The role of nitric oxide in the dorsomedial periaqueductal gray (dmPAG) column in cardiovascular responses in urethane-anesthetized male rats

BACKGROUND

The dorsomedial periaqueductal gray (dmPAG) is a mesencephalic area and has numerous functions including cardiovascular regulation. Because nitric oxide (NO) is present in the dmPAG, here we investigate, the probable cardiovascular effect of NO in the dmPAG.

METHODS

Five groups (n = 6 for each group) were used as follows: (1) control; (2) L-NAME (N^G -nitro-L-arginine methyl ester, a NO synthase inhibitor, 90 nmol); (3) L-arginine (L-Arg, a precursor for NO, 60 nmol); (4) Sodium nitroprusside (SNP, a NO donor, 27 nmol); and (5) L-Arg + L-NAME. The cardiovascular parameters were recorded by a Power Lab device after cannulation of the femoral artery. Drugs were injected using a stereotaxic instrument. The changes (∆) in systolic blood pressure (SBP), mean arterial pressure (MAP), and heart rate (HR) were calculated at different times and compared to the control group.

RESULTS

Microinjection of L-NAME significantly increased ∆SBP, ∆MAP, and ∆HR more than saline (from p < 0.05 to p < 0.001). L-Arg only significantly increased ∆HR (p < 0.05). In the L-Arg + L-NAME group, the above parameters also significantly increased (from p < 0.01 to p < 0.05) but not as significantly as with L-NAME alone. Microinjection of SNP significantly decreased ∆SBP and ∆MAP more than in the control and L-NAME groups (from p < 0.01 to p < 0.001), but ∆HR did not change significantly.

CONCLUSION

The results indicated that NO in dmPAG has an inhibitory effect on cardiovascular responses in anesthetized rats.

Enhancement in Tonically Active Glutamatergic Inputs to the Rostral Ventrolateral Medulla Contributes to Neuropathic Pain-Induced High Blood Pressure

Neuropathic pain increases the risk of cardiovascular diseases including hypertension with the characteristic of sympathetic overactivity. The enhanced tonically active glutamatergic input to the rostral ventrolateral medulla (RVLM) contributes to sympathetic overactivity and blood pressure (BP) in cardiovascular diseases. We hypothesize that neuropathic pain enhances tonically active glutamatergic inputs to the RVLM, which contributes to high level of BP and sympathetic outflow. Animal model with the trigeminal neuropathic pain was induced by the infraorbital nerve-chronic constriction injury (ION-CCI). A significant increase in BP and renal sympathetic nerve activity (RSNA) was found in rats with ION-CCI (BP, n = 5, RSNA, n = 7, p < 0.05). The concentration of glutamate in the RVLM was significantly increased in the ION-CCI group (n = 4, p < 0.05). Blockade of glutamate receptors by injection of kynurenic acid into the RVLM significantly decreased BP and RSNA in the ION-CCI group (n = 5, p < 0.05). In two major sources (the paraventricular nucleus and periaqueductal gray) for glutamatergic inputs to the RVLM, the ION-CCI group (n = 5, p < 0.05) showed an increase in glutamate content and expression of glutaminase 2, vesicular glutamate transporter 2 proteins, and c-fos. Our results suggest that enhancement in tonically active glutamatergic inputs to the RVLM contributes to neuropathic pain-induced high blood pressure.

Cardiovascular responses elicited by continuous versus intermittent electrical stimulation of the aortic depressor nerve in conscious rats

AIMS

Short-term (seconds or minutes) continuous electrical activation of the aortic depressor nerve (ADN) in conscious rats has been successfully used to investigate baroafferent function in experimental hypertension, heart failure, and peripheral inflammation. The aim of this study was to characterize the hemodynamic responses elicited by longer periods (60min) of continuous or intermittent electrical baroreflex activation.

MAIN METHODS

Wistar rats were implanted with an electrode around the left ADN and a catheter into a femoral artery. The systolic, diastolic and mean arterial pressure and heart rate were recorded in subjects randomly assigned to continuous or intermittent electrical stimulation. The time-course of cardiovascular responses in conscious rats was examined during longer-term (60min) continuous (n=6) or intermittent (5s ON/3s OFF; n=10) electrical stimulation (0.5mA; 0.25ms; 30Hz) of the ADN.

KEY FINDINGS

The prompt (20s) hypotensive response was greater under continuous stimulation, but no difference was detected in the bradycardic response. The hypotensive response was sustained only by continuous stimulation while no sustained bradycardia was observed in either protocol.

SIGNIFICANCE

These findings indicate that continuous stimulation of the ADN is more effective in reducing arterial pressure over a longer period (60min) of stimulation. Nevertheless, both protocols - continuous or intermittent - were unable to elicit a sustained bradycardia.

Acute stress affects the global DNA methylation profile in rat brain: modulation by physical exercise

The vulnerability of epigenetic marks of brain cells to environmental stimuli and its implication for health have been recently debated. Thus, we used the rat model of acute restraint stress (ARS) to evaluate the impact of stress on the global DNA methylation and on the expression of the Dnmt1 and Bdnf genes of hippocampus, cortex, hypothalamus and periaqueductal gray (PAG). Furthermore, we verified the potential of physical exercise to modulate epigenetic responses evoked by ARS. Sedentary male Wistar rats were submitted to ARS at the 75th postnatal day (PND), whereas animals from a physically active group were previously submitted to swimming sessions (35-74th PND) and to ARS at the 75th PND. Global DNA methylation profile was quantified using an ELISA-based method and the quantitative expression of the Dnmt1 and Bdnf genes was evaluated by real-time PCR. ARS induced a decrease in global DNA methylation in hippocampus, cortex and PAG of sedentary animals and an increased expression of Bdnf in PAG. No change in DNA methylation was associated with ARS in the exercised animals, although it was associated with abnormal expression of Dnmt1 and Bdnf in cortex, hypothalamus and PAG. Our data reveal that ARS evokes adaptive changes in global DNA methylation of rat brain that are independent of the expression of the Dnmt1 gene but might be linked to abnormal expression of the Bdnf gene in the PAG. Furthermore, our evidence indicates that physical exercise has the potential to modulate changes in DNA methylation and gene expression consequent to ARS.

Evidence for brainstem network disruption in temporal lobe epilepsy and sudden unexplained death in epilepsy

The symptoms witnessed in unexplained death in epilepsy (SUDEP) suggest a breakdown of central autonomic control. Since the brainstem plays a crucial role in autonomic control, the objectives of this study were 1. To investigate if temporal lobe epilepsy (TLE) is associated with brainstem atrophy and to characterize it using graph Analysis 2. To compare the findings with those in two probable TLESUDEP. T1 images were obtained from 17 controls, 30 TLE (16 with mesial-temporal-sclerosis (TLE-MTS) and 14 without (TLE-no)) and from 2 patients who died of SUDEP. The brainstem was extracted, warped onto a brainstem atlas and Jacobian determinants maps (JDM) calculated. SPM8 was used to compare the JDMs at the group level, z-score maps were calculated for single subject analysis. Brainstem regions encompassing autonomic structures were identified based on macroscopic landmarks and mean z-scores from 5 × 5 × 5 voxel cubes extracted to calculate a new measure called atrophy-similarity index (ASI) for graph analysis. TLE-MTS had volume loss in the dorsal mesencephalon. The SUDEP cases had severe and more extensive volume loss in the same region. Nodal degrees and participation coefficients were decreased and local efficiency increased in SUDEP compared to controls. TLE is associated with volume loss in brainstem regions involved in autonomic control. Structural damage in these regions might increase the risk for a fatal dysregulation during situations with increased demand such as following severe seizures.

Patients with temporal lobe epilepsy (TLE) were studied.

Two had died of Sudden Unexplained Death in Epilepsy (TLE-SUDEP)The brainstem was studied with deformation-based morphometry and graph analysis TLE has volume loss in the dorsal mesencephalon.TLE-SUDEP have more extensive brainstem damage and evidence for network breakdown.