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1 Physiology, University of Tennessee Health Science Center, Memphis, Tennessee, United States
* To whom correspondence should be addressed. E-mail: cleffler{at}physio1.utmem.edu.
Astrocytes can act as intermediaries between neurons and cerebral arterioles to regulate vascular tone in response to neuronal activity. Release of glutamate from presynaptic neurons increases blood flow to match metabolic demands. CO is a gasotransmitter that can be related to neural function and blood flow regulation in the brain. The present study addresses the hypothesis that glutamatergic stimulation promotes perivascular astrocyte CO production and pial arteriolar dilation in the newborn brain. Experiments used anesthetized newborn pigs with closed cranial windows, piglet astrocytes and cerebrovascular endothelial cells in primary culture, and immunocytochemical visualization of astrocytic markers. Pial arterioles and arteries of newborn pigs are ensheathed by astrocytes visualized by glial fibrillary acidic protein (GFAP) staining. Treatment (2h) of astrocytes in culture with L-2-alpha aminoadipic acid (L-AAA), followed by 14 hr in toxin free medium, dose-dependently increased cell detachment suggesting injury. Conversely, 16h of continuous exposure to L-AAA caused no decrease in endothelial cell attachment. In vivo, topical L-AAA (2mM, 5h) disrupted the cortical glia limitans histologically. Such treatment also eliminated pial arteriolar dilation to the astrocyte-dependent dilator, ADP, and to glutamate, but not to isoproterenol or CO. Glutamate stimulated CO production by the brain surface that also was abolished following L-AAA. In contrast, tetrodotoxin blocked dilation to NMDA, but not to glutamate, isoproterenol, or CO, or the glutamate-induced increase in CO. The concurrent loss of CO production and pial arteriolar dilation to glutamate following astrocyte injury suggests astrocytes may employ CO as a gasotransmitter for glutamatergic cerebrovascular dilation.
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