Effect of central noradrenaline depletion on corticosterone levels and gastric ulcerations in rats

Systemic Interleukin-1β stimulates the simultaneous release of norepinephrine in the paraventricular nucleus and the median eminence

Interleukin-1beta (IL-1beta), a cytokine with pronounced central effects such as fever, anorexia, analgesia, etc., is also known to activate the hypothalamo-pituitary-adrenal (HPA) axis. Corticotropin releasing hormone (CRH) neurons located in the hypothalamus are important for HPA activation. The cell bodies of CRH neurons are located in the paraventricular nucleus (PVN) and their terminals are present in the median eminence (ME). Although the catecholamines, norepinephrine (NE) and dopamine (DA) are believed to be crucial factors in the stimulation of CRH neurons, it is not clear if they affect the cell bodies or terminals of these neurons to cause HPA activation. This study was done to determine if IL-1beta affects NE and DA release at the level of CRH cell bodies or their terminals. Adult male Sprague-Dawley rats were implanted with two push-pull cannulae, one in the PVN and another in the ME, and were subjected to push-pull perfusion. They were treated either with 0, 1 or 5 microg of IL-1beta. Perfusates were collected for 2 h after treatment and analyzed for NE concentrations using HPLC-EC. NE levels in the control and low dose groups did not change significantly during the entire period of observation both in the PVN and ME. In contrast, treatment with 5 microg of IL-1beta produced a marked increase in NE release in the PVN at 20 and 40 min post-treatment. NE release in the ME increased from 10 to 140 min post-treatment. There were no significant changes in the release of DA from both these areas. These results indicate that IL-1beta increases NE levels both in the PVN and in the ME and this could be a possible mechanism by which it stimulates the HPA axis.

Serotonin modulates the suppressive effects of corticosterone on proliferating progenitor cells in the dentate gyrus of the hippocampus in the adult rat

This series of experiments explores the interaction between corticosterone and serotonin (5-HT) in the regulation of cell proliferation in the dentate gyrus of the adult rat. Intracerebroventricular 5,7-DHT (5,7-dihydroxytryptamine) (either 200 or 300 microg) resulted in highly significant depletion of 5-HT as measured by high performance liquid chromatography in the frontal cortex but had no effect on the number of proliferating cells in the dentate gyrus by measuring 5-bromo-2'-deoxyuridine (BrdU) and Ki-67 cytochemistry. Treatment with PCPA (p-chlorophenylalanine: a tryptophan hydroxylase inhibitor: 300 mg/kg initially followed by 100 mg/kg/day) resulted in reduced proliferation as measured by Ki-67 after 3 days treatment, but not by BrdU uptake, and not after 14 days treatment by either method. In addition, injection of corticosterone (10-40 mg/kg/day) for 8 days significantly reduced proliferation in the dentate gyrus, as expected, measured by both BrdU uptake and Ki-67 immunostaining. Adrenalectomized (ADX) rats with a replacement subcutaneous pellet of corticosterone showed reduced proliferation when given additional corticosterone (10 mg/kg/day for 8 days), but this was prevented by 5-HT depletion (i.c.v. 5,7-DHT). Finally, a dose-response study showed that progressive doses of corticosterone (0-40 mg/kg/day) in ADX rats resulted in diminished suppression of proliferation in 5-HT-depleted compared with 5-HT-intact rats. These results strongly suggest that 5-HT regulates the sensitivity of proliferating cells in the dentate gyrus to corticosterone.

Noradrenergic lesion antagonizes desipramine-induced adaptation of NMDA receptors

Repeated administration of the tricyclic antidepressant, desipramine, for 28 days to mice effected a decrease in the potency of glycine to displace [3H]5,7-dichlorokynurenic acid (5,7-DCKA) in mouse cortical homogenates. Pre-treatment with the noradrenergic neurotoxin DSP-4, while having no effect alone, attenuated the desipramine-induced effect. The present findings support a norepinephrine-dependent adaptation of the NMDA receptor complex in vivo following chronic desipramine treatment. The inter-relationship of norepinephrine and glutamate transmission may provide insight into the mechanism underlying the action of antidepressant drugs.

Organization of the coeruleo-vestibular pathway in rats, rabbits, and monkeys

Inputs from locus coeruleus (LC) appear to be important for altering sensorimotor responses in situations requiring increase vigilance or alertness. This study documents the organization of coeruleo-vestibular pathways in rats, rabbits and monkeys. A lateral descending noradrenergic bundle (LDB) projects from LC to the superior vestibular nucleus (SVN) and rostral lateral vestibular nucleus (LVN). A medial descending noradrenergic bundle (MDB) projects from LC to LVN, the medial vestibular nucleus (MVN), group y and rostral nucleus prepositus hypoglossi (rNPH). There is a characteristic, specific pattern of innervation of vestibular nuclear regions across the three species. A quantitative analysis revealed four distinct innervation density levels (minimal, low, intermediate and high) across the vestibular nuclei. The densest plexuses of noradrenergic fibers were observed in the SVN and LVN. Less dense innervation was observed in the MVN, and minimal innervation was observed in the inferior vestibular nucleus (IVN). In monkeys and rabbits, rostral MVN contained a higher innervation density than the rat MVN. In monkeys, the rNPH also contained a dense plexus of fibers. Selective destruction of terminal LC projections (distal axons and terminals) by the neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) resulted in a dramatic reduction of immunoreactive fibers within the vestibular nuclear complex of rats, suggesting that the source of these immunoreactive fibers is LC. Retrograde tracer injections into the vestibular nuclei resulted in labeled cells in the ipsilateral, caudal LC and adjacent nucleus subcoeruleus. It is hypothesized that the regional differences in noradrenergic innervation are a substrate for differentially altering vestibulo-ocular and vestibulo-spinal responses during changes in alertness or vigilance.

Column-switching high-performance liquid chromatographic system with a laser-induced fluorimetric detector for direct, automated assay of salivary cortisol

In order to measure human stress, an easy and rapid, fully automated method for the determination of cortisol in saliva has been developed, using column-switching high-performance liquid chromatography with laser-induced fluorescence detection, which involves post-column labeling with sulfuric acid. The developed system requires only 0.1 ml of saliva, and a simple pretreatment consisting of dilution and filtration is sufficient. The column-switching system consisted of a Polymer-Coated Mixed-Functional silica (PCMF) column for deproteinization, and a CN column for frontal concentration and separation. An ODS column in place of the CN provided a better separation, but required a post-column make-up of water for safe reaction. Detection limit of cortisol was 8 fmol (signal-to-noise ratio = 3), which is adequate for routine determination of normal levels of cortisol (1-20 pmol/ml). The analysis time was about 40 min and reproducibility was excellent with an R.S.D. of less than 5%.

Restraint stress in biomedical research: an update

Since the publication of our initial review of restraint stress in 1986, much work has continued with this technique, either as a tool for the investigation of other pharmacological, physiological, or pathologic phenomena or with restraint stress itself serving as the object of the study. As we noted in 1986, the major use of restraint has been for the induction of stress responses in animals and, more specifically, for the investigation of drug effects, particularly as they affect typical stress-related pathology--gastrointestinal, neuroendocrine, and immunological agents have been extensively studied. In compiling this update on restraint stress and its effects, we noted an increasing emphasis on central nervous system mechanisms in peripheral disease, especially gastrointestinal disease. In particular, many CNS-active agents have been tested for their effects on gastric and duodenal lesion formation and gastric secretion, including antidepressants, antipsychotics, anxiolytics, noradrenergic, serotonergic, dopaminergic, and peptidergic compounds. Some of these agents are especially active in the gastrointestinal tract even when administered centrally, further solidifying the concept of a brain-gut axis. The present update includes studies of: methods and procedures, pre-restraint manipulations, post-restraint/healing effects, and drug effects. In addition, a current bibliography of reports that have employed restraint is included.

The neurobiology of stress ulcers

We have reviewed the neurobiology of stress ulcers from animal models to potential pharmacotherapeutic mechanisms. The evidence strongly supports the hypothesis that certain stress-related gastric lesions are 'brain-driven' events which may be more effectively managed through central manipulations than by altering local, gastric factors. Recent advances in the use of anxiolytic and antidepressant drugs in the management of stress-related gastric mucosal injury further supports the contention that a brain-gut axis, which may have nervous, peptidergic and classic monoaminergic components, modulates the intricate and complicated pattern of communication between the brain and the stomach. Delineation of the precise pathways which make up this communication as well as their manipulation by various pharmacological agents will be the focus of future research endeavour.

Centrally administered NPY stimulated gastric acid and pepsin secretion by a vagally mediated mechanism

We investigated the possible roles of centrally administered neuropeptide Y (NPY) on gastric secretion, serum gastrin levels and gastric mucosal blood flow in anesthetized rats. Centrally administered NPY dose-dependently stimulated gastric acid and pepsin secretion. The stimulatory effect of intracerebroventricular administration of NPY was more potent than that of intracisternal administration. Centrally administered NPY also increased gastric secretion in the central noradrenaline depleted rats. In contrast, intravenously administered NPY had no influence on gastric secretion. These stimulatory effects were abolished by vagotomy or atropine pretreatment. The serum gastrin levels did not change after central NPY injection. Although intravenously administered NPY slightly increased gastric mucosal blood flow, centrally administered NPY slightly diminished gastric mucosal blood flow. These results indicate that centrally administered NPY markedly influences gastric functions in the rat.

Distinct, developmentally regulated brain mRNAs direct the synthesis of neurotransmitter transporters

The Xenopus laevis oocyte expression system was utilized to define developmental and structural properties of neurotransmitter transporter mRNAs and the pharmacological characteristics of encoded carriers independent of the complexities of brain tissue preparations. Poly(A)+ RNA from dissected brain regions of neonatal and adult rats was microinjected into Xenopus oocytes and the expression of Na(+)-dependent neurotransmitter transporters determined 48 h later. Transport studies conducted with oocytes injected with RNAs derived from juvenile rat tissues indicate a region- and transporter-specific, postnatal increase in mRNA abundance as a major factor in the developmental changes observed for brain high-affinity amino acid uptake systems. Both L-glutamic acid (Glu) and gamma-aminobutyric acid (GABA) uptake systems were detectable by day 3 in postnatal forebrain mRNA and became progressively enriched during the next 2 weeks of forebrain development. In contrast, brainstem Glu and GABA transporter enrichment was 60-70% of adult values by day 3 and exceeded adult levels by day 10. Parallel determinations of L-glutamic acid decarboxylase mRNA abundance during development argue for distinct regulatory influences on mRNAs directing transmitter synthesis and reuptake. Glycine uptake could not be detected at any point of forebrain development and exhibited a gradual postnatal rise to adult levels over the first 3 postnatal weeks of brainstem development. Uptake studies conducted with well-characterized inhibitors of Glu, GABA, dopamine, and choline transport (D-aspartate, nipecotic acid, nomifensine, and hemicholinium-3, respectively) revealed that oocyte transporters encoded by adult rat brain mRNAs retained antagonist sensitivities exhibited by in vitro brain preparations. In addition, a differential regional sensitivity to the Glu transport antagonist dihydrokainate (1 mM) was observed, lending support to previous reports of region-specific Glu transporter subtypes. To determine the structural diversity present among brain transporter mRNAs, poly(A)+ RNA was size-fractionated on linear (10-31%) sucrose density gradients prior to oocyte injection. These experiments revealed two mRNA size classes (2.4-3.0 kb, 4.0-4.5 kb) independently capable of directing the synthesis of Glu, GABA, and glycine transporters. In regions other than the cerebellum, Glu and GABA transporter activities migrated as single, yet distinct, peaks of 4.0-4.5 kb. In contrast, both Glu and GABA transporters exhibited major peaks of activity at 2.5-3.0 kb with size-fractionated cerebellar mRNA. Brainstem glycine uptake exhibited a broad sedimentation profile, with peaks apparent at 2.4 and 4.0 kb. Taken together, these findings indicate previously unappreciated complexity in mRNA structure and regulation which underlies the expression of amino acid neurotransmitter uptake systems in the rodent CNS.

Positive relationship between the catecholaminergic turnover and the DST results in depression

In the past some workers have reported positive relationships between indices of noradrenaline activity and measures of hypothalamic-pituitary-adrenal (HPA)-axis function. In order to investigate these relations, the authors measured noradrenaline, adrenaline and vanillylmandelic acid (VMA) in 24 h urine samples of 72 depressed females. Serum adrenocorticotrophic hormone (ACTH) and cortisol concentrations were determined before and after administration of 1 mg of dexamethasone. Cortisol non-suppressors exhibited a significantly higher noradrenaline, adrenaline and VMA excretion as compared to cortisol suppressors. We determined significantly positive correlations between the postdexamethasone cortisol values and the excretion rates of noradrenaline and VMA. These indices of noradrenaline activity correlated neither with the baseline cortisol and ACTH nor with the postdexamethasone ACTH values.

Studies on the interaction between ICV effects of CRF and CNS noradrenaline depletion

The role of an intact locus coeruleus (LC) noradrenergic system for the central effects of corticotropin-releasing factor (CRF) was studied. Rats were treated with N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride (DSP-4), a highly selective noradrenergic neurotoxin permanently affecting mainly the LC system. This procedure did not affect the activation of the sympathetic nervous system, as measured by plasma catecholamine levels, after either intracerebroventricular (ICV) or intraperitoneal (IP) administration of 8-micrograms CRF. Neither was the increased emotionality seen in an open field test after ICV injection of CRF altered. However, the ulceroprotective effect of 8-micrograms CRF ICV during a 2-hr water restraint stress was significantly antagonized by pretreatment with DSP-4, while CRF did exhibit an ulceroprotective effect after IP administration to DSP-4-treated animals. Our data indicate that the ulceroprotective effect of CRF under restraint stress is, at least partly, dependent on an intact locus coeruleus noradrenergic system.

Paradoxical DSP-4 effects: protection against gastric erosions and depletion of mucosal glycoproteins

We have previously reported that rats pretreated with the central noradrenergic neurotoxin DSP-4 are protected against 23 h restraint-induced gastric erosions. To elucidate the peripheral mechanisms of this protection, we undertook direct biochemical analyses of the gastric mucosa in terms of glycoproteins and proteins. A simple method for preparation of gastric mucosa devoid of the muscular stomach wall tissue is described. A restraint-induced decrease in gastric mucosal wet weight and mucosal glycoprotein content was revealed. Restraint had no effect on mucosal protein content, and no changes were found in gastric wall glycoprotein or protein content. Despite showing protection against restraint-induced gastric erosions, unrestrained DSP-4-treated animals exhibited reduced mucosal wet weight and mucosal glycoprotein content when compared to unrestrained controls. After the stress period, no significant differences on mucosal weight or glycoproteins could be detected between control and DSP-4-treated animals. The results indicate that the protective effect of DSP-4 in this paradigm is not due to enhanced gastric mucosal protection against erosive factors. We suggest that an additional effect of central nervous NA depletion by DSP-4 may be elimination of aggressive factors which precipitate overt ulcers.

Noradrenergic mechanisms in the central amygdalar nucleus and gastric stress ulcer formation in rats

Microinjections of noradrenaline (NA, 0.3, 3.0 and 30.0 micrograms) into the central amygdalar nucleus (CEA) produced dose-related attenuations of cold restraint (3 h at 4 degrees C) induced gastric ulcer formation in rats. On the other hand, stress ulcer aggravating effects were seen with beta-adrenoceptor antagonist, propranolol (10 micrograms) but not with the alpha-adrenoceptor antagonist, prazosin (1 and 10 micrograms). Moderate enhancements of gastric stress lesions were also seen with the NA release inhibitor clonidine (1 microgram) and the neurotoxin DSP-4 (25 micrograms). Further, pretreatment of rats with intra-amygdalar (i.am.) propranolol but not prazosin, antagonized and reversed the gastric cytoprotective effects of NA. The results indicate that beta-adrenoceptor-mediated NAergic mechanisms at the level of the CEA are important for the maintenance of gastric mucosal integrity during immobilization stress.

The effect of partial noradrenergic denervation on corticosterone secretion in the rat

DSP4(N-(-2-chloroethyl)-N-ethyl-2-bromobenzylamine) treatment significantly decreased the noradrenaline content in the hippocampus, frontal cortex and hypothalamus of the rat brain. DSP4 treatment did not affect plasma corticosterone levels. Clonidine, an alpha2-adrenoceptor agonist, had no effect on corticosterone secretion in either DSP4- or saline-treated rats. Isoproterenol, a beta-adrenoceptor agonist, significantly stimulated corticosterone secretion. This effect was inhibited by the prior administration of the beta-adrenoceptor antagonist propranalol. DSP4 treatment did not alter the isoproterenol-induced stimulation of corticosterone secretion. The administration of a high dose of dexamethasone (100 micrograms/kg, i.p.) significantly decreased the plasma corticosterone concentration of saline-treated controls, while an intermediate dose (25 micrograms/kg, i.p.) did not suppress corticosterone release significantly. DSP4-treatment did not influence dexamethasone-induced suppression of corticosterone secretion. These results show that significant decreases in noradrenaline content in the hippocampus, frontal cortex and hypothalamus appear to have no effect on the regulation of corticosterone secretion and that corticosterone secretion may be stimulated by catecholamines via beta-adrenoceptors.

On the role of the dorsal noradrenergic bundle in learning and habituation to novelty

In Experiment 1, the performance of vehicle control rats and rats with 6-hydroxydopamine-induced lesions of the dorsal noradrenergic bundle (DB) was examined in acquisition and extinction of bar pressing and in spontaneous and food-reinforced alternation in a T-shape maze. Plasma corticosterone levels in basal conditions, after chronic food restriction, after transportation to a novel environment, and after sessions of either rewarded or nonrewarded bar pressing were assayed. DB lesions produced a significant decrease of spontaneous alternation and a significant but small resistance to extinction, without reliably altering either corticosterone responses or instrumental spatial alternation. In Experiment 2, bar-press extinction and instrumental alternation were reexamined in new groups of control rats and rats with DB lesions without any blood collection procedures. The DB lesions did not reliably alter either behaviors on any measures. Taken together, these data indicate no consistent effects of forebrain noradrenaline depletion on either extinction or spatial memory or pituitary-adrenocortical function. However, the impairment of spontaneous alternation found in a previous study was confirmed. These findings are discussed in terms of the proposed roles of the dorsal noradrenergic bundle in learning and habituation to novelty.

The association of MHPG to dexamethasone suppression test status

The results of the dexamethasone suppression test (DST) were compared to levels of 24-hour 3-methoxy-4-hydroxyphenylglycol (MHPG) in 60 patients with unipolar depression. DST nonsuppressors had significantly higher levels of MHPG than did DST suppressors. The possible implications of this finding are discussed.

Brain neurotransmitter systems mediating behavioral deficits produced by inescapable shock treatment in rats

The effect of inescapable footshock (IS) upon rats' motor activity (the open field and forced swim tests) was studied in rats subjected to drugs, and neurotoxin treatments, affecting their central neurotransmitter systems. The agonists of GABA-receptor complex, dopamine, noradrenaline and serotonin neuronal systems, as well as the cholinergic antagonist, partially reversed motor suppression induced by IS, while the dopamine agonist, chlorpromazine, and the cholinergic antagonist, physostigmine, potentiated it. The effects of chemical lesions of the brain monoaminergic neurons with p-chlorophenylalanine (pCPA), N-chloro-ethyl-2,2-bromo-benzylamine (DSP-4), 6-hydroxydopamine (6-OHDA) and 5,7-dihydroxytryptamine (5,7-DHT) were more complex, depending upon the extent of monoamine depletion, and the kind of test applied. It is concluded that a decrease in the brain noradrenergic, serotonergic, dopaminergic and GABAergic neuronal activity, as well as the central cholinergic hyperactivity, might contribute to the behavioral suppression after IS. Thus the central mechanisms of behavioral deficits produced by IS involve multiple neurotransmitter systems, and the analysis of their role in more complicated behavioral patterns must also take into account changes in animals' baseline and stimulated motor activity.

Some aspects of stress and depression

1. The role of stress in depressive illness is discussed together with utility of the "learned helplessness" model and some neuropharmacological correlates of uncontrollable shock. 2. Similarities and differences between chronic antidepressant treatment and chronic stress treatment regimes are reviewed. 3. Finally the role of adaptive process in stress on antidepressant treatments is discussed.

Intracerebroventricular neuropeptide Y protects against stress-induced gastric erosion in the rat

The effects of intracerebroventricular administration of neuropeptide Y (NPY) on stress-induced gastric erosion in the rat were investigated. Animals were exposed to water immersion stress after a single injection of 2 nmol NPY. Stress-induced erosion was reduced by approximately 50%. The plasma corticosterone levels were not affected. We interpret the protective effect of NPY as a manifestation of its sedative properties.

The anterior midline cortex and adaptation to stress ulcers in rats

Rats with bilateral radio-frequency lesions of the anterior midline cortex were subjected to either single or repeated immobilization stress treatments. As previously demonstrated, the lesions greatly reduced gastric pathology in the acute stress treatment. Conversely, the lesions were found to aggravate gastric pathology in animals stressed repeatedly, thus eliminating the adaptive (i.e., pathology-reducing) effects of repeated stress seen in controls. The role of the anterior midline cortex in stress and stress adaptation is discussed with reference to noradrenergic mechanisms.