Play is a common and developmentally important behaviour in young mammals. Specifically in Norway rats (Rattus norvegicus), reduced opportunity to engage in rough-and-tumble (RT) play has been associated with impaired development in social competence. However, RT play is a complex behaviour having both a kinematic aspect (i.e., performing complex 3D manoeuvres during play fights) and a social aspect (interacting with a playful partner). There has been little research so far on disentangling the two aspects in RT play, especially on how these two aspects affect the affective appraisal of the intense physical contact during play. To examine the developmental effects of kinematic and social play reduction on affective appraisal in rats, we subjected male Long-Evans rats from 21 days old to RT play experience that was reduced either kinematically (through playing in a low ceiling environment) or socially (through playing with a less playful Fischer-344 rat). Starting at 35 days, we measured their production of positively (50-kHz) and negatively (22-kHz) valenced ultrasonic vocalisations (USVs) in a 2-min standardised human-rat play procedure that mimicked the playful sequences of nape contact, pinning, and belly stimulation (‘tickling’) for ten days. We hypothesised that the rats with kinematically or socially reduced play would perceive the ‘tickling’ less positively and thus emit positive ultrasonic vocalisations at lower rates compared to control rats with non-reduced play experience. Our results confirmed that each of the treatments reduced play differently: while the kinematic reduction abolished playful pinnings entirely, the social reduction decreased the pinnings and made play highly asymmetric. During the tickling procedure, rats mostly produced 50 kHz USV, indicating that they appraised the procedure as positive. There was a wide inter individual variance and high individual consistency in rats’ USV responses to ‘tickling’. Crucially, neither the kinematically nor the socially reduced play experience affected either type of USV production when rats were ‘tickled’. This finding indicates that the ability to appraise play-like interactions as positive remains unaffected even when the kinematic or the social aspect of play experience was substantially curtailed.

中文翻译：

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减少运动和社交游戏体验对大鼠人鼠游戏情感评估的影响

玩耍是年轻哺乳动物的一种常见且对发育重要的行为。特别是在挪威大鼠（Rattusnorvegicus）中，参与打闹（RT）游戏的机会减少与社交能力发展受损有关。然而，RT 游戏是一种复杂的行为，同时具有运动学方面（即，在游戏战斗期间执行复杂的 3D 动作）和社交方面（与顽皮的伙伴互动）。迄今为止，很少有研究能够理清 RT 游戏中的这两个方面，特别是这两个方面如何影响游戏过程中激烈身体接触的情感评估。为了检查运动学和社交游戏减少对大鼠情感评估的发展影响，我们让 21 天大的雄性 Long-Evans 大鼠接受 RT 游戏体验，这些体验要么在运动学上（通过在低天花板环境中玩耍）要么在社交上（通过和一只不那么顽皮的 Fischer-344 老鼠玩耍）。从第 35 天开始，我们在 2 分钟的标准化人鼠游戏程序中测量了它们产生的正价 (50-kHz) 和负价 (22-kHz) 超声波发声 (USV)，该程序模仿了颈背接触、固定等有趣的序列。和腹部刺激（“发痒”）十天。我们假设，与游戏体验未减少的对照大鼠相比，运动学或社交性游戏减少的大鼠对“发痒”的感知程度较低，因此以较低的速率发出积极的超声波发声。我们的结果证实，每种治疗方法减少游戏的方式不同：虽然运动学减少完全消除了玩耍的固定，但社会减少减少了固定并使游戏高度不对称。在搔痒过程中，大鼠大多产生 50 kHz USV，表明它们对该过程的评价是积极的。大鼠对“痒痒”的 USV 反应存在较大的个体差异和较高的个体一致性。至关重要的是，当老鼠被“挠痒痒”时，运动学和社交性减少的游戏体验都不会影响任何类型的 USV 生产。这一发现表明，即使游戏体验的运动学或社交方面被大幅削弱，将类似游戏的互动评价为积极的能力仍然不受影响。