Biology subjects

Quillfeldt, J. A.

Publications and source records attributed to Quillfeldt, J. A..

3 recordsLinked to original sources

bioRxiv2024

Multiple context discrimination in adult rats: sex variability and dynamics of time-dependent generalization of an aversive memory

Memory generalization involves the transfer of conditioned fear responses to novel contexts, a phenomenon observed in systems consolidation, whereby a time-dependent reduction in discrimination precision occurs due to the reorganization of brain regions supporting memory retrieval. To understand the fine temporal structure of this process across sexes, young adult female and male rats were trained in contextual fear conditioning and tested in the same or one of three distinct novel contexts at 2, 28 or 45 days post-training. Neutral contexts were designed to allow graded levels of fear expression relative to the training context, and sex differences were evident at the recent memory test. This pattern, however, disappeared over time due to partial generalization, with fear converging into similar, higher values, grouped into two levels for both sexes. In all experiments, females were better discriminators and displayed lower fear responses than males, apparently prioritizing different sensory modalities, with multivariate analysis suggesting that chamber size was salient for females and floor texture for males. This study is the first to compare fear responses between adult female and male rats across multiple neutral contexts and timepoints revealing several dimorphic findings.

neuroscience↗

bioRxiv2020

Conflict-mediated tasks for studying the act of facing threats in pursuit of rewards

Survival depends on the ability of animals to avoid threats and approach rewards. Traditionally, these two opposing motivational systems have been studied separately. In nature, however, they regularly occur simultaneously. When threat- and reward-eliciting stimuli (learned or unlearned) co-occur, a motivational conflict emerges that challenges individuals to weigh available options and execute a single behavioral response (avoid or approach). Previous animal models using approach-avoidance conflicts have often focused on the ability to avoid threats by forgoing the opportunity to obtain rewards. In contrast, behavioral tasks designed to capitalize on the ability to actively choose to execute approach behaviors despite threats are lacking. Thus, we developed three conflict-mediated tasks to directly study rats confronting threats to obtain rewards guided by innate and conditioned cues. One conflict task involves crossing a potentially electrified grid to obtain food on the opposite end of a straight alley, the second task is based on the step-down threat avoidance paradigm, and the third one is a modified version of the open field test. We used diazepam to pharmacologically validate conflict-mediated behaviors in our tasks. We found that, regardless of whether competing stimuli were conditioned or innate, a low diazepam dose facilitated taking action to obtain rewards in the face of threats during conflict, without affecting choice behavior when there was no conflict involved. Using this validated set of innate/learned conflict-mediated tasks could help understand the underlying brain mechanisms that allow animals to confront threats, by actively suppressing defensive responses, to achieve goals.

neuroscience↗

bioRxiv2020

Time-course of systems consolidation and fear memory generalization in adolescent rats of different sex

Generalization is an adaptive process that allows animals to deal with threatening circumstances similar to prior experiences. Systems consolidation is a time-dependent process in which memory loses it precision concomitantly with reorganizational changes in the brain structures that support memory retrieval. In this, memory becomes progressively independent from the hippocampus and more reliant on cortical structures. Generalization, however, may take place much faster in adult animals depending on the presence of sex hormones. Notwithstanding its relevance, there are few studies on sex differences in memory modulation. Here, a contextual fear discrimination task was used to investigate the onset of memory generalization and hippocampus-independence in adolescent male and female rats (P42-49). Subjects were tested 2, 7, 14, 21 or 28 days after training, with females showing memory generalization from day 21 on, whereas males surprisingly unable to discriminate contexts at any time. Ovariectomized females, however, displayed an early onset of generalization. Consistently, pre-test pharmacological blocking of dorsal hippocampus was able to impair memory retrieval in females, but not in males, which indicate that precise memory is dependent on the hippocampus. To our notice, this is the first report of a memory systems consolidation process - expressed in its two dimensions, neuroanatomical and qualitative - in adolescent female rats, and one that can also be accelerated by the reduction of sex hormones through ovariectomy. It is also unprecedented that despite adolescent male rats being able to remember fear learning, they did not discriminate contexts with any precision.

neuroscience↗