Hippocampus? OR...

POST-TRAINING CB1 CANNABINOID RECEPTOR AGONIST ACTIVATION DISRUPTS LONG-TERM CONSOLIDATION OF SPATIAL MEMORIES IN THE HIPPOCAMPUS T.Yim, N. Hong, M. Ejaredar, J. McKenna, & R. McDonald

Cannabis sativa Positive effects Negative effects Euphoria Analgesia Reduction of intraocular pressure Appetite enhancement Anti-emetic Negative effects Attention and memory deficits Hallucinations Respiratory disease

Medical Marijuana

Cannabis sativa THC (D9-tetrahydrocannabinol) Equal affinity to CB1R and CB2R CB2R found in periphery CB1R found in CNS Anandamide (N-arachidonylethanolamine) = natural ligand Made from arachadonic acid Can be converted to PGF2a Made in the hippocampus, cortex and cerebellum

THC Location of CB1R Hippocampus Basal ganglia Substantia nigra

Previous Studies CB1R activation in dorsal hippocampus impairs spacial memory in rodents Reversible by CB1R blockade Not clear which stage is affected Acquisition, consolidation, or retrieval?

Objective Determine if cannabinoid activation affects memory consolidation Activate CB1R after daily training in Morris water maze Assess spatial recall at various retention intervals

Materials and Methods 111 male Long-Evans rats 6 day training in MWM 1.5 m diameter, .5 m deep Invisible platform NE quadrant, 28 cm from perimeter Multiple colored posters in room for cues

Morris water maze

Materials and Methods Place learning Training for 6 consecutive days 8 swimming trials per day 2 trials from each of 4 starting positions (N, S, E, W) Trial began when rat was placed in water, ended when rat reached platform or after 60 s

Materials and Methods Probe test Invisible platform removed from water maze Rats placed in pool facing wall from due west Test begins when rat is released in water and ends after 30 s

Experiment 1 Systemic injections of WIN 64 rats assigned to one of four treatment groups .5mg/kg, 1mg/kg, 3mg/kg, or DMSO(control) Injections made within 5 min of last swim of each of the 6 training days Probe test given at two retention periods 1 week and 4 weeks post-training

Experiment 2 Intrahippocampal infusions of WIN All rats received bilateral cannulae implantation to dorsal hippocampus 47 rats assigned to one of three groups Control, 2.5ug WIN, 5.0ug WIN Injections made within 5 min of last swim of each of the 6 training days Probe test given at two retention periods 1 week and 4 weeks post-training

Results Experiment 1

Results Experiment 1

Results Experiment 1

Results Experiment 2

Results Experiment 2

Results Experiment 2

Histology Location of cannulae

Discussion CB1 agonist WIN impairs consolidation of long term memory Spares spatial acquisition and short term retention Consolidation impairment due to CB1R rather than CB2R activation CB2R not expressed in hippocampus Isolated consolidation with post-training administration

Discussion Short-term vs Long-term NMDA-R blockade in dorsal hippocampus impairs long-term not short-term memory CB1R activation inhibits long term potentiation Suppress NMDA-R by inhibiting vg-Ca2+ and activating K+ channels

Discussion Effects of WIN may be dose dependent Related to acetylcholine tone Low dose WIN enhance cholinergic efflux High dose WIN inhibit cholinergic activity Low levels of Ach required for memory consolidation during post-training slow-wave sleep