Evelyn H. Schlenker

Cardiorespiratory and metabolic responses to injection of bicuculline into the hypothalamic paraventricular nucleus (PVN) of conscious rats.

Stimulation of the PVN increases mean arterial pressure (MAP) and heart rate (HR). However, little is known about its role in modulating ventilation. We tested the hypothesis that the stimulation of the PVN by microinjection of bicuculline methiodide (BMI), a gamma-aminobutyric acid (GABA)(A) receptor antagonist, increases ventilation in conscious rats. Oxygen consumption was also evaluated to determine if the ventilatory responses were associated with increases in metabolic rate. Male Sprague--Dawley rats were instrumented with femoral catheters to measure MAP and HR and cannulae were implanted 1 mm above the PVN. After 5 to 7 days of recovery, metabolic, ventilatory, and cardiovascular responses to artificial cerebrospinal fluid (aCSF) and BMI were evaluated. Rats were given a 50 nl unilateral microinjection of aCSF (the vehicle control) followed by 50 n1 of BMI (1 mM) into the other side. Microinjection of BMI significantly increased MAP compared to aCSF (145+/-4 vs. 124+/-5 mmHg, P<0.02), HR to 460+/-17 from 362+/-22 breaths/min (P<0.01). Ventilation increased by 300% (P=0.01) by stimulating frequency of breathing (176+/-14 compared to 79+/-12 breaths/min, P<0.005) and increasing tidal volume. Concomitantly, O(2) consumption doubled (P<0.006). These data suggest that in the PVN GABA receptors may be important regulators of cardiopulmonary and metabolic function in conscious rats.

Endogenous opioids modulate ventilation in the obese Zucker rat

This study evaluated the modulatory role of endogenous opioids on ventilation in young and mature, lean and obese male Zucker rats. Naloxone, an opioid receptor antagonist, and saline (control) were administered subcutaneously to awake rats, and ventilation in air and in response to an hypoxic and an hypercapnic gas challenge measured. In response to naloxone young, obese but not lean rats exhibited a marked increase of ventilation in all three conditions. Older obese Zucker rats that were morbidly obese breathed at a frequency of over 200 breaths per minute and showed only a modest increase of ventilation in response to naloxone. Older lean rats increased ventilation with naloxone only when exposed to hypercapnia. Unlike the stimulatory effects hypoxia and hypercapnia had on ventilation in older, lean rats, the ventilatory responses of the obese, older rats to hypoxia and to hypercapnia were blunted. We conclude that the obese Zucker rat may be a good animal model to assess how chest wall loading and endogenous opioids interact in the development of ventilatory control abnormalities.

Sex-specific densities of estrogen receptors alpha and beta in the subnuclei of the nucleus tractus solitarius, hypoglossal nucleus and dorsal vagal motor nucleus weanling rats.

In rats ventilatory responses to N-methyl-d-aspartate (NMDA) receptor modulation are sexually dimorphic and may be altered by manipulating brain levels of estrogen receptors. Here we used image analysis and immunohistochemistry in weanling male and female rats to quantitate areas and densities of ER alpha and ER beta-positive neurons within medullary regions associated with cardiopulmonary regulation including the hypoglossal nucleus, subnuclei of the nucleus of the solitary tract (NTS), and the dorsal motor nucleus of the vagus. Weanling rats were selected because ventilation, metabolic rate, and body and brain weights are comparable at this age and there are no large fluctuations in plasma hormone levels. Females, relative to males, had smaller areas in the A2 region and parts of the NTS. Counts and densities for ER alpha were greater in females than males in almost all regions studied. In contrast sex differences in ER beta were found in fewer nuclei, but in those higher counts and densities were noted in females. In general, ER beta-positive neurons in the brainstem regions examined were less prevalent than ER alpha neurons. Thus, in weanling rats sex affected ER alpha and ER beta neuronal densities in brainstem regions associated with cardiopulmonary regulation that may be responsible for sex differences in control of breathing.

Ventilatory Responses of Aged Male and Female Rats to Hypercapnia and to Hypoxia

Ventilatory parameters such as tidal volume, minute ventilation (VE), and inspiratory flow rate decrease in 24- vs. 12-month-old male and female rats. Differences between male and female values are maintained with age. Ventilatory response male and female rats exhibit to hypercapnia is altered by a decrease of the intercept, but not the slope value. The pattern of breathing exhibited by young females and males in response to hypercapnia (i.e. an increase of VT and f) is different than that noted in old males and females (i.e. an increase in VT only). In contrast, the ventilatory response both of slope and intercept male rats show by 24 months is decreased compared to the 12-month value; but the slope value is actually increased in the older vs. younger female rats in response to hypoxia.

Frequency responses to hypoxia and hypercapnia in carotid body-denervated conscious rats.

The ventilatory response to brief, severe hypoxia is biphasic consisting of an initial facilitation followed by a slowing of breathing frequency (fR). After the hypoxic stimulus is removed, fR drops below baseline levels. This phenomenon is called the post-hypoxic frequency decline (phfd). These fR changes are due to reciprocal changes in expiratory time (TE), mediated by the ventrolateral pontine A5 region (J. Physiol. (London) 497 (1996) 79; Am. J. Physiol. 274 (1998) R1546). The purpose of this study was to determine if carotid body input is required for full manifestation of phfd by quantifying ventilation in intact and carotid sinus denervated rats in response to hypoxic, and contrasted with hypercapnic stimuli. Following carotid denervation the initial facilitation of fR was eliminated in response to hypoxia, but the phfd remained. In contrast the pattern in response to increased CO2 remained constant before and after carotid denervation. These results suggest that phfd is not dependent upon carotid body stimulation, but is mediated centrally.

Effects of thyroidectomy, T4, and DITPA replacement on brain blood vessel density in adult rats

In hypothyroid patients, altered microvascular structure and function may affect mood and cognitive function. We hypothesized that adult male hypothyroid rats will have significantly lower forebrain blood vessel densities (BVD) than euthyroid rats and that treatment with 3,5-diiothyroprionic acid (DITPA) (a thyroid hormone analog) or thyroxine (T(4)) will normalize BVDs. The euthyroid group received no thyroidectomy or treatment. The other three groups received thyroidectomies and pellets. The hypothyroid group received a placebo pellet, the DITPA group received an 80-mg DITPA-containing pellet, and the T(4) group received a 5.2-mg T(4) slow-release pellet for 6 wk. Body weights, cardiac function, and body temperatures were measured. A monoclonal antiplatelet endothelial cell adhesion antibody was used to visualize blood vessels. The euthyroid group averaged body weights of 548 +/- 54 g, while the hypothyroid group averaged a body weight of 332 +/- 19 g (P value < 0.001). Relative to the euthyroid group, the DITPA-treated group was significantly lighter (P value < 0.05), while the T(4)-treated group was comparable in body weight to the euthyroid group. The same trends were seen with body temperature and cardiac function with the largest difference between the euthyroid and hypothyroid groups. BVD in the euthyroid group was 147 +/- 12 blood vessels/mm(2) and in hypothyroid group 69 +/- 5 blood vessels/mm(2) (P = 0.013) but similar among the euthyroid, DITPA, and T(4) groups. These results show that hypothyroidism decreased BVD in adult rat forebrain regions. Moreover, DITPA and T(4) were efficacious in preventing effects of hypothyroidism on cardiac function and BVD.

Inactivated and live, attenuated influenza vaccines protect mice against influenza:Streptococcus pyogenes super-infections

Mortality associated with influenza virus super-infections is frequently due to secondary bacterial complications. To date, super-infections with Streptococcus pyogenes have been studied less extensively than those associated with Streptococcus pneumoniae. This is significant because a vaccine for S. pyogenes is not clinically available, leaving vaccination against influenza virus as our only means for preventing these super-infections. In this study, we directly compared immunity induced by two types of influenza vaccine, either inactivated influenza virus (IIV) or live, attenuated influenza virus (LAIV), for the ability to prevent super-infections. Our data demonstrate that both IIV and LAIV vaccines induce similar levels of serum antibodies, and that LAIV alone induces IgA expression at mucosal surfaces. Upon super-infection, both vaccines have the ability to limit the induction of pro-inflammatory cytokines within the lung, including IFN-γ which has been shown to contribute to mortality in previous models of super-infection. Limiting expression of these pro-inflammatory cytokines within the lungs subsequently limits recruitment of macrophages and neutrophils to pulmonary surfaces, and ultimately protects both IIV- and LAIV-vaccinated mice from mortality. Despite their overall survival, both IIV- and LAIV-vaccinated mice demonstrated levels of bacteria within the lung tissue that are similar to those seen in unvaccinated mice. Thus, influenza virus:bacteria super-infections can be limited by vaccine-induced immunity against influenza virus, but the ability to prevent morbidity is not complete.

Altered Control of Ventilation in Streptozotocin-Induced Diabetic Rats

Abstract The purposes of this study were (i) to determine if ventilatory control is altered in streptozotocin (STZ)-induced diabetic rats and (ii) to determine whether insulin treatment of diabetic rats could prevent ventilatory abnormalities. Male Sprague-Dawley rats were randomly assigned to three groups: control (n = 10), diabetic (n = 9), and diabetic treated with insulin (n = 9). The diabetic group exhibited a progressive reduction of tidal volume, minute ventilation, and CO2 production compared with the control and diabetic treated with Insulin groups over the 4 week period. Furthermore, the ventilatory responses to the hypercapnic (3%, 6%, 9% CO2) and hypoxic (10% O2) gas challenges were significantly less in the diabetic rats than those of the control and diabetic and Insulin treated groups by the third and fourth week. Ventilation and ventilatory responses to hypercapnia and hypoxia were similar in the control group and the diabetic treated with insulin group at the end of the study. In conclusion, uncontrolled diabetes induced in rats by STZ treatment resulted in altered control of ventilation that could be prevented by insulin therapy.

Elimination of the post-hypoxic frequency decline in conscious rats lesioned in pontine A5 region.

A decrease in the frequency of breathing following a hypoxic exposure that is below baseline values is called the post-hypoxic frequency decline (phfd) and is due to an elongation of expiratory time (TE). We hypothesized that lesioning the pontine A5 region would eliminate the phfd in conscious rats. Fourteen conscious male rats that demonstrated a phfd received lesions either within the A5 region (n=9) or outside this region (controls, n=5). Compared with pre-lesion values, body temperature decreased and frequency of breathing was lower during exposure to air, hypoxia, and hypercapnia in A5-lesioned, but not in the control-lesioned rats. No effect of A5 lesions was noted on tidal volume. Rats with A5 lesions no longer exhibited a phfd, and TE values following hypoxia were comparable to baseline TE values. These data suggest that the A5 region of the ventrolateral pons modulates the phfd in conscious rats and affects frequency of breathing in response to both hypoxia and hypercapnia.

Effects of naloxone on oxygen consumption and ventilation in awake golden syrian hamsters

Endogenous opioids are known to inhibit chemoreception and ventilatory control. The opioid antagonist naloxone stimulates ventilation by removing this inhibition. To study whether the effects of opiate receptor antagonism are mediated by a central or a peripheral mechanism, we administered equal doses of naloxone hydrochloride (NHCl, an agent that crosses the blood-brain barrier) and naloxone methiodide (NM, an agent that does not cross the blood-brain barrier) to awake golden Syrian hamsters. Both naloxone preparations significantly increased the oxygen consumption (46% for NHCl and 90% for NM) in these animals relative to saline. Naloxone hydrochloride, but not NM, stimulated ventilation (30%) and tidal volume (34%) when the animal was subjected to a hypercapnic challenge, predominantly sensed in the brain. In contrast, both naloxones stimulated ventilation by 52% compared to saline treatment when the hamsters were exposed to a hypoxic challenge, predominantly sensed peripherally. These results suggest that endogenous opioids modulate both central and peripheral chemoreception in the hamster.