Social behavior deficits following Serotonin 2A Receptor constitutive deletion

SACSON AGOSTINA; MORICI, JUAN FACUNDO; BEKINSCHTEIN, PEDRO; NOELIA V WEISSTAUB

Congreso; ACNP; 2021

ACNP

Background:  Social behavior is defined asinteractions among individuals, mostly from the same species that offers mutualbenefits and comprise different actions which are based on social interaction (SI).Deficits in SI are a hallmark of different psychiatric disorders, including autismspectrum disorders. Serotonin (5-HT) is involved in a wide variety of brainfunctions, from early development and throughout the lifespan of the individualthat includes emotional and social behavior. Changes in 5-HT levels, as well assome activity of key molecules within the system have been associated withdeficits in SI. Serotonin 2A receptors (5-HT2aR) are one of the main excitatoryserotonergic receptors. Social deficits in humans were associated with 5-HT2aRhypofunction. Interestingly, 5-HT2aR agonists increase social interaction inhumans and animal models suggesting that 5-HT2aR might modulate SI. We startedto investigate the role of 5-HT2aR in SI using a genetic mouse model. We arepresenting preliminary data regarding the role of 5-HT2aR in socialinteraction. Methods: We used genetically modified males and females mice (htr2a-/-) and theirlittermates controls (htr2a+/+).  P90 orolder animals were exposed to different behavioral paradigms: three-chamberssocial interaction test. Animals were exposed to a three-compartment blackrectangular maze that contained a holed Plexiglass cylinder that would enclosea juvenile same-sex animal or an object. Mice were habituated to the chamberfor 20 minutes. 24hs later, the subjects were placed in the central compartmentfor 5 minutes before allowing them to explore the maze. Social interaction wasevaluated during a 10-min period. For the pharmacological experiment, htr2a+/+male mice were cannulated using a stereotaxic frame (mPFC; AP= +3.20 mm, LL=±0.75 mm, DV= −3.50 mm) under anesthesia (ketamine/xylazine) and led to recoverfor 5 days. Fifteen minutes before the experiment, mice were infused with MDL11,939 (300 ng/µl) or vehicle (5% DMSO). Dominance tube:  Mice werehabituated to a plexiglass 30 cm long cylinder for 5 minutes during 5 consecutivedays. Tests are conducted among cagemates using a round-robin design in which twomice were placed, each at one of the entries until one retreated. Rank isassessed by the number of times a particular mouse wins. Olfactory habituationtest: Mice were exposed to cotton swabs from the top of a clean homecageembedded in different odors. We used water, a non-social odorant (almondextract), and two social odorants (same sex and opposite sex). Each odor waspresented three times consecutively for 2 minutes with an ITI of 1 minute.Analysis:  All behaviors were recordedusing a webcam. Offline analysis was conducted using Stopwatch+ (EmoryUniversity).  Discrimination index (DI)was calculated for the SI test. Statistical analysis: Data were analyzed using R 4.1.0. For all analyzes,the normality used in the Shapiro-Wilk test was evaluated. Homoscedasticity wastested by the Levenne test. If appropriate, we choose parametric statistics.For multiple comparisons, the ANOVA test was used. Posthocs were performedusing the Tukey's test. When only two groups were compared, Welch's t-test forindependent samples or a t-test for dependent samples was used. For thedominance tube test, we used a mixed linear model with genotype as abetween-subject variable and day of testing as a within-subject variable.Results:htr2a-/- male and female mice show decreased socialinteraction in the SI test compared with same sex htr2+/+ mice (Males: t (16.37) = 3.8, p = 0.0015. d = 1.54,power = 0.99. Females: t (23.76) =-2.99, p = 0.0062. d = 1.17, power = 0.98). Though therewere no differences between sex (F(1, 45) = 0.2323, p = 0.6322), thedeficit observed in females appeared to be stronger, since only for females htr2a-/-the DI was not different from zero (t (11)= 1.298, p = 0,2208). The deficitappeared to be due to the lack of 5-HT2aR expression throughout their lifespan,since local infusion of MDL 11,939 into the medial prefrontal cortex of male htr2a+/+mice before the social interaction test did not generate any differencecompared with the response observed in vehicle treated mice (t (6) = -0.33, p= 0.75). The deficit observed appeared to depend on 5-HT2aRforebrain population, since restoring 5-HT2aR expression in htr2a-/-;Emx1-Cre-/+ mice rescued the deficit observed in the social interactiontask (F (3, 33) = 6.754, p = 0,0011). Hierarchy is the result ofsocial interaction among multiple individuals. Preliminary studies of hierarchyusing the dominance tube test showed no significant differences between htr2a-/-and htr2a+/+ males (χ2(1) = 0.51, p = 0.47) and females (χ2(1) = 0.28,p = 0.6) mice .Odor is a key cuefor SI, that could underlie the effects observed in the social interactiontest. In an odor habituation test, we found that htr2a-/- and htr2a+/+mice solve the task similarly. Conclusions:Our preliminary results suggested that 5-HT2aR are required for socialinteraction in mice. This deficit is observed in male as well as female htr2a-/-mice, with a small tendency to a stronger deficit in females. The reducedsocial interaction observed in the three-chamber task appeared to be due to adevelopmental or chronic role of 5-HT2aR and is dependent on the excitatoryforebrain 5-HT2aR population. Taken together, these results suggest theimportance of 5-HT2aR as a major modulator of social behavior.