GABA mechanisms of the nucleus of the solitary tract regulates the cardiovascular and sympathetic effects of moxonidine

Assessment of drug-drug interactions between moxonidine and antiepileptic drugs in the maximal electroshock seizure test in mice

Hypertension is a common comorbid condition with epilepsy, and drug interactions between antihypertensive and antiepileptic drugs (AEDs) are likely in patients. Experimental studies showed that centrally active imidazoline compounds belonging to antihypertensive drugs can affect seizure susceptibility. The purpose of this study was to assess the effect of moxonidine, an I₁ -imidazoline receptor agonist, on the anticonvulsant efficacy of numerous AEDs (carbamazepine, phenobarbital, valproate, phenytoin, oxcarbazepine, topiramate and lamotrigine) in the mouse model of maximal electroshock. Besides, the combinations of moxonidine and AEDs were investigated for adverse effects in the passive avoidance task and the chimney test. Drugs were administered intraperitoneally (ip). Moxonidine at doses of 1 and 2 mg/kg ip did not affect the convulsive threshold. Among tested AEDs, moxonidine (2 mg/kg) potentiated the protective effect of valproate against maximal electroshock. This interaction could be pharmacodynamic because the brain concentration of valproate was not significantly changed by moxonidine. The antihypertensive drug did not cause adverse effects when combined with AEDs. This study shows that moxonidine may have a neutral or positive effect on the anticonvulsant activity of AEDs in patients with epilepsy. The enhancement of the anticonvulsant action of valproate by moxonidine needs further investigations to elucidate potential mechanisms involved.

Effect of adzuki bean sprout fermented milk enriched in γ-aminobutyric acid on mild depression in a mouse model

This study focused on the ability of adzuki bean (Vigna angularis) sprout fermented milk, which is rich in γ-aminobutyric acid (GABA), to relieve anxiety and mild depression. A high-yield GABA-producing strain, Lactobacillus brevis J1, from a healthy cow was screened, and its physiological and probiotic properties were evaluated. The effect of adzuki bean sprout fermented milk was investigated in vivo in a chronic depression mouse model. The results showed that Lb. brevis J1 had excellent probiotic properties, grew well at low pH and 3% NaCl, and adhered to the surface of HT-29 cells. The GABA-enriched (241.30 ± 1.62 µg/mL) adzuki bean sprout fermented milk prepared with Streptococcus thermophilus, Lactobacillus bulgaricus, and Lactobacillus plantarum, and Lb. brevis J1 can reduce and possibly prevent mild depression-like symptoms in mice (C57/B6) by increasing social interaction and enhancing the pleasure derived from movement. The research revealed that the GABA_B-cyclic AMP-protein kinase A-cAMP-response element binding protein (GABA_B-cAMP-PKA-CREB) signaling pathway was related to the depression-like symptoms and that levels of 5-hydroxytryptamine, norepinephrine, and dopamine in the hippocampus of mice increased after treatment with the adzuki bean sprout fermented milk. Our results suggest that GABA-enriched dairy products have the potential to prevent or treat mild depression-like symptoms in mice, which suggests a new approach for a dietary therapy to treat chronic social stress.

GABAB receptors in the hypothalamic paraventricular nucleus mediate β-adrenoceptor-induced elevations of plasma noradrenaline in rats

In the brain, various neurotransmitters such as noradrenaline and GABA regulate peripheral sympathetic functions. Previously, it has been reported that both β-adrenoceptor activation and GABA_B receptor activation in the brain are involved in the elevation of plasma noradrenaline levels. However, it is unknown whether these pathways interact with each other. In the present study, we examined the relationship between the central actions of β-adrenoceptor activation and GABA_B receptor activation with regard to plasma noradrenaline responses using urethane-anesthetized rats. Intracerebroventricular pretreatment with the GABA_A receptor antagonist bicuculline did not affect the β-adrenoceptor agonist isoproterenol-induced elevation of plasma noradrenaline levels. In contrast, pretreatment with the GABA_B receptor antagonist CGP 35348 suppressed the isoproterenol-induced elevation of noradrenaline levels. Intracerebroventricular pretreatment with the β-adrenoceptor antagonist propranolol did not alter the GABA_B receptor agonist baclofen-induced elevation of plasma noradrenaline levels. We next examined the central effects of β-adrenoceptor activation on GABA release in the paraventricular hypothalamic nucleus (PVN), the major integrative center for sympathetic regulation in the brain. Intracerebroventricular administration of isoproterenol increased GABA content in PVN dialysates. In addition, baclofen microinjected unilaterally into the PVN resulted in elevated plasma levels of noradrenaline, but not adrenaline. Finally, unilateral blockade of GABA_B receptors in the PVN suppressed the isoproterenol-induced elevation of plasma noradrenaline level. Our results suggest that activation of β-adrenoceptors in the brain, likely in the PVN, induces GABA release in the PVN, which in turn activates GABA_B receptors in the PVN, leading to elevated plasma noradrenaline.

Cardiovascular Effects Mediated by Imidazoline Drugs: An Update

OBJECTIVE

Clonidine is a centrally acting antihypertensive drug. Hypotensive effect of clonidine is mediated mainly by central α2-adrenoceptors and/or imidazoline receptors located in a complex network of the brainstem. Unfortunately, clonidine produces side effects such as sedation, mouth dry, and depression. Moxonidine and rilmenidine, compounds of the second generation of imidazoline drugs, with fewer side effects, display a higher affinity for the imidazoline receptors compared with α2-adrenoceptors. The antihypertensive action of these drugs is due to inhibition of the sympathetic outflow primarily through central I1-imidazoline receptors in the RVLM, although others anatomical sites and mechanisms/receptors are involved. Agmatine is regarded as the endogenous ligand for imidazoline receptors. This amine modulates the cardiovascular function. Indeed, when administered in the RVLM mimics the hypotension of clonidine.

RESULTS

Recent findings have shown that imidazoline drugs also exert biological response directly on the cardiovascular tissues, which can contribute to their antihypertensive response. Currently, new imidazoline receptors ligands are in development.

CONCLUSION

In the present review, we provide a brief update on the cardiovascular effects of clonidine, moxonidine, rilmenidine, and the novel imidazoline agents since representing an important therapeutic target for some cardiovascular diseases.

Neurocardiology: Cardiovascular Changes and Specific Brain Region Infarcts

There are complex and dynamic reflex control networks between the heart and the brain, including cardiac and intrathoracic ganglia, spinal cord, brainstem, and central nucleus. Recent literature based on animal model and clinical trials indicates a close link between cardiac function and nervous systems. It is noteworthy that the autonomic nervous-based therapeutics has shown great potential in the management of atrial fibrillation, ventricular arrhythmia, and myocardial remodeling. However, the potential mechanisms of postoperative brain injury and cardiovascular changes, particularly heart rate variability and the presence of arrhythmias, are not understood. In this chapter, we will describe mechanisms of brain damage undergoing cardiac surgery and focus on the interaction between cardiovascular changes and damage to specific brain regions.