Neurons and Hormones 3

Transcription

1 Neurons and Hormones 3 Neural Command Centers Behavioral Schedules Daily rhythms: internal and external factors Long-term rhythms: internal and external factors Priorities & the Social Environment Hormones & reproductive behavior Hormones & aggressive behavior

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3 Hormones & reproductive behavior Animals often show a positive correlation between reproductive behavior and gonadal hormones: associated reproductive pattern e.g., Green anole, Guinea pig, Japanese quail But sometimes not (dissociated reproductive pattern) e.g., Red-sided garter snake

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5 Effects of castration & testosterone therapy on male guinea pigs

6 Testosterone (T) is converted to estradiol by brain aromatase Japanese quail Male will peer through window at female Removal of testes eliminates sexual interest in female T treatment restores interest in female In general, many effects of T on behavior are mediated by aromatase in brain What about sexual behavior in quail?

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8 Male red-sided garter snakes emerging from hibernation are ready to mate Southern Manitoba - largest concentration of snakes in the world. In excess of 50,000 snakes congregate at dens under ground The dens are a network of crevasses and caverns It is only by amassing below the frost line that the snakes are able to survive the harsh Manitoba winters. Males emerge before females

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10 Dissociated reproduction in the red-sided garter snake Male garter snakes have high levels of T in the blood and sperm production before going into hibernation (autumn) BUT very low levels of T in blood when they emerge and during mating (spring) What happens if you remove testes after males emerge from hibernation in spring (right before females emerge)? What about long-term effects of castration (captive snakes in lab)?

11 Castration will reduce the sexual behavior in spring if the male is castrated before the previous autumn s rise in T. T might prime the necessary circuits before hibernation

12 Outline Neural Command Centers Behavioral Schedules Daily rhythms: internal and external factors Long-term rhythms: internal and external factors Priorities & the Social Environment Hormones & reproductive behavior Hormones & aggressive behavior

13 Testosterone and aggression From studies on birds, John Wingfield proposed that the relationship between T and aggression is dependent upon social context. Correlations between T and aggression are found during periods of social instability (but not social stability) This is called the Challenge Hypothesis Can look at T levels in a variety of species which differ in patterns of male-male interaction Birds: greatest diversity of social structures, easily observed and captured in the field

14 Captive white-crowned sparrows (WCSP) Male WCSP were castrated and given either T implants or empty implants (controls). The birds were housed together for 6 months and no relationship between aggression and T was observed. But this was a stable environment. When a new male was introduced, aggression went up much more in the T-implanted males.

15 Wild song sparrows during the breeding season Removal studies. Replacement males have higher levels of T than controls (no removal) Neighbors of a T-implanted male have to deal with his persistent aggression - and their T levels rise as a result. Simulated territorial intrusion (decoy male and song playback) elevates T levels in territory owner

16 Arctic latitude Tropics

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18 Song sparrows In males, robust territorial aggression yearround, except during molt During non-breeding season, the testes are completely regressed

19 No clear role for gonads in autumn In autumn, plasma T and estradiol levels are non-detectable (plasma = blood without the cells) In autumn, no effect of castration on territorial behavior Dissociated pattern of aggressive behavior as with the reproductive behavior of red-sided garter snakes A role for non-gonadal hormones in autumn?

20 Aromatase in song sparrow brain Catalyzes conversion of androgens to estrogens Aromatase mrna is present in male song sparrow brain in autumn

21 Effect of aromatase inhibitor in autumn

22 DHEA In humans, DHEA is inert & secreted by adrenals & converted into active sex steroids (T and estradiol) within target tissues

23 Plasma DHEA in male song sparrows in autumn

24 Periphery Brain T T E 2 testis adrenal gland DHEA DHEA T E 2