Nicotine Induces Maternal and Fetal Inflammatory Responses Which Predispose Intrauterine Infection Risk in a Rat Model.

INTRODUCTION: Both smoking and infection adversely impact pregnancy. Previously, our group identified in a rodent model that 6 mg/kg/d nicotine increased the risk of fetal infection at gestation day (GD) 18. Here, we investigate lower nicotine doses. METHODS: Pregnant Sprague-Dawley rats received nicotine infusion at 0, 1, or 3 mg/kg/d (no, low-, and mid-dose nicotine, respectively) from GD 6, with intravenous inoculation with Mycoplasma pulmonis (MP) at 107 CFU (N = 20) or sterile broth (sham) (N = 11) on GD 14. Uterus and fetuses were retrieved on GD 18 for MP culture and histopathologic evaluation of maternal and fetal inflammatory responses (MIR and FIR). RESULTS: At 1 mg/kg/d nicotine, MP colonization rates were decreased, from 100% (9 of 9) to 40% (2 of 5) of MP-inoculated dams (p = .03), and 59% (66 of 111) to 39% (24 of 62) of fetuses (p = .01), versus no nicotine. Low-dose nicotine resulted in increased MIR and FIR in the sham-inoculated group; in the MP-inoculated group, this resulted in reduced relative risk (RR) for placental colonization (RR, 95% CI with high MIR = 0.14, 0.02 to 0.65; FIR = 0.38, 0.12 to 0.93). In contrast, 3 mg/kg/d nicotine treatment did not alter colonization rates; furthermore, FIR was completely suppressed, even in the face of placental or amniotic fluid colonization. CONCLUSION: The 1 mg/kg/d nicotine dose decreased risk of intrauterine infection, with increased MIR and FIR. The 3 mg/kg/d nicotine dose inhibited FIR, and increased risk for intrauterine infection. Nicotine alterations of the intrauterine environment were markedly dose-dependent. IMPLICATIONS: Nicotine exposure alters intrauterine infection and inflammation in a dose-dependent manner, potentially impacting fetal development and programming. Previous work in a rodent model showed that high-dose nicotine (6 mg/kg/d) exposure exacerbated intrauterine infection during pregnancy. The current study found that low-dose nicotine (1 mg/kg/d) exposure reduced colonization of placenta and amniotic fluid; this decrease was associated with increased intrauterine inflammation. Exposure to mid-dose nicotine (3 mg/kg/d) suppressed fetal inflammation. Elucidation of underlying mechanisms of these phenomena will inform public health and clinical care decisions, particularly in the context of risk assessment of nicotine replacement therapy during pregnancy for smoking cessation.

The importance of bone marrow and the immune system in driving increases in blood pressure and sympathetic nerve activity in hypertension.

NEW FINDINGS: What is the topic of this review? This manuscript provides a review of the current understanding of the role of the sympathetic nervous system in regulation of bone marrow-derived immune cells and the effect that the infiltrating bone marrow cells may have on perpetuation of the sympathetic over-activation in hypertension. What advances does it highlight? We highlight the recent advances in understanding of the neuroimmune interactions both peripherally and centrally as they relate to blood pressure control. ABSTRACT: The sympathetic nervous system (SNS) plays a crucial role in maintaining physiological homeostasis, in part by regulating, integrating and orchestrating processes between many physiological systems, including the immune system. Sympathetic nerves innervate all primary and secondary immune organs, and all cells of the immune system express ß-adrenoreceptors. In turn, immune cells can produce cytokines, chemokines and neurotransmitters capable of modulating neuronal activity and, ultimately, SNS activity. Thus, the essential role of the SNS in the regulation of innate and adaptive immune functions is mediated, in part, via ß-adrenoreceptor-induced activation of bone marrow cells by noradrenaline. Interestingly, both central and systemic inflammation are well-established hallmarks of hypertension and its co-morbidities, including an inflammatory process involving the transmigration and infiltration of immune cells into tissues. We propose that physiological states that prolong ß-adrenoreceptor activation in bone marrow can disrupt neuroimmune homeostasis and impair communication between the immune system and SNS, leading to immune dysregulation, which, in turn, is sustained via a central mechanism involving neuroinflammation.

Small-hairpin RNA and pharmacological targeting of neutral sphingomyelinase prevent diaphragm weakness in rats with heart failure and reduced ejection fraction.

Heart failure with reduced ejection fraction (HFREF) increases neutral sphingomyelinase (NSMase) activity and mitochondrial reactive oxygen species (ROS) emission and causes diaphragm weakness. We tested whether a systemic pharmacological NSMase inhibitor or short-hairpin RNA (shRNA) targeting NSMase isoform 3 (NSMase3) would prevent diaphragm abnormalities induced by HFREF caused by myocardial infarction. In the pharmacological intervention, we used intraperitoneal injection of GW4869 or vehicle. In the genetic intervention, we injected adeno-associated virus serotype 9 (AAV9) containing shRNA targeting NSMase3 or a scrambled sequence directly into the diaphragm. We also studied acid sphingomyelinase-knockout mice. GW4869 prevented the increase in diaphragm ceramide content, weakness, and tachypnea caused by HFREF. For example, maximal specific forces (in N/cm2) were vehicle [sham 31 ± 2 and HFREF 26 ± 2 ( P < 0.05)] and GW4869 (sham 31 ± 2 and HFREF 31 ± 1). Respiratory rates were (in breaths/min) vehicle [sham 61 ± 3 and HFREF 84 ± 11 ( P < 0.05)] and GW4869 (sham 66 ± 2 and HFREF 72 ± 2). AAV9-NSMase3 shRNA prevented heightening of diaphragm mitochondrial ROS and weakness [in N/cm2, AAV9-scrambled shRNA: sham 31 ± 2 and HFREF 27 ± 2 ( P < 0.05); AAV9-NSMase3 shRNA: sham 30 ± 1 and HFREF 30 ± 1] but displayed tachypnea. Both wild-type and ASMase-knockout mice with HFREF displayed diaphragm weakness. Our study suggests that activation of NSMase3 causes diaphragm weakness in HFREF, presumably through accumulation of ceramide and elevation in mitochondrial ROS. Our data also reveal a novel inhibitory effect of GW4869 on tachypnea in HFREF likely mediated by changes in neural control of breathing.

Impact of gestational nicotine exposure on intrauterine and fetal infection in a rodent model.

We investigated the interaction between prenatal nicotine exposure and intrauterine infection using established rat models. Beginning at gestation day (GD) 6, dams were continuously infused with either saline or 6 mg/kg/day nicotine (Nic). At GD 14, dams received either sterile broth or 105 colony-forming units Mycoplasma pulmonis (MP), resulting in four treatment groups: control (4 dams, 33 fetal units); MP only (5 dams, 55 fetal units); Nic only (5 dams, 61 fetal units), and Nic + MP (7 dams, 82 fetal units). At GD 18, nicotine exposure significantly increased (P ≤ 0.02) the percentage of amniotic fluids and fetuses infected by MP but did not impact colonization rates of maternal sites. Nicotine exposure significantly reduced the numbers of MP in the placenta required for high microbial loads (≥104 color-changing units) in the amniotic fluid (P < 0.01). Fetal inflammatory response lesions were most extensive in the Nic only and Nic + MP groups (P < 0.0001). Control and MP only placentas were interleukin (IL)10-dominant, consistent with an M2/Th2 environment. Placentas exposed to nicotine shifted to a neutral environment, with equivalent levels of interferon gamma (IFNG) and IL10. Both IL6 and tumor necrosis factor (TNF) levels in amniotic fluid were highly elevated when both nicotine and infection were present. Our study suggests that prenatal exposure to nicotine increases the risk for intrauterine infection, lowers the infectious dose required to breach the placental barrier and infect the amniotic fluid and fetus, and alters the pathology and inflammatory profile associated with maternal and fetal sites.

Brain-derived neurotrophic factor modulates angiotensin signaling in the hypothalamus to increase blood pressure in rats.

Brain-derived neurotrophic factor (BDNF) expression increases in the paraventricular nucleus of the hypothalamus (PVN) in response to hypertensive stimuli including stress and hyperosmolarity. However, it is unclear whether BDNF in the PVN contributes to increases in blood pressure (BP). We tested the hypothesis that increased BDNF levels within the PVN would elevate baseline BP and heart rate (HR) and cardiovascular stress responses by altering central angiotensin signaling. BP was recorded using radiotelemetry in male Sprague-Dawley rats after bilateral PVN injections of adeno-associated viral vectors expressing green fluorescent protein (GFP) or myc epitope-tagged BDNF fusion protein. Cardiovascular responses to acute stress were evaluated 3 to 4 wk after injections. Additional GFP and BDNF-treated animals were equipped with osmotic pumps for intracerebroventricular infusion of saline or the angiotensin type-1 receptor (AT1R) inhibitor losartan (15 µg·0.5 µl(-1)·h(-1)). BDNF treatment significantly increased baseline BP (121 ± 3 mmHg vs. 99 ± 2 mmHg in GFP), HR (394 ± 9 beats/min vs. 314 ± 4 beats/min in GFP), and sympathetic tone indicated by HR- and BP-variability analysis and adrenomedullary tyrosine hydroxylase protein expression. In contrast, body weight and BP elevations to acute stressors decreased. BDNF upregulated AT1R mRNA by ∼80% and downregulated Mas receptor mRNA by ∼50% in the PVN, and losartan infusion partially inhibited weight loss and increases in BP and HR in BDNF-treated animals without any effect in GFP rats. Our results demonstrate that BDNF overexpression in the PVN results in sympathoexcitation, BP and HR elevations, and weight loss that are mediated, at least in part, by modulating angiotensin signaling in the PVN.

Prenatal nicotine exposure leads to epigenetic alterations in peripheral nervous system signaling genes in the testis of the rat.

BACKGROUND: Prenatal nicotine exposure (PNE) has been documented to cause numerous deleterious effects on fetal development. However, the epigenetic changes promoted by nicotine exposure on germ cells are still not well understood. OBJECTIVES: In this study, we focused on elucidating the impact of prenatal nicotine exposure on regulatory epigenetic mechanisms important for germ cell development. METHODS: Sprague-Dawley rats were exposed to nicotine during pregnancy and male progeny was analyzed at 11 weeks of age. Testis morphology was analyzed using frozen testis sections and expression of germ cell markers was examined by RT-qPCR; histone modifications were assessed by Western Blot (WB). DNA methylation analysis was performed by methylation-specific PCR of bisulfite converted DNA. Genome-wide DNA methylation was analyzed using Methylated DNA immunoprecipitation (MeDIP)-seq. We also carried out transcriptomics analysis of pituitary glands by RNA-seq. RESULTS: We show that gestational exposure to nicotine reduces germ cell numbers, perturbs meiosis, affects the expression of germ line reprogramming responsive genes, and impacts the DNA methylation of nervous system genes in the testis. PNE also causes perturbation of gene expression in the pituitary gland of the brain. CONCLUSIONS: Our data demonstrate that PNE leads to perturbation of male spermatogenesis, and the observed effects are associated with changes of peripheral nervous system signaling pathways. Alterations in the expression of genes associated with diverse biological activities such as cell migration, cell adhesion and GABA signaling in the pituitary gland underscore the complexity of the effects of nicotine exposure during pregnancy.

Nicotine Exposure during Rodent Pregnancy Alters the Composition of Maternal Gut Microbiota and Abundance of Maternal and Amniotic Short Chain Fatty Acids.

Tobacco smoking is the leading cause of preventable death. Numerous reports link smoking in pregnancy with serious adverse outcomes, such as miscarriage, stillbirth, prematurity, low birth weight, perinatal morbidity, and infant mortality. Corollaries of consuming nicotine in pregnancy, separate from smoking, are less explored, and the mechanisms of nicotine action on maternal-fetal communication are poorly understood. This study examined alterations in the maternal gut microbiome in response to nicotine exposure during pregnancy. We report that changes in the maternal gut microbiota milieu are an important intermediary that may mediate the prenatal nicotine exposure effects, affect gene expression, and alter fetal exposure to circulating short-chain fatty acids (SCFAs) and leptin during in utero development.

Midbrain modulation of the cardiac baroreflex involves excitation of lateral parabrachial neurons in the rat.

Activation of the dorsal periaqueductal gray (PAG) evokes defense-like behavior including a marked increase in sympathetic drive and resetting of baroreflex function. The goal of this study was to investigate the role of the lateral parabrachial nucleus (LPBN) in mediating dorsal PAG modulation of the arterial baroreflex. Reflex responses were elicited by electrical stimulation of the aortic depressor nerve (ADN) at 5 Hz or 15 Hz in urethane anesthetized rats (n=18). Electrical stimulation of the dorsal PAG at 10 Hz did not alter baseline mean arterial pressure (MAP) but did significantly attenuate baroreflex control of heart rate (HR) evoked by low frequency ADN stimulation. Alternatively, 40 Hz dorsal PAG stimulation increased baseline MAP (43+/-3 mm Hg) and HR (33+/-3 bpm) and attenuated baroreflex control of HR at both ADN stimulation frequencies. Reflex control of MAP was generally unchanged by dorsal PAG stimulation. Bilateral inhibition of neurons in LPBN area (n=6) with muscimol (0.45 nmol per side) reduced dorsal PAG-evoked increases in MAP and HR by 50+/-4% and 95+/-4%, respectively, and significantly reduced, but did not completely eliminate dorsal PAG attenuation of the cardiac baroreflex. Bilateral blockade of glutamate receptors in the LPBN area (n=6) with kynurenic acid (1.8 nmol) had a similar effect on dorsal PAG-evoked increases in MAP, HR and cardiac baroreflex function. Reflex control of MAP was unchanged with either treatment. These findings suggest that the LPBN area is one of several brainstem regions involved in descending modulation of the cardiac baroreflex function during defensive behavior.

Respiratory responses elicited by rostral versus caudal dorsal periaqueductal gray stimulation in rats.

The periaqueductal gray (PAG) is a central neural region essential for defense behavior and coordination of accompanying autonomic responses. Activation of rostral versus caudal dorsal (dPAG) regions mediates different cardiovascular response patterns. Stimulation of the dPAG also elicits increased respiratory activity, however, it is unknown if there is a regional difference in dPAG modulation of respiratory pattern. The present study was undertaken to identify whether activation of rostral vs caudal dPAG modulates respiration differently. In anesthetized, spontaneously breathing rats, chemical and electrical stimulation in rostral and caudal dPAG evoked an increased respiratory frequency (f(R)) with significant shortening of both inspiratory (Ti) and expiratory time (Te). Stimulation in the dPAG also evoked significant increases in electromyography activity of the diaphragm (dEMG), arterial pressure, and heart rate. Caudal dPAG stimulation evoked a greater increase in f(R) due to a significantly greater decrease in Ti and Te than the rostral dPAG. Caudal dPAG stimulation also evoked a greater increase in baseline dEMG activity and elicited a significantly greater increase in dEMG amplitude above baseline than rostral dPAG. There was a rostro-caudal difference in the post-stimulus respiratory recovery response, with the caudal dPAG eliciting a longer sustained effect. No regional differences were identified in the arterial blood pressure and heart rate during dPAG stimulation. The results demonstrate that the magnitude of the respiratory response during and immediately after activation of the caudal dPAG is greater than during rostral dPAG stimulation.

Blockade of orexin receptors attenuates the cardiovascular response to air-jet stress in spontaneously hypertensive rats.

This study tested the hypothesis that orexin plays a role in the elevated pressor response to acute stress in the spontaneously hypertensive rat (SHR). The pressor response to air jet stress (AJS) (n=11/group) was 2.5 times greater in vehicle treated SHR versus Wistar (WIS) rats. Systemic delivery of 30mg/kg of the dual orexin receptor antagonist almorexant did not significantly change resting mean arterial pressure (MAP) but did attenuate the pressor response elicited by AJS to a greater extent in the SHR compared to the Wistar rats (~65% versus ~33% reduction respectively; n=6/group). Alternatively 100mg/kg almorexant reduced resting MAP in the SHR (~25mm Hg drop) and attenuated both the heart rate (HR; ~50% reduction) and MAP (~62% reduction) response to AJS in both strains (n=6/group). Systemic application of SB-334867 (3mg/kg), an orexin receptor type 1 antagonist (n=5/group), selectively reduced resting MAP and attenuated the HR response to AJS in the SHR but had no effect on the pressor response in either strain. The potential role of endogenous orexin release in cardiovascular control in the SHR was linked to a significant increase in brain-derived neurotrophic factor mRNA expression in the hypothalamus and elevated orexin receptor expression (type 2 only) in the dorsal pons when compared to WIS (n=4/group). These results demonstrate that the exaggerated pressor response in the SHR to stress is linked to increased orexin receptor activation and possibly altered orexin receptor expression in the dorsal pons and BDNF expression in the hypothalamus.

Low-dose mirtazapine increases genioglossus activity in the anesthetized rat.

STUDY OBJECTIVES: To examine the effects of mirtazapine on genioglossus and diaphragmatic electromyogram activity in the anesthetized rat. DESIGN: Parallel-group study. SUBJECTS: Sprague-Dawley adult male rats, 10 in each of 3 groups were studied. INTERVENTIONS: After anesthesia with 1.2 g/kg of urethane, a tracheostomy and bilateral vagotomy were performed. Femoral arterial and venous lines were placed, and fine wire hook electrodes were implanted into the genioglossus and diaphragm muscles. MEASUREMENTS: After a baseline period of measurement, either saline, 0.5 mg/kg of mirtazapine, or 5.0 mg/kg of mirtazapine was injected via the intraperitoneal route, and measurements were made for the next 3 hours. The average peak and tonic values of the moving time average of the genioglossus and diaphragm electromyogram for hours 1, 2, and 3 were determined and expressed as a percentage of the corresponding average value during the baseline (preinjection) monitoring period. RESULTS: At 0.5 mg/kg of mirtazapine, the peak genioglossus electromyogram was significantly higher than in control conditions over hours 2 and 3. At 5.0 mg/kg of mirtazapine, the genioglossus electromyogram was significantly lower than in control conditions for the first 2 hours of monitoring. The peak diaphragmatic electromyogram was slightly but significantly lower in the mirtazapine 5.0-mg/kg group than in controls. CONCLUSIONS: Mirtazapine, at a dose similar to one used clinically, increased genioglossus activity. We hypothesize that, at this dose, the ability of mirtazapine to increase serotonin and norepinephrine or block type-3 serotonin receptors predominated. At the higher dose of mirtazapine, the type-2 blockade effect predominated and genioglossus activity decreased.

Chronic heart failure alters orexin and melanin concentrating hormone but not corticotrophin releasing hormone-related gene expression in the brain of male Lewis rats.

OBJECTIVE: The aim of this study was to investigate the effect of chronic heart failure (HF; 16 weeks post left coronary artery ligation) on the brain's orexin (ORX) and related neuropeptide systems. METHODS: Indicators of cardiac function, including the percent fractional shortening (%FS) left ventricular posterior wall shortening velocity (LVPWSV) were assessed via echocardiography at 16 weeks post myocardial infarction or sham treatment in male Lewis rats (n=5/group). Changes in gene expression in HF versus control (CON) groups were quantified by real-time PCR in the hypothalamus, amygdala and dorsal pons. RESULTS: HF significantly reduced both the %FS and LVPWSV when compared to CON animals (P<0.02). In the hypothalamus ORX gene expression was significantly reduced in HF and correlated with changes in cardiac function when compared to CON (P<0.02). No significant changes in hypothalamic ORX receptor (type 1 or type 2) gene expression were identified. Alternatively hypothalamic melanin concentrating hormone (MCH) gene expression was significantly upregulated in HF animals and negatively correlated with LVPWSV (P<0.006). In both the amygdala and dorsal pons ORX type 2 receptor expression was significantly down-regulated in HF compared to CON. ORX receptor type 1, CRH and CRH type 1 and type 2 receptor expressions were unchanged by HF in all brain regions analyzed. CONCLUSION: These observations support previous work demonstrating that cardiovascular disease modulates the ORX system and identify that in the case of chronic HF the ORX system is altered in parallel with changes in MCH expression but independent of any significant changes in the central CRH system. This raises the new possibility that ORX and MCH systems may play an important role in the pathophysiology of HF.

Parabrachial neurons mediate dorsal periaqueductal gray evoked respiratory responses in the rat.

The neural substrates mediating autonomic components of the behavioral defense response reside in the periaqueductal gray (PAG). The cardiovascular components of the defense response evoked from the dorsal PAG (DPAG) have been well described and are dependent, in part, on the integrity of neurons in the region of the parabrachial nucleus as well as the rostral ventrolateral medulla. Descending pathways mediating the ventilatory response associated with activation of DPAG neurons are unknown. The present study was undertaken to test the hypothesis that parabrachial area neurons are also involved in mediating the respiratory response to DPAG stimulation. In urethane-anesthetized, spontaneously breathing rats, electrical stimulation of the DPAG significantly increased respiratory rate, arterial pressure, and heart rate. Changes in respiratory frequency were associated with significant decreases in inspiratory and expiratory durations. After bilateral inhibition of neurons in the lateral parabrachial nucleus (LPBN) region with 5 mM muscimol (n = 6), DPAG-evoked increases in respiration and heart rate were attenuated by 90 +/- 6 and 72 +/- 13%, respectively. The pressor response evoked by DPAG stimulation, however, was attenuated by only 57 +/- 6%. Bilateral blockade of glutamate receptors with 20 mM kynurenic acid (n = 6) in the LPBN also markedly attenuated DPAG-evoked increases in respiration and heart rate (65 +/- 15 and 53 +/- 9% reduction, respectively) but only modestly changed the DPAG-evoked pressor response (34 +/- 16% reduction). These results demonstrate that LPBN neurons play a significant role in the DPAG-mediated respiratory component of behavioral defense responses. This finding supports previous work demonstrating that the dorsolateral pons plays a significant role in mediating most physiological adjustments associated with activation of the DPAG.

Respiratory response to activation or disinhibition of the dorsal periaqueductal gray in rats.

The neural substrates mediating autonomic components of the behavioral defense response have been shown to reside in the periaqueductal gray (PAG). The cardiovascular components of the behavioral defense response have been well described and are tonically suppressed by GABAergic input. The ventilatory response associated with disinhibition of the dorsal PAG (dPAG) neurons is unknown. In urethane-anesthetized, spontaneously breathing rats, electrical stimulation of the dPAG was shown to decrease the expiration time and increase respiratory frequency, with no change in time of inspiration. Baseline and the change in diaphragm electromyograph also increased, resulting in an increase in neural minute activity. Microinjection of bicuculline methobromide, a GABA(A)-receptor antagonist, into the dPAG produced a similar response, which was dose dependent. Disinhibition of the dPAG also produced a decrease in inspiration time. These results suggest that GABA(A)-mediated suppression of dPAG neurons plays a role in the respiratory component of behavioral defense responses. The respiratory change is due in part to a change in brain stem respiratory timing and phasic inspiratory output. In addition, there is an increase in tonic diaphragm activity.

Increased c-Fos expression in select lateral parabrachial subnuclei following chemical versus electrical stimulation of the dorsal periaqueductal gray in rats.

The parabrachial nucleus (PBN) is located in the rostral dorsolateral pons and has been identified as a critical relay for cardiovascular responses (sympathoexcitation and baroreflex attenuation) evoked by the dorsal periaqueductal gray (PAG). We examined the pattern of c-Fos protein immunoreactivity throughout the rostral-caudal extent of the PBN in four groups of anesthetized male Sprague-Dawley rats to identify the specific PBN regions activated by dorsal PAG stimulation. Both electrical stimulation and chemical (0.3 mM bicuculline methobromide) activation of the dorsal PAG elicited a selective increase in Fos-like immunoreactivity (FLI) in the superior lateral and central lateral subnuclei of the rostral lateral PBN (LPBN) relative to surgery and blood pressure control groups. In the middle LPBN chemical stimulation of the dorsal PAG selectively increased FLI in the central lateral subnucleus while electrical stimulation increased FLI in the Kolliker-Fuse area only. Finally, in the caudal LPBN only electrical stimulation of the dorsal PAG induced significant changes in FLI above control. Significant changes in FLI in the medial PBN were not observed under any experimental conditions. These results confirm neuroanatomical data demonstrating that neurons in superior lateral and central lateral subnuclei of the rostral and middle LPBN are the primary targets of the dorsal PAG. Our results also demonstrate that this descending projection to the central lateral and superior lateral subnuclei of the LPBN is in part excitatory. Finally, our results raise the possibility that neurons in the central lateral subnucleus of the middle and rostral LPBN are integrally involved in descending modulation of sympathetic drive associated with dorsal PAG activation.

Activation of the dorsal periaqueductal gray in the rat induces Fos-like immunoreactivity in select non-cholinergic mesopontine neurons.

Autonomic responses evoked from the dorsal periaqueductal gray (dPAG) have been reported to be mediated in part by acetylcholine release in the medulla. To identify the possible origin of cholinergic neurons activated by dPAG stimulation, the pattern of Fos-like immunoreactivity (FLI) in the mesopontine cholinergic cell groups was examined in three groups of urethane anesthetized rats. Relative to surgery (n=6) and blood pressure control groups (n=6), chemical disinhibition of the dPAG (n=10) induced a significant increase in FLI in the lateral dorsal tegmental nucleus (LDTg) but not the pedunculopontine tegmental nucleus. LDTg neurons stained for choline acetyltransferase immunoreactivity however did not co-label for FLI. Other pontomesencephalic regions outside of the dPAG demonstrating a significant increase in FLI relative to controls included the lateral and ventrolateral columns of the PAG, the cuneiform nucleus, dorsal raphe, and the microcellular tegmental nucleus. These findings suggest that acetylcholine release in during dPAG stimulation does not originate from mesopontine neurons.

Selective augmentation of genioglossus electromyographic activity by L-5-hydroxytryptophan in the rat.

The present study was undertaken to determine the effects of intravenous L-5 hydroxytryptophan (5HTP), the immediate precursor of serotonin, on the electromyographic (EMG) activity of the genioglossus (gEMG) and diaphragm (dEMG) in the spontaneously breathing, vagotomized anesthetized male Sprague-Dawley rats (urethane 1.2-1.4 g/kg). Sequential administration of saline and 0.05-, 0.1-, 0.2-, 1-, and 5-mg/kg doses of 5HTP were given intravenously every 15 min. There was a significant increase (percent change from predrug) in both gEMG and dEMG amplitude at 1.0 and 5.0 mg/kg of 5HTP compared to saline. The percent increase in gEMG induced by 1.0 and 5.0 mg/kg 5HTP however was significantly greater than the increase in dEMG. There was no significant change in heart rate (HR), mean arterial blood pressure (MAP), or respiratory rate at any of the doses of 5HTP tested. These results suggest that intravenous 5HTP at doses of 1 and 5 mg/kg preferentially increased the gEMG in the anesthetized rat compared to the dEMG. We hypothesize that at appropriate doses serotonin precursors could increase genioglossus activity in humans during sleep and help maintain upper-airway patency.

Effect of DOCA/salt hypertension on CRF expression in the amygdala and the autonomic stress response in conscious rats.

The effects of DOCA/salt treatment on amygdala-area CRF gene expression and the autonomic response to air jet stress (AJS) were evaluated in conscious male Sprague Dawley (SD) rats. Fifteen days of DOCA/salt treatment significantly increased resting arterial pressure (AP), decreased resting heart rate (HR) and significantly reduced regional CRF mRNA compared to controls (23±7% vs. 100±26%) independent of changes in regional CRF receptor expression. Twenty min of AJS elicited a rise in AP (~15mmHg) that was similar in both DOCA/salt animals (n=11) and controls (n=6). Alternatively, increases in HR were significantly different in the DOCA/salt animals compared to controls; including one group of DOCA/salt animals (n=5) which responded with an attenuated HR response at the onset of AJS (low-responders) and a second group (n=6) which demonstrated an elevated HR response to AJS (high-responders), specifically during the last 10min of AJS. The divergent HR responses to AJS in the DOCA/salt animals were linked to differences in resting heart rate variability. During recovery HR returned to baseline within 10min in both control and the low responder DOCA group but indicators of spontaneous baroreflex gain only increased significantly in controls. HR in the high-responder DOCA animals did not return to baseline during the same period. These results show that DOCA/salt treatment triggers downregulation of CRF gene expression in the region of the amygdala and significantly alters the HR response to acute stress but does not alter the pressor response to stress compared to normotensive controls.

Role of lateral parabrachial opioid receptors in exercise-induced modulation of the hypotensive hemorrhage response in conscious male rats.

Some of the benefits of exercise appear to be mediated through modulation of neuronal excitability in central autonomic control circuits. Previously, we identified that six weeks of voluntary wheel running had a protective effect during hemorrhage (HEM), limiting both the hypotensive phase of HEM and enhancing recovery. The present study was undertaken to evaluate the role of opioid release in the lateral parabrachial nucleus (LPBN) on the response to severe HEM in chronically exercised (EX, voluntary) versus sedentary (SED) controls. Male Sprague Dawley rats were allowed either free access to running wheels (EX) or normal cage conditions (SED). After 6 weeks of "training" animals were instrumented with a bilateral cannula directed toward the dorsolateral pons and arterial catheters. After a recovery period, animals underwent central microinjection of either vehicle (VEH; n=3/group) or the opioid receptor antagonist naloxone (NAL; n=6/group) followed by withdrawal of 30% of their total estimated blood volume. Following VEH injection, the drop in MAP during and following HEM was significantly attenuated in the EX vs SED animals. Alternatively, NAL microinjection in the dorsolateral pons (20 µM, 200-500 nl) reversed the beneficial effect of EX on the HEM response. NAL microinjection in SED rats did not significantly alter the response to HEM. These data suggest chronic voluntary EX has a beneficial effect on the autonomic response to severe HEM which is mediated, in part, via EX-induced plasticity of the opioid system within the dorsolateral pons.

Stress-induced changes in c-Fos and corticotropin releasing hormone immunoreactivity in the amygdala of the spontaneously hypertensive rat.

The present study was undertaken to test the hypothesis that dysregulation of the amygdala contributes to the exaggerated autonomic response to stress in an animal model of essential hypertension. Spontaneously hypertensive (SHR) and normotensive Wistar male rats were chronically instrumented and exposed to 20 min of either air jet stress (AJS) or air noise alone (CON). AJS induced a significant increase in both heart rate and arterial pressure that was greater in the SHR. AJS induced a significant increase in c-Fos-like immunoreactivity (FLI) throughout the caudal-rostral extent of the basolateral, medial, and central (CEA) subnuclei of the amygdala. Differences in FLI between strains were localized to the rostral CEA and the SHR expressed significantly less FLI. AJS also induced a significant increase in the number of corticotrophin releasing hormone (CRH) positive neurons in the CEA. Differences between strains were localized to the caudal CEA and the number of CRH-positive cells was significantly greater in the SHR. The stress-induced increase in CRH labeling in caudal CEA of the SHR was coupled to a greater increase in FLI in the rostral locus coeruleus (LC) of the SHR versus the Wistar. AJS also induced significant increases in FLI in several hypothalamus subnuclei, but no strain-related differences were identified. These results suggest for the first time that dysregulation of CRH-positive cells in the caudal CEA and reduced excitation and/or exaggerated inhibition of rostral CEA neurons may contribute to the exaggerated cardiovascular response to stress in the SHR, possibly through descending modulation of the rostral LC.