Estrogen stimulates neuronal plasticity in the deafferented hypothalamic arcuate nucleus in aged female rats

The hypothalamic arcuate nucleus (ARCN) was examined ultrastructurally 3 weeks after the complete deafferentation of the medial basal hypothalamus (MBH) with the island isolation technique in ovariectomized aged female rats (720-930 days of age). The mean numbers of axodendritic and axosomatic synapses in the ARCN decreased to about one-third of those in the intact controls. However, the treatment with estradiol benzoate (2 micrograms/day) during the 3 weeks following the day of brain surgery brought about a marked increase in the numbers of these synapses. The data suggest that the ARCN neurons of aged female rats still retain plasticity to react to deafferentation under influences of estrogen.     

Properties of synaptic transmission from the reticular formation dorsal to the facial nucleus to trigeminal motoneurons during early postnatal development in rats

We previously reported that electrical stimulation of the reticular formation dorsal to the facial nucleus (RdVII) elicited excitatory masseter responses at short latencies and that RdVII neurons were antidromically activated by stimulation of the trigeminal motor nucleus (MoV), suggesting that excitatory premotor neurons targeting the MoV are likely located in the RdVII. We thus examined the properties of synaptic transmission from the RdVII to jaw-closing and jaw-opening motoneurons in horizontal brainstem preparations from developing rats using voltage-sensitive dye, patch-clamp recordings and laser photostimulation. Electrical stimulation of the RdVII evoked optical responses in the MoV. Combined bath application of the non-N-methyl-d-aspartate (non-NMDA) receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), and the NMDA receptor antagonist DL-2-amino-5-phosphonopentanoic acid (APV) reduced these optical responses, and addition of the glycine receptor antagonist strychnine and the GABA_A receptor antagonist bicuculline further reduced the remaining responses. Electrical stimulation of the RdVII evoked postsynaptic currents (PSCs) in all 19 masseter motoneurons tested in postnatal day (P)1–4 rats, and application of CNQX and the NMDA receptor antagonist (±)-3(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP) reduced the PSC amplitudes by more than 50%. In the presence of CNQX and CPP, the GABA_A receptor antagonist SR95531 further reduced PSC amplitude, and addition of strychnine abolished the remaining PSCs. Photostimulation of the RdVII with caged glutamate also evoked PSCs in masseter motoneurons of P3–4 rats. In P8–11 rats, electrical stimulation of the RdVII also evoked PSCs in all 14 masseter motoneurons tested, and the effects of the antagonists on the PSCs were similar to those in P1–4 rats. On the other hand, RdVII stimulation evoked PSCs in only three of 16 digastric motoneurons tested. These results suggest that both neonatal and juvenile jaw-closing motoneurons receive strong synaptic inputs from the RdVII through activation of glutamate, glycine and GABA_A receptors, whereas inputs from the RdVII to jaw-opening motoneurons seem to be weak.     

Effect of extirpation of the cervical sympathetic ganglia on postnatal development of the paraventricular hypothalamic nucleus in rats

Experimental data on the role of adaptive and trophic influences of the sympathetic nervous system in the postnatal development of the hypothalamus are described. It was shown by karyocytometry that after extirpation of the cervical sympathetic ganglia (CSG) in rats ontogenetic development of the neurosecretory cells of the paraventricular nucleus (PVN) is delayed and changes are observed in the blod vessels. Manifestation of the effect of sympathectomy coincided with the onset of intensive growth of the cytoplasm of PVN cells. Sympathectomy was more effective in the case of extirpation of the CSG from young rats than from adult animals.Laboratory of Development of Nervous Activity of Animals in Ontogeny, I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. (Presented by Academician of the Academy of Medical Sciences of the USSR V. N. Chernigovskii.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 86, No. 7, pp. 107–110, July, 1978.     

隔核ghrelin对糖尿病胃动力障碍大鼠胃运动影响及下丘脑弓状核的潜在调控机制

 目的：研究隔核ghrelin对糖尿病(DM)大鼠胃运动的调控, 并探讨下丘脑弓状核与隔核间ghrelin通路对胃运动的调控机制。方法：链脲佐霉素腹腔注射制备DM大鼠模型;荧光免疫组化和real-time PCR方法检测DM大鼠隔核内ghrelin受体GHS-R1a表达变化;大鼠胃表面固定感应片在体记录胃运动并计算胃运动变化率;荧光金逆行示踪方法显示下丘脑弓状核和隔核间纤维联系,并采用中枢注射药物、核团损毁或电刺激等方法观察核团纤维联系对DM大鼠胃运动的调控作用。结果：（1） DM大鼠隔核GHS-R1a表达低于正常大鼠（P<0.05）,胃运动明显减弱,胃收缩幅度和频率显著降低（P<0.05）。（2）隔核注射ghrelin增强正常和DM大鼠胃运动（P<0.05）,且呈量效关系。（3） 荧光金在注射入隔核7 d后逆行至弓状核内神经元,其中部分神经元为ghrelin免疫阳性神经元;（4）正常大鼠体内,损毁隔核对胃运动和电刺激弓状核引起的胃运动变化无显著影响（P>0.05）;而对DM大鼠,损毁隔核减弱胃运动和电刺激弓状核后胃运动（P<0.05）。（5）隔核微量注射ghrelin受体阻断剂［D-Lys-3］-GHRP-6未显著改变正常大鼠电刺激弓状核后胃运动变化（P>0.05）,但可减弱DM大鼠电刺激弓状核引起的胃运动变化（P<0.05）。结论:隔核ghrelin和下丘脑弓状核-隔核间ghrelin通路在糖尿病大鼠胃运动调控中发挥重要作用。     

Testosterone inhibition of tyrosine hydroxylase expression in the hypothalamic arcuate nucleus

Immunohistochemistry was used to detect tyrosine hydroxylase (TH)-containing neurons in the hypothalamic arcuate nucleus in male rats. Two weeks following castration, the number of TH-positive cells was significantly greater than in intact controls. The castration-responsive TH-positive cells were uniformly distributed throughout the mediolateral extent of the arcuate nucleus. Treatment with testosterone significantly suppressed the castration response, whereas neither estradiol nor 5 alpha-dihydrotestosterone were effective. The number of TH-positive arcuate neurons in the female was similar to that in the male. Ovariectomy did not affect the number of TH-positive neurons. These findings indicate that TH expression is tonically inhibited in the tuberoinfundibular dopaminergic system of the male rat by testosterone.     

Beta-endorphin-, adrenocorticotrophic hormone- and neuropeptide y-containing projection fibers from the arcuate hypothalamic nucleus make synaptic contacts on to nucleus preopticus medianus neurons projecting to the paraventricular hypothalamic nucleus in the rat

The nucleus preopticus medianus is known to be situated in a key site in pathways regulating the paraventricular hypothalamic nucleus. To investigate the innervation pattern to nucleus preopticus medianus neurons by afferent fibers containing beta-endorphin, adrenocorticotrophic hormone and neuropeptide Y, a retrograde tracing method was combined with immunohistochemistry for these peptides in the rat. In the first experiment with injection of a retrograde tracer in the nucleus preopticus medianus, retrogradely labeled neurons were found in many regions throughout the brain. Among these, the arcuate hypothalamic nucleus contained a number of retrogradely labeled neurons showing immunoreactivity to the neuropeptides examined. About 20%, 20% and 40% of retrogradely labeled arcuate hypothalamic nucleus neurons showed beta-endorphin, adrenocorticotrophic hormone and neuropeptide Y immunoreactivity, respectively. About 18% and 57% of retrogradely labeled neurons in the nucleus tractus solitarius and ventrolateral medulla, respectively, were immunoreactive to neuropeptide Y. There were many more neuropeptide Y-immunoreactive projections to the nucleus preopticus medianus from the arcuate hypothalamic nucleus than those from the medulla. None of the retrogradely labeled neurons in the medulla showed immunoreactivity to beta-endorphin or adrenocorticotrophic hormone. In the second experiment with injection of a retrograde tracer in the paraventricular hypothalamic nucleus, electron microscopic observation revealed that retrogradely labeled neurons in the nucleus preopticus medianus were in synaptic contact with beta-endorphin-, adrenocorticotrophic hormone- and neuropeptide Y-immunoreactive axon terminals.The present finding indicates that nucleus preopticus medianus neurons projecting to the paraventricular hypothalamic nucleus are innervated by beta-endorphin-, adrenocorticotrophic hormone- and neuropeptide Y-containing arcuate hypothalamic nucleus neurons in addition to being innervated by neuropeptide Y-containing catecholaminergic medullary neurons which have been reported in our previous study.     

Orexigen-sensitive NPY/AgRP pacemaker neurons in the hypothalamic arcuate nucleus

The hypothalamic arcuate nucleus (ARC) integrates and responds to satiety and hunger signals and forms the origins of the central neural response to perturbations in energy balance. Here we show that rat ARC neurons containing neuropeptide Y (NPY) and agouti-related protein (AgRP), which are conditional pacemakers, are activated by orexigens and inhibited by the anorexigen leptin. We propose a neuron-specific signaling mechanism through which central and peripheral signals engage the central neural anabolic drive.     

The effects of metergoline and 8-OH-DPAT injections into arcuate nucleus and lateral hypothalamic area on feeding in female rats during the estrous cycle

The present study examined the effects of local injections of metergoline (MET, an antagonist of 5-HT1/2 receptors, 2 and 20 nmol) and 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT, selective 5-HT1A receptor agonist, 0.6 and 6 nmol) into the arcuate nucleus (ARC) and the lateral hypothalamus (LH), on ingestive and non-ingestive behaviors of female rats. These effects were examined during the diurnal periods of diestrus and estrus in rats adapted to eat a wet mash diet (enriched with 10% sucrose) during 1h for 3 consecutive days at the recording chamber. The results showed that 8-OH-DPAT injected into the LH significantly reduced food intake at all doses and both cycle stages, while in the ARC these treatments evoked hypophagia only at the highest 8-OH-DPAT dose and only at the estrous phase. MET administered into the ARC (at all doses) failed to affect food intake during both estrous stages. On the other hand, food intake decreased after injection of both doses of MET into the LH of rats during estrous and diestrus phases. In estrus stage, injections of the higher dose of 8-OH-DPAT into the ARC and into the LH decreased the duration of feeding. Latency to start feeding, drinking, and non-ingestive behaviors were not affected by 8-OH-DPAT or MET treatments in the ARC or the LH in both cycle phases. These results indicated that 5-HT1A receptors participate in the serotonergic control of feeding-related mechanisms located at the ARC and the LH. These feeding-related serotonergic circuits in both areas are possibly affected by ovarian hormones that could increase sensitivity of ARC neurons to the hypophagic effects of 8-OH-DPAT or increase the efficacy of satiety signals that terminate feeding. In addition, the present data indicated that serotonergic inputs do not exert a tonic inhibitory activity on the ARC and the LH feeding-related circuits.     

营养性肥胖大鼠弓状核促性腺激素释放激素的表达变化以及对精子发生的影响

目的:探讨营养性肥胖大鼠弓状核神经肽Y(NPY)、瘦素受体(ob-R)及与生殖相关的促性腺激素释放激素(GnRH)表达变化以及对精子发生的影响.方法:免疫组织化学观察NPY、ob R及GnRH在肥胖模型组下丘脑弓状核的表达情况以及睾丸支持细胞雄激素结合蛋白(ABP)表达变化;流式细胞分析检测睾丸生精细胞周期的改变.并测定血清中瘦素、睾酮、卵泡刺激素(FSH)和黄体生成素(LH)的水平.结果:肥胖大鼠血清中瘦素水平较对照组明显升高,睾酮、FSH、LH水平较对照组明显降低;下丘脑弓状核NPY表达较对照组增强,ob-R及GnRH表达较对照组减弱,ABP表达较对照组减弱;肥胖大鼠S期细胞显著下降,G2/M期细胞的百分数明显增多.结论:营养性肥胖大鼠由于神经内分泌代谢失调而引起GnRH水平降低,导致下丘脑垂体睾丸轴功能失调引起睾丸间质细胞及支持细胞功能降低,致使精子发生障碍,可能导致不育.     

损毁弓状核对大鼠骨组织形态计量学的影响

目的： 研究损毁下丘脑弓状核对大鼠骨组织形态计量学的影响。 方法： SD大鼠于出生后第1、3、5、7、9 d皮下注射10％谷氨酸单钠(MSG)（4 g/kg BW），对照组同法注射等体积生理盐水，并设MSG毒性对照组，于70 d龄同法注射MSG，各组大鼠皆存活至160 d。用3％戊巴比妥钠腹腔麻醉，用4％多聚甲醛经左心室行全身灌注，取脑作下丘脑弓状核冠状面切片，HE染色。取右侧胫骨常规脱钙，石蜡包埋，矢状面连续切片，胶原特殊染色，用于显示骨小梁结构。HE染色用于破骨细胞计数。图像分析仪对弓状核正中隆起切面和骨组织进行照片和计量。用放免法测血清中GH（生长素）、E2（雌二醇）和T（睾酮）含量。 结果： MSG大鼠弓状核神经细胞数量显著减少，GH和E2、T水平明显降低，骨量显著减少，发生骨质疏松，NS组和MSG毒性对照组弓状核、GH、E2、T和骨组织无明显改变。 结论： ①MSG大鼠骨组织的改变不是MSG对垂体和骨组织的毒性作用所致；②下丘脑弓状核参与骨代谢的调控；③通过GH和性激素作用是ARC参与骨代谢调控的重要途径。     

Electrophysiological properties and synaptic responses of cells in the trigeminal principal sensory nucleus of postnatal rats

In the rodent brain stem trigeminal complex, select sets of neurons form modular arrays or "barrelettes," that replicate the patterned distribution of whiskers and sinus hairs on the ipsilateral snout. These cells detect the patterned input from the trigeminal axons that innervate the whiskers and sinus hairs. Other brain stem trigeminal cells, interbarrelette neurons, do not form patterns and respond to multiple whiskers. We examined the membrane properties and synaptic responses of morphologically identified barrelette and interbarrelette neurons in the principal sensory nucleus (PrV) of the trigeminal nerve in early postnatal rats shortly after whisker-related patterns are established. Barrelette cell dendritic trees are confined to a single barrelette, whereas the dendrites of interbarrelette cells span wider territories. These two cell types are distinct from smaller GABAergic interneurons. Barrelette cells can be distinguished by a prominent transient A-type K(+) current (I(A)) and higher input resistance. On the other hand, interbarrelette cells display a prominent low-threshold T-type Ca(2+) current (I(T)) and lower input resistance. Both classes of neurons respond differently to electrical stimulation of the trigeminal tract. Barrelette cells show either a monosynaptic excitatory postsynaptic potential (EPSP) followed by a large disynaptic inhibitory postsynaptic potential (IPSP) or just simply a disynaptic IPSP. Increasing stimulus intensity produces little change in EPSP amplitude but leads to a stepwise increase in IPSP amplitude, suggesting that barrelette cells receive more inhibitory input than excitatory input. This pattern of excitation and inhibition indicates that barrelette cells receive both feed-forward and lateral inhibition. Interbarrelette cells show a large monosynaptic EPSP followed by a small disynaptic IPSP. Increasing stimulus intensity leads to a stepwise increase in EPSP amplitude and the appearance of polysynaptic EPSPs, suggesting that interbarrelette cells receive excitatory inputs from multiple sources. Taken together, these results indicate that barrelette and interbarrelette neurons can be identified by their morphological and functional attributes soon after whisker-related pattern formation in the PrV.     

Copulatory behavior and hypothalamic estrogen and progestin receptors in chronically insulin-deficient female rats

The effects of relatively short- or long-term diabetes on sexual receptivity and proceptivity and on hypothalamic estrogen and progestin receptors were examined in rats fed regular chow or high fat diet. Ovariectomized, streptozotocin-induced chronically insulin deficient and normal rats received sequential treatments with 2 μg estradiol benzoate (EB) and 1 mg progesterone (P) 10 days following the induction of diabetes and were tested for lordosis and soliciting behaviors. Nondiabetic rats fed either diet displayed significantly higher lordosis and solicitation behaviors than chow-fed diabetics, and fat-fed diabetic animals displayed behavior levels intermediate to those of nondiabetic and chow-fed rats. Ten days after the induction of diabetes, the levels of hypothalamic estrogen receptors of chow-fed diabetics were significantly lower than nondiabetics with the fat-fed diabetic group showing intermediate levels. However, 70 days after streptozotocin treatment diabetic rats had significantly lower estrogen receptors than nondiabetics regardless of the diet. Treatment of long-term (70 days) diabetic rats with 1–2 U of U-100 Lente insulin for 24 hr or 7 days was ineffective in restoring the hypothalamic estrogen receptor concentrations to those of nondiabetics. Three weeks following induction of diabetes, induction of cytoplasmic progestin receptors by EB treatment was significantly impaired in diabetic animals fed either chow or high fat diet. Although the reproductive dysfunctions present in short-term diabetic female rats may be due in part to chronic fuel deprivation, it appears that the long-term maintenance of cytosol estrogen receptor level is dependent on other actions of insulin. Furthermore, restoration of hypothalamic estrogen receptors in long-term diabetic rats may require either longer than 7 days of insulin therapy or another mode of treatment (e.g., sex hormones). The behavioral improvement of diabetic animals on HF diet could be accounted for by mechanisms other than enhancement of EB-induced cytoplasmic progestin receptors.     

Electron microscopy of synaptic structures in olfactory cortex of early postnatal rats.

Layer 1 of the rat olfactory cortex has been studied with the electron microscope at birth and at several consecutive postnatal days up to 14 days of age. Special attention was directed towards synaptic structures and axons of the lateral olfactory tract (LOT). Numerous mature synapses are seen at birth and estimates were made of their subsequent increase in number. In addition, immature synapses are seen and mature postsynaptic sites occur with atypical, partial, multiple or no contact. The findings suggest: (1) considerable prenatal synaptogenesis in contrast to other cortical systems; (2) the maturation of the postsynaptic site may precede that of the presynaptic contact and vesicle accumulation; (3) there may be competition by more than one process for one postsynaptic specialization; (4) the non-innervated sites may result from deafferentation caused by prenatal cell death, although no degeneration was seen, and the atypical contacts may be a stage in the reinnervation of these sites; (5) the LOT develops in parallel with the synaptic neuropil and (6) by 14 days of age the area closely resembles adult tissue.     

Dendritic arborization and axon trajectory of neurons in the hypothalamic arcuate nucleus of the rat--updated

Neurons in the hypothalamic arcuate nucleus (arcuate neurons) were traced on Golgi-impregnated sections. Dendrites of arcuate neurons showed characteristic orientation patterns. Dendrites along the lateral side follow the convex border of the nucleus by running parallel to the tanycyte processes. Neurons located in the ventrolateral portion of the nucleus have dendrites running parallel to the basal surface of the hypothalamus. Fine, beaded axons of arcuate neurons project mostly ventrally, and less frequently dorsally and dorsolaterally. Ventrally projecting axons converge towards the tuberoinfundibular sulcus which emerges into the ventral portion of the arcuate nucleus from below.     

Dendritic arborization and axon trajectory of neurons in the hypothalamic arcuate nucleus of the rat

Summary Dendritic arborization patterns of neurons in the hypothalamic arcuate nucleus and the course of their axons outside the median eminence were studied using Golgi material, electron microscopic detection of degenerated axon terminals following surgical interference, and horseradish peroxidase technique.Two kinds of neurons can be distinguished in the arcuate nucleus: small fusiform and somewhat larger polygonal cells. Fusiform neurons having two, sparsely arborizing stem dendrites are localized mainly in the medial and dorsal parts of the nucleus. A variant of the fusiform neurons (pear shaped cells) has only one dendritic stem, and the axon originates at the other pole of the neuron. These latter cells are found along the ependymal wall of the third ventricle. Polygonal neurons which occupy the ventral and lateral portions of the nucleus have 4–5 repeatedly branching stem dendrites. In addition to the well known course of the axons of the arcuate neurons towards the median eminence, there are axons of both fusiform and polygonal cells which leave the nucleus in lateral or dorsolateral direction. Axons having this course frequently issue a collateral branch along the first 100–150 m of their trajectory.A knife-cut through the arcuate nucleus or along its lateral border resulted in degeneration of axon terminals in the area between the arcuate and ventromedial nuclei, and in a ventromedial sector of the ventromedial nucleus itself. A cut located in the area between the arcuate and ventromedial nuclei caused degenerated axon terminals over a large part of the ventromedial nucleus with a considerable increase in the ventromedial portion.Labeled fusiform and polygonal neurons can be seen in the arcuate nucleus following the injection of horseradish peroxidase into the lateral hypothalamus.The results suggest unequivocally that the neurons in the arcuate nucleus have efferent connections not only towards the median eminence but also to the hypothalamic ventromedial nucleus and lateral hypothalamic area.     

Characteristic of hypothalamic kisspeptin expression in the pubertal development of precocious female rats

To investigate the potential role of kisspeptin in the advance onset of puberty in precocious puberty, model rats induced by danazol were used to study the developmental expression of hypothalamic kisspeptin. Kisspeptin immunoreactive cells were observed in the arcuate nucleus (ARC), periventricular nucleus (PeN) and preoptic area (POA) in model rats on the day of onset-puberty. On the day of post-puberty, however, the number of kisspeptin immunoreactive cells in ARC and PeN decreased while the number of those cells in POA increased. Kisspeptin immunoreactive cells were not detected in hypothalamus in both normal and model rats at their pre-puberty stages. Furthermore, the expression of hypothalamic Kiss-1 mRNA reached top on the day of onset-puberty in both of the normal and model rats, and the expression of Kiss-1 mRNA increased significantly in the model rats compared with those in the normal ones. Our results indicated that kisspeptin might involve in the advance onset of puberty in danazol induced female precocious model rats.     

The effects of gonadal steroid manipulation on the expression of Kiss1 mRNA in rat arcuate nucleus during postnatal development

Kisspeptins, encoded by Kiss1 gene, play pivotal roles in the regulation of reproduction. Recently, several studies reported a sex difference in Kiss1 expression in the arcuate nucleus (ARC) during the neonatal period. In this study, we investigated the effect of gonadal steroid manipulation on the sex difference in Kiss1 expression in ARC of rats. At neonatal and prepubertal stages, females had a greater number of Kiss1 neurons than the males. Gonadectomy at those stages resulted in significant increases in the Kiss1 neuron number and the sex differences disappeared. We also confirmed the expression of estrogen receptor ?? in kisspeptin neurons in neonates. Altogether, our results indicate that ARC Kiss1 expression is negatively regulated by gonadal steroids from early postnatal stages, and that the sex difference in ARC Kiss1 expression is attributed to the difference in circulating gonadal steroid levels. We also found that neonatal estrogenization inhibits Kiss1 expression and impairs negative feedback system.     

The effect of arcuate nucleus transplantation on the development of the anterior pituitary in monosodium glutamate-treated rats

Treatment with monosodium glutamate (MSG) during the neonatal period is known to produce a selective lesion of the arcuate nucleus in rat brain, which is the major site of production of growth hormone releasing-hormone (GRH), followed by a secondary reduction in growth hormone (GH) synthesis in the anterior pituitary. Normal arcuate nuclei from hypothalamic areas of newborn rats were transplanted into the third ventricles of 27-day-old rats which were treated with MSG on alternate days for the first 10 days of life. Ninety days after birth, the anterior pituitaries were examined for GH synthesis by immunohistochemical staining with GH antiserum. The results indicated that the impaired GH synthesis in the anterior pituitary treated with MSG was partially restored in some recipients by grafts of arcuate nuclei in which the GRH-containing neurons were clearly detected by immunohistochemical staining with GRH antiserum.