Fig. 3: Effects of 5-HT2A and 5-HT1A antagonism on reversal learning in control and psilocybin-treated rats.

Following the final training session pre-treatment with either saline (vehicle control), the 5-HT2AR antagonist MDL100907, or the 5-HT1AR antagonist WAY100635, was followed 30 min later by treatment with either saline (A) or psilocybin (L) before reversal of reward contingencies the following day, with first reversal day performance accuracy highlighted (B, M, respectively). While 53/5% (8/15) of Saline+SAL rats reached reversal day 1 criterion, 0% (0/9) of MDL + SAL treated rats did so (C), showing global impairment compared to Saline+SAL across nearly all outcome measures, achieving significantly lower session accuracy (D, SAL + > MDL+ p = .0221), earning fewer pellets (E, SAL + > MDL+ p = .0324), and making fewer target (F, SAL + > MDL+ p = .0292) and non-target (G, SAL + > MDL+ p = 0.0048) pokes in the session. While there was no delay in task engagement (time from device access to first poke; H, SAL+ vs MDL+ p = 0.4572), target poke latency was increased (I, SAL + < MDL+ p = 0.0502) in the 6/9 rats that made a target poke, and only 3/9 rats earned a single pellet (i.e. made at least 5 target pokes; (J) time from first poke to earning first pellet, SAL+ vs MDL+ p = 0.1507), even though task engagement duration did not differ (time from first to final poke; (K), SAL+ vs MDL+ p = 0.6048). Conversely, WAY + SAL resulted in 53.8% (7/13) of rats reaching criterion, nearly identical to Saline+SAL, with these groups being similar across most measures except WAY + SAL having fewer non-target pokes (G, SAL + > WAY+ p = 0.0041) despite an elongated target poke latency (I, SAL + < WAY+ p = 0.0244). With 75% (12/16) of Saline+PSI rats reaching reversal day 1 criterion, MDL + PSI treatment produced a moderate decrease to 55.6% (5/9) reaching criterion (N), although only a non-significant decrease in accuracy (O, SAL+ vs MDL+ p = 0.2837), while there was a trend toward fewer pellets (P, SAL + > MDL+ p = 0.0698) and target pokes (Q, SAL + > MDL+ p = 0.0542), and a significant reduction in non-target pokes (R, SAL + > MDL+ p = 0.0210) across the session, with no differences in any latency measures (S–U, all SAL+ vs MDL+ ps > .2991) or session duration (V, SAL+ vs MDL+ p = 0.4345). In contrast, WAY + PSI produced severe impairment with only 15.4% (2/13) of rats reaching criterion, with significantly reduced session accuracy (O, SAL + > WAY+ p = .0024), pellets earned (P, SAL + > WAY+ p = 0.0015), and target pokes (Q, SAL + > WAY+ p = 0.0013), and delayed target poke latency (T, SAL + < WAY+ p = 0.0212, with only 10/13 rats achieving a target poke) compared to Saline+PSI, whilst there were no differences for non-target pokes (R, SAL+ vs WAY+ p = 0.9497), first poke latency (S, SAL+ vs WAY+ p = 0.1636), relative first pellet latency (U, SAL+ vs WAY+ p = 0.2588, although only 7/13 earned a pellet), nor session duration (V, SAL+ vs WAY+ p = 0.7309). Bar graphs show mean ± SEM with individual data points. *p < 0.05, **p < 0.01. SAL saline, PSI psilocybin, SAL+ saline pre-treatment, MDL + MDL100907 pre-treatment; WAY + WAY100635 pre-treatment. For main ANOVA results and full statistical analysis details see Fig. 3 Statistics Table.