Additional file 1: Supplemental figures S1-S9. Figure S1. Nlgn3−/y rats display reduced classic freezing behaviour in a contextual fear conditioning paradigm. Figure S2. Freezing analysed as “paw immobility response” (all four paws unmoving but allowing for movement of head and neck). Figure S3. WT and Nlgn3−/y rats show similar activity in an open field, rotational platform & marble interaction tasks. Figure S4. Effect of repeated footshocks & thermal stimulus on WT and Nlgn3−/y rats. Figure S5. Intrinsic properties of PAG cells recorded from WT and Nlgn3−/y rats. Figure S6. Hyperexcitability of dorsal, but not ventral PAG neurons in 8-10 week old Nlgn3−/y rats. Figure S7. PAG LFPs during fear recall are significantly shorter duration in Nlgn3−/y rats. Figure S8. Defensive reactions were not elicited by electrical stimulation of primary somatosensory cortex in WT or Nlgn3−/y rats. Figure S9. Western blots showing lack expression of NLGN3 in Nlgn3−/y rats both in sensory cortex and periaqueductal grey.