Changes in Action Potential Properties in the Ferret Prefrontal Cortex During Adolescence

Ferrets have a gyrencephalic brain with an organization that resembles more to humans than rodents. This animal model has been used in studies of visual cortex development and plasticity, sensory processing, multisensory integration, traumatic brain injury, and decision making. Surprisingly, there is no convention of what defines adulthood in the ferret. Studies have considered ferret adulthood as early as P90 and as late as 2 years. Adolescence is a period of development characterized by physical maturation, risk-taking behavior, and impulsivity. Although physical maturation, including puberty, co-occurs with adolescence, they do not indicate when adulthood is reached. For instance, although puberty in humans is completed by 16-17 years of age, the human brain continues to mature until approximately 23-25 years of age with the prefrontal cortex (PFC) maturing latest. Therefore, the functional maturation of the PFC is proposed to act as a marker of the conversion between adolescence and adulthood. We conducted whole-cell patch clamp of pyramidal neurons (PNs) in Layer 5 from acute slices from the prelimbic cortex portion of ferret medial PFC at three different ages after puberty (P120, P180, and P220). Injected current-firing curves indicate that the amount of current needed to elicit the same number of action potentials (APs) increases between P120 and P220. In addition, we observed an increase in sag amplitude that was accompanied by a reduction in rheobase. Our findings show that excitability of PNs in this region changes between the ages investigated, which suggests that ferret PFC does not mature before P220.