What is the precise trigger for a cat to go into heat or come out of it? I understand the basics. What I am looking for specifically is the physiological reactions and brain chemistry changes. Does anyone know this or know where I can find it?

The precise trigger is most likely the photoperiod...the ratio of light to darkness at different times of the year...there will be a time when this ratio is just right and synchronizes the species mating responses to occur more or less simultaneously. I think the Pineal Gland in the brain plays a part and ultimately responds to the increasing duration of light signals originating from the optical system by reducing production of melatonin which triggers the hormonal sequence that initiates the mating urge.

 

This little article should put you on the right track:

 

http://www.ehow.com/about_5153051_effects-melatonin-reproductive-functions.html

 

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