Effects of progesterone on male-mediated infant-directed aggression

Area of Science:

• Neuroscience
• Behavioral Biology
• Endocrinology

Background:

• Parental behavior and infanticide are observed in many species.
• The neural regulation of transitions between parental care and infanticide is not well understood.
• Progesterone (P) and its receptor (PR) inhibit parental behavior and promote infanticide in male mice.

Purpose of the Study:

• To investigate the mechanisms underlying progesterone's effects on male mouse behavior.
• To test the hypothesis that progesterone withdrawal, similar to female pregnancy, enhances parental behavior in males.
• To determine if progesterone withdrawal triggers the onset of parental behavior in adult male mice.

Main Methods:

• Virgin male mice were administered progesterone (P) or vehicle for 21 days.
• Behavioral tests for parental care and infanticide were conducted 5 days post-treatment.
• Serum levels of P and testosterone (T) were measured at the time of behavioral testing.

Main Results:

• Progesterone treatment increased the proportion of males exhibiting infanticide towards pups.
• Neither parental care initiation nor quality was affected by progesterone treatment.
• Serum P and T levels did not differ between groups, indicating ongoing hormone elevation is not required for infanticide.

Conclusions:

• Progesterone withdrawal does not initiate parental behavior in male mice.
• Prior exposure to progesterone induces persistent infanticidal behavior in adult male mice.
• This suggests a mechanism where prior hormonal exposure, not withdrawal, influences aggressive behaviors.