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.

G protein-coupled lysophosphatidic acid receptors stimulate proliferation of colon cancer cells through the beta-catenin pathway

By: Ming Yang, Wendy W Zhong, Neelam Srivastava, Anthony Slavin, Jianxin Yang, Timothy Hoey and Songzhu An

Background: G coupled protein receptors LPA1, LPA2, and LPA3 have been shown to mediate lysophosphatidic acid stimulation, which is associated with the proliferation of colon cancer cells.  Two important oncogenic transformation genes related to colorectal cancer proliferation are c-myc and cyclin D1; both in which can be transcribed as a result of the beta-catenin pathway.  It has been observed that with the inhibition of beta-catenin degradation a nuclear summation of beta-catenin leads to increased levels of these deadly oncogenic proteins.  However, the mechanism in which LPA stimulation was involved with both the colorectal cancer proliferation and the beta-catenin pathway were both unknown.

Objective: Using HCT116 and LS174T adenocarcinoma cell lines, it was sought to identify which LPA receptors were responsible for colorectal cancer cell proliferation, and what mechanism was induced during this process.

Results:

• With the treatment of LPA to HCT116 and LS174T cells, colon cancer cells underwent proliferation in a dose dependent response over a concentration titration of  .01 micromolar-1.0micromolar LPA.  Cells were then analysed for the expression of LPA1, LPA2, and LPA3 mRNA, revealing significant levels of only LPA2 and LPA3, not LPA1.
• HCT116 and LS174T cells were than transfected with siRNA of LPA2 and LPA3 showing a direct decrease in cell proliferation and tumor volume. Beta-catenin siRNA similarly reduced colon cell proliferation, even though the treated cells were induced with LPA, corresponding to the belief that LPA induction stimulates the beta-catenin pathway increasing colon cancer growth.  
•  It was then shown with Western Blot analysis that when induced with LPA the phosphorylation of GSK3beta via cPKC, a multicomplex protein that stabalizes beta-catenin and prevents degradation, increases drastically.  From this it was deduced that the phosophorylation of GSK3beta was one of the ways that LPA stimulated the beta-catenin pathway.
• Lastly, the activation of the beta-catenin pathway via both LPA2 and LPA3 was research.  It was found using siRNA knockdowns for both receptors that both were efficient in increasing the beta-catenin pathway, which further increased the proliferation of both HCT116 and LS174T colorectal cancer cells.

-JI

Visualization of nigrosome 1 and its loss in PD: Pathoanatomical correlation and in vivo 7 T MRI.

Blazejewska AI, Schwarz ST, Pitiot A, Stephenson MC, Lowe J, Bajaj N, Bowtell RW, Auer DP, Gowland PA.
Neurology. 2013 Aug 6;81(6):534-40. PMID: 23843466
 

Objective:   Parkinson’s Disease (PD) is a progressive neurological disease marked by the loss of dopamine-producing cells in the midbrain area known as the substantia nigra (SN).  Diagnosis, and consequently therapy, usually occurs after pathognomonic motor symptoms occur, brought about by the loss of greater than 60% of the dopaminergic cells in the SN.  In this paper, diagnostic regions of the SN, known as nigrosomes, were examined by MRI in order to identify changes that could lead to earlier diagnosis of PD.

Results:

·         Areas defined by staining were able to be matched to and overlaid on MRI scans.  In the sample from the PD patient, the structure corresponding to nigrosome 1 (the area most affected by PD) could be seen on MRI, but lacked neuromelanin and staining for tyrosine hydroxylase (TH), two markers for the dopaminergic neurons in the SN.

·         The nigrosome 1 was examined in healthy volunteers with T2 weighted imaging with a 7T and a 3T scanner.  The 3T scanner could show the nigrosome, but with a lower-signal-to-noise ratio.  When compared to the nigrosome 1 of people suffering from PD, neuroradiologists blinded to the patients’ statuses could correctly classify their state of healthy in 7/8 controls and 10/10 of PD patients.

Conclusions:

·         The nigrosome 1 region of the SN can be accurately identified on a 7T MRI scanner using T2 weighted imaging.

·         Due to experimental design and small sample size, no definite conclusion can be drawn about this technique’s ability to identify PD patients before the onset of motor symptoms.  Longitudinal studies will be needed in populations being investigated for the progression of PD.

Methods:    Post-mortem human brains were acquired, formalin fixed, and imaged with a 7T MRI scanner.  The midbrains were then sectioned in to 5um slices for immunostaining.  Additional scans were done on live healthy controls and live patients with PD (diagnosed with traditional methods and shown to respond to standard therapy).  Further scans were done at 3T in order to investigate the feasibility of visualizing nigrosome 1 in a lower magnetic field.

-DH

KNOCKDOWN OF TYROSINE HYDROXYLASE IN THE NUCLEUS OF THE SOLITARY TRACT REDUCES ELEVATED BLOOD PRESSURE DURING CHRONIC INTERMITTENT HYPOXIA.

Bathina CS, Rajulapati A, Franzke M, Yamamoto K, Cunningham JT, Mifflin SW.
Am J Physiol Regul Integr Comp Physiol. 2013 Sep 18. [Epub ahead of print]. PMID: 24049117

Objective:   Sleep apnea produces chronic intermittent hypoxia (CIH) that causes elevations in sympathetic nerve activity and arterial pressure as a result of arterial chemoreceptor (CR) activation and subsequent activation of the NTS.  Since the CRs seem to preferentially activate the NTS A2 noradrenergic neurons, the role of these A2 neurons was examined by comparing the effect of CIH on wild type and tyrosine hydroxylase (TH) knockout rats.

Results:

·         Rats that had TH knocked down in the NTS with shRNA showed reduced change in MAP in the dark phase and a greater heart rate than controls.  Changes in heart rate persisted in normoxic phases in control rats, but not in knockdown rats.

·         In knockdown rats, there was a significant reduction in FosB immunoreactive cells in the PVN, but not in the controls.  This change did not significantly extend to the RVLM.

-DH