Effects of testosterone and social interactions on adult neurogenesis in male rats.

Vermont Genetics Network Annual Retreat, August 7 2013Mark D. Spritzer

Department of Biology, Middlebury College

Hormones

Adult neurogenesisSpatial cognition

Social interactions

Adult Neurogenesis1. Proliferation, survival, and differentiation of new neurons

from stem cells in adult brain.

2. Occurs mainly in dentate gyrus and sub-ventricular zone.

3. Measured using thymidine analogs (BrdU) or endogenous markers.

Aimone et al. 2006

Hippocampus

The rat hippocampus

DentateGyrus

CA1

CA3

CA2Granulecell layer

Hilus

GCL

hilus

Cell proliferation

Cell survival

hilus

gcl 100 m

10 mhilus

gcl

Neurogenesis is necessary for forming spatial memories

1. Environmental enrichment improves spatial learning and memory and increases neuron survival (Kempermann et al. 1997; van Praag et al. 1999).

2. Chronic stress impairs adult neurogenesis and spatial learning and memory (Mirescu & Gould 2006; Stranahan et al. 2006).

3. Rats given spatial learning task have increased neuron survival (Epp et al. 2008; Gould et al. 1999).

4. Blocking neurogenesis impairs spatial memory • Irradiation of hippocampus (Raber et al. 2004; Snyder et al. 2005).

• Transgenic mice (Dupret et al. 2008; Jessberger et al. 2009).

Reduced neurogenesis is symptomatic of disease

1. Age-related dementia• Aging impairs spatial memory and reduces

neurogenesis (Drapeau et al. 2003).

• Hippocampus is key site of neurodegeneration in Alzheimer’s disease (Steiner et al. 2006).

• Neurogenesis dysregulated in AD patients (Arendt 2000; Li et al. 2007).

2. Chronic depression• Chronic stress reduces neurogenesis and is correlated

with increase risk of depression (Diamond et al. 1996; Pham et al. 2003 ).

• Antidepressants enhance neurogenesis (Duman & Monteggia 2006).

Testosterone and hippocampal neurogenesis

1. Testosterone has no effect on cell proliferation (Spritzer & Galea 2007; Carrier & Kabbaj 2012; Ho et al. 2012).

2. Castration reduces adult neurogenesis in male rats via decreased cell survival (Spritzer & Galea 2007; Wainwright et al. 2011).

3. 30 days of testosterone injections enhanced neurogenesis in castrated male rats via an androgen- dependent pathway (Spritzer & Galea 2007).

4. Effects of castration only observed in socially isolated rats (Spritzer et al. 2011).

5. Rats lacking androgen receptors show no change in neurogenesis in response to testosterone implants (Hamson et al. 2013).

How does testosterone influence different stages of neural development?

Methods• 9 groups of adult male rats(N = 8/group)

− 3 injection doses: Oil, 0.250 mg, 0.500 mg− 3 time periods: cell proliferation

axon extension neuron maturation

• All groups injected with 200 mg/kg BrdU on Day 0• All groups perfused 16 days after BrdU injection

High dose of testosterone increased neurogenesis

1-5 6-10 11-150

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Sex and hippocampal neurogenesis

1. Aggressive interactions cause a decrease in neurogenesis among subordinates (Kozorovitskiy & Gould 2004; Thomas et al. 2007).

2. Sexual interactions enhance neurogenesis in female mice (Shingo et al. 2003).

3. Single sexual interaction enhanced cell proliferation and 14 days of sex prior to BrdU injections enhanced neurogenesis in male rats (Leuner et al. 2010; Glasper & Gould 2013).

How does sex influence different stages of neural development?

Methods

Methods• 4 groups of adult male rats(N = 10-12/group)

- Control: no sexual interactions- Experimental: 5 days of 30 min sexual interactions

with estrus female on specified days.

• All groups injected with 200 mg/kg BrdU on Day 0• All groups perfused 16 days after BrdU injection

Sexual interactions had no effect on neurogenesis

Control Days 1-5 Days 6-10 Days 11-150

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Testosterone increases only on first day of sexual interactions.

baseline 1 3 5 7 9 11 13 150123456789

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Conclusions

1. High dose (0.500 mg T) of short duration (5 days) increased adult neurogenesis.

2. Later stages of neural development may be more strongly impacted by testosterone?

3. Acute bouts of sexual interactions have no effect on adult neurogenesis.

4. Testosterone is increased only on first day of a series of sexual interactions.

Thank You!• Middlebury students: Kelsey Calhoun, Shannon

Engelman, Zach Schneider-Lynch, Ethan Roy, Leanne Shulman

• Collaborators: Liisa Galea, Jennifer Barker• Funding: Middlebury College, Department of

Biology, Sigma Xi, Vermont Genetics Network

Effects similar in dorsal and ventral hippocampus

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Dorsal GCL

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Ventral GCL

Male sexual behavior cycles!

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