Alpha 2- and beta-adrenergic stimulation of corticosterone secretion in rats

Anesthesia can alter the levels of corticosterone and the phosphorylation of signaling molecules

Objective

Neuroscience research using laboratory animals has increased over the years for a number of reasons. Some of these studies require the use of anesthetics for surgical procedures. However, the use of anesthetics promotes several physiological changes that may interfere with experimental results. Although the anesthetics and methods of delivery used to vary, one of the most common is ketamine associated with another compound such as xylazine. We aimed to evaluate the effect of ketamine and xylazine (KX) on corticosterone levels and on the degree of phosphorylation of p44/42 (ERK1/2), Src kinases and calcium/calmodulin-dependent kinase II (CAMKII). We also compared the effects of KX on sleep deprivation, which is known to affect the hormonal profile including corticosterone.

Results

We found that the use of KX can increase corticosterone levels and alter the degree of phosphorylation of signaling proteins.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13104-021-05763-w.

Acute isoproterenol induces anxiety-like behavior in rats and increases plasma content of extracellular vesicles

Several clinical observations have demonstrated a link between heart rate and anxiety or panic disorders. In these patients, β-adrenergic receptor function was altered. This prompted us to investigate whether the β-adrenergic receptor agonist isoproterenol, at a dose that stimulates peripheral β-adrenergic system but has no effects at the central nervous system, can induce anxiety-like behavior in rats. Moreover, some possible messengers involved in the peripheral to brain communication were investigated. Our results showed that isoproterenol (5 mg kg(-1) i.p.) increased heart rate, evoked anxiety-like behavior, did not result in motor impairments and increased extracellular vesicle content in the blood. Plasma corticosterone level was unmodified as well as vesicular Hsp70 content. Vesicular miR-208 was also unmodified indicating a source of increased extracellular vesicles different from cardiomyocytes. We can hypothesize that peripheral extracellular vesicles might contribute to the β-adrenergic receptor-evoked anxiety-like behavior, acting as peripheral signals in modulating the mental state.

Systemic administration of leptin decreases plasma corticosterone levels: role of hypothalamic norepinephrine

Leptin, an adipocyte-derived hormone, is known to regulate a variety of neuroendocrine functions. It inhibits the hypothalamo-pituitary-adrenal axis (HPA) in several animal models, however, the exact mechanism by which it does so is not known. Since norepinephrine (NE) is a key regulator of the HPA axis, we hypothesized that leptin could suppress HPA activity by decreasing NE levels. To study this, we implanted adult male Sprague-Dawley rats with both a push-pull cannula in the paraventricular nucleus (PVN) and a catheter in the jugular vein. Animals were treated with either 0 or 100 microg or 500 microg of recombinant rat leptin (Lep). Push-pull perfusion was performed from 1000-1600 h. Perfusate samples were collected every 30 min and analyzed for NE levels using HPLC-EC. Blood samples were collected every 60 min and analyzed for corticosterone (CS) levels. To further understand the role of NE in this phenomenon animals were treated with either an alpha1-adrenergic agonist, phenylephrine (PHE; 0.5 mg/kg BW), an alpha2-adrenergic agonist, clonidine (CLON; 0.6 mg/kg BW), or a beta-adrenergic agonist, isoproterenol (ISO; 0.2 mg/kg BW) alone or in combination with 500 microg of Lep. Pre-treatment and hourly post-treatment blood samples were collected, plasma was separated and analyzed for CS levels. Leptin administration decreased NE release in the PVN significantly by 30 min (p<0.05). It also significantly reduced plasma CS levels at 240 and 300 min (p<0.05). Administration of either PHE or CLON in combination with leptin prevented the leptin-induced decrease in CS. In contrast, administration of ISO along with leptin did not prevent the leptin-induced decrease in CS. These results indicate that leptin decreases hypothalamic NE and plasma CS and that this effect is most probably mediated through alpha-adrenergic receptors.

Extrahypothalamic corticotropin-releasing hormone mediates (-)-nicotine-induced elevation of plasma corticosterone in rats

(-)-Nicotine activates the hypothalamic-pituitary-adrenal axis via an activation of the brainstem catecholaminergic neurons in rats. The present study was undertaken to clarify the mechanisms involved in the (-)-nicotine-induced activation of brainstem catecholaminergic neurons in anesthetized rats. Physostigmine (a cholinesterase inhibitor) (0.31 and 0.77 micromol/animal, i.p.) dose-dependently elevated plasma corticosterone in the presence of scopolamine (a muscarinic receptor antagonist) (2.3 micromol/animal, i.p.). (-)-Nicotine (250 and 500 nmol/animal, i.c.v.) dose-dependently elevated plasma corticosterone with concomitant noradrenaline release in the hypothalamic paraventricular nucleus. The (-)-nicotine (500 nmol/animal, i.c.v.)-induced elevation of corticosterone was abolished by phentolamine (an alpha-adrenoceptor antagonist) (0.66 micromol/animal, i.c.v.), and attenuated by (+/-)-sotalol (a beta-adrenoceptor antagonist) (0.97 micromol/animal, i.c.v.). The (-)-nicotine-induced increases of plasma corticosterone and hypothalamic noradrenaline release were abolished either by hexamethonium (a nicotinic acetylcholine receptor antagonist) (1.8 micromol/animal, i.c.v.), CP-154,526 (butyl-ethyl-[2,5-dimethyl-7-(2,4,6-trimethylphenyl)-7H-pyrrolo[2,3-d]pyrimidin-4-yl]amine) (a selective CRF-1 receptor antagonist) (1.3 micromol/animal, i.c.v.) or indomethacin (a cyclooxygenase inhibitor) (1.2 micromol/animal, i.c.v.). These results suggest that (-)-nicotine elevates plasma corticosterone by CRF-1 receptor- and prostaglandin-mediated noradrenaline release in the paraventricular nucleus in rats.

The role of alpha-adrenoceptors in the amnestic effect of intracerebroventricular dexamethasone

Corticosteroids exert dual enhancing or impairing effects on cognitive functions. While their memory-enhancing effects have been well investigated, the mechanisms involved in their amnestic effects are not completely understood. Thus, we examined the role of alpha-adrenoceptors on dexamethasone-induced amnesia using step-through passive avoidance test in rat. Intracerebroventricular (i.c.v.) injection of dexamethasone (5 and 10 microg per rat) decreased the retention latencies. Likewise, intraperitoneal administration of alpha(2)-adrenoceptor agonist clonidine (0.1-0.3 mg kg(-1)) but not alpha(2)-adrenoceptor antagonist yohimbine (0.5-2 mg kg(-1)) decreased the retention latency. Yohimbine pre-treatment decreased the amnestic effects of dexamethasone or dexamethasone plus clonidine. On the other hand, intraperitoneal administration of alpha(1)-adrenoceptor agonist phenylephrine (0.5-2 mg kg(-1)) per se increased, while prazosin at 2 mg kg(-1) decreased the retention latency. Administration of phenylephrine before dexamethasone completely reversed the amnestic effect of the latter, while prozosin did not affect dexamethasone-induced amnesia. These data suggest that dexamethasone may induce its amnestic effect through activation of alpha(2)-adrenoceptors, leading to decreased alpha(1)-adrenergic activity.

The effects of anesthetics on stress responses to forebrain ischemia and reperfusion in the rat

Rats exposed to forebrain ischemia have reduced injury when anesthetized with isoflurane versus fentanyl + N(2)O. The protection caused by isoflurane is reversed by trimethaphan. We hypothesized that these anesthetic-dependent effects on ischemic outcome can be associated with altered stress responses to ischemia. Rats were randomized to four treatments: isoflurane; fentanyl + N(2)O; isoflurane + trimethaphan; or isoflurane + metyrapone. Severe forebrain ischemia was then induced for 10 min. Plasma and brain corticosterone, tumor necrosis factor (TNF)-alpha, and interleukin (IL)-6 were assayed. Plasma corticosterone concentrations were similar in the isoflurane and isoflurane + trimethaphan groups, but greater than in the fentanyl + N(2)O and isoflurane + metyrapone groups. Brain corticosterone was similar among all groups except isoflurane + metyrapone, in which values were markedly reduced. The addition of metyrapone to isoflurane also reduced plasma TNF-alpha; however, values among other groups were similar. There were no differences among groups for brain TNF-alpha. Plasma IL-6 concentrations were below the limit of detection. Brain IL-6 concentrations were increased by ischemia; however, there was no difference among groups. In conclusion, there were no differences between the isoflurane and isoflurane + trimethaphan groups for any of the measured stress markers. Further, there was little difference between the isoflurane and fentanyl + N(2)O groups, except for plasma corticosterone concentration. Accordingly, isoflurane neuroprotection and its reversal by trimethaphan appear to be independent of effects on the stress responses measured in this study.

IMPLICATIONS

Differential anesthetic effects on ischemic outcome are independent of effects on adrenergic/noradrenergic responses to ischemia. The absence of a consistent differential effect of anesthetics on either corticosterone or cytokine responses to ischemia serves to further refute the hypothesis that isoflurane neuroprotection can be attributed to dampening of adverse stress responses to ischemic insults.

Catecholaminergic involvement in the control of aggression: hormones, the peripheral sympathetic, and central noradrenergic systems

Noradrenaline is involved in many different functions, which all are known to affect behaviour profoundly. In the present review we argue that noradrenaline affects aggression on three different levels: the hormonal level, the sympathetic autonomous nervous system, and the central nervous system (CNS), in different, but functionally synergistic ways. Part of these effects may arise in indirect ways that are by no means specific to aggressive behaviour, however, they are functionally relevant to it. Other effects may affect brain mechanisms specifically involved in aggression. Hormonal catecholamines (adrenaline and noradrenaline) appear to be involved in metabolic preparations for the prospective fight; the sympathetic system ensures appropriate cardiovascular reaction, while the CNS noradrenergic system prepares the animal for the prospective fight. Indirect CNS effects include: the shift of attention towards socially relevant stimuli; the enhancement of olfaction (a major source of information in rodents); the decrease in pain sensitivity; and the enhancement of memory (an aggressive encounter is very relevant for the future of the animal). Concerning more aggression-specific effects one may notice that a slight activation of the central noradrenergic system stimulates aggression, while a strong activation decreases fight readiness. This biphasic effect may allow the animal to engage or to avoid the conflict, depending on the strength of social challenge. A hypothesis is presented regarding the relevance of different adrenoceptors in controlling aggression. It appears that neurons bearing postsynaptic alpha2-adrenoceptors are responsible for the start and maintenance of aggression, while a situation-dependent fine-tuning is realised through neurons equipped with beta-adrenoceptors. The latter phenomenon may be dependent on a noradrenaline-induced corticosterone secretion. It appears that by activating very different mechanisms the systems working with adrenaline and/or noradrenaline prepare the animal in a very complex way to answer the demands imposed by, and to endure the effects caused by, fights. It is a challenge for future research to elucidate how precisely these mechanisms interact to contribute to functionally relevant and adaptive aggressive behaviour.