Biology subjects

Vercammen, L.

Publications and source records attributed to Vercammen, L..

5 recordsLinked to original sources

bioRxiv2025

Pharmacological blockade of opioid receptors in the ventrolateral periaqueductal gray does not affect avoidance acquisition or performance in rats

Avoidance learning involves associating a behavioral response with the omission of an expected threat, but the neural mechanisms that drive this learning remain unclear. Research on fear extinction points to a critical role for opioid receptors in the ventrolateral periaqueductal gray (vlPAG) in computing the aversive prediction error signal that is generated when there is a difference between expected and actual aversive events. Based on these fear extinction findings, we hypothesized that vlPAG opioid signaling might also support the early stages of avoidance learning. To test this, 15 Wistar rats (7 females, 8 males) received intra-vlPAG infusions of either naloxone hydrochloride (n = 7, 2.5 g/0.5 l), a non-selective opioid receptor antagonist, or vehicle (n = 8, 0.5 l), immediately before the first and second session of two-way active avoidance training. No infusions were given before the third session, to examine avoidance performance under continued, drug-free acquisition. For the fourth and final session, drug conditions were reversed to examine the acute effect of naloxone on already established avoidance performance. Our results indicate that unilateral intra-vlPAG naloxone, at the tested dose and timing, did not significantly impair avoidance acquisition, nor its performance. These findings do not support a role for opioid signaling in the vlPAG during the initial learning or expression of two-way active avoidance.

animal behavior and cognition↗

bioRxiv2025

The rewarding properties of safety signals established by a two-way active avoidance task in male rats

Actively avoiding threatening stimuli or situations is an adaptive defensive strategy that minimizes the risk of potential harm. Despite the prominent role avoidance plays in our daily lives, the mechanisms that reinforce avoidance behavior remain incompletely understood. Accumulating evidence implicates the mesolimbic dopamine reward system in the acquisition of avoidance, suggesting that the omission of an aversive event may acquire rewarding properties and function as a positive reinforcer of avoidance behavior. In a series of six experiments (N = 246 male Wistar rats), we examined whether safety signals that coincide with successful avoidance responses in a two-way active avoidance (2WAA) task facilitate avoidance acquisition and acquire reward-like properties, by assessing whether they elicit approach behavior and support the acquisition of a novel instrumental response. Although the presentation of a safety signal accelerated avoidance learning in some experiments, the effect was not consistent. Furthermore, the safety signal neither elicited approach behavior nor supported the acquisition of a novel instrumental response. Together, these findings question whether safety signals in avoidance learning acquire rewarding properties detectable through behavioral measures.

animal behavior and cognition↗

bioRxiv2025

Differential effects of chronic restraint stress on two active avoidance tasks in rats

Although avoidance can serve an adaptive function in daily life, excessive or persistent avoidance can form a debilitating symptom of anxiety-related disorders. The transition from adaptive to maladaptive avoidance remains poorly understood, but stress is a potential contributing factor. We investigated the effects of chronic restraint stress on two active avoidance procedures: two-way active avoidance (2WAA) and platform-mediated avoidance (PMA). Whereas 2WAA entails a low-cost response, avoidance in the PMA task comes with a cost, i.e., no access to food. We hypothesized that chronic restraint stress would hinder avoidance acquisition in the 2WAA task, but increase avoidance acquisition in the PMA task. In two experiments, male and female rats underwent either chronic restraint stress or a control procedure. In Experiment 1, all rats (N = 31) were then trained in a 2WAA acquisition and extinction procedure, in two contexts. Stressed rats showed significantly reduced avoidance acquisition, while extinction was unaffected. In Experiment 2 (N = 32), stressed rats and controls were trained in a PMA acquisition and extinction procedure. Contrary to our hypothesis, we did not find effects on avoidance acquisition, although we found group and sex differences in lever press suppression. All rats gradually extinguished defensive behaviors during extinction. Overall, chronic restraint stress had limited effects on PMA, but significantly impaired avoidance acquisition in the 2WAA task without affecting its extinction. These divergent effects may relate to differences in response cost or differences in safety of the context (i.e., a permanent safe area in PMA, but not in 2WAA). HighlightsO_LIChronic restraint stress impaired acquisition of two-way active avoidance C_LIO_LIChronic restraint stress did not impact acquisition of platform-mediated avoidance C_LIO_LIChronic restraint stress did not impact extinction of avoidance in either task C_LIO_LIMinor sex differences were observed across both tasks C_LI

animal behavior and cognition↗

bioRxiv2024

The impact of systemic blockade of dopamine receptors on the acquisition of two-way active avoidance in rats.

Active threat avoidance is a core aspect of adaptive and maladaptive behavior, yet its underlying mechanisms are not fully understood. Prior studies concluded that pharmacologically blocking dopaminergic receptors (DRs) disrupted avoidance acquisition, but it remains unclear whether such effects on learning persist during a drug-free follow-up test. To assess the involvement of D1R and D2R in avoidance acquisition, we conducted two experiments. In Experiment 1, thirty-six male Wistar rats underwent a single avoidance training session involving 30 tone-shock pairings. Rats could avoid the shock by moving to the opposite compartment of the shuttle box. Twenty minutes before training, rats received either D1R antagonist SCH 23390 (0.05 mg/kg), D2R antagonist sulpiride (20 mg/kg), or vehicle. While sulpiride did not affect avoidance, 0.05 mg/kg SCH 23390 significantly reduced the number of avoidance responses. In a separate test, 0.05 mg/kg SCH 23390 also reduced locomotor activity. In Experiment 2 (N = 24), a lower dose of SCH 23390 (0.025 mg/kg) was administered, and a drug-free avoidance test under continued reinforcement was added 24 hours later to test for sustained effects of D1R blockade on avoidance in the absence of acute drug effects. Although animals avoided less with SCH 23390 in the system, this effect did not persist 24 hours later, suggesting that effects of D1R blockade during avoidance training might reflect an acute disruption of secondary processes involved in the performance of avoidance behavior rather than an actual impairment of avoidance learning.

animal behavior and cognition↗

bioRxiv2022

No evidence that post-training D2R dopaminergic drug administration affects differential fear responding in rats

The neurotransmitter dopamine plays an important role in the processing of emotional memories, and prior research suggests that dopaminergic manipulations immediately after fear learning can affect the retention and generalization of acquired fear. The current study focuses specifically on the role of dopamine D2 receptors (D2Rs) in adult, male Wistar rats. In a series of five experiments, D2R (ant)agonists were injected systemically immediately after differential cued fear conditioning (CS+ followed by shock, CS- without shock). All five experiments involved the administration of the D2R agonist quinpirole at different doses versus saline (n = 12, 16 or 44 rats/group). Additionally, one of the studies administered the D2R antagonist raclopride (n = 12). One day later, freezing during the CS+ and CS- was assessed. We found no indications for an effect of quinpirole or raclopride on fear generalization during this drug-free test. Importantly, and contradicting prior research in mice, the evidence for the absence of an effect of quinpirole (1 mg/kg) on fear generalization was substantial according to Bayesian analyses and was observed in a highly powered experiment (N = 87). We did find acute behavioral effects in line with the literature, for both quinpirole and raclopride in a locomotor activity test.

neuroscience↗