Medial prefrontal cortex processes threatening stimuli in juvenile rats.

To survive, all mammalian species must recognize and respond appropriately to threatening stimuli. In adults, the prelimbic medial prefrontal cortex (mPFC) appears to be involved in fear expression, whereas the infralimbic mPFC mediates fear extinction. In juvenile rats (PN26), the mPFC receives information on potential predators but does not act on it.

Norepinephrine mediates contextual fear learning and hippocampal pCREB in juvenile rats exposed to predator odor.

Predator odors induce unconditioned fear in the young animal and provide the opportunity to study the mechanisms underlying unlearned and learned fear. In the current study, cat odor produced unlearned, innate fear in infant (postnatal age 14; PN14) and juvenile (PN26) rats, but contextual fear learning occurred only in juveniles. It was hypothesized that contextual fear learning in juveniles is mediated by norepinephrine.

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

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 (infants), 26-d-old (juveniles), and 38- to 42-d-old (adolescents) rats to represent different developmental and social milestones.

Effects of the stimulus and chamber size on unlearned fear across development.

Predator odors have been found to induce unconditioned fear in adult animals and provide the opportunity to study the mechanisms underlying unlearned and learned fear. Predator threats change across an animal's lifetime, as do abilities that enable the animal to learn or engage in different defensive behaviors. Thus, the objective of this study was to determine the combination of factors that successfully induce unlearned fear to predator odor across development.