Manganese-enhanced MRI to evaluate neurodegenerative changes in a rat model of kainic acid-induced excitotoxicity

Authors: Melda Apaydin...Dilek Taskiran

Background: Kainic acid is a neuro-excitotoxic agent that can be used to study neurodegeneration in animals such as rats. As a specific agonist to kainate receptors kainic acid is able to modulate transmission and excitability. For this study, MeMRI was used to study in-vivo changes of neurons in response to kainic acid-induced excitotoxicity.

Methods:

• KA unilateral injections
• MeMRI (I.P 40mg/kg one injection)
• Bax immunohistochemistry
• Timm's Staining

Results:

• Hyperintensity was observed, as expected, in the hippocampal area in the side of the KA-injections. With a significant difference found between the ipsilateral sites of the injection and the contralateral sites.
• Bax immunohistochemistry was used to assess apoptotic cell death in regions induced with KA, and revealed a significant increase in the KA treated regions compared to the saline treated regions.
• The Timms staining showed increased mossy fiber sprouting and axonal plasticity in CA1 and CA3 granule cells in the hippocampus in KA treated regions compared to the control regions.

~JI

Recording sympathetic nerve activity chronically in rats: surgery techniques, assessment of nerve activity, and quantification

Stocker, S.D. and Muntzel, M.S. Recording sympathetic nerve activity chronically in rats: surgery techniques,assessment of nerve activity, and quantification. Am J Physiol Heart Circ Physiol 305: H1407–H1416, 2013. This review article covers the latest advances in recording chronically from sympathetic nerves focussing on recordings in rats. The article goes in significant details on the methods and provides some nice diagrams for recording from lumbar, renal, and splanchnic nerves. It also has a very good section on "Distinguishing Between Sympathetic Nerve Bursts, Background Noise, and Electrical Artifacts." This would be a good primer for anyone who is just starting to recording from sympathetic nerves or wants a refresher on what to look for in determining very good, versus good, versus bad sympathetic nerve recordings. Another section entitled "Time Course and Reasonable Expectations of Chronic SNA Recordings in Rats" covers topics like the Postimplant recovery period where sympathetic activity tends to be high because of a number of stress-related effects of surgery. The last section covers "Analysis of SNA Signals" and breaks down the signals into components like frequency of bursts versus amplitude of bursts. Since we record all of our raw nerve activity on the Powerlab, this could be a useful way to do some data mining and look for specific changes in sympathetic nerve activity betweeen active and sedentary animals that we might not have seen simply comparing voltages between groups. All-in-all this is a very useful review and I would consider required reading for anyone involved in experiments examining sympathetic nerve recordings, chronic or acutely. ~PJM

NTS A2a adenosine receptors inhibit cardiopulmonary chemoreflex of sympathetic outputs

Zeljka Minic, Donald O'Leary, Tadeusz Scislo

Background:
The nucleus of the solitary tract is known to be a primary modulator of the cardiopulmonary chemoreflex (CCR) via adenosine receptors (A1 and A2a). Unlike the rest of the CNS, the A2a is the primary receptor within the NTS compared to the A1 receptors.  Stimulation of the A2a receptors in the NTS shows regional specific changes in sympathetic nerve activity output such as decreases in RSNA or increases in pre-ASNA.  Here the question was whether stimulation of the A2a receptors in the NTS would promote region specific inhibition of the CCR.

Methods:

• Microinjections into the NTS
• Neuron recording

Results:
Although it is seen that stimulation of A2a receptor causes differential effects on SNA, it was shown in this study that stimulation of A2a receptor causes universal inhibition of CCR responses. Presenting for the first time, that A1 and A2a receptors my function synergistically to control cardiovascular reflexes through different mechanisms.

~JI

Tonic Glutamatergic Input in the Rostral Ventrolateral Medulla Is Increased in Rats With Chronic Heart Failure

Tonic Glutamatergic Input in the Rostral Ventrolateral Medulla Is Increased in Rats With Chronic Heart Failure by Wei-Zhong Wang, Lie Gao, Han-Jun Wang, Irving H. Zucker, Wei Wang This is a paper from the Nebraska group in which they looked at tonic excitation of the RVLM in chronic heart failure (CHF) rats. Microinjections of kynurenic acid (NMDA and AMPA receptor antagonist), AP5 (NMDA receptor antagonist), or CNQX (AMPA receptor antagonist) into the RVLM of CHF but not sham rats each reduced resting blood pressure and renal sympathetic nerve activity (RSNA). In addition direct recordings from single unit bulbospinal RVLM neurons revealed that kynurenic acid decreased the already elevated firing frequency of RVLM units from CHF but had not sham rats. Sham rats were those that had had the open chest surgery required for the coronary ligation CHF model without actually tying off the coronary artery. Sham and coronary ligated animals were studied 6-8 weeks after the ligation or sham surgery. The conclusions of the paper are that glutamate activing via both NMDA and non-NMDA (likely AMPA) receptors located on RVLM neurons contributes to elevations in resting RVLM neuronal firing and increased basal SNA in heart failure. Because antagonists were used it was not possible to determine whether the increase glutamate neurotransmission was due to increased input or a change in post-synaptic receptors or transduction mechanisms. Because unit recordings confirmed a glutamate senstive increase in resting firing frequency these data suggests that elevated SNA was due at least in part to increased firing of RVLM neurons rather than downstream changes at the level of the spinal cord or sympathetic ganglion. A prime region that could contribute to increase glutamatergic input is the paraventricular nucleus of the hypothalamus, a brain regions that has been extensively studied by this group in previous studies related to heart failure. Finally, the PVN is known to be overactive in CHF animals and it also has direct glutamatergic projections to the RVLM so it's logical to expect it is this connection that serves to drive excessive SNA in CHF. ~PJM

Diet-induced obesity severely impairs myelinated aortic baroreceptor reflex responses

Belinda H. McCully, Virginia L. Brooks and Michael C. Andresen

Obesity leads to impaired baroreceptor reflex responses. This article investigated whether the baroreflex input to the brainstem about  around resting or non resting bp was altered. They basically stimulated the aortic depressor nerve (ADN) on one side after removal of the carotid nerve inputs to the brainstem was removed. All animal were put on a high fat diet and those that became obese were put into the obese prone group and those that did not meet the criteria for obesity were put into the obesity resistant group. If the animal were somewhere in between then the animals were thrown out.They then did used different voltages to stimulate the ADN  in order to to see if there were differences between control, obese resistant and obese prone animal. The data showed that the OP had attenuated  response to stimulation of the ADN at lower volts compared to the other two groups. 

Conclusion: This data suggests that Obesity lead to to impaired baroreceptor reflex control of resting blood pressure.

-MD

Hedgehog signaling and primary cilia are required for the formation of adult neural stem cells.

Authors: Young-Goo Han..Arturo Alvarez-Buylla

Background: Granule neurons in the hippocampal denate gyrus, more specifically the subgranular zone (SGZ), receive information from the cortex and higher brain regions and participates in learning and memory formation.  During development these granule neurons are developed from granule neuron precursors (GNP) that continue to develop substantially directly after the birth and less rapid throughout the rest of a lifetime.  Recently, it has been found that the cilia on cells plays a substantial role during development, by concentrating receptors and signal transducers required for growth using the intraflagellar transport machinery (IFT).  This article shows how cilia along with Shh signaling are essential for establishment and expansion of GNP's in the postnatal denate gyrus.

Methods:

• cell counting
• in-situ hybridization
• qPCR

Results:

• Cilia null mice (Kif3a) were found to have normal morphology of the Ammon's horn on the hippocampus, however the denate gyruses were much smaller and more disorganized when compared to the wild-type mice. GNP's in the mutant mice were also found to be disorganized and reduced, with only 1/3 as many as the wildtype located in the granual layer instead of the SGZ. To verify the results were in fact from the loss of primary cilia, another mutation was induced to mice that inhibited Ift88, a gene encoding for essential subunits of IFT particles.  As shown in previously in Kif3a, Ift88 mice 1/3 of the primary cilia was disfuctional leading to severe decrease in GNP proliferation. Finally it was shown that primary cilia are responsible for properly functioning transcription signal pre and post birth such as Shh, Smo, and SmoM2.  Concluding, that primary cilia in the developing and postnatal nervous system are critical in correspondence of Shh, Smo, and SmoM2 signalling in establishing and expanding granule nuclear precursor cells that allow for the proper growth of the hippocampal denate gyrus.

      ~JI  

Monoclonal Antibodies Defining Distinctive Human T Cell Surface Antigens

Authors: Patrick C. Kung...Stuart F. Schlossman

Background: Before 1979 monoclonal antibodies were produced using heteroantiserums that randomly discovered a correct matching antibody to the specific antigen.  This was seen through rosetting, a process in which antibodies form a flower pattern around a matching antigen present on a erythrocyte. Unfortunately, even when a correct antibody was found, only low titers could be produced, making them clinically irreverent. In this paper, a new technique is introduced that greatly improves the production of monoclonal antibodies, specifically looking at monoclonal antibodies for human T-cell surface antigens.

Methods:

• The hybridoma technique
• Immunofluorescence and Flow Cytometry

Results

• In order to create monoclonal antibodies, myeloma is fused with mouse spleen cells that contain the antigen of interest.  At this time antibody producing plasma cells will bind with cancer plasma cells, and the rest of the plasma and cancer cells will dying.  The remaining fusion cells are then cultured and capable of producing high titers of the specific monoclonal antibody of interest.
• To distinguish which antibodies produced bound to the correct T-cell of interest, fluorescent flow cytometry was utilized.  Multiple T-cell types were introduced to the antibodies of interest with the assumption the antibody would bind to one T-cell type.  This culture was then introduced to fluorescence that attached only to bound antibodies.  Following, the culture was run through a flow cytometer and the fluorescent cells were characterized to evaluate antibody specificity to human T-cells.  After this was done three different monoclonal antibodies were recognized to have specific binding to unique human T-cells. 

        ~JI

Traits of fear resistance and susceptibility in an advanced intercross line

       

       Author: Jeffifer L. McGuire...Luke R. Johnson

       

       Background:

       Learned and fear based memories are a crucial aspect of survival, that have been found to be heritable in animals as well as humans. It is also known that patients who suffer from anxiety disorders such as post-traumatic stress disorder (PTSD) and depression have a stronger acquisition of conditioned fear. For future endophenotyping of altered fear and memory processing among high risk patients for anxiety disorders, it is key to identify a physiological profile for fear resistance and susceptibility.

       Methods:

•        Advanced intercross lines (AIL’s) are generated through selectively-random breeding over multiple generations, reducing the linkage of nearby alleles. Two AIL’s were created in this study, fear-susceptible mice and fear-resistant mice. Both of these mouse models once selected then underwent a three day analysis in order to study context fear and conditioned fear.
•        ELISA assay and qPCR to quantify specific hormone levels
•        Manganese-enhanced Magnetic Resonance Imaging

      Results:

      •      Differences between F-S and F-R were present between and within training and test days. Small difference in F-S and F-R freezing during the first tone, is significant in showing lower levels of anxiety in F-R mice, being a shock is not induced until after the first tone. After both the second tone during training day and after the cue test on day 2 the F-S mice had high percentage of freezing than F-R. However, intensely trained F-R mice showed similar freezing patterns to F-S mice, and in some cases even greater.

      •      F-S mice secreted greater amounts of morning corticosterone than F-R mice. Correspondingly, there are greater CRH mRNA expression levels in F-S mice compared to F-R Mice. However, CRHR1 expression levels were lower in F-S mice compared to the F-R mice. Mineral Corticoid Receptor (MR) was also lower in F-S mice compared to F-R mice. Finally, there was no significant expression difference of GR levels in F-S and F-R mice.

     •      Using MeMRI, it was discovered first that both groups on average had  the same hippocampal volume with no significant differences in either cohort. Importantly, after normalized to the F-R cohort, F-S mice were shown to have increased calcium dependent activity in the fear learning circuit. The F-S group predominantly showed neuronal activities in the hippocampus, which is known to play a key role in contextual fear conditioning. 

~JI

Non-invasive imaging of neuroanatomical structures and neural activation with high-resolution MRI.

Non-invasive imaging of neuroanatomical structures and neural activation with high-resolution MRI.

Herberholz J, Mishra SH, Uma D, Germann MW, Edwards DH, Potter K.

Front Behav Neurosci. 2011 Mar 31;5:16.  PMID: 21503138

In their previous work, the authors of this paper had shown that traditional MRI was not powerful enough to resolve structures in crayfish brain.  In this paper, the authors showed that manganese-enhanced MRI (MEMRI) offers the ability to resolve the structures that could not be visualized by traditional MRI.  They also compared the results of two different imaging systems (14.1T and 9.4T) and found both to have sufficient power to yield reliable results.

The authors of this paper gave juvenile crayfish, which lack blood barriers, injections of manganese (various concentrations) directly in to the hemolymph over 2-3 minutes. Imaging was performed after varying times (15-30mins) in order to allow neuronal uptake of manganese. Some crayfish had one antenna nerve stimulated throughout the injection and during the “waiting period” to examine activity-dependent manganese uptake.  To prevent motion artifacts, some crayfish had their cephalothoraces embedded in agarose during imaging, which was removed before return to their home tanks.

Some of their more interesting results were that while T1-weighted images could show differences in activity-dependent uptake, T2-weighted images were unable to show those differences, but still allowed them to visualize structure better than traditional MRI.  They also found a range of uptakes, ipsi/contralateral stimulation-induced differences, and signal-to-noise-ratios between individual crayfish, seemingly to be due to differences in basal activity and response to assorted stimuli.  This is a point to consider and something that I imagine we will encounter in our own MEMRI studies.

-DH

Manganese ion enhances T1-weighted MRI during brain activation: an approach to direct imaging of brain function.

Manganese ion enhances T1-weighted MRI during brain activation: an approach to direct imaging of brain function.

Lin YJ, Koretsky AP.

Magn Reson Med. 1997 Sep;38(3):378-88. PMID: 9339438

In this groundbreaking paper, the authors laid the foundation for what would come to be called manganese-enhanced magnetic resonance imaging, or MeMRI.  In this early study, they administered manganese (Mn2+) via a cannula in the right common carotid artery after unilateral disruption of the blood brain barrier (BBB) by osmotic-shock with a hypertonic mannitol solution.

They came to a number of very important conclusions in this paper. First, they confirmed that Mn2+ transport across an intact BBB is slow and seems to be mediated by transferrin. This was was evidenced by increased signal in areas known to have a high iron content.  Second, they were able to show (by glutamate injection as well as by decreasing anesthesia and causing an increase in endogenous glutamate signaling) that increased neuronal activity leads to increased Mn2+ uptake.  Third, they were able to show that Mn2+ administration to an awake and behaving animal caused activity-dependent enhanced contrast in cortical regions.  Fourth, and most importantly to the studies we are beginning in our own lab, they were able to show activity-dependent increases in signal intensity in the area of the cortex corresponding to the rat’s paw after repeated electrical stimulation of the paw (see included figure).

Although some of the methods described in this paper would not be applicable to our research or have been replaced in favor of less invasive methods that were later developed, this 15 year old paper is an excellent example of MeMRI’s potential, much of which is only now being fully developed and adopted by a variety of fields.

-DH

Sympathoinhibitory pathway from caudal midline medulla to RVLM is independent of baroreceptor reflex pathway

J.R. Potas and R.A.L Dampney

The authors of this paper were interested in whether the caudal midline medulla was causing sympathoinhibitory effects in response to glutamate stimulation by either causing activation of CVLM neurons or direct inhibition of RVLM neurons. In order to iinvestigate this question they injected kynurenate into CVLM and looked at responses to glutamate stimulation of CMM. they found that the sympathoinhition caused by activation of CMM was not inhibited. Next they wanted to see if blockade of GABA receptors in the RVLM would blunt the response. So they blocked the left RVLM so they would not get profound drops in bp and SNA and then they injected bicuculline into the RVLM and looked at responses to CMM stimulation. They found that the response was significantly blunted.

Conclusion: The sympathoinhibitory effects of CMM on the cardiovascular system is not due to activation of CVLM neurons but due to another pathway that ultimately leads to inhibition of RVLM neurons.
-M.D.

The importance of serotonin in exercise-induced adult neurogenesis: new evidence from Tph2-/- mice.

Beckman D, Santos LE.

J Neurosci. 2013 Sep 4;33(36):14283-4. doi: 10.1523/JNEUROSCI.2911-13.2013.

This is a journal club article which is a short review of recent papers in the Journal of Neuroscience.  It's a great way to get the skinny on new papers being published in the journal.  Typically these are done by students and postdocs to summarize the important findings of papers in their as well as provide additional insight and commentary.

The particular Journal Club deals with the topic of 5HT or serotonin and its role in exercise-induced neurogenesis, or the formation of new brain cells in the brain.  Only until recently was it believed that the brain only produced a fixed number of cell and even then these have been restricted to the dentate gyrus and olfactory bulb.  Although we are doing some studies to address whether there are different numbers of certain types  of neurons, we don't know if this is because the neurons we study are changing phenotypes or if they are going through apoptosis and/or whether they going through neurogenesis.  Again we study relative changes between groups so still don't know if it's the exercise or the inactivity causing changes.

Anyway this is nice quite read implicated the role of serotonin in exercise induced neurogensis.  Dr. Mateika has some of these animals so he and are going to discuss the paper with him and see what kind of avenues we can pursue.

PJM

Emerging Role of SUMOylation in Placental Pathology

D. Baczyk a,*, S. Drewlo a,1, J.C.P. Kingdom a,b
Introduction

Preeclampsia is one of the most common placental disease states that can be experienced during pregnancy.  With common symptoms such as hypertension and proteinurea, preeclampsia can cause serious injuries to both the mother and the fetus, including death, if not treated.  One cause thought to induce preeclampsia is SUMOylation of placental development regulating factors such as GMC1. SUMO, refering to small ubiquitan related-modifier, in a non disease state is attached to target proteins via isopeptide bonds and is responsable for the regulation of nuclear proteins.  However, UBC9 mediated SUMOylation can be stimulated under certain external conditions such as hypoxia or ROS.  Ultimately, leading to decreased transcription activity.

Goal
Determine whether SUMOylation is upregulated in pateints with preeclampsia, and whether this upregualtion is due to UBC9?

Methods

Tissue Collection

Immunohistochemistry

Reverse Transcription and qRT-PCR

Western Blotting

Results 

• ·        Using qRT-PCR mRNA expression levels of SUMO1 were found to be elevated in IUGR and Preeclamsia patients compared to healthy women in the early first, late first, and 2^nd trimesters. Whereas, the SUMO2 and SUMO3 proteins were found to have higher expression levels only in preeclamsia patients.
• ·         This was then followed by Western Blotting which also showed increased protein levels of SUMO1/2/3 in patients with PE vs. the age matched controls.
• ·         They next wanted to evaluate the effects of UBC9 on SUMOylation, so qRT-PCR was performed for the second time along with western blotting examining the levels of mRNA and protein expression for UBC9.  The results revealed increased levels of both mRNA and protein expression in preeclamsia patients compared to the age-related control group.
• ·         The last tests done were qRT-PCR on placental tissues cultured under hypoxic conditions for 3hrs and 24hrs.  Interestingly, after three hours of hypoxia mRNA levels of UBC9 and SUMO1/2/3 were significantly increased compared to the control tissues cultured under normal conditions.  However, after 24 hours of hypoxic conditions this was not the case. None of the mRNA levels tested after 24 hours were found to have significantly increased.

Future Studies

As novel as this study was, there was no mechanism shown liking UBC9 mediation to SUMOylation which should be done in the future.  

The Ventrolateral Medulla and Sympathetic Regulation of Arterial Pressure

Ann M. Schreihofer and Alan F. Sved (pgs. 78-82)

The ventrolateral medulla is a defined region of the brainstem currently thought to be responsible for sympathetic control of cardiovascular function.  Contained within the ventrolateral medulla are neuronal longitudinal columns that are organized into function zones deemed as pressor or depressor regions corresponding to the effect they have on autonomic cardiovascular function. The neurons in these functional zones can expand from the rostral most point at the ponto-medullary junction caudally to the spinal cord. The most studied region in the ventolateral medulla was named the rostral ventrolateral medulla (RVLM), however there are many other important regions such as the caudal ventrolateral medulla (CVLM), the caudal pressor area, and the medullo-cervical pressor area. The pressor regions, particularly the RVLM, cause vasoconstriction of arterial vessels within the body.  Where as depressor regions inhibit pressor regions in response to the baro-reflex, with a final result of a decrease in vasoconstriction.  Glutamate is the main neurotransmitter released within the pressor areas that contain bulbospinal catecholaminergic neurons, non-catecholaminergic neurons, and A1 neurons. Another common neurotransmitter in the ventrolateral medulla is gamma-Aminobutyric acid referred to as GABA.  GABAergic neurons make up the depressor regions of the ventrolateral medulla, primarily the CVLM. It is the active combination of the pressor and depressor neurons in functional zones of the ventrolateral medulla, that regulate sympathetic control of the cardiovascular system.

-JAI

Fluorescent activated cell sorting (FACS): a rapid and reliable method to estimate the number of neurons in a mixed population

Sole`ne Sergent-Tanguy, Carine Chagneau, Isabelle Neveu, Philippe Naveilhan

J Neurosci Methods. 2003 Oct 15;129(1):73-9.

Central nervous system consists of a mixed population of cells such as neurons, astrocytes and microglia. Immunolabelling was the only way to characterize them until the authors from this study employed flow cytometry to ascertain the proportion of different types of cells in primary cultures. Specific antibodies were used against intracellular markers such as Tuj-1 and GFAP to differentiate between neurons and astrocytes using flow cytometry. An important advantage of flow cytometry is that it can be used for quantitative studies of heterogeneous cultures. This technique will be particularly useful for our lab since we can retrogradely label the spinally projecting C1 neurons using a tracer such as CtB and collect these cells specifically using flow cytometry and perform future studies. Also it will be interesting to know how different types of cells are populated within the rostrocaudal extent of the RVLM.

-Madhan

Confounding neurodegenerative effects of manganese for in vivo MR imaging in rat models of brain insults.

Confounding neurodegenerative effects of manganese for in vivo MR imaging in rat models of brain insults.

Bouilleret V, Cardamone L, Liu C, Koe AS, Fang K, Williams JP, Myers DE, O'Brien TJ, Jones NC.

J Magn Reson Imaging. 2011 Oct;34(4):774-84

Manganese-enhanced magnetic resonance imaging (MeMRI) is an exciting new technique which is being adopted by many groups.  However, there is not yet a consensus on appropriate dosages, number of repeat administrations, etc.  This is important because high levels of manganese can be neurotoxic, leading to a condition known as manganism.  Somewhat similar to parkinson’s disease, manganaism presents with motor controls, neurodegeneration, and psychiatric disturbances.  To examine the cumulative effects of repeated treatments with a high concentration of manganese, this paper compares the effects of repeated standard MRI (sMRI) with repeated MeMRI.

They used lateral fluid percussion injury (FPI, something akin to a mini squirt gun, at over 3 atmospheres, shot directly in to the sensory-motor cortex) in rats.  These rats were then monitored for anxiety, motor abilities, depression, stress responsivity, epilepsy, weight, etc.  One group was given sMRI scans at one week before, and one week, one month, three months, and six months after the injury.  The other group underwent MEMRI (100mg/kg intraperitoneally, 24hrs pre-scan) at one week before, and one day, one week, one month, and six months after the injury.

MEMRI did not change neuromotor scores during the 3 days following the injury, but it did result in a significantly lower body weight than sMRI controls.  Lower weight gain was also seen in FPI sMRI rats when compared to sham-injury sMRI controls. The same effect was seen with the increases in brain volume at the one month and six month points.  The greatest regional effects corresponded to the areas injured by FPI, suggesting that manganese toxicity may occur in cells which have already sustained insult.

The MEMRI rats showed a strong increase in anxiety over sMRI rats (per elevated plus maze test, time spent in closed arms), as well as significant increase in depression-like behavior (decreased consumption of sucrose water). Interestingly, Mn2+ treatment seemed to lead to a decrease in post-traumatic stress epilepsy.

-DH

Baroreflex Function after Spinal Cord Injury

Baroreflex Function after Spinal Cord Injury

Aaron A. Phillips, Andrei V. Krassioukov, Philip N. Ainslie, and Darren E.R. Warburton. Journal of Neurotrauma. October 10, 2012, 29(15): 2431-2445. doi:10.1089/neu.2012.2507.

In this review, the authors performed a series of meta-analyses of existing studies on people with spinal cord injuries in order to draw new hypotheses about changes in baroreflex sensitivity caused by autonomic dysfunction after spinal cord injury.  By comparing a variety of data, (e.g. orthostatic intolerance, renin-angiotensin levels, blood pressure, heart rate, etc.,) in patients with injuries at high, middle, and low levels of the spinal cord, the authors were able to find new evidence of whether the dysfunction occurred due to arterial hardening, decreased sympathetic signaling, etc.

It was be noted that due to incomplete data and the large variability in the severity of spinal cord injuries in the studies they analized and the variability in locations at which these injuries occurred, drawing conclusions is exceedingly difficult, especially when considering the small sample size.

-DH

Dependence of sympathetic vasomotor tone on bilateral input from the rostral ventrolateral medulla in the rabbit: role of baroreceptor reflexes

J. Horiuchi and R.A.L. Dampney

It has been observed that bilateral but not unilateral inactivation of RVLM leads to profound decreases in BP. However, the mechanism that allows for one RVLM under intact baroreceptor conditions to be able to maintain bp is unknown. The current study investigated both unilateral and bilateral inhibition of RVLM on blood pressure and sympathetic output. Method: Following removal of aortic and carotid baroreceptors along with bilateral vagii removal muscimol was injected in the right RVLM and then the left rvlm. MAP, rSNA were recorded along with HR.Results: The response to unilateral blockade of rvlm in SAD rabbits drop MAP to that of spinal levels. It also caused a dramatic fall in rSNA in SAD rabbits when compared to intact rabbits.

Conclusion: Data suggests that the baroreflex is important for maintaining BP and SNA when the activity of RVLM neurons is impaired.

Brain stem control of arterial pressure in chronic arterial baroreceptor-denervated rats

Authors: Ann M. Schreihofer, Satoru Ito, and Alan F. Sved

Unlike acute denervation, chronic denervation condition lead  normal sympathetic vasomotor tone. So the authors wanted to examine what is driving sympathetic vasomotor tone. Methods: Sinoaortic denervation (SAD) or NTS lesion was done and the rats were allowed to recovery for one week. Then several microinjecion protocols were done while recording BP responses. Results: BP responses to α₁  adrenergic  injections relieved no differences between control and chronic SAD rats. This data suggests that vascular reactivity is not altered in response to chronic denervation. They also did a spinal transection at the T1 level and BP responses were no different between the control and chronic SAD rats. These results demonstrate that supraspinal regions are still response for control of BP under chronic SAD conditions. In order to investigate the role that RVLM is playing in the control of BP under chronic SAD conditions, they microinjected muscimol into RVLM bilaterally. Results showed that control and NTS lesioned and chronic SAD rats had similar responses. This showed that the RVLM is important to the control of sympathetic vasomotor tone under both intact and chronic SAD conditions. Next they wanted to investigate CVLM GABAergic input to RVLM. After inhibition of CVLM with muscimol they saw no differences between groups. This showed that even after removal of barorecptor inputs to the brain stem, the CVLM is still able to maintain the same level of GABAergic input to RVLM. They saw similar differences for glutamergic input to CVLM between groups. Demonstrating that the same of activation of CVLM neurons is occurring  even in the absence of baroreceptors. 

Conclusion: Under chronic SAD conditions, the CVLM receives baroindependent glutamergic input. This allows for the CVLM to still provide gabaergic input to RVLM in order to maintain BP in chronic denervated rats.