The Premammillary Nucleus of the Hypothalamus Is Not Necessary for Photoperiodic Timekeeping in Female Turkeys (\u3cem\u3eMeleagris gallopavo\u3c/em\u3e)

In birds, seasonal reproduction is regulated by day length, with long days in the spring activating the hypothalamic-pituitary-gonadal axis and reproductive behaviors. The photoreceptors mediating this process remain unknown, but recently, the premammillary nucleus (PMM) of the hypothalamus has been implicated as the site of photoperiodic signaling in turkeys. We performed electrolytic lesions of the PMM to elucidate its role in the photoactivation and maintenance of egg production in female turkeys. Our results show that ablation of the PMM does not alter the normal lay cycle. No differences were found between lesioned birds and sham controls in the latency to lay following photostimulation, nor in subsequent egg production over a period of 29 weeks. No differences in the incidence of gonadal regression were found, indicating that the PMM is not essential for the termination of breeding. We conclude that any role of the PMM in photoperiodic regulation, if it exists, is redundant with other components of the system

Negative binomial regression analysis of lay latency as a function of lesion category.

<p>Negative binomial regression analysis of lay latency as a function of lesion category.</p

Hypothesis tests for main effects and differences between lesion categories following negative binomial regression analysis of weekly egg production over time.

<p>Hypothesis tests for main effects and differences between lesion categories following negative binomial regression analysis of weekly egg production over time.</p

Negative binomial regression analysis of total egg production as a function of lesion category.

<p>Negative binomial regression analysis of total egg production as a function of lesion category.</p

Egg production curves are not affected by PMM lesion.

<p>The mean weekly egg production for each group is plotted over time (in weeks). S group = blue; U group = red.</p

Weekly egg production is not affected by PMM lesion.

<p>Plots show the individual means (diamonds) for weekly egg production over the duration of the study. Group means are indicated by horizontal lines. S group = blue; U group = red.</p

PMM lesions.

<p>Thionin-stained coronal sections of the hypothalamus show the PMM area of representative sham (A), lesion (B), and partial lesion (C) birds. The top panels (438x total magnification) show PMM area detail, while the bottom panels (73x total magnification) show general location within the caudal hypothalamus. In the top panels, the red squares demarcate an intact PMM (A) and the remaining PMM cells resulting from a partial lesion (C). The darkly stained material in (B) and (C) is damaged tissue resulting from the lesion.</p