Transcript Two different coma models - Max Planck Institute for Biological

Two different coma models
Yaohui Tang
Max-Planck-Institute for Biological Cybernetics
What is coma?
• Coma is a state of unconsciousness, which is marked by a lack
of awareness and response to external stimulus.
Steven Laureys, et al, The Lancet, 2004
Cerebral metabolism in different brain states
Conscious
Locked-in syndrome
MCS
Vegetative state
Steven Laureys, et al, The Lancet, 2004
Important pathways and brain nucleus for
arousal
• Reticulo-thalamo-cortical pathway (widely accepted)
Basilar artery occlusion (BAO)
• Thalamus-Basal forebrain (BF)-Parabrachial nucleusprecoeruleus area (PB-PC)
Neurotoxin stereotaxic injection (NSI)
Basilar artery
• One of three major arteries feeding
the circle of Willis
• Situated on the ventral surface of the
brainstem
• Supplies the major portion of the blood
flow to the brainstem
SCA: superior cerebellar artery
AICA: anterior inferior cerebellar artery
PICA: posterior inferior cerebellar artery
Tracey Baird, et al, Neurocritical Care, 2004
Basilar artery occlusion
Single point occlusion
Two points occlusion
D-M
M-P
D-P
Purpose: develop a reproducible rat
model of brain stem ischemia
• In 11 rats, the basilar artery was occluded at
a single point along its length.
Basilar
artery
• 12 rats underwent occlusion at two
points 3 mm apart at various sites along the
length (above AICA or below AICA)
Results
Single-point or two-point BAO reduced peakto-peak amplitude of the cortical SEPs by
>50% within 15 minutes
The SEPs gradually recovered over 3-4
hours, and the response amplitudes exceeded
baseline values in seven of the 17 rats by 4
hours after occlusion.
By 24 hours after basilar artery occlusion,
amplitudes and latencies returned to baseline
values.
HE staining
No infarct in any rat with
single-point basilar artery occlusion
Two-point occlusion above or below
the AICA produced brain stem
infarcts
Two-point BAO below AICA
Two-point BAO above AICA
Conclusion
• Basilar artery occlusion at any single point between the foramen
magnum and the circle of Willis in 11 rats did not produce
histologically detectable infarcts in the brain at 12-24 hours.
• Two-point occlusions of the basilar artery in 12 rats produced
variable infarcts between the occlusion sites but no ischemic lesions
elsewhere.
• Basilar artery occlusions invariably suppressed cortical
somatosensory evoked potentials by >50%.
Background
• Arousal pathway passed through the paramedian midbrain reticular
formation and bifurcated at the diencephalon into two branches, into the
thalamus and hypothalamus
• Most neurons participating in these pathways from the rostral pons and
caudal midbrain:
Noradrenergic locus coeruleus
Serotoninergic dorsal pedunculopontine
Laterodorsal tegmental nuclei
Parabrachial nucleus
However their functions in awake/sleep are unknown.
Methods
1st part
• Pathogen-free adult male Sprague-Dawley rats (275–300 g)
• Lesions of the thalamus: injecting 50 nl of a 10% solution of ibotenic acid
bilaterally
• Lesions of the basal forebrain: injecting a 0.1% solution of either IgG192saporin or orexin-saporin (OX-SAP) at four different sites (ibotenic acid
cause rats to die; high dose (125ng) OX-SAP kill all noncholinergic
neurons and 88% of cholinergic neurons; 100ng OX-SAP kill all
noncholinergic neurons and 19% of cholinergic neurons)
• To kill cholinergic BF neurons specifically, 1ug IgG 192-saporin was
injected into the lateral ventricle.
• EEG/EMG were continuous recorded on day 7 postoperatively.
• c-Fos immunohistochemistry (an indirect indicator of neurons firing, it gives
a rough indication of the degree to which neurons have been receiving
excitatory inputs that elevate cyclic AMP or intracellular calcium)
2nd part
• Using cholera toxin subunit B (CTB) to retrogradely trace inputs to the BF
and thalamus from sites in the brainstem to define the cell groups
• In situ hybridization for the vesicular glutamate 2 transporter (VGLUT2), to
determine which of these cells were likely to be glutamatergic.
3rd part
• Using local injections of orexin-saporin to ablate neurons in the
parabrachial nucleus and precoeruleus region
• EEG/EMG were continuous recorded at 7 days postoperatively.
• c-Fos immunoreactivity
Results
Ibotenic acid induced lesions of the thalamus
Effects of thalamus lesions on c-Fos expression
and Sleep-wake behavior
A slight decrease in theta power during the subjective night after thalamus lesion
Summary 1
• Thalamus lesions, even with an extensive lesion, did not affect EEG/EMG
pattern, sleep/wake pattern, c-fos expression and behavior, except a slight
decrease in theta power during the subjective night.
• No coma-like syndrome was observed.
Nonselective lesions of the BF
10 days after OX-SAP, 7/11 rats exhibited a coma-like state
• EEG at all times was dominated by sub-delta (<1 HZ EEG) activity.
Effects of BF lesions on the c-Fos expression
A dozen cholinergic cells are the only surviving
Neurons
Minimal c-fos expression in neocortex
High expression in TMN and LC
C-Fos expression on nonselective and
selective lesions of the BF
Effects of BF lesions on the EEG pattern induced by
continuous stimulation
By continuous gentle touch, rats maintained a tonically active EMG.
EEG showed a monotonous slow-wave activity
No coma-like behaviors were induced in Ch BF lesions
or Non-Ch BF lesions
Summary 2
1. BF is a critical relay for maintaining the waking pattern of behavior, EEG
and cFos expression.
2. Both cholinergic and noncholinergic (mainly GABAergic) BF neurons
work jointly in control of cortical arousal. Either component alone is
capable of supporting cortical arousal.
Source of inputs to the BF neurons?
Retrograde tracer CTB injection to S1 to search
which provides arousal inputs to the BF
• Large numbers of neurons in the
medial PB (MPB)
• Small number in the PC
• Almost all the CTB labeled cells
in the PC and PB also expressed
VGLUT2, indicating PB/PC
provide glutamatergic inputs to
the BF
PB/PC lesions induced by OX-SAP injection
Comatose happened 10 days after injection
LPB and MPB lesions increased sleep
Bulk of EEG power was <1 HZ after PB/PC lesion
Low level of c-Fos in the neocortex
Effects of PB/PC lesions on the EEG pattern induced
by continuous stimulation
By continuous gentle touch, rats maintained a tonically
active EMG. EEG showed a monotonous slow-wave activity
Summary 3
1. PB/PC is critical for achieving and maintaining an activated EEG and a
waking state.
2. PB/PC-BF-neocortical axis controls neocortical arousal
Important points of the study
• 1. Challenge widely accepted view of comatose model (thalamus)
• 2. Provide solid evidence that PB/PC-BF-Cortex may constitute a critical
pathway for maintaining a waking cortical state.
Thanks for your attention