Changes in heart rate patterns by lipopolysaccharide and intermittent hypoxia-ischemia in 7-day-old rats

Interactive effects of maternal cigarette smoke, heat stress, hypoxia, and lipopolysaccharide on neonatal cardiorespiratory and cytokine responses

Maternal cigarette smoke (CS) exposure exhibits a strong epidemiological association with Sudden Infant Death Syndrome, but other environmental stressors, including infection, hyperthermia, and hypoxia, have also been postulated as important risk factors. This study examines whether maternal CS exposure causes maladaptations within homeostatic control networks by influencing the response to lipopolysaccharide, heat stress, and/or hypoxia in neonatal rats. Pregnant dams were exposed to CS or parallel sham treatments daily for the length of gestation. Offspring were studied at postnatal days 6-8 at ambient temperatures (T_a) of 33°C or 38°C. Within each group, rats were allocated to control, saline, or LPS (200 µg/kg) treatments. Cardiorespiratory patterns were examined using head-out plethysmography and ECG surface electrodes during normoxia and hypoxia (10% O₂). Serum cytokine concentrations were quantified from samples taken at the end of each experiment. Our results suggest maternal CS exposure does not alter minute ventilation (V̇e) or heart rate (HR) response to infection or high temperature, but independently increases apnea frequency. CS also primes the inflammatory system to elicit a stronger cytokine response to bacterial insult. High T_a independently depresses V̇e but augments the hypoxia-induced increase in V̇e Moreover, higher T_a increases HR during normoxia and hypoxia, and in the presence of an immune challenge, increases HR during normoxia, and reduces the increase normally associated with hypoxia. Thus, while most environmental risk factors increase the burden on the cardiorespiratory system in early life, hyperthermia and infection blunt the normal HR response to hypoxia, and gestational CS independently destabilizes breathing by increasing apneas.

Cardiorespiratory control and cytokine profile in response to heat stress, hypoxia, and lipopolysaccharide (LPS) exposure during early neonatal period

Sudden infant death syndrome (SIDS) is one of the most common causes of postneonatal infant mortality in the developed world. An insufficient cardiorespiratory response to multiple environmental stressors (such as prone sleeping positioning, overwrapping, and infection), during a critical period of development in a vulnerable infant, may result in SIDS. However, the effect of multiple risk factors on cardiorespiratory responses has rarely been tested experimentally. Therefore, this study aimed to quantify the independent and possible interactive effects of infection, hyperthermia, and hypoxia on cardiorespiratory control in rats during the neonatal period. We hypothesized that lipopolysaccharide (LPS) administration will negatively impact cardiorespiratory responses to increased ambient temperature and hypoxia in neonatal rats. Sprague-Dawley neonatal rat pups were studied at postnatal day 6-8. Rats were examined at an ambient temperature of 33°C or 38°C. Within each group, rats were allocated to control, saline, or LPS (200 μg/kg) treatments. Cardiorespiratory and thermal responses were recorded and analyzed before, during, and after a hypoxic exposure (10% O2). Serum samples were taken at the end of each experiment to measure cytokine concentrations. LPS significantly increased cytokine concentrations (such as TNFα, IL-1β, MCP-1, and IL-10) compared to control. Our results do not support a three-way interaction between experimental factors on cardiorespiratory control. However, independently, heat stress decreased minute ventilation during normoxia and increased the hypoxic ventilatory response. Furthermore, LPS decreased hypoxia-induced tachycardia. Herein, we provide an extensive serum cytokine profile under various experimental conditions and new evidence that neonatal cardiorespiratory responses are adversely affected by dual interactions of environmental stress factors.

Galantamine, an acetylcholinesterase inhibitor, reduces brain damage induced by hypoxia-ischemia in newborn rats

AIM

Our aim is to elucidate whether galantamine, known as an acetylcholinesterase inhibitor, reduces brain damage induced by hypoxia-ischemia (HI).

STUDY DESIGN

7-day-old Wistar rats were used. Rats were subjected to left carotid artery ligation followed by 2 h of hypoxia (8% oxygen). We injected galantamine intraperitoneally just before hypoxia (5.0 mg/kg, n=14; 2.5 mg/kg, n=9; 1.0mg/kg, n=11) and after hypoxia (5.0mg/kg, n=7) to determine its neuroprotective effect. An equivalent volume of saline was administered as a control before (n=31) and after hypoxic load (n=7). We also examined the production of IL-1β in the ligated hemisphere side after injection of galantamine (prior hypoxia; 5.0 mg/kg, n=7) or saline (n=8). Brains were analyzed 7 days after HI.

RESULTS

Two of the 5.0 mg/kg galantamine pre-treated rats and a post-treated rat died during experiments. The remaining survived and 5.0mg/kg galantamine pre-treated rats showed a marked reduction of brain damage (p<0.01) compared with the control. The other galantamine groups had severe brain damage similar to controls. Microglial accumulation was significantly reduced in rats pre-treated with 5.0 mg/kg of galantamine compared to control rats on both the hippocampus (p=0.02) and cortex (p<0.01). In contrast, the other galantamine groups showed a lower suppressive effect on microglial accumulation compared to the control. Galantamine significantly reduced IL-1β productions when compared to the control (p<0.01).

CONCLUSION

Pre-treatment of galantamine reduced brain damage with a suppressive effect on microglial accumulation and IL-1β production in a newborn rat model of HI.