Neuropeptide Changes in Transgenic Mice as a Model of Alzheimer

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Neuropeptide Changes in Transgenic Mice as a
Model of Alzheimers Disease

• Laurel Johnson
• Laboratory of Psychoneuroendocrinology
• Mentor Garth Bissette, PhD

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Why study Alzheimers Disease?

• Alzheimers Disease is a progressive
  neurodegenerative disease that occurs in later
  years of ones life.
• Current estimates are that 40 of people who
  reach the age of 80 years will have AD.
• Since todays population is living longer, AD is
  becoming more prevalent among the older
  generations.
• The only drugs currently available for the
  treatment of AD do not improve cognitive
  function.
• The CRF, Somatostatin, and Acetylcholine levels
  of patients with AD are altered.
• Researchers need a good model to test drugs for
  the treatment and cure of AD.

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Transgenic Mice

• Tg2576 Swedish mutation that overexpresses the
  human gene Amyloid Precursor Protein 695, and was
  developed by Karen Hsiao in 1996.
• The gene was derived from a large Swedish family
  with early onset familial AD.
• Between 11-13 months Beta Amyloid content
  increases between 6-14 fold in the brain.
• By 6 months mice exhibit increased locomotor
  activity and aggressiveness.
• By 12 months mice have impaired spatial memory.
• After the 12 month period mice have increasing
  impaired spatial and working memory.

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Opto-varimex Monitoring Apparatus
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Locomotor Activity

• Opto-varimex Monitoring Apparatus
• Consists of 8 clear Plexiglas boxes with sawdust
  covering the bottom and a clear Plexiglas top.
• The boxes are 42.5cm long by 42.5cm wide, and
  20.5cm deep.
• Monitors the animals locomotion with infrared
  beams.
• Each time a beam is broken by the animals
  movement inside the box, a score of one is
  recorded.
• The apparatus is connected to a Columbus
  Instruments Photocell Activity Monitor computer
  system which keeps a record of the scores
  recorded over a 15 minute time period.

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Locomotor Activity Box
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Columbus Instruments Photocell Activity Monitor
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Locomotor ActivityDistance Travelled
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Morris Water Maze
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Morris Water Maze

• Day One Visible platform in the north quadrant
• - Subject enters pool facing the wall in west
  quadrant.
• Subject is given two minutes to reach platform.
• Subject is placed on platform if not reached
  within two minute trial.
• Subject swims until platform is reached in less
  than sixty seconds for three consecutive trials.
• If a subject does not complete the task they must
  repeat day one of testing the following day.
• Day Two Visible platform in east quadrant
• Procedure is repeated the same as day one.
• Upon successful completion of day two trials,
  subject is given one trial with the invisible
  platform.
• Day Three Invisible platform in east quadrant
• Subject enters the pool in random quadrants
  facing the wall.
• Subjects who successfully complete day three
  trials are then given one trial without the
  platform.
• Subjects that do not complete trials are not
  placed on the platform afterwards.
• Subjects that do not successfully complete three
  consecutive trials within the ten trial limit are
  deemed unsuccessful and do not repeat day three
  of testing.

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I DID IT!!!
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Ethovision
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Subjects that Failed to complete Day one of
Water Maze Task
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Morris Water Maze
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Corticotropin-Releasing Factor (CRF)

• CRF is a 41 amino acid containing neuropeptide
  that is the major physiological regulator of the
  hypothalamic pituitary-adrenal axis.
• In addition to its neuroendocrine role, CRF has
  been shown to fulfil many of the requisite
  neurotransmitter criteria.
• CRF circuits occur throughout the brain in
  cortical and subcortical regions.
• Behaviorally, CRF produces fear and anxiety in
  animals.
• CRF is found in decreased levels in humans with
  AD, and appears in these decreased levels earlier
  than both Somatostatin and Acetylcholine.
• CRF concentrations are reduced by 50 in AD
  cortex at death and CRF neurons degenerate.
• Post-synaptic CRF receptors are up-regulated in
  proportion to CRF concentration decrease in AD
  cortex.

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Somatotropin-Release Inhibiting Factor
(Somatostatin, SRIF)

• SRIF inhibits the release of most pituitary
  hormone regulatory factors from the hypothalamus.
• Exists as either a 14 or 28 amino acid containing
  neuropeptide.
• SRIF deficits occur after CRF, similar to
  Acetylcholine according to the level of dementia
  at death.
• Like CRF, SRIF levels decrease by 50 in AD
  cortex at death, but SRIF neurons are not seen to
  degenerate.
• Unlike CRF, there is no upregulation of
  post-synaptic receptors and SRIF receptors
  decrease in post-mortem tissue.

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Implications of Study

• If decreases in CRF and Somatostatin are found in
  our transgenic mice then this would show that
  this model is a good model of human AD
  neurochemical pathology.
• If these neurochemical changes do not coincide
  with the changes occurring in human AD, then this
  casts further doubt on the hypothesis that
  Beta-Amyloid produces the neuropathology seen in
  AD.

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CRF and SRIF in Post-mortem Samples
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Conclusions

• In these transgenic mice, CRF and Somatostatin
  levels were not found to be decreased in cortical
  regions when compared to the controls. This does
  not coincide with the decreases found in human
  post-mortem samples.
• The Beta-Amyloid hypothesis proposes that
  Beta-Amyloid neurotoxicity causes
  neurodegeneration in the AD brain.
• If the Beta-Amyloid hypothesis is correct, then
  why do we not see the same cortical decreases in
  the mice as we do in humans?

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Acknowledgements

• My Mentor, Dr. Garth Bissette
• Program Director, Dr. Ian Paul
• Jennifer Horgan
• Martha Thrasher
• Kim Rogers
• NSSP Scholars Mentors
• Tracie Findley (Mom)
• Mike Wallis

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THANK YOU
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References

• Davis KL et al. (1999) Neuropeptide abnormalities
  in patients with early Alzheimers Disease.
  Arch. Gen. Psychiat. 56 981-987.
• Beal M.F. et al. (1985) Reduced numbers of
  somatostatin receptors in the cerebral cortex in
  Alzheimers Disease. Science. 229 289-291.
• Bissette, G. et al. (1998) Regional neuropeptide
  pathology in Alzheimers Disease
  Corticotropin-releasing factor and Somatostatin.
  J. Alzheimers Disease. 1 1-15.
• Hsiao K. (1998) Strain dependent and invariant
  features of transgenic mice expressing Alzheimer
  amyloid precursor proteins. Progress in Brain
  Research. Vol. 117, pp.335-341.
• Bissette, G. (1997) Neuropeptides and Alzheimers
  Disease Pathology. Annals of New York Academy of
  Sciences. 814 17-29.