Pentobarbital attenuates stress-induced increases in noradrenaline release in specific brain regions of rats

Organic cation transporter 3 contributes to norepinephrine uptake into perivascular adipose tissue

Perivascular adipose tissue (PVAT) reduces vasoconstriction to norepinephrine (NE). A mechanism by which PVAT could function to reduce vascular contraction is by decreasing the amount of NE to which the vessel is exposed. PVATs from male Sprague-Dawley rats were used to test the hypothesis that PVAT has a NE uptake mechanism. NE was detected by HPLC in mesenteric PVAT and isolated adipocytes. Uptake of NE (10 μM) in mesenteric PVAT was reduced by the NE transporter (NET) inhibitor nisoxetine (1 μM, 73.68 ± 7.62%, all values reported as percentages of vehicle), the 5-hydroxytryptamine transporter (SERT) inhibitor citalopram (100 nM) with the organic cation transporter 3 (OCT3) inhibitor corticosterone (100 μM, 56.18 ± 5.21%), and the NET inhibitor desipramine (10 μM) with corticosterone (100 μM, 61.18 ± 6.82%). Aortic PVAT NE uptake was reduced by corticosterone (100 μM, 53.01 ± 10.96%). Confocal imaging of mesenteric PVAT stained with 4-[4-(dimethylamino)-styrl]-N-methylpyridinium iodide (ASP(+)), a fluorescent substrate of cationic transporters, detected ASP(+) uptake into adipocytes. ASP(+) (2 μM) uptake was reduced by citalopram (100 nM, 66.68 ± 6.43%), corticosterone (100 μM, 43.49 ± 10.17%), nisoxetine (100 nM, 84.12 ± 4.24%), citalopram with corticosterone (100 nM and 100 μM, respectively, 35.75 ± 4.21%), and desipramine with corticosterone (10 and 100 μM, respectively, 50.47 ± 5.78%). NET protein was not detected in mesenteric PVAT adipocytes. Expression of Slc22a3 (OCT3 gene) mRNA and protein in PVAT adipocytes was detected by RT-PCR and immunocytochemistry, respectively. These end points support the presence of a transporter-mediated NE uptake system within PVAT with a potential mediator being OCT3.

Pavlovian autoshaping procedures increase plasma corticosterone and levels of norepinephrine and serotonin in prefrontal cortex in rats

Pavlovian autoshaping procedures provide for pairings of a small object conditioned stimulus (CS) with a rewarding substance unconditioned stimulus (US), resulting in the acquisition of complex sequences of CS-directed skeletal-motor responses or autoshaping conditioned responses (CRs). Autoshaping procedures induce higher post-session levels of corticosterone than in controls receiving CS and US randomly, and the enhanced post-session corticosterone levels have been attributed to the appetitive or arousal-inducing effects of autoshaping procedures. Enhanced corticosterone release can be induced by aversive stimulation or stressful situations, where it is often accompanied by higher levels of norepinephrine (NE) and serotonin (5-HT) in prefrontal cortex (PFC) but not in striatum (ST). Effects of autoshaping procedures on post-session corticosterone levels, NE contents in PFC, and 5-HT contents in PFC and ST were investigated in male Long-Evans rats. Post-session blood samples revealed higher corticosterone levels in the CS-US Paired group (n = 46) than in the CS-US Random control group (n = 21), and brain samples revealed higher levels of PFC NE and 5-HT in CS-US Paired group. Striatal 5-HT levels were unaltered by the autoshaping procedures. Autoshaping procedures provide for appetitive stimulation and induce an arousal-like state, as well as simultaneous stress-like changes in plasma corticosterone and monoamine levels in PFC. Autoshaping, therefore, may be useful for the study of endocrine and central processes associated with appetitive conditions.

The effects of different anaesthetic treatments on the adreno-cortical functions and glucose levels in NZW rabbits

The effects of five anaesthetics on the corticosterone, cortisol and glucose concentrations were investigated in the NZW rabbit. Sixty animals were assigned to 6 treatment groups (n= 10 per group): control ( iv saline solution injection), ketamine (10 mg/kg iv) with either xylazine (3 mg/kg iv) or diazepam (2 mg/kg iv), pentobarbitone (30 mg/kg iv), thiopentone (20 mg/kg iv) and fentanyl/droperidol (1 mg/kg sc). Plasma glucocorticoids were measured by competitive enzymeimmunoassay EIA and glucose by an autoanalyzer, previously validated for this species in both cases. Blood samples were obtained at 6 time-points: before injection, at 10, 30, 60, 120 min and 24 h after injection of the anaesthetics/saline. A significant decrease of plasma glucocorticoids at 10-60 min was observed in the pentobarbitone and fentanyl/ droperidol groups, whereas the administration of ketamine/diazepam or thiopentone stimulated plasma glucocorticoid release, principally in the recovery period. However, in the ketamine/xylazine group no changes were observed in the glucocorticoid levels, except for a significative increase of cortisol at 60-120 min. Glucose levels significantly increased after ketamine/diazepam administration and principally, after ketamine/xylazine treatment. The present data suggest that ketamine/xylazine has little effect on glucocorticoid levels and provides an adequate level of surgical anaesthesia, hence it would be the anaesthetic of choice, although the hyperglycaemic effect after injection has to be considered for any experimental procedures in rabbits.

The role of afferents to the locus coeruleus in the handling stress-induced increase in the release of noradrenaline in the medial prefrontal cortex: a dual-probe microdialysis study in the rat brain

This study was aimed to identify the neuronal pathways that mediate the handling stress-induced increase in the release of noradrenaline in the medial prefrontal cortex of the rat brain. For that purpose a microdialysis probe was implanted in the vicinity of the locus coeruleus and a second probe was placed in the ipsilateral medial prefrontal cortex. Receptor specific antagonists acting on the alpha(2)-adrenoceptor (50 microM idazoxan), GABA(A) (50 microM bicuculline), GABA(B) (100 microM (3, 4-Dichlorophenyl)methyl]propyl](diethoxymethyl) phosphonic acid; CGP 52432), acetylcholine (10 microM atropine), corticotropin releasing factor (CRF) (100 microM butyl-ethyl-[2,5-dimethyl-7-(2,4, 6-trimethyl-phenyl)-7H-pyrrolo[2,3-d]pyrimidin-4-yl]-amine; CP-154, 526), NMDA glutamate (300 microM (+/-)-3(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid; CPP) and non-NMDA glutamate receptors (500 microM 6,7-dinitroquinoxaline-2, 3-dione; DNQX) were infused into the locus coeruleus by retrograde dialysis, whereas extracellular noradrenaline was recorded in the ipsilateral medial prefrontal cortex. During infusion of the various compounds rats were gently handled for 10 min. Infusion of idazoxan potentiates the handling-induced increase in the release of noradrenaline in the medial prefrontal cortex. The infusions of, atropine, bicuculline, CGP 52432 and DNQX were without effect on the handling response. Infusion of the NMDA receptor antagonist CPP or the non-peptide CRF receptor antagonist CP-154,526 suppressed the stimulation of noradrenaline during stress. It is concluded that alpha(2)-adrenoceptors, NMDA glutamate receptors and CRF receptors modify the handling stress response of locus coeruleus neurones. The data suggest no major role for glutamatergic, GABAergic, or cholinergic afferents to the locus coeruleus in mediating the stress response.

The effect of acute, chronic and chronic intermittent stress on the central noradrenergic system

The objective of this investigation was to examine the immediate and long term effects of acute, chronic and chronic intermittent stress on the central noradrenergic system of rats. Male Sprague-Dawley rats were subjected to one hour of physical immobilization stress either as a single exposure, or as 14 exposures applied either on consecutive days, or randomly over 60 days. Animals were sacrificed immediately, 6 h and 24 h following the last stressor. Levels of norepinephrine (NE) and 3-methoxy-4-hydroxyphenylethylene-glycol sulfate (MHPG-sulfate) were measured in the hypothalamus, hippocampus, cerebral cortex and locus coeruleus region and beta-adrenergic receptor (BAR) density was determined in the cortex. Immediately after acute stress, a significant reduction in hypothalamic NE levels and marked increases in MHPG-sulfate levels in all four brain regions were observed. In contrast immediately after the last stressor of a chronic or chronic intermittent stress regimen, no change in NE concentration was observed while levels of MHPG-sulfate in the four brain regions showed a smaller increase than that observed after an acute stressor. Acute stress induced changes normalized within 6 h while chronic and chronic intermittently stressed animals had altered NE or MHPG-sulfate levels in certain brain regions for up to 6-24 h. Cortical BAR binding parameters remained unchanged after all stress paradigms.

Anesthesia during hormone administration abolishes the estrogen induction of preproenkephalin mRNA in ventromedial hypothalamus of female rats

Estrogen treatment increases preproenkephalin (PPE) mRNA levels in the ventromedial nucleus of the hypothalamus (VMH). Roy et al. (Brain Res., 337 (1985) 163-166) discovered that anesthesia during estrogen priming could reduce female rat sexual receptivity. In the present study we tested whether the action of estrogen to induce PPE gene expression in the VMH could be similarly affected by anesthesia. By quantitative in situ hybridization and slot-blot analysis techniques we found a 1.8-fold increase in PPE mRNA levels in the VMH after 1 hour of estrogen treatment in ovariectomized (OVX) Sprague-Dawley female rats. Anesthetizing the rats with pentobarbital for 1 h during the exposure to estrogen blocked the estrogen induction of PPE mRNA in the VMH. By way of contrast no changes in the PPE mRNA levels were observed in the caudate putamen. A similar trend was seen using chloral hydrate. It appears that neuronal activity is required for the early phase of estrogen induction of PPE mRNA levels in the VMH. This in turn could be correlated with changes in female sociosexual behaviors.

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.

Systemic signals contribute to induced morphological changes in the hypothalmo-neurohypophysial system

A systemic injection of hypertonic saline causes morphological changes in the supraoptic nucleus (SON) of the hypothalamus and the posterior pituitary, including withdrawal of astrocytic glial processes from among magnocellular neuroendocrine cells (MNCs) in the SON and increases in neural apposition with the basal lamina (BL) in the posterior pituitary. This study investigated whether systemic adrenalin provides a signal for these changes. Three groups of rats were given intraperitoneal injections of hypertonic (1.5 M) or normal (0.15 M) NaCl and were sacrificed 5 h after injection. One group was given no additional treatment, one group was anesthetized from prior to injection through perfusion, and one group was bilaterally adrenal-medullectomized several days prior to injections. Morphometric analysis of electron micrographs revealed rats given 1.5 M NaCl with no additional treatment showed expected changes in the SON and pituitary. Rats given 1.5 M NaCl and anesthetized showed diminished responses in the SON, and no changes in the pituitary compared to anesthetized rats given 0.15 M NaCl. No changes in withdrawal of glial processes from among MNCs or in neural apposition with the BL were seen in medullectomized animals. Thus, both anesthesia and adrenal-medullectomy interfere with signals for glial retraction and suggest that these responses are mediated by adrenalin.

Effect of repeated administration of novel stressors on central beta adrenoceptors

Subtypes of beta adrenoceptors were measured in 17 different areas of brain in rats exposed for 12 days to novel stressors. Mild stress such as individual housing and handling caused no change in beta 1 and beta 2 adrenoceptors in comparison with that measured in rats that were group housed and never handled. Exposure of rats to more severe stressors did reduce significantly the binding of 125I-iodopindolol (125I-IPIN) to beta 1 adrenoceptors, but not beta 2 adrenoceptors, only in the lateral and basolateral nuclei of the amygdala.

Anxiogenic beta-carboline FG 7142 produces activation of noradrenergic neurons in specific brain regions of rats

By measuring the levels of two major metabolites of rat brain noradrenaline (NA), 3-methoxy-4-hydroxyphenylglycol (MHPG) and 3,4-dihydroxyphenylglycol (DHPG), we investigated the effects of anxiogenic beta-carboline FG 7142, an inverse agonist of benzodiazepine (BZD) receptors, on brain noradrenergic activity of rats. Thirty min after treatment with FG 7142 (15 mg/kg IP), levels of both MHPG and DHPG in the hypothalamus, amygdala and thalamus, but not in the hippocampus and cerebral cortex, significantly increased. These increases were significantly antagonized by pretreatment with BZD receptor antagonist Ro 15-1788 (15 mg/kg, IP). Sixty min after treatment with FG 7142 at the same dose, significant increases in both metabolite levels occurred in the hypothalamus, amygdala, thalamus and cerebral cortex, and increases in MHPG levels only were observed in the hippocampus. These increases were significantly blocked by pretreatment with alpha 2-adrenoreceptor agonist clonidine (100 microgram/kg, IP). The present findings suggest that FG 7142 can produce increases in brain noradrenergic activity in specific brain regions by interacting with BZD receptors, and may support the hypothesis that hyperactivity of brain noradrenergic systems may be one neural mechanism in provocation of aversive emotional changes (anxiety, fear or panic).