Nicotine reinforcement and cognition restored by targeted expression of nicotinic receptors

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Nicotine reinforcement and cognition restored
by targeted expression of nicotinic receptors
Presentation by John Walker
Nature 436, 103-107(7 July 2005)
doi10.1038/nature03694 Received 25 January
2005 Accepted 28 April 2005
http//www.nature.com/nature/journal/v436/n7047/fu
ll/nature03694.html
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• Nicotine is not regulated by your body.
• Nicotine activates cholinergic neurons (which
  mainly use acetylcholine to communicate to other
  neurons).

Nicotine
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• Increased release of acetylcholine This
  cholinergic activity calls your
• body and brain to action, and this is the
  wake-up call that many
• smokers use to re-energize themselves throughout
  the day.
• Through these pathways, nicotine improves your
  reaction time
• and your ability to pay attention, making you
  feel like you can
• work better.

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• Increased release of dopamine in the reward
  pathways of your brain.
• Reinforces behaviors that are essential to your
  survival,
• like eating when you're hungry. When drugs like
  cocaine or
• nicotine activate the reward pathways, it
  reinforces your desire to
• use them again because you feel so at peace and
  happy afterwards.

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• Release of glutamate, a neurotransmitter involved
  in learning and
• memory - Glutamate enhances the connections
  between sets
• of neurons. These stronger connections may be
  the physical
• basis of what we know as memory. When you use
  nicotine,
• glutamate may create a memory loop of the good
  feelings you
• get and further drive the desire to use
  nicotine.

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• Increased synthesis of Endorphins small proteins
  that are often
• called the body's natural pain killer. It turns
  out that the chemical
• structure of endorphins is very similar to that
  of heavy-duty
• synthetic painkillers like morphine. This
  outpouring of chemicals
• gives you a mental edge to finish the race while
  temporarily masking
• the nagging pains you might otherwise feel.

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• Some diseases that nicotine might improve
  include
• Alzheimer's Disease - The first neurons lost to
  Alzheimers are
• cholinergic neurons in a specific region of the
  brain.
• Nicotine may improve the function of the neurons
  that are left and
• slow the onset of symptoms.
• Tourette's Syndrome - This disease produces tics
• (uncontrolled movements of the head, hands and
  other body parts)
• and violent urges in its sufferers. Nicotine
  patches that slowly deliver
• nicotine through the skin can reduce symptoms of
  people with
• Tourette's.

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• Neurotransmitters- chemical messengers, which
  communicate between neurons in the form of
  electric current (including acetylcholine,
  dopamine, serotonin, glutamic acid etc.).

Acetylcholine is released from one neuron and
binds to receptors on adjacent neurons.
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The ventral tegmental area (VTA)Prove that it
plays a significant role in cognitive functions.
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Gene Knock-invia transduction of lentiviral
vectors
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Figure 1 Lentivector-mediated expression of eGFP
and nAChR 2-subunit in the VTA.
a, Confocal section of VTA neurons expressing
eGFP (green). Tyrosine hydroxylase (TH, red)
indicates dopamine neurons (arrows).
GABA-containing neurons are TH-negative and are
identified by their neuronal morphology
(arrowheads and inset). b, 125I-epibatidine
autoradiography, coronal sections at -3.4 mm from
bregma. Arrows indicate the VTA (red) and the
substantia nigra (SN, black). The
interpeduncular nucleus (which shows persistent
epibatidine binding in 2-/- mice11) is directly
above the green asterisk. c, 125I-epibatidine
autoradiography in coronal sections at 1.42 mm
from bregma. The nucleus accumbens is shown in
blue (shading or outline) black arrowheads
indicate re-expressed binding sites in the median
forebrain bundle and olfactory tubercle.
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Figure 2 Effects of nicotine in vivo on dopamine
neuron firing and dopamine release.
a, Responses in firing frequency of VTA neurons
in WT (n 12), KO (n 15) and VEC (n 16)
mice, expressed as mean s.e.m. Asterisk, P lt
0.05 between VEC and WT mice hash symbol, P lt
0.05 between VEC and KO mice. b, Extracellular
dopamine levels in the nucleus accumbens shell,
showing area under curve values (AUC values,
mean s.e.m.) during a 2-h post-treatment
period. AUC values are expressed as a percentage
of dopamine levels of nicotine versus saline
treatment. Nicotine administration increases
dopamine release compared with saline in WT and
VEC mice (Fisher test single asterisk, P lt
0.0 5 three asterisks, P lt 0.001). Significant
differences in release between nicotine- treated
KO and WT and VEC mice are indicated (single hash
symbol, P lt 0.01 two hash symbols, P lt 0.001).
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Figure 3 Intra-VTA nicotine self-administration.
a, Number of self-administrations per daily
session of 10 trials, expressed as mean s.e.m.
Days 1 and 2 consisted of habituation (H) trials,
and days 39 involved nicotine self-administration
trials (A17), with 100 ng nicotine (as salt)
per self-administered dose. ANOVA revealed a
significant group effect (F2,22 8.315, P lt
0.01), session effect (F8,176 17.907, P lt
0.0001) and group session interaction
(F16,176 3.353, P lt 0.0001). Significant
differences were identified by Fisher's test
single asterisk, P lt 0.05 between KO and VEC
mice two asterisks, P lt 0.001 between KO and
VEC mice hash symbol, P lt 0.05 between WT and
VEC mice. b, Injection latency (mean s.e.m.)
decreased drastically in WT and VEC mice,
confirming expression of nicotine-seeking
behavior. Injection latency increased in KO
mice. ANOVA revealed a significant group effect
(F2,22 4.637, P lt 0.02), a significant session
effect (F8,176 10.771, P lt 0.0001) and a strong
group session interaction (F16,176 7.609, P lt
0.0001). Fisher post-hoc tests showed that mean
self-injection latency between VEC and KO mice is
significantly different from the fourth session
(A4) onwards (single asterisk, P lt 0.05 two
asterisks, P lt 0.001 hash symbol denotes a
significant difference (P lt 0.05) between WT and
VEC mice).
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Figure 4 VTA 2-subunit re-expression and
behaviors in open fields.
a, Time spent in exploration and navigation (mean
time s.e.m.). WT mice differ from KO mice in
both exploration (t 0.0076) and navigation
behaviours (t 0.0004). KO mice differ from VEC
mice in exploration (t 0.02) but not
navigation behaviour (t 0.056), whereas VEC
mice are not (or are only marginally) different
from WT mice (exploration, t 0.66 navigation,
t 0.049). Single asterisk, P lt 0.01 two
asterisks, P lt 0.001 NS, not significant. All
comparisons were made using t-tests. b, Mean
transition diagram. Frequency of shifting between
movement types (see Methods) is indicated by
arrow thickness, and conditional probabilities
(in percentages) are shown. Underlined numbers
are those transitions for which ANOVA revealed a
significant group effect (F2,27P)
(3.810.034) (3.800.035) (4.340.023) and
(4.480.021) for PAPI, PACA,CACI and CAPA,
respectively. c, Transition probability of PACA
(left) and CACI (right) for WT, KO and VEC
mice, shown as mean s.e.m. (single asterisk, P
lt 0.05 two asterisks, P lt 0.01).
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Summary

• Nicotine mobilizes multiple networks including
  ascending dopamine-, acetylcholine-
• and serotonin-mediated pathways together with
  glutamate- and GABA-containing
• neurons from multiple brain regions.

• Restoration of 2-nAChR receptors,
  specifically in the VTA and its axonal
  projections, restores the self-administration of
  nicotine. Thus, being a principal factor in
  nicotine reinforcement.

• Selective recovery of a complex cognitive
  behavior was successfully obtained
• (as a result of cholinergic action, for which we
  provide a molecular- 2-nAChR receptors-
• and anatomical basis- neurons originating in the
  VTA-.

• The efficiency of the lentivector technique in
  vivo in analyses was successfully
• illustrated (of the neural bases of spontaneous
  cognitive behaviors and their
• regulation by endogenous neurotransmitters and of
  a specific receptor species in the
• absence of external intervention).

• Molecular dissection of higher brain functions
  henceforth becomes accessible to
• in vivo investigation at the cellular and
  neuronal network level.