Neural and endocrine control of mating behavior in selected mating lines of chickens and quail

Several physiological systems generally known to be involved in the control of sexual behavior were studied in lines of chickens and quail genetically selected for high (HML) and low (LML) cumulative number of completed matings (CNCM).

In the initial experiment, discrete bilateral lesions were stereotaxically placed in the ruber nuclei of LML cocks. Contrary to published results, the LML cocks did not demonstrate an increase in mating behavior, but rather, the lesions caused a significant reduction in mating activity. Body weight and body temperature of the birds were not affected by the lesions, but blood packed cell volumes did increase significantly.

In the second experiment, LML cocks, as well as control Athens Canadian Randombred (AC) cocks, were utilized to study the effects of brain serotonin depletion on mating behavior in birds. Parachlorophenylalanine (PCPA) was employed for this purpose. Both the LML and the AC birds receiving PCPA showed significantly less mating activity than the birds receiving saline. However, drug toxicity may have influenced the results obtained.

The aromatization of androgens to estrogens and the effect on mating behavior was studied in a third experiment utilizing high and low mating line quail. Both testosterone propionate (TP) and estradiol benzoate (EB) precipitated mating behavior in HML quail in two different testing situations, whereas dihydrotestosterone was ineffective in this respect. In the LML quail, only EB was effective in eliciting mating behavior, and then only in the mating situation where aggressive behavior was not prerequisite (i.e. with a female model).

This experiment was repeated using replicated selected high and low mating lines of quail and a lower hormone dosage. The LML birds failed to respond to any of the treatments when the hormones were decreased. Birds from both of the replicate HML's responded to testosterone propionate; when presented with live females, but only one of the replicate lines (HML₂) receiving TP responded to the female model. Also, one of the replicate lines (HML₁) receiving EB exhibited mating behavior with live females, but not when exposed to the female model.

In the fourth experiment, the effects of exogenous hormones on the testes of the mating line quail was studied. Estradiol benzoate was found to cause complete regression on the gonads, while the administration of testosterone propionate resulted in a partial regression of the gonads. Dihydrotestosterone did not have a significant effect on the weight of the testes, but it did cause a significant increase in the diameter of the seminiferous tubules relative to vehicle controls.

In an attempt to increase the accuracy of stereotaxic surgery, the spatial relationships between several external cranial landmarks and brain nuclei were established. The data were employed to develop a multiple regression predictive equation. The utilization of three independent variables (external measurements) in the regression equation was found not to be significantly better than the usage of a single independent variable measurement, earbar-bregma distance.