Activity-Dependent Shedding of the NMDA Receptor Glycine Binding Site by Matrix Metalloproteinase 3: A PUTATIVE Mechanism of Postsynaptic Plasticity

Functional and structural alterations of clustered postsynaptic ligand gated ion channels in neuronal cells are thought to contribute to synaptic plasticity and memory formation in the human brain. Here, we describe a novel molecular mechanism for structural alterations of NR1 subunits of the NMDA receptor. In cultured rat spinal cord neurons, chronic NMDA receptor stimulation induces disappearance of extracellular epitopes of NMDA receptor NR1 subunits, which was prevented by inhibiting matrix metalloproteinases (MMPs). Immunoblotting revealed the digestion of solubilized NR1 subunits by MMP-3 and identified a fragment of about 60 kDa as MMPs-activity-dependent cleavage product of the NR1 subunit in cultured neurons. The expression of MMP-3 in the spinal cord culture was shown by immunoblotting and immunofluorescence microscopy. Recombinant NR1 glycine binding protein was used to identify MMP-3 cleavage sites within the extracellular S1 and S2-domains. N-terminal sequencing and site-directed mutagenesis revealed S542 and L790 as two putative major MMP-3 cleavage sites of the NR1 subunit. In conclusion, our data indicate that MMPs, and in particular MMP-3, are involved in the activity dependent alteration of NMDA receptor structure at postsynaptic membrane specializations in the CNS

Anterior cruciate ligament insufficiency: does delay in index surgery affect outcome in recreational athletes

The aim of the study was to see if delay in anterior cruciate ligament (ACL) reconstruction affects post-reconstruction outcome in recreational athletes. Sixty-two recreational athletes who had arthroscopic ACL reconstructions using quadruple hamstring grafts between 1997 and 2000 were retrospectively evaluated. Patients with less than 2 years’ follow-up, those with multi-ligament injuries, reconstructions for previous failed repairs, those whose injury date was unknown, those with pre-injury Tegner activity level greater than 7 (competitive athletes) and those lost to follow-up were all excluded. Forty-six patients (38 males) were entered. The mean follow up was 38 months and the mean time from injury to index ACL reconstruction was 27 months. Apart from two revisions there were no other significant complications. Forty-one (89%) patients were evaluated in a review clinic. There was a significant improvement in the post-reconstruction Lysholm scores and an improvement in the Tegner scores. The Spearman’s correlation coefficient between postoperative Lysholm score and the delay until surgery was −0.18 and the correlation coefficient between postoperative Tegner scores and the delay until surgery was 0.14. Thirty-five patients returned to sporting activity. Thirty-seven rated their knee as being normal or nearly normal and 35 said that their knee function was as they had expected it to be. Late ACL reconstruction does not adversely affect the outcome in recreational athletes. ACL reconstruction should be offered to these patients as there is a significant improvement in the knee function and patients are satisfied with the results

Extracellular Matrix Plasticity and GABAergic Inhibition of Prefrontal Cortex Pyramidal Cells Facilitates Relapse to Heroin Seeking

Successful treatment of drug addiction is hampered by high relapse rates during periods of abstinence. Neuroadaptation in the medial prefrontal cortex (mPFC) is thought to have a crucial role in vulnerability to relapse to drug seeking, but the molecular and cellular mechanisms remain largely unknown. To identify protein changes that contribute to relapse susceptibility, we investigated synaptic membrane fractions from the mPFC of rats that underwent 21 days of forced abstinence following heroin self-administration. Quantitative proteomics revealed that long-term abstinence from heroin self-administration was associated with reduced levels of extracellular matrix (ECM) proteins. After extinction of heroin self-administration, downregulation of ECM proteins was also present in the mPFC, as well as nucleus accumbens (NAc), and these adaptations were partially restored following cue-induced reinstatement of heroin seeking. In the mPFC, these ECM proteins are condensed in the perineuronal nets that exclusively surround GABAergic interneurons, indicating that ECM adaptation might alter the activity of GABAergic interneurons. In support of this, we observed an increase in the inhibitory GABAergic synaptic inputs received by the mPFC pyramidal cells after the re-exposure to heroin-conditioned cues. Recovering levels of ECM constituents by metalloproteinase inhibitor treatment (FN-439; i.c.v.) prior to a reinstatement test attenuated subsequent heroin seeking, suggesting that the reduced synaptic ECM levels during heroin abstinence enhanced sensitivity to respond to heroin-conditioned cues. We provide evidence for a novel neuroadaptive mechanism, in which heroin self-administration-induced adaptation of the ECM increased relapse vulnerability, potentially by augmenting the responsivity of mPFC GABAergic interneurons to heroin-associated stimuli