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

Activation of Corticotropin Releasing Factor Receptors in the Rostral Ventrolateral Medulla is Required for Glucose-Induced Sympathoexcitation

Megan E. Bardgett, Amanda L. Sharpe, Glenn M. Toney.Am J Physiol Endocrinol Metab (September 30, 2014). doi:10.1152/ajpendo.00291.2014.

Glucose leads to increased energy expenditure  through activation sympathetic nerve activity (SNA). The mechanism that leads to the activation of SNA is unknown. PVN and RVLM play an important role in the control of SNA and BP.  We already know that PVN not directly projects down to the IML in order to control SNA and BP but there is a direct projection to RVLM from PVN. Also neurons in the PVN are activated by glucose. The activity of RVLM is controlled mainly by Glutamate and GABA but we also know that there are other neurotransmitters that may be involved such as corticotropin releasing factor (CRF). So it has been shown that there are CRFergic neuron in the PVN. The hypothesis for the study in this article was that glucose leads to increases in SNA through activation of CRFergic neurons in the PVN that ultimately lead to activation of RVLM neuron by activating CRF receptor that lead to sympathoexcitation.  In order to prove this they provided anatomical along with function data. The data provided showed that glucose infusion elevates both LSNA and SSNA. They also demonstrated that glucose does, in fact, activate neurons in both RVLM and PVN. Not only that but the majority of PVN neurons that expressed c-fos was also a CRFergic neuron. As for RVLM, they showed that glucose activated a significant portion of TH RVLM neurons. Blockade of CRF receptor blunted the increases in LSNA and SSNA in response to glucose infusion. They also showed that kyn blocks the increase in SNA in response to glucose. Final they demonstrated that blockade of PVN blocked the response to glucose infusion. These data demonstrate that glucose leads to activation of SNA by activating CRFergic neurons in the PVN and this leads to the release of CRF and this leads to activation or the CRF receptor and this may facilitate the release of glutamate in the RVLM and this leads to increases in SNA and thus energy expenditure. I wonder how SNA in our model might behave in response to glucose infusion…-MD

CNS neuroplasticity and salt-sensitive hypertension induced by prior treatment with subpressor doses of ANG II or aldosterone

Sarah C. Clayton, Zhongming Zhang, Terry Beltz, Baojian Xue, and Alan Kim Johnson.

Am J Physiol Regul Integr Comp Physiol 306: R908–R917, 2014.First published April 2, 2014; doi:10.1152/ajpregu.00010.2014. Hypertension is obviously a problem in today’s society.  About 25% of all hypertensive patients are salt sensitive. However the mechanism that is responsible for salt sensitivity leading to hypertension is still not clearly understood. It has been shown that pretreatment with  nonpressor doses of ANG II and aldosterone can lead to enhanced responses to ANG II. This sensitization depends on a functional brain renin angiotensin aldosterone system. Long term changes in the CNS could occur in response to sensitization. This studied investigated whether BDNF a protein that plays a role in many models neuroplasticity is involved in the changes that are occurring in the lamina terminalis (LT) in response to sensitization to ANGII.  the study showed that pretreatment to ANGII or Aldosterone in the brain can lead sensitization to salt. They also showed that the BDNF is enhanced along with p38 MARK and pCREB in response to pretreatment to ANGII and aldosterone. These data demonstrate that pretreatment with subpressor doses of ANGII and aldosterone can lead long term structural changes by increasing the the BDNF pathway in LT and this contributes to the development of salt sensitivity. I wished they would have investigated the RVLM, wouldn’t that be interesting.-MD

Role of the hypothalamic arcuate nucleus in cardiovascular regulation

Hreday N. Sapru.Autonomic Neuroscience. Volume 175, Issues 1–2, April 2013, Pages 38–50.DOI: 10.1016/j.autneu.2012.10.016.  In ths review article the role of the arcuate nucleus was discussed.The arc is located in the hypothalamus and it has some projections that go to RVLM, NTS, CVLM, IML just to name some. The PVN receives the highest amount of projections from the arc when compared to the other regions mentioned above.  The arc extends to the median eminence, which is area that lacks a BBB. This allows for the arc to be exposed to leptin, glucose and angiotensin.  What I found most interesting was that stimulation of the arc can cause both depressor and pressor responses. When blood pressor is normal activation of the arc leads to depressor responses ( release of GABA, neuropeptide y, and beta endorphin) most likely due to inactivation of neurons in the PVN that project down to the spinal cord or RVLM and lead to decreased sympathetic activity. However when blood pressure is low, activation of neurons in the arc leads to pressor responses (most likely due to the release of glutamate). The baroreceptor reflex may play also play role in how blood pressure is modulated in response to activation of the arc neurons. It has been shown that following barodenervation, stimulation of the arc leads to pressor responses. This may suggest that the baroreceptors are important for providing inhibitory input on to glutamate releasing arc neurons. overall I thought that this could be a region that we investigate in the future since it could be

 playing a role in both  activation and inhibition of the rvlm neurons. -MD

Sympathoexcitation and pressor responses induced by ethanol in the central nucleus of amygdala involves activation of NMDA receptors in rats

Andrew D. Chapp , Le Gui , Michael J. Huber , Jinling Liu , Robert A. Larson , Jianhua Zhu , Jason R. Carter , Qing-Hui Chen. American Journal of Physiology - Heart and Circulatory Physiology Published 1 September 2014Vol. 307 no. 5, H701-H709DOI: 10.1152/ajpheart.00005.2014. Ingestion of alcohol leads to pressor and sympathoexicition. This purpose of this study was to elucidate the mechanism responsible for the activation of the sympathetic nervous system. By using microinjection technique they demonstrated that ethanol and acetate, a byproduct of ethanol caused pressor and increases in SSNA and LSNA when injected into the amygdala (CeA).  In order to determine whether this response is being mediated by glutamate, they injected kyn, an EAA receptor blocker, NMDAR blocker and a non NMDAR blocker mixed with ethanol. They found that Kyn and the NMDAR blocker both attenuated the pressor response and SSNA. Then in order to determine whether the RVLM was playing role in the response kyn was injected into the RVLM they found that this also attenuated the response. Finally they showed that anatomically there was an connection between RVLM and CeA and that NMDAR were present on CeA-RVLM neurons. These data show that alcohol and alcohol metabolites can lead to activation of RVLM neurons which may be the cause of increase sympathetic outflow in response to alcohol consumption.-MD

Modulation of inducible nitric oxide synthase (iNOS) expression and cardiovascular responses during static exercise following iNOS antagonism within the ventrolateral medulla

 

Pasarapa Towiwat, Siripan Phattanarudee,Timothy J. Maher, Ahmmed Ally. Mol Cell Biochem DOI 10.1007/s11010-014-2218-9.  The exercise pressor reflex leads to an increase in BP in response to static exercise. This reflex mediates its control over the cardiovascular system  by modulating the activity of CVLM and RVLM neurons. As we already know, there are different neurotransmitters that modulate the activity neurons in the RVLM and CVLM. It has been demonstrated in the literature that microdialysis of L- arginine into the CVLM lead to enhanced pressor response during static exercise along with decreased GABA release.  However, when L-arginine was infused into the RVLM blocked the cardiovascular responses to static exercise.  Blockade of both nNOS and eNOS lead to enhanced GABA and decrease glu in CVLM. Blockade of both nNOS and eNOS in the RVLM lead to enhanced Glu and decrease GABA.  Since it has been shown that blockade of iNOS in SHR leads to attenuation of there hypertensive state, This study wanted to further investigate the role of iNOS in the exercise pressor response.  They found that blockade of iNOS by infusion into the RVLM,  lead to attenuated HR and blood increase in response to activation of the exercise pressor reflex. they also showed a decrease in iNOS protein expression in the RVLM following blockade of iNOS in the RVLM and no change in CVLM. However, when the antagonist for iNOS was infused into CVLM they observed the response to activation of the exercise pressor reflex was potentiated. The protein expression of iNOS was not different when compared to controls for RVLM and CVLM. These data demonstrate that iNOS may be lead playing a role in the exciting neurons in the RVLM possibly through enhancing Glu and/or decreasing GABA release.-MD

GABAergic mechanism in the rostral ventrolateral medulla contribute to the hypotension of moxonidine

Wang et al. cardiovascular research (2011)89 473-481; doi:10.1093/cvr/cvq289. Moxonidine is a antihypertensive drug that is thought to act centrally. This study wanted to investigate whether GABA A receptor blockade would affect the effects of mononidine on the cardiovascular system, also whether GABA release and receptor expression was affected by moxonidine. What they found was that microinjection of moxonidine leads to decreases in BP, HR and RSNA.  When GABA A receptors and GABA B receptors were unilaterally blocked and they injected moxonidine into RVLM they were able to attenuate the BP, HR and RSNA decreases. They also did bilateral blockade of GABA A receptors in RVLM and gave moxonidine systemically and showed that bilateral blockade of GABA A receptors lead to attenuated decreases in BP, HR, and RSNA.  Intravenous administration of moxonidine leads to increase in the release of GABA. In response to a week of icv treatment with moxonidine, GABA ARα1 and GABA BR1 when compared to acsf control group. These data demonstrate that GABAergic neurotransmission in the RVLM are important for mediating the effects of moxonidine. -MD

Brain angiotensin- converting enzyme type 2 shedding contributes to the development of neurogenic hypertension

Huijing Xia, Srinivas sriramula, Kavaljit H. Chhabra, Eric Lazartigues.Circ Res.2013;113:1087-1096; doi:10.1161/circresaha.113.301811.

It has been shown that overactivity of the renin angiotensin system can lead to hypertension. Ace 2 is an enzyme that can convert angII to ang 1-7. Ang1-7 has an vasodilatory affect on vasculature.  Ace 2 is down regulated in hypertension further contributing to the dysfunction of the RAS. What is really interesting is that it has been shown that ectodomain of ACE2 is cleaved and can be found in CSF. Thus hypertension leads to ace 2 shedding. The question becomes what is responsible for the removal of ace 2 from the cell membrane. So the hypothesis was adam 17 is responsible for the cleavage of ace 2 and leading to the development of hypertension.  So they used transgenic mice in order to test there hypothesis. Using mice that had overexpression of Ace2 in neurons that were DOCA- high salt diet mice improved the spontaneous Baroreflex function. Ace2 overexpression also leads to decreased vasopressin release, norepinephrine, and ang II. Along with that vagal tone was restored and sympathetic drive to the heart and vasculature was brought back down to control levels. They knockdown adam 17 and showed that this prevented the development of hypertension and lead to a decrease in ace 2 shedding in the csf. These data demonstrate that hypertension that is due to a high salt diet may be leading to increased adam 17 expression and leading to decrease ace 2 expression on neurons and ultimately leading to hypertension. –MD

Leptin into the rostral ventral lateral medulla (RVLM) augments renal sympathetic nerve activity and blood pressure

Barnes and McDougal.Front. Neurosci.8:232.doi:10.3389/fnins.2014.0232.

Leptin is released from fat cells in order to promote satiety and increases energy expenditure. One mechanism by which leptin affects energy expenditure is by increasing sympathetic nerve  activity. Leptin signaling is mediated through the hypothalamus and has been shown to increase blood pressure and renal sympathetic nerve activity (RSNA).   we know that PVN sends projections to the RVLM and to the spinal cord to modulate sympathetic nerve activity. This study investigated if the leptin receptor is present in brainstem regions that control RSNA./For their anatomical studies they injected PRV into the  cortex of the kidney and did immunofluorescent staining for the leptin receptor (obrb). As for the functional studies they microinjected leptin and leptin receptor antagonist into the rvlm and recorded blood pressure and RSNA.  They found obrb positive cells in the C1/A1 region, VMM, caudal raphe and A5 area. Most of the PRV positive cells were found in the rostral portion of the RVLM (similar Nick’s paper) and found no difference between ipsilateral and contralateral RVLM.  They found that 65% of the C1/A1 region was double labeled.  As for the functional studies, they found that leptin lead to an increase in RSNA and BP. Injection of the antagonist prior to the leptin injection attenuated the BP and RSNA response.  Conclusion leptin release from fat cells is leading to increased energy expenditure via increasing sympathetic nervous system activity through activation of obrb receptors in the RVLM. MD

 

Cardiovascular effect of angiotensin-(1–12) in the caudal ventrolateral medullary depressor area of the rat

Tetsuya Kawabe, Kazumi Kawabe, and Hreday N. Sapru.Am J Physiol Heart Circ Physiol 306: H438–H449, 2014. First published November 27, 2013; doi:10.1152/ajpheart.00628. 2013. This study investigated whether ang 1-12 is leading to increased neuronal activity through AT1 Receptors in the cvlm. In Wistar rats, they recorded GSNA, BP, and HR  and used microinjection technique. They found that microinjections of ang 1-12 into cvlm lead to decreases in BP, HR and GSNA. Ang 1-12 mediates it response through AT1R. The activation of AT1R leads to the release of GABA from the terminals of CVLM neurons and acts on GABA receptors in the RVLM in order to cause sympathoinhibition.  In conclusion, Ang 1-12 maybe playing a role in the activation of neurons in the CVLM. I wonder if the level of Ang 1-12   is changing in response exercise…MD

Exaggerated Cardiovascular Stress Responses and Impaired β-Adrenergic–Mediated Pressor Recovery in Obese Zucker Rats

Gerard D’Angelo, James D. Mintz, John E. Tidwell, Ann M. Schreihofer,David M. Pollock, David W. Stepp.Hypertension. 2006;48:1109-1115.Obesity is a major risk factor for development of metabolic disorders. Besides the increased risk for metabolic disorders there increase in the pressor response that results from mental, physical and acute stress. Since α and β adrenergic receptors are important for determining vascular tone, changes in either receptor expression or sensitivity to norepinephrine or epinephrine. In a previous study this laboratory demonstrated that pressor responses to ganglionic blockade was not different between obese and lean zucker rats. They also demonstrated that isolated mesenteric resistance arteries responses to exogenous norepinephrine is attenuated when compared to lean zucker rats. They concluded from this data that there is elevated peripheral vascular resistance. Furthermore, it may be due suppressed β-adrenergic-mediated vasodilation. In this study they hypothesized that pressor responses to environmental stressors would be greater in the obese versus the lean zucker rats. The elevated pressor response in the obese zucker will be most likely due to attenuated vasodilation as a result of impaired β- adrenergic mechanisms. Obese and lean zucker rats ( and LZR, respectively)were implanted with telemetry probes in order to record blood pressure under conscience conditions. Following recovery animals were brought to a soundproof room and then the animals were put into restrainers and a baseline blood pressure and heart rate were monitored for fifteen minutes prior to the air jet stress. In a separate group of obese and lean zucker rats, following the fifteen minute control period propranolol was administered and then the air jet stress was initiated. They also instrument animals so they could determine blow flow to the mesenteric arteries and aorta.They also looked at cardiac output along with blood glucose, plasma levels of cholesterol and triglycerides. They also looked at thyroid hormones T3/T4.They found that OZR had higher baseline BP and HR variability. In response to stress the OZR the area under the curve (AUC) for blood pressure was significantly higher in obese untreated when compared to the LZR. the AUC 20 minutes post stress was significatly greater in the OZR when compared to LZR. There was also a significant increase in AUC following treatment with propranolol in the LZR. They further analyzed the role of β-adrenergic receptors following ganglionic blockade. prior to ganglionic blockade, β-adrenergic receptor blockade resulted concentration dependent decreases in MAP in both groups, however the OZR had attentuated response when compared to LZR. Following ganglionic blockade resulted in a similar trend. They also looked at hindlimb and mesenteric conductance. There were no differences in hindlimb conductance between OZR and LZR ganglionic blockade in response to β- adrenergic blockade. As for mesenteric conductance both group exhibit increases in conductance, however only at 0.05,0.1, 0.5 μmoles of isoproterenol is there an attenuation in the OZR response when compared to LZR. As for cardiac output, there is an increase in response to isoproterenol in both group however the OZR had attenuated changes in CO at 0.05 and 0.5 μmoles. These data suggest that Obesity may lead to attenuated β- adrenergic mediated vasodilation. This β- adrenergic mediated vasodilation is playing an important role in the recovery period for stress.-MD

Developmental changes in GABAergic neurotransmission to presympathetic and cardiac parasympathetic neurons in the brainstem

Olga Dergacheva , Carie R. Boychuk , David MendelowitzJournal of Neurophysiology Published 1 August 2013Vol. 110no. 672-679DOI: 10.1152/jn.01054.2012. This article was interesting because it investigated how postnatal development altered gabaergic neurotransmission specifically, the effects on parasympathetic cardiac and presympathetic neurons in the brainstem. This group was interested in how hypoxia and hypercapnia (H/H) may play role in this. They used retrograde labelling with CTB injected in the T2-T4 region of the spinal cord. Then at certain days postnatal p5, p20, p30 and they looked at GABAergic neurotransmission and how it was altered by hypoxia and hypercapnia. In the parasympathetic cardiac vagal neurons there was IPSCs in response to strychnine in P5, P20, and P30. However, the P20 had increased frequency and amplitude of IPSCs than the other groups. As for the cardiac parasympathetic neurons on the P20 frequency was altered in under control conditions when compared to the P5 and P30. In response to H/H in the P5 and P30 the IPSCs were reversed however in the P20 frequency and amplitude IPSC not altered for presympathetic neurons. H/H decreased IPSC frequency in P5,P20, and P30. In only decreased the amplitude in the P20. These data demonstrate P20 is an important developmental stage for parasympathetic and sympathetic development. The reason why this study is so important is because this age in rats is equivalent to the age when children tend to develop SIDS. This increased sensitivity to hypoxia/ hypercapnia may be a possible reason why SIDS. -MD

Exercise Training Lowers the Enhanced Tonically Active Glutamatergic Input to the Rostral Ventrolateral Medulla in Hypertensive Rats

Yan-Ping Zha, Yang-Kai Wang, Yu Deng, Ru-Wen Zhang, Xing Tan, Wen-Jun Yuan, Xiao-Ming Deng & Wei-Zhong Wang. doi: 10.1111/cns.12065 The study investigated how exercise can modulate glutamate neurotransmission. Using WKYs and SHRs that were sedentary (sed) or exercise trained (ext) they looked basal blood pressure (BP), which was significantly reduced in the SHRs-ext when compared to the SHRs-sed. HR was also significantly reduced in the SHR-ext when compared to the SHR-sed. Similarly, they saw that exercise also reduced the decrease in BP and HR that is caused by giving a glutamate receptor blocker. Kyn had little affect ion bp and HR responses in the WKYs. In order to determine whether the concentration of glutamate is altered they used HPLC and found that SHR-sed had a higher concentration of glutamate when compared to WKYs(both sed and ext) and also SHR-ext. Western blot was done in order to examine the amount of vglut2 protein being expressed in the RVLM . Results showed that the SHR-SED had more vglut2 compared to the other groups. Finally they wanted to determine where this glutamatergic input is originating from. Western blot was done on punches from the NTS, PVN and PRF for glutaminase2. They found a significant increase in NTS and PVN in SHR-seds for glutaminase2 when compared to SHR-ext. Overall message, exercise reduces glutamatergic input via reduction in concentration of glutamate in rvlm and also a reduction in glutamatergic inputs from NTS and PVN. Maybe we should start looking at NTS also because it could be providing some glutamatergic input to rvlm.-MD

Role of presympathetic C1 neurons in the sympatholytic and hypotensive effects of clonidine in rats

Ann M. Schreihofer and Patrice G. Guyenet . American Journal of Physiology - Regulatory, Integrative and Comparative Physiology Published 1 November 2000Vol. 279no. R1753-R1762. The rostral ventrolateral medulla (rvlm) is important to control of blood pressure (BP) and sympathetic nerve activity (SNA). Clonidine is an antihypertensive medication that acts as an agonist for α1 adrenergic receptor on axons and terminals of rvlm neurons. The purpose of this paper was to determine whether clonidine acted on spinally projecting c1 or no c1 in the rvlm in order to lower SNA and BP. What they found was that after injecting DβH- saporin the response to clonidine. This finding along with previous data from other labs that showed that injections of clonidine into the nucleus tractus solitarius (NTS) and in the intermediolateral cell column (IML) demonstrates that clonidine may act on several areas in the brain in order to have the antihypertensive affect that is known for.-MD

Stress-induced elevations of y-aminobutyric acid type A receptor-active steroids in the rat brain

ROBERT H. PURDY, A. LESLIE MORROW, PERRY H. MOORE, JR., AND STEVEN M. PAUL. Proc. Nati. Acad. Sci. USA. Vol. 88, pp. 4553-4557, May 1991 Neurobiology. They investigated the effects of stress on the production of pregestrone metabolites in the brain. They used adrenectomized and non-adrenalectomized rats in order to determine how csf levels of progesterone, allopregnanolone and pregnanolone in rats were altered in response to swim stress. They used a couple of techniques such as chromatography, and RIA or Radioimmuno assay. What they found was that in the adrenalectomized, adrenalectomized stressed and controls had undetectable amounts of allotetrahydroDOC in plasma and cortex, however the stressed rats had significant enhanced levels of allotetrahydroDOC in both cortex and plasma. As for progesterone was not altered in response to stress when compared to the control group however the adrenalectomized rats had significantly lower progesterone when compared to the control rats. As for the allopregnanolone, in response to swim stress the level was significantly higher when compared to control animals in the cortex and plasma. Another interesting finding is that the in the adrenalectomized rats there was reduced allopregnanolone. The most important point I got from this article is that allopregnanolane and allotetrahydroDOC have the ability to bind to the benzodiazepine site on the GABA receptor, thus potentiating the effects of GABA. Since it seems that doing a adrenalectomy, abolishes the increase in these steroid metabolites, adrenal gland may be important to modulating GABAergic mechanisms in the brain. -MD

Neurosteroid modulation of arterial baroreflex function in the rostral ventrolateral medulla

Cheryl M. Heesch. Autonomic Neuroscience Volume 161, Issues 1–2, 26 April 2011, Pages 28–33 DOI: 10.1016/j.autneu.2010.10.002This article was interesting because it showed that a microinjection of 3α-hydroxy-dihdroprogesterone may alter the GABAA receptor sensitivity. They microinjected of 3α-hydroxy-dihdroprogesterone into the RVLM of female virgin rats and looked at blood pressure and renal sympathetic nerve activity (rsna). They found that 15 minutes following the microinjection of 3α-hydroxy-dihdroprogesterone significantly reduced the baroreflex rsna gain in response to hypotension. However, when the inactive isomer of 3β-hydroxy-dihdroprogesterone was microinjected into the rvlm it did not alter the baroreflex. These data suggests that 3α-hydroxy-dihdroprogesterone may alter the activity of the GABAA receptor in the RVLM. Since 3α-hydroxy-dihdroprogesterone can be synthesized in the brain it may be possible that the synthesis of this metabolite could be altered under different pathophysiological conditions. I think that this relevant to us because we don’t know how production of neurosteroids in the brain is altered in exercise and this could be another future potential avenue that may be pursued.-MD

Rapid swim-stress reduces GABAA receptor α1 subunit mRNAs in the mouse hippocampus

Pascale Montipied, Avraham Weizman, Ronit Weizman, Karin A. Kook A. Leslie Morrow, and Steven M. Paul. Molecular Brain Research, 18 (1993)267-272. They investigated how swim training would affect GABAA receptor subunits mRNA expression in mice. They used a northern blot in order to quantify GABA receptor subunit mRNA expression in the hippocampus. They found that swim stress (or maybe training!!!) for 14 days significantly reduced GABA A receptor α1 subunit expression in the hippocampus. They also looked at GAD expression and β-actin and that was unchanged by 7 and 14 days of swim stress. What I thought was interesting was that the mentioned that adrenectomy that don’t see these changes in GABA A receptor α1 subunit expression. These data suggest that the adrenal glands may be playing a role in modulation of GABAA receptor α1 subunit expression. This could be due to release of adrenal steroids that are can alter GABA A receptor expression indirectly after a long exposure. Based on the finding from this paper, I think the adrenal nerve activity may be key to elucidating the mechanism that leads to changes in glutamate and gaba neurotransmission in the RVLM.-MD

c-fos identifies GABA-synthesizing barosensitive neurons in caudal ventrolateral medulla

Jane B. Minson, Ida J. Llewellyn-Smith, John P. Chalmers, Paul M. Pilowsky and Leonard F. Arnold. NeuroReport8, 3015-3021(1997). We know that CVLM provides barosensitive and non-barosensitive GABAergic input to RVLM. This study provides anatomical along with functional support for the previous statement. They microinjected CTB into the RVLM of Wistar rats and infused with PE for 60min. Following the infusion of Phenylephrine, the rats were perfused and used for immunohistochemistry. They looked at 3 things in this study 1.) Barosensitive neurons in the CVLM 2.) Examined whether these barosensitive neurons in CVLM project to the RVLM and 3.) Determined if the barosensitive neurons that were GABAergic or glutamatergic. The results showed that PE increased the BP of the rats and lead to increase Fos expression in CVLM and in the NTS but not in the RVLM. Fos expressing and RVLM projecting neurons were identified and located in the more rostral areas of CVLM. Most of these neurons were located rostral to obex. Next the phenotype of the neurons was investigated, in order to determine if the neurons expressed GAD, PAG and TH. There were no TH and GAD neurons identified. About 40% of Fos positive neurons were also GAD positive. Most of these neurons were located in the rostral portion of the CVLM. There was no difference between fos/ PAG and Fos/ TH when PE infused animals were compared to the saline group. The Fos/ PAG/ TH neurons are located in the caudal regions of the CVLM. The most interesting finding in my opinion is that they were able to identify PAG/ CTB and GAD/ CTB neurons in the CVLM. This suggests that CVLM provides both glutamatergic and GABAergic inputs to RVLM. Even though the PAG/CTB neurons were not Fos positive, maybe CVLM provides a tonic level of glutamate to RVLM. Is this driving the activity of spinally projecting RVLM neurons? Also could this glutamatergic drive be altered in SEDs and WRs? These are questions that we could potentially look into. -MD

Modulation of Bulbospinal Rostral Ventral Lateral Medulla Neurons by Hypoxia/Hypercapnia but Not Medullary Respiratory Activity

Carie R. Boychuk, Amanda L. Woerman, David Mendelowitz. Hypertension. 2012; 60:1491-1497 Published online before print October 29, 2012, doi: 10.1161/HYPERTENSIONAHA.112.197954. There is respiratory modulation of sympathetic nerve activity but the sites that are a responsible for this are unknown. The rvlm is located near respiratory neurons. The purpose of this study was to determine whether respiratory network pathways can drive rvlm activity. Also they tested whether hypoxia/ hypercapnia can modulate RVLM activity in brainstem slices. They injected CTB into the spinal cord and allowed the rats to recover for 3 to 5 days. They then euthanized the rats and they used bulbospinal neurons that were TH and CTB positive. They then recorded rhythmic inspiratory- related hypoglossal activity and spontaneous synaptic events in the RVLM bulbospinal neurons for 2 to 4 minutes. Then slices were infused with hypoxic /hypercapnic acsf for 10 minutes and then switched back to the control bath for 20 minutes. They showed that none of the bulbospinal rvlm had changes in glycinergic, GABAergic and glutamatergic events. However, in response to hypoxia/hypercapnia the slow firing increased their rate of firing and stayed elevated during the control period. The fast firing had a reduction in their firing rate after the hypoxic/hypercapnic event and returned to baseline firing during the control time period. In order to determine whether hypoxia/hypercapnic changes in rvlm neuronal activity were dependent on GABAergic and glycinergic neurotransmission, gabazine and strychnine were applied to slices. Applying gabazine and strychnine did not alter the neuronal activity alone. However, hypoxic/ hypercapnic events where blocked in the slow firing cells. From this study they concluded that inspiratory events do not affect RVLM neuronal activity in young rats. Also they showed that hypoxic /hypercapnic events can reverse gabaergic and glycinergic neurotransmission leading to increases in firing rate in C1 bulbospinal neurons slow firing in the RVLM. Finally, that fast firing c1 neurons in the rvlm response to hypoxia/hypercapnia are not due to modulation of gabaergic and glycinergic neurotransmission.-MD

Altered c-fos in Rostral Medulla and Spinal Cord of Spontaneously Hypertensive Rats

Jane Minson, Leonard Arnolda, Ida Llewellyn-Smith, Paul Pilowsky, John Chalmers. Hypertension. 1996; 27: 433-441 doi: 10.1161/01.HYP.27.3.433. Hypertension leads to elevated sympathetic nerve activity. We know that the RVM is important for tonic control of blood pressure and sympathetic nerve activity. The neurons located in the RVM are tonically active. C-fos is an early gene that is expressed in response to stimuli. In this particular study they wanted to investigate RVM neuronal activity in Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR) using c-fos. They also wanted to phenotype the cells by staining for serotonin and catecholamine. First they instrumented 16 to 18 week old WKY and SHR rats so they could record blood pressure and give an infusion of nitroprusside through femoral artery and vein, respectfully. Prior to the nitroprusside infusion, at 12 to 14 weeks CTB-gold was injected into the adrenal medulla and superior cervical ganglion. As for the controls there were two groups WKY and SHR rats that were just implanted with arterial and venous catheters but were not subject to surgical interventions. The infusion of nitroprusside leads to a fall in blood pressure in both groups along with reflex tachycardia. Obviously the saline did not cause a change in blood pressure and heart rate. The SHRs had an enhanced response to the nitroprusside infusion when compared to the WKYs. They then perfused the animal following the infusion and 60minute rest period. The prepared the tissue for immunostaining. Fos immunoreactivity was significantly higher in the nitroprusside group when compared to the saline WKYs. However, the SHRs had similar fos production between the saline and the nitroprusside group. But the SHR group still demonstrated higher fos immunoreactivity than the WKYs. They found that 50% of the TH positive neurons where positive for fos also in the nitroprusside group in the WKYs. As for the saline group, only a small amount was double labelled for fos and TH positive in WKYs. They also looked at serotonin neurons in the RVM. Fos immunoreactivity was not as prevalent in the serotonin population as it was in the TH population. They also looked at fos in the spinal cord. Both groups had a significant amount of fos in the T1-L1 segments s of the spinal cord. As for retrogradely labelled sympathetic preganglionic neurons, they found fos positive sympathetic preganglionic neurons projecting to the sympathoadrenal neurons in the SHRs. They were located in segments T7-T11 and accounted for 39% of all fos neurons in the SHRs. As for sympathetic preganglionic neurons projecting to the superior cervical ganglion there was a limited number found in the SHRs. In the WKYs, they found sympathetic preganglionic neurons projecting to the sympathoadrenal neurons in the t1-t13 region of the spinal cord. After nitroprusside 71% of the fos positive neurons were sympathetic preganglionic neurons projecting to the sympathoadrenal neurons in WKYs. As for the superior cervical ganglion, retrogradely labelled sympathetic preganglionic neurons were found in the T1-T5 region but now were immunoreactive for Fos after nitroprusside. The conclusion that was drawn from the studies at resting level in the SHRs, RVLM neuronal activity is elevated. This increased activity is driving the sympathoadrenal neurons mostly, and these neurons are contributing to the hypertension that is observed in the SHRs.-Mary