Respiratory Responses
to Chronic Hypoxia
and Hypercapnia
Stephen Reid
Centre for the Neurobiology of Stress
Department of Biological Sciences
University of Toronto Scarborough
Toronto, Ontario
Respiratory Responses to Chronic Hypoxia
and Hypercapnia
1. Environmental Hypoxia
2. Ventilatory Acclimatisation to Hypoxia (VAH) in Mammals
a. What is VAH?
b. Respiratory Control Systems
c. Mechanisms of VAH
d. The Role of Glutamate
e. The Role of GABA
3. Amphibian Responses to Chronic Hypoxia
a. Central Processes
4. Amphibian Responses to Chronic Hypercapnia
a. Central Processes
b. Olfactory Chemoreceptors
c. Arterial Chemoreceptors
d. Carbonic Anhydrase
Hypoxia in an Aquatic
Environment
Hypoxia in an Aquatic Environment
Anuran amphibians may
experience environmental
hypoxia and hypercapnia
during aquatic over-wintering
(Pinder et al., 1992).
African elephants swimming in a lake near Chobe,
Botswana while breathing through their trunks
Did the trunk evolve as a snorkel?
Aquatic ancestry?
West, JB. 2002. Why Doesn't the Elephant Have a Pleural Space?
News Physiol Sci 17: 47-50
Hypoxia in a Terrestrial
Environment: High Altitude
Hypoxia in a Terrestrial Environment: High Altitude
Copper mining at 4 000 metres in the Andes employs thousands
PO2 at 4 000m: 100 mm Hg
Ruppell’s Griffin (Gyps rueppellii):
The High Altitude Champion
A Ruppell’s Griffin (vulture) was
sucked into an engine of a British
Airways Vickers VC10* at 11 275
metres (37 900 ft) above
the Ivory Coast on Nov 29
1975. (2 km higher than
the summit of Everest)
*Design
ceiling: 47 000 ft
Hypoxic Hypercapnia in a Terrestrial
Environment: Life Underground
Hypoxic Hypercapnia in a Terrestrial Environment:
Life Underground
• 15-16% O2 and 2-3% CO2
in the tunnels
• 12-14% O2 and 5-6% CO2
in the soil
Talpid Moles
“No other mammal, not even the high altitude llama or the
diving seal, breathes this kind of [low quality] air”.
Quillam, Clarke and Salsbury (1971)
“…it is incumbent upon burrow-dwelling mammals to make
physiological adjustments to avoid excessive energy expenditure
in respiratory work while still insuring adequate O2 delivery
to their tissues”
Boggs et al (1984)
Adaptations to Hypoxia
Erythropoietin (stimulates red blood cell synthesis)
2, 3 Diphosphoglycerate (Enhances O2 delivery to the tissues)
Increased capillary density
Reduced plasma volume
Haemoglobin
Ventilatory Acclimatisation to Hypoxia:
Ventilation (ml/min/kg)
The Acute Hypoxic Ventilatory Response
1000
800
Sprague-Dawley Rats
2
600
400
1
200
Chronic Hypoxia
Control
0
40
60
80
100
120
140
Arterial Oxygen Tension (mmHg)
Acclimatisation to hypoxia results in:
1. An increase in overall ventilation when breathing room air.
2. An increased sensitivity to acute bouts of hypoxia (usually
manifests during isocapnic hypoxia and not poikilocapnic hypoxia).
Ventilatory Acclimatisation to Hypoxia:
The Acute Hypercapnic Ventilatory Response
Minute Ventilation
(ml/min/kg)
2500
*, +
*, +
*, +
Chronic Hypoxia
*, +
2000
1500
+
1000
*
*
*
6
8
Control
*
0
2
4
% Inspired CO2
Sprague-Dawley Rats
• Chronic hypoxia also augments the acute hypercapnic ventilatory response
Eskander and Reid, unpublished
Important Respiratory Control Sites
in the Mammalian Brainstem
PONS
Pontine Respiratory
Group
4th
ventricle
Pre-Bötzinger Complex/
Parafacial Nucleus
MEDULLA
Obex
Ventral Respiratory Group
Nucleus of the Solitary Tract
SPINAL
CORD
Alheid et al. 2002. J. Neurocytology, 31, 693-117.
Pulmonary
Stretch
Receptors
(Lung)
Higher Brain Centers
4th
ventricle
PONS
MEDULLA
Pulmonary
Vagus Nerve
Obex
Carotid sinus
nerve
Peripheral
Chemoreceptors
(Carotid Body)
Central
Chemoreceptors
(pH/CO2)
Phrenic
Nerve
SPINAL
CORD
Diaphragm
Breathing is produced in brainstem respiratory centres and is
modified by afferent input and central processes.
Mechanisms of Ventilatory Acclimatisation
to Hypoxia
1. An increase in the
sensitivity of the O2
chemoreceptors to
low levels of oxygen.
NTS
Phrenic
Nerve
1
Carotid Body
(O2 Chemoreceptors)
2
Diaphragm
Carotid Sinus
Nerve
2. An increase in the responsiveness of the CNS to input
from the carotid body.
Working Model
Chronic Hypoxia
Changes in glutamate- and GABA-mediated
neurotransmission in the nucleus
NTS
of the solitary tract (NTS)
An increase in the responsiveness of
the CNS to carotid body input
Ventilatory Acclimatisation to Hypoxia
Carotid
Body
Diaphragm
Excitatory Neurotransmission: Glutamate
Glutamate Receptors (Ion Channel Family)
NMDA
MK 801; Receptor channel blocker
Non-NMDA
AMPA
1. Systemic injection of MK801 (i.p. injection).
2. Bilateral injection of MK801 into the NTS.
Kainate
Ventilatory Acclimatisation to Hypoxia in the Lab
9 days of chronic hypoxia
(80 mmHg) in a hypobaric
chamber
Plethysmography is used to Measuring Breathing
in Conscious Unrestrained Rats
Ventilation (ml/kg/min)
Effects of Systemic MK801 on Breathing
N, Normoxia
CH, Chronic Hypoxia
*
1800
PreMK (CH)
5
1500
1200
6
Post MK (CH)
900
600
Post MK (N)
Pre MK(N)
3
*
Hypoxia
(10% O2)
1
2
4. ventilatory
acclimatisation
to hypoxia
Normoxia
(21% O2)
Systemic blockade of NMDA receptors with MK 801 alters the
hypoxic ventilatory response in control and chronically hypoxic rats.
Reid and Powell, J. Appl. Physiol. 2005
Ventilation (ml/kg/min)
Effects of MK 801 injected into the NTS
1800
1600
N, Normoxia
Pre (CH)
1400
CH, Chronic Hypoxia
1200
1000
800
600
Post (CH)
Pre (N)
Post (N)
VAH
400
Hypoxia
(10% O2)
Normoxia
(21% O2)
Blocking NMDA receptors in the NTS (with MK 801) abolishes the
hypoxic ventilatory response in chronically hypoxic, but not control, rats.
Reid and Powell, unpublished
Ventilation (ml/min/kg)
Ventilatory Acclimatisation to Hypoxia
in Mammals (Rats)
1000
800
2
600
400
1
200
Chronic
Hypoxia
Control
Changes due, in part,
to alterations in
NMDA- mediated
neurotransmission
(illustrated by the
MK801 treatment).
0
40
60
80
100
120
140
Arterial Oxygen Tension (mmHg)
Acclimatisation to hypoxia results in:
1. An increase in overall ventilation when breathing room air.
2. An increased sensitivity to acute bouts of hypoxia.
10
a
9
81200
7
b
a
61100
a
Saline (○)
5
1000b
4
10
900
Breathing Frequency
(breaths/min)
a, #
GABA (●)
200
180
160
15
20
25
30
800
b
700
c
10
140
15
a
a
10
15
20
25
30
a Saline (○)
GABA (●)
a
120
100
20
25
9 days of infusion
Minute Ventilation (ml/kg/min)
Tidal Volume (ml/kg)
GABA Infusion into the NTS in the Absence of Chronic
Hypoxia Leads to VAH-Like Changes in Breathing
1200
1100
b
1000
GABA (●)
a
900
b
800
Saline (○) a
a, #
a
700
10
15 20 25 30
Inspired O2 (%)
30
Inspired O2 (%)
Reid et al., unpublished
Baclofen and Muscimol Infusion into the NTS
(Acute Hypoxia)
1200
Baclofen: GABAB receptor agonist
Muscimol: GABAA receptor agonist
b, +
1100
1000
Minute
Ventilation
(ml/kg/min)
b
a, #, +
900
b, #
a, +
800
a
700
a
a
a
600
10
15
20
25
Baclofen (●)
Saline (○)
Muscimol (■)
30
Inspired O2 (%)
• Baclofen treatment increases breathing
• Muscimol treatment decreases breathing
Reid et al., unpublished
Changes in GABA-mediated
neurotransmission in the NTS may
account for VAH (when O2 is high).
Breathing in Amphibians
• Bimodal breathing
• Buccal-pressure pump
• Episodic breathing
Buccal Pressure
Episodic Breathing in Amphibians
Lung Pressure
B.
Breath hold with
lungs inflated
Buccal Pressure
10 sec
Buccal Oscillations
Lung Pressure
Inflation
Breath
Reid, Respir. Physiol. Neurobiol. 2007
Balanced
Breath
Lung Inflation
Cycle
Deflation
Breath
10 sec
Peripheral
Chemoreceptors
Central
Chemoreceptors
(pH/CO2)
Higher
Brain Centers
optic chiasma
medulla
Spinal cord
olfactory lobes
+ -
CRG(s)
-
NI
X/IX
Pulmonary
Vagus Nerve
VII
V
Pulmonary
Stretch
Receptors
optic tectum
“Respiratory Centers”
(site of central integration)
Breathing is produced in brainstem respiratory centres and is
modified by afferent input and central processes.
The Effects of Chronic Hypoxia
on Amphibian Breathing
Exposure to Chronic Hypoxia (or Hypercapnia) in the Lab
ProOx Controller
(set point of 10% O2)
ProCO2 Controller
(set point of 3.5% CO2)
Effects of Chronic Hypoxia and MK801 Treatment on
Breathing in Cane Toads (In vivo)
Breathing Trial
Chamber
Air
5%
O2
gas
in
gas
out
Computer Data Acquisition System
(Windaq DI-194)
Impedance Converter
A. Control: Saline Injection
20
15
*
*
10
5
0
N
H
Pre-Saline
Injection
Breathing Frequency (breaths/min)
Breathing Frequency (breaths/min)
25
25
20
15
10
5
Effects of Chronic
Hypoxia and MK801
Treatment on Breathing
in+ Cane Toads
(In vivo) #
D. Chronic Hypoxia: Saline Injection
0
N
H
Post-Saline
Injection
N
H
Pre-Saline
Injection
N
H
Post-Saline
Injection
15
*
10
5
0
McAneney et
Breathing Frequency (breaths/min)
Breathing Frequency (breaths/min)
25
25 E. Chronic Hypoxia: MK 801 Injection
Control
= Chronically
Toads
B. Control:
MK 801 InjectionNormoxic
*
N =20Exposure to Acute Normoxia (21%
20 O2)
H = Exposure to Acute Hypoxia (5% O2)
15
10
+
*
+
5
#
0
MK801 = NMDA (glutamate)
receptor channel blocker.
N
H
N
H
al., Pre-MK801
Respir. Physiol. Post-MK801
Neurobiol.
Injection
Injection
2007
N
H
Pre-MK801
Injection
N
H
Post-MK801
Injection
A. Control: Saline Injection
20
15
*
*
10
5
0
N
H
Pre-Saline
Injection
Breathing Frequency (breaths/min)
Breathing Frequency (breaths/min)
25
25
D. Chronic Hypoxia: Saline Injection
20
15
Line 2
10
+
Line 1
5
#
0
N
H
Post-Saline
Injection
N
H
Pre-Saline
Injection
N
H
Post-Saline
Injection
10
Breathing Frequency (breaths/min)
Breathing Frequency (breaths/min)
25
25 E. Chronic Hypoxia: MK 801 Injection
Control
= Chronically
Toads
B. Control:
MK 801 InjectionNormoxic
*
Chronic
Hypoxia = Exposure to 10 days
of 10% O2
20
20
N = Exposure to Acute Normoxia (21% O2)
+
H =15 Exposure*to Acute Hypoxia (5%15O2)
*
10
+
Line 1: Exposure to chronic hypoxia doesn’t alter “resting” breathing.*
5
5
#
Line 2: Chronic
hypoxia abolishes the acute
0
0 hypoxic ventilatory response.*
N
H
N
H
Pre-MK801
McAneney et al., Respir.
Physiol. Neurobiol.Post-MK801
2007
Injection
Injection
N
H
Pre-MK801
Injection
N
H
Post-MK801
Injection
*, Different from the response in mammals
20
15
10
5
0
N
H
Pre-Saline
Injection
Breathing Frequency (breaths/min)
*
*
25
B. Control: MK 801 Injection
*
D. Chronic Hypoxia: Saline Injection
20
15
10
+
5
#
0
N
H
Pre-Saline
Injection
25
N
H
Post-Saline
Injection
E. Chronic Hypoxia: MK 801 Injection
20
In 15control animals, MK801+augments
*
the10acute hypoxic ventilatory
response.*
*
10
5
0
N
H
Pre-MK801
Injection
25
N
H
Post-Saline
Injection
20
15
Breathing Frequency (breaths/min)
A. Control: Saline Injection
Breathing Frequency (breaths/min)
Breathing Frequency (breaths/min)
25
N
H
Post-MK801
Injection
+
5
0
*, Different from the
# response
in mammals where MK801
N
H
N
H
reduced
the
response.
Pre-MK801
Post-MK801
Injection
Injection
20
15
10
5
0
N
H
Pre-Saline
Injection
Breathing Frequency (breaths/min)
*
*
25
B. Control: MK 801 Injection
*
*
10
5
0
N
H
Pre-MK801
Injection
25
N
H
Post-MK801
Injection
D. Chronic Hypoxia: Saline Injection
20
15
10
+
5
#
0
N
H
Post-Saline
Injection
20
15
Breathing Frequency (breaths/min)
A. Control: Saline Injection
N
H
Pre-Saline
Injection
Breathing Frequency (breaths/min)
Breathing Frequency (breaths/min)
25
25
N
H
Post-Saline
Injection
E. Chronic Hypoxia: MK 801 Injection
20
15
10
+
*
+
5
#
0
N
H
Pre-MK801
Injection
N
H
Post-MK801
Injection
Mammal
(Rat)
versus
Amphibian
(Cane Toad)
Chronic Hypoxia
Increases Resting
Ventilation
Doesn’t Alter Resting
Ventilation
Chronic Hypoxia
Often augments the
acute hypoxic
ventilatory response.
Abolished the
acute hypoxic
ventilatory response.
Attenuates or abolishes
the acute hypoxic
ventilatory response.
Augments the
acute hypoxic
ventilatory response.
NMDA Channel
Blockade with
MK801
Effects of Chronic Hypoxia on Central
pH/CO2-Sensitive (Fictive) Breathing
Peripheral
Chemoreceptors
Central
Chemoreceptors
(pH/CO2)
Higher
Brain Centers
optic chiasma
medulla
Spinal cord
olfactory lobes
+ -
CRG(s)
-
NI
X/IX
Pulmonary
Vagus Nerve
VII
V
Pulmonary
Stretch
Receptors
optic tectum
“Respiratory Centers”
(site of central integration)
In Vitro Brainstem-Spinal Cord Preparation
Record activity from
the nerves that innervate
the respiratory muscles
(fictive breathing)
Recording
(suction)
electrode
O2
CO2
•
•
Used to study the central control of
breathing in the absence of peripheral input.
artificial
cerebral
spinal
fluid
(aCSF)
20°C
Central pH/CO2 chemoreceptors can be stimulated by altering
(lowering) the pH/CO2 of the artificial cerebral spinal fluid.
micromanipulator
Stiff Wire
electrode
Suction
electrode
Superfusion
chamber
Optic lobes
V
VII
IX/X
XII
Spinal cord
Breathing Patterns In Vitro
Single Breaths
Doublets
Episodes
Bullfrog (Rana catesbeiana)
Reid and Milsom (1998)
Chronic Hypoxia Attenuates Central pH/CO2
Chemosensitivity in the Cane Toad
25
Chronic Normoxia
20
Fictive
Breathing
Frequency 15
(fictive breaths
per minute)
10
Chronic Hypoxia
*
*
5
*, #
0
7.6
*, #
7.8
8.0
Artificial Cerebral Spinal Fluid pH
McAneney and Reid, Respir. Physiol. Neurobiol. 2007
Which respiratory control system is responsible for the chronic
hypoxia – induced decrease in pH/CO2-sensitive fictive breathing?
Peripheral
Chemoreceptors
Central
Chemoreceptors
(pH/CO2)
Higher
Brain Centers
optic chiasma
medulla
Spinal cord
olfactory lobes
+ -
CRG(s)
-
NI
X/IX
Pulmonary
Vagus Nerve
VII
V
Pulmonary
Stretch
Receptors
optic tectum
Removal of the Midbrain Converts Episodic Breathing
to Continuous Breathing
Episodic Fictive Breathing
(pre-transection; pH 7.8)
 ENG X
2 sec
3
Continuous Fictive Breathing
(post-transection; pH 7.8)
 ENG X
2 sec
American Bullfrog (Rana catesbieana)
Reid and Milsom, Respir. Physiol. 2000
1
2
3
Breathing Frequency (breaths/min)
The conversion from episodic to continuous breathing
is accompanied by an increase in breathing frequency.
*
8
7
6
5
4
3
2
1
0
1.
2.
3.
Removal of descending inputs prevents
breath clustering and increases
breathing frequency.
American Bullfrog (Rana catesbieana)
Reid and Milsom, Respir. Physiol. 2000
Midbrain Transection Restores the Central pH/CO2
Chemosensitivity Previously Blunted by Chronic Hypoxia
25
Fictive
Breathing
Frequency 20
(fictive breaths
per minute)
15
Chronic Normoxia
Chronic Hypoxia
*
10
5
*
Pre-Transection
*, #
3
*, #
0
7.6
7.8
8.0
Artificial Cerebral Spinal Fluid pH
McAneney and Reid, Respir. Physiol. Neurobiol. 2007
Midbrain Transection Restores the Central pH/CO2
Chemosensitivity Previously Blunted by Chronic Hypoxia
25
Fictive
Breathing
Frequency 20
(fictive breaths
per minute)
15
Chronic Normoxia
Post-Transection
Chronic Hypoxia
*
10
5
*
Pre-Transection
*, #
3
*, #
0
7.6
7.8
8.0
Artificial Cerebral Spinal Fluid pH
McAneney and Reid, Respir. Physiol. Neurobiol. 2007
Midbrain Transection Restores the Central pH/CO2
Chemosensitivity Previously Blunted by Chronic Hypoxia
25
Fictive
Breathing
Frequency 20
(fictive breaths
per minute)
15
Chronic Normoxia
Post-Transection
Chronic Hypoxia
*
10
5
*
Pre-Transection
*, #
3
*, #
0
7.6
7.8
8.0
Artificial Cerebral Spinal Fluid pH
McAneney and Reid, Respir. Physiol. Neurobiol. 2007
The Effects of Chronic Hypercapnia
on Amphibian Breathing
Chronic Hypercapnia Increases Central pH/CO2
Sensitive Fictive Breathing
35
*, +
30
Fictive
25
Breathing
Frequency 20
(fictive breaths 15
per minute)
10
5
9-10 days; 3.5% CO2
*, +
Chronic Hypercapnia
Control
*
0
7.4
Gheshmy et al., 2006
7.6
7.8
8.0
8.2
Artificial Cerebral Spinal Fluid pH
Which control system is responsible for the chronic hypercapnia
(CHC) – induced increase in pH/CO2-sensitive fictive breathing?
Fictive Breathing Frequency
HYPOTHESIS #1: Descending Inputs from the Midbrain
(as was the case with chronic hypoxia)
3
Pre = Pre-Transection
Post = Post-Transection
16
14
12
10
8
+*
6
+
4
2
CHC Pre
+
*
Control Pre
0
7.5
7.6
7.7
7.8
7.9
8.0
aCSF pH
Gheshmy et al., 2006
Fictive Breathing Frequency
HYPOTHESIS #1: Descending Inputs from the Midbrain
(as was the case with chronic hypoxia)
3
Pre = Pre-Transection
Post = Post-Transection
16
14
12
10
8
+*
6
*
+
4
2
CHC Pre
+
Control Post
Control Pre
*
0
7.5
7.6
7.7
7.8
7.9
8.0
aCSF pH
Gheshmy et al., 2006
Fictive Breathing Frequency
HYPOTHESIS #1: Descending Inputs from the Midbrain
(as was the case with chronic hypoxia)
3
16
Pre = Pre-Transection
Post = Post-Transection
+*
14
12
+
+
10
8
6
+*
CHC Post
*
+
4
2
CHC Pre
+
Control Post
Control Pre
*
0
7.5
7.6
7.7
7.8
7.9
8.0
aCSF pH
Gheshmy et al., 2006
HYPOTHESIS #2: CO2-Senstive Olfactory Chemoreceptors
High CO2
optic chiasma
medulla
Spinal cord
olfactory
lobes
+ -
CRG(s)
-
NI
X/IX
VII
V
optic tectum
Reduce Breathing Frequency
CHC → Increased Olfactory CO2 Chemoreceptor Input → Decrease
Breathing → This is not Advantageous → Increased Central pH/CO2
Chemoreceptor-Sensitive Breathing (Function) to Compensate?
HYPOTHESIS #2: The Effects of Olfactory Chemoreceptor
Denervation (OD) on Central pH/CO2-Senstive Fictive Breathing
Olfactory
Denervation (OD)
CHC or Control
Brainstem Preparations
Measure pH/CO2Sensitive Fictive
Breathing
Fictive Breathing Frequency
35
*+
#
30
Chronic Hypercapnia (CHC)
25
+#
20
15
+ #
Data with no OD
10
Control
5
0
7.5
7.6
7.7
7.8
7.9
8.0
aCSF pH
Gheshmy et al., 2007
HYPOTHESIS #2: The Effects of Olfactory Chemoreceptor
Denervation (OD) on Central pH/CO2-Senstive Fictive Breathing
Olfactory
Denervation (OD)
CHC or Control
Brainstem Preparations
Measure pH/CO2Sensitive Fictive
Breathing
Fictive Breathing Frequency
35
*+
#
30
Chronic Hypercapnia (CHC)
25
+#
20
15
+ #
Data with OD
10
Control
5
Control-OD
0
7.5
7.6
7.7
7.8
7.9
8.0
aCSF pH
Gheshmy et al., 2007
HYPOTHESIS #2: Olfactory Chemoreceptor Denervation (OD) Abolishes the
Chronic Hypercapnia (CHC)-Induced Augmentation of pH/CO2-Senstive
Fictive Breathing (Central Chemosensitivity)
Olfactory
Denervation (OD)
CHC or Control
Brainstem Preparations
Measure pH/CO2Sensitive Fictive
Breathing
Fictive Breathing Frequency
35
*+
#
30
Chronic Hypercapnia (CHC)
25
+#
20
15
+ #
Data with OD
10
5
Control
0
Control-OD
CHC – OD
7.5
7.6
7.7
7.8
7.9
8.0
aCSF pH
Gheshmy et al., 2007
HYPOTHESIS #3: Peripheral (Arterial) Chemoreceptors
in the Carotid Labyrinth and Aortic Arch
Low O2/High CO2
optic chiasma
medulla
Spinal cord
olfactory
lobes
+ -
CRG(s)
-
NI
X/IX
VII
V
optic tectum
Increase Breathing
CHC → Increased Arterial CO2 Chemoreceptor Input → Increased Central
Chemoreceptor Function → Increased pH/CO2-Sensitive Fictive Breathing.
The Ideal Experiment: Denervate the Carotid Labyrinth and Aortic Arch
1. Control
2. CHC
3. Chronic Hyperoxia
4. Chronic Hyperoxic
Hypercapnia (HH)
Brainstem Preparations
Measure pH/CO2Sensitive Fictive
Breathing
Fictive Breathing Frequency
HYPOTHESIS #3: Simultaneous Exposure to Chronic Hypercapnia
and Hyperoxia (Hyperoxic Hypercapnia; HH)
35
*@ $
Chronic Hypercapnia (CHC)
30
@$
25
20
@$
15
10
Control
5
0
7.5
7.6
7.7 7.8
aCSF pH
7.9
8.0
Gheshmy et al., 2007
1. Control
2. CHC
3. Chronic Hyperoxia
4. Chronic Hyperoxic
Hypercapnia (HH)
Brainstem Preparations
Measure pH/CO2Sensitive Fictive
Breathing
Fictive Breathing Frequency
HYPOTHESIS #3: Simultaneous Exposure to Chronic Hypercapnia
and Hyperoxia (Hyperoxic Hypercapnia; HH)
35
*@ $
Chronic Hypercapnia (CHC)
30
@$
25
20
@$
15
10
Control
5
0
*
7.5
7.6
7.7 7.8
aCSF pH
7.9
8.0
Chronic
Hyperoxia
Gheshmy et al., 2007
1. Control
2. CHC
3. Chronic Hyperoxia
4. Chronic Hyperoxic
Hypercapnia (HH)
Brainstem Preparations
Measure pH/CO2Sensitive Fictive
Breathing
Fictive Breathing Frequency
HYPOTHESIS #3: Simultaneous Exposure to Chronic Hypercapnia and
Hyperoxia (Hyperoxic Hypercapnia; HH) Abolishes the Chronic Hypercapnia
(CHC)-Induced Increase in Central pH/CO2-Sensitive Fictive Breathing
35
*@ $
Chronic Hypercapnia (CHC)
30
@$
25
20
@$
15
10
5
0
*
*
7.5
7.6
7.7 7.8
aCSF pH
7.9
8.0
Control
Chronic HH
Chronic
Hyperoxia
Gheshmy et al., 2007
Total Fictive Ventilation
(×10-2 V·s·min-1)
The Role of Carbonic Anhydrase in the Chronic Hypercapnia
(CHC) – Induced Increase in pH/CO2 Sensitive Fictive
Breathing
14
b, +
Chronic Hypercapnia
12
10
08
06
04
02
00
b
a
b
Control
a, b
a
7.6
7.8
8.0
aCSF pH
Srivaratharjah and Reid, unpublished
Leopard Frogs (Rana pipiens)
A Putative Model of Central pH/CO2 Sensing
CA: Carbonic
Anhydrase
1. Inhibit CA with Acetazolamide
cell permeant
2. Add exogenous CA
not cell permeant
Fictive Breathing Before and After Acetazolamide
(ACTZ) Treatment
Control
Chronic Hypercapnia
Pre-ACTZ
1µM ACTZ
10µM ACTZ
7.5 sec
Inhibition of carbonic anhydrase with ACTZ abolishes the CHC-induced
increase in fictive breathing.
Srivaratharjah and Reid, unpublished
Acetazolamide (ACTZ) Treatment Abolishes the CHC-Induced
Increase in Fictive Breathing
Total Fictive Ventilation (X 10-2 V.sec.min-1)
Control
Chronic Hypercapnia
12
12
Pre-ACTZ
Pre-ACTZ
8
8
1µM ACTZ
4
1µM ACTZ
4
0
10µM ACTZ
0
7.6
7.8
aCSF pH
8.0
10µM ACTZ
7.6
7.8
aCSF pH
8.0
This suggests that an increase in CA activity/amount is involved in the CHCinduced increase in fictive breathing.
Srivaratharjah and Reid, unpublished
Addition of Exogenous CA had no Effect on Fictive Breathing
Total Fictive Ventilation (X 10-2 V.sec.min-1)
Control
Chronic Hypercapnia
20
20
15
15
10
10
Pre-CA
5
Pre-CA
CA Washout
5
CA
CA Washout
0
CA
7.6
7.8
aCSF pH
8.0
0
7.6
7.8
aCSF pH
This suggests that intracellular, rather than extracellular CA is involved
regulating CO2-sensitive fictive breathing.
8.0
Srivaratharjah and Reid, unpublished
Respiratory Responses to Chronic Hypoxia
and Hypercapnia
1. Environmental Hypoxia
2. Ventilatory Acclimatisation to Hypoxia (VAH) in Mammals
a. What is VAH?
b. Respiratory Control Systems
c. Mechanisms of VAH
d. The Role of Glutamate
e. The Role of GABA
3. Amphibian Responses to Chronic Hypoxia
a. Central Processes
4. Amphibian Responses to Chronic Hypercapnia
a. Central Processes
b. Olfactory Chemoreceptors
c. Arterial Chemoreceptors
d. Carbonic Anhydrase
Acknowledgements
Amphibian Studies
Rat Studies
Jessica McAneney (PhD Student; ongoing)
Andrew Peters (PhD Student; ongoing)
Afshan Gheshmy (BSc; 2004: MSc; 2006)
Kajenny Srivaratharjah (BSc; 2007; MSc; 2008)
Angelo Noronha (BSc; 2004)
Sarangan Uthayalingam (BSc; 2004)
Jasmin Manga (BSc; 2004)
Robert Vukelich (BSc; 2005)
Donela Besada (BSc; 2006)
Ali Anari (BSc; 2006)
Alex Cui (BSc; 2007)
Sean Chung (MSc; 2005)
Jeff Knight (BSc; 2007: MSc; 2008)
Balinda Phe (MSc; 2008)
Mukarram Khan (BSc; 2005)
Irene Bekit (BSc; 2006)
Tony Eskander (BSc; 2006)
Daniel Fingrut (BSc; 2006)
Manu Maldeniya (BSc; 2008)
Stephen Chan (BSc; 2009)
Collaborators
Dr. Frank Powell, UCSD
Dr. Kevin Campbell, Univ. Manitoba
Dr. Suzanne Erb, U of T
Dr. Gwen Ivy, U of T
Dr. Katie Gilmour, Ottawa U.
Funding
NSERC; CFI; OIT
Ontario Thoracic Society
Francis Families Foundation
Canadian Society of Zoologists
2009 Annual Meeting
May 12 to 16 2009, University of Toronto
Scarborough (UTSC)
For information contact
csz2009@utsc.utoronto.ca or visit
our web site
http://www.utsc.utoronto.ca/~csz2009/