Bonnie L. Metzger

Effects of Environment on Enhancing Functional Plasticity following Cerebral Ischemia

Given the brain’s capacity to recover from injury, plasticity may be enhanced following cerebral ischemia through environmental manipulation. Thus, the purpose of this study was to (1) determine the effects of early exposure to an enriched environment following ischemia on functional plasticity and (2) examine the relationship between morphological and behavioral plasticity. Adult female rats (n = 38) were divided into ischemia and control groups. Each group was further randomized to either standard (SC) or enriched conditions (EC). After 4 days of environmental exposure, rats were tested for 6 days in the water maze. Control and ischemia rats exposed to EC have increased total dendritic length (P < 0.05) as well as increased number of dendritic segments in the apical (P < 0.05) region of the hippocampal area compared to those housed in SC; furthermore, increased dendritic spine density in the apical (P < 0.05) region was also seen. Behavioral testing showed that ischemia rats exposed to SC have longer swim latencies (P < 0.05) and greater directional heading errors (P < 0.05) than ischemic rats exposed to EC; the latter group performed similar to controls. It is concluded that EC may be a potentially useful therapy in the recovery of spatial memory impairments seen after ischemia.

BOWEL PREPARATION FOR COLECTOMY AND RISK OF Clostridium difficile INFECTION

BACKGROUND: Mechanical bowel preparation before colectomy is controversial for several reasons, including a theoretically increased risk of Clostridium difficile infection. OBJECTIVE: The primary aim of this study was to compare the incidence of C difficile infection among patients who underwent mechanical bowel preparation and those who did not. A secondary objective was to assess the association between C difficile infection and the use of oral antibiotics. DESIGN: This was an observational cohort study. SETTING: The Michigan Surgical Quality Collaborative Colectomy Project (n = 24 hospitals) participates in the American College of Surgeons-National Surgical Quality Improvement Program with additional targeted data specific to patients undergoing colectomies. PATIENTS: Included were adult patients (21 years and older) admitted to participating hospitals for elective colectomy between August 2007 and June 2009. MAIN OUTCOME MEASURE: The main outcome measure was laboratory detection of a positive C difficile toxin assay or stool culture. RESULTS: Two thousand two hundred sixty-three patients underwent colectomy and fulfilled inclusion criteria. Fifty-four patients developed a C difficile infection, for a hospital median rate of 2.8% (range, 0–14.7%). Use of mechanical bowel preparation was not associated with an increased incidence of C difficile infection (P = .95). Among 1685 patients that received mechanical bowel preparation, 684 (41%) received oral antibiotics. The proportion of patients in whom C difficile infection was diagnosed after the use of preoperative oral antibiotics was smaller than the proportion of patients with C difficile infection who did not receive oral antibiotics (1.6% vs 2.9%, P = .09). LIMITATIONS: The potential exists for underestimation of C difficile infection because of the studys strict data collection criteria and risk of undetected infection after postoperative day 30. CONCLUSIONS: In contrast to previous single-center data, this multicenter study showed that the preoperative use of mechanical bowel preparation was not associated with increased risk of C difficile infection after colectomy. Moreover, the addition of oral antibiotics with mechanical bowel preparation did not confer any additional risk of infection.

Effect of Position On Cardiovascular Response During the Valsalva Maneuver

Sudden cardiac death (SCD) has frequently been associated with the Valsalva maneuver (VM), which is characterized by sudden intense changes in systolic blood pressure (SBP) and heart rate (HR). The purpose of this study was to examine the effect of manipulating body position on the intensity of SBP and HR changes during the VM. Thirty-two men and 32 women (35–55 years) without a history or signs of cardiovascular disease (CVD) were studied. Subjects produced a VM of 40 mmHg for 10 seconds in each of five randomly assigned bed (flat, sidelying, 30° elevated, 70° elevated) and chair positions. Age covaried with SBP and HR responses to the VM. When age relationships were factored out, the most intense changes in SBP during the VM occurred in the 30° and 70° elevated and chair positions. Persons with a history of atherosclerotic CVD, on bedrest, should be positioned with the head of the bed flat to reduce cardiovascular risks associated with the VM.

Effects of Age on Autonomic Cardiovascular Responsiveness In Healthy Men and Women

Blood pressure and heart rate responses to the Valsalva maneuver (straining) were used to quantify the effects of age on autonomic cardiovascular responsiveness in 110 healthy men and women, 30 to 76 years. In general, aging was associated with diminished sympathetic responsiveness during strain. In women, however, the predominant age effect was a significant reduction in bradycardic response to systolic blood pressure overshoot following release of strain. When present, age-related differences in cardiovascular responses to the Valsalva maneuver were manifest by age 45. These findings are consistent with an age-related diminution of autonomic cardiovascular responsiveness in healthy adults. Moreover, they suggest that interventions to reduce the frequency and intensity of straining may be especially important in older adults in order to minimize health risks associated with rapid, abrupt changes in blood pressure.

Long-Term Exercise Training Selectively Alters Serum Cytokines Involved in Fever

Long-term exercise training selectively alters serum cytokines involved in fever. Chronic exercise training has a number of effects on the immune system that may mimic the physiological response to fever. Female rats that voluntarily exercise on running wheels develop an elevated daytime core temperature after several weeks of training. It remains to be seen whether the elevation in daytime temperature involves inflammatory patterns characteristic of an infectious fever. We assessed whether chronic exercise training in the rat would alter levels of cytokines involved in fever. Female Sprague Dawley rats at 45 days of age weighing 90—110 g were divided into two groups (exercise and sedentary) and housed at an ambient temperature of 22°C. Interleukin-1 beta (IL-1β), interleukin-6 (IL-6), interleukin-10 (IL-10), tumor necrosis factor alpha (TNF-α), iron, and zinc levels were analyzed. Rats underwent 8 weeks of exercise on running wheels. Exercise led to altered levels of some key cytokines that are involved in fever. Exercise animals had significantly higher IL-1β levels and lower IL-10 levels compared to sedentary animals. Although IL-6 levels were slightly lower in the exercise animals, these levels were not significantly affected by training. TNF-α activity was similar in the two groups. Training also led to a slight increase in serum zinc and decrease in serum unsaturated iron binding capacity (UIBC). The data suggest that chronic exercise training evokes immune responses that mimic some, but not all, aspects of fever. This may explain why exercise leads to elevated daytime core temperature.

Nutrient composition: Effects on appetite in monkeys with oral factors held constant

The effects of macronutrients on appetite and total caloric intake in monkeys (Macaca mulatta) was studied using a new feeding and infusion system which yoked intragastric infusion of various nutrients to oral ad lib intake and removed the confounding factor of palatability from the assessment of nutrient effects on feeding behavior. A suction-activated liquid diet feeding system provided free access to a nutritionally complete diet, with 1 ml of diet delivered orally by pump with each discrete suck by the monkey. A second pump was yoked to the oral feeding pump and delivered various nutrients directly into the stomach via an implanted intragastric cannula. Thus, while oral diet composition remained constant, the net diet reaching the stomach varied over ranges of 28 to 77% carbohydrate, 16 to 65% fat and 7 to 36% protein. No significant differences in total caloric intake were observed between intakes of diets with net composition of high carbohydrate or high fat. When protein was increased to 36%, total caloric intake was generally reduced, and this effect was sustained for at least 3 weeks. Therefore, protein appears to have an increased specific satiating effect beyond the caloric content, when compared to carbohydrate or fat.

Effects of exercise conditioning on thermoregulatory responses to repeated administration of chlorpyrifos

Little is known about the effects of physical activity (i.e., exercise training) on susceptibility to environmental toxicants. Chlorpyrifos (CHP), an organophosphate (OP) insecticide, affects thermoregulation, causing an acute period of hypothermia followed by a delayed fever. Since exercise conditioning alters the thermoregulatory responses of rodents, this study examined whether exercise training would alter the thermoregulatory response to repeated CHP administration in the female Sprague-Dawley rat. Core temperature (T(c)) and motor activity (MA) were monitored by radiotelemetry in rats housed at an ambient temperature (T(a)) of 22 degrees C. The rats either were provided with continuous access to running wheels (exercise group) or were housed in standard cages without wheels (sedentary group). The exercise group rats ran predominantly at night with an average of 7.6 km/24h. After 8 weeks the rats in both groups were gavaged daily with corn oil or 10mg/kg CHP (dissolved in corn oil) for 4 days. CHP induced an immediate hypothermic response followed by a delayed fever throughout the next day in the sedentary group rats after the first three doses of CHP. The exercise group rats showed no hypothermia after the first dose of CHP. However, they became hypothermic after the second and third doses of CHP. The exercise group rats developed a smaller daytime fever after each dose of CHP compared to the sedentary group rats. Overall, exercise training attenuated the hypothermic and febrile effects of repeated CHP. Thus, the data suggest that a sedentary lifestyle may increase the sensitivity to OP insecticides. Exercise training was also associated with a more rapid recovery of plasma cholinesterase activity.

Cholecystokinin Effects on Feeding, Glucose, and Pancreatic Hormones in Rhesus Monkeys

The effects of cholecystokinin on feeding, and on plasma glucose and pancreatic hormone responses to a mixed-meal were determined in lean rhesus monkeys. Following an overnight fast the octapeptide of cholecystokinin (CCK-8) was administered intravenously over a 6 minute period coincident with the initiation of free feeding or an intragastric infusion of a mixed liquid diet. CCK-8 inhibited feeding and delayed the plasma glucose and insulin response to a mixed-meal. The threshold for the feeding effect ranged from 30 to 120 ng/kg/min across monkeys and did not extend beyond 15 minutes of the start of the CCK infusion. The delays in plasma glucose and insulin were not dependent on rate or amount of food entering the stomach. Further, there were no alterations from basal levels in plasma glucose or insulin prior to the onset of CCK-induced feeding inhibition. There was no evidence that CCK-8 stimulated insulin release, nor was the usual close relationship between plasma glucose and insulin levels in response to a mixed-meal changed by CCK-8.

Effects of Exercise Conditioning on Thermoregulatory Response to Anticholinesterase Insecticide Toxicity

Chronic exercise conditioning has been shown to alter basal thermoregulatory processes (change in thermoregulatory set point) as well as the response to infectious fever. Chlorpyrifos (CHP), an organophosphate insecticide, also affects thermoregulation, causing an acute period of hypothermia followed by a delayed fever. This study examined whether chronic exercise training in the rat alters the thermoregulatory response to CHP. Core temperature and motor activity were monitored by radiotelemetry in female Sprague-Dawley rats housed individually at an ambient temperature of 22 °C. The rats were either given continuous access to running wheels or housed in standard cages without wheels. The exercise group ran predominately at night. After 8 weeks, the rats were gavaged with corn oil or 15 mg/kg CHP. CHP induced a transient hypothermic response followed by a delayed fever, beginning 1 day after exposure. Relative to controls, Tc decreases were not significantly different between the exercise (1.6 °C) group and the sedentary (0.5 °C) group given CHP. The sedentary and exercise group administered CHP developed a fever the day after CHP treatment. The fever response was greater in the sedentary group and persisted for approximately 3 days postinjection. Fever of the exercise group persisted for just one-half of 1 day after CHP. It is well known that chronic exercise training improves aerobic capacity; however, trained rats were not protected from the hypothermic effects of CHP. Training did ameliorate the febrile effects of CHP. Thus, exercise training may afford protection to the toxic effects of organophosphate insecticides.

What it takes: perspectives from developing nurse scientists.

The need for nurse scientists has never been greater, given the complexity of health problems facing our world and the rising cost of providing care to prevent and treat them. The development of nurse researchers is critical to preserve and advance the scientific foundation of the discipline. In this article, two successful doctoral students present their personal views about the cognitive and behavioral transformation they experienced during their program of study, highlighting what they believe to be important resources that enhance doctoral education and sharing how they overcame the challenges encountered. The framework of transformational leadership is used to highlight important aspects of their development as nurse scientists. Action steps for attracting a greater number of nurses to a career in science are recommended.