Brock, J. A. | bioRxiv Science

bioRxiv2025

Neocortical Layer-5 tLTD Relies on Non-Ionotropic Presynaptic NMDA Receptor Signaling

In the textbook view, NMDA receptors (NMDARs) act as coincidence detectors in Hebbian plasticity by fluxing Ca2+ when simultaneously depolarized and glutamate bound. Hebbian coincidence detection requires that NMDARs be located postsynaptically, but enigmatic presynaptic NMDARs (preNMDARs) also exist. It is known that preNMDARs regulate neurotransmitter release, but precisely how remains poorly understood. Emerging evidence suggest that NMDARs can also signal non-ionotropically, without the need for Ca2+ flux. At synapses between developing visual cortex layer-5 (L5) pyramidal cells (PCs), preNMDARs rely on Mg2+ and Rab3-interacting molecule 1{beta} (RIM1{beta}) to regulate evoked release during periods of high-frequency firing, but they signal non-ionotropically via c-Jun N-terminal kinase 2 (JNK2) to regulate spontaneous release regardless of frequency. At the same synapses, timing-dependent long-term depression (tLTD) depends on preNMDARs but not on frequency. We therefore tested if tLTD relies on non-ionotropic preNMDAR signaling. We found that tLTD at L5 PC[->]PC synapses was abolished by pre- but not postsynaptic NMDAR deletion, cementing the view that tLTD requires preNMDARs. In agreement with non-ionotropic NMDAR signaling, tLTD prevailed after channel pore blockade with MK-801, unlike tLTP. Homozygous RIM1{beta} deletion did not affect tLTD, but wash-in of the JNK2 blocker SP600125 abolished tLTD. Consistent with a presynaptic need for JNK2, a peptide blocking the interaction between JNK2 and Syntaxin-1a (STX1a) abolished tLTD if loaded pre- but not postsynaptically, regardless of frequency. Finally, low-frequency tLTD was not blocked by the channel pore blocker MK-801, nor by 7-CK, a non-competitive NMDAR antagonist at the co-agonist site. We conclude that neocortical L5 PC[->]PC tLTD relies on non-ionotropic preNMDAR signaling via JNK2/STX1a. Our study brings closure to long-standing controversy surrounding preNMDARs and highlights how the textbook view of NMDARs as ionotropic coincidence detectors in plasticity needs to be reassessed.

neuroscience↗

bioRxiv2023

Passive surveillance for shrimp pathogens in Penaeus vannamei submitted from 3 Regions of Latin America

Multiple PCR analyzes were performed using 19 different primer sets to open and broaden the search spectrum for shrimp pathogens. In addition, multiple primer pairs for 10 pathogens were compared to see if there were differences in selectivity or sensitivity among them. Some pathogens that did not present histological lesions were detected. The most important outcome was that selection of appropriate primers was the most critical factor in obtaining reliable results. We found high variability in results among primers and we learned it was prudent to seasonally assess among them for the best set selection. It is important to understand that a PCR positive test result alone does not confirm the presence of a viable pathogen or a disease state. Nor, as might be expected, does it mean that the positive PCR test results will be necessarily accompanied by histological lesions characteristic of the targeted pathogen. However, the use of appropriately selected primers sets can reveal whether there is an evolution in the result spectrum over time and if some pathogens disappear or reappear or new ones emerge. In general, most shrimp presented coinfections that consisted of the presence of WzSV8, DHPV, chronic midgut inflammation and tubule distension/epithelial atrophy consistent with Pir A/B toxicity. Also included were RLB/NHPB, microsporidia, striated muscle necrosis, gregarines in the hindgut caecum (gametocyte stage, and not associated with tegumental glands but glands that line the mouth and anus) and encysted, presumed nematode larvae. WzSV8 was newly discovered in gonads. Histological changes and the presence of spheroids in the lymphoid organ were considered as healthy host responses of often unidentified cause.

pathology↗