Neurons in the rostral ventrolateral medulla (RVLM) regulate blood pressure through direct projections to spinal sympathetic preganglionic neurons. Only some RVLM neurons are active under resting conditions due to significant, tonic inhibition by gammaaminobutyric acid (GABA). Withdrawal of GABA A receptor-mediated inhibition of the RVLM increases sympathetic outflow and blood pressure substantially, providing a mechanism by which the RVLM could contribute chronically to cardiovascular disease (CVD). Here, we tested the hypothesis that sedentary conditions, a major risk factor for CVD, increase GABA A receptors in RVLM, including its rostral extension (RVLM RE ), both of which contain bulbospinal catecholamine (C1) and non-C1 neurons. We examined GABA A receptor subunits GABA Aα1 and GABA Aα2 in the RVLM/RVLM RE of sedentary or physically active (10-12 weeks of wheel running) rats. Western blot analyses indicated that sedentary rats had lower expression of GABA Aα1 and GABA Aα2 subunits in RVLM but only GABA Aα2 was lower in the RVLM RE of sedentary rats. Sedentary rats had significantly reduced expression of the chloride transporter, KCC2, suggesting less effective GABA-mediated inhibition compared to active rats. Retrograde tracing plus triple-label immunofluorescence identified fewer bulbospinal non-C1 neurons immunoreactive for GABA Aα1 but a higher percentage of bulbospinal C1 neurons immunoreactive for GABA Aα1 in sedentary animals. Sedentary conditions did not significantly affect the number of bulbospinal C1 or non-C1 neurons immunoreactive for GABA Aα2 .These results suggest a complex interplay between GABA A receptor expression by spinally projecting C1 and non-C1 neurons and sedentary versus physically active conditions. They also provide plausible mechanisms for both enhanced sympathoexcitatory and sympathoinhibitory responses following sedentary conditions.

The cardioprotective effects of female hormones/female sex are well‐described. In particular, several studies demonstrate the importance of female hormones on regulation of sympathetic outflow, a primary contributor to normal blood pressure as well as cardiovascular disease. Protective effects of ovarian hormones may include actions in the rostral ventrolateral medulla (RVLM), a brain region critical to sympathetic outflow and blood pressure. However, the time course and mechanisms by which sex‐differences contribute to excitation and inhibition of RVLM neurons are not fully elucidated; particularly in sexually immature animals, which lack higher levels of reproductive hormones. Therefore, we hypothesized that in the presence of lower levels of reproductive hormones, sexually immature females may exhibit increased glutamate (excitatory) receptors and decreased GABAA (inhibitory) receptors, indicative of an excitatory profile in the RVLM. To test our hypothesis, we obtained brain punches from the RVLM of four week old, male and female Sprague‐Dawley rats (n=3 ea), and processed them for western blotting. The NMDA (NR1) subunit was expressed in the RVLM of both sexes, but was expressed at a higher level in females compared to males (1.10±0.08 vs. 0.65±0.10 protein/GAPDH, respectively). The GABAAα1 subunit was also expressed in the RVLM of both sexes, but was expressed at lower levels in females compared to males (0.61±0.08 vs. 0.79±0.10 protein/GAPDH, respectively). These results suggest that prior to the onset of sexual maturity, a lower level of female hormones may increase the relative excitability of the RVLM and lead to greater sympathoexcitation in females compared to males. These experiments illustrate the importance of studying the time course and level of sexual maturity of animals in studies involving the influence of reproductive hormones. We are currently performing in vivo studies to examine the functional correlates of a greater excitatory profile in the RVLM of female rats, and to what extent sexual maturation influences the RVLM in both sexes. Support or Funding Information (HL096787‐07; AHA25810010) This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Various fatty acyl lipid mediators are derived from dietary polyunsaturated fatty acids (PUFAs) and modulate nociception. The modern diet is rich in linoleic acid, which is associated with nociceptive hypersensitivities and may present a risk factor for developing pain conditions. Although recommendations about fatty acid intake exist for some diseases (e.g. cardiovascular disease), the role of dietary fatty acids in promoting pain disorders is not completely understood. To determine how dietary linoleic acid content influences the accumulation of pro- and anti-nociceptive fatty acyl lipid mediators, we created novel rodent diets using custom triglyceride blends rich in either linoleic acid or oleic acid. We quantified the fatty acyl lipidome in plasma of male and female rats fed these custom diets from the time of weaning through nine weeks of age. Dietary fatty acid composition determined circulating plasma fatty acyl lipidome content. Exposure to a diet rich in linoleic acid was associated with accumulation of linoleic and arachidonic acid-derived pro-nociceptive lipid mediators and reduction of anti-nociceptive lipid mediators derived from the omega-3 PUFAs. Our findings provide mechanistic insights into exaggerated nociceptive hypersensitivity associated with excessive dietary linoleic acid intake and highlight potential biomarkers for pain risk stratification.

The rostral ventrolateral medulla (RVLM) contains bulbospinal neurons that contribute to normal and pathologically‐related increases in sympathetic nerve activity. Both structural and functional forms of neuroplasticity occur in the RVLM following sedentary versus physical active conditions, and are subregion specific. For example, in the rostral subregion of the RVLM, sedentary rats exhibit greater sympathoexcitation in response to glutamate microinjections (functional neuroplasticity) as well as more extensive dendritic branching (structural neuroplasticity), both consistent with increased excitability. Although these findings suggest a link between subregion‐specific neuroplasticity in the RVLM and inactivity‐related cardiovascular diseases, the mechanisms mediating these alterations remain unknown. The role of brain‐derived neurotrophic factor (BDNF) is well established in the field of neuroplasticity in terms of neuronal growth and remodeling. It has also been proposed that BDNF serves as a neurotransmitter in brainstem regions involved in sympathetic outflow. Whether sedentary conditions alter levels of the mature form of BDNF (mBDNF, which promotes dendritic branching) or the pro‐form of BDNF (proBDNF, which inhibits dendritic branching) in the RVLM is unknown. The purpose of this study was to test the hypothesis that mBDNF is increased and proBDNF is decreased in more rostral regions of the RVLM, particularly in sedentary rats. To test this hypothesis, male Sprague‐Dawley rats were divided into two groups: physically active (running wheels) and sedentary (without wheels, n=6 ea). Animals were housed for 10–12 weeks before sacrificing for fresh tissue removal. Frozen brainstems were cryosectioned at 80 μm, from which bilateral tissue punches were obtained for Western blotting. Punches were pooled based on their location relative to the caudal pole of the facial nucleus (FN+480; FN+240; FN‐240; FN‐480 μm), as determined in cresyl violet‐stained, post‐punched sections. The RVLMs of sedentary and active rats exhibited rostrocaudal‐dependent levels of mBDNF, with rostral regions exhibiting significant increases compared to caudal regions (main effect; p=0.039). However, sedentary rats exhibited significantly less mBDNF at FN+240 to FN‐480 (p<0.05 vs active). proBDNF levels were also lower in sedentary rats (p<0.05) as were TrkB receptors, the primary receptor for mBDNF (p<0.001; full length‐TrkB; p=0.002; truncated‐TrkB), suggesting an overall decrease in mBDNF signaling in sedentary rats. These results further demonstrate activity‐dependent neuroplasticity in subregions of the RVLM, but do not support a contribution of mBDNF towards the increased dendritic branching in rostral regions of the RVLM following sedentary conditions. In contrast, reductions in the pro‐form of BDNF and loss of its inhibitory effect on dendritic branching may contribute to increased dendritic branching in sedentary animals. Future studies could also examine BDNF‐induced alterations in synaptic transmission as well as other neurotrophic growth factors, all of which may contribute to increased cardiovascular disease in sedentary individuals via influences on sympathetic outflow.Support or Funding InformationHL096787‐07; AHA25810010This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

A sedentary lifestyle is a major risk factor for cardiovascular disease (CVD). CVD is often associated with enhanced activation of the sympathetic nervous system. The sympathetic nervous system is under tonic and phasic control by the rostral ventrolateral medulla (RVLM). In sedentary rats, there is enhanced sympathoexcitation in response to glutamatergic activation of the RVLM. Since the activity of RVLM is tonically restrained by γ‐amino‐butyric acid (GABA), we hypothesized that sedentary conditions may also lead to decreased responsiveness to GABA in RVLM when compared to physically active conditions. In Inactin anesthetized, sedentary (SED) or physically active (EX) rats, mean arterial pressure (MAP), heart rate (HR) and splanchnic sympathetic nerve activity (sSNA) were recorded during unilateral microinjection of GABA (30 nl, 0.3–600 mM) into the RVLM. Following GABA injections, the contralateral RVLM was inhibited with 90 nl of 2mM Muscimol and the GABA injections were repeated. There were no significant differences between SED or EX conditions for MAP, HR and sSNA responses to GABA both before and after contralateral blockade of the RVLM. Based on our results the enhanced sympathoexcitation seen in our sedentary model is not due to reduced responsiveness to GABA and may be due to enhanced responsiveness to excitatory neurotransmission. (Supported by R01‐HL096787; R01‐HL096787‐S1)