areas CA1 and CA3) were investigated. Growth of seizure activity in the amygdala and VMH as partial kindling progressed was essential for behavioral change. In addition, interictal long-term potentiation of potentials evoked in the VMH and in the BNST by pulsed stimulation of the amygdala followed partial kindling or afterdischarge threshold determination in the ventral perforant path. A lasting interictal increase in inhibition in area CA3 and a lasting interictal failure of inhibition in area CA1 of the ventral hippocampus also followed partial kindling. These changes in limbic physiology were related to the behavioral changes produced by partial kindling. The analysis revealed the importance of the amygdalo-VMH pathway in increased defensive response to rats. The amygdalo-BNST pathway is not important in mediating defensive response to prey, but it is implicated in suppression of some types of predatory aggression. Finally, changes in neural inhibition in the ventral hippocampus in areas CA1 and CA3 are associated with changes in both defensiveness and predatory aggression.     

Uptake and utilization of metabolites in specific brain sites relative to feeding status

Two experiments were conducted to assess potential alterations in fatty acid and glucose metabolism within specific brain sites in relation to the feeding status of the rat. An in vivo serial analysis of brain palmitate and glucose uptake demonstrated that hypothalamic uptake of these substrates was reciprocally altered with respect to satiety. Hypothalamic uptake of palmitate was increased by 300% and uptake of glucose was decreased by 30% in fasted compared with fed rats. Other regional differences were observed and discussed in the text. An in vitro analysis showed that hypothalamic fatty acid oxidation was affected by feeding status. The ventrolateral hypothalamus (VLH) of fasted rats had 45% greater rates of fatty acid oxidation than VLH of fed rats. No alterations were observed for VLH glucose oxidation and ventromedial hypothalamic glucose and fatty acid oxidation when comparing fed and fasted rats. Other brain sites did not show variance for glucose and fatty acid metabolism relative to feeding status. Fatty acid uptake and subsequent metabolism in the hypothalamus and other brain sites may be one component of food intake control and energy balance regulation.     

Hypothalamic modulation of energy expenditure

The acute effects of electrical stimulation of the hypothalamus on energy expenditure as measured by indirect calorimetry were investigated in 20 unanaesthetized rats. Thirty sec of stimulation increased both O2 consumption and respiratory quotient (R.Q.). The largest magnitude hypermetabolic response (39% mean peak increase in O2 consumption) was produced by stimulation of the ventromedial hypothalamic nucleus. Stimulation of the lateral hypothalamus produced hypermetabolic effects similar to but smaller than those produced by medial stimulation. A number of considerations suggest that the hypermetabolism is not secondary to changes in motor activity, carbohydrate utilization or blood glucose levels. Consequently, these data suggest that the hypothalamus modulates energy expenditure through changes in non-shivering thermogenesis. These metabolic changes may modulate the effects of various hypothalamic manipulations on body weight.