Olfactory bulb removal and its effects on reproduction in rodents

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Olfactory bulb removal and its effects on
reproduction in rodents

• Andrew Clark
• Eco/Evo 208
• November 10, 2004

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A review of past experiments

• Brunjes, P. C. 1992. Lesson from lesions the
  effects of olfactory bulbectomy. Chemical Senses.
  17 729-763.
• Included 406 citations

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Olfactory Bulbectomy

• Studies include effects on
• anosmia
• hormones
• circadian rhythms
• aggression
• activity
• learning
• development
• maternal behavior
• thermoregulation
• heart rate
• sexual behavior physiology

(Brunjes, 1992)
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Ideal Surgical Experimental Procedures

• Pretest to determine if subjects are sexually
  competent.
• Surgery
• Bulbectomy (exposure and aspiration of olfactory
  bulb)
• Sham Operation (exposure of bulbs alone)
• Experiments
• Euthanization of bulbectomized individuals for
  histological data
• bulbs may be partially removed

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Problems with some past studies

• Explaining effects of bulbectomy should not be
  based on anosmia alone
• Clear description of surgical methods lacking
• Few histological data from post-mortem
  examinations
• Partial removal of olfactory bulb might have
  presented inadequate results
• bulb remnants may be sufficient enough to
  maintain olfaction

(Brunjes, 1992)
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Specific References

• Donovan, B. T. P. C. Kopriva. 1965. Effect of
  removal or stimulation of the olfactory bulbs on
  the estrous cycle of the Guinea pig.
  Endocrinology. 77 213-217.
• Horton, L. W. B. A. Shepherd. 1979. Effects of
  olfactory bulb ablation on estrus-induction and
  frequency of pregnancy. Physiology Behavior.
  22 847-850.
• Lumia, A. R., Zebrowski, A. F., M. Y. McGinnis.
  1987. Olfactory bulb removal decreases androgen
  receptor binding in amygdala and hypothalamus and
  disrupts masculine sexual behavior. Brain
  Research. 404 121-126.

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Overall Hypothesis

• Removal and/or stimulation of the olfactory bulbs
  in mammals (Rodenta) will induce changes in their
  reproductive physiology, which in turn will
  decrease reproductive activity.

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Introduction (Donovan Kopriva, 1965)

• Subject the Guinea pig
• inspired by a previous experiment on bulbectomy
  in the pig
• similar sexual cycles to the pig
• Purpose
• to determine the effect of removal and electrical
  stimuli of olfactory bulbs on reproduction in the
  guinea pig

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Methods (Donovan Kopriva, 1965)

• Bulbectomized Guinea Pigs
• cycle lengths compared with normal females
• estrus determined by vaginal smears ( cornified
  cells)
• mating frequencies compared with normal females
• Electrically Stimulated Guinea Pigs
• no bulbectomies
• cycle lengths compared with non-stimulated Guinea
  pigs

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Results (Donovan Kopriva, 1965)

• Bulbectomized Guinea Pigs
• No significant difference in cycle lengths
  between experimental control groups.
• Significant difference in mating occurrences
  between experimental control groups.
• However pregnancy and delivery were normal for
  experimental guinea pigs that mated

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Results (Donovan Kopriva, 1965)

• Electrically Stimulated Guinea Pigs
• No significant difference in cycle lengths
  between electrically stimulated groups and
  control groups

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Conclusions (Donovan Kopriva, 1965)

• Olfactory bulbs
• not needed for estrus cycling in the Guinea pig
• contradicts findings from earlier experiment on
  the pig
• could be necessary for inducing mating behaviors

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Introduction (Horton Shepherd, 1978)

• Subject the Prairie vole (Microtus ochrogaster
  ochrogaster).
• Reflex ovulators
• estrus in females induced by male odors
• Hypothesis
• estrus induction in M. o. ochrgaster is dependent
  on intact olfactory bulbs.

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Methods (Horton Shepherd, 1978)

• Groups under study
• Intact (IC)
• Sham-operated (SC)
• Partially bulbectomized (PB)
• Completely bulbectomized (CB)
• Estrus cycling indicated by lordosis

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Results (Horton Shepherd, 1978)

• No significant differences
• in lordosis and pregnancy between IC and SC
• in lordosis and pregnancy between PB and SC
• Significant reduction in lordosis and pregnancy
• CB vs IC, CB vs SC, and CB vs PB

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Conclusions (Horton Shepherd, 1978)

• Estrus induction in M. o. ochrogaster depends on
  olfactory stimuli
• Still in question
• 4 pregnant CB females that did not show lordosis
• the effects of partial bulbectomy

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Introduction (Lumia et al., 1987)

• Subject male rats
• Hypothesis
• Bulbectomy will reduce androgen receptor levels
  in limbic structures
• amygdala
• hypothalamus
• preoptic area
• septum
• Decreased androgen receptor binding will be
  correlated with reduced masculine copulatory
  behavior

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Methods (Lumia et al., 1987)

• 2 groups of sexually experienced male rats
• Bulbectomized
• Sham operated
• Measured
• copulatory behavior (achieving gt 2 ejaculations)
• concentrations of cell nuclear androgen binding
  in limbic structures

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Results (Lumia et al., 1987)

• Bulbectomy significantly reduced percentage of
  sexually experienced males that achieved
  ejaculation
• P lt 0.007
• P lt 0.009
• P lt 0.001
• P lt 0.004

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Results (Lumia et al., 1987)

• Bulbectomy significantly reduced concentrations
  of androgen-receptor binding in amygdala and
  hypothalamus
• P lt 0.05
• P lt 0.025

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Conclusion (Lumia et al., 1987)

• Olfactory and limbic structures
• important in modulating androgen receptor
  interactions
• Bulbectomy
• reduces androgen receptor binding
• impairs sexual behavior in male rats

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Overall Conclusions

• Female Rodents
• Olfactory Bulbs
• needed for estrus cycling and mating behavior
• importance may vary between species of rodents
• Male Rodents
• Olfactory Bulbs and Limbic Structures
• needed for androgen-binding at receptors
• affects mating behavior

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Questions Comments?