Recent evidence suggests that psychedelic drugs can exert beneficial effects on anxiety, depression, and ethanol and nicotine abuse in humans. However, the hallucinogenic side effects of psychedelics often preclude their clinical use. Lysergic acid diethylamide (LSD) is a prototypical hallucinogen and its psychedelic actions are exerted through the 5HT2A serotonin receptor (5HT2AR). 5HT2AR activation stimulates Gq and arrestin (Arr) mediated signaling. To separate effects of these signaling modes, we have used Arr1 and Arr2 mice. We find that LSD stimulates motor activities to similar extents in WT and Arr1 KO mice, with non-significant effects in Arr2 KOs. LSD robustly stimulates many surrogates of psychedelic drug actions including head twitches, grooming, retrograde walking, and nose poking in WT and Arr1 KO animals. In contrast, LSD only slightly stimulates head twitches in Arr2 KO mice, without effects on retrograde walking or nose poking. The 5HT2AR antagonist MDL100907 (MDL) blocks these LSD effects. LSD also disrupts prepulse inhibition (PPI) in WT and Arr1 KOs. PPI is unaffected in Arr2 KOs. MDL restores PPI in WT mice, but this antagonist is without effect and haloperidol is required in Arr1 KOs. LSD produces a biphasic body-temperature response in WT mice, a monophasic response in Arr1 KOs, and is without effect in Arr2 mutants. Both MDL and the 5HT1AR antagonist, WAY100635 (WAY), block the effects of LSD on body temperatures in WT mice, whereas WAY is effective in Arr1 KOs. Collectively, these results reveal that LSD produces diverse behavioral effects through Arr1 and Arr2, and that the psychedelic drug-like actions of LSD appear to require Arr2.

32 33 G protein-coupled receptor kinase-interacting protein 2 (GIT2) and GIT1 are highly similar, sharing 34 the same domain structure and many binding partners. The most important GIT partners are the 35 p21-activated protein kinase-interacting exchange factor (PIX) proteins, since through homomeric 36 and heteromeric interactions, GIT and PIX proteins form oligomeric GIT/PIX complexes. Oligomeric 37 GIT/PIX complexes function both as regulators of small GTP-binding proteins and as scaffolds for 38 signalling molecules, including p21-activated protein kinases (PAKs). Deficits in learning and 39 memory have been demonstrated in GIT1 knockout mice, and it has been assumed that GIT2 also 40 would affect learning and memory. Unexpectedly, we find that GIT2-deficient mice respond 41 normally in multiple tests of learning and memory, and have normal hippocampal long-term 42 potentiation. Further, we find no evidence that GIT2 regulates ADHD-like phenotypes. To 43 investigate why GIT2 and GIT1 differ so markedly in the brain, we identified the major isoform of 44 GIT2 in the brain as a previously uncharacterized splice variant, GIT2(DBCE). This variant cannot 45 dimerize or form oligomeric complexes with PIX proteins, and is thus incapable of regulating PAK 46 in synapses, compared to oligomeric GIT1/PIX complexes. Because localized activation of PAK in 47 synapses is required for structural plasticity underlying cognitive performance, loss of monomeric 48 GIT2(DBCE) in the brain does not influence these responses. 49 50 Methods 109 110 Plasmids 111