12–16 week old male Long Evans rats (HsdBlu:LE – Envigo, USA) were used as residents. To encourage territoriality, each male resident was housed in a large cage (80*50*40 cm) with an ovariectomized female Long Evans rat that underwent tubal ligation for at least one week before the screening. The screening consisted of measuring attack latency and submission time in RSD sessions on five consecutive days to select rats displaying the desired aggressive behavior and exclude rats showing signs of violence (attack latency <10 s and attempts to kill the intruder by attacking vital zones), or non-aggressive behavior (attack latency>60s, absence of submission or submission time >120s, or the resident being submitted) (Moraga-Amaro et al., 2022 (link)).
The RSD protocol was performed between 1 and 4 p.m. Female Long Evans rats were removed from the resident cages 1 h before the exposure of the experimental rat. The session lasted 1 h and started with the introduction of the experimental rat in the cage of the resident, after which they were allowed to interact until the experimental rat showed a submissive posture for at least 5 s or after 10 min of interaction. Subsequently, the experimental rat was placed inside a wire mesh cage and put back in the cage of the resident to allow for visual, auditory, and olfactory interactions for the remainder of the 1 h. The experimental rat was exposed to five different residents for five consecutive days. Control rats were placed in a wire mesh cage inside a clean cage for a duration of 1 h.
RSDjuv and RSDadu rats were individually housed during the RSD protocol and the period thereafter during which the behavioral tests and PET scan took place, i.e. on day 35–46 and day 63–74, respectively, as social interaction during group housing can counteract the effect of social defeat. The control group remained housed in pairs during the RSD protocols. Hereafter the rats were group housed again.
The RSD protocol was performed between 1 and 4 p.m. Female Long Evans rats were removed from the resident cages 1 h before the exposure of the experimental rat. The session lasted 1 h and started with the introduction of the experimental rat in the cage of the resident, after which they were allowed to interact until the experimental rat showed a submissive posture for at least 5 s or after 10 min of interaction. Subsequently, the experimental rat was placed inside a wire mesh cage and put back in the cage of the resident to allow for visual, auditory, and olfactory interactions for the remainder of the 1 h. The experimental rat was exposed to five different residents for five consecutive days. Control rats were placed in a wire mesh cage inside a clean cage for a duration of 1 h.
RSDjuv and RSDadu rats were individually housed during the RSD protocol and the period thereafter during which the behavioral tests and PET scan took place, i.e. on day 35–46 and day 63–74, respectively, as social interaction during group housing can counteract the effect of social defeat. The control group remained housed in pairs during the RSD protocols. Hereafter the rats were group housed again.
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