Lesion of medullary catecholaminergic neurons is associated with cardiovascular dysfunction in rotenone-induced Parkinson's disease rats.

Zhang Z, Du X, Xu H, Xie J, Jiang H.
Eur J Neurosci. 2015 Sep;42(6):2346-55. doi: 10.1111/ejn.13012. Epub 2015 Jul 30.

-Direct link here
In this paper, they examined relationships in the loss of dopaminergic neurons in the substantia nigra with loss of catecholaminergic neurons in the RVLM in rat model cases of rotenone-induced Parkinson's Disease (PD). This is an interesting study because symptoms signifying sympathatic disorders (e.g. instability in heart rate and blood pressure, orthostatic intolerance, etc) are frequently linked with PD and are some of the early warning signs of the disease. They gave rats i.p. injections of rotenone, the insectiside that is known to induce a condition highly similar to PD, and examined groups at different time points. They found that, similar to humans, issues with control of blood pressure (and decreases in plasma epinephrine and norepinephrine) arose before the loss of midbrain dopaminergic neurons or the appearance of motor symptoms. They also noted a decreased influence of low frequencies on heart rate after rotenone, suggesting a decrease in sympathetic never activity. Most interestingly, they noted that there was a loss of TH and DBH positive neurons and a decrease of TH and DBH proteins in the RVLM. These changes occurred early, despite the fact that loss of catecholaminergic neurons occurred later and not at all in the CVLM and NTS, respectively.
So the big questions after reading this paper are what makes C1 neurons so sensitive to rotenone and what else wipes them out? Neuroplasticity is one thing, because it can be reversible... but losing them entirely is another. -DH

Injections of Algesic Solutions into Muscle Activate the Lateral Reticular Formation: A Nociceptive Relay of the Spinoreticulothalamic Tract.

Panneton WM, Gan Q, Ariel M.
PLoS One. 2015 Jul 8;10(7).

I wanted to take a look at this paper mainly because it is fairly similar to some of what we have done in our lab. Instead of stimulating the sciatic nerve, the injected algesic solutions (capsaicin, 6% NaCl, or low pH) into the gastrocnemius muscle, perfused the rats, and then compared the number of Fos+ cells in a number of regions involved in processing and responding to noxious stimuli. The number of Fos+ neurons in these regions was compared to the Fos+ neurons found in saline-injected rats. They analyzed the rostral and cuadal pons, rostral and caudal medulla, and the spinal cord.

Focusing on their results that correspond to our areas of research, they found that algesia caused more Fos+ neurons in both the RVLM and the CVLM, and not much in the RVMM (compare this to facial air puffs causing activation in the RVMM, but not in the RVLM, in last year's paper from the Dampney group), and that some of them were catecholaminergic neurons. Interestingly, even though the algesic solutions were injected unilaterally, Fos+ were not significantly different between sides of the brainstem - this either conflicts with other results (Pillowski group), or adds support to the idea of differential control. -DH

Differences in respiratory changes and Fos expression in the ventrolateral medulla of rats exposed to hypoxia, hypercapnia, and hypercapnic hypoxia

Jun Wakai, Daichi Takamura, Ryosuke Morinaga, Nobuaki Nakamuta, Yoshio Yamamoto
Respiratory Physiology & Neurobiology. Volume 215, 15 August 2015, Pages 64–72

The purpose of this paper was to try to reconcile the confusing and sometimes conflicting data that had previously been published on the differential effects of hypoxia and hypercapnia. In these experiments, they exposed rats to 2 hours of hypoxia, hypercapnia, or hypoxia plus hypercapnia. In this paper, they defined the rVLM as the region ventral to the facial nucleus, the mVLM as the region our lab generally considers the rVLM, and the cVLM was same thing we know it to be. They found that hypoxia increased respiratory frequency and Fos+ neurons in mVLM (our RVLM) and cVLM. Hypercapnia caused increased tidal volume, Fos+ neurons in the rVLM, RTN, and mVLM (our RVLM). Hypoxic hypercapnia caused a mixed result with increased tidal volume and Fos+ neurons in entire VLM. When they costained for FOS and DBH, they found that the Fos+ rVLM neurons were not DBH+, some of the cVLM and mVLM (our RVLM) neurons were double positive while some weren't.
They end the paper by speculating that based on their results and previous anatomical studies, hypoxia changes SNA activity through A1/C1 neurons in the cVLM (slightly different than our take) and hypercapnia changes activity through A1/C1 neurons in the RTN (which may partially include our RVLM). -DH

Functional mapping of rat barrel activation following whisker stimulation using activity-induced manganese-dependent contrast

Jun-Cheng Weng, Jyh-Horng Chen, Pai-Feng Yang, Wen-Yih I. Tseng,
NeuroImage. Volume 36, Issue 4, 15 July 2007, Pages 1179–1188

In this paper they studied the well-established neuroanatomy of the rat sensory cortical whisker barrels, but with MEMRI. Previous functional imaging methods involved imaging WHILE stimulating the whiskers, so they decided to use MEMRI to identify the neuronal uptake of manganese BEFORE imaging.
They gave i.p. manganese and used mannitol to rupture the blood brain barrier, anesthetized the rats, and then hooked their whiskers up to a speaker for 3 hours (with the cone torn out to eliminate sound). For controls, they cut the contralateral whiskers, as well as imaging a separate group of sham/non-stimulated rats.
They subtracted the image intensity of control rats from experimental rats to eliminate non-whisker-related image enhancement (e.g. hippocampus, hypothalamus, and amygdala). The only enhanced contrast that remained was in the whisker barrel barrel that corresponded to the stimulated whiskers. -DH

Cardiovascular and respiratory responses to chronic intermittent hypoxia in adult female rats

Souza GM, Bonagamba LG, Amorim MR, Moraes DJ, Machado BH.
Exp Physiol. 2014 Dec 16. doi: 10.1113/expphysiol.2014.082990

Volumes of research indicate that males are more susceptible to developing hypertension than premenopausal females. There is also data that shows that obstructive sleep apnea, a form of chronic intermittent hypoxia (CIH), leads to hypertension and that this apnea is more common in men than women. However, data linking this apnea to differences in men and women is scarce and a bit controversial.  In this study they looked at female rats exposed to CIH and examined changes in breathing patterns and blood pressure.
In this paper, they used a different CIH protocol than what was in some of the other papers I recently blogged. Here, they did 9 minutes of normoxia, and used nitrogen displacement to bring oxygen levels down to 6% for 40seconds, before being brought back to normoxia for another 9 minutes. This continued for 8hrs a day for 35 days. Rats were anesthetized and fitted with a femoral catheter to record arterial pressure. Respiratory activity was recorded 30 minutes after placing the rat inside of the plethysmographic chamber.
What they noticed was that CIH really messed up female rats’ cardiovascular system - they weighed less than controls (273 vs 347g), they had higher systolic (136 vs 129mmHg), diastolic (92 vs 86mmHg), and mean arterial pressures (111 vs 104mmHg), as well as increased heart rate (400 vs 376bpm). The systolic pressure was also more variable in CIH females. However, the dramatic changes seen in the cardiovascular system was not reflected in the respiratory system. Compared to controls, CIH rats didn’t have higher minute volume, tidal volume, or respiration frequency. However, short and long term variability was indeed higher in CIH rats.
Because respiratory and cardiovascular systems are coupled, they looked at how this relation changed between rat groups.  CIH rats had a stronger fall in MAP during deep breaths, and were more likely to have an apneic event after a deep breath than control rats, and the apnea lasted longer as well. They noted that their results were very comparable to the results of a different study on male rats that used the same protocol, but conflicted with another study in female rats that used a different CIH protocol which said that females DO NOT experience the strong changes seen in this paper. This suggests that females may have some protection against the changes, presumably due to differences in hormone levels, but that protection can be overcome by more severe CIH.  -DH

Neural control of the circulation: how sex and age differences interact in humans.

Joyner MJ, Barnes JN, Hart EC, Wallin BG, Charkoudian N.

Compr Physiol. 2015 Jan 1;5(1):193-215.

For reasons I am probably not at liberty to discuss, some of us in the lab have been discussing the differences in autonomic function between males and females. So I was pretty happy to see a review that had some of this information in it. As an added bonus, it discusses these differences mostly in humans (because we all need to focus on the transnational application of our basic science) with animal data where no human data was available.  Added bonus 2 is that this review comes from some reputable people, so it’s well-written and easy to understand.

In the review, they touched on a lot of topics, ranging from how (muscle) sympathetic nerve activity may be correlated with blood pressure in any given young man, but not from young man to young man, and not at all in young women. They also included various difficulties in experimental techniques (conduction speed differences between sympathetic and parasympathetic systems), neurotransmitter turnover times, and receptor availability/activity with modulation by different factors.  A couple of interesting things I learned were that even though estrogen is widely thought to prevent high SNA and blood pressure, conflicting data has also shown that high estrogen can sometimes correlate with high SNA, and that the age related changes seen in women after menopause will also occur regardless of menopause, and may just be related to age.  Confusing stuff.

Anyway, I liked this review a lot. I were running a lab, I would probably add it to the list of early required reading for new students. –DH

Chronic intermittent hypoxia increases sympathetic control of blood pressure: role of neuronal activity in the hypothalamic paraventricular nucleus.

Sharpe AL, Calderon AS, Andrade MA, Cunningham JT, Mifflin SW, Toney GM.

Am J Physiol Heart Circ Physiol. 2013 Dec;305(12):H1772-80.

This is a very slightly older paper from some of the same people I posted about last weekend. They were still looking to see how chronic intermittent hypoxia (CIH) could affect lumbar and renal sympathetic nerve activity (LSNA and RSNA), based on the existing theory that CIH causes hyperactivity of the chemoreflex, and the changes happen by way of the paraventricular nucleus (PVN). This time, the parameters of the CIH were: O2 levels were reduced to 10% for 6 minutes, 10x per hour, for 8 hours a day, for 7 consecutive days.

In this study they found that, compared to control rats, CIH rats had significantly higher MAP by day 3, with differences in heart rate not reaching significance. Rats exposed to 7 days of CIH had a greater reduction in MAP after ganglionic blockade (hexamethonium) than was seen in control rats, which indicated that CIH rats have increased sympathetic tone. Furthermore, muscimol inactivation of PVN caused greater reductions of lumbar SNA and MIP in CIH rats than controls, which also supports the idea that CIH rats have higher sympathetic tone. Furthermore, when CIH rats were given hypertonic saline directly in to the carotid artery, they showed a larger increase in LSNA (but not in RSNA) than control rats did. This suggests that there may be a greater LSNA responsiveness in CIH rats, and NOT a blunted/ceiling effect due to the higher SNA tone. This is also interesting on the basis that it adds more data to the idea of differential control of SNA. -DH

Adenosine reduces GABAergic IPSC frequency via presynaptic A1 receptors in hypothalamic paraventricular neurons projecting to rostral ventrolateral medulla

Tae Hee Han,Soo Hwa Jang,So Yeong Lee,Pan Dong Ryu. Neuroscience Letters

Volume 490, Issue 1, 18 February 2011, Pages 63–67. doi:10.1016/j.neulet.2010. 12.026. The paraventricular nucleus (PVN) is a brain region that has projections that go to RVLM and down to the IML in order to modulate sympathetic outflow. The purpose of this study was to determine whether adenosine was was playing a role in modulating gaba release from PVN-RVLM neurons. Using young male Sprague-Dawley they labelled PVN-RVLM neurons by injecting Fluospheres- Red into the RVLM and they allowed the animal to recover for 5-7 days. the brain was sectioned and the labelled PVN neurons were selected for recording. In response to adenosine, they saw inhibitory postsynaptic currents . When compared to the before activity there was a decrease in firing but not in amplitude and the response was concentration dependent. Then they used antagonist to A 1 receptor and the A2  receptor  and saw that there was no change in the firing of the neuron. however, when adenosine was given  after the  microinjection of the A1 antagonist they found that the iPSCs was inhibited.  the microinjection of  the A2 antagonist  did not prevent the IPSCs that occur in response to  adenosine injection. These data demonstrate that adenosine is playing a  role presynaptically  in attenuating GABA release and this mediated by adenosine acting on A1 receptors. -MD

Acute intermittent optogenetic stimulation of nucleus tractus solitarius neurons induces sympathetic long-term facilitation.

Yamamoto K, Lalley PM, Mifflin SW.

Am J Physiol Regul Integr Comp Physiol. 2014 Dec 17:ajpregu.00381.2014

                In this paper, they built on previous work that showed that the effect of acute intermittent hypoxia (AIH) on long term facilitation (LTF) of phrenic nerve activity (PNA) and renal sympathetic nerve activity (RSNA) seems to be routed through the nucleus tractus solitarius (NTS), and that you could induce the same effect by electrical stimulation of the carotid sinus, even without hypoxia. They took this idea a step further by causing expression of channelrhodopsin in the caudal NTS, via a virus that would cause preferential expression in glutamatergic neurons.

                Once they had this system in operation, they compared the effects of AIH with the effects of acute intermittent optogenetic stimulation (AIO) on RSNA and PNA immediately after, and 60 minutes after periods of stimuli. They found that AIO in the caudal NTS produces a similar, but weaker, response to that seen after AIH (RSNA and PNA increased by 60% and 100% after AIO, but by 80 and 130% after AIH).  They also found that, while both stimuli increased the power spectral density of RSNA and PNA at their own primary frequencies, neither stimulus was able to increase synchronization of PNA with RSNA. -DH