Objective

1. Exposure to Prenatal Carbon Monoxide and Postnatal Hyperthermia:Short and Long-Term Effects on Neurochemicals and Neuroglia in the Developing Brain Author: Tolcos M et al Carmen L. Trinidad

2. Objective • Investigate the development of the brain after daily exposure to CO during gestation, alone or in combination with exposure to hyperthermia

3. Maternal cigarette smoking during pregnancy • Spontaneous abortion • Intrauterine growth restriction • Sudden infant death syndrome (SIDS)

4. Cigarette Smoke • Agents responsible for adverse effects of smoking • Nicotine • CO • Hydrogen cyanide

5. Carbon Monoxide (CO) • Crosses placenta where it binds to fetal hemoglobin reducing the oxygen content in the blood • Alterations in levels of norepinephrine and serotonin in the brain • Lesions in cerebral white matter, brainstem, basal ganglia

6. Risk Factors for SIDS • Central nervous system is vulnerable to hyperthermic stress • Increased permeability to blood-brain barrier (helps maintain stable environment required for normal brain function) • Decreased cerebral blood flow, neuronal damage • Edema • Hyperthermia may be induced by: • overwrapping, excessive room heat, infection

7. Experimental Procedure • Pregnant guinea pigs • 10 in control group - • chamber exposed to room air • 11 in experimental group - • exposed to 200 p.p.m CO for 10h/day • 23 to 25 days of gestation until term (68 day)

8. Experimental Procedure • Birth • offspring weighed and removed from chamber and raised in air for • 1 week - 5 control & 7 experimental • 8 weeks - 5 control & 4 experimental • Postnatal day 4 • all newborns returned to chamber • 23°C - normal temperature • 35°C - hyperthermia

9. Tissue Preparation • Newborns were anesthetized and brains were removed and weighed at postmortem • Sections removed and stained with .01% thionin: • forebrain - cerebral cortex, white matter, striatum, hippocampus, and thalamus • medulla • cerebellum

10. Results • CO exposure during pregnancy had no affect on litter size or birth weight • No difference in body or brain weight at 1wk or 8 wks • All treated animals were normal and showed no signs of neurological deficits

11. Structural Analysis • Sections were analyzed for structural damage (lesions) • areas of necrosis • infarction (tissue death) • aggregations of glia (support the function of neurons) • 10 sections for each brain region

12. Lesions in the brains of 8 wk olds exposed to prenatal CO & postnatal hyperthermia (COH) • Region COH (n=6) • cerebral Hemisphere • cerebral cortex >20 • subcortical white matter 5-10 • thalamus 10-20 • basal ganglia 5-10 • hippocampus 5-10 • cerebellum <5 • medulla 10-20

13. Fig1

14. Structural Analysis Results • No lesions or structural abnormalities in brains at 1 wk after birth • Prenatal CO & postnatal hyperthermia at 8wks: • aggregations of glia - gliosis results in response to neuronal loss • lesions in medulla, thalamus, basal ganglia, hippocampus, and cerebellum

15. Results (cont’d) • No difference in medulla comparing to control at 1 or 8 wks • No difference in the area of cerebellum or ratio of the area to CO-exposed animals compared to controls of 1 wk • No difference in 8 wk olds exposed to CO and hyperthermia

16. Immunohistochemical Analysis • Glial Fibrillary Acidic Protein (GFAP) - characteristic of the glial cells that surround and insulate nerve cells • Optical density test was performed using immunoreactive products to determine the distribution of GFAP-IR (immunoreactivity) • 3 sections of medulla: caudal, midmedulla, rostral medulla

17. Immunohistochemical Results • Combination of CO exposure and hyperthermia - increase in GFAP-IR in medulla • 4 hrs of hyperthermia can result in an increase in GFAP-IR in the hypoglossal nucleus but no neuronal loss • Occurs in response to the effects of hyperthermia in the CO treated groups

19. Optical Density of GFAP-IR • There were no significant differences in the OD at 1wk after birth in any medullary region • nucleus tractus solitarius (NTS) • hypoglossal nucleus • area postrema • At 8 weeks the combination of prenatal CO and postnatal hyperthermia resulted in increase in GFAP-IR in NTS, hypoglossal, & postrema when compared to control groups

20. Conclusion • Study investigated the development of the brain in 1& 8 week old guinea pigs after daily exposure to modest levels of CO throughout the last 60% of gestation • alone • in combination with exposure to hyperthermia on day 4 after birth • Neither of these treatments affected brain or body weights at 1 or 8 weeks, but effects on the structure & neurochemistry were seen

21. Major Findings • Combination of chronic prenatal CO exposure & postnatal hyperthermia resulted in lesions throughout brain • Brief hyperthermic episode can have significant effects on the neurotransmitter content of the neonatal brainstem • Prenatal CO exposure and postnatal hyperthermia have complex, interactive, and time dependent effects on neuronal neurochemistry and neuroglial proliferation

22. References • Chen et al. 1991. Effect of mild hyperthermia on the ischemic infarct volume after middle cerebral artery occlusion in the rat. Neurology 41-1131-35 • Browne CA et al. 2000. Infant autonomic function is altered by maternal smoking during pregnancy. Early Hum Dev 59: 209-18. • Tolcos M et al. 2000. Exposure to Prenatal Carbon Monoxide andPostnatal Hyperthermia:Short and Long-Term Effects on Neurochemicals and Neuroglia in the Developing Brain. Experimental Neurology 162: 235-246.