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

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

Dorsal noradrenergic bundle lesions fail to alter opiate withdrawal or suppression of opiate withdrawal by clonidine

Previous work has shown that clonidine effectively supresses many of the signs of opiate withdrawal. The present study was designed to test the hypothesis that the supression of opiate withdrawal by clonidine is mediated by forebrain noradrenergic projections of the locus coeruleus. Two groups of 24 rats each were subjected to either a 6-hydroxydopamine lesion of the dorsal noradrenergic bundle (Lesion group) or a sham, vehicle injection (Sham group). All rats were made dependent on morphine by subcutaneous implantation of one 75 mg silastic morphine pellet for three days followed by 3 more days with two additional 75 mg pellets. Following removal of the morphine pellet, withdrawal was precipitated in all rats by subcutaneous injection of 4 mg/kg of naloxone. Pretreatment 10 min. before withdrawal with clonidine (0.1 or 0.2 mg/kg) produced a significant attenuation of withdrawal signs as compared to saline injected rats; this effect was equally significant in both sham and lesion groups. Lesions of the locus coeruleus had no effect on withdrawal, nor did they affect the ameliorating action of clonidine. These results substantiate the observation that clonidine can effectively attenuate signs of opiate withdrawal in the rat, but fail to support the hypothesis that these effects are mediated by the forebrain projections of the locus coeruleus.     

In vivo catechol activity in the rat locus coeruleus following different nociceptive stimuli and naloxone.

The nucleus locus coeruleus (LC) has been implicated in the processing of spinal reflexes following noxious stimuli. It has been demonstrated that noxious stimuli activate LC neuronal firing, but little is known about the neurochemical changes that might occur following such activation. To determine the effects of different noxious stimuli on LC neuronal activity, anaesthetized rats were exposed to mechanical (tail pinch), thermal (55 degrees C water), and chemical (5% Formalin injected in the hind paw) stimuli; the catechol oxidation current (CA.OC), an index of noradrenergic neuronal activity, in the locus coeruleus was monitored using differential normal pulse voltammetry. In addition, the effect of the opioid antagonist naloxone on the CA.OC in the LC was examined. Exposure to both mechanical and chemical stimuli significantly increased CA.OC indicating an increase in LC noradrenergic neuronal activity, while the thermal stimulus had no effect. Treatment with naloxone (1 mg/kg i.v.) had no effect on CA.OC in the LC. The results show a differential responsiveness of LC noradrenergic neurons to different modes of noxious stimuli and fail to demonstrate a tonic opioid regulation of these neurons in the anaesthetized rat.     

Failure of reversal of cardiovascular responses of clonidine by centrally administered naloxone in anaesthetised rats

Central effects of naloxone on the cardiovascular responses of centrally administered clonidine were studied in anaesthetised normotensive, renal DOCA-salt hypertensive and morphine dependent rats. Clonidine (5 micrograms/ICV) produced significant decrease in blood pressure and heart rate in all the groups of rats in a dose dependent manner. Naloxone (2 micrograms/ICV) failed to reverse the responses of clonidine in all the rat groups. In morphine dependent normotensive and morphine dependent renal DOCA-salt hypertensive rats, the responses of clonidine were further enhanced in the presence of naloxone. Our observations clearly indicate that clonidine does not influence endogenous opioid system for producing cardiovascular effects.     

Naloxone doesn't determine the response of growth hormone to clonidine in obese patients

The effect of naloxone (opioid receptor blocker) on the impairment of growth hormone (GH) release after clonidine (alfa 2-adrenergic agonist) was investigated in 10 volunteer obese subjects. The patients (4 males and 6 females, 16-22 year old) with fat excess (15 +/- 2 kg) estimated by bioelectrical impedance analysis (BIA) were studied repeatedly. The patients, were perfused by a slow saline infusion. 30 min later they received a bolus dose of clonidine (150 micrograms p.o.), followed 30 min later by a bolus dose of naloxone (10 mg i.v.) or a corresponding volume of isotonic sodium cloride (I.S.) for control. No significant changes occurred in blood GH concentration after clonidine administration and naloxone did not induce GH response at clonidine. These results suggest that in obese subjects the impairment of GH release after clonidine is not mediated via receptors sensitivity to naloxone.     

Clonidine and morphine increase atrial natriuretic peptide secretion in anesthetized rats

In order to determine whether the activity of central alpha 2-adrenergic and opioid receptors influence plasma atrial natriuretic peptide (ANP) levels, clonidine and morphine were infused into the lateral cerebral ventricle for 45 min in anesthetized Sprague-Dawley rats. The central administration of a low dose of clonidine (10 ng/min) caused a significant increase in plasma ANP without changing arterial blood pressure or central venous pressure. Pretreatment with yohimbine (5 micrograms/min) completely blocked the effect of clonidine. Central infusion of morphine (100 ng/min) also elevated plasma ANP levels and naloxone (5 micrograms/min) blunted this effect. Intravenous infusion of the same dose of clonidine or morphine did not affect plasma ANP levels. Moreover, the effect of clonidine on plasma ANP was partially blocked by pretreatment with naloxone (5 micrograms/min). These results suggest that central alpha 2-adrenergic and opioid receptors may be involved in ANP secretion.     

Opioid peptides within the midbrain periaqueductal gray suppress affective defense behavior in the cat

The effects of the methionine-enkephalin analog [D-Ala2-Met5]-enkephalinamide (DAME) upon the threshold for affective defense behavior were determined following microinjections placed into midbrain periaqueductal gray sites from which this response was elicited. Affective defense behavior was elicited by electrical stimulation through a cannula electrode situated in the dorsal aspect of the midbrain periaqueductal gray. Dose-response curves characterizing the effects of DAME upon affective defense behavior were determined utilizing the following doses: 0.25, 0.5 and 1.0 microgram in 0.5 microliter saline, pH = 7.4 or vehicle control (saline). Response thresholds were tested 10-30, 30-60, 60-90, 120-150, 180-210, 1440-1470 and 2880-2910 min postinjection. The results obtained indicated that injections of DAME at a dose of 1.0 microgram/0.5 microliter produced significant, long duration elevations in affective defense thresholds, lasting up to 1440-1470 min postinjection. Lower doses of DAME (0.25 and 0.5 microgram/0.5 microliter) also resulted in significant increases in affective defense thresholds, but these effects were of shorter durations (60-90 and 120-150 min) postinjection, respectively. The suppressive effects of DAME were blocked when animals were pretreated with naloxone (10 micrograms/0.5 microliter) microinjected into the same midbrain periaqueductal gray site into which 0.25 microgram DAME was injected and affective defense behavior was elicited.     

延髓弧束核微量注射可乐宁对自发性高血压大鼠...

In order to study whether atrial natriuretic factor (ANF) is involved in the depressor effect of clonidine, microinjection of the latter into nucleus tractus solitarii (NTS) was carried out in anesthetized stroke-prone spontaneously hypertensive rats (SHRsp) and normotensive Wistar-Kyoto (WKY) rats. Each strain was randomly divided into three groups by injecting: (1) clonidine (1.0 microgram/0.2 microliter); (2) yohimbine (3.3 micrograms/0.2 microliter) followed by (1); (3) artificial cerebral spinal fluid (ACSF, 0.2 microliter) as control. A decrease of blood pressure and heart rate and a suppression of ANF release elicited by clonidine were significantly greater in SHRsp than in WKY rats. After blockade of alpha 2-receptor with yohimbine, the hypotensive effect of clonidine was blocked completely in WKY rats, but only partially in SHRsp, while the suppression effect on ANF release was eliminated in both strains. In addition, the decrease of plasma catecholamine produced by clonidine could also be blocked after yohimbine. The results suggest that ANF probably does not contribute to the depressor effect of centrally administered clonidine, while in SHRsp the decrease of plasma ANF might be a blood pressure-dependent compensatory response.     

Modulation of theta-activity in the septo-hippocampal system by the alpha-2-adrenoreceptor agonist clonidine

The influence of the alpha 2-adrenoreceptors agonist clonidine on the neuronal activity of the medial septal area (MS) and hippocampal EEG was studied in unanaesthetized rabbits. A slight and short-term decrease in the theta-rhythm modulation in the MS neuronal activity and/or EEG was revealed in 30.4% of tests after the bilateral intraventricular injection of a small dose of clonidine (0.5 microgram/5 microliters of water). On the contrary, a high dose of clonidine (5 micrograms/5 microliters) substantially enhanced the theta modulation in 100% of tests. The frequency of the theta bursts in the MS increased, on average, by 1.6 +/- 0.18 Hz (from 5.25 +/- 0.19 to 6.8 +/- 0.17 Hz). The regularity of the theta modulation became almost twice higher: the time constant of damping increased from 0.34 +/- 0.04 to 0.60 +/- 0.08 s. Increase in the neuronal activity in the MS produced by the high dose of clonidine was always accompanied by appearance of continuous stable theta waves in the EEG; the spectral power in the theta range increased, on average, by 480 +/- 98%. This strong effect arose suddenly but was relatively short-lasting (12 +/- 3.5 min) and usually abruptly terminated. It is concluded that the noradrenergic system has a double control over the theta oscillations through the alpha 2-adrenoreceptors agonist. In low concentrations the agonist clonidine acts on the high affinity inhibitory presynaptic autoreceptors reducing the noradrenaline release and suppressing the theta activity. In a high dose clonidine predominantly acts on postsynaptic (low affinity) adrenoreceptors substantially increasing the frequency and regularity of the theta bursts in the activity of septal neurons. Presumably, different types of alpha 2-adrenoreceptors participate in regulation of the theta oscillations in different functional states. It is suggested that the noradrenergic locus coeruleus is a functional synergist of the activating reticular formation participating in the urgent phasic activation of the septohippocampal system during the action of sudden strong stimuli.     

Reversal of fentanyl/fluanisone neuroleptanalgesia in the rabbit using mixed agonist/antagonist opioids

The reversal of the neuroleptanalgesic combination of fentanyl/fluanisone using mixed agonist/antagonist opioids has been investigated in the rabbit. All of the compounds studied (naloxone, nalbuphine, meptazinol, butorphanol, buprenorphine, pentazocine, doxapram) reversed the respiratory depression and sedation produced by fentanyl/fluanisone. Fentanyl/fluanisone produced profound analgesia for 180 min, which was rapidly and completely antagonized by naloxone. The mixed agonist/antagonist opioids produced a reduction in the degree of analgesia but, in contrast to naloxone, analgesic activity persisted from 120 min (meptazinol) to 420 min (buprenorphine). Administration of buprenorphine to rabbits anaesthetized with fentanyl/fluanisone and midazolam confirmed that the reversal of respiratory depression was accompanied by the return of arterial pH, PCO2 and PCO2 to preanaesthetic values. The use of neuroleptanalgesic anaesthetic regimens, which have been shown to provide effective surgical anaesthesia, combined with reversal using a mixed agonist/antagonist opioid to provide postoperative analgesia, appears to be a valuable refinement of current laboratory animal anaesthetic practice.     

Feeding, drinking and temperature responses to intracerebroventricular beta-endorphin in the domestic fowl

Four experiments were conducted to evaluate the effect of beta-endorphin (beta-END) on feeding, drinking and colonic temperature in rapidly growing (Rock-Cornish; RC) and slow growing (Single-Comb White Leghorn; SCWL) stocks of chickens. In the first experiment RC cockerels were injected intracerebroventricularly (ICV) with 0, 1.5, 3.0 and 6.0 micrograms of beta-END. In the second experiment RC cockerels were injected ICV with 0.5, 1.0 and 2.0 micrograms of beta-END. Experiments 3 and 4 were conducted identically to Experiment 1 and 2, respectively, except SCWL were used. Administration of beta-END at levels between 1.5 and 6.0 micrograms produced a significant curvilinear increase in feeding in both RC and SCWL chicks. In RC chicks, feeding was significantly elevated at 45 min and from 90 through 240 min postinjection, whereas in SCWL chicks feeding was increased from 90 through 300 min postinjection. Water intake was depressed in RC and SCWL from 60 through 90 min and from 30 through 60 min postinjection, respectively. Significant increases in water occurred at 180 and 300 min postinjection in SCWL. beta-END also induced a significant hyperthermia in RC and SCWL from 30 through 240 min and from 15 through 180 min postinjection, respectively. At low levels of beta-END, i.e., 0, 0.5, 1.0 and 2.0 micrograms, feeding, drinking and body temperature were significantly increased in both stocks. Feeding in RC chicks was stimulated in a linear fashion from 180 through 300 postinjection while feeding in SCWL was stimulated in a curvilinear manner from 180 through 240 min postinjection.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of water deprivation on the centrally-mediated hypertensive response to clonidine in freely moving, normotensive rats

Effects of water deprivation on pressor responses to centrally and peripherally administered clonidine was investigated in freely moving, normotensive rats with chronic guide cannula and catheters implanted into the abdominal aorta via the femoral artery. In normal hydrated rats, intracerebroventricularly (i.c.v.) injected clonidine (10 and 20 micrograms) produced a dose-dependent and long-lasting rise in mean blood pressure (MBP) concomitant with a decrease in heart rate. However, a significant depressor response was not observed for up to 90 min. In 48 hr dehydrated rats, the pressor response to i.c.v. injected clonidine (10 and 20 micrograms) was significantly depressed and a depressor response appeared. Intravenously (i.v.) administered clonidine (25 micrograms/kg) in normal hydrated rats also produced a long-lasting pressor response following an initial rapid rise in MBP. The long-lasting pressor response to i.v. injected clonidine was abolished after water deprivation for 48 hr, whereas the initial rise in MBP was less affected. These results suggest that clonidine elicits centrally-mediated pressor response, which is influenced by body fluid volumes.     

刺激蓝斑及电针对大鼠脊髓背角神经元伤害性反应的影响

以往的工作表明,蓝斑（LC）-去甲肾上腺素能神经元系统在痛觉调制和针刺镇痛中起着重要作用,本文用电生理学方法研究刺激LC和电针对大鼠脊髓背角神经元伤害性反应的影响,其主要结果如下：1、刺激LC或电针有明显抑制脊髓背角神经元伤害性反应的作用。2、损毁中缝大核和腹腔注射纳洛酮并不明显影响刺激LC的抑制效应。3、α2受体激动剂氯压啶能加强刺激LC或电针的抑制效应,而α受体阻断剂酚妥拉明在一定程度上能削弱这种抑制效应,这些实验结果提示,刺激LC和电针可激活LC神经元,通过其下行纤维,在脊髓水平释放NE,通过α2受体,阻断伤害性信息的传递。     

Liberation of cyclic AMP and catecholamine from the heart during left stellate stimulation in the anesthetized dog

In open-chest pentothal-chloralose anesthetized dogs, plasma catecholamine and cyclic AMP levels were evaluated in the aortic and coronary sinus blood, during stimulations of the left ansa subclavia (1, 2, and 4 Hz). Basal aortic and coronary sinus catecholamine levels were respectively 0.373 +/- 0.090 and 0.259 +/- 0.048 ng/mL and cyclic AMP levels averaged 21.4 +/- 1.4 and 20.9 +/- 1.6 pmol/mL. Statistically significant increases in cyclic AMP levels were induced by sympathetic stimulations at 1 Hz (2.0 +/- 0.6 pmol/mL, 2 Hz (2.5 +/- 1.2 pmol/mL) and 4 Hz (6.5 +/- 1.5 pmol/mL), concomitantly with elevations of coronary sinus catecholamine levels. Sotalol (5 mg/kg) abolished the increases in coronary sinus cyclic AMP levels induced in coronary sinus cyclic AMP output averaged 282 +/- 30 pmol/min (1 Hz), 662 +/- 160 pmol/min (2 Hz), and 1679 +/- 242 pmol/min (4 Hz). Sympathetically induced cyclic AMP output (4Hz) was blunted by sotalol (-81 +/- 14 pmol/min). Aortic cyclic AMP levels were not significantly influenced by stellate stimulation. Intense correlations were found between increased in coronary sinus plasma catecholamines and cyclic AMP concentration levels (r = 0.81, slope - 1.45, ordinate = -1.42, n = 15) as well as between delta cyclic AMP output versus delta catecholamine output values in the coronary sinus (r = 0.93. slope output levels. Intracoronary infusion of phenylephrine (10 micrograms/min) or nitroprusside (200 micrograms/min) had no influence on cyclic AMP plasma levels whereas aortic and coronary sinus levels were respectively increased 5.5 +/- 1.9 and 7.3 +/- 1.4 pmol/mL during the administration of isoproterenol (5 micrograms/min). These data suggested that plasma cyclic AMP constitutes a sensitive index of cardiac beta-adrenergic activity elicited by the release of endogenous catecholamine during stellate stimulations.     

Hemodynamic responses and c-Fos changes associated with hypotensive hemorrhage: standardizing a protocol for severe hemorrhage in conscious rats

The central mechanisms underlying the transition from compensation to decompensation during severe hemorrhage (HEM) are poorly understood. Furthermore, a lack of consistency in HEM protocols exists in the current literature. This study assessed the cardiovascular response and Fos-like immunoreactivity (FLI) in specific brain regions following severe HEM at three rates (2, 1, or 0.5 ml.kg(-1).min(-1)) in conscious rats. Heart rate (HR) and arterial pressure were recorded during the withdrawal of 30% of total blood volume (TBV). Data from animals hemorrhaged at the fast (F-HEM, n = 6), intermediate (I-HEM, n = 7), or slow (S-HEM, n = 7) rates were compared with saline (SAL, n = 5) and hypotensive (hydrazaline-induced, HYDRAZ, n = 5) controls. All HEM rates produced similar degrees of hypotension at the time of 30% TBV withdrawal. All HEM rates also produced bradycardia, but the change in HR was only significant in the F-HEM and I-HEM groups. Associated with I-HEM and F-HEM, but not HYDRAZ treatment were significant increases in FLI in the caudal ventrolateral periaqueductal gray (PAG), the central lateral nucleus of the rostral parabrachial nucleus, and locus coeruleus compared with SAL treatment. I-HEM also induced significant increases in FLI in the dorsomedial PAG, A7 region, and the cuneiform nucleus compared with SAL. S-HEM did not induce any significant change in FLI. Our results suggest that HEM at a rate of 1 ml.kg(-1).min(-1) may be most useful for investigating the potential role of the rostral brainstem regions in mediating hemorrhagic decompensation in conscious rats.     

Antagonistic effects of naloxone on CCK-octapeptide induced satiety and rumino-reticular hypomotility in sheep

Continuous intracerebroventricular (ICV) infusion of CCK-octapeptide (CCK8) was performed in ewes fitted with a permanent cannula into the lateral cerebral ventricle and Nichrome electrodes on the reticulum in order to record its electrical activity. In the first series of experiments, subsequently repeated in 12 h fasted animals, CCK8 was infused during the first hour of a 3 hour period of feeding at 2.5, 5 and 10 ng.kg-1.min-1. The same series of infusion were performed 20 min after ICV injection of 2.4 and 10 micrograms.kg-1 of naloxone. CCK8 reduced significantly in a dose related manner the food intake (r = 0.95; P less than 0.01) and the frequency of cyclic spike bursts associated to biphasic contractions of the reticulum observed during feeding (r = 0.89; P less than 0.01). At 5 and 10 ng.kg-1.min-1, the reduction of food intake reached 46.2 and 52.6% during the period of infusion; the basal and stimulated (feeding) frequency of reticular contractions were nearly halved. Previous ICV administration of naloxone (2.4 micrograms.kg-1) partially blocked the effects of CCK8 infusion on both food intake (72%) and reticular frequency (54% basal, 67% stimulated). The CCK8 induced effects on both food intake and frequency of reticular contraction were completely abolished after a previous 10 micrograms.kg-1 injection of naloxone. These results suggest that the central effects of CCK8 on feeding behavior and forestomach motility involve similar central structures and are mediated through opiate receptor structures.     

Effect of alpha-adrenoreceptors in the control of spontaneous motility and morphine withdrawal syndrome.

The effects of different alpha-2 agonists on the spontaneous motility in naive and morphine tolerant mice were studied. Clonidine caused a reduction at the lower (1-3 micrograms Kg-1 i.p.) and higher (100 micrograms Kg-1 i.p.) doses and no effect at 10-30 micrograms Kg-1 i.p. in naive mice, while an increase was found at the intermediate doses (10-30 micrograms Kg-1 i.p.) in morphine tolerant mice. The clonidine-induced inhibition on spontaneous motility at the lower and higher doses was prevented both in naive and tolerant mice by idazoxan pretreatment. In morphine-treated animals the increase induced by clonidine was antagonized by prazosin. The action of guanabenz and guanfacine on locomotion differed from clonidine, by producing inhibition only at higher doses (100-300 micrograms Kg-1 i.p.). Clonidine, but not guanfacine or guanabenz, prevented the withdrawal syndrome precipitated by naloxone. Thus the only alpha-2 agonistic properties do not appear sufficient to explain the prevention of morphine abstinence by clonidine in mice, which can represent a single model to screen anti-withdrawal drugs.     

Identification by electron spin resonance spectroscopy of free radicals produced during autoxidative melanogenesis

Free radicals produced during the autoxidation of 3,4-dihydroxyphenylalanine (DOPA) and other catechol(amine)s to melanins have been studied using electron spin resonance spectroscopy. Magnetic parameters for the radical intermediates have been determined, allowing the radicals to be unambiguously identified. Three types of radical are formed: the primary radical from one-electron oxidation of the parent catechol(amine); and two secondary radicals, one formed via OH- substitution, the other via cyclization. The formation of these radical species can be linked to molecular products formed during catecholamine oxidation and melanin formation.     

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

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

Progressive weakening of the response of key enzymes of liver glycogen metabolism to permanently increased plasma epinephrine levels

In adult male rats anaesthetized with pentobarbital the intravenous infusion of 0.5 micrograms.kg-1.min-1 of epinephrine increased liver phosphorylase a activity within 5 min, whereas later a weakening of the hormone effect was observed. After increasing the infusion rate to 1.0 micrograms.kg-1.min-1 and extending the study to more parameters, the diminishing effect on phosphorylase was confirmed and a similar response was established for liver cAMP. Concomitantly, a decrease and recovery of liver glycogen synthase a activity was observed. In rats with permanent catheters in one of their tail arteries for obtaining blood samples, the plasma epinephrine levels were shown to be permanently increased (from cca 1 pmol.ml-1 before infusion of 1.0 micrograms.kg-1.min-1 to more than 30 pmol.ml-1 during infusion) and remained at steady levels throughout the infusion. Therefore, the weakening of the epinephrine effect should be ascribed to changes at (or beyond) the catecholamine receptor level. A hitherto undescribed decrease of total glycogen synthase activity was observed during the infusions.