Complex Housing, but Not Maternal Deprivation Affects Motivation to Liberate a Trapped Cage-Mate in an Operant Rat Task

Abstract

Early life environment influences the development of various aspects of social behavior, particularly during sensitive developmental periods. We studied how challenges in the early postnatal period or (early) adolescence affect pro-social behavior. To this end, we designed a lever-operated liberation task, to be able to measure motivation to liberate a trapped conspecific (by progressively increasing required lever pressing for door-opening). Liberation of the trapped rat resulted either in social contact or in liberation into a separate compartment. Additionally, a condition was tested in which both rats could freely move in two separate compartments and lever pressing resulted in social contact. When partners were not trapped, rats were more motivated to press the lever for opening the door than in either of the trapped configurations. Contrary to our expectations, the trapped configuration resulted in a reduced motivation to act. Early postnatal stress (24 h maternal deprivation on postnatal day 3) did not affect behavior in the liberation task. However, rearing rats from early adolescence onwards in complex housing conditions (Marlau cages) reduced the motivation to door opening, both in the trapped and freely moving conditions, while the motivation for a sucrose reward was not affected.

Male rats emit aversive 44-kHz ultrasonic vocalizations during prolonged Pavlovian fear conditioning

“…On the other hand, 44-kHz calls were likely omitted as the analyses were restricted to canonical groups, i.e. flat 22-kHz and short 50-kHz calls, with a sharp dividing frequency border between the two (e.g., Kalamari et al, 2021, Potasiewicz et al, 2020, Turner et al, 2019) or even a frequency ‘safety gap’ between 22-kHz and 50-kHz vocalizations (e.g., Silkstone and Brudzynski, 2019, Garcia et al, 2015). Moreover – many older bat-detectors had limited frequency-range detection (e.g., up to 40 kHz in Sales, 1991), when stress-evoked types of ultrasonic calls were being established.…”

An opinion on the interpretation of social release in rats

“…In the author's opinion, asserting that pro-social functioning is a correct description of door opening in the social release paradigm does not take into consideration the previously mentioned critical papers (e.g. [11,13,14,20]). This becomes more concerning in their follow-up paper where there is no commentary at all on the controversy concerning why rats release trapped conspecifics [27].…”

“…The authors proposed that opening to release the soaked rat was pro-socially motivated [18], but once again critical voices presented another explanation that did not rely on an inference of empathy [19]. This time Schwartz et al [19] showed that the release of the trapped rat was maintained by '(a) the social contact offered by the released rat, and (b) the reinforcing value of proximity to a pool of water' ( [20], abstract). In other words, both Schwartz et al [19] and Silberberg et al [12] showed the importance of social reinforcement within different variants of the social release paradigm.…”

“…Tomek et al [26] include two of several papers that are critical to rodent empathy (i.e. [14,20]) but state that '… there is no universal agreement as to whether these behaviours are expression of empathy-like or social contact motivated behaviours. Regardless, we assert that such behaviours can be viewed as representative of pro-social functioning' ( [26], p. 682).…”

“…In other words, both Schwartz et al [19] and Silberberg et al [12] showed the importance of social reinforcement within different variants of the social release paradigm. Furthermore, Kalamari et al [20] recently observed a reduced motivation to open the door with a trapped rat, compared to when there was no trapped rat. It is perhaps not surprising then that in mice similar openingto-release behaviour was first described as helping [21], comparable to Bartal et al [7] before it was shown that the mice were just interested in the restraining device [22].…”