Olfactory bulb removal and its effects on reproduction in rodents

1. Olfactory bulb removal and its effects on reproduction in rodents Andrew Clark Eco/Evo 208 November 10, 2004

2. 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

3. Olfactory Bulbectomy Studies include effects on: anosmia hormones circadian rhythms aggression activity learning development maternal behavior thermoregulation heart rate sexual behavior & physiology

4. 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

5. 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

6. 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.

7. 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.

8. 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

9. 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

10. 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

11. Results (Donovan & Kopriva, 1965) Electrically Stimulated Guinea Pigs: No significant difference in cycle lengths between electrically stimulated groups and control groups

12. 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

13. 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.

14. Methods (Horton & Shepherd, 1978) Groups under study: Intact (IC) Sham-operated (SC) Partially bulbectomized (PB) Completely bulbectomized (CB) Estrus cycling indicated by lordosis

15. 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

16. 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

17. 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

18. 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

19. 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

20. Results (Lumia et al., 1987) Bulbectomy significantly reduced concentrations of androgen-receptor binding in amygdala and hypothalamus * = P < 0.05 ** = P < 0.025

21. 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

22. 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

23. Questions & Comments?