Wheel Running Alters Serotonin (5-HT) Transporter, 5-HT1A, 5-HT1B, and Alpha1b-Adrenergic Receptor mRNA in the Rat Raphe Nuclei

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Wheel Running Alters Serotonin (5-HT)
Transporter, 5-HT1A, 5-HT1B, and
Alpha1b-Adrenergic Receptor mRNA in the Rat Raphe
Nuclei
Greenwood et al 2005
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Depression

• Thought to be an overall decrease in serotonin
  transmission through out the central nervous
  system.
• Antidepressants are designed to reverse this
  process.

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Raphe

• Serotonin output center of the brain
• Thought to be a big source of action for SSRIs
• Prevents the reuptake of serotonin increasing
  neurotransmission
• Treats depression

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Previous Work

• Voluntary wheel running acts as an antidepressent
  in models
• Forced swim
• Chronic mild stress
• Learned helplessness
• 6 weeks wheel running lowers the activity of 5HT
  neurons in the dorsal raphe nucleus (DRN) during
  uncontrollable stress
• Prevents learned helplessness

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MM

• Male Fischer F344 rats individually housed
• 1212hr light/dark cycle
• Lights on at 6AM
• 1wk acclimatization with locked running wheels
• Ad libitum food and water
• Unlocked wheels for 3 days, 3 wks, 6wks

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What was looked at
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Serotonin Transporter (5-HTT)(SERT)
Reuptakes 5-HT
Pre
5-HTT
Pre-synapse
5-HT
Post
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Serotonin 1A 1B receptors(5-HT1A 5-HT1B)

• Located on soma, dendrites and axon terminals
• Act as auto receptors that inhibit
• Synthesis of 5-HT
• Release of 5-HT
• Ultra short loop negative feedback

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Alpha1B Adrenergic Receptor (a1b ADR)

• Coupled Gp-protein / IP3 / Ca
• Norepinephrine binds
• Stimulates Raphe Increases 5-HT output

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5-HTT, 5-HT1A, 5-HT1B, a1b-ADR

• What technique was used?

• Problems with this technique

• In situ hybridization
• Measures mRNA levels
• Assumed there is a direct correlation with protein

• Translation?
• Binding to receptors?

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Why were these 4 things looked at?

• Estimated that all 5HT neurons in raphe contain
  these things
• All of these things can modulate serotonin
  transmission in the raphe

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Changes in distance and weight
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Dorsal Raphe Nucleus (DRN) Median Raphe Nucleus
(MR)
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!
Increase
!
a1b-ADR
5-HTT
5-HT1A
5-HT1B
Decrease
!
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Seritonin transporter mRNA levels (5-HTT)
Relative 5-HTT mRNA levels integrated optical
density
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As far as 5HTT is concerned
See a decrease in raphe mRNA
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Alpha 1B Adrenergic Receptor levels (a1b-ADR)
Relative alpha 1b-ADR mRNA levels Integrated
optical density
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a1b-ADR (NE receptor)

• NE systems are activated by acute exercise
• From locus ceruleus
• The increased NE levels may down regulate
  receptors

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Seritonin 1B Receptor levels (5-HT1B)
Relative 5-HT1B mRNA levels Integrated optical
density
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5-HT1B
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5-HT1B Autoreceptor

• Trend of decreasing overall
• Exercise and SSRIs decrease
• Ventral DRN did show a significant decrease
• Selective innervations of certain areas?
• Caudate putamen
• Cortex
• In a separate study, increased 1B makes rats more
  anxiety prone
• suggests an increased capacity to synthesize
  presynaptic 5-HT1B receptors and could account
  for diminished serotonin neurotransmission in
  learned helplessness (Neumaier JF, et al)

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Seritonin 1A Receptor levels (5-HT1A)
Relative 5-HT1A mRNA levels Integrated optical
density
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5-HT1A autoreceptor

• Increased after running
• More negative feedback
• Opposite of antidepressant treatment
• Increased AND decreased levels of 5-HT1A have
  been seen in suicides or depressed subjects
• Theres more to this story

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5-HT1A

• Learned helplessness(LH) appears to be dependent
  on hyperactivation and sensitization of DRN 5-HT
  neurons. (Takase et al)
• LH can also be attenuated by 6wks voluntary wheel
  running (greenwood)
• 5-HT1A increasing after 6 weeks may provide a
  means of protection from LH
• Possibly other depression models as well

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Further investigations

• Interesting correlation between the time
  dependent effects of both running and
  antidepressants
• 6 wks but not 3wks of running overcomes learned
  helplessness in shuttle box (Greenwood)