Widespread sites of brain stem ventilatory chemoreceptors

1993 ◽  
Vol 75 (1) ◽  
pp. 5-14 ◽  
Author(s):  
E. L. Coates ◽  
A. Li ◽  
E. E. Nattie
Keyword(s):  
Brain Stem ◽  
Central Chemoreceptors ◽  
Maximum Value ◽  
Brain Ph ◽  
Chemosensitive Areas ◽  
Tissue Acidosis ◽  
Central Chemoreception ◽  
End Tidal ◽  
The Brain ◽  
Stimulation Of

We produced local tissue acidosis in various brain stem regions with 1-nl injections of acetazolamide (AZ) to locate the sites of central chemoreception. To determine whether the local acidosis resulted in a stimulation of breathing, we performed the experiment in chloralose-urethan anesthetized vagotomized carotid-denervated (cats) paralyzed servo-ventilated cats and rats and measured phrenic nerve activity (PNA) as the response index. Measurements of extracellular brain tissue pH by glass microelectrodes showed that AZ injections induced a change in pH at the injection center equivalent to that produced by an increase in end-tidal PCO2 of approximately 36 Torr and that the change in brain pH was limited to a tissue volume with a radius of < 350 microns. We found AZ injections sites that caused a significant increase in PNA to be located 1) within 800 microns of the ventrolateral medullary surface at locations within traditional rostral and caudal chemosensitive areas and the intermediate area, 2) within the vicinity of the nucleus tractus solitarii, and 3) within the vicinity of the locus coeruleus. Single AZ injections produced increases in PNA that were < or = 69% of the maximum value observed with an increase in end-tidal PCO2. We conclude that central chemoreceptors are distributed at many locations within the brain stem, all within 1.5 mm of the surface, and that stimulation of a small fraction of all central chemoreceptors can result in a large ventilatory response.

Brain stem responses to electrical stimulation of ventral vagal gastric fibers

1989 ◽  
Vol 257 (1) ◽  
pp. G24-G29
Author(s):  
W. D. Barber ◽  
C. S. Yuan
Keyword(s):  
Electrical Stimulation ◽  
Brain Stem ◽  
Time Of Arrival ◽  
Neuronal Responses ◽  
Proximal Stomach ◽  
Afferent Fibers ◽  
Sensory Modalities ◽  
The Mean ◽  
The Brain ◽  
Stimulation Of

The brain stem neuronal responses to electrical stimulation of gastric branches of the ventral vagal trunk serving the proximal stomach were localized and evaluated in anesthetized cats. The responses were equally distributed bilaterally in the region of nucleus solitarius in the caudal brain stem. The mean latency of the response was 289 +/- 46 (SD) ms, which translated into a conduction velocity of less than 1 m/s based on the distance between the stimulating and recording electrodes. The responses consisted of single and multiple spikes that showed slight variability in the latency, indicating orthodromic activation via a synapse in approximately 98% of the responses recorded. Forty two percent of the units tested showed evidence of convergence of input from vagal afferent fibers in different branches of the ventral vagal trunk that served the proximal stomach. The resultant activity pattern of the unitary response appeared to be the product of 1) the gastric sensory input or modality conveyed by the afferent source and 2) the time of arrival and diversity of modalities served by other gastric afferents impinging on the unit. This provides a mechanism capable of responding on the basis of specific sensory modalities that dynamically reflect ongoing events monitored and conveyed by other gastric afferents in the region.

Differential Patterns of Spinal Sympathetic Outflow Involving a 10-Hz Rhythm

1999 ◽  
Vol 82 (2) ◽  
pp. 841-854 ◽  
Author(s):  
Gerard L. Gebber ◽  
Sheng Zhong ◽  
Craig Lewis ◽  
Susan M. Barman
Keyword(s):  
Brain Stem ◽  
Phase Angle ◽  
Sympathetic Nerves ◽  
Phase Relations ◽  
Sympathetic Outflow ◽  
Free Running ◽  
The Difference ◽  
Electrical Stimuli ◽  
The Brain ◽  
Stimulation Of

Time and frequency domain analyses were used to examine the changes in the relationships between the discharges of the inferior cardiac (CN) and vertebral (VN) postganglionic sympathetic nerves produced by electrical activation of the midbrain periaqueductal gray (PAG) in urethan-anesthetized, baroreceptor-denervated cats. CN-VN coherence and phase angle in the 10-Hz band served as measures of the coupling of the central oscillators controlling these nerves. The 10-Hz rhythm in CN and VN discharges was entrained 1:1 to electrical stimuli applied to the PAG at frequencies between 7 and 12 Hz. CN 10-Hz discharges were increased, and VN 10-Hz discharges were decreased when the frequency of PAG stimulation was equal to or above that of the free-running rhythm. In contrast, stimulation of the same PAG sites at lower frequencies increased, albeit disproportionately, the 10-Hz discharges of both nerves. In either case, PAG stimulation significantly increased the phase angle between the two signals (VN 10-Hz activity lagged CN activity); coherence values relating their discharges were little affected. However, the increase in phase angle was significantly more pronounced when the 10-Hz discharges of the two nerves were reciprocally affected. Importantly, partialization of the phase spectrum using the PAG stimuli did not reverse the change in CN-VN phase angle. This observation suggests that the increase in the CN-VN phase angle reflected changes in the phase relations between coupled oscillators in the brain stem rather than the difference in conduction times to the two nerves from the site of PAG stimulation. In contrast to the effects elicited by PAG stimulation, stimulation of the medullary lateral tegmental field induced uniform increases in the 10-Hz discharges of the two nerves and no change in the CN-VN phase angle. Our results demonstrate that changes in the phase relations among coupled brain stem 10-Hz oscillators are accompanied by differential patterns of spinal sympathetic outflow. The reciprocal changes in CN and VN discharges produced by PAG stimulation are consistent with the pattern of spinal sympathetic outflow expected during the defense reaction.

Evidence for central chemoreception in the midline raphe

1996 ◽  
Vol 80 (1) ◽  
pp. 108-115 ◽  
Author(s):  
D. G. Bernard ◽  
A. Li ◽  
E. E. Nattie
Keyword(s):  
Cerebrospinal Fluid ◽  
Brain Stem ◽  
Focal Region ◽  
Central Chemosensitivity ◽  
Tissue Acidosis ◽  
Central Chemoreception ◽  
Injection Location

We injected acetazolamide (AZ; 5 x 10(-6) M; 1 nl; n = 14), its inactive analogue 2-acetylamino-1,3,4-thiadiazole-5-sulfon-t-butylamide (5 x 10(-5) M; n = 6), or mock cerebrospinal fluid (n = 5) into the caudal raphe in the midline brain stem of anesthetized paralyzed ventilated rats. These AZ injections have been shown to produce a focal region of tissue acidosis with a radius < 350 microns and are used as a probe for sites of central chemosensitivity. Compared with control injections, AZ injection into the raphe, as demonstrated by anatomic analysis of injection location, significantly increased the amplitude of the integrated phrenic neurogram over 10-40 min. Not all raphe injections produced such a response. AZ injections identified as responders (n = 8 of 14) increased integrated phrenic amplitude 43.3 +/- 10.7% (SE) of baseline 20 min after the injection. We conclude that the midline caudal raphe contains sites of ventilatory chemoreception.

Excitation of lumbar motoneurons by the medial longitudinal fasciculus in the in vitro brain stem spinal cord preparation of the neonatal rat

1993 ◽  
Vol 70 (6) ◽  
pp. 2241-2250 ◽  
Author(s):  
M. K. Floeter ◽  
A. Lev-Tov
Keyword(s):  
Spinal Cord ◽  
Brain Stem ◽  
Short Latency ◽  
Medial Longitudinal Fasciculus ◽  
Paired Pulse ◽  
Long Latency ◽  
The Brain ◽  
Pulse Stimulation ◽  
Stimulation Of

1. The excitation of lumbar motoneurons by reticulospinal axons traveling in the medial longitudinal fasciculus (MLF) was investigated in the newborn rat using intracellular recordings from lumbar motoneurons in an in vitro preparation of the brain stem and spinal cord. The tracer DiI (1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine) was introduced into the MLF of 6-day-old littermate rats that had been fixed with paraformaldehyde to evaluate the anatomic extent of this developing pathway. 2. Fibers labeled from the MLF by DiI were present in the cervical ventral and lateral white matter and a smaller number of labeled fibers extended to the lumbar enlargement. Patches of sparse terminal labeling were seen in the lumbar ventral gray. 3. In the in vitro preparation of the brain stem and spinal cord, MLF stimulation excited motoneurons through long-latency pathways in most motoneurons and through both short-(< 40 ms) and long-latency connections in 16 of 40 motoneurons studied. Short- and longer-latency components of the excitatory response were evaluated using mephenesin to reduce activity in polysynaptic pathways. 4. Paired-pulse stimulation of the MLF revealed a modest temporal facilitation of the short-latency excitatory postsynaptic potential (EPSP) at short interstimulus intervals (20–200 ms). Trains of stimulation at longer interstimulus intervals (1–30 s) resulted in a depression of EPSP amplitude. The time course of the synaptic depression was compared with that found in EPSPs resulting from paired-pulse stimulation of the dorsal root and found to be comparable. 5. The short-latency MLF EPSP was reversibly blocked by 6-cyano-7-nitroquinoxaline (CNQX), an antagonist of non-N-methyl-D-aspartate glutamate receptors, with a small CNQX-resistant component. Longer-latency components of the MLF EPSP were also blocked by CNQX, and some late components of the PSP were sensitive to strychnine. MLF activation of multiple polysynaptic pathways in the spinal cord is discussed.

Effects of insulin on the cardiovascular integrating mechanisms of brain stem in cats

1993 ◽  
Vol 265 (4) ◽  
pp. E609-E616 ◽  
Author(s):  
S. W. Kuo ◽  
J. H. Hsieh ◽  
W. C. Wu ◽  
H. T. Horng ◽  
L. R. Shian ◽  
...  
Keyword(s):  
Brain Stem ◽  
Cardiovascular Responses ◽  
Serum Glucose ◽  
Ventrolateral Medulla ◽  
Reticular Nucleus ◽  
Motor Nucleus ◽  
Renal Nerve ◽  
Pressor Responses ◽  
The Brain ◽  
Stimulation Of

In 65 cats anesthetized with alpha-chloralose and urethane, the effects of insulin on cardiovascular responses to stimulation of various structures in the brain stem were studied. The threshold dose of insulin injected intravenously that produced systemic hypoglycemia was 5-10 U/kg. Subthreshold hypoglycemic doses of insulin were used intracerebroventricularly (0.25 U/kg) or intracerebrally (2 mU in 200 nl). Sixty minutes after intravenous insulin, when serum glucose concentrations decreased from 158 to 43 mg/100 ml, pressor responses to stimulation of the periaqueductal gray of midbrain (PAG), locus coeruleus (LC), dorsal medulla (DM), ventrolateral medulla (VLM), and parvocellular reticular nucleus (PVC) decreased significantly. Depressor and bradycardiac response to stimulation of paramedian reticular nucleus or dorsal motor nucleus of vagus (DMV) decreased significantly as well. Thirty minutes after intracerebroventricular insulin, pressor responses of PAG, DM, and the bradycardiac response of DMV decreased significantly. Thirty minutes after intracerebral insulin, pressor responses and renal nerve activities of LC (but not PAG), VLM, DM, and PVC decreased significantly. A similar but faster onset (5 min) of depression of cardiovascular responses on stimulating the LC, VLM, DM, and PVC was observed in another six acutely midcollicular-decerebrate cats recovered from halothane anesthesia. These findings suggest that insulin directly inhibits the vasomotor structures of the brain stem and decreases the pressor responses to stimulation.

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