Electrophysiological characteristics of identified kidney-related neurons in adult rat spinal cord slices.

Neurosci Lett. 2010 May 3;474(3):168-72. doi: 10.1016/j.neulet.2010.03.036. Epub 2010 Mar 18. Derbenev AV, Duale H, Rabchevsky AG, Smith BN. In this paper, they wanted to characterize the preganglionic kidney-related cells in the IML, so they applied a transynaptic pseudorabies virus within the kidney to label them. 84 hours later the animals were perfused with ice cold ringer, and slices of the spinal cord were made and used for whole cell patch clamp on labeled cells. Co-stains were performed for their PRV eGFP marker as well as ChAT (as well as the biocytin that was present in their recording electrode), showing that these kidney-related cells were mostly cholinergic, with 3 or more primary dendrites, and which area of the IML they were most likely to be in (lateral edge of they gray matter). During recording of GFP labeled cells, they were able to see that there were frequent GABA-A related small inhibitory postsynaptic currents and glutamate-mediated small excitatory postsynaptic currents. Since they saw increased glutamate signaling, they propose that the cells are under tonic glutamatergic activation. I'm not sure that severed in vitro presynaptic axons are entirely representative of an intact in vivo physiological system, but I'm still kind of new to this and there's probably a lot of work that's been done that could teach me a thing or two. -DH

Sympathetic Neural Regulation of Blood Pressure: Influences of Sex and Aging

E. C. J. Hart , N. Charkoudian PhysiologyPublished 1 January 2014Vol. 29no. 8-15DOI: 10.1152/physiol.00031.2013 In this review, they discussed how the things we study, particularly splanchnic sympathetic nerve activity, is reflected in humans (via microneurography measures of muscle sympathetic nerve activity) and how nerve activity changes with age. Apparently, MSNA is a good measure of peripheral resistance, but not a good measure of blood pressure since SNA doesn’t correlate well with blood pressure until people are in their forties or fifties. However, it is inversely related to cardiac output in young men but not in women unless the young women are using beta blockers. Old women are more like old men, suggesting that there may be a gender-linked change in the activity or effect of beta-adrenergic receptors. -DH

Sympathetic nerve activity and peripheral vasodilator capacity in young and older men.

Am J Physiol Heart Circ Physiol. 2014 Mar;306(6):H904-9. doi: 10.1152/ajpheart.00181.2013. Epub 2014 Jan 10. Hart EC, Wallin BG, Barnes JN, Joyner MJ, Charkoudian N. In this paper, they looked at the fact that high MuscleSNA in young men can be cancelled out by a decreased vasoconstriction response to adrenergic stimuli and a lower cardiac output, where older people with increased SNA tend to have higher blood pressure. What they found was that younger men with high MSNA have decreased responses to intra-arterial vasodilators, but older men do not. Their conclusion was that young men can regulate their blood pressure better than older men, who showed no relationship between MSNA and the effect of vasodilators. They point out that since older men tend to have higher basal MSNA, they may not be able to regulate their blood pressure as well. Mechanistically, this makes sense in older men since fast firing nerves can't fire much faster and their downstream effect is already near its maximum. However, I don't know why this doesn't hold true for younger men, other than how they say that other vasoconstrictor mechanisms may come in to play. -DH

Large-scale, high-density (up to 512 channels) recording of local circuits in behaving animals.

J Neurophysiol. 2014 Mar;111(5):1132-49. doi: 10.1152/jn.00785.2013. Epub 2013 Dec 18. Berényi A, Somogyvári Z, Nagy AJ, Roux L, Long JD, Fujisawa S, Stark E, Leonardo A, Harris TD, Buzsáki G. In this paper, they did something pretty mazing. They engineered an implantable device, which was made of 5 small electrode arrays, each with 32 recording probes. This, and its assorted electronic accoutrements, fit on a mouse's head (although it looked somewhat comically large). Looks aside, they were able to record field potentials on 256 channels from within the mouse's brain. They talk about how they had to do a lot of software multiplexing, so the recordings are not exactly simultaneous, but they switch recording channels once every 1.5 microseconds, which lets them sample every channel in sequence in less than 50 microseconds, still giving them an overall sample rate of 20KHz. If that's not cool enough, they were able to double the hardware on rat brains and record from 512 cortical sites. Coolness factor aside, this is awesome because they were able to reconstruct microcircuitry within the brain and see which cells had monosynaptic inputs on which other cells. That's not easy to do, but when you have 512 probes going at once, I guess that makes some things easier than ever. -DH

Leptin and splanchnic sympathetic nerve activity and heart rate

Baoxin Li, Zhigang Shi, Priscila A. Cassaglia, Virginia L. Brooks Hypertension is available at http://hyper.ahajournals.org DOI: 10.1161/HYPERTENSIONAHA.111.00518 In this article they tested whether leptin was acting in the Forebrain or in the brainstem in order to cause increases in sympathetic nerve activity. They also wanted to know what effects leptin had on the baroreceptor reflex. So they recorded splanchnic sympathetic activity (SSNA), Lumbar sympathetic activity (LSNA), renal sympathetic activity (RSNA) along with mean arterial pressure (MAP) and heart rate (HR). First they gave SNP and PE in order to generate a baroreflex curve. Then they infused leptin 3ug and 1.5 ug into the lateral cerebral ventricle (LV) and also the fourth ventricle (4V). They want to know if leptin was also affecting parasympathetic to the heart, so they gave methscopolamine an anticholinergic agent through iv. Their results showed that after one hour and two hours there was a significant increase in LSNA and RSNA compared to control levels for 3ug infusion into the LV. With the 1.5 ug infusion into the LV they saw an significant increase only after two hours for LSNA compared to the control. Also there was significant increase in SSNA in response to the 3ug LV infusion compared to the control. When they generated the baroreflex curves for animal before and after leptin infusion they found that lumbar both doses infused into the LV increase the baroreflex gain and increase the baroreflex maximum. As for the RSNA, LV 3ug infusion leads to increases in the baroreceptor reflex gain and maximum. SSNA the LV 3ug infusion lead only to an increase in baroreflex maximum. When leptin is given under control conditions it causes an increase in HR. When they at leptin effects on parasympathetic and sympathetic innervation to the heart they found that methscopolamine prevented leptin from altering HR. They also tested leptin in the brainstem and found no significant results to report. The conclusion was that leptin mediates its effects on different sympathetic beds and blood pressure by acting in the forebrain. Leptin actions in the forebrain also restrain parasympathetic activity to the heart. -MD

Differentiation of two cardiovascular regions within caudal ventrolateral medulla

SERGIO L. CRAVO, SHAUN F. MORRISON, AND DONALD J. REIS Am. J. Physiol. 261 (Regulatory Integrative Comp. Physiol. 30): R985-R994, 1991 The caudal ventrolateral medulla provides GABAergic input to the rostral ventrolateral medulla. We know that CVLM neurons receive glutamatergic input from the nucleus of the solitary tract (NTS) that leads to inhibition of RVLM and depressor and sympathoinhibition. However, in some studies were they lesioned the CVLM, laboratories prior to this point in time would get different results. Some reported that baroreceptor reflex remained intact another lab reported the complete opposite finding. So this laboratory hypothesized that baroreceptor and non-baroreceptor sensitive neurons in the CVLM were separated from one another. So in order to test this hypothesis they instrumented rats so they could record blood pressure, splanchnic sympathetic nerve activity and also ECG. They first did an aortic depressor nerve (AND) stimulation in order to activate the baroreceptor reflex. This resulted in decreases in bp pans sSNA. Next the blocked the rostral portion of the CVLM using kainic acid and repeated the ADN stimulus. They found that the ADN response was eliminated. However, when the kainic acid was microinjected in the caudal portion of the CVLM the response to ADN stimulation remained. These data suggest that the rostral portion of the CVLM is important phasic inhibition and the caudal for tonic inhibition. -MD

Role of ventrolateral medulla in vasomotor response to cerebral ischemia

Dampney and Moon Am J Physiol. 1980 Sep;239(3):H349-58. In this article they wanted to investigate whether the ventrolateral medulla was responsible for the pressor response that occurs in response to cerebral ischemia in anesthetized paralyzed rabbits. They lesioned the ventrolateral medullar reticular formation, this produced depressor responses. They gave 40ug/ml norepinephrine in order to bring blood pressure near baseline blood pressure values before lesion. Then cerebral ischemia was induced and this caused no change in the animals that received electrical destruction of the ventrolateral medullar reticular formation when compared to the control pressor responses to CIR. When the dorsal medulla was electrically destroyed the pressor responses still persisted in response to CIR. They also lesioned the ventrolateral medulla area more laterally and they found that this did not alter the pressor response that occurred in response to the CIR. They also did some mapping of the ventrolateral medulla using electrophysiology because this area had not been characterized before this. Overall they showed that the ventrolateral medulla is playing an important role in mediating the CIR response. -MD

Baroreflex sensitivity analysis: spontaneous methodology vs. Valsalva’s maneuver

Huan Yang, Jason R. Carter Clin Auton Res. 2013 Jun;23(3):133-9. doi: 10.1007/s10286-013-0195-9. Epub 2013 May 16. Baroreflex is an important mechanism that helps to maintain blood pressure. We know that dysfunction of the arterial baroreflex has been associated with hypertension. The baroreflex sensitivity (BRS) is an index of autonomic baroreflex control sympathetic outflow or heart rate. In order to determine sympathetic (sBRS) you to estimate responses in muscle sympathetic nerve activity to changes in diastolic arterial pressure (DAP). In order to determine cardiovagal BRS (cBRS) is estimated by response in heart rate to changes in systolic arterial pressure (SAP). There are two non-pharmacological methods that can be used to determine BRS in humans. Those methods are spontaneous assessments using weighted regression analyses to examine changes in MSNA (sBRS) or heart rate (cBRS) as they relate to resting oscillation in DAP or SAP and also the valsalva maneuver (VM). Since no one so far has compared the two assessments in order to determine if they are reliable within an individual for sBRS and cBRS. They hypothesized that spontaneous BRS assessed via spontaneous methods would be positively correlated to VM BRS. 26 young subjects age around 22 were used. They all had to meet a certain criteria. They recorded blood pressure using a sphygmomanometer while the subjects were engaged in the VM. They also recorded measured the peroneal nerve activity in the right leg. They found that the spontaneous blood pressure oscillations were positively correlated with the VM sBRS. However spontaneous cBRS was not correlated te VM cBRS. These data suggest that methods using to evaluate sBRS are reliable. -MD

Reduced plasma volume and mesenteric vascular reactivty in obese Zucker rats

Schreihofer, Ann M., Clark D. Hair, and David W. Stepp. "Reduced plasma volume and mesenteric vascular reactivity in obese Zucker rats." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 288.1 (2005): R253-R261. In this study both obese Zucker rats (OZR) and lean Zucker rats (LZR) were tested for blood volume to mass ratio for a better understanding of dose responses in obese animals. Following each group of rats was then tested for vascular reactivity (via changes in MAP) to α1 agonists norephinephrine and phenylephrine using body weight as a dose determinant and then plasma volume as a dose determinant. Finally, the study then examined changes in vascular resistance by measuring blood flow in the mesenteric, renal, and hindquarter circulations after the administration of phenylephrine. Previous reports found that OZR are slightly hypertensive compared to LZR, exhibit higher baseline SNA, and have increased pressor responses to ganglionic blockade, which was also the case in this study. Novel to this study however, the Schreihofer group discovered OZR have consistent plasma volumes which then correlate to lower plasma volume/mass ratios. When this idea was then applied to drug administration and doses were determined based upon plasma volume instead of body weight no significant differences in ΔMAP or ΔHR were found following the injections of norepinephrine or phenylephrine. However, after the injection of phenylephrine OZR trended towards increased ΔHR compared to LZR. The study then went on to find that OZR had reduced changes in mesenteric vascular resistance, similar changes in renal resistance, and increased changes in hindquarter resistance when compared to the LZR. These results indicate that changes in vascular reactivity in an OZR compared to LZR are probably not the major cause in the difference in pressor activity following ganglionic blockade. Instead, the authors hypothesize that the difference is probably due to dysfunction in sympathetic control. What this study was able to show was the idea of adrenergic reactivity remodeling in OZR that may contribute to peripheral vascular disease in obese diabetics if the phenomenon presents itself true for humans as well. ~JI

VGLUT1 and VGLUT2 Innervation in autonomic regions of intact and transected rat spinal cord

Llewellyn‐Smith, Ida J., et al. "VGLUT1 and VGLUT2 innervation in autonomic regions of intact and transected rat spinal cord." Journal of Comparative Neurology 503.6 (2007): 741-767. This paper looked at the innervation of autonomic regions of the spinal cord via VGLUT1 and VGLUT2 vesicles before and after spinal cord injury induced by complete spinal cord transections. VGLUT1 and VGLUT2 mRNA were also examined in order to look at protein synthesis before and after the spinal cord was transected. What the study found was that the majority of sympathetic pre-ganglionic neurons, as well as parasympathetic pre-ganglionic neurons are innervated by VGLUT2 vesicles in rats with an intact spinal cord. However, it was found that autonomic interneurons seems to be innervated more by VGLUT1 vesicles in rats without spinal transections. After spinal transections were performed at the level of T4/T5 in rats, no significant difference in VGLUT2 innervation of the IML were found. The most plausible explanation for this being that the IML is highly innervated by interneurons which would not have been affected by the spinal cord being transected. On the other hand, it was discovered that 11 weeks following a spinal cord transection VGLUT1 immunoreactivity significantly increased. Although no mechanism was verified for the increase seen, it can be extrapolated that after a spinal injury there is a certain neuroplasticity occurring at the level of the spinal cord in order to produce the increases of VGLUT1 observed. It also seems that the plasticity taking place is creating hyper-excitable reflexes in comparison to rats with an intact spinal cord. This information is important to our study, to know that spinal plasticity is possible when using manganese as a retrograde tracer in order to study neural activity at the level of the RVLM. ~JI

The effect of air puff stress on c-Fos expression in rat hypothalamus and brainstem: central circuitry mediating sympathoexcitation and baroreflex resetting

Teri M. Furlong, Lachlan M. McDowall, Jouji Horiuchi, Jaimie W. Polson and Roger A. L. Dampney European Journal of Neuroscience, pp. 1–10, 2014 doi:10.1111/ejn.12521 In response to psychological stress there is an increase in sympathetic nerve activity (SNA). The purpose of this article is to determine if this increase in SNA is because of activation of the RVLM in response to psychological stress. They looked at c-fos expression in the brain along with a retrograde tracer injection into NTS in order to determine if there are other areas projecting to NTS that may be involved in the psychological stress response. So rats were exposed to air puffs this is considered an unconditioned stressor. The control group did not receive the air puff exposure. The results showed that that there was a significant increase in c-fos in PVN, DMH, PeF, LH, MeA, BLA, dorsomedial, dorsolateral and ventrolateral PAG, LC, the VLM, and the medial portion of the NTS when compared to controls. They also looked at TH immunoreactivity and found that there were very few TH positive and c-fos neurons in the RVLM. They did see a significant amount of C-fos and TH positive neurons in the CVLM in the stressed group when compared to controls. They also looked at serotonin and found that there was a significant increase in c-fos and 5-HT labelled cells in the lateral portion of the mid line raphe in stressed rats compared to controls. They looked at the retorgradely labelled cells and found that CTB labelled cells in th PVN,DMH, PeF LH, CeA lateral PAG, PB there was only a significant number of CTB and c-fos found in PVN PeF and vlPAG when compared to controls. These data suggests that there are several regions that play role in sympathetic activation in response to psychological stress however the RVLM is not a major player.-MD

Role of the Rostral Ventrolateral Medulla in the Arterial Hypertension in Chronic Renal Failure

Adriana P. Castilho Dugaich, Elizabeth B. Oliveira-Sales, Nayda P. Abreu, Mirian A. Boim, C´assia T. Bergamaschi, and Ruy R. Campos SAGE-Hindawi Access to Research International Journal of Hypertension Volume 2010, Article ID 219358, 6 pages doi:10.4061/2010/219358 It has been purposed that during chronic renal failure (CRF) there is an increase in reactive oxygen species (ROS). This may occur because ang II leads to an increased activity of NAD(P)H oxidase, which is responsible for the majority of superoxide that are produced. NAD(P)H is composed of gp91phox and p22 phox. The cytoplasmic components are p40phox p47phox, p67phox and the small G protein Racla. When ang II binds to AT1 receptor this leads to the cytoplasmic units binding to the membrane subunits and activating the NAD(P)H enzyme and this leads to the production of O2-. The purpose of this study is to quantify p47phox and gp91phox expression in RVLM, along with AT1 receptor expression in the RVLM. They also want to identify the role of AT1 in the superoxide production. So they injected candestan an AT1 antagonist. They also scavenged for superoxides by injecting tempol. Finally they tested inhibitory signaling specifically they looked at GABAergic responsiveness in the RVLM, by giving GABA./they found that AT1 mRNA was significantly decreased in CRF compared to controls in the brainstem. P47phox and gp91phox gene expression in RVLM in CRF group was significantly higher compared to controls. As for the microinjection portion of the study they found that Tempol resulted in decreases in MAP in CRF and not in controls. Also GABA caused larger decreases in MAP in CRF compared to controls. The candestan did not significantly change MAP. These data suggest that there is an increase in superoxide production but it is not due to AT1 receptor activation.-MD