Abstract
The midbrain periaqueductal gray (PAG) is involved in many basic survival behaviors that affect respiration. We hypothesized that the PAG promotes these behaviors by changing the firing of preinspiratory (pre-I) neurons in the pre-Bötzinger complex, a cell group thought to be important in generating respiratory rhythm. We tested this hypothesis by recording single unit activity of pre-Bötzinger pre-I neurons during stimulation in different parts of the PAG. Stimulation in the dorsal PAG increased the firing of pre-I neurons, resulting in tachypnea. Stimulation in the medial part of the lateral PAG converted the pre-I neurons into inspiratory phase-spanning cells, resulting in inspiratory apneusis. Stimulation in the lateral part of the lateral PAG generated an early onset of the pre-I neuronal discharge, which continued throughout the inspiratory phase, while at the same time attenuating diaphragm contraction. Stimulation in the ventral part of the lateral PAG induced tachypnea but inhibited pre-I cell firing, whereas stimulation in the ventrolateral PAG inhibited not only pre-I cells but also the diaphragm, leading to apnea. These findings show that PAG stimulation changes the activity of the pre-Bötzinger pre-I neurons. These changes are in line with the different behaviors generated by the PAG, such as the dorsal PAG generating avoidance behavior, the lateral PAG generating fight and flight, and the ventrolateral PAG generating freezing and immobility. J. Comp. Neurol. 521: 3083–3098, 2013. © 2013 Wiley Periodicals, Inc.
Highlights
Breathing, vagi-intact, pentobarbitoneanesthetized adult rats (n 5 22) had the following respiratory and cardiovascular parameters: inspiration time (Ti) 0.30 6 0.05 seconds, expiration time (Te) 0.50 6 0.10 seconds, respiratory frequency (RF) 75 6 10 breaths/ minute, blood pressure (BP) 100 6 5 mm Hg, heart rate (HR) 380 6 5 beats/minute, arterial blood pH 7.4 6 0.01, PaCO2 35.2 6 3.0 Torr, and PaO2 120.5 6 5.0 Torr
The dense cluster of pre-I cells was found in a region 12.60–12.84 mm caudal to bregma, 2–2.5 mm lateral to the midline, and 2–3 mm below the dorsal surface
The dorsal periaqueductal gray (PAG) modulation of the pre-I neurons had no impact on their rhythmogenic property, because they remain timelocked with the diaphragm
Summary
Experiments were designed and performed at The University of Sydney. Approval for the study was obtained from the institutional Animal Care Ethics Committee. After the localization of a pre-I neuron and optimization of its spike discharge, stimulation took place in the dorsal, lateral, and ventrolateral PAG, and changes in the activity of the same pre-I cell were recorded. The moment when a pre-I cell was detected in the ventrolateral medulla, a 3–6-nl DLH solution was injected at the recording site via the NaCl barrel. For staining the recording area, in eight of a total of 22 animals, rhodamine-B microspheres, added to the DLH electrode, were used to stain the pre-I neuron recording sites. The location of these rhodamine microspheres was assessed later through fluorescence microscopy. The X-axis represents a frequency spread from 0 to 1 kHz, and the Y-axis represents arbitrary units (AU)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
