Functional connectivity between the hippocampus and prefrontal cortex (PFC) is essential for associative recognition memory and working memory. Disruption of hippocampal-PFC synchrony occurs in schizophrenia, which is characterized by hypofunction of NMDA receptor (NMDAR)-mediated transmission. We demonstrate that activity of dopamine D2-like receptors (D2Rs) leads selectively to long-term depression (LTD) of hippocampal-PFC NMDAR-mediated synaptic transmission. We show that dopamine-dependent LTD of NMDAR-mediated transmission profoundly disrupts normal synaptic transmission between hippocampus and PFC. These results show how dopaminergic activation induces long-term hypofunction of NMDARs, which can contribute to disordered functional connectivity, a characteristic that is a hallmark of psychiatric disorders such as schizophrenia.T he hippocampus to medial prefrontal cortex (PFC) projection is important for executive function and working and long-term memory (1, 2). Glutamatergic neurons of the ventral hippocampal cornu ammonis 1 (CA1) region project directly to layers 2-6 of ipsilateral PFC, and this connection synchronizes PFC and hippocampal activity during particular behavioral conditions (3-5). Disruption of hippocampal-PFC synchrony is associated with cognitive deficits that occur in disorders such as schizophrenia (6). Hippocampal-PFC uncoupling can be achieved by NMDA receptor (NMDAR) antagonism (7), and NMDAR hypofunction is a recognized feature of schizophrenia (8). However, it is unclear, first, how changes in NMDAR function at this synapse may arise, and second, how NMDAR hypofunction affects hippocampal-PFC synaptic transmission.Canonically, NMDARs are considered to contribute little to single synaptic events, but the slow kinetics of NMDARs contribute to maintaining depolarization, leading to the generation of bursts of action potentials (9-13). Furthermore, NMDARs coordinate spike timing relative to the phase of field potential oscillations (14, 15). NMDAR transmission itself undergoes synaptic plasticity (16,17), and this can have a profound effect on sustained depolarization, burst firing, synaptic integration, and metaplasticity (9,11,18,19). In PFC, NMDARs are oppositely regulated by dopamine receptors; D1-like receptors (D1Rs) potentiate and D2-like receptors (D2Rs) depress NMDAR currents (20). Interestingly, NMDAR hypofunction (8, 21) and dopamine D2 receptor activity (22) are potentially converging mechanisms contributing to schizophrenia (23).We now examine the contribution of NMDARs to transmission at the hippocampal-PFC synapse. We show that NMDAR activity provides sustained depolarization that can trigger action potentials during bursts of hippocampal input to PFC. We next demonstrate that dopamine D2 receptor-dependent long-term depression (LTD) of NMDAR transmission profoundly attenuates summation of synaptic transmission and neuronal firing at the hippocampal-PFC input. These findings allow for a mechanistic understanding of how alterations in dopamine and NMDAR function can lead t...

Objective: Cannabis consumption during adolescence has been reported as a risk-factor for psychotic-like experiences (PLEs) and schizophrenia. However, brain developmental processes associated with cannabis-related PLEs are still ill-described. Method: 706 adolescents from the general population that were recruited by the IMAGEN consortium had structural MRI scans both at 14 and 19 years-old. We used deformation-based morphometry to map voxel-wise brain changes between the two time points, using the pairwise algorithm in SPM12b. We used an a-priori region of interest (ROI) approach focusing on the hippocampus/parahippocampus to perform voxel-wise linear regressions. Life time cannabis consumption was assessed using the European School Survey Project on Alcohol and other Drugs (ESPAD) and PLEs were assessed with the Comprehensive Assessment Psychotic-like experiences (CAPE). We first tested whether hippocampus/para-hippocampus development was associated with PLEs. Then, we formulated and tested an a-priori simple mediation model where uncus development mediates the association between lifetime cannabis consumption and PLEs. Results: We found that PLEs was associated with reduced expansion within a specific region of the right hippocampus/para-hippocampus formation, the uncus (p=0.002 at the cluster level, p=0.018 at the peak-level). The partial simple mediation model revealed a significant total effect from lifetime cannabis consumption to PLEs (b=0.069 95CI [0.04-0.1], p=2 x 10-16), as well as a small yet significant, indirect effect of right uncus development (0.004, 95IC [0.0004-0.01], p=0.026).

No abstract

No abstract