Latrophilin-3 conditional knockout in tyrosine hydroxylase neurons (Lphn3-Th-Cre) compared with Lphn3 global KO rats: Role of Lphn3 in tyrosine hydroxylase neurons on cognitive and behavioral effects of this ADHD susceptibility gene

Latrophilin-3 (LPHN3) is a brain specific adhesion G-protein coupled receptor associated with elevated risk of attention deficit hyperactivity disorder (ADHD). We developed a global Lphn3 knock-out (gKO) rat using CRISPR/Cas9 to delete exon-3. Here we report the development of a floxed Lphn3 rat crossed with tyrosine hydroxylase (Th-Cre) rats to create a conditional Lphn3 KO rat specific for catecholaminergic- positive cells. The gKO rats are hyperactive and have egocentric and allocentric navigation deficits but showed sparing of conditioned contextual and novel object recognition memory. Here we compared gKO and cKO rats controlling for litter effects. Both gKO and cKO rats were hyperactive and were impaired in egocentric navigation in the Cincinnati water maze (CWM) with deficits greater in gKO rats. The gKO rats were impaired in allocentric navigation in the Morris water maze (MWM) whereas cKO rats were only slightly affected compared with WT, cre, and floxed rats. Striatal tyrosine hydroxylase and dopamine D1 receptors were not significantly different in either model, nor were NMDA-NR1 or NMDA-NR2 in the hippocampus. We previously showed, however, that dopamine is released more rapidly in the striatum of gKO rats by fast- scan cyclic voltammetry. The cKO model shows an important role of catecholamines in the phenotype of LPHN3 disruption and add evidence that this synaptic protein plays a role in neuroplasticity that are consistent with ADHD.