DOI: 10.5061/dryad.v9s4mw6x4
title: Effects of chronic THC in adolescence on rat play behaviours

description: Background: Cannabis use remains a major public health concern, and its
 use typically begins in adolescence. Chronic administration of
 ∆9-tetrahydrocannabinol (THC), the main psychoactive compound in cannabis,
 during adolescence can produce deficits in adult learning and memory,
 stress reactivity and anxiety. One possible mechanism behind the
 disruptions in adulthood from adolescent exposure to THC includes changes
 in social behaviours, such as social play, which has been shown to be
 critical to socio-cognitive development. Methods: Here, using an
 established animal model of adolescent THC exposure in male and female
 Long–Evans rats, we explored the effects of THC on play behaviour during
 the chronic administration period. Following puberty onset, as indicated
 by external changes to the genitalia, THC (5mg/kg) was administered for 14
 days. Play behaviour was assessed seven days following the onset of the
 injection period at approximately 1 hour post treatment. The frequency of
 nape attacks, the likelihood and tactics of defensive behaviour, and pins
 were scored and analyzed. Results: THC exposure decreased playfulness in
 adolescent rats including the number of attacks, likelihood of defense and
 pins compared to control and vehicle treated rats. Conclusion: This
 suggests that THC suppresses both the attack and defense components of
 social play. This is an important finding because there is evidence that
 attack and defense may be mediated by different mechanisms. Furthermore,
 the effect of THC exposure decreasing playfulness occurred similarly in
 males and females. This study contributes to understanding the long-term
 ramifications of adolescent THC exposure on healthy brain development.
 Disruptions in social behaviour during this period could have long-term
 consequences on adult brain and behaviour, and the interaction between the
 pharmacological effects of THC and the subsequent effects of decreased
 sociality should be considered.
description: A total of 48 Long–Evans rats (24 females and 24 males; RRID:
 RGD_18337282) were used. Following weaning, male and female rats were
 randomly assigned and counterbalanced to their experimental groups:
 comparison control (CC; N=6), control (CON; N=6) vehicle (VEH; N=6) or THC
 (N=6) so that each quadrad included one same-sex partner subject from each
 experimental group. Treatment began following puberty onset using the
 external changes to the genitalia, which reliably signal the onset of
 puberty. THC (in 1:1:18 solution of ethanol: cremaphor:saline) was
 administered <i>i.p</i>. at a dose of 5 mg/kg once a day
 starting on the day of puberty onset for 14 days. VEH groups were given a
 vehicle injection once a day for 14 days. Play behaviour consisted of
 placing two play partners in large, clear Plexiglas arena filled to a
 depth of ~1–2 cm with Betacob bedding. Play was recorded for 10 min in the
 dark using a video camera with night-shot capacity. Play behaviour was
 assessed at least seven days following the onset of the injection period
 ~1 hour after treatment. 24 hours before play trials partners were
 separated and housed individually. Within a quadrad, all treatment rats
 (CON, VEH and THC) were paired with the CC rat for play bouts. The order
 of play bouts with the CC was counterbalanced. The frequency of nape
 attacks (in which the snout of one partner moves towards the nape of the
 other), the likelihood of the partner receiving a nape attack defending
 itself to avoid contact and if it did defend itself, and the tactics used
 to do so were scored. The total frequency of nape attacks per 10 min were
 scored and analyzed, but as defense is contingent on attack, the frequency
 of defense was expressed as a percentage of attacks received, and the
 types of defense were expressed as a percentage of defended attacks.
 Defense can involve either evasion (the head and neck are turned away from
 the attacker) or facing defense (the defender turns to face the attacker).
 The percentage of evasion provides a measure of attempts by rats to avoid
 playful contact. In facing defense, the rats can either remain standing or
 roll over to supine, with the percentage of the latter providing a measure
 of the rat’s motivation to gain and maintain close body contact. A common
 configuration resulting from attack and defense in the juvenile period is
 for one rat to lie on its back and the partner to stand over it
 (<i>i.e.</i>, a pin). As the absolute number of pins per trial
 was also scored to provide insight into the pattern of
 interaction.
description: The readme file contains an explanation of each of the variables
 in the dataset. Information on how the behaviours were scored can be found
 in the manuscript referenced above.