1. The Hippocampus and Serotonin
Receptors:

2. A table of contents
•
•
•
•
Characteristics of the Raphe Nuclei
Function of the Raphe Nuclei
Malfunction of the hippocampus in depression
Serotonin Receptors (5-HTRs) and Signal
Transduction
• 5-HT innervations in the hippocampus
• Signal Transduction of the pyramidal cells
• Summary
1

3. A table of contents
•
•
•
•
Characteristics of the Raphe Nuclei
Function of the Raphe Nuclei
Malfunction of the hippocampus in depression
Serotonin Receptors (5-HTRs) and Signal
Transduction
• 5-HT innervations in the hippocampus
• Signal Transduction of the pyramidal cells
• Summary
2

4. What is depression? And What’s the cause
Major depression is one of the most common mood
disorders(over 20% of U.S. for over 18 yo during life, NIH).
Symptoms: A loss of interest, Change of mood representations,
Impairment of social, occupational, or educational function,
Sleep problem(Insomnia or hypersomnia), indecisive, Suicidality,
Worthlessness(DSM-IV, 1994)
Why Serotonin?:
Low levels of serotonin in the patients(Serotonin-deficiency
theory)[Lacasse, Plos Med., 2005]
Strong evidence:
Selective Serotonin Reuptake Inhibitors(SSRI) -> induction of
extracellular serotonin increase
• Major antidepressant drugs(about -70%)
However, detailed etiology is still unknown.
3

5. Aim of This Independent Study
Some discrepancies:
1) A slow effect of SSRI on mood even after acute
treatment[Harmer, BJPsychiatry, 2009]
2) SSRI is not completely effective(Dopamine theory, BDNF
theory)[Dunlop, Arch Gen psychiatry, 2006;Trivedi, The New England Journal
Serotonergic projections
of Medicine, 2006]
On the other hand….(several indication)
1)15 subgroups of Serotonin (5-HT) receptor family and
different effect on neurons
2) Region-dependent distribution of the receptors
3) Strong Serotonergic innervations related with several brain
regions in the depression patients(the hippocampus, the basal
ganglia, and the amygdala).
4

6. Presumption of depression
Presumption:
• Neuronal network might cause
differential effect on multiple brain
regions due to different receptor
types of serotonin.
Purpose of this seminar
• Summary of detailed survey of
serotonin innervations
5

7. A table of contents
• Characteristics of the Raphe Nuclei
• Serotonin Receptors (5-HTRs) and Signal
Transduction
• Malfunction of the hippocampus in depression
• 5-HT innervations in the hippocampus
• Signal Transduction of the pyramidal cells
• Summary
6

8. Serotonin (5-HT)
• One of monoamine
neurotransmitters
• 5-HT, tryptophan, and
melatonin are related
metabolites.
• Breathing rhythms, heart
rate, locomotion, circadian
rhythms, emotions, and
neurogenesis.
7

9. General Characteristics of Raphe Nuclei
Classification:
The raphe nuclei: serotonin (5-HT) containing neuron clusters(Midline of the brainstem)
• Subdivisions in rats:
B1: Raphe Pallidus, B2: Raphe Obscurus, B3: Raphe magnus, B4: Raphe
Obscurus(dorsolateral part), B5: Raphe Pontis, B6: Dorsal Raphe Nucleus(caudal
part), B7: Dorsal Raphe Nucleus(Principal part), B8:Median Raphe Necules(Main
party), B9:Dorsal Pontine Tegmentum
• 85% of 5-HT neurons in Rostral(B7, B8) part of human brains[Hornung, J. Chemi.
Neuroana. 2003]
[Siegel, 2008]
Fig 2 Caudal
part(B13), Rostral(B7, B
8)
[Stahl S., 1996]
revised by CNS
8

10. General Characteristics of Raphe Nuclei
DR: cell size(3040um), fusiform,
darkly stained
MR: cell size(1012um), oval, ligh
tly
stained[Verte., 20
07]
[Vertes and Linley, International Congress
Series, 2007]
Dorsal Raphe(DR) projections in rat:
the ventral tegmental area(VTA), the substantia
nigra pars compacta(SNc), some regions of
hypothalamus, amygdala complexes, dorsal and
ventral striatum, lateral septum(LS), the
entorhinal(EC), medial orbital (MO) and the medial
prefrontal cortex (mPFC), the hippocampus.
(anterograde tracer with PHA-L[Vertes and
Linley, 2007])
Median Raphe(MR) projections in rat:
the interpeduncular nucleus, VTA, medial
mammillary nucleus, parts of the midline and
intralaminar thalamus, the lateral
habenula, septum, ventral striatum(Nucleus
accumbens), the hippocampus, medial septum
(MS)[Vertes J.Comp. Neurol, 1999; Vertes and
Blue: dopaminergic nuclei
Linley, 2007].
Red: Amygdala related
Orange: Basal Ganglia
Brown: hippocampus
9

11. Reciprocal links between DRN and MRN
“We are brothers and friends, but…”
DRN affects MRN, but MDR does not affect much.
DRN
unknown
MRN
Glu application into the DRN[Mokler, 2009]
Mutual connections in rats and hamster[Vertes and et
al., 1988, 1991, 1999; Tisheler and Morin, Brain Res., 2003]
The mean of extracellular 5-HT: DRN(15.6 ± 2.4 fmol/20ul
= 0.78 ± 0.12 nmol/l; n = 16), MRN(10.6 ± 1.3 fmol/20ul =
0.53 ± 0.065 nmol/l; n=16)[Mokler, Brain Res., 2009]
Putative Firing rate of 5-HT neurons: DRN(1.34 ± 0.09
Hz), MRN(0.54 ± 0.05 Hz)[Judge., etal, Neurochemi., 2006]
Glu application into the MRN[Mokler, 2009]
11

12. Function of DRN -Patience and ImpulsivityPatience and Impulsivity
1. Activation 5-HT Neurons in DRN
during waiting delayed rewards
2. Negative correlation between 5-HT
activity and Wait Error.
Omission trials counted by removal of nosepoking.
[Miyazaki et al., Mol Neurobiol, 2012]
12

13. Disruption of theta rhythms by stimulation of
Serotonergic neurons in MRN
(cited from UCLA facility)
[Hsiao et al., Behavioral Brain Resarch,2012]
MS – DBB: Medial septum-diagonal band of Broca
LHA: Lateral hypothalamic area
Hypocretin: Orexin
Theta Rhythms (4 - 10 Hz): relationship with memory
consolidation in the hippocampus and possible to be
induced by stress
Induction of Inescapable foot shook by MS-DBB
Prevention of theta rhythms by lesion of MS – DBB[]
14
[Hsiao et al., Behavioral B. Res., 2013]

14. A table of contents
•
•
•
•
Characteristics of the Raphe Nuclei
Function of the Raphe Nuclei
Malfunction of the hippocampus in depression
Serotonin Receptors (5-HTRs) and Signal
Transduction
• 5-HT innervations in the hippocampus
• Signal Transduction of the pyramidal cells
• Summary
15

15. Malfunction of hippocampal neurogenesis hypothesis
Slow effect of SSRI or Antidepressant
drugs (AD) -> Morphological changes
(?)
• Brain-Derived Neurotrophin Factor (BDNF) -> Induction of
Neuro-proliferation -> Promotion of Neurogenesis
• Decrease of BDNF by stress in hippocampus[Smith et
al., 1995]
• BDNF mRNA promotion by AD drugs[Nibuya, J. Nuro., 1995]
[Berton, Nature Neuro., 2006]
Chronic ADs increase
neurogenesis in Rat
hippocampus[Malberg, J.
Neuro., 2000]
16

16. Measurement of helplessness and anxiety
The Forced Swim Test:
Check immovability of mice
Normal: Try to avoid water
Abnormal: Be quiet.
Interpretation: immovability shows despair.
The Novelty Suppressed Feeding (NSF)
test
Check amount of foods in a novel
environment after removal of feeding.
Interpretation: hesitation for rewards shows
level of anxiety of a new environment.
17

17. Malfunction of hippocampal neurogenesis hypothesis
The novelty suppressed feeding[Kuteeva, Springer, 2010].
Selective inhibition of neurogenesis -> Prevention of
Antidepressant Drugs effects[Santarelli et
al., Science, 2003]
Hippocampal volume reduction in
depression patients
[Bremner JD., CNS, 2002]
18

18. A table of contents
•
•
•
•
Characteristics of the Raphe Nuclei
Function of the Raphe Nuclei
Malfunction of the hippocampus in depression
Serotonin Receptors (5-HTRs) and Signal
Transduction
• 5-HT innervations in the hippocampus
• Signal Transduction of the pyramidal cells
• Summary
19

19. Subtypes
Agonists
5-HT1A
Tetalin, 5-MeODMT, BAY, 8-OHDOAT
5-HT1B
5-HT1D
Antagonists
G protein
Localization
Serotonin Receptors
Function
Spiperone,
WAY-100135
Gi(AC↓,
open K+),
Go(close
Ca2+)
Hippocumpus,the lateral septum,entorhinal
and cingular cortices, dorsal raphe nucleus
Autoreceptor,
Heteroreceptor
(unselective)
TFMPP,
CGS12066B,Sumat
riptan, L694247
Isamoltane,
GR-55562, SB
224289, SB236057
Gi(AC↓)
SN,globus pallidus,caudate
putamen,ventral pallidum,entopeduncular
nucleus,hippocampus, cortex,VTA
Autoreceptor
Sumatriptan, PNU
109291, BRL 15572
GR-127935
Gi(AC↓)
SN,globus pallidus,caudate putamen,ventral
pallidum,entopeduncular
nucleus,hippocampus, cortex,VTA
Autoreceptor
5-HT1E
Gi(AC↓)
The caudate,putamen amygdala,and cortical
areas(Bruinvels, 1994)
5-HT1F
Gi(AC↓)
hippocumpus cortical areas
5-HT2A
DOI, DOB, α-Me5HT
ritanserin(vged
o ,1989)
Gq(PLC)↑
Cortex, claustrum, hippocampus,
hypothalamus, basal ganglia
5-HT2C
SB-243213(Blackbu
rn et al., 2002)
Mesulergine,
SB-242084,
RS-102221
Gq(PLC)↑
the chroid plexus, the frontal cortex,the
limbic system,hippocumpus,septum,hypot
halamus, striatum,nucleus
accumbens,rhombencephalon,spin al cord
Post synaptically
expressed
[Filip, 2009;Hoyer,
20
2002]

20. Subtypes
Agonist
s
Antagonists
G protein
Localization
5-HT3
α-Me-5HT
DAU 6215
Zacopride, Odanserton,
Granisotron
Zatosetron
None(Ion channels-influx
Na+, Ca2+, efflux K+)
the caudal medulla, forebrain, SN, N. AC,
prefrontl cortex, striatum
SDZ-205557
GR-125487
Gs(AC↑)
limbic regions, the olfactory system, striatum,
medial habenula, hippocampus
5-HT5A
Gi/o(AC↓)
Hippocampus, hypothalamus, olfactory bulb,
cortex, thalamus, striatum, pons
5-HT5B
?
Habenula, raphe nucleui, hippocampus(in
rodents); pseudogene(in humans)
Lisuride, Colozapine
SB271046
Gs(AC↑)
Striatum, olfactory tubercle, N. Acc,
Clozapine, Amitryptline
Gs(AC↑)
hypothalamus, thalamus, brain stem, striatum,
cerebral cortex.
5-HT4
SC53116
5-HT6
5-HT7
LSD
GABA-containing cells in neocortex, olfactory
cortex, hippocampus, amygdala
21
[Filip, 2009;Hoyer, 2002]

21. Serotonin receptors and Signal Transduction
a
22
[Berumen et al., The Scientific World Journal,2012]

22. Serotonin Receptors and Signal Transduction
• a
[Berumen et al., The Scientific World Journal,2012]
23

23. Serotonin Receptors and Signal Transduction
• a
24
[Berumen et al., The Scientific World Journal,2012]

24. 25

25. 26

26. A table of contents
•
•
•
•
Characteristics of the Raphe Nuclei
Function of the Raphe Nuclei
Malfunction of the hippocampus in depression
Serotonin Receptors (5-HTRs) and Signal
Transduction
• 5-HT innervations in the hippocampus
• Signal Transduction of the pyramidal cells
• Summary
27

27. Hippocampus and 5-HT Ascending
Projections
MR fibers in
dorsal
Hippocampu
s[Vertes, 199
9]
Mouse Brain(cited from NeuroDigi)
PHA-L MR fibers in ventral Hippocampus[Vertes, 1999]
PHA-L 5-HT fibers[Morin et al., 1999]
PHA-L MR fibers to hippocampus[Morin et al., 1999]
CC: Central Gray
GCL: granule cell layer
Mo: Molecular layer of
Dentate Gyrus
PCL: Pyramidal Layer
SLM: Stratum lacunosummoleculare
SR: Stratum radiatum
28
SOr: Stratum oriens

28. Serotonin Receptor Expression in the mouse
hippocampus
• a
5Hippo. Localization
HTR
1A
granular, pyramidal N., and some glia
(Presynaptic R as well)
1B
Presynaptic N. of DRN or MRN
2A
granular, pyramidal, and astrocytes
2C
CA3 pyramidal.
3A
CA2 and C3 Pyramidal N.
4
Cholinergic axon
5A
Astrocytes
5B
CA1 pyramidal cells
7
CA1 neurons
29

29. Serotonin Receptor Expression in the mouse
hippocampus
• a
GCL: Granule cell layer, Glu
ML: molecular layer,
Hilus:
30

30. SSRI induces
neurogenesis[Santralli, 2003]
-> 5-HT increase in DG.
• a
[Berumen et al., The Scientific World Journal,2012]
Q1. Which receptor is dominant?
Assumption(As) . Maybe 5-HT1AR,
and linking to inhibition of AC.
31

31. SSRI induces
neurogenesis[Santralli, 2003]
-> 5-HT increase in DG.
• a
Q1. Which receptor is dominant?
Assumption(As). Maybe 5-HT1AR,
and linking to inhibition of AC.
Q2. Express where?
[Berumen et al., The Scientific World Journal,2012]
32

32. SSRI induces
neurogenesis[Santralli, 2003]
-> 5-HT increase in DG.
• a
Q1. Which receptor is dominant?
Assumption(As). Maybe 5HT1AR, and linking to inhibition of
AC.
Q2. Express where?
a) Induction of neurogenesis by 5HT1A agonist in DG[Grabiec, 2009].
b) Inhibition of cell proliferation by
5-HT1A
antagonist[Radley, JJ., 2002].
[Berumen et al., The Scientific World Journal,2012]
33

33. SSRI induces
neurogenesis[Santralli, 2003]
-> 5-HT increase in DG.
• a
Q1. Which receptor is dominant?
Assumption(As). Maybe 5-HT1AR,
and linking to inhibition of AC.
Q2. Express where?
a) Induction of neurogenesis by 5HT1A agonist in DG[Grabiec, 2009].
b) Inhibition of cell proliferation by
5-HT1A antagonist[Radley, JJ.,
2002].
As:
1. GABA > Pyramidal
How b) happen?
[Berumen et al., The Scientific World Journal,2012]
34

34. SSRI induces
neurogenesis[Santralli, 2003]
-> 5-HT increase in DG.
• a
Q1. Which receptor is dominant?
Assumption(As). Maybe 5-HT1AR,
and linking to inhibition of AC.
Q2. Express where?
a) Induction of neurogenesis by 5HT1A agonist in DG[Grabiec, 2009].
b) Inhibition of cell proliferation by
5-HT1A antagonist[Radley, JJ.].
As:
1. GABA > Pyramidal
How b) happen?
2. Pyramidal > GABA
5-HT1A G protein activates cAMP?
[Berumen et al., The Scientific World Journal,2012]
35

35. SSRI induces
neurogenesis[Santralli, 2003]
-> 5-HT increase in DG.
• a
Q1. Which receptor is dominant?
Assumption(As). Maybe 5-HT1AR,
and linking to inhibition of AC.
Q2. Express where?
a) Induction of neurogenesis by 5HT1A agonist in DG[Grabiec, 2009].
b) Inhibition of cell proliferation by
5-HT1A antagonist[Radley, JJ.].
As:
1. GABA > Pyramidal
How b) happen?
2. Pyramidal > GABA
5-HT1A G protein activates cAMP?
3. Other receptors? Other G
proteins?
4. 5-HT increase in DG?
[Berumen et al., The Scientific World Journal,2012]
36

36. Signal Transduction of Pyramidal neurons
Unknow
n
37
[Dumen et al., 2012]

37. Summary
• 1. Serotonergic neurons project to the basal
ganglia, the amygdala complex, the
hippocampus, and others.
• 5-HT affect neurogenesis as well as anxiety.
• Differential 5-HTRs’ expression in
hippocampus.
• A causal receptor is still unknown.
38

38. Discussion Time
Dance of the Rats[17c, Germany]
39