In vitro responses of neurons in the periaqueductal gray to hypoxia and hypercapnia.
Hypoxia-sensitive neurons in the caudal hypothalamus (CH) have been shown to project to the periaqueductal gray (PAG) which, in turn, sends descending projections to an area of the ventrolateral medulla (VLM) containing neurons inherently excited by hypoxia. The purpose of this study was to determine if neurons in the PAG are excited by hypoxia or hypercapnia in an in vitro environment. Extracellular responses to hypoxia and hypercapnia of neurons located throughout the PAG were recorded in a rat brain slice (400-500 microm thick) preparation. Hypoxic (10% O(2)/5% CO(2)/85% N(2)) and hypercapnic (7% CO(2)/93% O(2)) stimuli were delivered to the tissue through gas bubbled into the brain slice chamber. A majority (39 of 53) of the neurons tested responded to hypoxia. Of these neurons, 92% responded to hypoxia with an increase in firing rate. Neurons in the dorsolateral/lateral regions increased firing rates to a greater extent than neurons located in ventrolateral regions. All neurons tested (n=6) also responded to hypoxia after perfusion of the tissue with a low Ca(2+)/high Mg(2+) solution to block classic synaptic transmission. Only a small proportion (7/33) of neurons tested responded to hypercapnia. These findings indicate that neurons in the periaqueductal gray region of the brain have an inherent responsiveness to hypoxia and, thus, may contribute to the overall coordination of cardiorespiratory responses to systemic hypoxia.
Department of Molecular and Integrative Physiology and College of Medicine, University of Illinois at Urbana-Champaign, 524 Burrill Hall, 407 South Goodwin Avenue, Urbana, IL 61801, USA.
J M
JM
Kramer
P C
PC
Nolan
T G
TG
Waldrop
D000818:Animals; D006935:Hypercapnia / Q000473:pathology*; D002534:Hypoxia, Brain / Q000473:pathology*; D008297:Male; D009474:Neurons / Q000473:pathology*; D010100:Oxygen / Q000494:pharmacology; D010313:Partial Pressure; D010487:Periaqueductal Gray / Q000473:pathology*; D051381:Rats; D017207:Rats, Sprague-Dawley
D010100:Oxygen