Effects of antidepressants maprotiline and fluxilan on sympatho-adrenomedullary system in stressed rats

Effects of Blockage of Peripheral Choline, Serotonin, and Dopamine Receptors on Heart Rhythm Variability in Rats under Conditions of Stimulation of Neurotransmitter Systems

Stimulation of the serotoninergic system (5-hydroxytryptophan, 50 mg/kg; fluoxetine, 3 mg/kg) induced a significant increase in HR and a reduction in the amplitude of all waves of the heart rhythm variability. Stimulation of the dopaminergic system (L-DOPA and amantadine, 20 mg/kg each) resulted in a moderate increase in HR and amplitudes of low-frequency (LF) and very-low-frequency (VLF) waves of the heart rhythm variability. Successive blockade of nicotinic (hexamethonium, 7 mg/kg) and muscarinic cholinergic receptors (atropine, 1 mg/kg) leads to a significant decrease in the variability of cardiointervals (almost to complete levelling) both under control conditions and after stimulation of the neurotransmitter systems. Serotonin receptor blockade (promethazine, 2 mg/kg) did not affect HR, but reduced the amplitude of LF- and VLF-waves. Under conditions of serotoninergic system stimulation, the blockade of serotonin receptors was followed by a significant HR acceleration without changes in heart rhythm variability; blockade of dopamine receptors (sulpiride, 1 mg/kg) induced HR acceleration and increase in the amplitude of LF- and VLF-waves; blockade of dopamine receptors under conditions of dopamine system stimulation was followed by a significant increase in HR and a decrease in the amplitude of all waves of the heart rhythm variability. It can be hypothesized that serotonin- and dopaminergic systems affect the heart rhythm via cardiomyocyte receptors and via modulation of activity of the adrenergic and cholinergic systems. The effects of serotonin- and dopaminergic systems can be considered as synergic in the CNS, and antagonistic at the periphery.

Effect of Atropine on Adrenergic Responsiveness of Erythrocyte and Heart Rhythm Variability in Outbred Rats with Stimulation of the Central Neurotransmitter Systems

Single injection of muscarinic cholinoceptor blocker atropine (1 mg/kg) to outbred male rats reduced β-adrenergic responsiveness of erythrocytes (by 2.2 times) and the content of epinephrine granules on erythrocytes (by 1.5 times), significantly increased HR and rigidity of the heart rhythm, and manifold decreased the power of all spectral components of heart rhythm variability. Stimulation of the central neurotransmitter systems increased β-adrenergic responsiveness of erythrocytes (by 15-26%), decreased the number of epinephrine granules on erythrocytes (by 25-40%), and increased HR and cardiac rhythm intensity. These changes were most pronounced after stimulation of the serotoninergic system. Administration of atropine against the background of activation of central neurotransmitter systems did not decrease β-adrenergic responsiveness of erythrocytes (this parameter remained at a stably high level and even increased during stimulation of the dopaminergic system), but decreased the number of epinephrine granules on erythrocytes, increased HR, and dramatically decreased the power of all components of heart rhythm variability spectrum. The response to atropine was maximum against the background of noradrenergic system activation and less pronounced during stimulation of the serotoninergic system. Thus, substances that are complementary to cholinergic receptors modulated adrenergic effect on the properties of red blood cells, which, in turn, can modulate the adrenergic influences on the heart rhythm via the humoral channel of regulation. Stimulation of central neurotransmitter systems that potentiates the growth of visceral adrenergic responsiveness weakens the cholinergic modulation of the adrenergic influences, especially with respect to erythrocyte responsiveness. Hence, changes in the neurotransmitter metabolism in the body can lead to coupled modulation of reception and reactivity to adrenergic- and choline-like regulatory factors at the level of erythrocyte membranes, which can be important for regulation of heart rhythm.

Maternal restraint stress during pregnancy negatively affects behaviors and antioxidant capacity of offspring rats (Rattus norvegicus)

This study evaluated the effect of maternal restraint stress during the gestation period on behaviors, biochemical parameters, and antioxidant capacities of offspring rats (Rattus norvegicus (Berkenhout,1769)) at weaning age. Behaviors, plasma biochemical indices, and antioxidant ability of the liver, soleus muscle, and gastrocnemius muscle of mother and (or) offspring rats were analyzed. Significant increases were found in the immobility and swinging behavior frequencies of offspring male rats; no difference was found in behaviors of female rats. The antioxidant indices including superoxide dismutase, nitric oxide synthase, and total antioxidant capacity in the soleus muscle of offspring male rats were significantly decreased in the restraint group. Female offspring rats showed significant lower glutathione and higher malondialdehyde levels in the gastrocnemius muscle and liver, respectively. No difference was found in the productive performance and plasma biochemical indices of maternal rats, nor in the biochemical parameters of the two groups of weaning rats. The results suggested that maternal chronic stresses negatively affected the behaviors and antioxidant abilities of offspring rats, and that these effects possibly have a greater impact on offspring male rats than on female rats.

Emotional Stress and Cardiovascular Complications in Animal Models: A Review of the Influence of Stress Type

Emotional stress has been recognized as a modifiable risk factor for cardiovascular diseases. The impact of stress on physiological and psychological processes is determined by characteristics of the stress stimulus. For example, distinct responses are induced by acute vs. chronic aversive stimuli. Additionally, the magnitude of stress responses has been reported to be inversely related to the degree of predictability of the aversive stimulus. Therefore, the purpose of the present review was to discuss experimental research in animal models describing the influence of stressor stimulus characteristics, such as chronicity and predictability, in cardiovascular dysfunctions induced by emotional stress. Regarding chronicity, the importance of cardiovascular and autonomic adjustments during acute stress sessions and cardiovascular consequences of frequent stress response activation during repeated exposure to aversive threats (i.e., chronic stress) is discussed. Evidence of the cardiovascular and autonomic changes induced by chronic stressors involving daily exposure to the same stressor (predictable) vs. different stressors (unpredictable) is reviewed and discussed in terms of the impact of predictability in cardiovascular dysfunctions induced by stress.

Resident intruder paradigm-induced aggression relieves depressive-like behaviors in male rats subjected to chronic mild stress

Background

Accumulating epidemiological evidence shows that life event stressors are major vulnerability factors for psychiatric diseases such as major depression. It is also well known that the resident intruder paradigm (RIP) results in aggressive behavior in male rats. However, it is not known how resident intruder paradigm-induced aggression affects depressive-like behavior in isolated male rats subjected to chronic mild stress (CMS), which is an animal model of depression.

Material/Methods

Male Wistar rats were divided into 3 groups: non-stressed controls, isolated rats subjected to the CMS protocol, and resident intruder paradigm-exposed rats subjected to the CMS protocol.

Results

In the sucrose intake test, ingestion of a 1% sucrose solution by rats in the CMS group was significantly lower than in control and CMS+RIP rats after 3 weeks of stress. In the open-field test, CMS rats had significantly lower open-field scores compared to control rats. Furthermore, the total scores given the CMS group were significantly lower than in the CMS+RIP rats. In the forced swimming test (FST), the immobility times of CMS rats were significantly longer than those of the control or CMS+RIP rats. However, no differences were observed between controls and CMS+RIP rats.

Conclusions

Our data show that aggressive behavior evoked by the resident intruder paradigm could relieve broad-spectrum depressive-like behaviors in isolated adult male rats subjected to CMS.

Perturbation of mitiglinide metabolism by chronic unpredicted mild stress in rats

Many diabetic patients complicated with wild to severe depression. It is unclear in diabetic medication whether depression perturbs the drug metabolic process of the hypoglycemic agents or not. The present study was designed to investigate the impact of chronic unpredicted mild stress (CUMS) -induced depression on mitiglinide (MGN) pharmacokinetics in rats. Adult female Sprague-Dawley rats in CUMS group were subjected to different types of stressors and the stress procedures lasted for 8 weeks. Control group without receiving stress had free access to food and water. Open-field test and 5-HT levels were assayed to evaluate the depression. After CUMS all rats were given 2.5 mg/kg of mitiglinide per os. The blood samples were collected at different time and mitiglinide plasma concentration was measured by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Non-compartmental statistical moment analysis was processed with DAS software. In CMUS-induced depression group, peak concentration (Cmax), peak time (Tmax), area under curve (AUC0 → ∞), mean residence time (MRT0 → ∞), and half-life (T1/2z) were reduced while total plasma clearance (CLz/F) was increased compared to control group. These preliminary results indicated that CUMS-induced depression alter the drug metabolic process of mitiglinide in rats. This finding will be significant in clinic.

Elevated dopamine D2 receptor in prefrontal cortex of CUMS rats is associated with downregulated cAMP-independent signaling pathway

Because depression is associated with significant morbidity and functional disability, it is important to reveal the mechanism of action. A variety of studies have suggested the involvement of dopaminergic receptors in the pathophysiological mechanism of non-stress-associated depression-like behavior in rodents. Nevertheless, controversy exists about whether chronic stress acts on dopaminergic receptors in the prefrontal cortex. Thus, we investigated the level of dopamine D2 receptors (DRD2) and the possible mechanisms involved in a chronic unpredictable mild stress (CUMS) rat model of depression. The results showed CUMS-induced, depression-like symptoms in the rat, characterized by reduced sucrose consumption and body mass, and increased duration of immobility in a forced swimming test. Moreover, chronic stress upregulated the expression of DRD2 but downregulated protein kinase A (PKA), transcription factor cAMP response element binding protein (CREB), and phospho-CREB (p-CREB) in the prefrontal cortex, as demonstrated by Western blot. Notably, in the rat model of depression, decreased cyclic adenine monophosphate (cAMP) levels and PKA activity were present at the same time, which is consistent with clinical findings in depressed patients. Our findings suggested that dopaminergic system dysfunction could play a central role in stress-related disorders such as depression.

Effects of repeated maprotiline and fluoxetine treatment on gene expression of catecholamine synthesizing enzymes in adrenal medulla of unstressed and stressed rats

1 Repeated maprotiline (a noradrenaline reuptake inhibitor) and fluoxetine (a serotonin reuptake inhibitor) treatment on gene expression of catecholamine biosynthetic enzymes were examined in adrenal medulla of unstressed control and chronic unpredictable mild stressed rats. 2 Maprotiline did not change gene expression of catecholamine biosynthetic enzymes in control and stressed rats. 3 Fluoxetine increased gene expression of tyrosine hydroxylase (TH) and dopamine-β-hydroxylase (DBH), but did not phenylethanolamine N-methyltransferase in both unstressed and chronic unpredictable mild stressed animals. 4 In conclusion, we have demonstrated that repeated administration of fluoxetine enhanced gene transcription of TH and DBH and subsequently stimulates noradrenaline synthesis in adrenal medulla of control and stressed rats.

Coping style predicts the (in)sensitivity for developing hyperinsulinemia on a high fat diet in rats

The aim of this study was to explore interactions between coping style and diet as risk factors for developing insulin resistance in rats. We hypothesized that rats characterized by a passive coping strategy are more susceptible for developing insulin resistance and visceral obesity than proactively coping rats, particularly on a high (45%) fat diet. This hypothesis was tested by comparing 1) insulin and glucose responses to an intravenous glucose tolerance test (IVGTT), and 2) body fat distribution, in two rat models for passive and proactive coping styles. We found that the most extremely passive rats are characterized by elevated insulin levels during a IVGTT, even on chow. Moderately passive rats display normal insulin responses under chow conditions, but develop insulin resistance on a high fat diet. Proactive rats are remarkably resistant to insulin resistance and visceral obesity, even when overfeeding on a high fat diet. Carcass analysis revealed that passive rats are characterized by increased epididymal fat deposition, which is in line with the observed differences in insulin resistance. We conclude that a passive personality is prone to develop insulin resistance and visceral obesity on a palatable fat diet and a proactive personality might be protected against the development of diet-induced insulin resistance.