Glutamatergic, GABAergic, and endocannabinoid neurotransmissions within the dorsal hippocampus modulate the cardiac baroreflex function in rats

A New Target of Electroacupuncture Pretreatment Mediated Sympathetic Nervous to Improve MIRI: Glutamatergic Neurons in Fastigial Nucleus of the Cerebellum

Ischemic heart disease is a fatal cardiovascular disease that irreversibly impairs the function of the heart, followed by reperfusion leading to a further increase in infarct size. Clinically, we call it myocardial ischemia-reperfusion injury (MIRI). A growing number of clinical observations and experimental studies have found electroacupuncture (EA) to be effective in alleviating MIRI. This study attempts to investigate whether glutamatergic neurons in fastigial nucleus (FN) of the cerebellum are involved in EA pretreatment to alleviate MIRI via sympathetic nerves, and the potential mechanisms of EA pretreatment process. A MIRI model was established by ligating the coronary artery of the left anterior descending branch of the heart for 30 minutes, followed by 2 hours of reperfusion. Multichannel physiological recordings, electrocardiogram, cardiac ultrasound, chemical genetics, enzyme-linked immunosorbent assay and immunofluorescence staining methods were combined to demonstrate that EA pretreatment inhibited neuronal firing and c-Fos expression in FN of the cerebellum and reduced cardiac sympathetic firing. Meanwhile, EA pretreatment significantly reduced cardiac ejection fraction (EF), shortening fraction (SF), percentage infarct area, decreased myocardial norepinephrine (NE), creatine kinase isoenzyme MB (CK-MB) concentrations, and improved MIRI-induced myocardial tissue morphology. The results were similar to the inhibition of glutamatergic neurons in FN. However, the activation of glutamatergic neurons in FN diminished the aforementioned effects of EA pretreatment. This study revealed that glutamatergic neurons in FN of the cerebellum is involved in EA pretreatment mediated sympathetic nervous and may be a potential mediator for improving MIRI.

Agarwood essential oil inhalation exerts antianxiety and antidepressant effects via the regulation of Glu/GABA system homeostasis

Depression and anxiety are common diseases that endanger the physical and mental health of individuals. Agarwood incense inhalation has been used as a traditional Chinese medicine for relaxation and to improve sleep for centuries. In a previous study by the authors it was demonstrated that agarwood essential oil (AEO) injection exerted anxiolytic and antidepressant effects. Therefore the present study further investigated the anxiolytic and antidepressant effects of AEO inhalation on anxiolytic mice induced by M-chlorophenylpiperazine and depressive mice induced by chronic unpredictable mild stress. The results demonstrated that AEO exerted a significant anxiolytic effect, whereby autonomous movements were inhibited during the light dark exploration test and open field test. Furthermore, the tail suspension test and the forced swimming test demonstrated that AEO also exerted an antidepressant effect, whereby the immobility times were decreased. Moreover, AEO was determined to increase the levels of 5-hydroxytryptamine, γ-aminobutyric acid (GABA) A receptor (GABA_A) and glutamate (Glu) in anxiolytic mice and inhibit the levels of GABA_A and Glu in depressive mice. Further investigations into how AEO affected the Glu/GABA system demonstrated that AEO markedly increased the protein expression levels of GABA transaminase (GABAT), glutamate metabotropic receptor 5 (GRM5), glutamate ionotropic receptor AMPA type subunit 1 (GluR1) and vesicular glutamate transporter 1 (VGluT1). Furthermore, AEO reduced the expression levels of GABAT, glutamate ionotropic receptor NMDA type subunit 2B and GRM5, and enhanced the expression levels of GluR1 and VGluT1. These results demonstrated that AEO potentially possesses antianxiety and antidepressant properties. The present study determined that the mechanism was related to the regulation of Glu/GABA neurotransmitter system homeostasis.

D-Serine: A Cross Species Review of Safety

Background:D-Serine, a direct, full agonist at the D-serine/glycine modulatory site of the N-methyl-D-aspartate-type glutamate receptors (NMDAR), has been assessed as a treatment for multiple psychiatric and neurological conditions. Based on studies in rats, concerns of nephrotoxicity have limited D-serine research in humans, particularly using high doses. A review of D-serine's safety is timely and pertinent, as D-serine remains under active study for schizophrenia, both directly (R61 MH116093) and indirectly through D-amino acid oxidase (DAAO) inhibitors. The principal focus is on nephrotoxicity, but safety in other physiologic and pathophysiologic systems are also reviewed. Methods: Using the search terms "D-serine," "D-serine and schizophrenia," "D-serine and safety," "D-serine and nephrotoxicity" in PubMed, we conducted a systematic review on D-serine safety. D-serine physiology, dose-response and efficacy in clinical studies and dAAO inhibitor safety is also discussed. Results: When D-serine doses >500 mg/kg are used in rats, nephrotoxicity, manifesting as an acute tubular necrosis syndrome, seen within hours of administration is highly common, if not universal. In other species, however, D-serine induced nephrotoxicity has not been reported, even in other rodent species such as mice and rabbits. Even in rats, D--serine related toxicity is dose dependent and reversible; and does not appear to be present in rats at doses producing an acute Cmax of <2,000 nmol/mL. For comparison, the Cmax of D-serine 120 mg/kg, the highest dose tested in humans, is ~500 nmol/mL in acute dosing. Across all published human studies, only one subject has been reported to have abnormal renal values related to D-serine treatment. This abnormality did not clearly map on to the acute tubular necrosis syndrome seen in rats, and fully resolved within a few days of stopping treatment. DAAO inhibitors may be nephroprotective. D-Serine may have a physiologic role in metabolic, extra-pyramidal, cardiac and other systems, but no other clinically significant safety concerns are revealed in the literature. Conclusions: Even before considering human to rat differences in renal physiology, using current FDA guided monitoring paradigms, D-serine appears safe at currently studied maximal doses, with potential safety in combination with DAAO inhibitors.

Proof of mechanism and target engagement of glutamatergic drugs for the treatment of schizophrenia: RCTs of pomaglumetad and TS-134 on ketamine-induced psychotic symptoms and pharmacoBOLD in healthy volunteers

Glutamate neurotransmission is a prioritized target for antipsychotic drug development. Two metabotropic glutamate receptor 2/3 (mGluR2/3) agonists (pomaglumetad [POMA] and TS-134) were assessed in two Phase Ib proof of mechanism studies of comparable designs and using identical clinical assessments and pharmacoBOLD methodology. POMA was examined in a randomized controlled trial under double-blind conditions for 10-days at doses of 80 or 320 mg/d POMA versus placebo (1:1:1 ratio). The TS-134 trial was a randomized, single-blind, 6-day study of 20 or 60 mg/d TS-134 versus placebo (5:5:2 ratio). Primary outcomes were ketamine-induced changes in pharmacoBOLD in the dorsal anterior cingulate cortex (dACC) and symptoms reflected on the Brief Psychiatric Rating Scale (BPRS). Both trials were conducted contemporaneously. 95 healthy volunteers were randomized to POMA and 63 to TS-134. High-dose POMA significantly reduced ketamine-induced BPRS total symptoms within and between-groups (p < 0.01, d = -0.41; p = 0.04, d = -0.44, respectively), but neither POMA dose significantly suppressed ketamine-induced dACC pharmacoBOLD. In contrast, low-dose TS-134 led to moderate to large within and between group reductions in both BPRS positive symptoms (p = 0.02, d = -0.36; p = 0.008, d = -0.82, respectively) and dACC pharmacoBOLD (p = 0.004, d = -0.56; p = 0.079, d = -0.50, respectively) using pooled across-study placebo data. High-dose POMA exerted significant effects on clinical symptoms, but not on target engagement, suggesting a higher dose may yet be needed, while the low dose of TS-134 showed evidence of symptom reduction and target engagement. These results support further investigation of mGluR2/3 and other glutamate-targeted treatments for schizophrenia.

Differential roles of hippocampal nNOS and iNOS in the control of baroreflex function in conscious rats

The baroreflex is a prominent moment-to-moment mechanism regulating the blood pressure. The hippocampus is a limbic structure in which has been pointed out as part of central network regulating baroreflex. However, the local neurochemical mechanisms involved in control of baroreflex function are not completely understood. Thus, this study aimed to investigate the involvement of nitrergic neurotransmission present in the dorsal hippocampus in baroreflex control of heart rate in conscious rats. For this, we evaluated the effect of bilateral microinjection into the dorsal hippocampus of either the nitric oxide (NO) scavenger carboxy-PTIO, the selective neuronal nitric oxide synthase (nNOS) inhibitor Nω-Propyl-l-arginine (NPLA) or the selective inducible nitric oxide synthase (iNOS) inhibitor 1400 W in bradycardia evoked by blood pressure increases in response to intravenous infusion of phenylephrine, and tachycardia caused by blood pressure decreases evoked by intravenous infusion of sodium nitroprusside. Bilateral microinjection of carboxy-PTIO into the dorsal hippocampus decreased the baroreflex tachycardic response without affecting the reflex bradycardia. Hippocampus treatment with NPLA increased the baroreflex bradycardia gain without affecting the reflex tachycardia. Bilateral hippocampal treatment with 1400 W decreased the reflex tachycardia and increased the baroreflex bradycardic response. Overall, these findings provide evidence that hippocampal nitrergic mechanisms acting in a NOS isoform-specific manner plays a prominent role in control of baroreflex function. Indeed, the results indicate that nNOS and iNOS exerts an inhibitory influence on reflex bradycardia, whereas iNOS mediates the reflex tachycardia.

GABAergic contribution to the muscle mechanoreflex-mediated heart rate responses at the onset of exercise in humans

Previous studies have indicated that central GABAergic mechanisms are involved in the heart rate (HR) responses at the onset of exercise. On the basis of previous research that showed similar increases in HR during passive and active cycling, we reasoned that the GABAergic mechanisms involved in the HR responses at the exercise onset are primarily mediated by muscle mechanoreceptor afferents. Therefore, in this study, we sought to determine whether central GABA mechanisms are involved in the muscle mechanoreflex-mediated HR responses at the onset of exercise in humans. Twenty-eight healthy subjects (14 men and 14 women) aged between 18 and 35 yr randomly performed three bouts of 5-s passive and active cycling under placebo and after oral administration of diazepam (10 mg), a benzodiazepine that produces an enhancement in GABA_A activity. Beat-to-beat HR (electrocardiography) and arterial blood pressure (finger photopletysmography) were continuously measured. Electromyography of the vastus lateralis was obtained to confirm no electrical activity during passive trials. HR increased from rest under placebo and further increased after administration of diazepam in both passive (change: 12 ± 1 vs. 17 ± 1 beats/min, P < 0.01) and active (change: 14 ± 1 vs. 18 ± 1 beats/min, P < 0.01) cycling. Arterial blood pressure increased from rest similarly during all conditions ( P > 0.05). Importantly, no sex-related differences were found in any variables during experiments. These findings demonstrate, for the first time, that the GABAergic mechanisms significantly contribute to the muscle mechanoreflex-mediated HR responses at the onset of exercise in humans. NEW & NOTEWORTHY We found that passive and voluntary cycling evokes similar increases in heart rate and that these responses were enhanced after diazepam administration, a benzodiazepine that enhances GABA_A activity. These findings suggest that the GABAergic system may contribute to the muscle mechanoreflex-mediated vagal withdrawal at the onset of exercise in humans.