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. 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 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


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


Olfactory Bulbectomy

  • Studies include effects on:

    • anosmia

    • hormones

    • circadian rhythms

    • aggression

    • activity

    • learning

    • development

    • maternal behavior

    • thermoregulation

    • heart rate

    • sexual behavior & physiology

(Brunjes, 1992)


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


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)


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.


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.


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


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


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


Results (Donovan & Kopriva, 1965)

  • Electrically Stimulated Guinea Pigs:

    • No significant difference in cycle lengths between electrically stimulated groups and control groups


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


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.


Methods (Horton & Shepherd, 1978)

  • Groups under study:

    • Intact (IC)

    • Sham-operated (SC)

    • Partially bulbectomized (PB)

    • Completely bulbectomized (CB)

  • Estrus cycling indicated by lordosis


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


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


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


Methods (Lumia et al., 1987)

  • 2 groups of sexually experienced male rats:

    • Bulbectomized

    • Sham operated

  • Measured:

    • copulatory behavior (achieving > 2 ejaculations)

    • concentrations of cell nuclear androgen binding in limbic structures


Results (Lumia et al., 1987)

  • Bulbectomy significantly reduced percentage of sexually experienced males that achieved ejaculation

    • * = P < 0.007

    • ** = P < 0.009

    • *** = P < 0.001

    • **** = P < 0.004


Results (Lumia et al., 1987)

  • Bulbectomy significantly reduced concentrations of androgen-receptor binding in amygdala and hypothalamus

    • * = P < 0.05

    • ** = P < 0.025


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


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


Questions & Comments?


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