Biology subjects

Poulos, A. M.

Publications and source records attributed to Poulos, A. M..

4 recordsLinked to original sources

bioRxiv2026

Sex-Specific Development in the Persistence of Stress-Induced Enhancement of Fear Learning in Juvenile and Adult Rats

It is estimated that approximately fifty percent of the population will encounter at least one traumatic event during their lifetime; however, only six percent develop Posttraumatic Stress Disorder (PTSD), a trauma-related disorder characterized by persistent alterations in affect and cognition, including an exaggerated fear response. It is well established that females (9.7%) are more than twice as likely as males (3.6%) to be diagnosed with PTSD. Nevertheless, a significant challenge remains in understanding how the severity of traumas experienced in childhood versus adulthood influences PTSD development across sexes. To address this challenge effectively, the adoption of preclinical animal models that accurately reflect these key characteristics is crucial. The Stress Enhanced Fear Learning (SEFL) paradigm in rodents encapsulates some of these complexities associated with PTSD, such as persistent fear sensitization following exposure to acute trauma. This study investigates how stress severity and developmental timing affect the long-term maintenance of SEFL in male and female rats. Juvenile and adult rats were initially subjected to no stress (control, context only), low stress (1 footshock), moderate stress (3 footshocks), or high stress (15 footshocks), followed by an extinction session either one day (recent) or sixty days (remote) later. Subsequently, to evaluate SEFL in a new context, all subjects received a single footshock and were tested the following day. Shortly after stress induction, all groups displayed SEFL. Although the effects persisted for sixty days in adult males and juvenile females, even at the lowest stress level, they were significantly reduced in juvenile males and adult females. These findings offer novel insights into sex-related differences in the persistence of SEFL and introduce new considerations regarding how the timing of developmental stressors influences future threat encoding and fear responses.

animal behavior and cognition↗

bioRxiv2025

Importance of Apparatus Scaling in Novel Object Recognition for Juvenile and Adult Rats.

The growing interest in ontogenetic studies of learning and memory, along with early-life perturbations, has led to the use of younger rodents as a key biological variable in many investigations. This development prompts an important question about whether procedures and apparatuses designed for studying learning and memory in adults should be simply adapted for use with younger and smaller rodents. The current study examined how arena size affects novel object recognition (NOR) performance in juvenile and adult rats. A commonly used larger arena reliably detected novel object preference in adults but not in juveniles. Adjusting the arena size based on average weight differences between age groups improved the consistency of NOR performance in juvenile rats. Sex differences were observed: adult males performed reliably across all arena sizes, whereas adult females required larger arenas to demonstrate effective NOR performance. These findings highlight the importance of tailoring arena dimensions to developmental stage and sex for accurate cognitive assessment. Specifically, they support the use of weight-based arena scaling as a methodological approach in developmental neurobehavioral research and emphasize the importance of careful design when studying female rodents. Future studies should explore similar environmental adjustments for other behavioral tests in juvenile and female populations.

animal behavior and cognition↗

bioRxiv2022

Retrieval and Savings of Contextual Fear Memories Across an Extended Retention Interval in Juvenile and Adult Male and Female Rats

Adult rodents exhibit an exceptional ability to retrieve context fear memories across lengthy retention intervals. In contrast, these same memories established in juvenile rodents are susceptible to significant forgetting. While much of this original work has focused on male rodents, emerging research indicates that the mechanisms of context fear conditioning in females may be sexually dimorphic. If so, these female memories may exhibit a unique mnemonic profile from male rats that may be probed using single-trial conditioning, extended retention intervals, and savings procedures. The current study aimed to examine the longevity of contextual fear memories established in 24-day-old juvenile and 90-day-old Long-Evans male and female rats. Testing at the 1-day retention interval, adults exhibited greater conditioning than juvenile males, while in females, conditioning did not differ between juvenile and adult rats. In adults, males displayed greater conditioning than females, while in juveniles, males and females reached similar conditioning levels. At the 60-day retention interval, adult sex differences were maintained; however, juvenile rats failed to retrieve this remote contextual fear memory. Next, we examined whether a savings trial and test procedure could recover these remotely established juvenile memories in both males and females. Following a 60-day retention test, the now adult rats were presented with an additional context-shock pairing to assess the level of saving in both male and female rats. While this procedure produced greater conditioning in males than females, the relative amounts of the savings of this early life memory were similar in males and females. Lastly, the recovery of this memory exhibited significant generalization relative to previously unshocked juveniles and was similar in males and females. The results of these experiments indicate that adult sex differences in contextual fear memory are maintained across an extended retention interval, while in juveniles, there were no significant sex differences. In addition, male and female rats failed to retrieve an initial juvenile memory at an extended retention interval. However, these memories could be recovered with a single reminder of the original juvenile experience.

animal behavior and cognition↗

bioRxiv2022

Contributions of Gonadal Hormones in the Sex-Specific Organization of Context Fear Learning

It is widely established that gonadal hormones are fundamental to modulating and organizing the sex-specific nature of reproductive-related behaviors. Recently we proposed that context fear conditioning may emerge in a sex-specific manner organized prior to the pubertal surge of gonadal hormones. Here we sought to determine the necessity of male and female gonadal hormones secreted at critical periods of development upon context fear learning. We tested the organizational hypothesis that perinatal and pubertal gonadal hormones play a permanent role in organizing contextual fear learning. We demonstrate that the life-long absence of gonadal hormones by perinatal orchiectomy (oRX) in males and ovariectomy (oVX) in females resulted in a reduction of CFC in adult males and an enhancement of CFC in adult females. In females, the gradual introduction of estrogen before conditioning partially rescued this effect. However, the decrease of CFC in adult males was not rescued by introducing testosterone before conditioning. Next, at a further point in development, preventing the pubertal surge of gonadal hormones by prepubertal oRX in males resulted in a reduction in adult CFC. In contrast, in females, prepubertal oVX did not alter adult CFC. However, the adult introduction of estrogen in prepubertal oVX rats reduced adult CFC. Lastly, the adult-specific deletion of gonadal hormones by adult oRX or oVX alone or replacement of testosterone or estrogen did not alter CFC. Consistent with our hypothesis, we provide initial evidence that gonadal hormones at early periods of development exert a vital role in the organization and development of CFC in male and female rats.

animal behavior and cognition↗