Processing cardiovascular information in the vlPAG during electroacupuncture in rats: roles of endocannabinoids and GABA

Stephanie C. Tjen-A-Looi, Peng Li, and John C. Longhurst Susan Samueli Center for Integrative Medicine, Department of Medicine, School of Medicine, University of California, Irvine, Irvine, California J Appl Physiol 106: 1793–1799, 2009. First published March 26, 2009; doi:10.1152/japplphysiol.00142.2009. The arcuate nucleus (ARC) provides excitatory to the ventrolateral periaqueductal gray (vlPAG) which then inhibits the activity of bulbospinal neurons in the RVLM. Previously this lab showed that electroacupuncture leads to reductions in GABA in the vlPAG. Suggesting the EA promotes increased inhibition on RVLM neurons and therefore decreased sympathetic nervous system activity. For this study they hypothesized that during EA endocannabinoids acting on CB1 receptor presynaptically inhibit GABA release to disinhibit the vlPAG and lead to decrease RVLM neuronal activity and ultimately decreased sympathetic output. So looked at how EA would affect gastric distention responses. When gastric distention occurs it causes a pressor response They found that EA reduced blood pressure responses significantly. They also in fatty acid amide hydrolase inhibitor, which will lead to enhanced endocannabinoids release into the vlPAG. They found that this also attenuated blood pressure responses to gastric distention. Then they gave Gabazine and then the fatty acid hydrolase inhibitor into the vlPAG and found that the gastric distention cause pressor they found similar finding with AM251, a CB1 receptor blocker. Finally they gave both Gabazine and AM251 a CB1 receptor blocker and saw that the gastric diction was still able to cause a pressor response. These findings suggest that EA leads ti attenuated sympathetic output by disinhibition of vlPAG which leads to inhibition of the neuronal activity in the RVLM. -MD

Pregnancy increases baroreflex-independent GABAergic inhibition of the RVLM in rats

Lyudmyla Kvochina, Eileen M. Hasser, and Cheryl M. Heesch Department of Biomedical Sciences and Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri Am J Physiol Regul Integr Comp Physiol 293: R2295–R2305, 2007. First published September 26, 2007; doi:10.1152/ajpregu.00365.2007. During pregnancy there is an increase in blood volume, cardiac output, mild tachycardia along with decreased arterial blood pressure. This study wanted to test if arterial baroreflex-independent GABAergic inhibition is enhanced in near-term pregnancy compared to non-pregnancy. Also because there is an interaction between Ang II and GABA and there is an upregulation of the renin-angiotensin system, they wanted to know if activation of AT1 receptors in RVLM might be different between pregnant and non-pregnant rats. In sinoaortic denervated pregnant rat Ang II was injected before blockade of AT1 receptors. In response to Ang II there was an increase in MAP and renal sympathetic nerve activity. However after blockade of AT1 receptors the response to ANG II was blocked. They also compared PE responses between non pregnant and pregnant rats before and after SAD. They found that before the SAD the change in MAP was greater in the non-pregnant compared to the pregnant. As for RSNA it was similar and HR responses in pregnant were greater than non-pregnant. After SAD the MAP was greater than pre-SAD baseline but in the pregnant animals the MAP pressure went below Pre-SAD level after 90 minutes. In response to Bicuculline, pressor and sympathoexcitation were observed however the responses in pregnant were greater. Bicuculline after AT1 blockade responses lead to attenuated responses compared to just bicuculline alone. These data suggest that baroreflex independent GABAergic inhibition might be responsible for the blunted sympathoexcitation during pregnancy and that AT1 receptors may be playing a greater role in GABAergic inhibition-MD

Hormones and the Social Brain

Authors: B. McEwen Glucocorticoids are well known steroid hormones released from the adrenal glands in response to multiple situations including immune response, metabolism, development, and other behaviors. It was recently found, that glucocorticoids may also play a role in stress related neuronal regulation by specific regulatory factors and cellular interactions. Specifically, the affects glucocorticoids have on neuronal gene-environment interactions. Novel studies have recognized glucocorticoids as co-regulators on dopaminoceptive neurons as well as dopaminergic neurons. Meaning that glucocorticoids are playing a role to regulate the neurons that accept dopamine as a neurotransmitter, and are not just directly affecting neurons that are producing dopamine. In more detail, it was found that glucocorticoids in mice bearing a risk allele for neuropsychiatric disorders increased methylation of gene responsible for tyrosine hydroxylase, reducing the amounts of dopamine in the cell. It was also found that these mice had increasing D2 receptors. However, by blocking the glucocorticoid receptor RU486 the molecular, neurochemical, and behavioral effects were prevented. These findings are relevant to many human psychotic diseases, such as depression and addiction, and get us one step closer to understanding many human psychiatric diseases. ~JI

Differential effects of acute and chronic exercise on plasticity-related genes in the rat hippocampus revealed by microarray.

Eur J Neurosci. 2002 Sep;16(6):1107-16. Molteni R, Ying Z, Gómez-Pinilla F. In this study the authors determined the effects of acute and chronic voluntary periods of exercise on the expression of genes in the hippocampus. The authors used a predesigned microarray with 1176 cDNAs primarily expressed in the brain. The animals were allowed to run voluntarily for a period of 3, 7 and 28 days. Sedentary animals were used as control. Genes associated with glutamatergic system such as NMDAR-2A, NMDAR-2B and excitatory amino acid carrier-1 was upregulated, where as GABAA receptor and GAD 65 were down-regulated. BDNF genes were consistently up-regulated across all different exercise groups. The authors hypothesized a potential mechanism by which exercise modulates neuronal plasticity in the hippocampus. It was suggested elevated BDNF expression under active conditions could affect both the pre and post synaptic terminals. TrKB receptor, the primary mediator of BDNF was also up-regulated in active animals. TrKB signaling affected the up-regulation of several downstream genes such as MAP-KI, MAP-KII, PKC gamma and CaM-KII. The authors also suggest that exercise could affect the pre synaptic genes such as synapsin, synaptotagmin and syntaxin to modulate the release of neurotransmitters such as glutamate. In the post synaptic terminal, the effects of exercise could be mediated by calcium influx through the NMDA receptor. The expression of calcium2+/calmodulin dependent protein kinase II was also up-regulated in exercise, which could activate the MAP-K cascade. Activated MAP-K could act on a nuclear target, transcription factor CREB, the expression of which is also up-regulated in exercise. -Madhan

Physical Exercise Prevents Stress-Induced Activation of Granule Neurons and Enhances Local Inhibitory Mechanisms in the Dentate Gyrus

J Neurosci. 2013 May 1;33(18):7770-7. Schoenfeld TJ, Rada P, Pieruzzini PR, Hsueh B, Gould E. “Physical exercise is known to reduce anxiety”. The ventral hippocampus is an important region that is involved in the regulation of stress and anxiety. In this study, the authors investigated the effects of exercise (running) on the ventral hippocampus after subjecting the animals to anxiety provoking stimulus. The authors tested the expression of c-fos and arc as an indirect measure to evaluate neuronal activation after performing cold water swim stress in sedentary and running mice. Stress increased the expression of the proteins tested under sedentary condition but not under active condition. In order to test whether running modifies the inhibitory activation to a stressor, the authors measured the expression of c-fos and arc by inhibitory interneurons, amount of GABA release and expression of vesicular GABA transporter (vGAT) in the hippocampus. Running increased the local inhibitory mechanisms in the hippocampus, showed by enhanced expression of vGAT and extracellular GABA release during cold water swim stress. Further blocking of GABAA receptors with bicuculline in the ventral hippocampus reversed the anxiolytic effect of running. These findings suggest that the running plays an important role in improving the regulation of anxiety through inhibitory mechanisms in the ventral hippocampus. - Madhan

Determination of the detectable concentration of manganese used in neuronal MEMRI and its effect on cortcal neurons in vitro

Authors: Y. Zhang...X. Jiang Introduction: As with many new techniques, MeMRI presents a great opportunity for in vivo and in vitro studies on the plasticity of multiple tissue types, including neuronal. With a paramagnetic characteristic and the ability to act as a Calcium analong, manganese poses as a viable contrast agent for functional and anatomical MRI. As a trace mineral, manganese naturally acts at low concentrations as a co-factor for multiple enzymes in the body. However like most things, at high concentrations manganese is considered toxic. What this study did was examine the concentration of Mn2+ sufficient for a significant increase in signal intensity during an MRI, as well as determine the concentration of Mn2+ necessary to produce neurotoxic affects. Methods: -Cultured primary cortical neurons -Immunocytochemistry -MeMRI aquisition -Intracellular Mn2+ accumulation using mass spectrometry -Cell viability, cytotoxicity, intracellular ROS, and TUNEL assays Conclusion: Two important findings came from the following experiment. 1) Mn2+ intensity does not induce a significant signal intensity at a concentration less than .05mM MnCl2 and 2) Mn2+ exposure at concentrations greater than .05mM MnCl2 produce nuerotoxic effects such as decreased cellular viability as well as membrane integrity, intracellular ROS formation, and apoptosis. Based off of these two discoveries, it was determined that for in vitro neuronal MeMRI .05mM MnCl2 is the critical concentration that allows for a significant signal intensity and limited amounts of toxicity to the cells. As important as these results are, there has still been no concrete studies done examining neurotoxcity in vivo as a result of chronic manganese injections. This does however give the field a solid preliminary base to start with. ~JI

The novel endocannabinoid receptor GPR18 is expressed in the rostral ventrolateral medulla and exerts tonic restraining influence on blood pressure

Anusha Penumarti and Abdel A. Abdel-Rahman Published on January 15, 2014 as DOI:10.1124/jpet.113.209213 It has been shown previously that an agonist for GPR18, abnormal cannabidiol (ab cbn) given systemically causes decreases in blood pressure. In this article they wanted to see if GPR18 was present in the CNS. They used several techniques in order to determine if GPR18 was present in RVLM. First they functional identified GPR18 using immunofluorescence on TH expressing neurons in the RVLM. Next they looked at whether GPR18 had a functional role in the control of cardiovascular responses. So they did intra-RVLM dose response injection of ab cbn they found that it caused decreases in BP and tachycardia in a dose dependent matter. When they gave O-1918 a GPR18 antagonist it caused increases in BP and bradycardia. They showed that activation of GPR18 causes reduction in reactive oxygen species (ROS). Tissue was collected after either giving ab cbn or O-1918 and they used a protein assay in order to qualitatively determine ROS in the RVLM. They used dihydroethidium staining (DHE) was used to show that ROS was present in RVLM. The data from this study shows that GPR18 is present in the RVLM and that activation of this receptor not only cause decreases in BP but also decreases ROS. -MD

Functional cardiovascular action of L-cysteine microinjected into pressor sites of the rostral ventrolateral medulla of the rat

Yumi Takemoto DOI 10.1007/s00726-013-1651-5 Received: 15 October 2013 / Accepted: 12 December 2013 This article investigated whether L-Cysteine was playing a role in controlling cardiovascular responses in the RVLM. They first identified RVLM using glutamate and then they injected different doses of L-cysteine (1mM -100mM). In order to see if glutamate receptors are playing a role in mediating this response they injected antagonists MK801 for NMDA or CNQX for AMPA and then they repeated the L-cysteine. They found that L-cysteine caused significant increases in arterial blood pressure (ABP) and heart rate (HR). They noticed that only when the antagonists were injected together that the L-cysteine actions were blocked. These data suggest that L-cysteine mediates it effects on the cardiovascular system by acting on NMDA and non NMDA receptors.-MD

Mangenese-enhanced MRI reflects seizure outcome in a model mesial temporal lobe epilepsy.

By: Dedeurwaerdere..O'Brien Introduction: Over the past few decades, mangenese-enhanced magnetic resonance imaging (MeMRI) has been developed as a tool in studying brain structure and neuronal activity in vivio. As a paramagnetic ion, it works as a functioning contrast agent for MR imaging, with the benefits of being essentially non-toxic at low doses. Utilizing this technique, this paper was able to look at neurological changes in an epileptic model compared to a normal standard, in order to better understand the changes occurring in various sub-fields of the hippocampus. In the kainic acid-induced epileptic model (KASE) increases in mossy fibre were seen compared to the normal non-epileptic model. Methods: -Implantation of guide cannula in order to induce Kainic Acid-Induced Epilepsy (KASE) -MeMRI acquisition and analysis -Video EEG Monitoring -Histology Results: The chronic stage KASE model experienced decreased hippocampal volume and enlarged ventricle. Where as, early and chronic KASE models were seen to have significantly decreased CA1 sub-regions of the hippocampus. Interestingly, after MeMRI analysis it was found that both the DG and CA1 regions had increased mangenese voxel intensities in the KASE model. It turned out that an inverse correlation was found between MeMRI signal intensity in the DG of the chronic model and future epileptic seizing. It was also observed using histology, that chronic KASE models had increased mossy fibre sprouting. However, this increase did not correlate with spontaneous seizing or MeMRI voxel intensity. It is thought that increased mossy fibre growth may have been counterbalanced in MeMRI by overall cell loss. It is still uncertain as to why an inverse correlation was found between MeMRI intensity and future seizing in the chronic KASE model, and needs further investigation. ~JI

Median preoptic nucleus and subfornical organ drive renal sympathetic nerve activity via a glutamatergicmechanism within the paraventricular nucleus.

Am J Physiol Regul Integr Comp Physiol. 2012 Feb 15;302(4):R424-32. Llewellyn T, Zheng H, Liu X, Xu B, Patel KP. “The paraventricular nucleus (PVN) of the hypothalamus is involved in the neural control of sympathetic drive, but the precise mechanism(s) that influences the PVN is not known”. The authors hypothesized that glutamatergic activation of higher brain centers such as the median preoptic nucleus (MnPO) and subfornical organ (SFO) could influence PVN. To test this hypothesis, the authors performed several microinjection experiments. First they injected a retrograde tracer into the PVN and visualized it in the MnPO and SFO confirming a neuroanatomical connection. Second they activated MnPO by microinjection of NMDA or bicuculline and demonstrated an increase in RSNA, blood pressure and heart rate. To test whether these effects are mediated through PVN, they blocked PVN using AP5 (glutamate receptor blocker) and repeated the experiment and found MnPO activation after blocking PVN does not produce the same cardiovascular effects, suggesting the effects are mediated through PVN. Further firing activity of PVN neurons were tested by activation of neurons in the MnPO. Finally, similar to MnPO, SFO was activated before and after blockade of PVN. Changes in RSNA, blood pressure and heart rate were recorded. The findings from this study suggest that glutamatergic activation of the PVN is at least partially mediated by activation of MnPO and SFO. -Madhan

Effects of exercise training on SFO-mediated sympathoexcitation during chronic heart failure.

Am J Physiol Heart Circ Physiol. 2014 Jan;306(1):H121-31. Llewellyn TL, Sharma NM, Zheng H, Patel KP. “Exercise training (ExT) has been shown to reduce sympathetic drive during heart failure (HF)”. Recently the authors from this laboratory showed that the paraventricular nucleus (PVN) of the hypothalamus was activated in rats with HF and exercise training (EXT) normalized this effect but the mechanisms that mediate the enhanced activation of the PVN are unknown. Subfornical organ (SFO) is a circumventricular organ that lacks blood brain barrier and has been shown to have neuronal connections with the PVN. In the present study, the authors hypothesized that SFO is activated in HF and contributes to the regulation of sympathetic drive in HF. To test this hypothesis, the authors performed several experiments. First, they induced HF in normal SD rats and found these rats had increased neuronal activity in the SFO compared to normal rats. Second, angiotensin II was microinjected in the SFO, which increased renal SNA, blood pressure and heart rate in the HF animals compared to rats without HF. Third, Losartan (AT1 receptor blocker) was microinjected in the SFO to confirm that angiotensin II effects are mediated through AT1 receptor. Losartan decreased RSNA in HF rats. Finally biochemical changes of AT1 receptors in the SFO showed elevated expression in HF rats. Exercise treatment reversed the changes at each experimental condition. These findings suggests that enhanced ang II in the SFO contributes to the activation of SFO and in turn leads to sympathoexcitation in HF and these effects could be reversed by exercise training. - Madhan

Cardiovascular Toxicities Upon Manganese Exposure

By: y. Jiang and W. Zheng Some of the first recorded signs of manganese(Mn) toxicity were observations made by Kobert in the late 1800's, showing that Mn salts can decrease blood pressure certain animals models. Since, multiple studies have been done to examine Mn toxicity, both in human and animal models, producing a variety of inconclusive results. In animals models, chronic Mn has been correlated to decreases in myocardial action potential durability that leads to increased calcium free conditions in the myocardiocytes. As an effect of less calcium a decline in contractile force is seen. However, acute models were found to have no effects on dog ECG's. On the other hand, outside of the heart acute doses of Mn also has some effects on blood vessel tone. Specifically, following high doses of acute Mn (10mg/kg), perfused through the inferior vena cava, is vasodialation and significant decreases blood pressure. Even less studies have been done looking at human Mn toxicity. From limited current literature, cardiovascular toxicity in humans its been shown correlated to chronic exposure, most due from environmental contamination in factories and mines. Overall, women tend to be more susceptible then men, however both sex's have been showed increased vasodialation and decreased heart rates due to decreased parasympathetic sensitivity. Possible mechanisms for this include reduced levels of serotonin, which causes vasoconstriction, and reduced superoxide dismutase activity causing increased vasodialation. In conclusion, studies examining Mn cardiovascualar toxcicity are still much needed for animal and human models. It does seems that some cardiovascular toxicities in both models can occur with chronic exposure to Mn. To what extent and exactly what mechanism these effects are occurring are still unknown. ~JI

Pregnancy decreases GABAergic inhibition of the hypothalamic paraventricular nucleus

Physiology & Behavior 97 (2009) 171–179 doi:10.1016/j.physbeh.2009.02.018 Lyudmyla Kvochina, Eileen M. Hasser, Cheryl Heesch During pregnancy it has been shown that the baroreflex ability to increase sympathetic nerve activity is attenuated in response to low blood pressures. However resting sympathetic tone for heart rate and the vasculature was still elevated during pregnancy. The purpose of this study was to see if tonic GABAergic inhibition in PVN is decreased in response to pregnancy. They used pregnant and non-pregnant female Sprague Dawley rats in order to conduct their study. They microinjected AT1 receptor blocker before GABA A receptor blockade in PVN, they showed attenuation in the increase in BP and RSNA in response to GABA AR blockade. They also added an excitatory amino acid receptor blocker with the AT1 receptor blocker in order to determine the effect it would have on GABA A receptor blockade. They found that the response was to GABA A receptor blockade was completely eliminated in pregnancy. They also added kyn with AT 1 receptor blockade and showed no difference in AT1 receptor blockade alone in pregnancy. They also showed that increases in RSNA in response to GABA A receptor blockade were attenuated in pregnant rats. The conclusion is that GABAergic inhibition of presympathetic nerves in PVN may be decrease which may be the cause of the enhanced resting symapathetic nerve activity. -MD

Does acute hyperglycemia alter rat aortic depressor nerve function

Braz journal of Medical Biological Research (2007) 40: 15567-1576 Issn 0100-879x D.A Huber, J. M. do Carmo, J.A. Castania, R. Fazan Jr. and H.C. Salgado It has been shown that diabetes alters baroreflex function. In this present study they wanted to determine what arm of the baroreflex is being altered in response to diabetes. So the recorded the left aortic depressor nerve activity and blood pressure responses. They checked baroreflex activity before and 30minutes after infusion of 0.9% saline, 30% glucose, or 30% mannitol. They assessed baroflex activity in two ways one was by a single bolus of Phenylephrine (8ug/kg) and sodium nitroprusside (16ug/kg) and the other way was by remove and replacing blood in order to change blood pressure by 10mm Hg. What they found was that acute changes of glucose or mannitol in the blood do not lead to changes in the afferent arm of the baroreflex. This finding suggests that the changes that occur in the baroreflex in response to diabetes may be occurring either in the central nervous system or the efferent arm of the baroreflex. -MD

Inhibition of brown adipose tissue thermogenesis by neurons in the ventrolateral medulla and in the nucleus tractus solitarius.

Am J Physiol Regul Integr Comp Physiol. 2010 Jul;299(1):R277-90. Cao WH, Madden CJ, Morrison SF “Neurons in the ventrolateral medulla (VLM) and in the nucleus tractus solitarius (NTS) play important roles in the regulation of cardiovascular and other autonomic functions”. In this study, the authors demonstrated how activation of neurons in the VLM and intermediate NTS affected brown adipose tissue (BAT) thermogenesis. The authors performed a series of microinjection experiment in chloralose/urethane-anesthetized rats to test their hypothesis. First they tested the effects of activation of neurons in the VLM on cold evoked BAT thermogenesis. NMDA (glutamate agonist) was injected in the VLM to observe that it reversed the cold-evoked increase in BAT SNA, thermogenesis and end-expired CO2. Second they tested the effects of disinhibition of neurons in the VLM or in the NTS on BAT thermogenesis under different conditions using bicuculline (GABA-A receptor antagonist), which reversed the increase in BAT SNA, thermogenesis and end-expired CO2. Finally the tested the effects of inhibition of neurons in the VLM and NTS using muscimol (GABA-A receptor agonist), which produced increases in BAT SNA, thermogenesis and end-expired CO2. These effects were reversed using injection of glycine in the rRPa. These findings suggest that BAT thermogenesis is inhibited by activation of VLM and NTS neurons. -Madhan

α2 Adrenergic receptor-mediated inhibition of thermogenesis.

J Neurosci. 2013 Jan 30;33(5):2017-28. Madden CJ, Tupone D, Cano G, Morrison SF. “α2 adrenergic receptor (α2-AR) agonists have been used as antihypertensive agents, in the management of drug withdrawal, and as sedative analgesics”. In this study, the authors investigated the effects of α2-AR agonists as antipyretic agents. Clonidine (α2-AR agonist) was administered into the rostral raphe pallidus area (neurons in this region regulate sympathetic outflow to brown adipose tissue (BAT), which regulates thermogenesis), which inhibited BAT sympathetic nerve activity and thermogenesis. The authors reversed the effects of clonidine injection by administration of α2-AR antagonist idazoxan into rRPa. The effects of α2-AR agonists were also tested using systemic injections of its agonists, which produced responses similar to central administration. An interesting observation in the present study involves the use of CtB as a retrograde tracer from rRPa and pseudorabies virus as a transynaptic tracer from BAT to demonstrate that VLM was the source of catecholaminergic input to the rRPa and these neurons are synaptically connected to BAT. Furthermore, the authors used optogenetic technique to stimulate the neurons in the VLM and thereby activate 2-ARs in the rRPa, which inhibited BAT SNA. Taken together these findings suggest that α2-AR agonist can be used to treat excessive body temperature during fever. -Madhan

In vivo manganese MR imaging of calcium influx in spontaneous rat pituitary adenoma.

Cross DJ, Flexman JA, Anzai Y, Sasaki T, Treuting PM, Maravilla KR, Minoshima S. AJNR Am J Neuroradiol. 2007 Nov-Dec;28(10):1865-71 During a study on aged rats, the authors of this paper found that some of their critters had spontaneously developed pituitary adenomas. Not wanting to waste “bad” animals, they reasoned that they could use these rats to study the calcium-dependent release of hormones with manganese (Mn) enhanced magnetic resonance imaging. Because Mn enters cells through calcium channels, they used Mn as a way to study uptake of calcium in to cancerous neuroendocrine cells. They found that adenomas took up the Mn faster than pituitaries from normal rats, and that they were able to absorb it faster. However, efflux seemed to be about the same between groups from about 2 days on. The increase in pituitary voxel intensity showed dose-dependent decreases when an L-type calcium channel blocker was given intranasally to the rats with almost a complete block at the 3-uL 5mg/mL dose (rat weight not mentioned). Using radioactive fluorodeoxyglucose (FDG) and PET scans, they saw that manganese uptake was greatest in more metabolically active tissue and was correlated with tumor size, though FDG uptake was not as well correlated with tumor size. What I found most interesting about this paper was not addressed in the text; that the signal intensity was still strong (15%ish) even after 10 days. In our own lab we recently saw a rat with an unexpectedly high signal after 12 days, so maybe reading more papers like this could help us figure out where we should be setting our expectations. -DH

Pharmacological rescue of mitochondrial deficits in iPSC-derived neural cells from patients with familial Parkinson's disease.

Cooper O, Seo H, Andrabi S, Guardia-Laguarta C, Graziotto J, Sundberg M, McLean JR, Carrillo-Reid L, Xie Z, Osborn T, Hargus G, Deleidi M, Lawson T, Bogetofte H, Perez-Torres E, Clark L, Moskowitz C, Mazzulli J, Chen L, Volpicelli-Daley L, Romero N, Jiang H, Uitti RJ, Huang Z, Opala G, Scarffe LA, Dawson VL, Klein C, Feng J, Ross OA, Trojanowski JQ, Lee VM, Marder K, Surmeier DJ, Wszolek ZK, Przedborski S, Krainc D, Dawson TM, Isacson O. Sci Transl Med. 2012 Jul 4;4(141):141ra90 This was a paper I read that I really thought I was going to like, but once I read through it something seemed to be missing. I thought that there were some experiments that probably should have been done that didn’t get included in the paper, and some things that were in there without a good rationale or explanation. Then again, I could have just missed out on finding their explanations… In this paper, the authors used fibroblasts isolated from people which were found positive for markers of familial Parkinson’s disease. They attempted to test the interaction of familial mutations and different chemical stressors by making the fibroblasts into induced pluripotent stem cells and then differentiating them into neural cells. They assessed the health of the induced dopaminergic neurons by measuring mitochondrial function as the mutations they studied were in PINK1 and LRRK2, two proteins known to be involved in mitochondrial turnover. So what kind of things do I think were missing? Well, one thing that concerned me was that the cultures of differentiated “neural cells” they used included dopaminergic cells along with non-dopaminergic and immature cells in unspecified proportions. All cells were treated the same way (with drugs that did not act specifically on dopaminergic cells), but the observed effects were attributed to the dopaminergic cells. One obvious thing that I would have done was to use a chemical stressor with a good specificity to dopaminergic cells, like MPTP. People have known how MPTP induces parkinsonism by selective dopaminergic neurotoxicity for decades, so why they would leave out something like that is kind of a mystery to me. I don’t want to bash the paper, because I liked the idea and some of the results, but it seems like the experimental design was lacking, or maybe that there were so many groups/authors each doing a part of the study that nobody could really agree on one central thread that they should follow. Given that we’re starting some new studies with a lot of input and help from different people/specialties, the hazard of this kind of thing has been wobbling around in my brain for a while. I’m just hoping that we can manage to keep our eyes on the prize of forming a grand unified theory of RVLM and not get caught with too many fingers in the pie. Also I’m hoping to stop mixing my metaphors. -DH

Neurosteroid modulation of arterial baroreflex function in the rostral ventrolateral medulla

Cheryl M. Heesch A positive modulator of GABA A receptors is progesterone metobilite 3α-hydroxy-dihydroprogesterone. We know that during pregnancy and ovarian cycle that the amount of progesterone fluctuates depending on the stage. The purpose of this study was to investigate the effects of pregnancy on pregnancy and if this could be imitated in non-pregnant rats. In order to test this GABA and 3α-OH-DHP or 3β-OH-DHP was injected into the RVLM. They used GABA in order to find RVLM.The right NTS was lesion in order to prevent baroreflex compensation. Then the baroreflex was tested before and after the injections. They found that the MAP baseline between the active metabolite 3α-OH_DHP and the inactive metabolite 3β-OH-DHP. When they checked the baroreflex they found that the difference within group for the active metabolite compared to the control value was different. As for the inactive the found no difference in comparison to control values. They found that 3α-OH-DHP lead to suppression of arterial baroreflex sympathoexcitation. -MD

Cardiovascular response to group I metabotropic glutamate receptor activation in NTS

C. Michael Foley, Helen W. Vogl, Patrick J. Mueller, Meredith Hay, and EileenM. Hasser The NTS plays a role in arterial baroreflex. We know that glutamate is the primary neurotransmitter. This article primary focus was group 1 mGLU receptors role in the control of the cardiovascular system. They recorded LSNA along with blood pressure. They microinjected 3,5 dihydroxyphenylglycine (DHPG) is a selective group 1 mGLUR agonist, and 1-aminocyclopentane-1S3 R dicarboxylic acid (ACPD) is a general mGLUR agonist. Both caused similar decreases in blood pressure and LSNA. Next they tested whether mGLUR receptor blockade would prevent the responses seen previously with DHPG and ACPD. They found in α-methyl-4-carboxyphenylgylcine blocked DHPG and ACPD responses. Next they looked at ionotropic glutamate receptors role in mediating the DHPG and ACPD response. They found that kyn did not attenuate DHPG response but potentiated the ACPD response. These data show that DHPG and ACPD activate group I mGLUR and that even in the presence of ionotropic glutamate receptor blocade they are able to still cause changes in blood pressure and nerve activity. -MD