Sequential Photoperiodic Programing of Serotonin Neurons, Signaling and Behaviors During Prenatal and Postnatal...

Area of Science:

• Neuroscience
• Developmental Biology
• Behavioral Science

Background:

• Early life environmental stimuli critically influence neurodevelopment.
• The brain's serotonergic system, vital for mood regulation, is sensitive to photoperiod (daylight duration).
• Neurodevelopmental disorders are linked to early life disruptions.

Purpose of the Study:

• To investigate sensitive developmental periods for photoperiodic programming of serotonin neurons and behavior.
• To determine the distinct roles of prenatal versus postnatal photoperiod exposure.
• To understand the sequential programming of neuronal excitability, serotonin levels, and affective behaviors.

Main Methods:

• Mice were exposed to long (LD 16:8) or short (LD 8:16) photoperiods during specific prenatal or postnatal windows.
• Examined dorsal raphe nucleus (DRN) serotonin neuron excitability, midbrain serotonin/metabolite levels, and affective behaviors at P30 and P50.
• Compared effects of prenatal-only, postnatal-only, and continuous photoperiod exposures.

Main Results:

• Prenatal exposure to long photoperiods alone programmed increased DRN serotonin neuron excitability, persisting into adulthood.
• Long photoperiod exposure elevated serotonin and metabolite levels and reduced depressive-like behaviors.
• Prenatal programming of excitability was necessary but insufficient for behavioral and signaling changes; postnatal exposure was required.

Conclusions:

• Photoperiodic programming of serotonin function is a sequential process.
• Prenatal photoperiod exposure establishes neuronal excitability, a foundational step.
• Postnatal photoperiod exposure further modulates serotonin signaling and affective behaviors, conferring protective effects against depressive-like behaviors.