Withdrawal from cocaine conditioning progressively alters AMPA receptor-mediated transmission in the ventral hippocampus.

Drugs of abuse, such as cocaine, produce aberrant changes in synaptic transmission and plasticity that emerge throughout withdrawal. One region of the brain that displays a high degree of synaptic plasticity, as well as connectivity with mesolimbic structures such as the nucleus accumbens, is the ventral hippocampus (vH). Here, we investigated the effects of an escalating cocaine dosing schedule on vH CA1 excitatory transmission by measuring place preference and recording excitatory postsynaptic currents (EPSCs) at three different withdrawal time points: withdrawal day (WD) 2, 9 or 28. Behaviourally, this escalating cocaine-conditioning protocol was capable of producing conditioned place preference that persisted through WD28. Physiologically, cocaine conditioning produced an increase in vH excitatory transmission on WD2 that appeared to be the result of an increase in calcium-impermeable (CI)-AMPA receptor density. Excitatory transmission was still enhanced in cocaine-treated animals on WD9; however, a significant increase in the contribution of calcium-permeable (CP)-AMPA receptors to EPSCs was detected as compared with WD2. By WD28, these CP-AMPA receptors provided a major contribution to vH CA1 excitatory transmission, resulting in synaptic responses distinct from WD2 and WD9. Taken together, these results highlight progressive changes in vH synaptic transmission during withdrawal that may enhance cocaine contextual associations.

Lacto-N-fucopentaose-III ameliorates acute and persisting hippocampal synaptic plasticity and transmission deficits in a Gulf War Illness mouse model.

AIMS: The present study investigated if treatment with the immunotherapeutic, lacto-N-fucopentaose-III (LNFPIII), resulted in amelioration of acute and persisting deficits in synaptic plasticity and transmission as well as trophic factor expression along the hippocampal dorsoventral axis in a mouse model of Gulf War Illness (GWI). MAIN METHODS: Mice received either coadministered or delayed LNFPIII treatment throughout or following, respectively, exposure to a 15-day GWI induction paradigm. Subsets of animals were subsequently sacrificed 48 h, seven months, or 11 months post GWI-related (GWIR) exposure for hippocampal qPCR or in vitro electrophysiology experiments. KEY FINDINGS: Progressively worsened impairments in hippocampal synaptic plasticity, as well as a biphasic effect on hippocampal synaptic transmission, were detected in GWIR-exposed animals. Dorsoventral-specific impairments in hippocampal synaptic responses became more pronounced over time, particularly in the dorsal hippocampus. Notably, delayed LNFPIII treatment ameliorated GWI-related aberrations in hippocampal synaptic plasticity and transmission seven and 11 months post-exposure, an effect that was consistent with enhanced hippocampal trophic factor expression and absence of increased interleukin 6 (IL-6) in animals treated with LNFPIII. SIGNIFICANCE: Approximately a third of Gulf War Veterans have GWI; however, GWI therapeutics are presently limited to targeted and symptomatic treatments. As increasing evidence underscores the substantial role of persisting neuroimmune dysfunction in GWI, efficacious neuroactive immunotherapeutics hold substantial promise in yielding GWI remission. The findings in the present report indicate that LNFPIII may be an efficacious candidate for ameliorating persisting neurological abnormalities presented in GWI.

Lacto-N-fucopentaose-III (LNFPIII) ameliorates acute aberrations in hippocampal synaptic transmission in a Gulf War Illness animal model.

Approximately one-third of Persian Gulf War veterans are afflicted by Gulf War Illness (GWI), a chronic multisymptom condition that fundamentally presents with cognitive deficits (i.e., learning and memory impairments) and neuroimmune dysfunction (i.e., inflammation). Factors associated with GWI include overexposures to neurotoxic pesticides and nerve agent prophylactics such as permethrin (PM) and pyridostigmine bromide (PB), respectively. GWI-related neurological impairments associated with PB-PM overexposures have been recapitulated in animal models; however, there is a paucity of studies assessing PB-PM-related aberrations in hippocampal synaptic plasticity and transmission that may underlie behavioral impairments. Importantly, FDA-approved neuroactive treatments are currently unavailable for GWI. In the present study, we assessed the efficacy of an immunomodulatory therapeutic, lacto-N-fucopentaose-III (LNFPIII), on ameliorating acute effects of in vivo PB-PM exposure on synaptic plasticity and transmission as well as trophic factor/cytokine expression along the hippocampal dorsoventral axis. PB-PM exposure resulted in hippocampal synaptic transmission deficits 48 h post-exposure, a response that was ameliorated by LNFPIII coadministration, particularly in the dorsal hippocampus (dH). LNFPIII coadministration also enhanced synaptic transmission in the dH and the ventral hippocampus (vH). Notably, LNFPIII coadministration elevated long-term potentiation in the dH. Further, PB-PM exposure and LNFPIII coadministration uniquely altered key inflammatory cytokine and trophic factor production in the dH and the vH. Collectively, these findings demonstrate that PB-PM exposure impaired hippocampal synaptic responses 48 h post-exposure, impairments that differentially manifested along the dorsoventral axis. Importantly, LNFPIII ameliorated GWI-related electrophysiological deficits, a beneficial effect indicating the potential efficacy of LNFPIII for treating GWI.

Cocaine conditioning induces persisting changes in ventral hippocampus synaptic transmission, long-term potentiation, and radial arm maze performance in the mouse.

The effects of drugs of abuse, such as cocaine, on learning and memory processes are thought to contribute to drug craving and relapse susceptibility. Using an Escalating (Esc) or Double Escalating (2x Esc) cocaine i.p. dosing schedule with the conditioned place preference (CPP) model we investigated the persisting effects of cocaine conditioning on long-term potentiation (LTP) in the CA1 region of the ventral hippocampus (vH), and spatial working memory in a radial arm maze (RAM) task. Interestingly, vH LTP was increased 4 weeks after the last injection day in animals that received only saline vehicle injections. A single pre-treatment with the kappa-opioid receptor antagonist, norbinaltorphimine (norBNI), blocks this stress-like effect of the conditioning protocol on vH LTP without altering the behavioral responses of the animals to cocaine. In animals that received the 2x Esc/norBNI cocaine conditioning, vH LTP was significantly decreased compared to those that received saline vehicle 4 weeks after the last dose. These 2x Esc/norBNI treated animals also exhibited a significant leftward shift in the stimulus-response curve of the baseline field excitatory postsynaptic potential (fEPSP) measurements. A separate group of 2x Esc/norBNI displayed an impaired ability to learn a spatial working memory RAM task compared to saline-conditioned mice following a similar 4 week abstinence period. Together, these results demonstrate that cocaine-induced alterations in synaptic transmission and LTP in the vH are associated with persisting drug-induced impairments in learning and memory performance.

Proteasome inhibition augments new protein accumulation early in long-term synaptic plasticity and rescues adverse Aß effects on protein synthesis.

Protein degradation plays a critical role in synaptic plasticity, but the molecular mechanisms are not well understood. Previously we showed that proteasome inhibition enhances the early induction part of long-term synaptic plasticity for which protein synthesis is essential. In this study, we tested the effect of proteasome inhibition on protein synthesis using a chemically induced long-lasting synaptic plasticity (cLTP) in the murine hippocampus as a model system. Our metabolic labeling experiments showed that cLTP induction increases protein synthesis and proteasome inhibition enhances the amount of newly synthesized proteins. We then found that amyloid beta (Aß), a peptide contributing to Alzheimer's pathology and impairment of synaptic plasticity, blocks protein synthesis increased by cLTP. This blockade can be reversed by prior proteasome inhibition. Thus, our work reveals interactions between protein synthesis and protein degradation and suggests a possible way to exploit protein degradation to rescue adverse Aß effects on long-term synaptic plasticity.