The role of the medial prefrontal cortex in innate fear regulation in XXXX , juveniles, and adolescents.

@entity1 @entity1639 @entity1246 @entity35
In adult animals, the medial prefrontal cortex (mPFC) plays a significant role in regulating emotions and projects to the amygdala and periaqueductal gray (PAG) to modulate emotional responses. However, little is known about the development of this neural circuit and its relevance to unlearned fear in pre-adulthood. To address these issues, we examined the mPFC of 14-d-old ( @entity1 ), 26-d-old (juveniles), and 38- to 42-d-old (adolescents) @entity35 to represent different developmental and social milestones. The expression patterns of the neuronal marker @entity1639 were used to assess neurological activity. Muscimol, a @entity1246 agonist, was used to inactivate the prelimbic and infralimbic mPFC subdivisions (400 ng in 200 nl). Animals were exposed to either a threatening or nonthreatening stimulus that was ecologically relevant and age specific. Freezing was measured as an indicator of innate fear behavior. The data indicated that the mPFC is neither active nor responsive to innate fear in @entity1 @entity35 . In juveniles, the prelimbic mPFC became responsive in processing aversive sensory stimulation but did not regulate freezing behavior. Finally, during adolescence, inactivation of the prelimbic mPFC significantly attenuated freezing and decreased @entity1639 expression in the ventral PAG. Surprisingly, across all ages, there were no significant differences in @entity1639 levels in the medial and basolateral/lateral amygdala when either mPFC subdivision was inactivated. Together, unlearned fear has a unique developmental course with different brain areas involved in unlearned fear in the immature animal than the adult. In particular, the mPFC neural circuitry is different in young animals and progressively develops more capacities as the animal matures.
