Intraventricular 5,7-Dihydroxytryptamine Increases Thyrotropin-Releasing Hormone Content in Regions of Rat Brain

Rats received intraventricular (i.v.t.) injections of 5,7-dihydroxytryptamine (5,7-DHT) (100-600 micrograms). Some animals also received intraperitoneal injections of the 5-hydroxytryptamine uptake blocker fluoxetine (FX) (20 mg/kg) or the norepinephrine uptake blocker desmethylimipramine (DMI) (48 mg/kg) 30-90 min prior to i.v.t. 5,7-DHT. Rats were killed between 2 and 35 days following i.v.t. 5,7-DHT, brains were dissected, and regions were assayed for thyrotropin-releasing hormone (TRH) by radioimmunoassay. Dose-dependent increases in TRH content following i.v.t. 5,7-DHT were noted in the brainstem and hippocampus. DMI pretreatment blocked the increase in hippocampal TRH, but not in brainstem TRH. FX pretreatment was ineffective in blocking any increases in TRH content. These results suggest differential regulation of regional TRH content by interactions with specific neurotransmitter systems.     

Spinal β-adrenergic receptors’ activation increases the blood glucose level in mice

We examined the role of spinally located β-adrenergic receptors in the regulation of the blood glucose level. The intrathecal (i.t.) injections with dobutamine (β₁-adrenergic receptor agonist) or terbutaline (β₂-adrenergic receptor agonist) caused an elevation of the blood glucose level, whereas metoprolol (β₁-adrenergic receptor antagonist) or butoxamine (β₂-adrenergic receptor antagonist) did not. In addition, i.t. pretreatment with pertussis toxin (PTX) attenuated the hyperglycemic effect induced by dobutamine or terbutaline. Moreover, plasma insulin level was increased by dobutamine but not by terbutaline, and PTX reduced dobutamine-induced up-regulation of the plasma insulin level. Terbutaline significantly increased plasma corticosterone level, and PTX further enhanced terbutaline-induced corticosterone level. Furthermore, intraperitoneal (i.p.) pretreatment with hexamethonium- (a preganglionic blocker) attenuated dobutamine- and terbutaline-induced hyperglycemic effects. Our results suggest that activation of spinal β₁- and β₂-adrenergic receptors produces hyperglycemic effects in a different manner. Spinally located PTX-sensitive G-proteins appear to be involved in hyperglycemic effect induced by terbutaline. Furthermore, dobutamine- or terbutaline-induced hyperglycemia appears to be mediated through the spinal nerves.     

Analysis of the mechanism of the stress-protective action of delta sleep-inducing peptide

By RIA there were studied the contents of corticosterone, ACTH, beta-endorphin and insulin in the blood plasma, met- and leu-enkephalin in different regions of the rat brain and in the adrenal glands after a 6-hour immobilization. The stress increased the content of corticosterone, ACTH, beta-endorphin, but not insulin in the blood plasma, and the levels of met-enkephalin in the adrenal glands, but decreased the met-enkephalin contents in the striatum. The injection of DSIP (0.1 mg/kg, i/p) blocked partly the elevation of corticosterone only. The authors propose, that stress-protective action of DSIP is realized with the involvements of the hypothalamo-pituitary-adrenal gland system.     

Involvement of the GABAA/benzodiazepine chloride ionophore receptor complex in the 5,7-DHT Induced anticonflict effect.

The effects of drugs interacting with the GABAA/benzodiazepine chloride ionophore receptor complex (GABAA/BDZ-RC) on the anticonflict and biochemical effects observed after intracerebroventricular (i.c.v.) administration of 5,7-dihydroxytryptamine (5,7-DHT; 450 micrograms -14 days) were investigated in the rat using a modified Vogel's drinking conflict test. The GABAergic antagonistic drugs bicuculline, picrotoxin and Ro 15-4513 all counteracted the 5,7-DHT induced anxiolytic-like action in doses that did not alter the behavior per se, whereas flumazenil was ineffective in this respect. Also i.c.v. administration of 5-HT antagonized the 5,7-DHT induced anticonflict effect. Furthermore, 5,7-DHT-lesioned animals appeared more sensitive to the anticonflict effects of diazepam than sham-lesioned controls. The 5,7-DHT treatment produced marked depletions of 5-HT in the limbic system (80-90%) and hippocampus (90-95%), and an increase in the 5-HIAA/5-HT quotient in hippocampus. The effects on the levels of noradrenaline were comparatively small. The doses of bicuculline and picrotoxin antagonizing the 5,7-DHT induced anticonflict effect did not uniformly influence 5-HT levels or 5-HIAA/5-HT quotients. It is suggested that the anxiolytic-like effect observed in 5,7-DHT-lesioned rats in Vogel's drinking conflict test involves enhanced transmission at the GABAA/BDZ-RC.     

Studies on the physiological role and mechanism of action of neuropeptide Y in the regulation of luteinizing hormone secretion in the rat

It has been recently shown that intraventricular or systemic injection of neuropeptide Y (NPY) can produce a decrease in plasma luteinizing hormone (LH) levels in castrated rats of both sexes. In order to evaluate the physiological role of NPY in the regulation of LH secretion in the female rat, we proceeded to immunoneutralization experiments using specific antibodies to NPY. Injection of 0.5 ml antiserum to NPY produce a 20-fold increase of LH plasma levels, whereas injection of preimmune serum did not modify the plasma concentrations of LH. To investigate the possibility that catecholamines or serotonin might be involved in the effect of NPY in LH secretion, castrated rats were treated with alpha-methylparatyrosine (alpha-MPT), an inhibitor of catecholamine biosynthesis, or received an i.c.v. injection of the neurotoxin 5-7-dihydroxytryptamine (5,7-DHT) prior to the intraventricular injections of NPY. The pretreatment with alpha-MPT could not prevent the decrease of plasma LH induced by NPY injection whereas the pretreatment with 5,7-DHT reversed the effect of NPY injection. The anatomical connection between LH-releasing hormone (LHRH) and NPY neuronal systems were also investigated using double immunostaining technique. It appeared that NPY endings are in apposition to LHRH cell bodies in the preoptic area in proximity to the organum vasculosum of the lamina terminalis (OVLT).(ABSTRACT TRUNCATED AT 250 WORDS)     

The short term effects of 5,7-dihydroxytryptamine on peripheral serotonin stores in Rhodnius prolixus and their long-term recovery

The serotonin neurotoxin 5,7-dihydroxytryptamine (5,7-DHT) appears to affect invertebrate systems differently from vertebrate ones. The basis for toxicity in vertebrates appears to involve the intraneuronal actions of monoamine oxidase (MAO) upon the toxin. In insects, MAO is not present in appreciable amounts. In this study, we demonstrate that in vitro 5.7-DHT competitively inhibits the uptake of [³H]serotonin by serotonergic neurohaemal areas. The apparent K_M increases from 4.9 × 10⁻⁷ to 1.7 × 10⁻⁶ M. This neurotoxin also causes a significant release of previously accumulated [³H]serotonin in nominally Ca²⁺-free saline. While 5,7-DHT does not affect the uptake of [³H]tryptophan, it reduces the subsequent synthesis of [³H]serotonin. In vivo, the tissues appear to have recovered 2 weeks after toxin treatment, as determined by immunohistochemistry. At 24 h, 1 week and 2 weeks after injection, the tissues are able to take up and release [³H]serotonin normally. 1 and 2 weeks after injection, insects ingest a normal-sized blood meal, a behaviour acutely disrupted by 5,7-DHT treatment. The results of this and other invertebrate studies suggest that 5,7-DHT does not destroy serotonergic neurons, as it does in vertebrates. 5,7-DHT may be a more useful tool to study the functions of serotonin in invertebrates as one may transiently affect serotonin stores.     

Immediate and Long-Term Effects of 5,7-Dihydroxytryptamine on Rat Striatal Serotonergic Neurons Measured Using In Vivo Voltammetry

The immediate and long-term effects of the selective serotonergic neurotoxin 5,7-dihydroxytryp-tamine (5,7-DHT) on rat striatal serotonergic neurons were examined after its intracerebroventricular administration using in vivo voltammetry. Extracellular concentration of 5-hydroxyindoles increased immediately following intracerebroventricular 5,7-DHT injection (200 g in 24 l, 18 min), peaked at 1.5-2 h, and returned to normal by 4 h. 5,7-DHT diffused to the contralateral striatum in detectable amounts 9 to 12 min after the start of injection and returned to basal levels by 1.5 h. Three to 6 days after 5,7-DHT lesions, 5-hydroxytryptophan administration produced an increase in striatal 5-hydroxyindoles that was greater than that produced in pre-lesioned rats. This effect was maximal at 14 to 17 days post-lesion, and remained even after 50 days. The short-term effect of 5,7-DHT may be attributable to increased serotonin release, inhibition of uptake, or monoamine oxidase inhibition. The long-term effect of 5,7-DHT lesions may attributable to increased synthesis of serotonin or decreased reuptake in remaining serotonergic neurons.     

Effects of naloxone on plasma corticosterone in the opiate-naive rat

Naloxone HCl (NX) has long been considered to be a pure narcotic antagonist, having an effect only subsequent to pretreatment with a narcotic. Characteristically, low doses of NX have been used to antagonize the effects of analgesic doses of narcotics and to precipitate withdrawal in chronically treated animals. In this study, the effects of high doses of NX (2.0–20.0 mg/kg) on changes in plasma corticosterone were examined in the opiate-naive animal. Using male rats with chronic intravenous catheters and one-way vision boxes, injections were made and serial blood samples were obtained in the conscious, unrestrained animal. The acute administration of NX to the opiate-naive animal produced a dose-related increase in plasma corticosterone with respect to both amplitude and duration. NX (10.0 mg/kg i.v.) produced a significant elevation in hormone level at 15 and 30 minutes. With NX (20.0 mg/kg i.v.) the duration of the response was extended to 60 minutes. To examine whether short-term tolerance to this effect could be produced, animals were given a single pretreatment with either NX (10.0 mg/kg) or saline i.v. Two hours later NX produced a similar elevation in hormone level in both groups. The effect of chronic injection of NX was also studied. Animals pretreated with either NX (10.0 mg/kg) or saline s.c. once daily for 7 days did not show a significant difference following the subsequent administration of NX. In both cases, a significant elevation of plasma corticosterone resulted. The results suggest that NX may have a direct effect on opiate receptors resulting in an elevation of plasma hormone levels or NX may be disrupting an endogenous opiate-receptor interaction producing a stress response.     

A topography and ultrastructural characterization ofin vivo 5,7-dihydroxytryptamine-labeled serotonin-containing neurons in the central nervous system ofAplysia californica

1. Several weeks after administration of 5,7-dihydroxytryptamine (5,7-DHT) to Aplysia, a dark pigmentation appears in serotonin-containing neurons, and this pigmentation allows visual identification of serotonergic neurons but does not appear to alter their physiology. 2. We have determined the distribution of labeled nerve cell bodies in the various ganglia of Aplysia and have characterized the pigment containing structures in both control and labeled neurons. 3. All neurons in this preparation, whether or not they utilize serotonin as a transmitter, contain pigment granules, and three types of pigment granules can be distinguished. After 5,7-DHT a new type of granule appears in serotonergic neurons, probably reflecting lysosomes that have accumulated serotonergic synaptic vesicles that contain the oxidized 5,7-DHT. 4. It remains unclear why this substance does not cause neurotoxicity in mollusks as it does in mammalian preparations.     

Effects of insulin and streptozotocin-induced diabetes on brain tryptophan and serotonin metabolism in rats

Previous work by other authors has shown hat insulin administration increases brain tryptophan levels and serotonin (5–HT) metabolism. The present study partially replicates these results and tests whether these effects could be due to insulin-induced hypoglycemic stress, since stressers such as immobilization or food deprivation also increase brain tryptophan and 5-HT metabolism. Ingestion of a dextrose solution by rats administered insulin (2 I.U./kg) prevents the extreme fall in blood glucose concentration and rise in plasma corticosterone following insulin injections alone. This treatment, however, produces a larger increase in brain tryptophan (30%) than insulin-injected rats allowed only tap water. The greater accumulation of brain tryptophan may reflect an additive effect of the endogenously released insulin to that exogenously administered, since ingestion of the dextrose solution could trigger insulin secretion. In addition, brain tryptophan and 5-HT metabolism were measured in streptozotocin-diabetic rats maintained on several different feeding schedules to control for the effects of hyperphagia. All groups of diabetics showed significant decreases of approx 30% in brain tryptophan concentrations, while 5-HT metabolism was unchanged. This deficit in brain tryptophan is reversed within 2 h after insulin administration (2 I.U./kg). These results indicate that changes in brain tryptophan and 5-HT metabolism following insulin injections are not due to hypoglycemic stress, and that brain tryptophan is low in diabetics but increases above normal after administration of insulin. The results are discussed with respect to the effects of insulin on plasma levels of the neutral amino acids and a possible direct effect of insulin on the uptake of tryptophan by brain.     

Serotonergic stimulation of pituitary-adrenocortical activity in rats: evidence for multiple sites of action

5-Hydroxytryptophan (5-HTP) elevated serum corticosterone concentrations when administered either intraperitoneally (i.p.) or intraventricularly. Inhibition of aromatic L-amino acid decarboxylase outside of the blood-brain barrier antagonized the corticosterone response, but only when the 5-HTP was given i.p. Stimulation of the pituitary-adrenocortical system by fenfluramine was not affected by 5,7-dihydroxytryptamine pretreatment, whereas the stimulation produced by quipazine administration was blocked by lesions of the basomedial hypothalamus. These results suggest that serotonergic drugs can act at multiple sites (i.e., both central and peripheral) to evoke a pituitary-adrenocortical response.     

Intrastriatal Injection of 5,7-Dihydroxytryptamine Decreased 5-HT Levels in the Striatum and Suppressed Locomotor Activity in C57BL/6 Mice

Effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and 5,7-dihydroxytryptamine (5,7-DHT) on striatal levels of dopamine (DA), 5-hydroxytryptamine (5-HT), and their metabolites, as well as on locomotor activity were investigated in C57BL/6 mice. The results showed that MPTP significantly increased locomotor activity and decreased striatal DA levels. However, injection of the serotonergic neurotoxin 5,7-DHT in the striatum, either alone or following high doses of MPTP, significantly decreased locomotor activity, and concomitantly decreased striatal levels of 5-HT and 5-HIAA. This study suggests that the increased locomotor activity may be due to increased striatal serotonergic activity which overcompensates for the DA deficiency. The locomotor hypoactivity, induced by 5,7-DHT, might be due to the decreased striatal levels of 5-HT and 5-HIAA.     

Interaction of the effects of glucose and stress hormones on the activity of key enzymes of liver glycogen metabolism in rats

Endogenous corticosterone released in protracted immobilization stress fails to increase the activity of liver glycogen synthase, perhaps because of the inhibition of synthase phosphatase by phosphorylase a. It was also found, that in rats subjected to acute immobilization stress the stimulation of the activity of both synthase a and total forms by glucose administered i.v. is depressed. Finally, in rats fasting for 24 h a paradoxical augmentation by glucose of the stimulatory effect of glycogenolytic hormones released in acute immobilization stress on phosphorylase a activity was observed.     

Serotonin involvement in the inhibition of luteinizing hormone (LH) release during immobilization in castrated male rats

The involvement of serotonin in mediating the inhibitory effect of immobilization stress on LH secretion in castrated male rats was examined by employing p-chlorophenylalanine (PCPA, 320 mg/kg, ip), an inhibitor of serotonin synthesis, and 5,6-dihydroxytryptamine (5,6-DHT, 50 micrograms, icv), a drug toxic to the indoleaminergic system. Immobilization stress suppressed pulsatile LH release and decreased mean plasma LH levels. Pretreatment with PCPA or 5,6-DHT apparently eliminated the inhibitory effect of immobilization stress on LH release. These results suggest the possible involvement of a serotoninergic mechanism in mediating the suppression of LH release induced by immobilization stress in castrated male rats.     

Analysis of the Mechanism underlying the Rhythm Reversal from Diurnal to Nocturnal in the Cricket Gryllus bimaculatus, with Special Reference to the Role of Serotonin

The cricket, Gryllus bimaculatus, shows a rhythm reversal from diurnal to nocturnal in about a week after the imaginal molt. In the present study, we investigated the role of serotonin (5-HT) in the rhythm reversal. The 5-HT content in the brain measured by HPLC equipped with an electrochemical detector gradually increased after the imaginal molt, and in fully nocturnal adults it was about 2 times of nymphal level. We then examined the effects of 5,7-dihydroxytryptamine (5,7-DHT), a selective neurotoxine to serotonergic neurons, on the locomotor rhythm. In most animals with 5,7-DHT (25 muM or 250 muM, 32.2 nl) injected into the brain, daytime activity significantly increased even after the rhythm reversal, while nighttime activity was not significantly affected, forming rather diurnal pattern. The serotonin content in the brain of animals injected with 250 muM 5,7-DHT was reduced by about 30%. On the basis of these results, possible involvement of 5-HT in the neural mechanism controlling the locomotor rhythm is discussed.     

脑内5-羟色胺减少对致痫大鼠癫痫发作及学习记忆的影响

目的:于中脑正中中缝核局部微量注射5,7-二羟色胺(5,7-DHT),探讨5-羟色胺(5-HT)与癫痫的关系及匹罗卡品(PILO)致痫大鼠学习记忆改变的可能机制。方法:成年SD大鼠随机分为PILO组、PILO+5,7-DHT组、空白对照组三组,然后根据是否出现癫痫持续状态(SE)再将PILO组分成:PILO+SE组和PILO-SE组两亚组;利用视频脑电图观察大鼠癫痫发作及皮层脑电变化;运用Morris水迷宫测评大鼠空间学习记忆水平;最后运用免疫组化法观察大鼠中缝核5-HT能神经元。结果:大鼠予以5,7-DHT(PILO+5,7-DHT组)处理后造模成功率、死亡率及慢性期自发性发作频率均增高;与空白组比较PILO+SE组中缝核5-HT能神经元数目有所下降(P<0.05),而PILO+5,7-DHT组下降更明显(P<0.01);与空白组比较PILO+SE组平均逃避潜伏期延长、穿越平台次数减少、原平台象限停留时间缩短(P<0.05),而与PILO+SE组比较PILO+5,7-DHT组变化不明显。结论:脑内5-HT水平的降低容易诱发癫痫发作,尚不能认为癫痫大鼠合并认知功能障碍与脑内5-HT水平下降有关。     

Comparative study of perturbations of peripheral markers in different stressors in rats

Stress has been implicated in the etiopathogenesis of several diseases. In the present study, the effects of acute (AS), chronic (CS), and chronic unpredictable stress (CUS) were studied on the ulcer index, adrenal gland mass, and biochemical and hormonal changes in rats. The stress was provided in the form of immobilization-immobilization for 150 min, once only, and for 10 consecutive days in CS and CUS. In CUS, animals received variable unpredictable stressors. Immediately after stress, animals were decapitated, blood was collected, and plasma was separated for the estimation of plasma glucose, triglyceride, cholesterol, creatine kinase (CK), corticosterone, and insulin. The adrenal gland and stomach were also dissected for mass and ulcer scoring, respectively. AS significantly increased the ulcer index, plasma glucose, CK, corticosterone, and insulin. CS and CUS significantly increased the ulcer index, adrenal gland mass, and corticosterone. In CS, a significant decrease in plasma triglyceride and cholesterol levels was found, but in CUS only cholesterol was decreased significantly. High CK activity and hyperglycemia maintain the energy demands of metabolism, and elevated corticosterone desensitizes the insulin receptor in AS. In CS and CUS, prolonged elevation of corticosterone shifts metabolism to utilization of lipids as a secondary substrate by gluconeogenesis. From our experiment, it is clear that AS causes maximum activation of energy metabolism, which becomes specific after habituation in prolonged CS. These biochemical manipulations in the body by using different types of stressors are good markers that can be of great use to understand, target, and manage stress-induced etiologies.     

Possible direct effect of serotonin on pituitary prolactin secretion: in vivo and in vitro studies

In this work we analyze the possibility of serotonin (5-HT)-releasing prolactin (PRL) through a direct action at the pituitary level. 5-HT (2 mg/kg i.v.) stimulates PRL secretion in hypophysectomized autotransplanted animals (HAG) significantly and this effect was not influenced by pretreatment with the dopaminergic antagonist domperidone. In perifused pituitaries, 5-HT administration (0.01, 0.1 and 1 microM for 90 min, or 1, 10, 100 microM for 15 min) was ineffective in stimulating PRL release. In pituitaries obtained from animals previously treated with the neurotoxic 5,7-dihydroxytryptamine (5,7-DHT) or vehicle and incubated in the presence of 5-HT (2.5, 5 and 10 microM), no response in PRL secretion was observed. These results suggested that 5-HT does not release PRL through a direct pituitary action, and that the effect observed in HAG animals could be mediated through the release of a PRL-releasing factor after 5-HT administration.     

Ameliorating effect and potential mechanism of Rehmannia glutinosa oligosaccharides on the impaired glucose metabolism in chronic stress rats fed with high-fat diet

The aim of this study was to determine whether the Rehmannia glutinosa oligosaccharides (ROS) ameliorate the impaired glucose metabolism and the potential mechanism in chronic stress rats fed with high-fat diet. The rats were fed by a high-fat diet and simultaneously stimulated by chronic stress over 5 weeks. Body weight, fasting plasma glucose, intraperitoneal glucose tolerance test (IPGTT), plasma lipids, gluconeogenesis test (GGT), glycogen content, and corticosterone, insulin and leptin levels were measured. The results showed that ROS administration (100, 200 mg/kg, i.g.) for 5 weeks exerted the effects of increasing the organ weights of thymus and spleen, lowering the fasting plasma glucose level, improving impaired glucose tolerance, increasing the contents of liver and muscle glycogen, decreasing the gluconeogenesis ability, plasma-free fatty acid's level, as well as plasma triglyceride and total cholesterol levels in chronic stress and high-fat fed rats, especially in the group of 200 mg/kg; while the plasma corticosterone level was decreased, and plasma leptin level was increased. These results suggest that ROS exert an ameliorating effect of impaired glucose metabolism in chronic stress rats fed with high-fat diet, and the potential mechanism may be mediated through rebuilding the glucose homeostasis in the neuroendocrine immuno-modulation (NIM) network through multilinks and multitargets.     

Nociceptin/orphanin FQ and related peptides reduce the increase in plasma corticosterone elicited in mice by an intracerebroventricular injection

Nociceptin/orphanin FQ (=N/OFQ), the endogenous ligand of ORL1 receptor (=NOP), has been reported to induce, in rodents, after intracerebroventricular (i.c.v.) administration, anti-stress and anxiolytic effects. We have observed that the handling of mice followed by an i.c.v. injection of saline, induced a marked increase in the plasma corticosterone level (+250%) measured 30 minutes later. When N/OFQ was injected intracerebroventricularly, using a 1 microg dose, the increase in plasma corticosterone was significantly lower than in saline injected mice. N/OFQ(1-13)NH(2), known as a NOP receptor agonist, at the same 1 microg dose, also induced a lesser increase in plasma corticosterone level than a saline i.c.v. injection. The pseudopeptide [Phe(1)-psi(CH(2)-NH)Gly(2)]N/OFQ(1-13)NH(2), defined either as an agonist or an antagonist of NOP receptor, at the 0.1 microg dose, behaved in a similar manner as N/OFQ, by decreasing the plasma corticosterone level. Finally, [Nphe(1)]N/OFQ(1-13)NH(2), although presumed to be a selective NOP receptor antagonist, also decreased the corticosterone level at the 0.1 microg dose. These observations suggest the implication of N/OFQ in the regulation of response to stress, through an action on the hypothalamo-pituitary-adrenocortical axis. Moreover, they evidence a similar effect of N/OFQ and N/OFQ(1-13)NH(2), but also of two other related peptides displaying antagonist properties on NOP receptors. These data suggest that several subtypes of N/OFQ receptors could exist.