Percent Final Height Is a Novel Method That Identifies Differences Between the Rate of Development in American Children of Different Races.

INTRODUCTION: The Greulich & Pyle (G&P) Radiographic Atlas of Skeletal Development uses hand x-rays obtained between 1926 and 1942 on children of Caucasian ancestry. Our study uses modern Caucasian, Black, Hispanic, and Asian children to investigate patterns of development as a function of percent final height (PFH). METHODS: A retrospective review, at a single institution, was conducted using children who received a hand x-ray, a height measurement taken within 60 days of that x-ray, and a final height. BA and CA were compared between races. PFH was calculated by dividing height at the time of the x-ray by their final height. To further evaluate differences between races in CA or BA, PFH was then modeled as a function of CA or BA using a fifth-degree polynomial regression, and mean ages at the 85th PFH were compared. Patients were then divided into Sanders stages 1, 2-4, and 5-8 and the mean PFH, CA, and BA of the Asian, Black, and Hispanic children were compared with the White children using Student t test. P values less than 0.05 were considered significant. RESULTS: We studied 498 patients, including 53 Asian, 83 Black, 190 Hispanic, and 172 White patients. Mean BA was significantly greater than CA in Black males (1.27 y) and females (1.36 y), Hispanic males (1.12 y) and females (1.29 y), and White females (0.74 y). Hispanic and Black patients were significantly more advanced in BA than White patients (P<0.001). At the 85th PFH, White and Hispanic males were older than Black males by at least 7 months (P<0.001), and White females were significantly older than Hispanic females by 6.4 months (P<0.001). At 85th PFH for males, Hispanic and Black males had greater BA than White males by at least 5 months (P<0.001), and Asian females had a greater BA than Black females by at least 5 months (P<0.001). Compared with White children, Hispanic children were significantly younger at Sanders 2-4 than White children, and Black children were skeletally older at Sanders 5-8. CONCLUSIONS: BA was greater than CA by ≥1 year in Black and Hispanic children, and that these children had a significantly greater BA than their White counterparts. Black males and Hispanic females reached their 85th PFH at younger ages, and Hispanic males and Asian females were the most skeletally mature at their 85th PFH. Our results suggest that BA and CA may vary as a function of race, and further studies evaluating growth via the 85th PFH may be necessary. LEVEL OF EVIDENCE: Therapeutic Study - Level IV.

Outcomes of Displaced Tibial Tubercle Fractures in Adolescents.

Tibial tubercle fractures are uncommon injuries. The purpose of this study is to report the outcomes of surgical treatment of displaced tibial tubercle fractures in adolescents. This study was approved by the College of Medicine Institutional Review Board. A retrospective review was performed at our institution for patients who underwent surgical treatment of tibial tubercle fractures. Patient demographics, injury characteristics, and outcomes were recorded. A p-value of <0.05 was considered statistically significant. Nineteen male patients were identified. The average age was 14.6 years, and the average body mass index was 25.8. Basketball (63%) was the most common mechanism of injury. No patient was treated with bicortical screws. Two patients had preoperative computed tomography. One patient presented with acute compartment syndrome (ACS), and fasciotomy was performed. Twelve patients (63%) without clinical signs of ACS received anterior compartment fasciotomy on a case-by-case basis according to surgeon's preference. No growth injury, including growth arrest, angulation, or shortening occurred. All patients returned to preinjury activities at an average of 18.5 weeks. Displaced tibial tubercle fractures in this series occurred in male adolescents during athletic activity. Unicortical screws/pins were used with no loss of fixation. Routine use of advanced imaging was unnecessary. One patient (5%) underwent fasciotomy. No growth arrest occurred. All patients returned to preinjury athletic activities.

Cross-sectional associations between neighbourhood walkability and objective physical activity levels in identical twins.

OBJECTIVES: Physical activity is a cornerstone of chronic disease prevention and treatment, yet most US adults do not perform levels recommended for health. The neighborhood-built environment (BE) may support or hinder physical activity levels. This study investigated whether identical twins who reside in more walkable BEs have greater activity levels than twins who reside in less walkable BEs (between-twin analysis), and whether associations remain significant when controlling for genetic and shared environmental factors (within-twin analysis). DESIGN: A cross-sectional study. SETTING: The Puget Sound region around Seattle, Washington, USA. PARTICIPANTS: The sample consisted of 112 identical twin pairs who completed an in-person assessment and 2-week at-home measurement protocol using a global positioning system (GPS)monitor and accelerometer. EXPOSURE: The walkability of each participants' place of residence was calculated using three BE dimensions (intersection density, population density and destination accessibility). For each variable, z scores were calculated and summed to produce the final walkability score. OUTCOMES: Objectively measured bouts of walking and moderate-to-vigorous physical activity (MVPA), expressed as minutes per week. RESULTS: Walkability was associated with walking bouts (but not MVPA) within the neighbourhood, both between (b=0.58, SE=0.13, p<0.001) and within pairs (b=0.61, SE=0.18, p=0.001). For a pair with a 2-unit difference in walkability, the twin in a more walkable neighbourhood is likely to walk approximately 16 min per week more than the co-twin who lives in a less walkable neighbourhood. CONCLUSIONS: This study provides robust evidence of an association between walkability and objective walking bouts. Improvements to the neighbourhood BE could potentially lead to increased activity levels in communities throughout the USA.

The Case for Integrating Health Systems to Manage Noncommunicable and Infectious Diseases in Low- and Middle-Income Countries: Lessons Learned From Zambia.

Noncommunicable diseases (NCDs) are the leading cause of death in the world, and 80% of all NCD deaths occur in low- and middle-income countries (LMICs). The COVID-19 pandemic has demonstrated that patients with NCDs are at increased risk of becoming severely ill from the virus. Disproportionate investment in vertical health programs can result in health systems vulnerable to collapse when resources are strained, such as during pandemics. Although NCDs are largely preventable, globally there is underinvestment in efforts to address them. Integrating health systems to collectively address NCDs and infectious diseases through a wide range of services in a comprehensive manner reduces the economic burden of healthcare and strengthens the healthcare system. Health system resiliency is essential for health security. In this article, we provide an economically sound approach to incorporating NCDs into routine healthcare services in LMICs through improved alignment of institutions that support prevention and control of both NCDs and infectious diseases. Examples from Zambia's multisector interventions to develop and support a national NCD action plan can inform and encourage LMIC countries to invest in systems integration to reduce the social and economic burden of NCDs and infectious diseases.

Operative Outcomes for Accessory Navicular in Adolescents.

The purpose of this study is to report the operative outcomes in a consecutive series of adolescent patients with symptomatic accessory navicular (AN). A retrospective review was conducted. Patient characteristics, operative techniques, and outcomes were recorded. Radiographs were used to identify the type of AN, skeletal maturity, and presence of concurrent pes planus. Twenty-two patients and 24 feet were studied. All 22 patients had an excision of the AN, and 19 patients had an additional reefing of the tibialis posterior tendon. At final follow up, 22 cases reported no pain, one had minimal pain, and one reported no change in pain. Symptomatic AN is more common in females. Surgery technique was not correlated with postoperative pain. Surgery eliminated pain in 91% of patients and can be safely performed in athletes with high rate of return to their previous athletic performance. (Journal of Surgical Orthopaedic Advances 31(1):053-055, 2022).

Endothelial Nitric Oxide Synthase (eNOS) and the Cardiovascular System: in Physiology and in Disease States.

Endothelial nitric oxide synthase (eNOS) plays a critical role in regulating and maintaining a healthy cardiovascular system. The importance of eNOS can be emphasized from the genetic polymorphisms of the eNOS gene, uncoupling of eNOS dimerization, and its numerous signaling regulations. The activity of eNOS on the cardiac myocytes, vasculature, and the central nervous system are discussed. The effects of eNOS on the sympathetic autonomic nervous system (SANS) and the parasympathetic autonomic nervous system (PANS), both of which profoundly influence the cardiovascular system, will be elaborated. The relationship between the eNOS protein with cardiovascular autonomic reflexes such as the baroreflex and the Exercise Pressor Reflex will be discussed. For example, the effects of endogenous nitric oxide (NO) are shown to be mediated by the eNOS protein and that eNOS-derived endothelial NO is most effective in regulating blood pressure oscillations via modulating the baroreflex mechanisms. The protective action of eNOS on the CVS is emphasized here because dysfunction of the eNOS enzyme is intricately correlated with the pathogenesis of several cardiovascular diseases such as hypertension, arteriosclerosis, myocardial infarction, and stroke. Overall, our current understanding of the eNOS protein with a focus on its role in the modulation, regulation, and control of the cardiovascular system in a normal physiological state and in cardiovascular diseases are discussed.

Ivermectin-treated cattle reduces blood digestion, egg production and survival of a free-living population of Anopheles arabiensis under semi-field condition in south-eastern Tanzania.

BACKGROUND: Anopheles arabiensis feed on cattle and contributes to residual transmission of malaria in areas with high coverage of long-lasting insecticide-treated nets and indoor residual spraying in East Africa. This study aimed to evaluate the effects of ivermectin-treated cattle as a complementary vector control tool against population of An. arabiensis under the semi-field conditions in south-eastern Tanzania. METHODS: The free-living population of An. arabiensis was allowed to forage on untreated or ivermectin-treated cattle in alternating nights within the semi-field system in south-eastern Tanzania. Fresh blood fed mosquitoes were collected in the morning using mouth aspirators and assessed for their blood meal digestion, egg production, and survivorship. The residual activity of ivermectin-treated cattle was also determined by exposing mosquitoes to the same treatments after every 2 days until day 21 post-treatments. These experiments were replicated 3 times using different individual cattle. RESULTS: Overall, the ivermectin-treated cattle reduced blood meal digestion in the stomach of An. arabiensis, and their subsequent egg production and survival over time. The ivermectin-treated cattle halved blood meal digestion in mosquitoes, but reduced their egg production for up to 15 days. The ivermectin-treated cattle reduced the survival, and median survival times (1-3 days) of An. arabiensis than control cattle. The daily mortality rates of mosquitoes fed on ivermectin-treated cattle increased by five-fold relative to controls in the first week, and it gradually declined up to 21 days after treatment. CONCLUSION: This study demonstrates that long-lasting effects of ivermectin-treated cattle on egg production and survival of An. arabiensis may sustainably suppress their vector density, and reduce residual transmission of malaria. This study suggests that ivermectin-treated non-lactating cattle (i.e. calves, heifers and bulls) could be suitable option for large-scale malaria vector control without limiting consumption of milk and meat by communities in rural settings. Furthermore, simulation models are underway to predict the impact of ivermectin-treated cattle alone, or in combination with LLIN/IRS, the frequency of treatment, and their coverage required to significantly suppress population of An. arabiensis and reduce residual transmission of malaria.

The impact of host species and vector control measures on the fitness of African malaria vectors.

Many malaria vector mosquitoes in Africa have an extreme preference for feeding on humans. This specialization allows them to sustain much higher levels of transmission than elsewhere, but there is little understanding of the evolutionary forces that drive this behaviour. In Tanzania, we used a semi-field system to test whether the well-documented preferences of the vectors, Anopheles arabiensis and Anopheles gambiae sensu stricto (s.s.) for cattle and humans, respectively, are predicted by the fitness they obtain from host-seeking on these species relative to other available hosts. Mosquito fitness was contrasted, when humans were fully exposed and when they were protected by a typical bednet. The fitness of both vectors varied between host species. The predicted relationship between host preference and fitness was confirmed in An. arabiensis, but not in An. gambiae s.s., whose fitness was similar on humans and other mammals. Use of typical, imperfect bednets generated only minor reductions in An. gambiae s.s. feeding success and fitness on humans, but was predicted to generate a significant reduction in the lifetime reproductive success of An. arabiensis on humans relative to cows. This supports the hypothesis that such human-protective measures could additionally benefit malaria control by increasing selection for zoophily in vectors.

Novel mRNA isoforms and mutations of uridine monophosphate synthetase and 5-fluorouracil resistance in colorectal cancer.

The drug fluorouracil (5-FU) is a widely used antimetabolite chemotherapy in the treatment of colorectal cancer. The gene uridine monophosphate synthetase (UMPS) is thought to be primarily responsible for conversion of 5-FU to active anticancer metabolites in tumor cells. Mutation or aberrant expression of UMPS may contribute to 5-FU resistance during treatment. We undertook a characterization of UMPS mRNA isoform expression and sequence variation in 5-FU-resistant cell lines and drug-naive or -exposed primary and metastatic tumors. We observed reciprocal differential expression of two UMPS isoforms in a colorectal cancer cell line with acquired 5-FU resistance relative to the 5-FU-sensitive cell line from which it was derived. A novel isoform arising as a consequence of exon skipping was increased in abundance in resistant cells. The underlying mechanism responsible for this shift in isoform expression was determined to be a heterozygous splice site mutation acquired in the resistant cell line. We developed sequencing and expression assays to specifically detect alternative UMPS isoforms and used these to determine that UMPS was recurrently disrupted by mutations and aberrant splicing in additional 5-FU-resistant colorectal cancer cell lines and colorectal tumors. The observed mutations, aberrant splicing and downregulation of UMPS represent novel mechanisms for acquired 5-FU resistance in colorectal cancer.

The fitness of African malaria vectors in the presence and limitation of host behaviour.

BACKGROUND: Host responses are important sources of selection upon the host species range of ectoparasites and phytophagous insects. However little is known about the role of host responses in defining the host species range of malaria vectors. This study aimed to estimate the relative importance of host behaviour to the feeding success and fitness of African malaria vectors, and assess its ability to predict their known host species preferences in nature. METHODS: Paired evaluations of the feeding success and fitness of African vectors Anopheles arabiensis and Anopheles gambiae sensu stricto in the presence and limitation of host behaviour were conducted in a semi-field system (SFS) at Ifakara Health Institute, Tanzania. In one set of trials, mosquitoes were released within the SFS and allowed to forage overnight on a host that was free to exhibit a natural behaviour in response to insect biting. In the other, mosquitoes were allowed to feed directly on from the skin surface of immobile hosts. The feeding success and subsequent fitness of vectors under these conditions were investigated on six host types (humans, calves, chickens, cows, dogs and goats) to assess whether physical movements of preferred host species (cattle for An. arabiensis, humans for An. gambiae s.s.) were less effective at preventing mosquito bites than those of common alternatives. RESULTS: Anopheles arabiensis generally had greater feeding success when applied directly to host skin than when foraging on unrestricted hosts (in five of six host species). However, An. gambiae s.s. obtained blood meals from free and restrained hosts with similar success from most host types (four out of six). Overall, the blood meal size, oviposition rate, fecundity and post-feeding survival of mosquito vectors were significantly higher after feeding on hosts free to exhibit behaviour, than those who were immobilized during feeding trials. CONCLUSIONS: Allowing hosts to move freely during exposure to mosquitoes was associated with moderate reductions in mosquito feeding success, but no detrimental impact to the subsequent fitness of mosquitoes that were able to feed upon them. This suggests that physical defensive behaviours exhibited by common host species including humans do not impose substantial fitness costs on African malaria vectors.

Does Cattle Milieu Provide a Potential Point to Target Wild Exophilic Anopheles arabiensis (Diptera: Culicidae) with Entomopathogenic Fungus? A Bioinsecticide Zooprophylaxis Strategy for Vector Control.

Background. Anopheles arabiensis is increasingly dominating malaria transmission in Africa. The exophagy in mosquitoes threatens the effectiveness of indoor vector control strategies. This study aimed to evaluate the effectiveness of fungus against An. arabiensis when applied on cattle and their environments. Methods. Experiments were conducted under semi-field and small-scale field conditions within Kilombero valley. The semi-field reared females of 5-7 days old An. arabiensis were exposed to fungus-treated and untreated calf. Further, wild An. arabiensis were exposed to fungus-treated calves, mud-huts, and their controls. Mosquitoes were recaptured the next morning and proportion fed, infected, and survived were evaluated. Experiments were replicated three times using different individuals of calves. Results. A high proportion of An. arabiensis was fed on calves (>0.90) and become infected (0.94) while resting on fungus-treated mud walls than on other surfaces. However, fungus treatments reduced fecundity and survival of mosquitoes. Conclusion. This study demonstrates for the first time the potential of cattle and their milieu for controlling An. arabiensis. Most of An. arabiensis were fed and infected while resting on fungus-treated mud walls than on other surfaces. Fungus treatments reduced fecundity and survival of mosquitoes. These results suggest deployment of bioinsecticide zooprophylaxis against exophilic An. arabiensis.

Modulation of pressor response to muscle contraction via monoamines following AMPA-receptor blockade in the ventrolateral medulla.

We hypothesized that cardiovascular responses to static muscle contraction are mediated via changes in extracellular concentrations of monoamines (norepinephrine, dopamine and serotonin) following the administration of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, an AMPA-receptor antagonist) into the rostral (RVLM) or caudal (CVLM) ventrolateral medulla. For the RVLM experiments (n= 8), a 2-min static muscle contraction increased the mean arterial pressure (MAP) and heart rate (HR) by 23 +/- 2 mmHg and 28 +/- 8 bpm, respectively. During this contraction, the concentrations of norepinephrine, dopamine, and serotonin within the RVLM increased by 278 +/- 52%, 213 +/- 23%, and 232 +/- 24%, respectively. Microdialysis of CNQX (1.0 microM) for 30 min into the RVLM attenuated the increases in MAP and HR ( 11 +/- 2 mmHg and 14 +/- 5 bpm) without a change in developed muscle tension. The levels of norepinephrine, dopamine, and serotonin within the RVLM were also attenuated. In contrast, microdialysis of CNQX into the CVLM (n= 8) potentiated the contraction-evoked responses in MAP ( 21 +/- 2 vs 33 +/- 5 mmHg) and HR ( 25 +/- 5 vs 46 +/- 8 bpm) without any effect on the monoamine levels within the CVLM region. These results suggest that AMPA-receptor blockade within the RVLM and CVLM has opposing effects on cardiovascular responses during static muscle contraction. In addition, such receptor blockade modulates extracellular concentrations of monoamines within the RVLM but not in the CVLM. These results provide evidence that AMPA receptors within the ventrolateral medulla play a role in exercise pressor reflex.

Effects of nitric oxide and GABA interaction within ventrolateral medulla on cardiovascular responses during static muscle contraction.

We hypothesized that nitric oxide (NO) has opposing roles in regulating cardiovascular responses within the rostral (RVLM) and caudal (CVLM) ventrolateral medulla by modulating release of gamma-aminobutyric acid (GABA). We have measured GABA concentrations within the RVLM and CVLM during increases in mean arterial pressure (MAP) and heart rate (HR) following a 2-min tibial nerve stimulation-evoked static muscle contraction before and after microdialysis of the NO precursor, L-arginine (1.0 microM), for 30 min, and after the NO inhibitor, L-NMMA (1.0 microM), for 30 min. In eight anesthetized rats, muscle contraction significantly increased MAP, HR and GABA levels within the RVLM area (from 0.53+/-0.09 to 1.22+/-0.10 ng/10 microl). Following microdialysis of L-arginine, muscle contraction augmented GABA levels (from 0.45+/-0.07 to 2.18+/-0.09 ng/10 microl) and attenuated changes in MAP and HR. Subsequent application of L-NMMA significantly decreased GABA levels (from 0.47+/-0.08 to 0.22+/-0.07 ng/10 microl) but potentiated MAP and HR responses to a muscle contraction. In contrast, muscle contraction significantly increased MAP and HR but decreased GABA concentrations within the CVLM (from 1.20+/-0.20 to 0.78+/-0.17 ng/10 microl). Following microdialysis of L-arginine, muscle contraction significantly attenuated GABA levels (from 1.34+/-0.19 to 0.33+/-0.10 ng/10 microl) and augmented changes in MAP and HR in response to muscle contraction. A subsequent microdialysis of L-NMMA into the CVLM reversed the effects of L-arginine. These results demonstrate that NO within the RVLM and CVLM differentially modulates cardiovascular responses during static muscle contraction and that NO influences exercise-induced cardiovascular responses by modulating GABA release within the ventrolateral medulla.

Simultaneous glutamate and gamma-aminobutyric acid release within ventrolateral medulla during skeletal muscle contraction in intact and barodenervated rats.

The purpose of this study was to determine if baroreflex modulates cardiovascular responses and neurotransmitter release within rostral (RVLM) and caudal (CVLM) ventrolateral medulla during static contraction of skeletal muscle using anesthetized rats. We evoked cardiovascular responses by a static muscle contraction and measured simultaneous release of glutamate and gamma-aminobutyric acid (GABA) in both the RVLM and CVLM using microdialysis probes, two inserted bilaterally into the RVLM and two into the CVLM. In intact anesthetized rats, a muscle contraction increased release of glutamate concomitantly in both the RVLM and CVLM along with significant increases in heart rate and arterial blood pressure. In contrast, concentrations of GABA increased within the RVLM, but decreased significantly within the CVLM during the pressor response. These changes were due to contraction-evoked activation of muscle afferents since tibial nerve stimulation following muscle paralysis failed to evoke glutamate, GABA, or any cardiovascular changes. On the other hand, static muscle contractions in baroreceptor denervated rats augmented the increases in heart rate and blood pressure. Furthermore, muscle contraction significantly enhanced the release of glutamate in the RVLM but attenuated its release in the CVLM. In addition, concentrations of GABA within the RVLM were attenuated following a muscle contraction in denervated rats without any changes in GABA within the CVLM. These results demonstrate that the baroreceptors influence cardiovascular responses to static muscle contraction associated with dynamic changes in glutamate and GABA release within the RVLM and CVLM.

Further evidence that extracellular serotonin in the rostral ventrolateral medulla modulates 5-HT(1A) receptor-mediated attenuation of exercise pressor reflex.

We determined changes in extracellular levels of glutamate, serotonin (5-HT), norepinephrine (NE), and dopamine (DA) within rostral ventrolateral medulla (RVLM) during 5-HT(1A)-receptor stimulation-mediated inhibition of cardiovascular responses to static muscle contraction using anesthetized rats. In ten rats, muscle contraction significantly increased (P<0.01) mean arterial pressure (MAP) by 29+/-4 mm Hg, heart rate (HR) by 25+/-3 bpm, and glutamate levels by 4.5+/-0.8 ng/5 microl. Microdialysis of a 5-HT(1A) receptor agonist, 8-OH-DPAT (10 mM), into the RVLM for 30 min attenuated cardiovascular responses to muscle contraction and had no effect on glutamate levels. A subsequent administration of 10 mM WAY100635, a 5-HT(1A) antagonist, into the RVLM antagonized the attenuating effects of 8-OH-DPAT. In another ten rats, muscle contraction significantly increased (P<0.01) MAP and HR by 20+/-2 mmHg and 25+/-8 bpm, respectively. In addition, levels of 5-HT, NE, and DA in the RVLM significantly increased (P<0.01) by 3.6+/-0.3, 3.2+/-0.3, and 3.3+/-0.4 pg/10 microl, respectively. Administration of 8-OH-DPAT (10 mM) into the RVLM for 30 min attenuated cardiovascular responses to muscle contraction and had no effects on NE and DA levels. However, the drug significantly attenuated 5-HT levels following a muscle contraction. Microdialysis of 10 mM WAY100635 into the RVLM reversed both cardiovascular and 5-HT changes. These results suggest that stimulation of 5-HT(1A)-receptors within the RVLM attenuates cardiovascular responses to static exercise via a reduction of extracellular 5-HT concentration and most likely not through changes in glutamate, NE or DA levels.

AMPA-receptor blockade within the RVLM modulates cardiovascular responses via glutamate during peripheral stimuli.

We investigated the effects of AMPA-receptor blockade in the rostral ventrolateral medulla (RVLM) on cardiovascular responses and extracellular concentrations of glutamate during two different types of stimuli that activate peripheral Adelta - and C-fiber polymodal nociceptors using anesthetized rats. First, mechanical stimulation was achieved by applying a bilateral hindpaw pinch for 5 s, and second, thermal stimulation was evoked by immersing bilaterally the hindpaw metatarsi in a 52 degrees C hot water bath for 4 s. Mechanical stimulation increased mean arterial pressure (MAP) by 23 +/- 1 mmHg and heart rate (HR) by 25 +/- 3 bpm (n= 8). Thermal stimuli increased MAP by 32 +/- 3 mmHg and HR by 27 +/- 4 bpm (n= 8). After controlled generation of mechanical or thermal stimulation, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 1.0 microM) was microdialysed bilaterally into the RVLM for 30 min. Administration of CNQX attenuated MAP and HR responses during a subsequent mechanical but not during thermal stimulation. Analyses of extracellular concentrations of glutamate within the RVLM bilaterally revealed an increase of this neurotransmitter within the RVLM during mechanical noxious stimulation. Concomitant with attenuation of the cardiovascular responses, glutamate concentrations were also decreased during the mechanical stimulation after administration of CNQX. These results demonstrate that the AMPA-receptor blockade within the RVLM that attenuates cardiovascular responses during mechanical stimulation is associated with a reduction in extracellular levels of glutamate. In addition, it appears that AMPA receptors in the RVLM do not play a role in mediating cardiovascular responses during thermal stimulation.

Effects of opioid receptor activation on cardiovascular responses and extracellular monoamines within the rostral ventrolateral medulla during static contraction of skeletal muscle.

During static muscle contraction, activation of opioid receptors alters the extracellular glutamate concentrations within the rostral ventrolateral medulla (RVLM). In addition, microdialysis of glutamate in the ventrolateral medulla (VLM) increases the release of norepinephrine (NE), dopamine (DA), and serotonin (5-HT). Therefore, we hypothesized that extracellular concentrations of these monoamines as well as cardiovascular responses during static skeletal muscle contraction would be modulated following administration of [D-Ala(2)]methionine enkephalinamide (DAME), an opioid receptor agonist, into the RVLM. Microdialysis of 100 microM DAME into the RVLM of 10 rats significantly (P<0.01) decreased extracellular levels (in pg/10 microl) of NE (from 3.3+/-0.3 to 1.9+/-0.3), DA (from 5.5+/-0.2 to 3.7+/-0.3), and 5-HT (from 6.1+/-0.8 to 3.6+/-0.2) during static exercise. After microdialysis of DAME, the exercise pressor reflex also significantly (P<0.01) decreased mean arterial pressure (MAP) by 13+/-3 mmHg and heart rate (HR) by 16+/-6 bpm, compared with control (MAP=22+/-4 mmHg and HR=31+/-7 bpm). Subsequently, after 30 min microdialysis of naloxone, an opioid receptor antagonist, muscle contraction increased the extracellular monoamine levels (in pg/10 microl, 3.8+/-0.3 NE; 5.2+/-0.3 DA; and 5.5+/-0.4 5-HT) similar to the control groups and evoked a reversal of cardiovascular responses. Similarly, 30 min of microdialyzing naloxone, added to the perfusing medium containing DAME, reversed the attenuating effects of DAME on monoamines, MAP, and HR during a muscle contraction. Furthermore, microdialysis of 100 microM naloxone alone for 30 min potentiated cardiovascular responses and monoamine levels during a muscle contraction. In summary, the present data demonstrates that microdialysis of DAME into RVLM attenuates the exercise pressor reflex mediated increases in MAP, HR and extracellular levels of biogenic monoamines. A subsequent microdialysis of naloxone reversed the effects suggesting that an opioidergic mechanism within RVLM modulates the exercise pressor reflex. Overall, the present study provides further insights into the opioidergic modulation of the exercise pressor reflex.

Glutamate neurotransmission and nitric oxide interaction within the ventrolateral medulla during cardiovascular responses to muscle contraction.

We previously reported that nitric oxide, within the RVLM and CVLM, plays an opposing role in modulating cardiovascular responses during static muscle contraction [B.J. Freda, R.S. Gaitonde, R. Lillaney, A. Ally, Cardiovascular responses to muscle contraction following microdialysis of nitric oxide precursor into ventrolateral medulla, Brain Res. 828 (1999) 60-67]. In this study, we determined whether the effects of administering L-arginine, a precursor for the synthesis of nitric oxide, and N(G)-monomethyl-L-arginine (L-NMMA), a nitric oxide synthase inhibitor, into the rostral (RVLM) and caudal (CVLM) ventrolateral medulla on cardiovascular responses elicited during static muscle contraction were mediated via an alteration of localized glutamate concentrations using microdialysis techniques. In experiments within the RVLM (n=8), muscle contraction increased MAP and HR by 21+/-2 mmHg and 22+/-3 bpm, respectively. Glutamate increased from 1.1+/-0.4 to 4.4+/- 0.6 ng/5 microl measured from bilateral RVLM areas. Microdialysis of L-arginine (1.0 microM) for 30 min attenuated the contraction-evoked increases in MAP, HR, and glutamate levels. After subsequent microdialysis of L-NMMA (1.0 microM) into the RVLM, contraction augmented the pressor and tachycardic responses and glutamate release. In experiments within CVLM (n=8), muscle contraction increased MAP and HR by 22+/-3 mmHg and 20+/-2 bpm, respectively. Glutamate increased from 0.8+/-0. 4 to 3.6+/-0.6 ng/5 microl measured from the CVLM. L-Arginine augmented the cardiovascular responses and glutamate release and L-NMMA attenuated all the effects. Results suggest that nitric oxide within the RVLM and CVLM plays opposing roles in modulating cardiovascular responses during static exercise via decreasing and increasing, respectively, extracellular glutamate levels.

Rostral ventrolateral medulla opioid receptor activation modulates glutamate release and attenuates the exercise pressor reflex.

We previously reported that the administration of [D-Ala(2)]methionine enkephalinamide (DAME), an opioid receptor agonist, into the rostral (RVLM) but not into the caudal ventrolateral medulla (CVLM), attenuated increases in mean arterial pressure (MAP) and heart rate (HR) during static muscle contraction that had been blocked by prior microdialysis of the opioid receptor antagonist, naloxone [Am. J. Physiol. 274 (1998) H139-H146]. In this study, we determine whether this RVLM-mediated opioidergic-modulation of cardiovascular responses is associated with localized changes in extracellular concentrations of glutamate, an excitatory amino acid, using microdialysis techniques in anesthetized rats. Muscle contraction increased MAP and HR by 37+/-5 mmHg and 23+/-3 bpm, respectively. Extracellular glutamate concentrations, determined using HPLC-ECD, increased from 0.8+/-0.2 to 6.6+/-1.2 ng/5 microliter in the bilateral RVLM areas. Microdialysis of DAME (100 microM) for 30 min attenuated the contraction-evoked increases in MAP, HR, and glutamate levels (20+/-4 mmHg, 10+/-2 bpm, and 1.8+/-0.2 ng/5 microliter, respectively). After microdialysis of naloxone (100 microM) for 30 min into the RVLM, muscle contraction blocked the attenuations (35+/-5 mmHg, 26+/-4 bpm, and 5.8+/-1.0 ng/5 microliter, respectively). Developed muscle tensions were similar throughout the protocol (676+/-38, 678+/-37 and 687+/-37 g, respectively). These results suggest that an opioidergic receptor-mediated mechanism within the RVLM attenuates cardiovascular responses during static exercise via modulating extracellular concentrations of glutamate in the RVLM.

Modulation of extracellular glutamate and pressor response to muscle contraction during NMDA-receptor blockade in the rostral ventrolateral medulla.

Recently our laboratory demonstrated increases in extracellular glutamate concentrations within the rostral ventrolateral medulla (RVLM) during static muscle contraction (Caringi, D.C., Maher, T., Chaiyakul, P., Asmundsson, G., Ishide, T., Ally, A. Pflügers Arch. Eur. J. Physiol., 435:465-471, 1998). In this study, we determined effects of microdialyzing D(-)2-amino-7-phosphonohepatanoic acid (AP-7), an NMDA-receptor antagonist, into the RVLM on changes in mean arterial pressure (MAP), heart rate (HR), and extracellular glutamate levels during muscle contraction in anesthetized rats. Bilateral placements of microdialysis probes into the RVLM were verified by perfusing L-glutamate and obtaining a pressor response. Muscle contraction for 2 min, increased MAP and HR by 22+/-4 mmHg and 28+/-5 bpm, respectively. Extracellular glutamate as determined by microdialysis increased from 0.8+/-0.2 to 6.3+/-1.2 ng/5 microl. Microdialysis of AP-7 (1.0 microM) for 30 min inhibited contraction-evoked MAP and HR responses (10+/-3 mmHg and 13+/-3 bpm) and attenuated increases in glutamate during muscle contraction. Developed tensions did not differ during contractions before and after AP-7. Results demonstrate that NMDA-receptor blockade in the RVLM inhibits cardiovascular responses during static muscle contraction via a reduction in extracellular glutamate levels.